Weather Forecasting Through the Ages

The Aqua Spacecraft
In 2002, the Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU), and the Humidity Sounder for Brazil (HSB) will be launched together on NASA’s Earth Observing System (EOS) Aqua satellite, a satellite that will also carry a Moderate Resolution Imaging Spectroradiometer (MODIS), two Clouds and the Earth’s Radiant Energy System (CERES) sensors, and an Advanced Microwave Scanning Radiometer for EOS (AMSR-E). The AIRS/AMSU/HSB sounding system will provide the capability for determining atmospheric temperature and moisture more accurately than ever before from space-based measurements. These measurements will be provided to the National Oceanic and Atmospheric Administration (NOAA), the European Centre for Medium-Range Weather Forecasts (ECMWF), and the weather community at large for assimilation into operational numerical weather prediction models. It is expected that assimilation of global AIRS/AMSU/HSB data, complementing other operational observations, should lead to a substantial improvement in the accuracy of mid- and long-range weather forecasts.

First TIROS image
The Aqua spacecraft, with pointers to the AMSU-A1, AMSU-A2, AIRS, and HSB instruments.

The AIRS/AMSU/HSB instrument suite builds on the technical heritage of NOAA’s High Resolution Infrared Sounder (HIRS) and Microwave Sounding Unit (MSU). The HIRS/MSU combination was the National Weather Service’s (NWS’s) operational weather sounding system for nearly twenty years, flying on numerous NOAA polar orbiting satellites. This system was enhanced in the late 1990s by the replacement of the four-channel MSU by a 20-channel AMSU, which includes Aqua’s AMSU and HSB channels. Looking toward further improvements in weather forecasts, the NWS has set measurement requirements for temperature at an accuracy of 1°C in layers 1 km thick and humidity at an accuracy of 20% in layers 2 km thick in the troposphere (the lower part of the atmosphere, where weather systems are of most relevance to human life and property). AIRS/AMSU/HSB will meet these requirements, allowing meteorologists to improve and extend their predictions and reduce the number of significant prediction mistakes, like failing to predict a major storm prior to a few hours before its arrival.



Weather Forecasting Through the Ages
Early History
Towards Numerical Prediction
Modern Tools of the Trade
The Aqua Spacecraft
Benefits to Society

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