Aerosonde Weather Page

 Why is the aerosonde needed for weather reconnaissance?

    During the past decade it has become clear that the key problem hindering progress in weather forecasting is the lack of weather observations over the oceans, particularly above the surface.   Numerical weather prediction models, the central forecast tools used by meteorologists, need to be initialized with a detailed three-dimensional description of the current weather conditions around the globe.  The better the initial description, the better the forecast.  Over land where there are numerous surface observations, radars, launching sites for balloon-launched instrument packages called radiosondes, and other observing assets, the forecast model initialization is relatively good.  But over the oceans, where there are only scattered ships, buoys, and high-level aircraft reports there are vast areas with few in-situ observations.   Figure 1, which presents the distribution of radiosonde sites around the world, highlights the oceanic data void probllem.  The result of this uneven observational network has been more skillful short-term (12-24h) forecasts over the eastern side of continents.  Thus, storm forecasts are generally more skillful along the U.S. East Coast than in Washington State or California.  Furthermore, many of the major forecast "busts" over the U.S. West Coast during recent years have been traced to poor model initialization over the Pacific.

      During the past decade, considerable advances in satellite observing technology have been made, with satellite-derived cloud distributions, cloud/water vapor track winds,  and temperature soundings making a substantial contribution to defining oceanic weather.  Unfortunately, there also major limitations to satellite observations, such as the inability to provide winds below dense cloud decks and often coarse vertical resolution.  Thus, some other approach is needed to collect weather observations above the oceans.  Improved sampling in these areas requires a means to deploy instruments economically over large distances.  Miniature autonomous aircraft, or Aerosondes, promise to meet this requirement, and similar needs in other earth sciences disciplines.

            How would aerosondes be used in support of weather prediction?

    If a dependable, long-range aerosonde could be developed, it would be an ideal oceanic weather observing platform.  Aerosondes could fly from near the surface to the upper troposphere, purpoising up and down in order to observe the atmosphere's vertical structure. (The aircraft would remain below the flight level of oceanic jet traffic, where observations are being taken anyway)  Using the upcoming global communication system based on a constellation of low-orbiting communications satellites, both  weather data and the aircraft information will be available continuously.

    Aerosondes have sufficient range to cover much territory of interest to forecasters in North America.  Even the current aircraft (handicapped  by an inefficient engine and unrefined aerodynamic design) have a still-air operating radius of about 1500 km, and thus could reconnoiter large expanses of the Arctic and the Gulf of Alaska ( red circles in Figure 2).  Work is underway on a new powerplant, and coupled with other improvements, should double the range of the aerosonde over the next two years (blue circles in Figure 2).  Since aerosondes are relatively slow (50-100 kts still-air speed), they would generally fly with the wind.  For observing the weather over the eastern Pacific, aerosondes could be sent from either Hawaii or Alaska to the west coast of North America, and  recovered aerosondes could be shipped back to the origin using commercial aircraft and reused.

  Aerosondes could be used in two modes over the oceans:  (1) following regular routes, depending on the wind speed or direction and (2) being targeted to where the observations are most needed.  The latter approach, also known as "targeted observing," is a developing technology with considerable promise. Two recent field experiments using weather instruments dropped from manned aircraft, FASTEX (over the Atlantic) and NORPEX (over the Pacific), have produced results suggesting the viability of the adaptive approach.  Since manned weather reconnaissance is extremely expensive, an alternative and less expensive approach, such as the aerosondes, is needed.
 

What are some other applications of the aerosonde technology?

    There are many applications of an unmanned weather observing platform such as the aerosonde:

1.    In support of atmospheric field experiments for studying fronts, hurricanes, cyclones, and sea breeze circulations, to name only a few.

2.    To probe tropical weather systems and to determine their environment for forecasting applications.

3.    To support military operations, both for improving weather model initialization and for determining weather conditions around navy ships and over coastal regions of interest.

4.    For environmental observations in support of air quality research and air pollution mitigation.
 

Where have aerosondes been used previously for weather reconnaissance?

    Major field projects in which the aerosonde has been used include:

MCTEX -Australia
Cape Blanco-Oregon
Bidyandanga-Western Australia
Port Hedland,-Western Australia
Tofino Trials - British Columbia
 

For further information:

Professor Cliff Mass                                                        Dr. Greg Holland
Department of Atmospheric Sciences                       Bureau of Meteorology Research Center
University of Washington                                                Melbourne, Australia
Seattle, Washington  98195

(206) 685-0910                                                                gjhol@amail.msn.com
cliff@atmos.washington.edu