Relationships Between Tropical India Ocean Basinwide Mode And Climate Anomalies In Maritime Continent Region In Boreal Summer

Using the monthly mean Sea Surface temperature (SST) data from Hadley Centre, the NCEP/NCAR monthly reanalysis, we have investigated the relationships between the India Ocean basinwide mode and the climate variations in the Maritime Continent.First of all, after removing signal of El Nino Modoki (IEM) out from SSTA,we have defined the EP SSTA index as IEPN over Ninol+2 area. Then we have analyzed the circulation variations related to these two indices and their influences on climate anomalies over the Maritime Continent (MC). By removing the long term trend and simultaneous and leading signals of two kinds of ENSO out from the India Ocean Basin-wide Mode (India Ocean Basinwide Mode, IOBM) index IIOB, we have defined the modified IOBM index (ImIOBK , ImIOBA , ImIOBlK , and ImIOBlA ) and analyzed the variations of IOBM and its association with climate anomalies over the Maritime Continent (MC). Results are summeried as follows:There are significant differences between EM and EP SSTA events as well as their effects. The IEM has higher power density on the cycle of 2-3 years, 8 years and period longer than a decade whereas the IEPN has higher power density on the cycle of 3-5 years and 6 years. In boreal summer, when IEM is in its positive phase,the tropical Pacific SSTA show a pattern of "negative-positive-negative". The SST anomalies are negative in most of the MC region. In the Pacific Ocean, the anomalous convergence in the lower troposphere and anomalous divergence in the upper troposphere are observed while in MC region, the anomalous divergence in the lower troposphere and anomalous convergence in the upper troposphere are observed.Corresponding to these anomalous convergence and divergence centers, there are two vertical circulations from central equatorial Pacific respectively to eastern equatorial Pacific and to central and eastern part of MC. There is also a vertical circulation from western part of MC to western part of India Ocean. The atmosphere in MC is heated in the north and cooled in the south. Precipitation in the south of 10°N is significantly less than normal while it is more than normal in the north of 10°N in MC region. When IEPN is in its positive phase, the tropical Pacific SSTA shows distribution of "negative in west and positive in east''. SSTAs in MC region distribute as "positive in west and negative in east". In the lower and higher troposphere, the divergence and convergence centers shift eastward as compared to those when IEM in its positive phase. The tropical circulation anomaly is of baroclinic structure in vertical. The atmosphere in MC is also heated in the north and cooled in the south. The precipitation in most areas of MC region is less than normal.When IOBM in its warm phase, India Ocean region undergoes an anomalous warm state in different seasons. The vertical motion of atmosphere over India Ocean changes large from a season to another. During boreal summer, the atmospheric updraft in most areas of India Ocean is possibly induced by the warmer sea temperature anomalies. After filtering the simultaneous signal of ENSO, it is found that the IOBM index ImIOBK and ImIOBA varies with periods of 3-5 years in boreal summer. When it is in its positive phase, SST in regions from the India Ocean to East China Sea is anomalously warmer. Precipitation in the western part of MC region is significantly more than normal while it is less than normal in the northeastern part of MC region. The anomalous convergence in the lower troposphere and anomalous divergence in the upper troposphere lead to both the upward motion and water vapor convergence to strengthen there, inducing more than normal rainfall in the western part of MC. In the northeastern part of MC region, the anomalous divergence in the lower troposphere and anomalous convergence in the upper troposphere is observed,which do not facilitate occurrences of more precipitation there. In the lower troposphere, the divergent flows emanating from eastern part of MC and West Pacific induce a pair of anomalous anticyclones to merge in northern and southern tropics,which look almost symmetrical about the equator. The abnormal diabatic heating over equatorial India Ocean excites the eastward propagating Kelvin wave,strengthening easterly anomaly along equator. This strengthened easterly facilitates the intensification of Rossby waves in the north and south tropical regions outside the MC region.After filtering leading signal of ENSO, it is found that the IOBM index ImIOBlk in boreal summer varies with periods of about 2 and 8 years whereas ImIOBlk does with periods of 3-4 and 8 years. When ImIOBlk is in its positive phase, India Ocean is cooled in the west and warmed in the east, when a large area of MC is warmed.Large precipitation anomalies zone in MC and India Ocean region are distributed mainly in latitudinal direction, the longitudinal distribution are negative-positive-negative in MC while negative-positive-negative-positive in India Ocean. These precipitation distributions can be explained by anomalous convergence and divergence in both the lower and upper troposphere along with the vertical motions in the equatorial region. The 2m temperature anomalies above the ground looks similar to those of the SST anomalies. The positive (negative) temperature anomalies are mainly caused by the positive (negative) anomalies of net long wave radiation and the increase (decrease) of solar radiation absorbed by the ground.