Friday October 28 CSL Meeting

The Role of Frozen Ground in Eurasian Surface-Atmosphere Interactions

Presenter: Oliver W. Frauenfeld
Time: Friday 28 October, 2:00-3:00 p.m.
Location: 805 O&M

Abstract: In recent decades, substantial changes have occurred across the high latitudes, particularly to the cryosphere. In the Arctic Ocean, sea ice extent and thickness have declined. In land areas, regional snow cover variability has been observed, and glaciers and ice sheets have experienced negative mass balance changes. Subsurface changes have also taken place in Northern soils. This presentation focuses on these changes in the soil thermal regime, specifically the permafrost and seasonally frozen ground regions of Eurasia. Using observational data, we find statistically significant long-term trends in a number of important indicator variables, including active layer depth, seasonal freeze depth, and the annual freezing/thawing index. Based on these changes, we next establish and quantify previously undocumented energy and moisture feedbacks of frozen ground degradation in response to climate change. Specifically, we focus on: 1) seasonally redistributed heat fluxes from the soil to the atmosphere, potentially capable of providing positive feedbacks to the atmosphere and resulting in amplified climate warming; and 2) altered surface moisture fluxes and precipitation patterns, with likely repercussions on the Arctic hydrologic cycle and its intensification. Soil heat flux trends are highly heterogeneous, but we do find evidence of statistically significantly increased heat flux to the soil during the warm season, and locations where there is an anomalous heat flux to the atmosphere during the cold season. However, concurrent changes in snow cover complicate these heat flux changes. Surface moisture flux variations indicate that different permafrost regions are characterized by different atmospheric moisture patterns, with analogous changes in the likelihood of precipitation. This suggests that instead of a uniformly intensifying Arctic hydrologic cycle as projected by climate models, concurrent changes in frozen ground distribution may decrease or ultimately even offset any intensification.

Annual change in probability (%) of July afternoon precipitation as a function of surface evaporative fraction (from Ford and Frauenfeld, 2016).

Reference:

Ford, T. W. and O. W. Frauenfeld, 2016: Surface-Atmosphere Moisture Interactions in the Frozen Ground Regions of Eurasia. Scientific Reports, 6, 19163, doi:10.1038/srep19163.