Relationship Between the Summertime Madden-Julian Oscillation and Deep Convective Structures

Benjamin Toms, Colorado State University

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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.

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. 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 convective elements' passage 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.

Abstract Author(s): Benjamin Toms, Susan van den Heever, Emily Riley Dellaripa, Stephen Saleeby