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Midwinter Arctic leads form and dissipate low clouds.
Xia Li1, Steven K Krueger2, Courtenay Strong2
1Department of Atmospheric Sciences, University of Utah, 135 S 1460 E, Salt Lake City, UT, 84112-0102, USA. xia.li@utah.edu.
Nature Communications
|January 12, 2020
Summary
Arctic sea ice leads, which influence energy balance, surprisingly have fewer clouds when lead concentrations are high. Newly frozen leads dissipate low clouds, decreasing infrared radiation and accelerating sea ice freeze-up.
Area of Science:
- Arctic climate science
- Sea ice physics
- Atmospheric boundary layer processes
Background:
- Leads (open water in sea ice) significantly impact Arctic surface energy balance during winter.
- Existing understanding suggests high lead concentrations enhance heat and moisture fluxes, promoting boundary layer cloud formation.
Purpose of the Study:
- To investigate the counterintuitive relationship between lead concentration and boundary layer cloudiness in the Arctic.
- To elucidate the physical mechanisms driving cloud formation or dissipation in relation to lead characteristics.
Main Methods:
- Composite analyses of surface-based and satellite observations.
- Three-dimensional cloud-resolving simulations.
Main Results:
- Observed abundant boundary layer clouds correlated with low lead flux periods.
- Fewer boundary layer clouds were observed during high lead flux periods.
- Simulations revealed newly frozen leads (high sensible, low latent heat flux) dissipate low clouds.
Conclusions:
- The observed high lead fractions likely comprise mostly newly frozen leads.
- Newly frozen leads reduce pre-existing low-level cloudiness.
- This reduction in cloudiness decreases downwelling infrared flux, accelerating sea ice freezing.
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