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A frequency analysis of ten years of surface atmospheric data at ocean weathership ’Papa’ Fissel, D. B.

Abstract

The standard 3-hourly meteorological observations from Ocean Weather Station "Papa" (50N 145W) for the period 1958 to 196 7 are examined. Power spectra of the wind speed, air pressure, air temperature, absolute humidity, and sea temperature are computed. The wind speed spectra from the open ocean environment are compared with those found at ether ocean, coastal and land stations. The seasonal spectra of these quantities averaged over each of the ten years indicate that the character of the activity changes both with respect to the size and frequency of the variations during the course of the year. Spectra are also computed for U•Ux, U•Uy, U•ΔT and U•Δq which through the bulk transfer formulas are representative of momentum, sensible heat and latent heat fluxes. The rotary power spectrum of the vector wind and vector wind stress show that clockwise rotations of the wind and the wind stress contain more energy than the anti-clockwise rotations. Cross-spectral values are computed between the vector wind and scalar quantities. As well, the cross-spectra between some of the various scalar quantities were examined. The effect of using data commonly available over the oceans on the computation of the bulk fluxes is examined. A comparison of the monthly wind stress and latent heat flux computed from the data organized into the format of the Marine Climatic Atlas with the directly calculated values show good agreement between the two methods, The sensible heat flux deviates more seriously, particularly in months of small fluxes. The effect on computing bulk fluxes from surface weather chart data is examined by computing these fluxes from vector averaged wind data. The use of this data format results in substantial reductions to the wind stress (magnitude reduced to one-half of the directly calculated value for an averaging period of one month). The latent heat flux is reduced by a factor of 0.53 and the sensible heat flux by a factor of 0.62 for the monthly averaging period.

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