Variability Of The Eurasian Soil Moisture In The Reanalysis And Its Interaction With Atmospheric Circulation In The Northern Hemisphere

Land surface is an important component of climate system, and has a significant impact on climate variation. In this paper, we collect four sets of widely-used soil moisture data, which include the European Centre for Medium Range Weather Forecasting (ECMWF)40-year reanalysis (ERA40)、Interim (ERA-Interim), the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data, and Global Soil Wetness Project product. Qualities of these four sets of soil moisture data over Eurasia are compared. After removing the influence of trends and the ENSO teleconnections, spatial distribution, seasonal variation and the center of variability are investigated. Empirical orthogonal function (EOF) analysis is used to examine seasonal variations of the leading mode in3-month Eurasian soil moisture and its decaying time-scale in the associated principle component (PC) time series. It is shown that the leading EOF modes of Eurasian soil moisture anomalies exhibit considerable persistence throughout the year; the decaying time-scale of the associate PC time series is about three to four months for all seasons. Soil moisture data from ERA40is demonstrated to have the largest commonality, so interactions between soil moisture over Eurasia and northern hemispheric circulation are investigated with this data set.Previous empirical or numerical studies have investigated the impact of soil moisture on the temperature, precipitation and regional atmospheric circulation, but have seldom examined the impact of soil moisture on hemispheric circulation, and the influence of tropical SST on SM and atmospheric circulation was rarely excluded in these studies. The main purpose of this study is to investigate the forcing of atmospheric circulation on variations of the Eurasian soil moisture and the possible feedback of persistent changes in Eurasian soil moisture on lagged large-scale atmospheric circulation in the44-year European Centre for Medium Range Weather Forecasting (ECMWF) reanalysis dataset.A lagged maximum covariance analysis is applied to investigate linear covariability between monthly Eurasian soil moisture (SM) and sea level pressure,500-hPa and200-hPa geopential height field in the Northern Hemisphere. The dominant signal is the atmospheric forcing of SM anomaly throughout the year. When the anticyclonic (cyclonic) atmospheric circulation dominates over the continent, there is negative (positive) soil moisture.In summer (JJA), autumn (SON) and winter (JFM) atmospheric signal resembling the negatively polarized Arctic Oscillation (AO) is significantly correlated with persistently changed soil moisture anomalies in the Eurasia continent up to the five months in the leading MCA modes. The predictability of the AO signal is highest when SM leads by5,3and3months for summer, autumn and winter atmospheric circulation respectively, and the maximum atmospheric perturbation at500hPa reaches20,25and50gpm in the MCA for JJA, SON and JFM season respectively. Moreover, the atmospheric signal is primarily equivalent barotropic for all three seasons. Soil moisture also has a substantial impact on precipitation and2m temperature, especially in middle and high latitudes. At last, regression analysis based on the SM anomaly centers of action from the MCA covariance patterns confirms that leading spring, summer and autumn soil moisture anomalies in the regions of subtropical North Africa, Western Europe and Siberia are significantly correlated to lagged summertime, wintertime and autumn atmospheric circulation. The leading time of Eurasian SM anomaly indicates an implication for skillful predictability of wintertime, summertime and autumn atmospheric variability.