The Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) is a truck-mounted C-band, Doppler radar that was deployed during the Dynamics of the Madden-Julian Oscillation (DYNAMO) / Cooperative Indian Ocean Experiment on interseasonal variability in the year 2011 (CINDY2011) campaign on Addu Atoll, Maldives. One of SMART-R’s objectives was to provide continuous volume scans of precipitating clouds during all phases of the Madden-Julian Oscillation (MJO) for the full duration of the campaign. Data from SMART-R is available for 2 October 2011 through 9 February 2012. Every 10 minutes a full volume scan was produced, which was subsequently run through quality control algorithms that, among other filters, performed a calibration correction, noise filtering, and an attenuation correction. It was observed that data from SMART-R appeared to be slanted towards the WNW, and after analysis, a 0.75◦ tilt correction was applied towards azimuth 285◦. The data was then converted into Cartesian coordinates and an additional noise filter was applied. NETCDF files with radial velocities and corrected reflectivity were produced. From the reflectivity observations, a suite of products including rain maps, echo- top heights and convective/stratiform separations were produced. A modified version of the convective/stratiform separation was developed in an attempt to classify shallow and weak convection more correctly. The modified algorithm utilizes an isolation parameter set to 10 km to the north, south, east, and west, a 10-dBz echo-top height threshold set to 9 km, and a 16-dBz reflectivity threshold at 3 km to ensure only isolated, shallow, and weak rain originally classified as stratiform, is reclassified as convection. Analyses of these products clearly suggest two MJO events occurring in October and November as indicated by the Wheeler and Hendon Multivariate MJO index. While stratiform rain almost always encompassed a larger area of the radar domain, convective rain was the larger producer of rain with the exception of active MJO periods. In addition, echo-top height counts are observed to increase in both vertical structure and frequency as the MJO initiates and becomes active over the radar domain. Possible connections are also made between echo-top height data and humidity retrievals from soundings launched on Addu Atoll. It appears that during MJO initiation, convective echo tops lead the moistening of the mid troposphere, while during suppressed phases, the convective echo tops lag behind the moistening of the mid troposphere. Wind shear also appears to be weaker during an active MJO event, and increase as the active MJO exits the region. From these observations, as well as other rain statistics including the diurnal cycle, indicators for a localized MJO index are proposed that are based on local radar and sounding data, rather than satellite and reanalysis observations of wind and outgoing long-wave radiation.

The Madden-Julian Oscillation (MJO), a tropical phenomenon that exists on the time scale of 30-90 days, commonly initiates over the Indian Ocean and slowly propagates into the western Pacific as a series of convective events, which have time scales on the order of hours or days. These events and the overall MJO convective envelope may interact with convectively coupled waves such as Kelvin waves that propagate more rapidly eastward with time scales of 3-5 days. Radar and sounding data collected during the DYNAMO/AMIE/CINDY2011 field campaign from October 2011 to February 2012 in the central Indian Ocean are used to study the interaction between Kelvin waves and the MJO in terms of atmospheric and cloud properties. The focus is on characterizing the precipitation characteristics, convective cloud spectrum, and atmospheric profiles of Kelvin waves during the active and suppressed phases of the MJO to gain insight on MJO initiation. Characteristics of waves identified using different satellite thresholds and filtering methods are compared. Composites of the radar and sounding observations are calculated for a total of ten Kelvin waves and three MJO events that occurred during the field campaign. Analyzed radar products include convective-stratiform classification of rain rate, rain area, and echo-top heights, as well as cloud boundaries. Sounding data includes profiles of wind speed and direction and relative humidity. Kelvin waves that occur during the suppressed MJO are convectively weaker than Kelvin waves during the active MJO, but display previously documented structure of low-level convergence and a moist atmosphere prior to the wave passage. During the active MJO, Kelvin waves have stronger convective and stratiform rain, and the entire event is longer, suggesting a slower moving wave. The Kelvin wave vertical structure is somewhat overwhelmed by the convective envelope associated with the MJO. When the MJO is developing, the Kelvin wave displays a moisture-rich environment after the passage, providing deep tropospheric moisture that is postulated to be important for the onset of the MJO. The convective cloud population prior to MJO initiation shows increased moisture and a population of low- to mid-level clouds. The moisture precedes shallow convection, which develops into the deep convection of the MJO, supporting the discharge-recharge theory of MJO initiation. Additionally, enhanced moisture after the passage of the pre-MJO Kelvin wave could also support the frictional Kelvin-Rossby wave-CISK theory of MJO initiation. With a better understanding of the interaction between the initiation of the MJO and Kelvin waves, the relationships between the environment and the onset of the convection of the MJO can be improved.