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 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 ϳ50 kJ cm Ϫ2 ). 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 ϳ110 kJ cm Ϫ2 ) 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 ϳ105-120 m and the upper-ocean heat content is ϳ80-120 kJ cm Ϫ2 ). 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.

Strong enhancement of chlorophyll a concentration by a weak typhoon

“…For this purpose, thermocline displacement is estimated to be directly proportional to typhoon-induced surface wind stress and inversely proportional to the typhoon's moving speed (Price et al 1994), as seen in Eq. (3), which can be understood according to the concept of translation time (Lin et al 2008). Such a concept assumes that the typhoon-induced response is directly proportional to the typhoon's diameter D and inversely proportional to the typhoon's moving speed U T .…”

Ocean Responses to Typhoon Namtheun Explored with Argo Floats and Multiplatform Satellites

“…Vast energy interchanges within the atmosphere and ocean as a result of air-sea interactions have a great effect on both weather and ocean dynamics. The ocean's responses include sea surface cooling (Price, 1981), enhanced entrainment and vertical mixing (Han, Ma, & Chen, 2012;Jacob, Shay, Mariano, & Black, 2000;Lin, Chen, Pun, Liu, & Wu, 2009;Lin, Wu, Pun, & Ko, 2008), inertial oscillation (Black & Dickey, 2008;Morozov & Velarde, 2008;Price, 1981), and enhanced phytoplankton blooming (D'Asaro, 2003;Han et al, 2012;Subrahmanyam, Rao, Rao, Murty, & Sharp, 2002;Sun, Yang, Xian, Lu, & Fu, 2010;Wang & Zhao, 2008;Xian, Sun, Yang, & Fu, 2012;Yang, Fu, Sun, Liu, & Feng, 2010).…”

The Ocean Observing System for Tropical Cyclone Intensification Forecasts and Studies

“…Thirty northwest Pacific category 5 typhoons that belong to the typhoon season of 1993-2005 were examined using observations corresponding to 13 years of satellite altimetry, in situ, and climatological upper ocean thermal structure data, best track typhoon data of the U.S. Joint Typhoon Warning Center (JTWC), and an ocean mixed layer model (Lin et al, 2008 ). In this region, it is possible that a typhoon may intensify to category 5 when travelling above waters with cyclonic or anticyclonic mesoscale features.…”