Land-atmosphere interaction effect on convective available potential energy during the initiation of moist convection

Thursday, 18 December 2014
Jun Yin1, Amilcare M Porporato1, James Rigby2 and John D Albertson1, (1)Duke University, Durham, NC, United States, (2)USDA Agricultural Research Service Oxford, Oxford, MS, United States
The initiation of moist convection, the timing when the atmospheric boundary layer (ABL) first crosses the lifting condensation level (LCL), is often treated as one of the important indicators of further development of deep convection and widely used to analyze the land-atmosphere interaction in different conceptual frameworks. Besides the timing of moist convection, the convective available potential energy (CAPE), another important indicator representing the positive buoyancy of an air parcel, displays a unique set of dynamics during the development of moist convection and is worth further attention and study for the development of simplified models of moist convection. Here, we couple a simple mixed layer model with a soil-plant-atmosphere continuum model to investigate the evolution of various convective indicators such as ABL, LCL, level of free convection (LFC), level of neutral buoyancy (LNB), and CAPE. Our preliminary results indicate that the crossing of ABL/LCL can have asynchronous behavior. For example, atmosphere with earlier ABL/LCL crossing does not necessary has higher CAPE. One typical example is found in the dry soil advantage regime, where dryer soil favors earlier ABL/LCL crossing but induces lower CAPE due the dry-air entrainment from quick ABL growth that consequently quenches the buoyancy of convection. This combination of multiple convection indicators may explain the phenomenon that storm intensity could be statistically stronger when triggered by wetter soil than by dryer soil as observed in some studies.