The Associations of Cloud and Precipitation with MJO as Revealed by Cloud Radar Measurements at the ARM Gan, Manus, and Darwin Sites

Description

Based on the AMIE/DYNAMO observations, we found very different correlation patterns between cloud field and thermodynamic structures at the Gan and Manus sites during the three observed MJO events. MJO events observed at the Gan site have tilted RH structure with time and height, which means lifting of moisture level at the pre-onset stage and low-level drying at the post-onset stage. However, MJO events observed at the Manus site do not have the obvious patterns as observed at the Gan site. To study the association of cloud and precipitation variations with MJO, we first develop an algorithm to identify precipitation profiles and partition them into deep convection and stratiform. Then we analyze the cloud and precipitation at time scales from 3 hours to half day. Results from the MJO events during the AMIE/ DYNAMO project show that there are precipitating clusters occurring at 2-5 day period within the local MJO envelopes of about 20-40 days. These precipitating clusters become deeper and more extensive as the moist builds up. They become weaker after the local MJO peaks as low level dries up. The more extensive the 2-5 day precipitating clusters are, the stronger the local MJO event is; the more frequent the 2-5 day precipitating clusters are, the longer the local MJO duration is. To further elaborate on the conclusions found during the AMIE/DYNAMO campaign, ARM long-term cloud radar and radiosonde observations at the Manus and Darwin sites from 2005 to 2010 are explored. We classify each local MJO event as strong-sustaining or weak according to its intensity and duration as indicated by the MJO index available from the NOAA/NCEP climate prediction center. We find significant differences in cloud field and thermodynamic structure between the strong-sustaining and weak MJO events.