Qingyu Wang - November 30

Boundary Layer, Urban Meteorology, and Land-Surface Processes

Evaluation of the impacts of land-surface processes on the PBL: A case study on cropland and grassland

Qingyu Wang

Tuesday, November 30

2:00 PM

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http://meet.google.com/fcr-hokz-ubf

Vegetation and soil moisture impact the surface energy partitioning, land-atmosphere feedbacks, and planetary boundary layer (PBL) characteristics. In this study, we simulated surface energy and PBL features in the single-column Weather Research and Forecast model (WRF) coupled with Noah-MP land surface model (WRF/Noah-MP) at two AmeriFlux sites (US-Ne1: cropland; US-Kon: grassland) on July 12th, 2018 when a drought was recorded. Flux tower observations of surface energy fluxes, soil moisture, and near-surface temperature at these two sites were used to compare to WRF/Noah-MP simulations. Both the simulations and observations showed the non-irrigated grassland tended to have larger daytime sensible heat fluxes and a deeper convective PBL than the irrigated cropland. If with the same amount of irrigated soil moisture as the cropland, the simulated transpiration of grassland was suppressed in Noah-MP probably because of the physiology parameter in the Rubisco-limited stage: maximum rate of carboxylation at 25ºC (VCMX25), which is also important in determining biogenic CO2 fluxes. Differences in vegetation characteristics have few contributions to surface energy partitioning and PBL development in highly wet or dry soil, whereas distinguishing most at intermediate surface-level soil volumetric water content (VWC ≈0.21m3 m-3), mainly due to transpiration rate differences between grassland and cropland. According to the transpiration formula in Noah-MP, a large stomatal resistance can explain the weak transpiration in the dry soil, but vapor pressure deficit (VPD) was the key factor in wet soil. A preliminary modification of vegetation and soil parameters in the single-column WRF/Noah-MP is also explored.