In this study, we describe results from a number of highly idealized WRF numerical simulations of the vertical temperature and moisture structures associated with stratiform precipitation and its evaporation. This study was motivated by earlier observation-based research suggesting that the temperature structures associated with stratiform precipitation in mesoscale convective systems and its evaporation can regulate the formation of new deep convection and, therefore, at least partly explain convection's strong dependence on humidity above the boundary layer (Virman et al. 2018).
The idealized simulations show that evaporation of stratiform precipitation alone can lead to temperature anomalies that are strong enough to affect the formation of deep convection. More specifically, we show that strong evaporative cooling collocated with weak subsidence warming results in a cold anomaly at roughly 560-750 hPa, whereas subsidence warming overcompensating weaker evaporative cooling at 750-900 hPa produces a warm anomaly there. The temperature structures are stronger when precipitation falls to initially drier air, propagate to the environment and persist for some time even after precipitation stopped. Our results suggest that stratiform precipitation and its evaporation should be correctly represented in numerical weather forecasting and climate models models in order for deep convection and its dependence on humidity to occur correctly in them.
References
Virman, M., M. Bister, V.A. Sinclair, J. Räisänen, and H. Järvinen, 2020: Vertical Temperature Structure Associated with Evaporation of Stratiform Precipitation in Idealized WRF Simulations. Journal of the Atmospheric Sciences, 77, 1851–1864, https://doi.org/10.1175/JAS-D-19-0111.1
Virman, M., Bister, M., Sinclair, V. A., Järvinen, H., and J. Räisänen, 2018: A new mechanism for the dependence of tropical convection on free‐tropospheric humidity. Geophysical Research Letters, 45, 2516– 2523. https://doi.org/10.1002/2018GL077032