The driftsonde observing system development

Dr. Hal Cole, NCAR Atmospheric Technology Division

The original motivation for the driftsonde development was to support research associated with the WMO THORPEX program. The goal is to develop a low-cost measurement system that can produce vertical profiles of in-situ measurements in forecast sensitive regions (i.e., 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 more limited (soundings from microwave only and a lack of satellite-derived wind fields). The transocean driftsonde flights will provide synoptic-scale high-vertical-resolution atmospheric profiles made by the 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 time of dropsonde deployment, the launch time of the balloon and to a limited extent the initial mission altitude. The GPS dropsonde currently 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, GPS navigation system, flight level PTH sensors, ballast system, power system and 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 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 mb or 363 m³ balloon, ii) a 50 mb or 1200 m³ balloon and iii) a ~25 mb or 2265 m³ balloon. The design of the driftsonde system will be discussed as well as future efforts and potential future field projects using the driftsonde. The design of the driftsonde electronics and communication system will also be discussed.