This case study focuses on the region immediately surrounding the S-PolKa radar stationed on Addu Atoll (0.7oS, 73oE) 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.