新闻阅读
A special MJO event with a double Kelvin wave structure
作者:重点实验室               发布时间:2017-9-13 15:35:45              浏览量:17

Article

A special MJO event with a double Kelvin wave structure

Journal of Meteorological Research

Zhu, Lili; Li, Tim

Abstract

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 free-atmospheric 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. 

DOI: 10.1007/s13351-016-6004-3


© 2017 气象灾害教育部重点实验室   版权所有
地址:江苏省南京市宁六路219号 气象灾害教育部重点实验室 邮编:210044
技术支持:南京趣汇网络科技有限公司