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I-I Lin

2012-09-18
11:35:00 - 12:00:00

101 , Mathematics Research Center Building (ori. New Math. Bldg.)

Category-5 tropical cyclones (TCs), Hurricane Katrina (2005) and supertyphoon Megi (2010) for example, are the most intense and devastating cyclones on earth. The majority (~ 70%) of these ‘super’ cyclones are formed in the western North Pacific Ocean (WNPO), imposing threats to nearly a billion people living in the Asian coasts. As understood from existing knowledge, the ocean condition required for reaching the extraordinary intensity of category-5 over the WNPO is not trivial. In addition to warm sea surface temperature (SST) of ~ 29 degrees Celsius or above, a sufficiently-thick layer of subsurface warm water beneath sea surface is also needed. Typically warm layer thickness, as characterized by high upper ocean heat content (UOHC),of more than 100 kj cm2 for a typhoon travels in moderate speed, is required. During typhoon season (July-October), meeting the warm SST requirement is usually possible. Due to strong solar radiation in summer, most part of the WNPO is characterized by uniformly warm SST of ≧ 29 degrees Celsius. However, it is more difficult to meet the subsurface requirements, since regions with such thick subsurface warm layer are more limited. Using 2 decades of satellite observations, we examine the long-term variability of the ocean condition in the MDR region. As will be presented, our results suggest that regions satisfying ocean’s subsurface condition for supertyphoons have increased significantly, a worrisome situation requires attention.

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