Characteristics Of Two Types Of Central Pacific El Ni(?)o And Numerical Simulations

Mainly based on monthly Hadley Center sea surface temperature datasets, ECMWF Ocean Reanalysis System 4 (ORAS4) subsurface temperature and ocean current datasets, NCEP/NCAR Reanalysis circulation datasets and Ni?o indices, the characteristics of two types of central Pacific (CP) El Ni?o (CP-Ⅰ El Ni?o and CP-Ⅱ El Ni?o) and coupled atmospheric processes are studied. On the basis of observations, the characteristics of atmospheric circulation are verified in the Community Atmospheric Model (CAM). The relationship between Climate Regime Changes and two types of CP El Ni?o also be studied. Major conclusions can be summarized as following:(1) There are two types of CP El Ni?o which mature in winter. CP-Ⅰ El Ni?o has symmetrical structure about the equator and the warming center locates at Ni?o4 regions. For CP-Ⅱ El Ni?o, the sea surface temperature anomalies (SSTA) change in phase between Ni?o4 regions and tropical northeast Pacific areas, with a banded and asymmetric structure of SSTA forming in the winter.(2) The subsurface temperature anomalies (SOTA) of these two types of El Ni?o and coupled atmospheric circulation are different. In the CP-Ⅰ El Ni?o winter, a zonal dipole mode forms between western and central eastern pacific, the meridional structure are also symmetric; the anomalous ascent of two-cells walker circulation is over equatorial Dateline, with convergent meridional wind anomalies in the equatorial areas, the Hadley circulation intensifies in the low latitude regions. In the CP-II El Ni?o winter, a zonal dipole mode confines in the western and central pacific, with tiny SOTA in the eastern pacific and meridional SOTA also confine in the north hemisphere; the cross-equatorial flow strengthens in the low level atmosphere, and the upwelling center of Walker circulation moves to north hemisphere. The Hadley circulation weakens in the low latitude regions to the contrary.(3) Sensitivity experiments verifies that the observed results are reliable. The atmospheric circulation response of CP-I El Ni?o perform as a zonal abnormal two-cells Walker circulation structure. The Gill response of the equatorial symmetric heat source are shown in the lower layers, meridional circulation structure are consistent with observations, but the response are weak in the 0～10°N. The atmospheric circulation response of CP-Ⅱ El Ni?o show that the northward movement of zonal circulation center. The Gill response of the equatorial single asymmetric heat source are shown in the lower layers, the change of Hadley circulation are consistent with the observations. The results of experiments also shows that the cooling in the Western Pacific of CP-Ⅱ El Ni?o adjusts the structure of atmospheric circulation significantly, it has important influence on the positions of the descending branch of the zonal circulation and the changes of the Hadley circulation.(4) There are close relationships between pacific climate regime change and two types of CP El Ni?o.1979～1996 (PER1) compared with 1997～2012 (PER2), the large scale circulation in the tropical regions are conducive to the development of the asymmetrical warming structure. The process of ocean dynamics are not conducive to the development of the equatorial Central-Eastern Pacific warming.