Sub-seasonal variations in afternoon surface heat fluxes for deciduous forests forest and cropland from flux tower observations in the U.S. Midwest Corn Belt

Authors: Mikael Hiestand*, , Andrew M. Carleton , Penn State Geography , Kenneth J. Davis , Penn State Meteologogy
Topics: Climatology and Meteorology, Land Use and Land Cover Change, Environment
Keywords: Hydroclimatology, latent heat, evapotranspiration, synoptic climatolgy, convective precipitation
Session Type: Virtual Paper
Day: 4/9/2021
Start / End Time: 9:35 AM / 10:50 AM
Room: Virtual 56
Presentation File: No File Uploaded

Spatial variations in latent (LE) and sensible (H) heat fluxes from deciduous forests and surrounding croplands of the U.S. Corn Belt likely influence convective precipitation by triggering nonclassical mesoscale circulations (NCMCs) in the atmospheric boundary layer. However, the influence of synoptic atmospheric conditions on inter-annual variations in the surface fluxes is unknown. AmeriFlux tower data from the Morgan Monroe State Forest and Bondville, Illinois (cropland) are used to develop nine-year afternoon (11am-7pm) climatologies of LE and H fluxes for the growing seasons (May-September) of 1999-2007. The Bondville cropland tower shows distinct variations in LE and H across the growing season, while the forest LE flux (Morgan Monroe) shows limited variation across the growing season, but significant sub-seasonal variability, especially toward the end of the growing season. To determine associations of the surface fluxes with the synoptic circulation, the North American Regional Reanalysis is used to develop a classification of Corn Belt sea level pressure patterns, augmented by near-surface vector winds (V1000). The frequencies of seven synoptic patterns so-derived show no significant inter-annual variations from the nine-year means, suggesting that synoptic circulations are not driving the observed variations in LE and H from either cropland or deciduous forest; rather, the interannual variations in surface fluxes from the croplands are driven by ambient changes in temperature and humidity. Additionally, estimates of the surface resistance to the LE flux suggest that the forest’s stomata modulate variations in LE across the growing season on local scales, especially during the mid-season peak of evapotranspiration.

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