A Special MJO Event with a Double Kelvin Wave Structure  

作　　者：Lili ZHU Tim LI 

机构地区：[1]Key Laboratory of Meteorological Disaster,Ministry of Education/Joint International Research Laboratory of Climate and Environmental Change/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters,Nanjing University of Information Science &Technology [2]International Pacific Research Center and Department of Atmospheric Sciences,University of Hawaii at Manoa

出　　处：《Journal of Meteorological Research》2017年第2期295-308,共14页气象学报（英文版）

基　　金：Supported by the National(Key)Basic Research and Development(973)Program of China(2015CB453200);National Natural Science Foundation of China(41475084,41630423,41575052,and 41375095);US National Science Foundation(AGS-1643297);US Office of Naval Research(N00014-16-12260);US Naval Research Laboratory(N00173-16-1-G906);Jiangsu Natural Science Foundation Key Project(BK20150062)of China;Jiangsu Shuang-Chuang Team Fund(R2014SCT001)of China;SOEST contribution number 9819;IPRC contribution number 1211;ESMC number 126

摘　　要：The second Madden–Julian Oscillation（MJO）event during the field campaign of the Dynamics of the MJO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011（DYNAMO/CINDY2011）exhibi ted an unusual double rainband structure.Using a wavenumber-frequency spectral filtering method,we unveil that this double rainband structure arises primarily from the Kelvin wave component.The zonal phase speed of the double rainbands is about 7.9 degree per day in the equatorial Indian Ocean,being in the range of convectively coupled Kelvin wave phase speeds.The convection and circulation anomalies associated with the Kelvin wave component are characterized by two anomalous convective cells,with low-level westerly（easterly）and high（low）pressure anomalies to the west（east）of the convective centers,and opposite wind and pressure anomalies in the upper troposphere.Such a zonal wind–pressure phase relationship is consistent with the equatorial free-wave dynamics.While the freeatmospheric circulation was dominated by the first baroclinic mode vertical structure,moisture and vertical motion in the boundary layer led the convection.The convection and circulation structures derived based on the conventional MJO filter show a different characteristic.For example,the phase speed is slower（about 5.9 degree per day）,and there were no double convective branches.This suggests that MJO generally involves multi-scales and it is incomplete to extract its signals by using the conventional filtering technique.The second Madden–Julian Oscillation（MJO）event during the field campaign of the Dynamics of the MJO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011（DYNAMO/CINDY2011）exhibi ted an unusual double rainband structure.Using a wavenumber-frequency spectral filtering method,we unveil that this double rainband structure arises primarily from the Kelvin wave component.The zonal phase speed of the double rainbands is about 7.9 degree per day in the equatorial Indian Ocean,being in the range of convectively coupled Kelvin wave phase speeds.The convection and circulation anomalies associated with the Kelvin wave component are characterized by two anomalous convective cells,with low-level westerly（easterly）and high（low）pressure anomalies to the west（east）of the convective centers,and opposite wind and pressure anomalies in the upper troposphere.Such a zonal wind–pressure phase relationship is consistent with the equatorial free-wave dynamics.While the freeatmospheric circulation was dominated by the first baroclinic mode vertical structure,moisture and vertical motion in the boundary layer led the convection.The convection and circulation structures derived based on the conventional MJO filter show a different characteristic.For example,the phase speed is slower（about 5.9 degree per day）,and there were no double convective branches.This suggests that MJO generally involves multi-scales and it is incomplete to extract its signals by using the conventional filtering technique.

关 键 词：Madden–Julian Oscillation（MJO） double Kelvin wave structure Wheeler–Kiladis space–time spectra evolution characteristics 

分 类 号：P433[天文地球—大气科学及气象学]