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Interactions Between Frozen Ground in the Russian Arctic and Atmospheric Circulation


NSF  This project is funded by NSF ARC grant 0612431

Objective

Rather than provide component-based analysis of specific surface-atmosphere interactions, we are investigating how the synoptic-scale circulation of the Northern Hemisphere atmosphere drives, and is driven by, changes in the freeze/thaw cycle in the Russian Arctic. The integrated effects of the atmosphere provide a first-order driver of changes in the distribution of frozen ground. Our work thus addresses a missing link in the Arctic climate system—the interactions between the largest cryospheric component, frozen ground, and regional to large-scale variations in the Northern Hemisphere atmosphere.

We hypothesize that:

  • atmospheric circulation anomalies over and upstream of the Russian Arctic induce changes in the soil thermal regime, which responds through soil temperature and freeze/thaw depth anomalies.
  • these freeze/thaw cycle anomalies are stored in the soil and alter the surface energy flux during the onset of winter, which results in feedbacks on the overlying atmosphere
  • snow and vegetation cover, also influenced by the atmosphere, provide further interactions and feedbacks between the ground thermal regime and atmospheric circulation.

Collaborators

Oliver W. Frauenfeld is the PI, and Tingjun Zhang and Mark C. Serreze are Co-Investigators.

Project Summary

Accelerated and amplified changes have characterized the northern high latitude climate system in recent decades. While many important processes that are driving, and driven by, Arctic climate change have been extensively studied, one area of research that has received relatively less attention involves quantifying and accounting for large-scale changes in the extent and distribution of frozen ground, both permafrost and seasonally frozen ground. Frozen ground covers up to 50.5 percent of the Northern Hemisphere land areas, and the near-surface soil freeze/thaw cycle extends over an even larger area. Frozen ground is therefore the single largest component of the cryosphere in terms of maximum area extent. The existence of permafrost and seasonally frozen ground is due to heat exchange between the ground surface and the overlying atmosphere, and the area extent and geographic distribution is therefore primarily forced by climate.

We are applying multivariate statistical analyses and modeling approaches to establish the patterns of variability and covariability in fields of soil temperature and freeze/thaw depth, and a number of atmospheric circulation variables—teleconnections, the polar vortex, and surface and tropospheric circulation fields. Snow cover and vegetation fields are being analyzed to establish the precise interactions, feedbacks, and pathways linking the soil thermal regime and atmospheric circulation.

Graph showing correlations between 1965 and 1998 circumpolar vortex and active layer depth averaged for permafrost region of Siberia
Correlations between the 1956-1998 circumpolar vortex and active layer depth averaged for the permafrost region of Siberia; correlations greater than ±0.3 (outside of the shaded box) are statistically significant at the 95 percent level. The strong concurrent positive correlations between active layer thickness in Siberia (60 to 140 degrees East) and the overlying lower atmosphere (700 and 500 hPa) represent a regional temperature response: a contracted vortex/atmospheric ridge corresponds to both a thicker (warmer) atmosphere and also allows milder midlatitude air masses to extend northward. The strong and significant correlation between the vortex over the Atlantic/western Europe (80 degrees West to 20 degrees East) indicates a weakening and northward movement of the Icelandic Low (positive NAO phase) in response to higher soil temperatures. A similar response has been reported between Eurasian snow cover and the NAO, where sparse snow cover in Siberia has the same effect on the NAO.

Chart showing heat transfer over the course of a year
We apply a heat transfer model with phase change for a theoretical active layer depth of 1.42 meters versus 1.29 meters. In general, the amount of heat flow from the soil towards the surface is up to 50 W/m2, which provides an idea of the magnitude of heat flow between the active layer and the atmosphere. The additional heat flux to the atmosphere from a mere 13 centimeters deeper active layer results in additional daily energy released to the atmosphere of up to 13.5 W/m2 (green line, about day 160 or early December). These positive heat flux anomalies persist for up to four months (late November to early March), and redistribute a substantial amount of energy to the atmosphere during the cold season. This simple example suggests that a significant feedback exists whereby changes in the freeze/thaw status affect the overlying atmosphere.

Related Resources

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