Interference Of Tropical Indian Ocean SSTA In Relationships Between The Central Pacific Type ENSO And Climate Variations In The Maritime Continent Region

Using the monthly mean data from NCEP/NCAR Reanalysis, the NOAA precipitation data, and the sea surface temperature from Hadley Center over period of 1979-2015, we have calculated the summer CP-type sea surface temperature anomaly (SSTA) index by employing the EOF-regression method proposed by Kao and Yu (2009). Based on this CP-type SSTA index, we have investigated the relationships between CP-type ENSO and the Maritime Continent climate anomalies during boreal summer. At the same time, we have also examined roles of Indian Ocean dipole (IOD) and Indian Ocean Basin-wide mode (IOBM) in interferences of the relationships between CP-type ENSO and the Maritime Continent climate anomalies, in filtering IOBM retaining the IOD signals and filtering the IOBM, IOD respectively. The results are summarized as follows.There are significantly negative (positive) precipitation and temperature anomalies in the key region of MC (Pacific) when positive CP-type SSTA events occur in summer. Meanwhile, in the part of MC region, large negative (positive)heating anomalies are observed, which drives the atmosphere to descend (ascend)there. The anomalous diabatic heating free of latent heat release is also negative(positive) there, thereby facilitating the negative (positive) precipitation. The MC region and the central Pacific are linked by the horizontal and vertical circulations.When the CP-type ENSO index is significantly positive, a pair of cyclonic(anticyclone) circulations are observed almost symmetrical about the equator in the lower (upper) troposphere between MC region and the Pacific, inducing the divergence (convergence) to be weaker in the eastern part of MC region and stronger in the western part of the region. The positive SSTA in equatorial central Pacific and atmospheric cooling anomalous in the key region of MC induce the anomalous westerly to be intensified, which in turn induces the SSTA in central equatorial Pacific to be warmer. This process explained by the Bjerkness mechanism facilitates in anomalous anti-Walker circulation between MC and equatorial central Pacific,which directly links the SSTA forcing in equatorial central Pacific to climate anomalies in MC region. In region between Peruvian coast and equatorial central Pacific, an anomalous Walker circulation is observed, which can also be explained by the Bjerkness mechanism. On the other hand, different from those direct connections as mentioned above, MC and the central Pacific regions are linked indirectly by vertical circulation along curve paths in the lower and middle latitudes outside equatorial zone. Those vertical circulations along arc/curve paths are not only related to anomalous local Hadley circulations but also related to the Rossby wave patterns in tropical region and the quasi-stationary Rossby waves in mid-latitudes.IOD does not modify the pattern of precipitation anomaly with negatives in maritime continent area. However, it influences the precipitation by shifting itsanomalies westward or eastward and enhancing the positive precipitation anomalies in the tropical Pacific region. IOD modifies the SSTA pattern in tropical Indo-Pacific.When the IOD index is in the same phase with CP-type SSTA index, the SSTA pattern in tropical Pacific looks like a dipole pattern whereas, when the IOD and CP-type SSTA indices are oppositely signed, the SSTA distribution in tropical Pacific looks like a triple pattern. Whenever the two indices are same or oppositely signed,the connections between SSTA in central Pacific and climate variations in MC are strengthened. The anomalous convergence (divergence) in the lower (upper)troposphere is observed in MC region in both the same and oppositely signed index years. The corresponding vertical circulation is well defined in region from MC to Pacific, thereby facilitating the negative precipitation in MC.Similarly, IOBM also plays a role in modulating the relations of CP-type SSTA with climate anomalies in MC. If neither IOD nor IOBM occurs, the CP-type SSTA-influenced anomalous precipitation pattern exhibits the negative anomalous precipitation in MC with positive anomalies in central equatorial Pacific when CP-type SSTA index is in its positive phase. Interestingly, the IOBM does not alter the pattern of CP-SSTA-influenced rainfall anomaly pattern, either. When IOBM exits, the surface air temperature changes in MC look consistent with the SSTA changes there. Whenever the IOBM index is same signed with or oppositely signed against the CP-SSTA index, there observes the anomalous convergence (divergence)in the lower (upper) troposphere in MC region. However, in oppositely signed years,the decent motion in MC is intensified anomalously,thereby strengthening the negative precipitation anomalies.All the above results are helpful for our better understanding how the CP-type ENSO influences not only the climate anomalies in MC region but also the circulation anomalies outside tropical region during boreal summer.