Radar Observations of the Cloud Population in the Developing Madden-Julian Oscillation

University Of Washington, Seattle WA

Investigators

Abstract

The Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign is the US component of an international experiment in late 2011/early 2012 in the Indian Ocean, the Cooperative Indian Ocean Experiment on Intraseasonal Variability (CINDY2011). The overarching goal of DYNAMO is to expedite understanding of processes key to MJO initiation over the Indian Ocean and to improve simulation and prediction of the MJO. The field campaign will include multiple radars, atmospheric sounding sites, a research aircraft, multiple research vessels, and oceanic measurements. The three main hypotheses of DYNAMO are: 1) Deep convection can be organized into an MJO convective envelope only when the moist layer has become sufficiently deep over a region of the MJO scale; the pace at which this moistening occurs determines the duration of the pre-onset state, 2) Specific convective populations at different stages are essential to MJO initiation, and 3) The barrier layer, wind- and shear-driven mixing, shallow thermocline, and mixing-layer entrainment all play essential roles in MJO initiation in the Indian Ocean by controlling the upper-ocean heat content and SST, and thereby surface flux feedback This award will allow for the collection and analysis of S-PolKa and other supersite radar data from the island of Gan. This data will be combined with complementary observational data to acquire key empirical characteristics of the populations of clouds and the humidity field to contribute to the testing of DYNAMO Hypotheses 1 and 2. The S-PolKa deployment during DYNAMO will be led by this research team. The study consists of four main parts: 1) Use of the available radar data to address Hypothesis II by showing how many clouds of each type make up the full cloud population, and how these different mixes of clouds combine to produce net heating, moisture, and momentum feedbacks as the MJO initiation progresses from the pre-onset, to onset, to post-onset stages. 2) Obtain data that show how the characteristics of the MJO cloud population evolve during the recharging of the humidity field by closely examining the direct interface between clouds and the developing environmental humidity profile in each of the initiation stages and in the transitions between stages. 3) Examine the performance of several models by comparing their depiction of the cloud population during the MJO initiation. 4) Establish whether the MJO initiation cloud population is consistent with or differs from radar echo populations observed in other parts of the oceanic tropics. The broader impacts of the work include the involvement of multiple graduate students in field research, and the contribution to the broader goals of the DYNAMO campaign to improve understanding of tropical convection, the predictability of the MJO, and downstream effects of the MJO on weather in the United States and other areas.