STUDY ON THE MAIN CLIMATE MODES OF SHANDONG PRECIPITATION AND THEIR RELATIONS WITH THE EAST ASIAN WESTERLY JET

Summer precipitation patterns of Shandong Province are relatively independent with regard to the whole eastern China region.To study the rules and causes of precipitation variations,three main climate modes-on the annual,seasonal,and climatic intra-seasonal oscillation(CISO) scales-are extracted using a harmonic analysis method based on daily precipitation of Shandong during 1965-2009 and multi-year averaged pentad precipitation at 722 stations in China during 1971-2000.Among the three precipitation climate modes,the annual mode is closely related to the annual cycle of Earth-Atmosphere thermal system,which is characterized by the periodic dry and wet seasons.The seasonal mode reflects the monsoon effect on precipitation and the main flood season’s contribution to annual precipitation variations.As an important climatic signal,the CISO mode is more evident during summer monsoon.The gradual modulations of the CISO mode,seasonal mode,and annual mode control the annual variation of precipitation.To study the relationship between precipitation climate modes and atmospheric circulations,an East Asian Westerly Jet Index(EAWJI) is defined in this paper.It is revealed that precipitation of Shandong is closely related to EAWJI in all climate modes.A wet or dry phase of each climate mode corresponds to a specific atmospheric circulation pattern.The phase of the annual mode is reverse to that of EAWJI.During the wet phase of the seasonal mode(weak phase of EAWJI),the atmospheric circulation in and around Shandong is characterized by upper-level divergence and low-level convergence.A reversed atmospheric circulation exists for the dry phase(strong phase for EAWJI).In the summer wet phase of CISO mode(strong phase of EAWJI),Shandong is controlled by upper-level divergence and low-level convergence.Again,the dry phase is corresponding to a reversed circulation structure.The methodology employed in this research,i.e.studying the precipitation climatic variations in terms of independent components of different temporal scales,provides a new approach for annual and seasonal precipitation prediction.

STUDY ON THE MAIN CLIMATE MODES OF SHANDONG PRECIPITATION AND THEIR RELATIONS WITH THE EAST ASIAN WESTERLY JET

Summer precipitation patterns of Shandong Province are relatively independent with regard to the whole eastern China region.To study the rules and causes of precipitation variations,three main climate modes—on the annual,seasonal,and climatic intra-seasonal oscillation(CISO) scales—are extracted using a harmonic analysis method based on daily precipitation of Shandong during 1965-2009 and multi-year averaged pentad precipitation at 722 stations in China during 1971-2000.Among the three precipitation climate modes,the annual mode is closely related to the annual cycle of Earth-Atmosphere thermal system,which is characterized by the periodic dry and wet seasons.The seasonal mode reflects the monsoon effect on precipitation and the main flood season’s contribution to annual precipitation variations.As an important climatic signal,the CISO mode is more evident during summer monsoon.The gradual modulations of the CISO mode,seasonal mode,and annual mode control the annual variation of precipitation.To study the relationship between precipitation climate modes and atmospheric circulations,an East Asian Westerly Jet Index(EAWJI) is defined in this paper.It is revealed that precipitation of Shandong is closely related to EAWJI in all climate modes.A wet or dry phase of each climate mode corresponds to a specific atmospheric circulation pattern.The phase of the annual mode is reverse to that of EAWJI.During the wet phase of the seasonal mode(weak phase of EAWJI),the atmospheric circulation in and around Shandong is characterized by upper-level divergence and low-level convergence.A reversed atmospheric circulation exists for the dry phase(strong phase for EAWJI).In the summer wet phase of CISO mode(strong phase of EAWJI),Shandong is controlled by upper-level divergence and low-level convergence.Again,the dry phase is corresponding to a reversed circulation structure.The methodology employed in this research,i.e.studying the precipitation climatic variations in terms of independent components of different temporal scales,provides a new approach for annual and seasonal precipitation prediction.