Effect of land surface interactions on low-level jet development and cloud convection processes: a mesoscale modeling study using the ARM CLASIC 2007 and IHOP 2002 field observations

Description

This study focuses on the analysis of vegetation and land surface feedbacks on three cases: the evolution of an early morning low-level jet (LLJ), drought conditions, and cloud processes during deep and shallow convection over the U.S. Southern Great Plains. A number of numerical experiments were conducted with the Weather Research Forecasting (WRF) – Advanced Research Version (ARW ver. 3). The study utilized observations for a LLJ event that observed on 3 June 2002, severe drought during 11–19 June 2006, and deep and shallow convection during 10–13 June 2007. Detailed, high resolution of soil moisture and temperature conditions were developed using an offline Land Data Assimilation System (LDAS) with a 3-km grid spacing for the innermost domain. Experiments were conducted to investigate the impact of different land surface processes related to soil moisture/temperature, vegetation representations, and heterogeneity on the atmospheric processes. Results were compared with CLASIC (Cloud and Land Surface Interaction Campaign); IHOP (International H20 Project); and ARM energy flux, dropsonde, and radiosonde data.

Diagnosis of the surface variables; low-level jet occurrence; rainfall distribution; and moisture transport, heating rate, and cloud processes showed that soil moisture and vegetation transpiration played an important role on each of the events studied: LLJ evolution and nocturnal rainfall, drought conditions, and deep and shallow convection events. The coupled models with high resolution soil moisture conditions (WRF-LDAS) and vegetation transpiration (WRF-GEM) improved prediction in speed and abrupt changes of wind direction over the region and predict more accurate energy balance and soil moisture during the drought conditions and cumulus convection . The changing land surface heterogeneity and decreasing plant stomatal resistance also modified the LLJ speed, and the strong gradients of fluxes and temperature initialized more convection in the region. The study provides one of the first results highlighting that land surface-vegetation-soil moisture feedbacks are important not only for daytime processes but also for improved simulation of early morning and nocturnal events, especially during drought conditions and cumulus convection.