MJO observed from AMEI/DYNOMO and ARM long term observation at TWP

The MJO is an intrapersonal fluctuation in the global tropics with a cycle of 30-60 days (Madden and Julian 1971, 1972). It is characterized by eastward propagation of regions of enhanced and suppressed tropical rainfall, associated with distinct patterns of lower and upper atmospheric circulation anomalies in the tropics. The ARM MJO Investigation Experiment (AMIE) campaign is associated with the CINDY/DYNAMO project to fully characterize the ensemble of convection associated with MJO with ARM cloud radars.

AMIE has two components: AMF2 on Gann Island in the Indian Ocean (AMIE-Gann), where the MJO enhanced convective phase initiates and starts its eastward propagation; and the ARM Manus site (AMIE-Manus) at the tropical western pacific, which is in the general area where the MJO usually starts to weaken in climate models. We find very different correlation patterns between cloud field and thermodynamic structure for three MJO events observed at these two locations. MJO events at Gann 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. Increases in high cloud lag behind low and middle level clouds. These features are consistent with the discharge-recharge mechanism (Blade and Hartmann 1993; Maloney and Hartmann 1998). However, MJO events at AMIE-Manus do not have the obvious patterns observed at AMIE-Gann. To further elaborate on the conclusions found during the AMIE campaign, ARM long-term cloud radar and radiosonde observations at the Manus and Darwin sites from 2005 to 2010, along with NCEP reanalysis data are investigated. We classify each local MJO event as strong-sustaining or weak according to its intensity and duration as indicated by the MJO index provided by the NOAA/NCEP climate prediction center. We find significant differences in cloud field and thermodynamic structure between the strong-sustaining and weak MJO events.