Interferences Of IOD In The ENSO-Effect On The Interannual Variations Of The Precipitation And Air Temperature In Asian And Australian Regions

Using NCEP/NCAR reanalysis data and monthly mean air temperature and rainfall data at 160 stations in China, we have investigated the individual influence of "pure" ENSO or "pure" Indian Ocean Dipole (IOD) events, and the combined influences of these two types of events on both the rainfall and the air temperature in Asian-Australian region. The results are summarized as follows:(1) The dominant periodicities as detected in the Indian Ocean Dipole Index (IODI) are the 3 year and 5year respectively. The 5 year period appears notablyduring the cold period of the Indian Ocean from 1958 to 1986 while the 3 year period appears distinctly during the warm period from 1987 to 1999.(2) Either "pure" ENSO or the "pure" IOD event has distinct effects on both the summertime precipitation and air temperature in China. When a positive (negative) IOD event co-occurs during an El Nino (La Nina) year, the moisture content and precipitation tend to increase (decrease) in the northern part of China. However, in the eastern part of China, rainfall tends to be less (more) than normal while the air temperature tends to be higher (lower) than normal in years when the positive (negative) IOD and El Nino (La Nina) events co-occur. The IOD has been proved henceforth to weaken the influences of ENSO events on the summertime rainfall and air temperature in the eastern part of China.(3) Both the "pure" ENSO and the "pure" IOD events have the same effects on the autumn rainfall in China. But the influences of them on autumn temperature in China are different. The precipitation in the southern part of China tends to increase (decrease) and that in the northern part of China tends to decrease (increase) in the year when the positive (negative) IOD and El Nino (La Nina) events co-occur. In the northeast part of China, the air temperature tends to be wormer (cooler) than normal while in Sichuan province, the air temperature tends to be lower (higher) than normal in years when the positive (negative) IOD and El Nino (La Nina) events co-occur.(4) Winter precipitation and temperature in Australian have also been influenced by either "pure" ENSO or "pure" IOD event. But the influence of the "pure" IODevent on winter rainfall and temperature in Australian is stronger than that of "pure" ENSO event. When a positive (negative) IOD event co-occurs during an El Nino (La Nina) year, the convectional circulation was suppressed (promoted) in Australian. In the northern part of Australian, the temperature tends to be lower (higher) than normal and in the western part of Australian, the temperature tends to be higher (lower) than normal in years when the positive (negative) IOD and El Nino (La Nina) events co-occur.