Observing Strategies for Tornadogenesis and Turbulent Coherent Structures Using Simulated Mobile Doppler Lidars and Rapid-Scan Radar

Recent numerical modeling studies have illustrated that turbulent coherent structures in a supercell’s environment may play a major role in tornadogenesis (Markowski 2020, 2024). These structures often exist in the convective boundary layer and lead to streaks of vertical vorticity (often greater than 0.05 /s) in the near surface layer as the result of horizontal wind speed gradients. When these streaks of vertical vorticity become collocated with the intense negative pressure perturbations associated with low-level mesocyclones, this ambient vorticity can be stretched and tilted into the vertical, potentially facilitating tornadogenesis. An idealized modeling study has shown that more coherent, larger wavelength vertical vorticity sources are likely most supportive of tornadogenesis (Parker 2023). Because these features exist in clear air, there are limited scatterers for radar observations, making it challenging to characterize them in supercell environments using radar observations alone. Doppler lidars complement radar observations by enabling better clear-air observations and improving near-surface measurements required to document these shallow turbulent structures.

To better understand the impact of turbulent coherent structures on tornadogenesis, we plan to utilize the MetroWeather Coherent Doppler Lidar (CDL), which is a high sensitivity mobile system, the National Severe Storm Laboratory’s Halo lidar mobile platform, and the Rapid X-Band Polarimetric (RaXPol) radar in coordination with the Low-Level Internal Flows in Tornadoes (LIFT) field campaign. Use of these instruments will allow us to characterize both the clear-air turbulent inflow and tornado formation in a supercell. In the current study, we simulate a tornadic supercell in a turbulent environment and use lidar and radar emulators to create an observation strategy for future deployments. This study uses the Cloud Model 1 (CM1) and excites turbulence in a supercell environment by introducing random potential temperature perturbations in the lowest 1 km of the domain. After allotting 12 hours of spin up for turbulence statistics to converge, a storm is initiated using a warm bubble. Using the lidar and radar emulators, we vary the location and scan strategy of each instrument relative to the storm to find the best complementary observation approach for capturing turbulent coherent structures and tornadogenesis.