FIGURE 3.7 Winds obtained by tracking clouds in successive infrared images. The height of the cloud is determined by the cloud’s temperature. Note that where there are no trackable clouds, no winds can be retrieved. SOURCE: NOAA.

TABLE 3.1 Satellite Data Used to Initialize Numerical Weather Prediction Models in 2006

Satellite Data

HIRS sounder radiances

AMSU-A sounder radiances

AMSU-B sounder radiances

GOES sounder radiances

GOES, Meteosat, GMS winds

GOES precipitation rate

SSM/I precipitation rates

TRMM precipitation rates

SSM/I ocean surface wind speeds

ERS-2 ocean surface wind vectors

QuikScat ocean surface wind vectors


AVHRR vegetation fraction

AVHRR surface type

Multisatellite snow cover

Multisatellite sea ice

SBUV/2 ozone profile and total ozone


MODIS winds

Altimeter sea-level observations

NOTE: Monthly statistics on the data used in NCEP’s models are available at

HIRS = High-Resolution Infrared Radiation Sounder; AMSU = Advanced Microwave Sounding Unit; GOES = Geostationary Operational Environmental Satellites; SSM = Special Sensor Microwave; ERS = European Remote Sensing Satellite; AVHRR = Advanced Very High Resolution Radiometer; SST = sea surface temperature; SBUV = Solar Backscattered Ultraviolet.

SOURCE: Lord (2006).

Figure 3.8 shows a time series of one measure of the skill of a representative numerical weather prediction model for 3-, 5-, 7-, and 10-day forecasts. The top line for each set of curves is for the northern hemisphere, where nonsatellite observations are plentiful; the bottom line is for the southern hemisphere, where nonsatellite observations are woefully few. Due largely to our increasing ability to use satellite observations effectively—that is, to assimilate the observations into numerical weather prediction models (e.g., Kalnay 2003)—the difference between northern hemisphere forecasts and southern hemisphere forecasts has steadily decreased, and the overall forecast skill has increased to the point that global 7-day forecasts are now as good as northern hemisphere 5-day forecasts were 25 years ago.

In addition, tests at NCEP show that data from just one satellite instrument, the Advanced Microwave Sounding Unit (AMSU), extend forecast usefulness by 1 day in the southern hemisphere and by about a half day in the data-rich northern hemisphere (Lord 2006). AIRS is also improving forecasting skill (Chahine et al. 2006), and there is evidence that satellite data, particularly QuikScat winds, are improving hurricane track forecasts (Zapotocny et al. 2007). Without question, improvement in numerical weather prediction—on which all forecasts more than a few hours ahead are based—is a major scientific accomplishment of Earth observations from space.

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