UBC Theses and Dissertations

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UBC Theses and Dissertations

Time variations of the Pacific equatorial undercurrent Curran, Terrence Alexander 1981

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TIME VARIATIONS OF THE P A C I F I C EQUATORIAL UNDERCURRENT by TERRENCE ALEXANDER CURRAN B. A . S c . , The U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF OCEANOGRAPHY We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BR IT ISH COLUMBIA Ma r ch 1981 (S) T e r r e n c e A l e x a n d e r C u r r a n , 1981 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department o r by h i s o r her r e p r e s e n t a t i v e s . I t i s understood t h a t c o p y i n g or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a llowed without my w r i t t e n p e r m i s s i o n . Department of O Cf/tA/O&RflPHV The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date M" SPR/L DF-fi 17/7Q} ABSTRACT T ime v a r i a t i o n s o f t h e P a c i f i c e q u a t o r i a l u n d e r c u r r e n t a t 150° w e s t l o n g i t u d e a r e d e s c r i b e d , b a s e d upon o b s e r v a -t i o n s f r o m t h e CSS P a r i z e a u d u r i n g J a n u a r y - F e b r u a r y 1 9 7 9 . T y p i c a l v e l o c i t y max ima were 80 cm s " 1 i n t h e e a s t w a r d d i r -e c t i o n and 60 cm s " 1 i n t h e n o r t h w a r d d i r e c t i o n n e a r t h e c o r e d e p t h a t 150 m e t r e s . A s s o c i a t e d s t a n d a r d e r r o r s we r e 15 cm s " 1 due t o u n c e r t a i n t y i n p r o b e m o t i o n and 5 cm s " 1 due t o i n h e r e n t c u r r e n t m e t e r n o i s e . S c a l a r f i e l d a n a l y s i s s u g g e s t s t h a t t h e mean z o n a l c u r r e n t f l o w i n t h e e q u a t o r i a l u n d e r c u r r e n t i s m o d u l a t e d by Ro s s b y waves w i t h p e r i o d s o f 30 d a y s . In t h e s u r f a c e l a y e r , waves w i t h p e r i o d s o f a p p r o x -i m a t e l y 17 days were d e t e c t e d . A d e t a i l e d d e s c r i p t i o n o f t h e c u r r e n t p r o f i l e r u s ed d u r i n g t h e e x p e r i m e n t i s i n c l u d e d i n t h e A p p e n d i x . i i T a b l e o f C o n t e n t s A b s t r a c t i i T a b l e o f C o n t e n t s i i i L i s t o f T a b l e s i v L i s t o f F i g u r e s v A c k n o w l e d g e m e n t v i i C h a p t e r 1. I n t r o d u c t i o n 1 C h a p t e r 2 . T ime v a r i a t i o n s o f t h e P a c i f i c E q u a t o r i a l U n d e r c u r r e n t 5 2 . 0 I n t r o d u c t i o n 5 2 . 1 E q u a t o r i a l u n d e r c u r r e n t v e l o c i t y s e c t i o n s 8 2 . 2 EUC s c a l a r s e c t i o n s 19 2 . 3 T i m e - v a r y i n g m e r i d i o n a l c i r c u l a t i o n 23 2 . 4 R e l a t i o n s h i p b e tween EUC v e l o c i t i e s and s c a l a r p r o p e r t i e s 30 2 . 5 Wave phenomena 33 C h a p t e r 3 . Summary 40 R e f e r e n c e s 42 A p p e n d i x 44 A l . I n t r o d u c t i o n 44 A 2 . A n a l o g u e S y s t em 45 A 3 . A c o u s t i c C u r r e n t M e t e r S y s t e m 45 A 4 . S e q u e n c i n g and T e l e m e t r y 51 A 5 . C a l i b r a t i o n 52 A 6 . P r o f i l i n g C o n s i d e r a t i o n s 53 A 7 . Summary 56 i i i L i s t o f T a b l e s T a b l e Page 1 S h i p d r i f t a t e a ch s t a t i o n a t 1 5 0 ° W l o n g i t u d e 1 1 2 I n t e g r a t e d z o n a l t r a n s p o r t s 1 4 3 M e r i d i o n a l d i v e r g e n c e o f n o r t h w a r d v e l o c i t y 2 7 4 V e r t i c a l v e l o c i t i e s i n mm s ~ 1 a t 1 5 0 ° VI 2 8 5 The rma l w i n d b a l a n c e 3 1 6 B a l a n c e o f t e r m s i n momentum e q u a t i o n 3 2 A l A n a l o g u e s e n s o r r a n g e s and r e s o l u t i o n s 4 5 i v L i s t o f F i g u r e s F i g u r e Page 1 C r u i s e t r a c k o f CSS P a r i z e a u d u r i n g J a n u a r y - F e b r u a r y 1979 6 2 Summary o f m e a s u r e m e n t s d u r i n g t h e f i r s t i n t e n s i v e o b s e r v i n g p e r i o d o f FGGE 7 3 P r o b e f o r c e b a l a n c e a t d i s c r e t e d e p t h 9 4 S h i p d r i f t w i t h 95% l i m i t s 12 5 T ime and f r e q u e n c y r e s p o n s e o f 6 5 - p o i n t l i n e a r - p h a s e l ow p a s s d i g i t a l f i l t e r 13 6 Z o n a l v e l o c i t y s e c t i o n s a t 1 5 0 ° W 1 o n g i t u d e 15 7 M e r i d i o n a l v e l o c i t y s e c t i o n s a t 1 50 ° W l o n g i t u d e 16 8 L o c a l w i n d s m e a s u r e d d u r i n g e x p e r i m e n t 17 9 E s t i m a t e d z o n a l v e l o c i t y a t 157° W l o n g i t u d e 20 10 T e m p e r a t u r e s e c t i o n s a t 150° and 1 5 7 ° W l o n g i t u d e 21 11 S a l i n i t y s e c t i o n s a t 150° and 1 5 7 0 W l o n g i t u d e 2 2 12 S i g m a - t s e c t i o n s a t 150° and 1 5 7 ° W l o n g i t u d e 24 13 Oxygen and p h o s p h a t e d i s t r i b u t i o n d u r i n g days 3 5 - 3 7 a t 150° W l o n g i t u d e 25 14 T i m e - v a r y i n g e q u a t o r i a l c i r c u l a t i o n 29 v L i s t o f F i g u r e s ( c o n t i n u e d ) F i g u r e Page 15 P e r i o d i n days o f s i n u s o i d a l c u r v e f i t t o s i g m a - t 35 16 A m p l i t u d e o f s i n u s o i d a l f i t t o p e r t u r b a t i o n s i g m a - t 36 17 Pha se o f s i n u s o i d a l f i t t o p e r t u r b a t i o n s i g m a - t 37 18 R a t i o o f r e s i d u a l s u m - o f - s q u a r e s ( s s q ) o f p e r t u r b a t i o n s i g m a - t t o t o t a l s s q 39 A l S y s t e m b l o c k d i a g r a m 46 A2 B l o c k d i a g r a m o f u n d e r w a t e r s e n s o r p a c k a g e 47 A3 P h o t o g r a p h o f u n d e r w a t e r u n i t 48 A4 O p e r a t i o n o f s i n g - a r o u n d c u r r e n t m e t e r 50 A5 P o l a r r e s p o n s e o f c u r r e n t m e t e r 54 A6 T y p i c a l v e l o c i t y p r o f i l e 57 v i A c k n o w l e d g e m e n t Many p e o p l e have a s s i s t e d i n t h e p r o d u c t i o n o f t h i s t h e s i s . F i r s t , I w i s h t o t h an k my s u p e r v i s o r , D r . R. W. B u r l i n g , f o r h i s k i n d l y e n c o u r a g e m e n t and s u p p o r t t h r o u g h o u t t h e t h e s i s w o r k , and e s p e c i a l l y f o r h i s p i t h y g r a s p o f t h e E n g l i s h l a n g u a g e . I have g r e a t l y b e n e f i t t e d f r o m h i s s p e c i a l a b i l i t y t o s t u d y a p r o b l e m f r o m many a n g l e s , and f r om h i s a s t u t e p h y s i c a l i n s i g h t . I a l s o f e e l a g r e a t d e b t o f g r a t i t u d e t o D r . M i k i o M i y a k e , whose i n i t i a t i v e and g u i d -ance b o t h l e d t o t h e d e v e l o p m e n t o f t h e p r o f i l i n g a c o u s t i c c u r r e n t m e t e r s y s t e m , and t o my p u r s u i t o f a h i g h e r d e g r e e . I mus t a l s o a c k n o w l e d g e t h e t e c h n i c a l a s s i s t a n c e o f R i c C o r m a n , J o h n L o v e , Dave Ramsden , and Dawson T r u a x f o r h a r d -wa re and p r o g r a m m i n g a s s i s t a n c e i n t h e d e v e l o p m e n t and t e s t -i n g o f t h e p r o f i l i n g c u r r e n t m e t e r s y s t e m . To a l l t h o s e members o f t h e I n s t i t u t e o f Ocean S c i e n c e s who made s p e c i a l e q u i p m e n t f r e e l y a v a i l a b l e and e x p e d i t e d t h e t h e s i s , I o f f e r my g r a t i t u d e . F i n a l l y , I w i s h t o t h ank S t a n H u g g e t t and Co r D e j o n g , and t h e c a p t a i n and c r ew o f t h e CSS P a r i z e a u who a s s i s t e d i n t h e d a t a c o l l e c t i o n . T hank s a l s o t o D r . R. E . Thomson f o r c h e c k i n g t h e A p p e n d i x f o r c o r r e c t n e s s , and D r . S t e v e Pond f o r c o n s t r u c t i v e l y c r i t i c i z i n g t he f i n a l t h e s i s d r a f t . The f i n a n c i a l s u p p o r t o f t h e O f f i c e o f Na va l R e s e a r c h g r a n t N 0 0 0 1 4 - 7 7 - G - 0 0 4 7 t o D r s . R. W. B u r l i n g and M. M i y a k e i s a l s o g r a t e f u l l y a c k n o w l e d g e d . v i i 1.0 INTRODUCTION S i n c e t h e d i s c o v e r y o f t h e e a s t w a r d s e q u a t o r i a l u n d e r -c u r r e n t i n t h e m i d - P a c i f i c by C r o m w e l l i n 1952 ( C r o m w e l l , 1 9 5 3 ) , and s u b s e q u e n t d i s c o v e r i e s o f s i m i l a r u n d e r c u r r e n t s i n t he A t l a n t i c and I n d i a n O c e a n s , a c o h e r e n t p i c t u r e o f t h e mean c h a r a c t e r i s t i c s o f t h e s e i n t e n s e n a r r o w c u r r e n t s has emerged ( G i l l , 1 9 7 5 ) . The u n d e r c u r r e n t s a r e a r e s p o n s e t o e a s t w a r d p r e s s u r e g r a d i e n t s t h r o u g h o u t t h e u p p e r l a y e r s o f t h e t r o p i c a l o c e a n ; t h e p r e s s u r e g r a d i e n t s e x i s t b e c a u s e t h e w i n d - d r i v e n w e s t w a r d s u r f a c e w a t e r f l o w i s i n t e r r u p t e d b y , and p i l e s up a g a i n s t , m e r i d i o n a l l a n d m a s s e s . The i s o p y c n a l s n e a r t h e e q u a t o r c h a r a c t e r i s t i c a l l y bow upwa rd s above t h e c o r e o f t h e u n d e r c u r r e n t and bow downwards b e l o w t h e c o r e , i n q u a l i t a t i v e c o n f o r m a n c e w i t h t he t h e r m a l w i n d e q u a t i o n ( G i l l , 1 9 7 5 , and W e i s b e r g e t a l , 1 9 7 9 ) : pgy 3u /3z = g dp/dy p = d e n s i t y p = v a r i a t i o n o f C o r i o l i s p a r a m e t e r w i t h l a t i t u d e y = n o r t h w a r d d i s t a n c e f r om e q u a t o r g = g r a v i t a t i o n a l a c c e l e r a t i o n u = z o n a l v e l o c i t y A s e c o n d b a s i c and w e l l known f e a t u r e o f t h e mean u n d e r c u r -r e n t f l o w i s t h e s u r f a c e d i v e r g e n c e due t o Ekman f l u x away 1 f r o m t h e e q u a t o r . The r e s u l t i n g s u b s u r f a c e c o n v e r g e n t e q u a -t o r i a l f l o w i n t u r n l e a d s t o s t r o n g e q u a t o r i a l u p w e l l i n g and m i x i n g . T h i s l e d t o a t h i r d b a s i c c o n c e p t a s s o c i a t e d w i t h mean e q u a t o r i a l c i r c u l a t i o n ( G i l l , 1 9 7 5 ) ; t h i s i s t h e n e t n o n l i n e a r t r a n s p o r t e q u a t o r w a r d o f e a s t w a r d momentum, w h i c h somewhat i n t e n s i f i e s e a s t w a r d s u b s u r f a c e f l o w . As G i l l e x p l a i n e d , t h e w e s t w a r d s u r f a c e w a t e r d i v e r g e s t o t h e n o r t h and s o u t h , r e s u l t i n g i n an e x c e s s o f e a s t w a r d momentum a t t h e d e p t h o f t h e u n d e r c u r r e n t . T h i s i d e a c o n f o r m s w i t h t h o s e f i r s t s u g g e s t e d by F o f f o n o f f and Mon tgomery ( 1 9 5 5 ) as an e x p l a n a t i o n f o r t h e e x i s t e n c e o f t h e u n d e r c u r r e n t . F i n a l l y , t h e s i m p l e s t e q u a t o r i a l mode l w h i c h i n c l u d e s an e q u a t o r i a l u n d e r c u r r e n t and c o r r e s p o n d s t o o b s e r v a t i o n s i s a w i n d - d r i v e n homogeneous s u r f a c e l a y e r o v e r l a y i n g a s t r a t i f i e d l a y e r , w i t h a deep homogeneous l a y e r b e l o w . M e a s u r e m e n t s t o 1973 were c h i e f l y c o n c e n t r a t e d i n t h e P a c i f i c . Mon tgome r y and S t r o u p ( 1 9 6 2 ) d e s c r i b e d some f e a t u r e s o f t he u n d e r c u r r e n t ; s p e c i f i c a l l y , t h e n o r t h w a r d t o n g u e o f a s u b s u r f a c e s a l i n i t y maximum w h i c h t e r m i n a t e s a b r u p t l y a t t h e e q u a t o r , and an e s t i m a t e d mean e q u a t o r i a l s u b s u r f a c e c o n v e r g e n c e o f t h e m e r i d i o n a l v e l o c i t y c o m p o n e n t s o f 4 cm s " 1 . K n au s s ( 1 9 6 0 , 1 9 6 6 ) made c a r e f u l m e a s u r e m e n t s o f t e m p e r a t u r e , s a l i n i t y , o x y g e n , p h o s p h a t e , and s i l i c a t e , and i n f e r r e d s t r o n g v e r t i c a l m i x i n g a n d / o r u p w e l l i n g . T a f t e_t aj_ ( 1973 ) we re amongs t t h e f i r s t t o o b s e r v e s u r f a c i n g o f t h e u n d e r c u r r e n t i n t h e P a c i f i c s o u t h o f t h e e q u a t o r , and a l s o i n t e r p r e t t e d c u r r e n t m e t e r d a t a as d e s c r i b i n g an u n d e r -2 c u r r e n t m e a n d e r . G r o v e s and M i y a t a ( 1 9 6 7 ) a n a l y z e d sea l e v e l r e c o r d s and d e t e c t e d w e a t h e r - i n d u c e d f l u c t u a t i o n s i n t h e t r o p i c a l c i r c u l a t i o n o f o r d e r f o u r t o f i v e d a y s . M a j o r e x p e d i t i o n s t o g a t h e r more m e a s u r e m e n t s o f t h e u n d e r c u r r e n t s i n t h e t h r e e o c e a n s t h e n c e a s e d u n t i l t h e G l o b a l A t m o s p h e r i c R e s e a r c h P r o g r a m (GARP) A t l a n t i c T r o p i c a l E x p e r i m e n t (GATE) i n 1 9 7 4 , t h e r e s u l t s o f w h i c h a r e now a p -p e a r i n g . One o f t h e g o a l s o f GATE was t o mea su r e l o n g p e r i o d waves and f l u c t u a t i o n s o f t h e A t l a n t i c E q u a t o r i a l U n d e r c u r r e n t . P h i l a n d e r and D u i n g ( 1 979 ) p r o v i d e d an o v e r -v i e w o f t h e m e a s u r e m e n t s . They r e p o r t e d t h a t a w i d e s p e c t r u m o f f r e q u e n c i e s was p r e s e n t i n t h e u n d e r c u r r e n t , w i t h p ea k s a t : ( a ) 3 -5 day s - f o r c e d i n e r t i a - g r a v i t y waves due t o a t m o s p h e r i c e x c i t a t i o n ; t h e r e a p p e a r e d t o be a c o n n e c t i o n t o sea l e v e l f l u c t u a t i o n s . ( b ) 1 6 - d a y meande r s - f l u c t u a t i o n s o f t h e u p p e r m i x e d l a y e r , p o s s i b l y due t o t r a d e w i n d f o r c i n g o r i n s t a b i l i t i e s i n s u r f a c e c u r r e n t s . ( c ) 3 0 - d a y , 1000 km waves - d o m i n a n t R o s s b y - g r a v i t y wave f l u c t u a t i o n s a t t h e l e v e l o f t h e c o r e o f t h e u n d e r c u r r e n t , p o s s i b l y a l s o due t o u n s t a b i 1 i t i e s i n s u r f a c e c u r r e n t s . ( d ) a n n u a l t r e n d - r e l a t e d t o t h e s e a s o n a l v a r i a t i o n s i n w i n d s t r e s s . 3 The a u t h o r s a l s o n o t e d t h a t t h e r e was some e v i d e n c e o f wave i n t e r a c t i o n w i t h mean u n d e r c u r r e n t f l o w , and t h e f l u c t u -a t i o n s i n t h e l o c a l w i n d s may be c l o s e l y t i e d t o u p w e l l i n g . F i n d i n g s by Bubnov and E g o r i k h i n ( 1 9 7 9 ) and W e i s b e r g ( 1 9 7 9 ) s u g g e s t t h a t w h i l e t h e z o n a l u n d e r c u r r e n t c i r c u l a t i o n i s s t a b l e , t he w e s t w a r d s u r f a c e f l o w s may be u n s t a b l e and t h e m e r i d i o n a l s t r u c t u r e i s h i g h l y v a r i a b l e . D ti i n g and H o l l o c k ( 1 9 7 9 ) d e t e c t e d 1 6 - d a y , 2000 km e q u a t o r i a l 1 y -t r a p p e d waves whose pha se s peed c o u l d be r e l a t e d t o o b s e r v e d v a r i a t i o n s i n A t l a n t i c E q u a t o r i a l U n d e r c u r r e n t z o n a l t r a n s -p o r t . The a im o f t h i s t h e s i s i s t o d e s c r i b e t i m e f l u c t u a t i o n s o f t h e P a c i f i c E q u a t o r i a l U n d e r c u r r e n t as o b s e r v e d a t 1 5 0 ° West L o n g i t u d e , w i t h p a r t i c u l a r e m p h a s i s on f l u c t u a t i o n s w i t h p e r i o d s o f two weeks t o one m o n t h . C o n f i r m a t i o n o f e a r l i e r m e a s u r e m e n t s o f mean u n d e r c u r r e n t q u a n t i t i e s w i l l a l s o be d e s c r i b e d . I t i s t o be a n t i c i p a t e d t h a t many o f t h e f i n d i n g s o f GATE i n t h e A t l a n t i c w i l l a l s o h o l d t r u e i n t h e P a c i f i c ; t h e m a j o r d i f f e r e n c e be tween t h e two o c ean b a s i n s b e i n g t h e much w i d e r e a s t - w e s t e x t e n t o f t h e P a c i f i c . 4 TIME VARIATIONS OF THE P A C I F I C EQUATORIAL UNDERCURRENT 2 . 0 INTRODUCTION As p a r t i c i p a t i n g members d u r i n g t h e f i r s t i n t e n s i v e o b -s e r v i n g p e r i o d o f t h e F i r s t GARP G l o b a l E x p e r i m e n t ( F G G E ) , C a n a d i a n s c i e n t i s t s c a r r i e d ou t work on CSS P a r i z e a u n e a r 150° W L o n g i t u d e i n t h e v i c i n i t y o f t h e e q u a t o r f r o m J a n u a r y 14 t o F e b r u a r y 2 0 , 1 9 7 9 , e x c e p t f o r a me r cy r un t o C h r i s t m a s I s l a n d ( 1 5 7 ° W l o n g i t u d e ) midway t h r o u g h t h e c r u i s e . Mo s t m e a s u r e m e n t s we re a l o n g 1 5 0 ° W c r o s s i n g t h e e q u a t o r ; one s e r i e s was a l o n g 157° W c r o s s i n g t h e e q u a t o r and two s e r i e s we re c o n d u c t e d o v e r a day o r so n e a r t h e e q u a t o r . The c r u i s e t r a c k i s shown i n F i g u r e 1. The p r i m a r y o b j e c t i v e was t h e c o l l e c t i o n o f s t a n d a r d s h i p m e t e o r o l o g i c a l d a t a , s u p p l e m e n t e d by u p p e r a i r b a l l o o n s o u n d i n g s t w i c e d a i l y . The s e c o n d a r y o b j e c t i v e was an o c e a n o g r a p h i c p r o g r a m i n c l u d -i n g b o t t l e s t a t i o n s , c o n t i n u o u s c o n d u c t i v i t y and t e m p e r a t u r e v e r s u s d e p t h (CTD) c a s t s , v e l o c i t y / C T D c a s t s , and m i c r o -s t r u c t u r e c a s t s w i t h a v a r i e t y o f i n s t r u m e n t s . T h i s r e p o r t w i l l c o n c e n t r a t e on t h e m e s o s c a l e t e m p e r a t u r e , s a l i n i t y , o x y g e n , p h o s p h a t e , and v e l o c i t y r e c o r d s o b t a i n e d by t h e t h r e e f o r m e r t e c h n i q u e s . The mea su r emen t t i m e s a r e summar-i z e d i n F i g u r e 2 . 5 10NCITUDE t50°W LONGITUDE 150* W i H H P « 1! 16 17 i — i — ; r — < — 1 — H 1 1 1 1 f-i o n u * *13 14 is H 1 1 1 h-16 17 ) • ,o « C e r e n t p . o h l e r (C P) • S T D . • C P b a t r l n • C P b0MI*> V e l o t l l y ' T» m p e . o f u r e m i c' o 1» - u c t u f t p r o f i l e r ( M S ) V D l o n i r o n • . C P. M S F i g u r e 2. Summary o f m e a s u r e m e n t s d u r i n g t h e f i r s t i n t e n s i v e o b s e r v i n g p e r i o d o f FGGE The CTD i n s t r u m e n t was a G u i l d l i n e Mark I I I , w h i l e t h e v e l o c i t y / C T D s y s t e m was a c u s t o m u n i t b u i l t a t t h e I n s t i t u t e o f Ocean S c i e n c e s . The l a t t e r u n i t c o n t a i n s a G u i l d l i n e CTD, t o g e t h e r w i t h an a c o u s t i c d o p p l e r c u r r e n t m e t e r ; t h r e e c o m p l e t e s c a n s o f a l l t e n s e n s o r o u t p u t s we re t e l e m e t e r e d t o t h e s u r f a c e ea ch s e c o n d i n f r e q u e n c y - s h i f t k e y e d f o r m a t ( s e e A p p e n d i x f o r more d e t a i l o f w h o l e p r o b e ) . The i n s t r u m e n t was t e t h e r e d t o t h e d r i f t i n g s h i p , and a p p r o x i m a t e l y 100 kg o f l e a d was a t t a c h e d a r o u n d t h e p r o b e t o m i n i m i z e t i l t . The i n s t r u m e n t was o p e r a t e d f r o m t h e s t e r n o f t h e s h i p , and c u r -r e n t m e t e r d a t a w i t h i n 10 m e t e r s o f t h e s u r f a c e were n e g -l e c t e d due t o i n d e t e r m i n a n t m a g n e t i c e f f e c t s on t h e i n s t r u -m e n t ' s c o m p a s s . 2 . 1 EQUATORIAL UNDERCURRENT VELOCITY SECTIONS K n o w l e d g e o f t h e m o t i o n o f t h e c u r r e n t m e t e r p a c k a g e i s f u n d a m e n t a l t o t h e mea su r emen t o f a b s o l u t e o c ean c u r r e n t s f r o m a d r i f t i n g s h i p . D u r i n g t h e P a r i z e a u c r u i s e , t h e p r o b e was l o w e r e d i n d i s c r e t e s t e p s and h e l d f o r a s u i t a b l e t i m e a f t e r v e r t i c a l e q u i l i b r i u m was e s t a b l i s h e d . The t e n s i o n i n t h e c a b l e , t h e d r a g f o r c e s i m p i n g i n g on t h e p r e s s u r e c a s e , and t h e n e t w e i g h t o f t h e p r o b e we re t h e n a s sumed t o be i n b a l a n c e ( F i g u r e 3). Any h o r i z o n t a l m o t i o n w h i c h t h e n o c -c u r e d was a s sumed t o be due t o s h i p ' s d r i f t . An a v e r a g e s h i p ' s d r i f t was c a l c u l a t e d f r om s a t e l l i t e f i x e s u s i n g t h e T r a n s i t S y s t e m . T r a n s i t i s a w o r l d w i d e p o s i t i o n i n g s y s t e m u s i n g s i x s a t e l l i t e s i n p o l a r o r b i t . 8 C a b l e T e n s i o n w p r o b e = 0 If ^- D r ag W F i g u r e 3. P r o b e f o r c e b a l a n c e a t d i s c r e t e d e p t h 9 T y p i c a l p o s i t i o n e r r o r s a t one p l a c e have s t a n d a r d d e v i -a t i o n s o f l e s s t h a n 40 m e t r e s ; t h e r e i s an a d d i t i o n a l s t a n -d a r d d e v i a t i o n w h i c h depends on t h e a c c u r a c y o f e s t i m a t e d s p e e d s and i s 400 m e t r e s p e r k n o t o f s p e ed e r r o r i n t h e e a s t - w e s t d i r e c t i o n and 100 m e t r e s i n t h e n o r t h - s o u t h d i -r e c t i o n ( S t a n s e l l , 1 9 7 8 ) . T he s e e r r o r s a r e l e s s t h a n 5 cm s ~ 1 and have n e g l i g i b l e e f f e c t s on e s t i m a t e s o f d r i f t v e l o c -i t i e s b e c a u s e t h e a v e r a g i n g t i m e i s s e v e r a l h o u r s . D u r i n g and s u b s e q u e n t t o t h e o c e a n o g r a p h i c m e a s u r e m e n t s a t e a ch s t a t i o n , t h e s h i p was a l l o w e d t o d r i f t w i t h t h e e n g i n e s s t o p p e d w h i l e s a t e l l i t e f i x e s were a c c u m u l a t e d . T a b l e 1 s u m m a r i z e s t h e s t a r t and end t i m e s o f t h e d r i f t p e r i o d s , t h e number o f u s a b l e s a t e l l i t e f i x e s , t h e c a l c u l a t e d n o r t h i n g and e a s t i n g d r i f t s , and t h e a s s o c i a t e d 95% e r r o r s . D u r i n g t h e e a r l y p o r t i o n o f t h e c r u i s e , d r i f t s were c o n s i s t e n t l y h i g h e r t h a n a t o t h e r t i m e s b e c a u s e t h e e n g i n e s were s l o w l y t u r n i n g t o m a i n t a i n s t e e r a g e . L i n e a r r e g r e s s i o n s w i t h f i x e s w e i g h t e d i n v e r s e l y t o n o r t h i n g and e a s t i n g s t a n d a r d d e v i -a t i o n s we re u s ed t o d e t e r m i n e d r i f t . The d r i f t s and 95% l i m i t s o f T a b l e 1 a r e p l o t t e d i n F i g u r e 4 ; t h e r e l a t i v e c o n -s i s t e n c y o f t h e c a l c u l a t i o n s i s e s p e c i a l l y e v i d e n t d u r i n g t h e l a t t e r h a l f o f t h e mea su r emen t p e r i o d . The e f f e c t s o f t h e f o u r - t o s i x - s e c o n d s w e l l p e r i o d t r a n s m i t t e d down t h e c a b l e t o t h e p r o b e a t a l l d e p t h s we r e c. m i n i m i z e d by f i l t e r i n g t h e r e c o r d e d v e l o c i t y s i g n a l s w i t h a 6 5 - p o i n t l i n e a r pha se l ow p a s s f i l t e r . The f i l t e r w e i g h t s and i t ' s f r e q u e n c y t r a n s f e r f u n c t i o n a r e shown i n F i g u r e 5; a l l f r e q u e n c i e s above 0 . 1 Hz were s u p p r e s s e d . 10 STN START END N* N DRIFT 95% L IM IT E DRIFT 95% L IMIT DDHHMM DDHHMM (m/ s ) (m / s ) (m / s ) (m / s ) EQOO 211712 212033 6 - . 4 2 4 8 . 3 624 - 1 . 2508 . 2 9 0 7 EQOO 220446 220638 3 - . 4 4 9 9 . 5 4 3 9 -1 . 2191 3 . 2 352 EQOO 220650 220834 3 - . 4 1 5 9 . 2 560 -1 . 2730 . 3 6 7 9 EQOO 221012 221546 3 - . 1 9 9 6 . 1 5 2 8 -1 . 2457 . 4 484 EQOO 221812 222132 4 - . 1 6 5 0 . 0 0 6 3 -1 . 2310 . 0 3 8 4 SO 20 231636 240002 9 - . 0 4 7 5 . 0 2 5 8 - 0 . 6450 . 0 414 S020 232040 240002 3 . 0 307 . 0 362 - 0 . 7055 . 1 5 4 6 SOI 5 240455 240658 4 . 0 2 9 0 . 1 1 5 9 - 0 . 3119 . 0 222 SOI 5 240816 241128 4 - . 0 1 3 7 . 0 117 - 0 . 3952 . 0 1 2 4 S010 241542 241727 3 . 1 3 9 4 . 4 260 - 0 . 8854 2 .1 736 S005 250316 250545 3 .6741 . 0 155 - 0 . 7684 . 1 0 6 3 S002 250916 251210 3 . 4 3 9 8 . 4 972 - 0 . 3955 .601 7 EQOO 251630 251818 4 . 3 4 1 4 . 0 8 9 9 - 0 . 6448 . 1 8 8 8 N002 252332 260551 4 . 3 4 4 2 . 2 2 6 9 - 0 . 4649 . 1 5 8 4 N005 260824 261100 4 . 3 425 . 0 6 8 0 - 0 . 7294 . 1 5 9 6 N010 261536 261846 5 . 2 824 .1 511 - 0 . 9696 . 1 084 NOT 5 270012 270547 4 . 2 425 . 2 2 0 9 -1 . 11 72 . 1 210 N020 270926 272302 11 .41 77 . 0 1 6 0 -1 . 1061 . 0 3 0 9 S010 350813 350945 3 . 1 3 2 8 . 0337 - 0 . 2100 . 1 6 2 8 S005 351613 351 830 4 .471 7 . 0 2 9 0 - 0 . 2818 . 1 452 S002 352021 352255 3 . 1 6 7 5 . 2391 - 0 . 6026 .2121 EQOO 360324 360610 5 .0281 . 1 4 2 2 -1 . 1224 . 2 1 6 3 N002 360753 361023 3 . 2 1 3 7 . 7673 - 0 . 5965 2 . 6 5 1 2 N007 361642 361 831 5 - . 0 2 5 2 . 1 0 3 9 - 0 . 9752 .3221 N010 362049 362334 3 - . 0 0 9 4 .1 162 -1 . 3530 2 . 3 0 7 3 N015 37041 4 370603 4 .1 380 . 1 0 0 2 -1 . 3064 . 9 4 9 8 N020 370917 371956 10 . 0 0 4 0 . 0 265 -1 . 081 7 .01 13 EQOO 381704 381906 5 - . 1 6 1 2 . 0 7 6 0 - 0 . 7184 . 1 2 5 7 EQOO 390244 391032 11 - . 1 6 3 5 . 0 096 - 0 . 6572 . 0 2 1 8 N005 391826 392156 4 - . 3 0 6 4 . 0 3 3 0 - 0 . 4741 .1161 N005 400328 401110 8 - . 2 3 8 7 .0231 - 0 . 7111 . 0 3 4 2 S020 410422 41 1713 11 - . 0 9 5 7 . 0 1 3 3 - 0 . 5110 . 0 2 2 8 SOI 5 412130 420326 3 - . 1 4 8 0 .01 31 - 0 . 3426 .1561 S010 420750 421040 3 - . 1 4 6 1 . 1 315 - 0 . 4078 . 0 3 9 9 S007 421502 421922 4 - . 2 5 4 0 . 0 2 6 8 - 0 . 4901 . 0631 S005 430234 430658 6 - . 2431 . 0 2 2 5 - 0 . 5810 .0331 S002 431122 431834 7 .1 102 .2001 - 0 . 3848 . 0 2 8 2 EQOO 432058 440326 3 . 0 0 6 5 . 0 604 - 0 . 5399 . 3 1 8 3 N002 440526 441042 4 . 0 6 0 2 . 0 5 0 3 - 0 . 5860 . 0 4 7 5 N005 441456 441820 7 . 0 237 . 0 877 - 0 . 8247 .0481 N807 451404 451608 4 . 2236 . 2 392 - 0 . 5119 . 2 3 1 0 N810 451 842 452214 4 . 2 775 . 0 992 - 0 . 6731 . 1 445 N815 460320 460942 9 . 1 3 7 8 . 0 1 0 8 - 0 . 7438 . 0 3 0 3 N820 461452 461754 5 . 4 202 . 0 652 - 0 . 5950 . 1 8 2 5 N830 470248 471024 8 . 6 884 . 0 336 - 0 . 6310 . 0 6 1 9 N840 471608 472146 4 . 6 697 . 0 4 3 2 - 0 . 8060 . 1416 N850 480440 481654 11 .3541 .0051 - 0 . 4334 . 0 0 9 9 T a b l e 1. S h i p d r i f t a t e a ch s t a t i o n a t 1 5 0 ° W l o n g i t u d e . N* i s number o f o b s e r v e d s a t e l l i t e p a s s e s . 11 o o o o CO —- in" » * Q O I— CH § § o m, 20 + T _ +1 " f t — i 25 + 30 35 40 T I M E ( D A Y S ) — i — 45 —i 50 o o o t o o i ° U_o a: -o i " < o LU • o m i 20 -H Z5 To — i — 35 + + i— 40 T I M E ( D A Y S ) + -H i 45 50 Figure 4 . Ship d r i f t with 9 5 % l i m i t s 12 J - o O • Ju o.oo 9.00 la.oo 27.00 38.00 43.00 S A M P L I N G I N T E R V A L S 34.00 63.00 72.00 N - 6 5 P A S S 3 A N D - . 0 0 0 TO . 0 0 3 S T O P B A N D - . 0 9 9 TO 1 . 5 0 0 -3.00 -2.30 -2.00 -1.30 -I.00 -0.50 LOG F R E Q U E N C Y ( H Z ) 0.00 0. 50 I .00 F i g u r e 5. T ime and f r e q u e n c y r e s p o n s e of 6 5 - p o i n t l i n e a r - p h a s e l ow p a s s d i g i t a l f i l t e r 13 The mean and s t a n d a r d d e v i a t i o n o f t h e m e a s u r e d r e l -a t i v e c u r r e n t c o m p o n e n t s a t f i x e d d e p t h s were t h e n com-p u t e d . O n l y a v e r a g e s o v e r t i m e s e x c e e d i n g 30 s e c o n d s and w i t h s t a n d a r d e r r o r s l e s s t h a n 15 cm/s we re a c c e p t e d . S e c -t i o n s o f z o n a l v e l o c i t i e s o f t h e t h r e e t r a n s e c t s a t 1 5 0 ° w e s t l o n g i t u d e a r e shown i n F i g u r e 6 , and t h e s e c t i o n s o f m e r i d i o n a l v e l o c i t i e s a r e shown i n F i g u r e 7 . The z o n a l v e l o c i t i e s e x h i b i t a maximum i n c u r r e n t i n -t e n s i t y d u r i n g T r a n s e c t 5 s i m u l t a n e o u s w i t h an i n c r e a s e i n c r o s s - s e c t i o n a l a r e a . T r a n s e c t s 5 and 6 a t 1 50 ° W show a s u r f a c i n g o f t h e u n d e r c u r r e n t a t 1 . 5 ° S; t h e l o c a l w i n d s d u r i n g t h i s t i m e , shown i n F i g u r e 8 , do n o t a p p e a r t o be c l e a r l y r e l a t e d t o t h e s u r f a c i n g . The i n t e g r a t e d t r a n s p o r t s o f t h e t h r e e z o n a l t r a n s e c t s we r e c ompu t ed by i n t e g r a t i n g t h e c u r r e n t f i e l d on t h e p l o t s u s i n g a p l a n i m e t e r and a r e shown i n T a b l e 2 . The J a n u a r y -F e b r u a r y m e a s u r e m e n t s a r e known t o have been made a t t h e T r a n s e c t J u l i a n Days T r a n s p o r t ( S v ) C r o s s - S e c t i o n a l A r e a ( m 2 ) 3 2 4 - 2 7 10 4 . 1 * 10 7 5 3 5 - 3 7 26 6 . 7 * 1 0 7 6 4 2 - 4 7 17 6 . 6 * 1 0 7 T a b l e 2 . I n t e g r a t e d Z o n a l T r a n s p o r t s ( l S v = 1 0 6 m 3 s " 14 LATITUDE (DEG) - 3 - 2 - I 0 1 2 3 , j __k i j i— 1 -J TRAH3ECT 3 LATITUDE (DEG) o Figure 6 . Zonal ve loc i ty sections at 1 5 0 W longitude Dots Indicate d iscre te samples. 15 16 17 t i m e o f min imum a n n u a l z o n a l t r a n s p o r t ( P h i l a n d e r , 1 9 7 3 ) . The c a l c u l a t e d t r a n s p o r t i s c o n s i s t e n t w i t h r e s u l t s o f o t h e r i n v e s t i g a t o r s ( e . g . see P h i l a n d e r , 1 9 7 3 , and F i r i n g , 1 9 8 0 ) . The m e r i d i o n a l v e l o c i t y s t r u c t u r e , F i g u r e 7, s u g g e s t s a n o m a l o u s n o r t h w a r d t r a n s p o r t t h r o u g h o u t a l m o s t a l l o f t h e u n d e r c u r r e n t r e g i o n d u r i n g t h e o b s e r v a t i o n p e r i o d s . I t d o e s n o t seem p o s s i b l e t o a t t r i b u t e t h e s e l a r g e v e l o c i t i e s t o u n -c e r t a i n t y i n s h i p d r i f t , due t o t h e c a s t - t o - c a s t c o n s i s t e n c y and r e l a t i v e l y s m a l l e r s u r f a c e and deep v a l u e s . Compass a l i g n m e n t was c a r e f u l l y c h e c k e d p r i o r t o t h e c r u i s e and t h u s i s n o t a s o u r c e o f s y s t e m a t i c e r r o r . F u r t h e r m o r e , t h e compass a n g l e was m o n i t o r e d d u r i n g a l l c a s t s , and no i n d i c a t i o n o f s t i c k i n g o r d ynam i c r e s p o n s e l i m i t a t i o n was o b s e r v e d . T e s t s w i t h m a n u f a c t u r e d d a t a , and w i t h o t h e r r e a l d a t a , have e s t a b l i s h e d t h e v a l i d i t y o f t h e p r o c e s s i n g a l g o r i t h m s . T h u s , t h e d a t a mus t be a c c e p t e d w i t h i n e x p e r i m e n t a l e r r o r . The t h r e e s e c t i o n s o f t h e m e r i d i o n a l c i r c u l a t i o n o f t h e u n d e r c u r r e n t i n F i g u r e 7 show n o r t h w a r d v e l o c i t y max ima n e a r t h e same l o c a t i o n as t h e e a s t w a r d v e l o c i t y max ima w h i c h a r e a l w a y s w i t h i n one d e g r e e o f t h e e q u a t o r ; t h i s f e a t u r e s u g -g e s t s t h a t w a t e r i s b e i n g e n t r a i n e d by t h e u n d e r c u r r e n t . To e x p l a i n t h e n o r t h w a r d s t r a n s p o r t w h i l e m a i n t a i n i n g n e g l i -g i b l e m e r i d i o n a l t r a n s l a t i o n o f t h e c o r e r e q u i r e s e i t h e r t h a t t h e u n d e r c u r r e n t w a t e r i s b e i n g v e r t i c a l l y and h o r i -z o n t a l l y m i x e d , o r t h a t t h e s u b s t a n t i a l d i v e r g e n c e o f t h e n o r t h w a r d s c o m p o n e n t s i s b a l a n c e d by c o n v e r g e n c e i n o t h e r c o m p o n e n t s . 18 The c o m p a r a b l e m a g n i t u d e s o f t h e m e r i d i o n a l and z o n a l c u r r e n t c o m p o n e n t s c o u l d be e x p l a i n e d by t h e p r e s e n c e o f an eddy d u r i n g t h e o b s e r v a t i o n p e r i o d w h i c h , i n t u r n , w o u l d l e a d t o a d e s c r i p t i o n i n t e r m s o f l o n g p e r i o d w a v e s . A s e c t i o n a t 157° W was c o m p l e t e d when t h e o p p o r t u n i t y a r o s e . U n f o r t u n a t e l y , s h i p d r i f t e s t i m a t e s by s a t e l l i t e c o u l d n o t be o b t a i n e d due t o t i m e c o n s t r a i n t s , and hence were e s t i m a t e d on t h e b a s i s o f p r i o r and s u c c e e d i n g m e a s u r e -men t s a t 1 50 ° W. O n l y t h e s e c t i o n o f z o n a l v e l o c i t y c ompon -e n t s a p p e a r e d t o have r e a s o n a b l e v a l u e s , and i s r e p r o d u c e d i n F i g u r e 9 . I t i s v e r y s y m m e t r i c when c ompa r ed t o t h e z o n -a l s e c t i o n s a t 150° W. 2 . 2 EUC SCALAR SECTIONS F i v e t e m p e r a t u r e s e c t i o n s we re c o m p i l e d a t 1 5 0 ° W and one a t 1 57 ° W. In a l l s e c t i o n s , shown i n F i g u r e 1 0 , t h e i s o t h e r m s dome upwa rd s above t h e t h e r m o c l i n e and d i p down-wa rd s b e l ow t h e t h e r m o c l i n e a t t h e e q u a t o r . F u r t h e r m o r e , t h i s i n v e r t e d symmet r y a p p e a r s t o be c o u p l e d w i t h t h e s t r e n g t h o f t he u n d e r c u r r e n t c o r e ; more i n t e n s e b o w i n g o c c u r s d u r i n g h i g h e r z o n a l t r a n s p o r t . The o b s e r v a t i o n s s u p -p o r t b o t h v e r t i c a l m i x i n g and u p w e l 1 i n g / d o w n w e l 1 i n g h y p o t h -e s e s . The s i x s a l i n i t y s e c t i o n s , F i g u r e 1 1 , show a p e r s i s t -e n t , h i g h s a l i n i t y c o r e (35 .6%) i n t r u d i n g f r om t h e s o u t h t o -wa r d s t h e e q u a t o r a t t h e d e p t h o f t h e c o r e o f t h e u n d e r c u r -r e n t ( n e a r 150 m) . D u r i n g t h e e x p e r i m e n t , a d i f f u s e r e g i o n o f l ow s a l i n i t y (34 .8%) was e v i d e n t n o r t h o f t h e e q u a t o r 19 " J O Figure 9. Estimated zonal velocity at ! 57W longitude 20 21 22 n e a r t h e c o r e . T s u c h i y a ( 1 9 6 8 ) n o t e d t h a t t h e n o r t h e r n l ow s a l i n i t y w a t e r o r i g i n a t e s o f f C a l i f o r n i a , w h i l e t h e h i g h s a l i n i t y s o u t h e r n w a t e r o r i g i n a t e s o f f S o u t h A m e r i c a . In t h e m i x e d l a y e r above t he u n d e r c u r r e n t c o r e , t h e s t e e p n e s s o f t h e i s o h a l i n e s a g a i n s u p p o r t v e r t i c a l m i x i n g o r t r a n s -p o r t . D e n s i t y s e c t i o n s , F i g u r e 1 2 , we re c ompu t ed f r o m t h e t e m p e r a t u r e and s a l i n i t y s e c t i o n s . The s h a r p p y c n o c l i n e i s l o c a t e d a t t h e d e p t h o f t h e c o r e o f t h e u n d e r c u r r e n t ; t h e r e i s some s u g g e s t i o n o f a b r o a d e n i n g o f t h e t h i c k n e s s o f t h e p y c n o c l i n e a t t h e e q u a t o r . The w a t e r above and be l ow t h e p y c n o c l i n e i s r e l a t i v e l y h omogeneou s . Oxygen and p h o s p h a t e s a m p l e s , F i g u r e 1 3 , we re c o l l e c t e d o n l y d u r i n g days 35 - 3 7 . They a r e q u i t e s i m i l a r t o t h e c o r r e s p o n d i n g t e m p e r a t u r e s e c t i o n i n t h a t t h e y show some dom ing o f t h e i s o p l e t h s above and d i s t i n c t dom ing b e l o w t h e u n d e r c u r r e n t c o r e . 2 . 3 T IME -VARYING MERIDIONAL CIRCULATION T h e r e was no a t t e m p t a t z o n a l s a m p l i n g , b e c a u s e t h e p r e s u p p o s e d l ow f r e q u e n c y (30 d a y s ) l o n g w a v e l e n g t h ( 1000 km) phenomena w o u l d n e c e s s i t a t e a l a r g e a r r a y o f s h i p s and good c o o r d i n a t i o n . H o w e v e r , t h e t r a n s e c t s c l o s e l y s p a c e d i n t i m e we re s u i t a b l e t o d e t e r m i n e w h e t h e r m i x i n g o r u p w e l -l i n g was t h e d o m i n a n t p r o c e s s a t t h e e q u a t o r . The c o n t i n u i t y e q u a t i o n w i t h z o n a l d i v e r g e n c e n e g l e c t e d s v / a y + 8w/3z = 0 23 24 LATITUDE (DEG) - 3 - 2 - I 0 I J! 3 8 u J o LATITUDE (DEG) - 3 - 2 - 1 0 I 2 3 o o o o a —i " m o w a F igu re 13. Oxygen and phosphate di st r i bt i on duri ng days 35-37 at 15.0W. I o ng i t ude P H O S P H A T E 25 was a p p l i e d t o d e t e r m i n e a p p r o x i m a t e u p w e l l i n g v e l o c i t i e s : w ( - h ) = / ( dv/dy) dz ( w(0)=0) The m e r i d i o n a l d i v e r g e n c e o f n o r t h - s o u t h v e l o c i t y , 9 v / 8 y , was c a l c u l a t e d by s u c c e s s i v e d i f f e r e n c e s and t h u s i s n o i s y . The r e s u l t s a r e t a b u l a t e d i n T a b l e s 3 and 4 . I f i t i s v a l i d t o n e g l e c t z o n a l d i v e r g e n c e , t h e f o l l o w -i n g i n t e r p r e t a t i o n o f t h e m e r i d i o n a l f l o w i s o f f e r e d . D u r i n g t r a n s e c t 3 , t h e r e i s u p w e l l i n g n o r t h and s o u t h o f t h e e q u a t o r i n t h e s u r f a c e l a y e r , and d o w n w e l l i n g a t t h e e q u a t o r . B e l ow t h e EUC c o r e , t h e r e i s d o w n w e l l i n g . When t h e m e r i d i o n a l v e l o c i t y p a t t e r n i s i n c l u d e d , t h e c i r c u l a t i o n p a t t e r n o f F i g u r e 14 r e s u l t s . T r a n s e c t 5 i s a g a i n ma r ked by u p w e l l i n g i n t h e s u r f a c e l a y e r away f r om t h e e q u a t o r , b u t t h e r e i s l i t t l e e v i d e n c e o f p r o n o u n c e d d o w n w e l l i n g a t t h e e q u a t o r . T r a n s e c t 6 i s mos t s u r p r i s i n g . The c a l c u l a t e d v e r t i c a l v e l o c i t i e s s u g g e s t u p w e l l i n g a t t h e e q u a t o r and c o m p e n s a t i n g d o w n w e l l i n g a t one d e g r e e n o r t h l a t i t u d e . An a l t e r n a t i v e e x p l a n a t i o n o f T r a n s e c t 6 w o u l d be n o i s e i n t h e l a t i t u d i n a l d i v e r g e n c e r e s u l t i n g f r om i n a p p r o p r i a t e l y c h o s e n a v e r a g i n g d i s t a n c e s o r , o f c o u r s e , t h e r e may be z o n a l c o n v e r g e n c e . In summary , t h e w a t e r i n t h e v i c i n i t y o f t h e u n d e r c u r r e n t c o r e a p p e a r s t o be t i m e - v a r y i n g and s u b j e c t t o b o t h u p w e l l i n g and d o w n w e l l i n g . A s s u m i n g a v e r t i c a l u p w e l l i n g r a t e o f 0 . 0 1 cm s - 1 a v e r a g e , i t w o u l d t a k e a p p r o x i m a t e l y f i f t e e n days f o r w a t e r i n t h e u n d e r c u r r e n t c o r e n e a r 150 m e t r e s t o r e a c h t h e s u r f a c e . 2 6 T r a n s e c t 3 - Days 24 t o 27 La t i t u d e Dep t h (m) 2S IS 0 IN 2N - 50 + 3 + 2 + 3 + 3 + 1 - 1 0 0 + 5 + 2 - 1 - 1 0 - 1 5 0 +3 +6 0 0 0 - 2 0 0 + 3 + 3 0 0 - 3 - 2 5 0 +2 0 - 3 - 3 0 0 +2 - 3 T r a n s e c t 5 - Days 35 t o 37 Dep t h (m) 2S IS 0 IN 2N - 50 +6 0 - 2 0 + 2 - 1 0 0 + 10 - 1 + 2 - 2 + 2 - 1 5 0 + 5 + 2 0 + 5 + 1 - 2 0 0 0 0 + 2 - 2 5 0 + 1 - 3 0 0 T r a n s e c t 6 - Days 43 t o 47 Dep t h (m) 2S IS 0 IN 2N - 50 + 2 0 0 - 1 0 0 0 + 6 - 1 0 - 1 5 0 0 + 10 - 6 - 2 0 0 + 1 0 + 15 -6 0 - 2 50 + 1 0 + 15 -5 0 - 3 0 0 + 10 - 5 0 T a b l e 3 . M e r i d i o n a l d i v e r g e n c e o f n o r t h - s o u t h v e l o c i t y ( * 1 0 - 6 s " M 27 T r a n s e c t 3 - Days 24 to 27 L a t i t u d e Depth (m) 2S IS 0 IN 2N -50 + 0.2 + 0.1 0 + 0.2 + 0.1 -100 + 0.4 +0.2 - 0 . 1 + 0.1 + 0.1 -150 + 0.6 +0.5 - 0 . 3 + 0.1 + 0.1 -200 + 0.7 + 0.6 - 0 . 5 + 0.1 - 0 . 1 -250 - 0 . 4 + 0.1 - 0 . 3 -300 +0.2 -0 . 4 T r a n s e c t 5 -- Days 35 to 37 Depth (m) 2S IS 0 IN 2N -50 + 0.3 0 - 0 . 1 0 + 0.1 -100 +0.8 - 0 . 1 0 - 0 . 1 + 0.2 -150 + 1.1 + 0.1 0 + 0.2 + 0.3 -200 0 + 0.2 + 0.4 -250 + 0.4 -300 T r a n s e c t 6 • • Days 43 to 47 Depth (m) 2S IS 0 IN 2N -50 + 0.1 0 0 -100 0 +0.4 - 0 . 5 -150 0 + 0.9 - 0 . 8 -200 0 + 1.7 - 1 . 1 -250 0 + 2.4 - 1 . 4 -300 +2.9 - 1 . 6 Table 4. V e r t i c a l v e l o c i t i e s in mm s~ 1 at 150° W 28 SOUTH Equa to r NORTH s u r f a c e I ( l o w e r m i x i n g r a t e s ) F i q u r e 14. T i m e - v a r y i n g e q u a t o r i a l c i r c u l a t i o n T r a n s e c t 3 — — T r a n s e c t s 5 & 6 29 2 . 4 RELATIONSHIP BETWEEN EUC V E L O C I T I E S AND SCALAR PROPERTIES In a b a s i c a t t e m p t t o l i n k t h e o b s e r v e d v e l o c i t y and s c a l a r p r o p e r t y d i s t r i b u t i o n , t h e e q u a t o r i a l t h e r m a l w i n d e q u a t i o n f o r z o n a l v e l o c i t y was e x a m i n e d : pgy 3u/ 3z = g 8 P / ay y / 0 P 3 a u / s z = g 3 2 p / 3 y 2 y = 0 The b a l a n c e be tween t h e t e r m s i s shown i n T a b l e 5 . In g e n e r a l t e r m s , t h e s i g n s o f t h e t e r m s a g r e e b u t t h e m a g n i t u d e s a r e s i g n i f i c a n t l y d i f f e r e n t . The r e s u l t s s u g g e s t t h a t a t b e s t p a r t o f t h e e a s t - w e s t f l o w i s g e o s t r o p h i c a l l y b a l a n c e d , w h i c h i s i n g e n e r a l a g r e e m e n t w i t h r e s u l t s i n t h e A t l a n t i c (Wei s b e r g _et _a j , 1 9 7 9 ) . An e s t i m a t e o f t h e r e l a t i v e s i z e s o f t h e t e r m s o f t h e momentum e q u a t i o n s , s i m i l a r t o t h a t o f K n a u s s ( 1 9 6 0 ) , was a t t e m p t e d . No z o n a l s a m p l i n g was p e r f o r m e d and t h u s z o n a l d i v e r g e n c e s c o u l d n o t be c o m p u t e d . The r e s u l t s , i n u n i t s o f 1 0 ~ 6 m s " 2 , we re c ompu t ed and a r e p r e s e n t e d i n T a b l e 6 . M a j o r unknowns a r e t h e r e l a t i v e i n f l u e n c e o f v e r t i c a l and h o r i z o n t a l f r i c t i o n and t h e z o n a l p r e s s u r e g r a d i e n t , w h i c h a r e p o t e n t i a l l y t h e l a r g e s t t e r m s . S p i r a l p a t t e r n s were o b -s e r v e d i n t h e c u r r e n t s as t h e m e t e r was l o w e r e d on s t a t i o n ; f u r t h e r m o r e , t h e s p i r a l s g e n e r a l l y r e v e r s e d d i r e c t i o n o f r o t a t i o n b e l o w t h e d e p t h o f t h e u n d e r c u r r e n t c o r e . Due t o t h e weak C o r i o l i s f o r c e a t t h e e q u a t o r , i t was n o t s u r p r i s -30 T r a n s e c t 3 T r a n s e c t 5 T r a n s e c t 6 LAT -2 -1 0 + 1 +2 -2 -1 0 + 1 + 2 -2 -1 0 + 1 + 2 - 50 _ — - 0 . 4 0.0 _ _ - 0 . 1 - 0 . 2 - 0 . 8 -1 .0 --100 0.3 - 1 . 2 0.0 - - 1 . 3 - 2 . 0 - 0 . 2 0.0 - 0 . 3 0.0 - 0 . 8 - 0 . 2 -150 - - 0 . 2 -0 .7 -0 .2 0.0 1.3 0.0 0.0 0.0 0.2 0.0 - 0 . 8 2.0 0 .0 -200 0.6 +1.0 0.2 0.0 0.5 1.0 0.0 0.1 0.6 1.0 0.5 0.1 -250 _ — - - 0.5 0.4 - - 0.8 - -(a) ju^ x l O " 2 s - 1 3Z LAT -2 -1 0 +1 + 2 -2 -1 0 + 1 + 2 -2 -1 0 + 1 + 2 D - 50 0.9 0.0 0.5 0.5 _ - 2 . 3 0 .9 E -100 _ 0.8 - 2 . 8 0.0 - - 3.0 - 4 . 7 0.5 - 0.0 0.7 - - 1 . 9 P -150 0.5 -1 .6 - 0 . 5 - 0.0 - 3 . 0 0.0 0.0 0.0 - 0 . 9 0.0 - 4.7 0 .0 T -200 1.4 2.3 0.5 - - - 1 . 2 2.3 4.6 0 .0 - 0 . 5 - 1 . 4 - 1.2 0.5 H -250 - - - - - - - 1 . 2 - - - — - 1 . 9 — — (b) 3U x 1 0 " 5 kg 3Z LAT -2 -1 0 + 1 + 2 -2 -1 0 + 1 + 2 -2 -1 0 + 1 + 2 D - 50 2.5 1.0 - 1 . 0 - 2 . 5 - 1 . 0 0.7 1.0 - 3 . 9 0.0 - 2 . 0 0.0^ 0.0 - 2 . 0 - 1 . 0 - 1 . 0 E -100 2.0 2.0 0.0 - 2 . 0 - 2 . 5 1.5 1.0 - 2 . 9 0.0 - 2 . 0 3.9 0.0 - 3 . 9 - 4 . 9 - 2 . 0 P -150 8.8 5.9 0.0 - 3 . 9 - 2 . 5 0.0 2.0 - 2 . 0 1.0 - 2 . 9 - 4 . 9 2.0 2.9 - 5 . 9 9.8 T -200 4 .9 0.0 0.0 0.0 0.0 - 2 . 9 2.9 - 3 . 9 3.9 2.0 - 1 . 0 - 1 . 0 1.0 1.0 1.0 H -250 0.0 0.5 - 0.0 2.0 - 1 . 5 3.9 0.0 0.0 0 .0 0 .0 1.0 1.0 (c ) g a p x 10" 5 kg m" *+. 9y Table 5. Thermal Wind Ba lance fa t the e q u a t o r , the terms are pB3u/az in (b) and g a 2 p/ 3y 2 i n (c) ) Term C u r r a n ( 1 9 8 1 ) K n a u s s ( 1 9 6 6 ) Mon th J a n u a r y - F e b r u a r y S e p t e m b e r - December 1979 1_96J u 0 . 8 m s - 1 1 . 0 m s - 1 v 0 . 4 m s - 1 0 . 0 5 m s " 1 w 0 . 1 x 1 0 - 3 m s - 1 0 . 0 5 x 1 0 - 3 m s - 1 u t uux vuy wuz Byu ( a t 1° ) 1 .0 m s - 2 2 . 0 m s - 2 - 2 . 0 m s-2 - 1 . 0 m s~2 0 . 1 m s - 2 +0.1 t o +0 .2 m s - 2 0 . 2 m s - 2 - 0 . 1 t o - 0 . 2 m s - 2 - 0 . 1 m s - 2 apx f r i c t i o n 0 . 2 6 m s - 1 •0 .30 m s - 1 T a b l e 6 . B a l a n c e o f t e r m s i n z o n a l momentum e q u a t i o n 32 i n g t h a t t h e s p i r a l d i r e c t i o n s a p p e a r e d n o t t o be c o u p l e d t o 1 a t i t u d e . In summary , i t i s i n t u i t i v e l y f e l t t h a t t h e d o m i n a n t b a l a n c e i s b e tween p r e s s u r e g r a d i e n t and h o r i z o n t a l and v e r t i c a l f r i c t i o n . Of t h e t e r m s w h i c h c o u l d be c a l c u l a t e d , t h e most i m p o r t a n t a p p e a r t o be t h e n o n l i n e a r t e r m s . 2 .5 WAVE PHENOMENA F l u c t u a t i o n s i n t he e q u a t o r i a l w a t e r , b o t h i n t h e c o r e and i n t h e o v e r l y i n g s u r f a c e w a t e r , have a t t r a c t e d t h e i n -t e r e s t o f many i n v e s t i g a t o r s . I t i s w e l l known t h a t a w i d e v a r i e t y o f waves can t h e o r e t i c a l l y e x i s t i n t h i s r e g i o n . T u r b u l e n t m i x i n g g e n e r a t e d by t h e s e waves i n t h e s h e a r r e g i o n above t h e EUC c o u l d p o s s i b l y e x p l a i n b o t h t h e r e l a t i v e l y homogeneous l a y e r s above and b e l o w t h e p y c n o c l i n e , and t h e u p w e l 1 i n g / d o w n w e l 1 i n g a c t i o n o b s e r v e d a t t h e e q u a t o r d e s c r i b e d i n S e c t i o n 2 . 3 . In t h e s e a r c h f o r waves w i t h p e r i o d s i n e x c e s s o f t e n d a y s , i t was d e c i d e d t o use d e n s i t y ( s i g m a - t ) p e r t u r b a t i o n s as a t r a c e p r o p e r t y . T h e r e we re s e v e r a l r e a s o n s f o r t h i s c h o i c e . F i r s t , t h e r e we re as many as n i n e s a m p l e s o f s i g m a - t a t e a ch l a t i t u d e - d e p t h p a i r , w h e r e a s t h e r e we re o n l y t h r e e u s a b l e t r a n s e c t s w h i c h i n c l u d e d v e l o c i t y m e a s u r e -m e n t s . S e c o n d l y , t h e n o i s e a s s o c i a t e d w i t h t h e s c a l a r mea-s u r e m e n t s was l o w , and i n d i v i d u a l r e a d i n g s c o u l d be i n d e -p e n d e n t l y c ompa r ed w i t h a n o t h e r CTD i n s t r u m e n t . T h i r d l y , t h e s c a l a r m e a s u r e m e n t s we re more t r a c t a b l e a n a l y t i c a l l y . 33 C o n v e n t i o n a l F o u r i e r a n a l y s i s c o u l d n o t be u t i l i z e d b e c a u s e t h e d a t a were s p a r s e and u n e q u a l l y s p a c e d . I n s t e a d , i t was a p r i o r i a s sumed t h a t t h e r e was a s i n g l e d o m i n a n t wave p e r i o d a t each l a t i t u d e - d e p t h p a i r , and a l e a s t - s q u a r e s s i n u s o i d a l c u r v e f i t t o d e t e r m i n e t h e p e r i o d s , p h a s e s , and a m p l i t u d e s was p e r f o r m e d i n d e p e n d e n t l y a t e a ch l a t i t u d e (2° S t o 2° N) and d e p t h (10 t o 250 m e t r e s ) . The f i t t e d s i n u -s o i d had t h e f o r m : s = s + S s i n (2iTt /T + <j>) w h e r e : s = o b s e r v e d s i g m a - t a t l a t i t u d e , d e p t h , and t i m e T = mean s i g m a - t S = a m p l i t u d e o f f l u c t u a t i o n T = p e r i o d o f f l u c t u a t i o n i n d a y s (j) = pha se o f f l u c t u a t i o n The t e c h n i q u e u s ed was a " p e r i o d g r a d i e n t " s e a r c h , w i t h a v a r i e t y o f s t a r t i n g p o i n t s f r o m 10 day s t o 30 d a y s . F o r s t a r t i n g v a l u e s o f 20 t o 30 d a y s , F i g u r e s 15 t o 17 we re g e n e r a t e d . F i g u r e 15 shows t h a t t h e d o m i n a n t p e r i o d i n t h e s u r f a c e l a y e r c o n v e r g e d t o a p p r o x i m a t e l y 17 d a y s , w h i l e i n t h e EUC c o r e t h e p e r i o d c o n v e r g e d t o a b o u t 30 days o r m o r e . S t a r t i n g v a l u e s a r o u n d 10 day s l e d t o p e r i o d s o f 9 d a y s i n t h e s u r f a c e l a y e r and 30 day s a t t h e EUC c o r e , b u t w i t h h i g h e r r e s i d u a l s . W h i l e t h e s e r e s u l t s a r e b a s e d upon l i m i t e d s a m p l e s o v e r 30 d a y s , i t i s s i g n i f i c a n t t h a t s i m i l a r 1 6 - d a y and 3 0 - d a y p e r i o d s were d e t e c t e d i n t h e A t l a n t i c . 34 LATITUDE (DEG) -2 ~ 1 1 0 1 1 2 ct. I S . 17. 1 7 . 3 6 . 4 3 . . 1 ! * • 1 7 . 4 0 . 3 1 . I t . " 17. 1 7 . 3 7 . 4 3 . 1 6 . 1 0 3 . 4 2 . 1 3 . 17. 19. 1 7 . 3 9 . 4 3 . 1 6 . 1 2 0 . 4 2 . S 4 . 17. 16. 1 7 . 3 7 . 4 3 . I t . 1 0 0 . 4 0 . it. 17. I S . 1 7 . 3 4 . 4 4 . I S . 2 4 9 . V 4 I . »». 17. i e . 1 7 . 3 3 . 4 3 . 1 3 . 1 6 . I S \ ) 9 1 . 17. 1 6 . 1 7 . SI. . 9 9 . 1 4 . 1 7 . t o . 17. 16. 1 7 . 3 3 . 3 2 . 1 4 . 1 7 . 1 6 7 s ti. y 17. 16. I S . 3 4 . 9 3 . 1 3 . 1 7 . 1 6 . I t . 16. \aJ 4 0 . 9 4 . 1 6 . 1 7 - 1 6 . '»•. I £ ^ _ i e . . 4 2 . **• I S . 32. 23. 4 4 . 3 8 . 9 3 . \ l 8 . 9 9 . 24. 37. 20. 41 . 3 7 . 9 3 . ' 3 9 . t s . 32. 39. 3.1 . 3 7 . 3 4 . 3 4 . 3 1 . 9 9 . 3 0 . 30. 37. 28. 5 6 . 3 3 . 9 2 . 3 1 . 9 6 . 9 0 . 26. 37. 29. 3 6 . 3 2 . 2 9 . 2 9 . 9 3 . 3 1 . 23. 38. t o . 3 7 . 3 1 . 9 2 . 2 6 . 3 3 . 2 7 . 22. 35. 2 9 . 3D. 3 4 . 2 9 . t a . 2 3 . 23. 33. .31 . 40. 3 ! . 2 9 . 2 9 . / 1 9 . ^ 2 0 . 20. 31 . 2 4 . 2 7 . 3 1 . J 2 0 . / 27. 28. 1 H . ) 22. 2 9 . 2 6 . to/ 1 9 . 23. 20. ' 2 4 . 2 9 . . 2 2 . 1 9 . 28. 24. 1 4 . 3 0 . 2 2 . / ' 1 3 . 1 9 . j S 3 . •M. \ 20. 20, 2 3 . 3 4 . 2 9 . 1 9 . M.j / 9 0 . I I . \ 30. fl. 2 3 . 2 9 . 1 4 . /is. . 2 3 . 12. 1 31 . i\ 1 9 ] 3 2 . 9 3 . U S . 2 3 . 17. / 33. t o i 3 4 . 2 3 . 1 3 . 2 l / 31 . Al. 2 o i 3 4 . 2 3 . 1 9 . 2 \ 41 . tlL 3 0 . 2 6 . 38. I B \ 2 7 . 2 3 . 19. . ' 2 0 . 22. 30. 1 9 . 2 3 . 2 2 . 2 3 . 2 4 . gure 15. P e r i o d (days ) of s i nusoi f i t t 0 si gma-t 35 Fi gure 1 6. Ampl i t ude of si nusoi f i t i o pert urbat i on si gma-t 36 LATITUDE (DEG) 3. -2 . _ 0 • 1 2 o - 1 l 1 l I -9. 1 1 . 16. 12. -15. 19. 16. 10. -16. -II. 12. 16. 13. -16. 20.. 17. 1 . -18. -13. 13. 17. 14. -17. 19. 18. -0. -18. Cn O -13. 13. 17. 14. -15. -20. -13. -4. -17. -12. 13. IS. 13. -13. 19. -18. -5. -17. -13. 13. 18. 14. -12. 19. ' -16. 13. -19. -10. ' 14. 19. 14. -9. 1^7. -14. 1 I . -13. -10. 14. 20. 14. -13. -13. -10. 1 1 . 19. -7. 14. -19. 1 1 . -14. -15. -14. 12. 15. O - 13. 12. 17. 5. 19. -17. -19. II. 14. o 12. 9. 9. 13. 17. -20. 16. 7. 0. 4. 19. -3. 15. 19. 18. 12. 12. 18. m -7. 17. -15. 16. 19. 19. 8. 14. -17. —i cn --18. -15. 16. 17. -15. -12. 18. 19. -18. -16. -18. -17. -19. 16. 14. 15. -20. 19. i . O -9. 18. -8. 20. -16. -11 . 19. 16. 19. -3. 19. -10. 19. -17. -17. -13. 16. -15. 1 . -20. -10. 16. 19. -9. -17. 5. -13. D CD ro o --0. 6. -17. -13. -13. -1 . 17. 14. -19. -1 1 . -10. -9. -18. -17. 5. . 3. 2. -6. > o -7. -7. 3. -6. -15. -8. 5. 6. 1 . ro cn --7. -3. 1 . 4. -7. -7. -6. -7. 7. 5. 15. -12. -12. -16. -17. -0. -18. -19. 17. -11. -2. -1 . -2. -4. 5. .5. 2. -1 . 6. 6. 17. 6. 3. -4. 12. -19. O -4. 1 . -19. -6. -9. -7. -8. -10. 3. 3. 1. 19. 20. -20. 17. -4. 10: -10. -19. 17. 1 . Co O -o 18. 19. 19. -2. 3. 3. 3. -15. -6. -4. -3. -2. -5. 4. 5. 5. -1 . Co. J Cn J O F i g u r e 1 7 . P h a s e of s i n u s o i d a l f • • . t o p e r t u r b a t i o n s i g m a - t ( d e g r e e s 37 The c o n s i s t e n c y w i t h l a t i t u d e and d e p t h t e n d s t o s u p p o r t t h e d o m i n a n t p e r i o d a s s u m p t i o n . The r e s u l t i n g p e r t u r b a t i o n a m p l i t u d e , shown i n F i g u r e 1 6 , d e m o n s t r a t e s t h a t t h e m a j o r i t y o f t h e e n e r g y i s a s s o c i a t e d w i t h t h e p y c n o c l i n e r e g i o n . The pha se r e s p o n s e , F i g u r e 17 , shows l i t t l e c o n s i s t e n t pha se s h i f t a c r o s s t h e c o r e o f t h e u n d e r c u r r e n t . In F i g u r e 18 , r e g i o n s o f g r e a t e r t h a n 20% e r r o r i n f i t we re c i r c l e d . I t may be seen t h a t t h e r e s i d u a l s u m - o f - s q u a r e s o f s i g m a - t a f t e r t h e f i t we re f r e q u e n t l y l e s s t h a n 10% n e a r t h e u n d e r c u r r e n t c o r e , i n d i c a t i n g t h a t t h e a s s u m p t i o n o f a d o m i n a n t p e r i o d i n t h i s r e g i o n was v a l i d . The s i n g l e - f r e q u e n c y c u r v e f i t g i v e s r e s u l t s w h i c h a r e r e m a r k a b l y s i m i l a r t o t h e o b s e r v a t i o n s o f o t h e r s m e n t i o n e d i n t h e i n t r o d u c t i o n . T h u s , a l t h o u g h t h e r e i s no s u p p o r t i n g z o n a l s a m p l e s f r o m w h i c h t h e wavenumber v e c t o r m i g h t be c a l c u l a t e d , i t i s s u g g e s t e d t h a t a Ro s s b y wave i n t e r a c t i n g w i t h t h e mean z o n a l f l o w has been o b s e r v e d . I t i s f u r t h e r s u g g e s t e d t h a t t h e v e r t i c a l s h e a r b e tween t h e w e s t w a r d s u r f a c e f l o w and t h e e a s t w a r d e q u a t o r i a l u n d e r c u r r e n t has D o p p l e r - s h i f t e d t h e p r e s umed Ro s s b y w a v e . 38 L A T I T U D E -1 o ( D E G ) F i gu r e 18. Percent r a t i o of res idua l s u m - o f - s q u a r e s of p e r t u r b a t i o n s i gma - t t o t o t a l s u m - o f - s q u a r e s 39 3 .0 CONCLUSIONS The P a c i f i c e q u a t o r i a l u n d e r c u r r e n t v e l o c i t y has been m e a s u r e d as a f u n c t i o n o f l a t i t u d e and d e p t h a t 150° W l o n g -i t u d e , o v e r a p e r i o d o f a p p r o x i m a t e l y 30 d a y s . The v e l o c i t y o f t h e u n d e r c u r r e n t a t t h e c o r e d e p t h ( n e a r 150 m e t r e s ) was t y p i c a l l y 80 cm s " 1 , w i t h a maximum o f 120 cm s " 1 . The me r -i d i o n a l v e l o c i t y a t t h e c o r e was t y p i c a l l y 60 cm s~ l . A s s o -c i a t e d w i t h t h e m e a s u r e m e n t s a r e a 15 cm s " 1 u n c e r t a i n t y i n t h e p r o b e m o t i o n and 5 cm s~ 1 i n h e r e n t c u r r e n t m e t e r n o i s e . I n t e g r a t e d z o n a l t r a n s p o r t s we re f o u n d t o v a r y f r o m 10 sv t o 26 sv t o 18 sv when s a m p l e d a t r o u g h l y t e n day i n t e r v a l s . The r e s u l t i n g i m p l i c a t i o n i s t h a t s a m p l i n g s h o u l d be l e s s w i d e l y s e p a r a t e d t h a n t e n day s i f s i g n i f i c a n t a l i a s i n g i s t o be a v o i d e d . R e s u l t s f r o m t h e c o n t i n u i t y e q u a t i o n s u g g e s t t h a t b o t h u p w e l l i n g and d o w n w e l l i n g may o c c u r a t t h e e q u a t o r . I t i s u n c l e a r as t o t h e r o l e o f h o r i z o n t a l and v e r t i c a l f r i c t i o n , b u t t h e r e l a t i v e l y homogeneous p r o p e r t i e s above and be l ow t h e p y c n o c l i n e t e n d t o s u g g e s t t h a t f r i c t i o n mus t p l a y a s i g n i f i c a n t r o l e . A t t h e e q u a t o r , f r i c t i o n i s t h e p r i m e c a n d i d a t e t o b a l a n c e t h e i n f l u e n c e o f t h e p r e s s u r e g r a d i e n t , a l t h o u g h i t a p p e a r s t h a t some o f t h e p r e s s u r e g r a d i e n t f o r c e i s g e o s t r o p h i c a l l y b a l a n c e d away f r o m t h e e q u a t o r . Mean z o n a l p r e s s u r e g r a d i e n t s have been c ompu t ed t o be a p p r o x -i m a t e l y 0 . 2 6 * 1 0 " 5 m 2 s " 2 ( T s u c h i y a , 1 9 7 8 ) . The i n f l u e n c e o f l o c a l w i n d s upon t h e o b s e r v e d e q u a t o r i a l d i s t r i b u t i o n i s n o t o b v i o u s . 40 F l u c t u a t i o n s i n t h e e q u a t o r i a l r e g i m e a p p e a r t o be i n -f l u e n c e d by 3 0 - d a y p e r i o d i c i t i e s i n t h e u n d e r c u r r e n t and 1 7 - d a y p e r i o d s i n t h e s u r f a c e l a y e r . I t i s h y p o t h e s i z e d t h a t t h e s e waves may be due t o l o n g t e r m v a r i a t i o n s i n t h e w i n d s t r e s s i n t h e e a s t e r n o c ean b a s i n . W h i l e t h e o b s e r v -a t i o n s s u p p o r t a d o m i n a n t f r e q u e n c y o f a p p r o x i m a t e l y 30 d a y s a t t h e d e p t h o f t h e c o r e o f t h e u n d e r c u r r e n t , t h e e n e r g y t r a n s f e r f r o m t h e l a r g e s c a l e w i n d s t r e s s v a r i a t i o n s t o t h i s s i n g l e d o m i n a n t f r e q u e n c y i s beyond t h e s c ope o f t h i s t h e s i s . The f l u c t u a t i o n s , s u p p o r t i n g s c a l a r o b s e r v a t i o n s , and n u m e r i c a l c a l c u l a t i o n s a r e c o n s i s t e n t w i t h a Ro s s b y wave i n t e r a c t i n g w i t h a mean u n d e r c u r r e n t f l o w . 41 REFERENCES B u b n o v , V . A . , and V . D . E g o r i k h i n , S t u d y o f w a t e r c i r c u l a t i o n i n t h e t r o p i c a l A t l a n t i c , Deep Sea R e s . , GATE S u p p l . I I t o V. 2 6 , 125 - 1 3 6 , 1 9 7 9 . C r o m w e l l , T . , C i r c u l a t i o n i n m e r i d i o n a l p l a n e i n t h e c e n t r a l e q u a t o r i a l P a c i f i c , J . M a r . R e s . , 1 2 , 196 - 2 1 3 , 1 9 5 3 . D u i n g , W. , and Z . H a l l o c k , E q u a t o r i a l waves i n t h e uppe r c e n t r a l A t l a n t i c , Deep Sea R e s . , GATE Supp l I I t o V . 2 6 , 161 - 1 78 , 1 9 7 9 . F o f o n o f f , N . P . , and R . B . M o n t g o m e r y , The E q u a t o r i a l U n d e r c u r r e n t i n t h e l i g h t o f t h e v o r t i c i t y e q u a t i o n , T e l l u s , 7, 518 - 5 2 1 , 1 9 5 5 . G i l l , A . E . , M o d e l s o f e q u a t o r i a l c u r r e n t s , P r o c . Symp. N u m e r i c a l M o d e l s o f Ocean C i r c u l a t i o n , N a t . A c a d . S c i . , W a s h i n g t o n , D .C . 1 9 7 2 , 181 - 2 0 3 , 1 9 7 5 . G r o v e s , G . W . , and M. M i y a t a , On w e a t h e r - i n d u c e d l o n g waves i n t h e e q u a t o r i a l P a c i f i c , J . M a r . R e s . , 2 5 , 115 - 1 2 6 , 1967 . K n a u s s , J . A . M e a s u r e m e n t o f t h e C r o m w e l l C u r r e n t , Deep Sea R e s . , 6 , 265 - 2 8 6 , 1 9 6 0 . K n a u s s , J . A . , F u r t h e r m e a s u r e m e n t s and o b s e r v a t i o n s t h e C r o m w e l l C u r r e n t , J . M a r . R e s . , 2 4 , 205 - 2 4 0 , 1 9 6 6 . M o n t g o m e r y , R . B . , and E . D . S t r o u p , E q u a t o r i a l W a t e r s and C u r r e n t s a t 150° W i n J u l y - A u g u s t 1 9 5 2 , O c e a n o g r . S t u d y 1, 68 p p . , J o h n s H o p k i n s U n i v . , B a l t i m o r e , Md. , 1 9 6 2 . P h i l a n d e r , S . G . H . , E q u a t o r i a l U n d e r c u r r e n t : M e a s u r e m e n t s and T h e o r i e s , R e v . G e o p h y s . Space P h y s , 11 ( 3 ) , 513 -5 7 0 , 1 9 7 3 . P h i l a n d e r , G . , and W. D u i n g , The o c e a n i c c i r c u l a t i o n o f t h e t r o p i c a l A t l a n t i c , and i t s v a r i a b i l i t y , d u r i n g GATE, Deep Sea R e s . , GATE S u p p l . I I t o V. 2 6 , 1 - 2 8 , 1 9 7 9 . S t a n s e l l , T . A . , The T r a n s i t N a v i g a t i o n S a t e l l i t e S y s t e m , Magnovox G o v e r n m e n t and I n d u s t r i a l E l e c t r o n i c s Company , 1 9 7 8 , 83 p p . T a f t , B . , B. H i c k e y , C . Wun s ch , and D. B a k e r , E q u a t o r i a l U n d e r c u r r e n t d e e p e r f l o w s i n t h e c e n t r a l P a c i f i c , Deep Sea R e s , 2 1 , 403 - 4 3 0 , 1 9 7 4 . 42 T s u c h i y a , M . , Uppe r w a t e r s o f t h e I n t e r t r o p i c a l P a c i f i c O c e a n , O c e a n o g r . S t u d y 4 , p p . , J o h n s H o p k i n s U n i v . , B a l t i m o r e , M d . , 1 9 6 8 . W e i s b e r g , R . H . , E q u a t o r i a l waves d u r i n g Ga t e and t h e i r r e l a t i o n t o t h e mean z o n a l c i r c u l a t i o n , Deep Sea R e s . , GATE S u p p l I I t o V. 2 6 , 179 - 1 98 , 1 9 7 9 . W e i s b e r g , R . H . , L. M i l l e r , A . H o r i g a n , and J . A . K n a u s s , V e l o c i t y o b s e r v a t i o n s i n t h e e q u a t o r i a l t h e r m o c l i n e d u r i n g GATE, Deep Sea R e s . , GATE S u p p l . I I t o V. 2 6 , 217 - 1 4 8 , 1 9 7 9 . 43 A p p e n d i x A l . INTRODUCTION The p r o f i l i n g a c o u s t i c c u r r e n t m e t e r s y s t e m t o be d e s c r i b e d was d e v e l o p e d i n e a r l y 1977 f o r t h e M i x e d L a y e r E x p e r i m e n t ( M I L E ) . I t has u n d e r g o n e c o n t i n u o u s d e v e l o p m e n t s i n c e t h a t t i m e , and has been u s ed i n num-e r o u s c o a s t a l s u r v e y s , as w e l l as d u r i n g t h e f i r s t i n -t e n s i v e o b s e r v i n g p e r i o d o f t h e F i r s t GARP G l o b a l E x p e r i m e n t ( F G G E ) . The s y s t e m i s d e s i g n e d t o mea su r e c o n d u c t i v i t y , t e m p e r a t u r e , p r e s s u r e , and o c e a n c u r r e n t v e l o c i t y a t a r a t e o f t h r e e t i m e s a s e c o n d f r o m a d r i f t i n g s h i p . A d d i t i o n a l l y , a f l u x g a t e m a g n e t i c compass and t h r e e o r t h o g o n a l a c c e l e r o m e t e r s a r e i n c l u d e d t o s e n s e t h e o r i e n t a t i o n o f t h e u n d e r w a t e r u n i t . D i g i t a l d a t a f r o m t h e p r o b e i s t e l e m e t e r e d t o t h e s u r f a c e o v e r a f r e q u e n c y - s h i f t k e y e d ( FSK ) l i n k a t 600 b a u d . The s u r -f a c e d a t a i s f i r s t r e c o r d e d on a n a l o g u e t a p e and t h e n d e c o d e d and p r e s e n t e d t o a c o m p u t e r f o r d a t a l o g g i n g . A r e a l t i m e a n a l o g u e d i s p l a y o f t h e raw d a t a i s c o n t i n -u o u s l y a v a i l a b l e v i a a d e m u l t i p i e x e r / d i g i t a l - t o -a n a l o g u e - c o n v e r t e r / s a m p l e - a n d - h o l d s u b s y s t e m . 44 F i g u r e A l , w h i l e a more d e t a i l e d d i a g r a m o f t h e u n d e r -w a t e r u n i t i s shown i n F i g u r e A 2 . The r e m a i n d e r o f t h e p a p e r w i l l c o n c e n t r a t e on t h e u n d e r w a t e r u n i t , a p h o t o -g r a p h o f w h i c h i s shown i n F i g u r e A 3 . A 2 . ANALOGUE SYSTEM The a n a l o g u e s e n s o r s i n c l u d e t h r e e o r t h o g o n a l a c c e l e r o m e t e r s , an Endeco f l u x g a t e m a g n e t i c c o m p a s s , and a G u i l d l i n e I n s t r u m e n t s Mark I I I CTD. The s e v e n s i g n a l s a r e a m p l i f i e d t o a f u l l s c a l e r a n g e o f 0 t o 5 v o l t s and s a m p l e d by a 1 2 - b i t CMOS a n a l o g u e - t o - d i g i t a l c o n v e r t e r . The n o m i n a l r a n g e and r e s o l u t i o n o f t h e a n a l o g u e s e n s o r s i s shown i n T a b l e A l . UNITS RANGE RESOLUTION SENSOR A c c e l e r o m e t e r t mi 1 1 i gee A c c e l e r o m e t e r Y m i l l i g e e A c c e l e r o m e t e r Z m i l l i g e e C o n d u c t i v i t y R a t i o T e m p e r a t u r e Deg r e e C P r e s s u r e D e c i b a r Compass d e g r e e - 8 0 0 t o +800 0 . 4 - 8 0 0 t o - 1 2 0 0 0 . 1 0 . 4 t o 1.6 0 . 0 0 0 3 0 t o 30 0 . 0 1 0 t o 800 0 . 2 0 0 t o 360 0 . 1 g e e = 9 . 8 1 m s " 2 T a b l e A l . A n a l o g u e S e n s o r Ranges and R e s o l u t i o n A 3 . ACOUSTIC CURRENT METER SYSTEM The a c o u s t i c c u r r e n t m e t e r u s e s a K a i j o Denke t h r e e - a x i s t r a n s d u c e r a r r a y and p r e a m p l i f i e r , w i t h c u s t o m CMOS t i m i n g and s e q u e n c i n g l o g i c . 45 W I N C H A N D • -SLIP R INGS A N A L O G TAPE RECORDER C ^ 1 FSK T D A T A UNDERWATER PROBE B R U S H 6 C H A N N E L RECORDER C U S T O M DECK UNIT 6 - O F - 1 6 A N A L O G O U T P U T S / C O M P U T E R S Y S T E M NINE T R A C K RECORDER F i g u r e A l . System b l o c k d i a g r a m G U I L D L I N E C,T,P E N D E C O C O M P A S S 1 2 - B I T A D D R E S S B U S ! 3 A X I S i I A C C H L E R O M E T E F t i -G A I N / OFFSET A N D FILTER K A I J O D E N K E C U R R E N T M E T E R — S A M P L E 16 C H A N N E L M U L T I -h H O L D A N D — P L E X E R A N A L O G TO D IG ITAL C O N V E R T E R S Y N C W O R D G E N E R A T O R t 7 P R O M j C O N T R O L L E R II i • 11 12 - B I T D A T A B U S D A T A S E R I A L I Z E R A N D M O D E M FSK V F i g u r e A 2 . . B l o c k d i a g r a m o f u n d e r w a t e r s e n s o r p a c k a g e . D i g i t i z i n g and T e l e m e t r y Power S u p p l y G u i l d l i n e CTD A c c e l e r o m e t e r s C u r r e n t M e t e r T r a n s c e i v e r s P r e s s u r e S e n s o r T e m p e r a t u r e S e n s o r C o n d u c t i v i t y C e l l •Three A x i s A c o u s t i c C u r r e n t M e t e r A r r a y F i g u r e A3. P h o t o g r a p h o f U n d e r w a t e r U n i t ' 48 The c u r r e n t me t e r u t i l i z e s a s i n g - a r o u n d t e c h n i q u e i n a t i m e - s h a r e d mode. As i n d i c a t e d i n F i g u r e A 4 , a 500 KHz p u l s e b u r s t f r o m one t r a n s d u c e r i s d e t e c t e d by an o p p o s i n g t r a n s d u c e r a f t e r p r o p a g a t i n g t h r o u g h a d i s t a n c e L t h r o u g h w a t e r . The d e t e c t e d p u l s e i s a m p l i f i e d and u s ed t o t r i g g e r a n o t h e r c y c l e , and so o n . A f t e r a s h o r t p e r i o d , a s t a b l e o s c i l l a t i o n o c c u r s w i t h f r e q u e n c y f up= c+v (1 ) L w h e r e : f u p = s i n g - a r o u n d f r e q u e n c y i n UP mode c = s p eed o f s ound v = w a t e r c u r r e n t c o m p o n e n t L = t r a n s d u c e r s p a c i n g The p u l s e f r e q u e n c y i s m u l t i p l i e d by a p h a s e - l o c k e d l o o p and g a t e d t o a t e n - b i t c o u n t e r . The s e q u e n c e i s r e v e r s e d a f t e r a s h o r t i n t e r v a l and t h e same c o u n t e r i s now d e c r e m e n t e d . P r o v i d e d t h a t t h e UP/DOWN c o u n t e r i s g a t e d f o r t h e same i n t e r v a l , i t may be shown t h a t t h e r e s i d u a l c o u n t i s d i r e c t l y p r o p o r t i o n a l t o w a t e r s p e e d . v= L * c o u n t ( 2 ) 2TN 49 o ! TRANSDUCER ' ' S ING ! TRANSDUCER BIDIRECTIONAL OSCILLATOR PULSE BURST DETECTOR U P C O N T R O L -D N C O N T R O L SEQUENCING ' U P LOGIC P R E S E T TO 512 1 0 - B I T O U T P U T U P DN 10-BIT COUNTER F i g u r e A4. O p e r a t i o n o f s i n g - a r o u n d c u r r e n t meter w h e r e : c o u n t = r e s i d u a l d o p p l e r c o u n t T = c o u n t e r g a t e i n t e r v a l N = p h a s e - l o c k e d l o o p m u l t i p l i e r r a t i o L = t r a n s d u c e r s p a c i n g The b a s i c r e s o l u t i o n o f t h e c u r r e n t m e t e r i s 0 . 5 c m s " 1 , w i t h a f u l l s c a l e r a n g e o f ± 256 c m s " 1 . A l l t h r e e c u r r e n t c omponen t s a l o n g t h e m e t e r a x e s a r e s a m p l e d i n 0 . 2 5 s e c o n d s , a t a r e p e t i t i o n r a t e o f 0 . 3 3 s e c o n d s . S e v e r a l f e a t u r e s o f o c e a n o g r a p h i c i n t e r e s t s h o u l d be n o t e d . F i r s t , as may be s een by e q u a t i o n ( 2 ) , t h e i n s t r u m e n t i s i n d e p e n d e n t o f t h e s p eed o f s ound i n w a t e r . S e c o n d , t h e o n l y p a r a m e t e r t h a t i s l i k e l y t o a l t e r t h r o u g h r o ugh h a n d l i n g i s t h e t r a n s d u c e r p a t h l e n g t h L. In f a c t , t h e a u t h o r has w i t n e s s e d t h e m e t e r b e c o m i n g u n s t o w e d i n r o ugh w e a t h e r , b e n t o u t o f s h a p e , and b e i n g q u i c k l y r e t u r n e d t o s e r v i c e w i t h t h e a i d o f a 20 cm r u l e r ( w i t h a c o n s e q u e n t e r r o r o f l e s s t h a n 0 . 5 % ) . A b l o c k d i a g r a m o f t h e b a s i c d o p p l e r c u r r e n t m e t e r i s shown F i g u r e A4 . A 4 . SEQUENCING AND TELEMETRY The p r o b e i s s e q u e n c e d by a p r o g r a m m a b l e r e a d - o n l y memory (PROM) , and t h e s e r i a l i z e d s i g n a l s a r e c o n v e r t e d t o s y n t h e s i z e d s i n u s o i d a l f r e q u e n c y - s h i f t s i g n a l s ( 1 0 7 0 / 1 2 7 0 H z ) ; p r o v i s i o n has been made t o i n c l u d e a 1 2 - b i t CMOS m i c r o p r o c e s s o r and a b i d i r e c t i o n a l t e l e m e t r y l i n k a t a f u t u r e t i m e . 51 A5. CAL IBRATION The c o n d u c t i v i t y , t e m p e r a t u r e , and p r e s s u r e s e n s o r s a r e s u p p l i e d as a l i n e a r modu l e by G u i l d l i n e I n s t r u m e n t s . C a l i b r a t i o n c o n s i s t s o f s e t t i n g g a i n s and o f f s e t s , and t h e n c o m p u t i n g a l i n e a r r e g r e s s i o n and s t a n d a r d d e v i a t i o n ( s d ) be tween t h e d i g i t a l o u t p u t and t h e a p p r o p r i a t e l y s t i m u l a t e d i n p u t . T e m p e r a t u r e c a l i -b r a t i o n s t a r t s w i t h a s t i r r e d b a t h a t i c e p o i n t u s i n g s h a v e d i c e , and t h e t e m p e r a t u r e s l o p e as t h e b a t h warms i s c ompa r ed w i t h t h a t o f a q u a r t z t h e r m o m e t e r (sd=0.01° C ) . P r e s s u r e i s c h e c k e d by c o m p r e s s i n g t h e p r e s s u r e gauge w i t h n i t r o g e n g a s , and m o n i t o r i n g t h e a p p l i e d p r e s s u r e w i t h a P a r o s c i e n t i f i c P r e s s u r e Compu t e r (sd=0.2 d b ) . C o n d u c t i v i t y i s c h e c k e d a g a i n s t a G u i l d -l i n e A u t o s a l u s i n g s e a w a t e r f r om b o t t l e s a m p l e s (sd=0.02 p p t ) . P r e c r u i s e and p o s t c r u i s e c o m p a r i s o n s have i n d i c a t e d n e g l i g i b l e d r i f t o f t h e CTD c a l i b r a t i o n s o v e r t i m e . The a c o u s t i c c u r r e n t m e t e r was c a l i b r a t e d i n t h e tow t a n k f a c i l i t i e s a t BC R e s e a r c h i n V a n c o u v e r and l a t e r a t t h e Canada C e n t r e f o r I n l a n d W a t e r s i n B u r -l i n g t o n , O n t a r i o . S i n c e t h e o n l y s h i f t i n c a l i b r a t i o n w h i c h i s l i k e l y t o o c c u r i s i n t r a n s d u c e r s p a c i n g , c a l -i b r a t i o n c o n s i s t s o f a d j u s t i n g t h e t r a n s d u c e r p a t h l e n g t h t o 20 cm and p l o t t i n g t h e p o l a r r e s p o n s e as t h e m e t e r i s r o t a t e d f o r a r a n g e o f c u r r e n t v e l o c i t i e s . 52 The p o l a r p a t t e r n f o r t h r e e c u r r e n t s p e ed s i s r e p r o -du c ed i n F i g u r e A 5 . I t c an be seen t h a t a 15% s p e e d e r r o r o c c u r s i n t h e v i c i n i t y o f t h e t r a n s d u c e r s u p -p o r t s , w h i c h d e c r e a s e s t o z e r o be tween t h e s u p p o r t s . The a n a l o g u e s i g n a l f r o m t h e Endeco compass e x h i b -i t e d n e g l i g i b l e e r r o r when t h e i n s t r u m e n t was swung t h r o u g h 360 d e g r e e s . P e r f o r m a n c e l i m i t s we re e s t a b -l i s h e d w i t h i n t h e a c c u r a c y o f t h e t e s t a r r a n g e m e n t o f a p p r o x i m a t e l y one d e g r e e . S h i p b o a r d t e s t s have i n -d i c a t e d t h a t a m a g n e t i c e f f e c t on t h e compass o c c u r s w h i c h i s s p e c i f i c t o e a c h s h i p and o p e r a t i n g l o c a t i o n . T e s t s by R. E. Thomson have shown t h a t t h e s e e f f e c t s a r e n e g l i g i b l e a t d e p t h s b e l ow f i v e m e t e r s . The a c c e l e r o m e t e r s we r e c a l i b r a t e d by s t a t i c a l l y d e f l e c t i n g t h e i n s t r u m e n t p a c k a g e i n s t e p s , i n t h e E a r t h ' s g r a v i t a t i o n a l f i e l d , and m e a s u r i n g t h e d i g i t a l r e s p o n s e a t e a c h s t e p . A 6 . PROF I L ING CONSIDERATIONS T i l t o f t h e u n d e r w a t e r u n i t can s i g n i f i c a n t l y a l -t e r t h e r e a d i n g s o f t h e c u r r e n t m e t e r c o m p o n e n t s . W i t h t h e p r o b e s t a t i c a t some d e p t h , t i l t e d a t t e n d e g r e e s i n a one m e t e r p e r s e c o n d h o r i z o n t a l c u r r e n t , t h e z -c omponen t o f t h e c u r r e n t m e t e r w i l l d i s p l a y 17 c m s - 1 w h i l e t h e r e s u l t a n t x y - c o m p o n e n t w i l l be 98 c m s " 1 . I f i n s t e a d , t h e p r o b e i s b e i n g l o w e r e d t h r o u g h s t i l l w a t e r w i t h a s i m i l a r t e n d e g r e e t i l t t h e x y - c o m p o n e n t and z - c o m p o n e n t r o l e s w i l l be r e v e r s e d . 53 50 CM/SEC F i g u r e A5. P o l a r r e s p o n s e of c u r r e n t m e t e r . C r o s s e s I n d i c a t e mean s p e e d , b a r s I n d i c a t e s t a n d a r d d e v i a t i o n . 54 The t i m e - a v e r a g e d a c c e l e r o m e t e r o u t p u t s d u r i n g m e a s u r e m e n t s have been p r o c e s s e d t o y i e l d t i l t s f r o m t h e v e r t i c a l a n d , t o g e t h e r w i t h t h e compass r e a d i n g , u s e d t o r o t a t e t h e c u r r e n t m e t e r o u t p u t t o n o r t h , e a s t , and v e r t i c a l p o i n t i n g c o o r d i n a t e s . The a p p r o p r i a t e t r a n s f o r m a t i o n f r o m x y z p r o b e c o o r d i n a t e s t o NEV g e o g r a p h i c c o o r d i n a t e s i s : whe re a,3,Y = a n g l e b e tween t h e v e r t i c a l and x , y , z a x e s e = c o u n t e r c l o c k w i s e a n g l e b e tween t h e h o r i z o n t a l p r o j e c t i o n o f t h e y - a x i s and m a g n e t i c n o r t h \> = c o u n t e r c l o c k w i s e a n g l e b e tween t h e h o r i z o n t a l p r o j e c t i o n o f t h e x - a x i s and m a g n e t i c n o r t h = e + c o s _ 1 ( - c o s a c o s t / s i n a s i n ^ ) <j> = c o u n t e r c l o c k w i s e a n g l e b e tween t h e h o r i z o n t a l p r o j e c t i o n o f t h e z - a x i s and m a g n e t i c n o r t h = if; ± c o s - 1 ( - c o s a c o s ^ / s i n a s i n t ) and t h e + s i g n i s c h o s e n by t h e s i g n o f co s 3 In p r a c t i c e , i t i s common t o a t t a c h 100 kg o f l e a d a r o u n d t h e i n s t r u m e n t t o m i n i m i z e t i l t e f f e c t s and o b v i a t e t h e above t r a n s f o r m a t i o n . 55 As s een i n F i g u r e A 5 , t h e e f f e c t o f t h e a c o u s t i c t r a n s d u c e r s u p p o r t s on t h e m e a s u r e d c u r r e n t c an be q u i t e l a r g e . T h i s e f f e c t c o u l d be c o m p e n s a t e d i n p o s t -c r u i s e p r o c e s s i n g , b u t g e n e r a l l y a f i n i s added t o o r i e n t t h e m e t e r away f r o m t h e h i g h d i s t o r t i o n z o n e s . T h i s has t h e added a d v a n t a g e o f i n c r e a s i n g t h e r a n g e o f m e a s u r a b l e c u r r e n t . The c u r r e n t i n d i c a t e d by t h e a c o u s t i c c u r r e n t m e t e r i s r e l a t i v e t o t h e i n s t r u m e n t p a c k a g e . C o n s e -q u e n t l y , t h e m o t i o n o f t h e p a c k a g e mus t be r e a s o n a b l y w e l l k nown . T h i s can be s u b d i v i d e d i n t o two c a t e -g o r i e s . D u r i n g s h a l l o w c a s t s t o 50 m e t e r s , t h e p r o f i l -i n g m e t e r i s a l w a y s i m m e d i a t e l y b e l ow t h e s h i p and t h u s h o r i z o n t a l m o t i o n i s s i m p l y c o m p e n s a t e d . F o r d e e p e r c a s t s t o 350 m e t e r s , and e s p e c i a l l y i n r e g i o n s o f h i g h f l o w , s t a n d a r d p r o c e d u r e has been t o l o w e r t h e i n s t r u -ment i n d i s c r e t e s t e p s , a l l o w i n g s t a b l e r e a d i n g s t o be t a k e n . P o s t c r u i s e p r o c e s s i n g i s t h e n u s ed t o remove t h e e f f e c t s o f s h i p d r i f t . The d i f f e r e n c e i n r e l a t i v e c u r r e n t m a g n i t u d e when t h e u n d e r w a t e r u n i t i s l o w e r e d i n d i s c r e t e s t e p s i s c ompa r ed t o a c o n t i n u o u s p r o f i l e i n F i g u r e A 6 . The e f f e c t s o f p r o b e m o t i o n and t y p i c a l i n s t r u m e n t n o i s e i s e v i d e n t . A 7 . SUMMARY A p r o f i l i n g a c o u s t i c c u r r e n t m e t e r f o r o c ean r e -s e a r c h has been d e s c r i b e d . The i n s t r u m e n t m e a s u r e s c o n d u c t i v i t y , t e m p e r a t u r e , d e p t h , and t h r e e c o m p o n e n t s o f o c e a n c u r r e n t . P r o b e o r i e n t a t i o n i s d e c o d e d f r o m compas s and a c c e l e r o m e t e r o u t p u t s . 56 V ( C M / S ) U ( C M / S ) TOTAL ( C M / S ) 0 5 0 100 - 1 0 0 - 5 0 0 5 0 0 5 0 100 4 0 0 — 1 . , —I —I F i gu r e A6 . v Ty pi c a l v e l o c i t y p r o f i I e d e m o n s t r a t i ng. ef f ec t s of " p r o b e mot i o n . S o l i d I i ne i n d ] c a t es c o n t i n u o u s p r o f i l e o b t a i n e d at 1 m/s I o w e r i ng r a t e , w h i l e c r o s s e s a r e 30 s e c o n d a v e r a g e s at f i xed dep t h s . 

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