Surface-Atmosphere Moisture Interactions in the Frozen Ground Regions of Eurasia.

Trent W Ford,Oliver W Frauenfeld

doi:10.1038/srep19163

Abstract

Climate models simulate an intensifying Arctic hydrologic cycle in response to climatic warming, however the role of surface-atmosphere interactions from degrading frozen ground is unclear in these projections. Using Modern-Era Retrospective Analysis for Research and Applications (MERRA) data in high-latitude Eurasia, we examine long-term variability in surface-atmosphere coupling as represented by the statistical relationship between surface evaporative fraction (EF) and afternoon precipitation. Changes in EF, precipitation, and their statistical association are then related to underlying permafrost type and snow cover. Results indicate significant positive trends in July EF in the Central Siberian Plateau, corresponding to significant increases in afternoon precipitation. The positive trends are only significant over continuous permafrost, with non-significant or negative EF and precipitation trends over isolated, sporadic, and discontinuous permafrost areas. Concurrently, increasing EF and subsequent precipitation are found to coincide with significant trends in May and June snowmelt, which potentially provides the moisture source for the observed enhanced latent heating and moisture recycling in the region. As climate change causes continuous permafrost to transition to discontinuous, discontinuous to sporadic, sporadic to isolated, and isolated permafrost disappears, this will also alter patterns of atmospheric convection, moisture recycling, and hence the hydrologic cycle in high-latitude land areas.

Highlights

We found significant negative surface EF trends in the southern half of the study region, attributable to increased SH with little to no appreciable change in LH
Increased July surface EF in the Central Siberian Plateau coincides with increased July afternoon precipitation
We find significant increases in surface EF, enhanced during the summer season

Summary

Interactions in the Frozen Ground

Climate models simulate an intensifying Arctic hydrologic cycle in response to climatic warming, the role of surface-atmosphere interactions from degrading frozen ground is unclear in these projections. Using Modern-Era Retrospective Analysis for Research and Applications (MERRA) data in high-latitude Eurasia, we examine long-term variability in surface-atmosphere coupling as represented by the statistical relationship between surface evaporative fraction (EF) and afternoon precipitation. Surface energy flux, and precipitation data are most readily available in Europe and North America, the majority of studies examining land-atmosphere interactions have investigated these regions. The daily morning EF anomalies and corresponding precipitation occurrences are used to build the logistic regression model, from which the probabilistic relationship between the two variables can be determined. The model output is the log odds ratio of afternoon precipitation occurrence and the slope of the regression represents the relationship between the two variables. The significance of the logistic regression was assessed using Wald’s chi-squared test[33]

Results

Summary and Conclusions

Additional Information