中东太平洋ITCZ对两类厄尔尼诺SST异常的敏感性试验

Sensitivity tests of the impacts from SST anomaly in two types of El Niňo on the ITCZ over central and eastern Pacific

利用MPAS-A(The Model for Prediction Across Scales-Atmosphere)模式设计了中东太平洋热带辐合带CEP-ITCZ(Intertropical Convergence Zone over Central and Eastern Pacific)对两类厄尔尼诺SST(Sea Surface Temperature)异常的敏感性试验,通过试验结果与两类厄尔尼诺年实际大气异常的对比,初步解释了CEP-ITCZ在两类厄尔尼诺年产生不同异常的可能原因。通过CP-EL试验发现,热带太平洋SST异常的第一模态会使中东太平洋低层风场辐合增强,但对辐合带的位置影响不大,与中部型厄尔尼诺对CEP-ITCZ的影响基本一致。通过EP-EL试验发现,热带太平洋SST异常的第二模态会使中东太平洋低层风场产生较大异常,辐合带中心向南移动,辐合带明显减弱增宽,与东部型厄尔尼诺对CEP-ITCZ的影响基本一致。

Intertropical Convergence Zone(ITCZ),as one of the important systems of tropical atmosphere,has important impacts on global atmospheric circulation.Due to a range of factors,regional ITCZ has different characteristics.Among them,the Central and Eastern Pacific ITCZ(CEP-ITCZ) is located to the north of the equator year round with high particularity relative to other regions.In addition to seasonal movement,the meridian position of CEP-ITCZ is usually affected by El Nino events.Some researchers have found that the CEP-ITCZ is slightly southward in Central Pacific El Nino(CP-El Nino) year,and the southward extent is less than that in Eastern Pacific El Nino (EP-El Nino) year.Therefore,taking into account that the location and intensity of CP-El Nino and EP-El Ni o are very different,their impacts on the CEP-ITCZ inevitably vary widely.Previous studies have not analyzed this variation in depth,especially the difference between the impacts from two types of El Ni o on the intensity of CEP-ITCZ.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,two sensitivity tests about impacts of SST anomaly on CEP-ITCZ were implied using MPAS-A(The Model for Prediction Across Scales-Atmosphere) model.Compared with the anomalies of real atmosphere in two types of El Nino years,the reasons why the CEP-ITCZ presents different characteristics in two types of El Nino were proposed.The results of CP-EL test show that due to the impact from the first mode of SST anomaly in the tropical Pacific,the anomalies of the meridional winds in the northern and southern hemispheres are comparable,and the anomalous cross-equatorial flow is weak,resulting in little changes in the CEP-ITCZ position.The anomalies of the meridional winds lead to the convergence zone slightly stronger.The precipitation of CEP-ITCZ is enhanced by both wind convergence and SST positive anomalies.These results are consistent with the anomalies of CEP-ITCZ in central pacific El Nino years.The results of EP-EL test show that due to the impacts from the first two modes of SST anomaly in the tropical Pacific,the anomalies of the meridional winds in the northern hemisphere are strong,which results in a higher extent of southward movement for the CEP-ITCZ.Due to the impacts from anomalous meridional wind,the anomalies of divergence show dipole-like pattern,which increases the width and weakens the central intensity of the convergence zone.These results are consistent with the anomalies of CEP-ITCZ in eastern pacific El Nino years.The second mode of SST anomaly may have an important impact on CEP-ITCZ.The intensities of the second mode of SST anomaly in two types of El Nino years are quite different,which results in the southward extent of CEP-ITCZ in CP-El Nino years is less than that in EP-El Nimo years,while the precipitation intensities of the CEP-ITCZ in two types of El Nino years are similar.