The Role of Multiscale Atmospheric Conditions in the Evolution of Convective Organization during MJO-1 of DYNAMO/CINDY/AMIE

The multiscale atmospheric interactions that create a change in convective behavior in the tropical Indian Ocean, such as that which occurs during the passage of the Madden-Julian Oscillation (MJO), are not yet fully understood. This analysis examines the evolution of convection that occurred during an MJO event in late-October 2011 of the DYNAMO/CINDY/AMIE field campaign. This period, referred to as MJO-1, was chosen to highlight the transition in convective organization observed and to characterize the convection during this MJO in greater detail.

This case study focuses on the region immediately surrounding the S-PolKa radar stationed on Addu Atoll (0.7^oS, 73^oE) in the Maldives. Preliminary dual-polarization radar analysis suggests a 2-day periodicity in areal coverage of reflectivity values in the S-PolKa domain, consistent with previous studies from TOGA COARE, MISMO, and DYNAMO/CINDY/AMIE. Vertical distributions of the areal coverage of weaker reflectivity values reveal 3 distinct periods: 1) bottom-heavy, 2) periodicity between top-heavy and bottom-heavy, and 3) predominantly top-heavy. The largest areal coverage occurs in the 2nd half of the MJO-1 passage over the radar, especially for higher reflectivity values. The dual-polarization particle identification indicates a similar periodicity in areal coverage for nearly all particle types, with the largest areal coverage similarly occurring in the latter half of MJO-1.

Initial analysis of the 200 and 850 mb winds from the Level 4 rawinsonde data suggests that the westerly wind burst (WWB) associated with MJO-1 propagated eastward to the DYNAMO array, although the westerly wind anomaly for this WWB was weaker than that during MJO-2 in late-November. The rawinsonde data shows a transition towards increased convective inhibition (CIN) and decreased total precipitable water (TPW) towards the end of MJO-1. There are mid- to low-level dry air intrusions visible in rawinsonde cross sections near Addu Atoll associated with the lower TPW values, which in turn is associated with a general lowering of TPW in the region as seen by satellite imagery. Furthermore, there is a shift towards more varying CIN and convective available potential energy (CAPE) in the latter half of the MJO passage.

High-resolution numerical model simulations with an outer domain encompassing the Indian Ocean basin will be performed to better understand the influence of large-scale conditions on the convection in this region of the Indian Ocean. These simulations will include nested domains at convection-allowing scales centered on Addu Atoll, which allows for comparison with the S-PolKa radar and investigation into mesoscale interactions that may influence the upscale convective organization in the vicinity. Using the multi-domain numerical simulations in conjunction with ECMWF reanalysis data and DYNAMO/CINDY/AMIE observations, parcel trajectory analysis will be performed to examine the origin of the air masses pertaining to the convection near the radar.