613 Seminar Florian Tornow/CU-GISS

Climate & Radiation Laboratory Virtual Seminar Series
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Florian Tornow
Columbia University/NASA Goddard Institute for Space Studies

On Aerosol-mediated Cloud Transitions in Cold Air Outbreaks as Informed by ACTIVATE

This presentation will cover ongoing research on marine cold air outbreaks (CAOs). This research is part of the multi-year NASA EVS-3 field campaign ACTIVATE that is devoting more than half its resources to a process-study focus on CAOs during wintertime and shoulder seasons off the mid-Atlantic coast. CAOs drastically affect the local energy budget by forming a (nearly) overcast deck consisting of roll-like boundary layer (BL) clouds that typically transition into a broken, open-cellular cloud field downwind. State-of-the-art earth system and weather forecast models struggle to faithfully represent CAOs and their radiative effects. 

We present a bottom-up approach to improve the representation of CAOs in models. This approach involves (1) targeted CAO sampling via two aircraft equipped with remote sensing and in-situ instrumentation, (2) understanding controlling factors of observed CAOs using large-eddy simulation (LES), and (3) evaluation of column physics in a climate model. This presentation will focus on steps (1) and (2).

For a CAO case in March 2020, we compare observed cloud and aerosol properties from LES that we run in a Lagrangian framework in that the LES domain follows the BL horizontal motion. We highlight the importance of mimicking instrument-like retrieval when comparing cloud ice properties.

Exploring controls on the overcast-to-broken cloud transition via LES, we emphasize the role of cloud ice in hastening transitions, thereby abbreviating the overcast state and its spatial extent. We show that ice affects CAO transitions primarily through riming-related processes. And we highlight the importance of a prognostic aerosol treatment to obtain cloud breakups in LES. 

To close, we summarize the common cloud micro- and macro-physical transition that we find across CAO cases in the NW Atlantic and in the North Sea, and provide an overview of factors driving transition speed that we identify in sensitivity experiments.

Short Bio:
Florian Tornow is a postdoctoral research scientist at the Center for Climate Systems Research at Columbia University and affiliated with the NASA Goddard Institute for Space Studies. Florian received his PhD from Freie Universität Berlin (Berlin, Germany) in 2018 where his research was focused on radiation flux estimates from the future ESA-JAXA satellite mission EarthCARE. Florian started his current position in 2019 with a focus on cloud-aerosol interactions in marine boundary layer clouds. 

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