A study of the Merritt Island, Florida sea breeze flow regimes and their effect on surface heat and moisture fluxes

Data collected during the Convective and Precipitation/Electrification Experiment were analyzed as part of an investigation of the sea breeze in the vicinity of Merritt Island, Florida. Analysis of near-surface divergence fields shows that the classical 24-hour oscillation in divergence over the island due to the direct sea breeze circulation is frequently disrupted and exhibits two distinct modes: the classical sea breeze pattern and deviations from that pattern. A comparison of clear day surface energy fluxes with fluxes on other days indicates that changes in magnitudes were dominated by the presence or absence of clouds. Non-classical sea breeze days tended to lose more available energy in the morning than classical sea breeze days due to earlier development of small cumulus over the island. A composite storm of surface winds, surface energy fluxes, rainfall, and satellite visible data was constructed. A spectral transmittance over the visible wavelengths for the cloud cover resulting from the composite storm was calculated. It is shown that pre-storm transmittances of 0.8 fall to values near 0.1 as the downdraft moves directly over the site. It is also found that under post-composite storm conditions of continuous clear sky days, 3.5 days are required to evaporate back into the atmosphere the latent heat energy lost to the surface by rainfall

Optimal measurement of surface shortwave irradiance using current instrumentation -- the ARM experience

Shortwave (solar) measurements of surface irradiance for clear sky conditions disagree with a number of different models. Betts used the European Center for Medium-range Forecasts (ECMWF) shortwave model to calculate surface irradiance that were 5-10 percent higher than measurements. Wild used a different formulation of the ECMWF shortwave model, but found that the model overpredicted clear-sky shortwave and average of 3 percent. Ding and Wang used data from the Atmospheric Radiation Measurement (ARM) program and found that the GENESIS GCM shortwave model, likewise, overpredicted clear-sky irradiance by about 4 percent. To help resolve the measurement dilemma, reference instruments were deployed in April 1996 at the Southern Great Plains ARM site central facility very near the shortwave measurements. The rest of the paper describes the experiment undertaken to ascertain total horizontal shortwave irradiance at the surface, including a separation of the direct normal and diffuse horizontal components. Results and a discussion of same concludes the paper