Tropical Cyclone Unusual Intensity and Structure Change in the Western North Pacific Observed by Reconnaissance Aircraft During TPARC/TCS08 and ITOP/TCS10

Abstract

ABSTRACT The combined Tropical Cyclone Structure (TCS-08) and THORPEX Pacific-Asia Regional Campaign (T-PARC) field programs during August and September 2008 and the combined Impact of Typhoons on the Ocean in the Pacific (ITOP) and TCS-10 field programs during August, September, and October 2010 have provided unique simultaneous observations of typhoon structure and intensity together with underlying oceanic conditions during rapid intensification and rapid decay events in the northwest Pacific Ocean basin during the tropical cyclone life cycle. A new observational strategy from aircraft reconnaissance, involving combination (‘COMBO’) deployments of Global Positioning System (GPS) dropwindsondes and Airborne expendable Bathythermographs (AXBTs) has allowed for simultaneous observations of TC structure and intensity while also observing oceanic eddy structure beneath the TC. This strategy, together with deployment of drifting buoys and floats ahead of the TC, has led to observations in Super-TYphoon (STY) Jangmi (2008) and STY Megi (2010) that show the ocean control over TC Rapid Intensification (RI) and Rapid Decay (RD) due to pre-existing warm and cold ocean eddy features, as well as the intensity-limiting effects of oceanic ‘cold wakes’ generated by Typhoons (TYs) Fanapi (2010) and Malakas (2010). Observations made during ‘unusual’ track changes in TY Fanapi illustrate how the TC passes over different ocean eddy features than would have occurred with a ‘normal’ straight track. These track changes led to unusual intensity changes due to subsequent movement over a warm ocean eddy feature that led to unexpected TC intensification, and this was followed by movement over shallow ocean mixed layers that led to strong ‘cold wake’ generation. This feature of ocean control then limited Fanapi’s intensification to values well below their Maximum Potential Intensity (MPI). In addition, ‘COMBO’ observations within pre-TC disturbances show contrasting impacts on typhoon development/non-development for cases of strong ocean control and weak environmental shear (pre-Fanapi, 2010) versus cases of weak ocean control and strong environmental shear (disturbance TCS025, 2008).