The driftsonde observing system development

The original motivation for developing a driftsonde observing system was to support research associated with the WMO's THORPEX program. The major goal for driftsonde is to develop a low-cost measurement system that can produce vertical profiles of in-situ measurements in forecast sensitive regions (i.e., targeted areas where numerical models predict that such measurements would improve the prediction of high impact weather events) as well as make soundings that will fill critical gaps in data coverage over oceanic and remote arctic and continental regions. Forecast sensitive regions that would be targeted for driftsondes are i) relatively void of in-situ measurements from radiosondes and commercial aircraft, ii) covered with extensive cloud shields so that satellite measurements are limited (e.g. soundings from microwave sounders only and a lack of satellite-derived wind fields). The across the ocean driftsonde flights will provide synoptic-scale high-vertical-resolution atmospheric profiles made by GPS dropsondes that would be difficult or impossible to obtain by deployment of aircraft alone. The targeting ability of the driftsonde will be accomplished, when possible, by controlling the launch location, the launch time of the balloon, the time of dropsonde deployment and to a limited extent the initial mission altitude (i.e. the wind field). The GPS dropsonde currently in use measures wind, temperature, pressure and relative humidity. The driftsonde system consists of a low-cost zero-pressure polyethylene balloon with attached gondola. Housed in the gondola are the system electronics which includes an embedded computer, a GPS navigation system, flight level PTH sensors, a ballast control system, a battery power system, an Iridium satellite two-way communication system, and 20 dropsonde tubes. The gondola can carry up to 20 of the current GPS aircraft dropsondes that can be dropped at predetermined times by computer or on command through a satellite link. The driftsonde gondola system is presently being modified to carry up to 50 of a new small, lightweight dropsonde. The driftsonde balloon normally flies at an altitude of ~16 kilometers (100-75 hPa) in the lower stratosphere or upper troposphere above the clouds and weather systems. However, three sizes of zero pressure balloons have been developed to date: i) a 100 hPa or 363 m3 balloon, ii) a 50 hPa or 1200 m3 balloon and iii) a ~25 hPa or 2265 m3 balloon. Discussions are also underway with the French (CNES) balloon program for a joint THORPEX research project in Africa that would utilize their new 12 meter diameter superpressure balloon and the NCAR driftsonde gondola carrying 50 dropsondes and flying at ~50 hPa to study African easterly waves and hurricane gensis. The design of the driftsonde system will be discussed as well as future development efforts and potential field programs using the driftsonde.