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Title: The Arctic Surface Heating Efficiency of Tropospheric Energy Flux Events
Abstract This paper examines the processes that drive Arctic anomalous surface warming and sea ice loss during winter-season tropospheric energy flux events, synoptic periods of increased tropospheric energy flux convergence ( F trop ), using the NASA MERRA-2 reanalysis. During an event, a poleward anomaly in F trop initially increases the sensible and latent energy of the Arctic troposphere; as the warm and moist troposphere loses heat, the anomalous energy source is balanced by a flux upward across the tropopause and a downward net surface flux. A new metric for the Arctic surface heating efficiency ( E trop ) is defined, which measures the fraction of the energy source that reaches the surface. Composites of high-, medium-, and low-efficiency events help identify key physical factors, including the vertical structure of F trop and Arctic surface preconditioning. In high-efficiency events ( E trop ≥ 0.63), a bottom-heavy poleward F trop occurs in the presence of an anomalously warm and unstratified Arctic—a consequence of decreased sea ice—resulting in increased vertical mixing, enhanced near-surface warming and moistening, and further sea ice loss. Smaller E trop , and thus weaker surface impacts, are found in events with anomalously large initial sea ice extent and more vertically uniform F trop . These differences in E trop are manifested primarily through turbulent heat fluxes rather than downward longwave radiation. The frequency of high-efficiency events has increased from the period 1980–99 to the period 2000–19, contributing to Arctic surface warming and sea ice decline.  more » « less
Award ID(s):
2026863
NSF-PAR ID:
10387909
Author(s) / Creator(s):
;
Date Published:
Journal Name:
Journal of Climate
Volume:
35
Issue:
18
ISSN:
0894-8755
Page Range / eLocation ID:
5897 to 5913
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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