Improved Understanding of Drivers of Upper-Level Updrafts and their Role in Producing Thunderstorm Overshooting Tops

Overshooting tops (OTs) are manifestations of deep convective updrafts that extend past the tropopause into the stratosphere. OTs can transport moisture and aerosols into the stratosphere and have been connected to the occurrence and intensity of severe weather hazards, such as tornadoes and hail. Recent work has shown a connection between OT characteristics, such as area (OTA) and depth (OTD), and midtropospheric updraft structure, but OTs apparently can also be modified by static stability in the lower stratosphere (LS). Here we use numerical simulations of OTs and their associated convective storms in idealized and real-case inspired environments to further our understanding of the impact of LS static stability on OTA and OTD. Consistent with our observational work, these simulations show that OTD depends significantly on LS static stability. In contrast, OTA tends to be relatively insensitive to LS static stability and is more closely related to midtropospheric updraft-core area, which in turn depends on the tropospheric vertical wind shear.

Further questions remain, however, on what drives updraft intensity aloft in ongoing OTs. Numerical simulations are being leveraged to understand the dynamical drivers of updrafts above the mid-troposphere. This will allow us to further develop the three-dimensional time-dependent model of a thunderstorm, including its extension into the stratosphere. Preliminary results indicate that parcels that spend longer amounts of time in the OT experience stronger dynamical pressure gradient forcings in the mid-to-upper troposphere (8-12 km) compared to parcels that spend short amounts of time or do not enter the OT.