Response of nocturnal convective systems to low-level jets and morning surface heating

Past research has long identified a nocturnal maximum in convective frequency over the central United States. Given the ramifications of such convective activity to severe weather forecasts, an understanding of the processes governing nocturnal storms is of interest. As the sun sets, the boundary layer stabilizes so that much of this nocturnal convection is assumed to be elevated (not ingesting near-surface air parcels). Recent work by the second author has elucidated several of the key dynamical processes governing these nocturnal convective systems as they transition from surface-based to elevated convection.

A well-known environmental feature that is frequently associated with nocturnal convection is the low-level jet (LLJ), which develops as the nocturnal boundary layer becomes increasingly stable. However, in the interest of isolating fundamental dynamical processes, Parker's initial experiments utilized a simplified vertical wind profile that did not vary in time. Therefore, a logical next step is to examine the effect of adding a LLJ to the low-level wind profile during the time of nocturnal cooling. The changes in wind shear can significantly modulate storm structure and organization, in turn altering the transition from surface-based to elevated convection. Of additional interest is how initially elevated nocturnal convection responds to the development of a well-mixed boundary layer as the sun rises, since nighttime storms can often persist through the overnight hours into the following morning. Idealized model simulations are used to study the impacts of these environmental modifications upon the storms' structures, intensity, lifting mechanisms, and air parcel sources.