Mesoscale Sea Surface Temperature Warm Anomalies Excite Trade Cumulus Generation in North Atlantic Trades: Satellite Observations and Large Eddy Simulations

Xuanyu Chen

CIRES CU Boulder - NOAA Physical Sciences Laboratory

Tuesday, May 21, 2024, 2:00 pm MT
DSRC Room GC402

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Abstract

Trade-wind cumuli play a crucial role in Earth’s energy budget due to their prevalence and net cooling effect. How these shallow clouds respond to a warming climate remains a key uncertainty for climate projections. The Atlantic Tradewind Ocean-Atmosphere Mesoscale Interaction Campaign (ATOMIC) provided a unique opportunity to investigate how relatively weak yet ubiquitous mesoscale sea surface temperature (SST) features impact trade cumulus cloudiness.

This talk will present complementary investigations using ATOMIC-validated satellite observations and cloud-resolving Large Eddy Simulations (LES). Composite analysis of the satellite observations shows in-phase modulations of daily mean cloudiness over weak sea surface temperature anomalies (0.25 K on average). These daily cloudiness anomalies are positively correlated with the 10-m neutral surface wind speed but are offset from the near-surface wind convergence. Idealized LES experiments conducted with the mean large-scale environmental conditions during ATOMIC reproduce these satellite composite results. LES results further suggest that the enhanced cloudiness signal over SST warm patches in the satellite composite mainly reflects enhanced cloudiness near cloud base below 1 km. LES results also show that the increased low-level cloudiness is driven by locally enhanced turbulence instead of surface convergence-induced upward motions. I further explain this turbulent-driven cloud formation process. Then the relative roles of enhanced surface sensible and latent heat flux over SST warm anomalies in initiating trade cumulus generation are discussed based on mechanism denial experiments.