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Energy balance fluxes in a subtropical city : Miami, FL.

University of British Columbia

This study presents summertime surface energy balance measurements from a suburb in west Miami, Florida, from May 13 (YD 133) to June 21 (YD 172), 1995. The incoming and outgoing shortwave, longwave, and the net all-wave radiation are measured directly, and both the sensible and latent turbulent heat fluxes are measured directly by eddy correlation. Results from this fieldwork are presented as an energy balance climatology, mainly using ensemble averages. The findings are compared with results from midlatitude suburban studies. The complete, directly observed suburban radiation balance is one of very few available. In conjunction with these data, derived surface characteristics, such as temperature, albedo and emissivity (e[sub 0]) are given. The clear sky midday albedo is observed to be 0.17, and e[sub 0] is estimated to be 0.97. Parameterizations to calculate various energy fluxes are evaluated using the Miami data. These include formulae to calculate the net radiation and incoming shortwave and longwave radiative fluxes, under both clear and cloudy sky conditions. Of the radiative formulae tested, the calculation of incoming shortwave from the net radiation is particularly effective, especially under cloudless skies. In contrast, some of the incoming longwave radiation equations are essentially useless in cloudy conditions. The sensible, latent, and storage heat fluxes are each presented as ensemble averages, and as fractions of the net radiation. The average daytime sensible heat flux normalized by the net radiation is 0.43, which is in the middle of the range of previous urban observations. The average daytime latent heat flux normalized by the net radiation is 0.27, which is reasonably similar to midlatitude suburban observations. The storage heat flux appears to play a significant role, although this is linked to the fact that it is calculated as a residual from, among others, the (low) latent heat flux. The average daytime storage heat flux normalized by the net radiation is 0.30, which is similar to the highest of such observations from other cities. Two energy partitioning parameters, the Bowen ratio (β) and the Priestley-Taylor a, as well as the McNaughton-Jarvis coupling factor (Ω), are used to gain insight into Miami's energy regime, and to more thoroughly compare it to those previously observed in other North American cities. The subtropical location is not found to significantly alter the urban energy balance partitioning, although some differences are noted. The Priestley-Taylor and Penman- Monteith parameterizations, which relate evaporation to available energy possess utility, whereas calculations using the aerodynamic approach that rely on empirical estimates of the surface roughness for heat as a fraction of that for momentum, are of questionable merit. The daytime average values of β, the Priestley-Taylor α, and Ω are observed to be 1.55, 0.51, and 0.4 respectively. Given the hot, wet location relatively high latent heat fluxes (evaporation) were anticipated, but not found. The Penman-Monteith equation was used as a framework to investigate the most likely reasons for this. This analysis provides support for the suggestion that the small vapour pressure deficit in Miami is a major part of the explanation for the unexpectedly low latent heat fluxes.

Thesis/Dissertation

application/pdf

2009-06-26

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http://hdl.handle.net/2429/9758

Geography

University of British Columbia

UBCV

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