Thursday, 21 April 2016
Plaza Grand Ballroom (The Condado Hilton Plaza)
The role of the island of Sumatra in tropical cyclone (TC) genesis over the Indian Ocean is investigated using comprehensive datasets from two recent tropical campaigns, the 2008-10 Year of Tropical Convection (YOTC) and the 2011 Dynamics of the Madden-Julian Oscillation or MJO (DYNAMO). Sumatra is a long, mountainous island straddling the equator, extending in a northwest-to-southeast direction from approximately 6°N to 6°S. Under typical environmental conditions, flow is partially blocked by the island. When the low-level flow is easterly, counter-rotating lee vortices are often produced over the Indian Ocean. Because the island spans the equator, both wake vortices are cyclonic. The YOTC and DYNAMO data sets reveal these cyclonic circulations downstream of Sumatra over the Indian Ocean on numerous occasions, most commonly during October through December. Once shed, the vortices move westward both north and south of the equator. During the 2.25 years covering the two campaigns, twelve wake vortices (~20% of the shed circulations identified) were tracked and observed to subsequently develop into TCs over the northern and southern Indian Ocean. In several cases, TC genesis was assisted by developing MJOs over the central Indian Ocean.
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