The Influence Of Warming In Indian Ocean Basin On MJO And Its Relation To The Change Of Winter Climate In China

Based on daily precipitation observations at 756 Chinese stations archived by the China Meteorological Administration during the period 1979-2010,atmospheric reanalysis datasets from NCEP/NCAR and ECMWF,CNRM-CM5 mode historical and RCP8.5 experiments output results,the influence of warming in Indian Ocean basin on MJO and its relationship with the change of winter precipitation in China is analyzed.The main conclusions are as follows:(1)The changes of MJO under the warming in Indian Ocean BasinUsing the sea surface temperature datasets and RMM index defined by Wheeler and Hendon(2004),the feature of MJO in winter were analyzed during the two different periods of 1979-1988 and 2001-2010 respectively.The results show that the warming in Indian Ocean Basin is significantly detected.The wave number-frequency power spectra shows that the background spectrum are similar in both decades,but the symmetric component of MJO had stronger variance,indicating that the MJO activities are more frequent in recent decade.Comparison of the phase frequency of MJO between the period of 1979-1988 and 2001-2010,it can be seen that the influence of warming in Indian Ocean basin on MJO mainly reflected in intensified amplitude of phase 6 and increased phase frequency in phase 5.(2)Mechanism of the changes of MJO intensity and phase frequencyUsing the reanalysis datasets,the reason of intensified amplitude of phase 6 and increased phase frequency in phase 5 in recent years from 2001 to 2010 were investigated.The results reveal that,the specific humidity in phase 4 has a westward-tilt structure,stronger positive moisture anomalies and more unstable stratification in the east of the convection center,favoring the generation of shallow convection and propagation ofMJO to the phase 5.Comparing the difference of specific humidity vertical profile of MJO phase 5 in two different decades,it could be found that the backward-tilt structure is weaken in recent decade.This structure suppresses eastward propagation of MJO,causing the MJO stay in phase 5.This two reason caused increasing of phase frequency in MJO phase 5.The MSE and boundary layer moisture had enhanced in phase 6 in 2001-2010,and the vertical moisture advection lead to the increasing of MSE anomalies and the horizontal moisture advection reduced the increasing of boundary layer moisture anomalies.The enhancement of both boundary layer moisture and MSE contributed to the intensification of phase 6.(3)Change of influence of MJO on winter temperature and precipitation in ChinaUsing the station datasets and reanalysis datasets,the relationship between MJO and winter temperature and precipitation in China were discussed.It is found that the changes were difference in different phase.In MJO phase 5,the intraseasonal precipitation decreased during the winter and intraseasonal temperature increased in most regions of China,the intraseasonal temperature decreased in southern China and increased in eastern China.In MJO phase 6,the intraseasonal precipitation decreased during the winter in most regions of China.Through the analysis of the circulation fields,it is found that local Hadley cell induced by MJO convection anomaly plays key role on China's winter climate variability.