A new tropical cyclone airborne observing strategy: 'Combo' GPS dropsonde and AXBT deployments from high altitude (300mb)

The first high altitude (300 MB) ‘combo' deployment of dropsondes and AXBTs into pre-genesis, incipient tropical cyclone (TC) systems within the Western North Pacific (WPAC) basin was conducted during the TPARC-Tropical Cyclone Structure (TPARC/TCS-08) field program. This strategy was repeated again during the Interaction of Typhoons over the Pacific experiment (ITOP/TCS10) in 2010. This sampling strategy enabled a unique view of the three dimensional (3-D) atmospheric (winds, temperature and moisture) and oceanic thermal environments in evolving tropical systems. Data sets from two non-developing tropical systems were inter-compared with pre-development phase of one typhoon (Typhoon Nuri) in 2008 and data from genesis and intensification phases of three typhoons were obtained in 2010.

Preliminary analysis of the WC-130J dropsondes and AXBTs indicated that the three of four systems in 2008 and two of three systems in 2010 developed within the WPAC oceanic region referred to as the ‘Southern Eddy Zone' between 16-24 degrees N, and that each featured a low-level, near-surface and mid-level vortex couplet with centers offset by as much as 150 km. The low-level circulation was centered in the clear on the western edge of the convective cluster, while the mid-level vortex was embedded within the convective complex. These features suggest an initial de-coupling of the low and mid-levels for the non-developers, possibly due to significant wind shear suggested by the satellite-derived cloud motions.

This strategy proved to be very successful during TPARC/TCS08 and again in ITOP/TCS10. This same strategy may prove effective in meeting emerging observational requirements for model initialization and validation in the Atlantic Basin as the use of coupled TC prediction models grows. This strategy of flying high in weak systems rather than flying low looking for closed circulations takes advantage of the high altitude and long range capability of the WC-130J aircraft and provides the ability to simultaneously map vertical atmospheric structure searching for signatures of mid-level as well as low-level spin-up at the earliest possible time while also mapping the surface wind field through use of the new Stepped Frequency Microwave Radiometer (SFMR), also flown on the WC-130J aircraft. Furthermore, simultaneous ocean vertical structure profiles reveal signatures of ocean eddies that may impact TC development and subsequent intensification. This type of strategy, especially in concert with G-IV and WC-130J surveillance flights in the storm environment would bring a powerful new set of observations into play that would be ideal not only for coupled model initialization and validation but for forecaster diagnostics regarding presence of initial vortex and potential for subsequent spin-up.