Different SST Anomalies Over The Indian Ocean And Impacts On Asian Climate In Two-Type E1Nino Developing Phase

This present work investigates impacts of sea surface temperature (SST) anomalies over the tropical Indian Ocean associated with two types of El Nino during boreal autumn. Then The differences in the seasonal evolution features of Indian Ocean Dipole (IOD) accompanied with two-type El Nino and their different impacts on Asian climate have been contrasted, based on the Met Office Hadley Center sea surface temperature (SST) analyses monthly SST, NCEP/NCAR reanalysis datasets, SODA datasets, GPCP monthly precipitation dataset, GPCC Global Precipitation Climatology Centre monthly precipitation dataset and NOAA’s Precipitation reconstruction Dataset (PREC). Major conclusion can be summarized as follows:(1) It is shown that the positive IOD-like SST anomaly occurs during both EP and CP El Nino autumns, but with a different probability. Most of EP El Nino events are accompanied by a strong positive IOD-like SST anomaly. However, a weak positive IOD-like SST anomaly appears during only half of the CP El Nino events, with the warm SST anomaly located slightly southward and centres in the Southern Indian Ocean.(2) It seems that IOD is closely related with the strength of EP El Nino and the location of CP El Nino. During the EP El Nino, strong relationship is found between the intensity of IOD and that of EP El Nino. That is, IOD tends to occur during the strong EP El Nino autumns, with a strong sinking and negative rainfall over the maritime continent. During the CP El Nino, however, the occurrence of IOD seems to be unrelated with the strength of CP El Nino. The location of the CP El Nino is a possible key effect on the intensity of IOD in autumn. For the CP El Nino autumns when an obvious IOD appears, the warming SST anomaly is located slightly eastward over the central Pacific with a strong sinking over the maritime continent and a significant easterly anomalies over the tropical Indian Ocean. While in the CP El Nino autumns during which no positive IOD-like SST anomaly occurs, the Pacific warming SST anomaly is located relatively further west. The anomalous sinking motion over the maritime continent and the easterly anomaly over the tropical Indian Ocean were very weak.(3) There are differences in the seasonal evolution features between the IOD accompanied with EP El Nino and that accompanied with CP El Nino. Here, we focus on the ocean-atmosphere coupled processes over the tropical Indian Ocean during the evolution of IOD. As to the seasonal evolution of the IOD co-occurred with EP El Nino, tropical western Indian Ocean warms up and the equatorial southeastern Indian Ocean cools off intensely in summer then peaks in autumn, results from the weak southwest summer monsoon over western Indian Ocean and anomalous strong easterly over eastern Indian Ocean. By comparison, the evolution of IOD during CP El Nino associated with anomalous strong easterly over eastern Indian Ocean and anomalous lower-tropospheric negative vortices winds over the central Indian Ocean. The dipole SSTA develops when the west pole of triple pattern SSTA decays, different from the IOD co-occurred with EP El Nino.(4) The impacts of two-type El Nino accompanied with IOD on the Asian Climate during the developing phases are different. In EP developing summer without IOD, an anomalous anti-cyclone (cyclone) occurs south (north) to Japan, the Western North Pacific sub-tropical high (WNPSH) extends northward and in favor of more rainfall in the Huaihe River Valley, Korean Peninsula and Japan. When IOD occurs, the relationship between EP and suppressed rainfall over the Indian is weakened, EP and strong IOD in flavor of more suppressed rainfall over the Maritime Continent (MC) and the atmosphere responds different over Western North Pacific (WNP) and East Asian (EA):WNP anomalous cyclone strengthen WNP summer monsoon (WNPSM), WNPSH retreats southward, anomalous rainfall locates northward associated with weak Eastern Asian summer monsoon(EASM), more rainfall over southern China results from strong anomalous anti-cyclone over the Philippines. During CP El Nino, the IOD in flavor of drier MC. Strong positive summer rainfall over southern China and the Indo China Peninsula and more autumn rainfall over southern China, eastern region of northeast China and the north of Japan, which associated with anomalous atmospheric systems located northward.