The NCAR GPS Dropwindsonde and Its Impact on Tropical Cyclone Operations and Research

The first atmospheric soundings were taken by instrumented kites during the 19th century, but the measurements were necessarily limited to regions close to the ground. The first recorded use of a balloon to carry instruments was in 1892, but it wasn't until 1929 that an instrument relayed data to the ground during a balloon ascent. During World War II, theodolites were used to track these radiosondes to estimate wind velocity, and the combined instrument was called the rawinsonde. The process was automated when the automated radio theodolite was invented.

On 27 July 1943, Army Air Corps Col. Joseph P. Duckworth and navigator Second Lt. Ralph M. O'Hair were the first to fly an aircraft into the eye of a hurricane, thus beginning the era of hurricane reconnaissance. In 1949, the U. S. military noted that they could release a radiosonde from aircraft to measured the surface pressure in the eye of a typhoon, thus obtaining an intensity estimate, and the dropsonde was born. The first such release in the Atlantic was in Hurricane Able in 1950.

Not until the 1970s was an instrument specifically designed to be released by aircraft developed.

The Omega navigation system was planned to be available around 1970, and the National Center for Atmospheric Research took the lead in developing a dropsonde using that technology. The instrument was dubbed the Omega dropwindsonde (ODW) and was used successfully during the Global Atlantic Research Program (GARP) Atlantic Tropical Experiment (GATE). The data resolution was somewhat course, and the wind finding did not consistently work in clouds or rain such as occurs in TC eyewalls. However, it did provide the first reliable wind soundings in the oceanic environment. Joanne Simpson saw the value in these observations and began a search for other uses of the instrument to keep the program going. Bob Burpee noted that an important reason for TC forecast failures was the lack of observations in the TC environment. They came up with the idea of dropping ODWs from the NOAA P3 aircraft for assimilation into operational numerical models. On 15 September 1982, the first of these “synoptic flow” missions was flown around Hurricane Debby. The ultimate success of these missions prompted Congress to authorize NOAA to purchase a Gulfstream-IV ((G-IV) high-altitude jet to fly operational missions when TCs threatened the United States.

Omega was getting old, but a new technology, the Global Positioning System, was coming online. By late 1996, the new GPS dropwindsonde, also developed by NCAR, replaced the old ODW for hurricane surveillance and reconnaissance. The first operational surveillance mission was conducted in July around Tropical Storm Claudette, but the G-IV flew only three missions in the Atlantic that year.

On 03 August, during a P3 research mission in Hurricane Guillermo (1997), Michael Black decided to deploy a GPS dropwindsonde in a hurricane eyewall for the first time. High-resolution kinematic and thermodynamic data were obtained in the eyewall for the first time, including a wind-speed measurement of > 78 ms-1. Since that time, the dropwindsonde system was installed on many aircraft globally. Thousands of dropwindsondes have been released in and around TCs worldwide, and nearly 400 research papers have been published in peer-reviewed journals. The new data helped to revolutionize TC science in the ensuing years. This talk will review changes to dropwindsonde technology since it was first used in TCs in 1982, and how the data have changed our understanding of TCs.