TCS08 Minority Report: how to prevent typhoons in the western North Pacific

During August and September of 2008, the Office of Naval Research in conjunction with the Naval Research Laboratory and the U. S. Air Force sponsored a major field experiment called Tropical Cyclone Structure 2008 (TCS08). The three scientific foci of the field experiment were tropical cyclone formation, structure change including intensity changes, and the processes leading to recurvature.

The Pacific basin climate during TCS08 was La Niña. Persistent low-level easterly winds dominated the tropics of the basin, and typhoon formation was shoved far to the west and north of normal. The strength of the low-level easterlies was extraordinary, with a persistent 2 SD easterly anomaly in the deep tropics (EQ to 10 N) for almost the entire period June through November. Other anomalies of note included: Persistent 200 mb west-wind anomalies; a dearth of TC origins from cloud clusters in the “ITCZ” (i.e., relatively few cloud clusters in the deep tropics became the seeds for TC genesis); a conspicuous absence of the monsoon trough; and, unusual convective activity in the subtropics that produced some controversial cyclones.

Much of the action in the subtropics was ignored. First and foremost, it was generally out of range of assets. However, many of these systems were not considered genuine tropical cyclones by a majority of participants (hence, this Minority Report). Much of the focus of the field experiment was devoted to “easterly waves” moving rapidly westward in the anomalous easterly flow in the deep tropics (5 to 15 N). These had extreme difficulty forming tropical cyclones. Because of the high magnitude of the low-level easterly wind anomalies, the western North Pacific looked quite like the norm for the Atlantic tropics. This was a recipe for a very quiet typhoon season.

This paper describes the unusual state of the climate and specific weather events (including the enhanced activity in the subtropics and the lack of activity in the tropics) during the field phase of the TCS08 experiment.