6/9/2022

The diurnal cycle of solar radiation over tropical and midlatitude summertime continents forces a strong evolution of atmospheric convection. As surface sensible and latent heat fluxes increase after sunrise, a dry convective boundary layer develops in the early morning hours. It proceeds with the formation of shallow convective clouds as the convective boundary layer deepens and may eventually lead to the transition from shallow to deep precipitating convection. Factors affecting shallow-to-deep convection transition have been studied in the past, but the early evolution of dry convection and how it affects the development of shallow convection and eventual transition to deep convection attracted much less attention.

This presentation will discuss a set of large-eddy simulations that considers the impact of the surface flux Bowen ratio, the partitioning of the surface heat flux into sensible and latent components, on the development of dry and eventually moist convection. The key point is that the Bowen ratio affects the surface buoyancy flux and thus the growth of the dry convective boundary layer before the moist convection onset. This has a strong impact on the development and organization of shallow convection and eventual transition to deep convection. Details of the simulation results will be discussed.

Dr Wojciech Grabowski is a Polish-American cloud physicist. He obtained his MSc and PhD degrees in Poland (from the University of Warsaw’s Physics Department and Polish Academy of Sciences, respectively) in the 1980s. He moved to the National Center for Atmospheric Research (NCAR) in 1987 after receiving a prestigious NCAR’s Advanced Study Program Postdoctoral Fellowship. He has been at NCAR since then, currently as a Senior Scientist (since 2005) at the Mesoscale and Microscale Meteorology Laboratory. His main areas of interest include computational fluid dynamics and numerical modeling in general, and more specifically modeling of cloud dynamics and microphysics, interactions of clouds with radiation and surface processes, and representation of these processes in numerical models of small-scale dynamics, weather, and climate. He obtained habilitation [a post-PhD degree, equivalent of the Doctor of Science (DSc)] from the Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland, in 1999. In 2013 he received the title of Professor of Physical Sciences of the Republic of Poland. He was a member of the Committee on Cloud Physics of the American Meteorological Society between 1995 and 1998, and a member of the International Commission on Clouds and Precipitation between 2000 and 2008. He is a Fellow of the Royal Meteorological Society and of the American Meteorological Society. He is the Affiliate Professor of the Faculty of Physics, University of Warsaw. Dr Grabowski published over 160 papers in atmospheric science journals and a similar number of papers in conference proceedings. His papers attracted over 11,000 citations (H=57, https://scholar.google.com/citations?user=WVjmW3wAAAAJ&hl=en) He served as a member of editorial boards for the Quarterly Journal of the Royal Meteorological Society (2001-2008), Atmospheric Science Letters (2000-2011), Journal of the Atmospheric Sciences (2006-2019), and the Journal of Advances in Modeling Earth Systems (JAMES, 2008- 2011).