Upper-Ocean Thermal Structure and the Western North Pacific Category 5 Typhoons. Part I. Ocean Features and the Category 5 Typhoons' Intensification

Abstract Category 5 cyclones are the most intense and devastating cyclones on earth. With increasing observations of category 5 cyclones, such as Hurricane Katrina (2005), Rita (2005), Mitch (1998), and Supertyphoon Maemi (2003) found to intensify on warm ocean features (i.e., regions of positive se...

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Bibliographic Details
Published in:Monthly weather review 2008-09, Vol.136 (9), p.3288-3306
Main Authors: LIN, I.-I, WU, Chun-Chieh, PUN, Iam-Fei, KO, Dong-Shan
Format: Article
Language:English
Subjects:
Altimeters
Altimetry
Amplification
Anomalies
Climate
Climatology
Cooling
Cyclones
Depth
Earth, ocean, space
El Nino
Enthalpy
Exact sciences and technology
External geophysics
Heat
Heat content
Height anomalies
Hurricanes
Isotherms
Marine
Meteorology
Mixed layer
Negative feedback
Ocean circulation
Ocean mixed layer
Oceans
Remote sensing
Remote sensing systems
Satellite altimetry
Sea surface
Thermal structure
Typhoon warnings
Typhoons
Wind shear
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Summary:Abstract Category 5 cyclones are the most intense and devastating cyclones on earth. With increasing observations of category 5 cyclones, such as Hurricane Katrina (2005), Rita (2005), Mitch (1998), and Supertyphoon Maemi (2003) found to intensify on warm ocean features (i.e., regions of positive sea surface height anomalies detected by satellite altimeters), there is great interest in investigating the role ocean features play in the intensification of category 5 cyclones. Based on 13 yr of satellite altimetry data, in situ and climatological upper-ocean thermal structure data, best-track typhoon data of the U.S. Joint Typhoon Warning Center, together with an ocean mixed layer model, 30 western North Pacific category 5 typhoons that occurred during the typhoon season from 1993 to 2005 are systematically examined in this study. Two different types of situations are found. The first type is the situation found in the western North Pacific south eddy zone (SEZ; 21°–26°N, 127°–170°E) and the Kuroshio (21°–30°N, 127°–170°E) region. In these regions, the background climatological warm layer is relatively shallow (typically the depth of the 26°C isotherm is around 60 m and the upper-ocean heat content is ∼50 kJ cm−2). Therefore passing over positive features is critical to meet the ocean’s part of necessary conditions in intensification because the features can effectively deepen the warm layer (depth of the 26°C isotherm reaching 100 m and upper-ocean heat content is ∼110 kJ cm−2) to restrain the typhoon’s self-induced ocean cooling. In the past 13 yr, 8 out of the 30 category 5 typhoons (i.e., 27%) belong to this situation. The second type is the situation found in the gyre central region (10°–21°N, 121°–170°E) where the background climatological warm layer is deep (typically the depth of the 26°C isotherm is ∼105–120 m and the upper-ocean heat content is ∼80–120 kJ cm−2). In this deep, warm background, passing over positive features is not critical since the background itself is already sufficient to restrain the self-induced cooling negative feedback during intensification.
ISSN:0027-0644
1520-0493
DOI:10.1175/2008mwr2277.1