Air-Ocean Factors throughout the Formation and Intensification of Typhoon Malakas during the Impact of Typhoons on the Pacific (ITOP) Field Program

The Impact of Typhoons on the Pacific (ITOP) program was conducted from 15 August through 20 October 2010. During that period, two WC-130J aircraft from the United States Air Force 53rd Weather Reconnaissance Squadron (Hurricane Hunters) operated from Andersen Air Base on Guam. During the course of the operations, tropical circulation systems were monitored by the ITOP science team to determine the likelihood for development into a tropical cyclone. Nearly forty such systems were identified and six tropical cyclones formed. However, the majority of the aircraft operations and flight hours were expended in Typhoon (TY) Fanapi, TY Malakas, and Supertyphoon (STY) Megi. Also, the majority of the dropwindsondes and airborne expendable bathythermographs (AXBTs) were deployed in these three major tropical cyclones. The primary objectives of ITOP were to examine the response of the ocean to typhoons and the impact due to variations in ocean characteristics on typhoon formation, intensity, and structure. The ocean environment of the Philippine Sea is defined by warm sea-surface temperatures and a deep thermocline that contributes to high ocean heat content. Immediately poleward of this region, approximately along 20oN the southern eddy zone defines the boundary between the high ocean heat content region of the Philippine Sea and the water of the subtropical North Pacific. The southern eddy zone contains a variety of warm and cold ocean eddies that vary in space and time. During ITOP, TY Fanapi and STY Megi formed and intensified in the favorable environment of the Philippine Sea. However, TY Malakas formed at the very equatorward edge of the southern eddy zone. Following formation, Malakas intensified while moving poleward through the eddy zone. A series of four aircraft missions were conducted during the formation and intensification of TY Malakas. During each flight, dropwindsondes and AXBTs were deployed in tandem to define the air-ocean characteristics of the eddy zone through which Malakas was moving. In particular, one flight was designed to conduct a series of race-track legs throughout the right-rear quadrant of the storm and over a well-defined cold ocean eddy. In this presentation, the dropwindsonsde and AXBT data are examined in conjunction with analyzed atmospheric and ocean model data to define the relative contributions of atmosphere and ocean factors during the formation and intensification of TY Malakas. Because of the poleward-moving track through the southern eddy zone, the relative role(s) of vertical wind shear and changing ocean conditions are defined.