Use of CYGNSS in Understanding the Onset and Convective Properties in a Weak MJO from the DYNAMO December 2011 Event

Despite over 40 years of research on the Madden-Julian Oscillation (MJO), there is much to be desired about low level convection and surface winds associated with the onset of the MJO. The CYclone Global Navigation Satellite System (CYGNSS) mission will be a step in the right direction for improving wind data collection and understanding of this oscillation. CYGNSS is a constellation satellite system that was created for observing tropical cyclones. With bi-static scatterometery and GPS signals, the CYGNSS satellites will be able to penetrate through rain and clouds in order to retrieve wind speed data at the ocean's surface. An increase in wind speeds over tropical waters is closely related to convection, therefore knowing the wind speed is crucial for understanding the MJO. This study examines the use of CYGNSS for improving MJO observations with the use of data from the DYNAmics of the MJO (DYNAMO) campaign. DYNAMO was located in the equatorial Indian Ocean, on and around the Maldives from September 2011 to March 2012. For this case, the weak December 2011 MJO is the focus in order to determine the usefulness of CYGNSS for such challenging events. With this December case, arguments arose even after the event began on whether or not it was truly an MJO. According to Gottschalck et al. (2013), an RMM index phase diagram shows that this weak event became definable on December 19, 2011 and died out by January 4, 2012. It fell into phases 4, 5, and 6 which correspond to the Maritime Continent and reached max amplitude of 2 standard deviations on the index.

In order to assess CYGNSS data before the satellites are launched, members of the CYGNSS Science Team created the End-to-End-Simulator (e2es). This simulator duplicates satellite path patterns as well as various configurations each satellite can be placed. The DYNAMO data is assimilated using the 3DVAR methodology within the Weather Research and Forecasting model (WRF) and comes from radars, scatterometers, buoys and soundings across the domain. Radars used include the NASA TOGA Doppler radar which was aboard the R/V R. Revelle and the S-PolKa radar located on the Addu Atoll, Maldives. Scatterometer data was supplied by the Advanced Scatterometer (ASCAT) and Oceansat-2 Scatterometer (OSCAT). After all the data are assimilated in WRF, the wind speed products are placed into the e2es to produce CYGNSS-like data and graphics. The e2es can adjust passage patterns, satellite configurations, and includes various other adjustable settings.

Within the December case, the focus was narrowed down to the 20th through 22nd because this was the time frame with the most amount of precipitation over the desired domains, and hence a key time period of MJO development and definition. These nested domains used in the WRF modeling and data assimilation experiments are at 9 km, 3 km, and 1 km resolutions, where the 9 km is the closest to the CYGNSS domain.

It will be important to know what mesoscale and convective processes look like from the point of view of CYGNSS. Having better data and understanding of MJO onsets will lead to improved MJO forecasting that is crucial for all populations surrounding the Indian and West Pacific Oceans. During the presentation, our progress to date will be described and discussed, while we will also emphasize our key findings related to the December 2011 MJO as related to the assimilated observations and CYGNSS dataset.