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Increasing Importance of Poleward Moisture Transport and Rainfall Sourced from North America for Arctic Sea Ice Loss

Presentation Date
Thursday, February 1, 2024 at 2:30pm - Thursday, February 1, 2024 at 2:45pm
The Baltimore Convention Center - 326



Predictability of September Arctic sea ice is considered limited to June when solar radiation begins to alter the energy exchange between the atmosphere and surface. However, summer sea ice forecasts initialized at the beginning of the melt season still exhibit very limited ability to accurately predict September sea ice relative to damped anomaly forecasts. More accurate initial conditions are key to improving skill in these dynamical forecasts, with previous studies suggesting moisture and heat transport into the Arctic, primarily from Eurasia, could precondition sea ice prior to the melt season by reducing surface albedo and increasing sensitivity of the system to the initiation and drivers of the melt season. We quantify the contributions from meridional moisture transport pathways using iCESM1 simulations with combined moisture source-region tagging and a select list of atmospheric state variables nudged to ERA5 reanalysis. We compare our results with free running configurations which struggle to capture the high-pressure pattern over Greenland that connects the Arctic to an important moisture source over North America during periods of strong summer sea ice loss. Constrained atmospheric circulation in these simulations highlights this understudied transport pathway originating from the United States and passing along western Greenland. This transport from North America brings with it predominantly liquid precipitation throughout the melt season compared to the more commonly examined Eurasian pathways that produce relatively more snowfall. Trends over the last four decades show an increasing influence on early melt season Arctic precipitation of the North American pathway despite a drying signal over the continent. The North American moisture transport pathway may serve as a previously unidentified but key driver of future Arctic climate change on seasonal to decadal timescales.

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