Due to the highly variable nature of the moisture field in the tropical marine boundary layer (TMBL), it has largely been characterized in terms of its mean state. Yet, when and where convection is initiated, how long clouds persist, and precipitation amount and distribution is controlled by the actual distribution of moisture. Existing data sets capable of characterizing the large-scale moisture field over the equatorial Indian Ocean (based largely on a combination of satellite and sounding measurements) are insufficient for understanding Madden-Julian Oscillation (MJO) initiation. The need for better resolved, more frequent, higher quality moisture measurements was one of the primary motivating factors for the joint Dynamics of the MJO (DYNAMO) Experiment in the Year 2011 - such data was deemed critical for testing many of the leading MJO initiation hypotheses. Despite the extensive set of measurements made to document the moisture field (including ~20,000 soundings), the extreme moisture variability in the TMBL documented during the Rain in Cumulus over the Ocean (RICO) Experiment indicates that these combined measurements may still be insufficient.
Previously developed radar product was used to map the mean mesoscale moisture field structure during RICO, based on Bragg scattering layers (BSLs) detectable with S-band dual-polarization radar (S-Pol). BSL analysis provides an unprecedented structural context for both marrying together and more accurately interpreting moisture retrievals generated at a variety of scales and resolutions. This proposal is centered on conducting BSL analysis on S-Pol data from DYNAMO. BSL results will be combined with other DYNAMO humidity retrievals (e.g. from satellite, soundings, scanning microwave radiometer) to produce the most complete mapping of the TMBL moisture field to date. TMBL moisture field statistics will be generated and the controls on its structure will be investigated (e.g., time of day, wind direction and speed, rain rate, MJO phase). Island induced biases will be examined through a new BSL-based analysis technique. DYNAMO statistical results will be compared to RICO's to look for key similarities and differences in TMBL structure. A BSL-based, large eddy simulation validation technique will also be explored.
Intellectual Merit: The research addresses fundamental science questions about moisture variability and the mean structure typifying the TMBL over the equatorial, central Indian Ocean. Comparison of DYNAMO and RICO results will likely reveal both key commonalities - that can then be assumed true for TMBLs in general, and statistical differences - perhaps from differences in large-scale dynamics.
Broader Impacts: The mapping of the TMBL moisture field structure will be extremely valuable for testing MJO initiation hypotheses. MJO contributes significantly to tropical intraseasonal variability and interacts with many systems to greatly enhance extreme weather events in the tropics and at higher latitudes. BSL analysis can also improve our ability to produce short-term forecasts.
