Sub-seasonal Variations in Surface Heat Fluxes under Different Synoptic Regimes for Remnant Forest and Cropland in the U.S. Midwest Corn Belt.

Latent heat (LE) and sensible heat (H) fluxes from deciduous forest patches within extensive rainfed croplands of the U.S. Corn Belt likely impact deep convection and precipitation during the growing season. To place these surface heat fluxes into their climatic and synoptic atmospheric contexts, data from AmeriFlux towers in Morgan Monroe State Forest and Bondville, Illinois, are used to develop a nine-year (1999-2007) "climatology" of afternoon latent and sensible heat for both land use/land cover (LULC) types. Daily sea-level pressure (SLP) and near-surface (1000 hPa) vector winds (V1000) from the North American Regional Reanalysis permit the development of a synoptic classification for the Corn Belt for the same period. The Bondville cropland tower shows annual variations in LE and H across the entire growing season, while variations in the forest LE and H are most apparent at the end of the growing season. Although there are no statistically significant differences in the frequencies of synoptic patterns across the nine-year study period, the type representing low pressure to the west and high pressure to the east with attendant southerly airflow was most frequent. Statistically significant differences in estimates of the surface resistance to the LE flux suggest that the forest's stomata modulate variations in LE across the growing season. Whereas, the estimated surface resistance of the crops showed little variation and was unlikely to impact variations in LE. Therefore, in Morgan Monroe State Forest, differences in surface resistance and stomatal control are more likely to be responsible for annual variations in surface heat fluxes than the synoptic variability during the 1999-2007 period.