Spatiotemporal Patterns Of Hydroclimate On Centennial And Decadal Time Scales In The Mid-latitude Northern Hemisphere

Moisture/precipitation variations between arid central Asia and mid-latitude monsoonal Asia are out-of-phase or anti-phased on different timescales during the Holocene,which is known as the ‘westerlies-dominated climatic regime'(WDCR).WDCR is a typical manifestation of regional hydroclimatic response to global change and analyzing the spatiotemporal variations of moisture/precipitation from a macro perspective can help further deepen the understanding of the patterns and driving mechanisms of hydroclimatic variations in the Northern Hemisphere.However,limited by the extremely uneven spatial distribution of research materials,there is still a lack of in-depth study on the spatiotemporal patterns and influencing factors of hydroclimatic variations on different timescales in the Northern Hemisphere.Therefore,based on the previous results,this paper uses four sets of monthly grid precipitation data of GPCC,CRU,ERA5-Land and PREC/L from 1960 to 2019 to analyze the spatiotemporal distribution of decadal precipitation variation under the background of modern climate for the land area in the mid-latitude Northern Hemisphere(20°?60°N).On this basis,using NOAA Pacific Decadal Oscillation(PDO)index and monthly grid data of sea surface temperature,monthly grid data of ERA5 geopotential field and horizontal wind field,NCAR Atlantic Multidecadal Oscillation(AMO)index and North Atlantic Oscillation(NAO)index,the spatiotemporal pattern and driving mechanism of decadal summer precipitation variation in the mid-latitude Northern Hemisphere are discussed from the perspective of ocean-atmosphere interaction.In addition,this paper further uses 186 high-resolution paleoclimate proxy records indicating moisture/precipitation variation and combines with paleoclimate reanalysis data to reveal the spatiotemporal variation characteristics of moisture/precipitation on the centennial scale in the mid-latitude Northern Hemisphere over the past millennium.The main conclusions are as follows:(1)Under the background of modern climate,the decadal summer precipitation in the mid-latitude Northern Hemisphere presents a spatial pattern of ‘+-' alternation.The decadal WDCR observed by predecessors is included in this spatial pattern of precipitation variation,which can be seen as its local expression on the mid-latitude Eurasian continent.In other seasons of decadal scale,the precipitation variation did not show some similar large-scale spatial distribution characteristics in the mid-latitude Northern Hemisphere.At the same time,in the current context of global warming,this spatial pattern of precipitation variation has not been much affected in parts of the Eurasian continent,but in the central and eastern North America,the spatial pattern of‘+-' alternation of precipitation is no longer obvious.(2)This spatial pattern of precipitation variation is closely related to a teleconnection wave train like the decadal ‘Silk Road Pattern(SRP)'.This teleconnection wave train may be caused by ocean-atmosphere interaction(e.g.AMO/NAO)over the North Atlantic.The wave train propagates along the latitude lines through the westerly jet and crosses the entire mid-latitude Northern Hemisphere.Each activity center has a deep barotropic structure and has an obvious indigenous change cycle of about 10 years and 26 years,which may be the main reason why the decadal summer precipitation presents ‘+-' alternating variation in the mid-latitude Northern Hemisphere under the background of modern climate.(3)Over the past millennium,there has also been a wide range of ‘+-'alternating pattern of moisture/precipitation on the centennial scale in the mid-latitude Northern Hemisphere,including the previously defined centennial WDCR.In this spatial pattern,the moisture/precipitation in the arid region of Central Asia variation inversely with that in the arid region of Northwest China on the east side,and in the same phase with that in the Mediterranean on the west side,showing the opposite variation relationship with the decadal precipitation in the region.In the future,it is necessary to verify whether this phenomenon is prevalent in the analysis results of other different types of data.