Convective Environments Across the Maritime Continent During the Boreal Summer Intraseasonal Oscillation

The boreal summer intraseasonal oscillation (BSISO), an off-equatorial mode of summertime tropical intraseasonal variability, is characterized by a convective dipole that propagates north and east across the Indo-West Pacific. While the BSISO itself is regional in scale, individual convective elements constitute the convective envelope within the positively active portion of the dipole. By considering the convective envelope as an agglomeration of mesoscale elements, it may be separated into distinct environments within which convective systems of varying morphology and structure occur.

We identify environments within which deep convection occurs during a canonical BSISO event using a simulation centered over the Maritime Continent. The Regional Atmospheric Modeling System (RAMS), an open-source cloud-resolving model with an integrated bin-emulating double-moment microphysics scheme, was used to simulate a 35-day period during July and August of 2007. The lateral boundaries were forced with ERA-Interim reanalysis, while the interior of the domain was allowed to freely evolve according to the model physics.

Within the simulation, the convective dipole propagates across the Maritime Continent, successfully generating convective elements including isolated continental convection, maritime mesoscale convective systems, and even a typhoon. The convective elements were identified using a cloud-top temperature tracking algorithm, and the respective environments were identified and clustered using agglomerative clustering. To account for the atmospheric feedbacks of deep convection, a lead-lag approach was taken to identify convective environments, in which the environments before, during, and after the passage of the convective elements were identified. Distinct characteristics exist between the convective environments across the southern and northern portions of the Maritime Continent. For example, across the South China Sea, convective clusters tend to develop mesoscale circulations more rapidly than those near the equator. Additional relationships between the convective morphology and the associated environments will be presented.

This work is funded as part of the Propagation of Intra-Seasonal Oscillations (PISTON) field campaign.