Field observations made in Hudson Valley region, NY during the Hudson Valley Ambient Meteorology Study (HVAMS) are analyzed to examine how terrain and land cover influence nocturnal mixing in real-world landscapes. Important terrain features such as local topographic concavity and site sheltering are shown to exhibit systematic influence on turbulent intermittency and on the consequent nocturnal heat and momentum fluxes. Very local obstacles have their most important effects on mixing during strong winds (> 5m/s). Local terrain concavity was found to be the more important factor influencing surface fluxes than sheltering for all classes of winds.
Methodology is presented to define a regional bulk Richardson number Ribr from operational and experimental soundings. Plots of Ribr versus network averaged surface heat and momentum fluxes were obtained for the intensive operational and long-term operational phases of HVAMS. Results indicate that the need for extra mixing, above bulk Richardson number critical (Ricr = ¼), in numerical weather prediction models (NWP), first invoked to avoid unrealistic cooling at surface and later hypothesized to be consequence of spatial averaging, is a consequence of spatial averaging of the local temperature and wind profiles in a heterogeneous landscape.
The area-site relative elevation (mz - z), a measure of terrain curvature, is a strong determinant of turbulent intermittency at the stations studied. For areas within one kilometer of a station this parameter is shown contain the same information as does the curvature of the least squares fitted local quadratic surface. The long-term data analysis shows that the spatial variation of nocturnal surface temperatures depends on mz-z , a finding not apparent from data obtained during the six-week intensive operational period during 2003.
Elements of the regional stable boundary layer (SBL) heat budget were evaluated using measured network-averaged heat flux data, observed stable boundary layer (SBL) cooling rates, and modeled radiative flux divergence data. Results show that the radiative flux divergence plays the major role in SBL cooling (> 60%). The turbulent sensible heat flux divergence was found to play a smaller role (< 30% of the total cooling) but can be as high as 40% with increasing background wind speeds.
|Advisor:||Fitzjarrald, David R.|
|Commitee:||Demerjian, Kenneth L., Lala, Gilbert G., Walcek, Chris|
|School:||State University of New York at Albany|
|Department:||Earth and Atmospheric Sciences-Athmospheric Science|
|School Location:||United States -- New York|
|Source:||DAI-B 72/06, Dissertation Abstracts International|
|Keywords:||Heat flux, Intermittent turbulence, Landscape, Radiative flux divergence, Stable boundary layers|
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