Sub-seasonal Variability Of Soil Moisture And Their Possible Linkages With Atmospheric Forcing

In order to explore the characteristics of soil moisture activities in 10-90 days,paper firstly discussed the variance distribution of soil moisture after seasonal filtering by using multiple sets of data.We evaluate the simulation ability of CESM model for soil moisture activities on sub-seasonal scales.Secondly,the relationship between external forcing factors and surface soil moisture and its possible influence mechanism were analyzed.At last,the internal relations between intraseasonal variation of soil moisture and precipitation has been preliminary investigated.These results aid in a more comprehensive understanding of the sub-seasonal characteristics of soil moisture and other land-surface factors over the word.The main conclusions can be summarized as follows:(1)ERA-Interim,NCEP,CFSR reanalysis data and GLDAS data are used to represent variability of the surface soil moisture over the world on sub-seasonal scales.The temporal-spatial differences and spectral features of surface soil moisture(SSM)on sub-seasonal scales over different key regions during the period of 1979-2017 have been studied in detail.Spatial and temporal heterogeneity of SSM on sub-seasonal time scales are clear.Variance of SSM across Northern China and Southern North America is significant in the northern hemisphere while Australia and southern Africa are key areas in south.Variance of SSM across northern China and southern America reaches a seasonal maximum in summer and decrease in the fall.The sub-seasonal variance intensity of different land surface factors is similar except for 100-200 cm soil moisture.(2)There are significant differences in seasonal variation of surface soil moisture in different key areas.The spectral periods concentrate mainly in 10-50 days through all seasons and regions.Cycle of Sub-seasonal change on SSM in the southern hemisphere is longer.The periodic characteristics of sub-seasonal variation of surface soil moisture occur equally in three sets of analytical data.(3)Intraseasonal variations occur in land surface and near-surface elements as well and there are similarities and differences across key areas and soil moisture.Subseasonal variability of soil moisture is positively correlated with latent heat flux while sensible heat flux is opposite.The relationship between long-wave,short-wave radiation flux and SSM is similar with that in surface soil temperature.(4)There is a positive correlation between soil moisture and soil temperature at high latitudes in spring while a negative correlation in other regions.When the soil temperature is 10-15 days ahead,there is a positive correlation between them in Africa and parts of Australia.A significant negative correlation between them can be noticed in most regions in summer.The first mode of spring precipitation SVD in North America is affected by multi-regional precipitation in different time periods.