Abstract
The role of remote ocean sea surface temperature (SST) in regulating tropical cyclone (TC) characteristics has been examined by performing numerical experiments with a regional scale model. Model simulations have been carried out to simulate typhoon Man-yi (July 2007), in our case study, under a range of SST conditions over the Indian Ocean and the South China Sea. The intensity and track of the cyclone have been systematically changed in sensitivity simulations of cool and warm SSTs over that region, following its peak phase. Warm oceans can substantially reduce the intensification of western North Pacific cyclones, whereas cool oceans can enhance their strength. This is intimately associated with the enhancement/weakening of the moisture supply through the moisture conveyor belt (MCB) in the lower troposphere, from the Indian Ocean and South China Sea into the vicinity of the cyclone center. When the MCB is interrupted over the South China Sea in warm SST occurrences, the large-scale transport of moisture into the cyclone system is significantly reduced, leading to the weakening of the cyclone intensity and to the eastward shift of its track. This study shows that changes in remote tropical ocean SST can also modulate TCs and thus can help in improving the forecasting of TC intensities and tracks.
Highlights
The western North Pacific basin is the most active region for tropical cyclones (TCs) in the world (Hope 1979; Ritchie and Holland 1999)
It is evident that sea level pressure (SLP) and vertically integrated moisture flux (VIMF) fields over the Indian Ocean and South China Sea are significantly changed in response to sea surface temperature (SST)
The warm SST anomalies over the Indian Ocean and the South China Sea favor the reinforcement of the monsoon trough over the Indian subcontinent and the Bay of Bengal
Summary
The western North Pacific basin is the most active region for tropical cyclones (TCs) in the world (Hope 1979; Ritchie and Holland 1999). Braun (2006) and Yang et al (2011) examined water budgets of TCs and pointed out that the oceanic source of water vapor within the inner core represents a very small portion of the horizontal import of vapor, and that the net horizontal convergence of vapor into the storm constitutes a large part of net condensation It is still uncertain, whether the secondary TC circulation alone does contribute to the horizontal import of vapor at low levels into the vicinity of the TC center. In the case of a typical typhoon (Man-yi, July 2007) that approached Japan, it was found that the total precipitable water around the typhoon center is maintained by the moisture supply from remote oceans rather than from the underlying ocean They (Kudo et al 2014) named this type of large-scale moisture transport from the tropics into the vicinity of the typhoon center the “moisture conveyor belt (MCB).”.
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