Spatial And Temporal Characteristics Of South Pacific Subtropical Dipole And Variability Of General Circulation

This study analyses the structure and variability of South Pacific Subtropical Dipole(SPSD) and SPSD general circulation effect in South Pacific Convergence Zone(SPCZ) by using Had ISST of Hadley center and atmospheric reanalysis data of NCEP-NCAR from 1948 to 2012. The main results show as follows:(1) What is the structure and variability of South Pacific Subtropical Dipole. South Pacific Subtropical Dipole is the first mode of SSTA EOF with ENSO signal removed(variance ratio contribution is 25%) with SSTA outphase from north-east to south-west. South Pacific Subtropical Dipole has four years period and a strong phase locking. During positive dipole events, North-East pole obtains heat and South-West pole loses heat, then matured dipole mode forms in austral spring(September to November). Dipole peaks in austral summer(December to February) and the heat budget reverses, so its North-East pole loses heat and South-West pole obtains heat with strength gradually weakening during autumn(March to May). Dipole events are selected according to time series of EOF’ first mode, and the number of El Ni?o and La Ni?a events is equal both in positive and negative dipole events which laterally confirms that dipole events is independent on ENSO.(2)The influence of SPSD on South Pacific Convergence Zone(SPCZ) during positive and negative dipole events. The peaking SPSD clearly affects location of SPCZ precipitation. During positive dipole event, composite analyses show that north-east pole(warm SST) is controlled by low pressure center, and convergent moisture moves up, so this area has more precipitation. However, south of south-west pole of dipole(cool SST) is controlled by high pressure center, and divergence moisture moves down, so this area has less precipitation, and the SPCZ moves toward north. Negative dipole event is opposite, north-east pole has less precipitation while south-west has more, so the location of SPCZ precipitation moves south. The analyses of vertical section show SST dipole affects atmosphere strongly from sea surface to middle-upper layer of troposphere. The location of precipitation doesn’t exactly agree with SST variability area, and perhaps because physical variable of atmosphere lean to south-west from under layer to upper layer due to the effect of ocean.(3)Typical cases without ENSO’s influence of only positive dipole year 1983 and only negative dipole year 1990 also show South Pacific Subtropical Dipole indeed affects SPCZ precipitation. During these two years, there are only dipole events without influence of El Ni?o and La Ni?a. The results of typical cases are the same as the composite results of dipole event, and north-east area has more precipitation during positive dipole event, and then SPCZ moves north. The SPCZ moves south during negative dipole event.The results of this study provide more knowledge of relationship between SPSD and SPCZ, and it’s better to understand climate change and air-sea interaction in south Pacific.