ITCZ(Intertropical Convergence Zone)is an important system in tropical regions.The anomalies of ITCZ have great impacts on the global atmospheric circulation.The research about how the anomaly of SST(sea surface temperature)impacts ITCZ is of great significance to the mechanism of air-sea interaction,climatic prediction and model assessment.In the passage,the monthly mean precipitation data from GPCP(the Global Precipitation Climatology Project)and CMAP(CPC Merged Analysis of Precipitation)and monthly mean SST data from ECMWF(the European Centre for Medium-Range Weather Forecasts)were used to investigate the characteristics of CEP-ITCZ(Central and Eastern Pacific ITCZ)in two types of El Ni(?)o.In order to comprehend the reasons why the CEP-ITCZ presents different characteristics in two types of El Ni(?)o,the Gill mode was used to attain the atmospheric anomalies which induced by the different heat source distribution in two types of El Ni(?)o.The responses of atmosphere in the Gill mode were consist with the anomalies of real atmosphere.Finally,two sensitivity tests were designed by MPAS-A(The Model for Prediction Across Scales—Atmosphere)model,the results of simulation were consist with the conclusions above mentioned.The main results and conclusions are as follows:(1)The latitude where the CEP-ITCZ exists is 7.60°N and the intensity of the CEP-ITCZ is 7.25 mm/day during usual years.By contrast,the CEP-ITCZ is located farther south by about 2.9°(0.2°)and the intensity is stronger by about 1.9 mm/day(1.7 mm/day)during the eastern(centre)Pacific El Ni(?)o.The area which has major effects on the position(intensity)of the CEP-ITCZ tends to locate in the eastern(centre)Pacific.Both the position and intensity of the CEP-ITCZ are the most(least)sensitive to the SST anomaly in the corresponding Ni(?)o area in April(September).(2)The second mode of SST anomaly has indirect effects on CEP-ITCZ by the response of the Rossby wave.During the period of centre Pacific El Ni(?)o,the second mode of SST anomaly is weak and the Rossby wave in the atmosphere strengthens the northern and southern hemispheres trade winds simultaneously.The anomaly of cross-equatorial flows is weak and the CEP-ITCZ moves southward a little.The wind convergence over ITCZ is more intensive,which is favor for the vertical transport of moisture.During the period of eastern Pacific El Ni(?)o,the second mode of SST anomaly is intensive and the Rossby wave in the atmosphere strengthens the meridional winds in northern hemisphere and causes the shift southward of CEP-ITCZ.The wind convergence zone is wider and weaker,which restrains the enhancement of vertical transport of moisture induced by increased evaporation.(3)The results of CP-EL test show that the first mode of anomaly of SST over low latitude pacific could strengthen the convergence of wind over centra and eastern pacific,but the anomaly of position of convergence zone is indistinctive.These results are consist with the anomalies of CEP-ITCZ in centra pacific El Ni(?)o years.According the EP-EL test,the second mode of anomaly of SST has a significant effect on the convergence of wind over centra and eastern pacific,the centre of convergence moves southward and the intensity of convergence zone is weaker and wider,which are consist with the anomalies of CEP-ITCZ in eastern pacific El Ni(?)o years. |