The Modern Era
Satellites are capable of providing a wealth of information. Around the earth, there are five geostationary orbiting satellites giving considerable coverage of the earth and its atmosphere. The United States has GOES East, positioned over the Equator at 75 degrees W longitude, and GOES West at 135 W longitude. Together these satellites provide complete continuous coverage over the entire United States. Usually a third GOES satellite is waiting in the wings to replace either GOES East or GOES West, if one should fail.
Other countries have also launched geostationary satellites. Japan has a Geostationary Meteorology Satellite (GMS) that covers portions of Asia and the Pacific. Over Europe, there is the METEOSAT, which observes Europe, parts of the Atlantic, Mediterranean, and Africa. India has INSAT, which watches over Asia and the Indian Ocean. GOES satellite imagery is used to track storms, look for patterns that set off severe weather such as thunderstorms and tornadoes, and monitor development. A new series of GOES systems provides vertical temperature and moisture profiles of the atmosphere. These profiles provide a more detailed cross-section of the atmosphere than radiosonde balloons alone deliver. Also, because water vapor emits infrared radiation, water vapor can be monitored. Water vapor imagery is especially helpful in examining the flow of moisture in a developing storm. Areas of dry-air intrusion can indicate sinking motions, which inhibit storm development. In addition laser instruments are used to detect wind motions.
ASOS is an Automated Surface Observing System. More than 850 of these systems are being installed in the United States to serve as the nation's primary surface weather observing network.
Polar-orbiting satellites are also very important in delivering detailed imagery of surface conditions. These satellites do not hover over the same point, but rather orbit from pole to pole. The GOES systems focus on weather forecasting while the polar-orbiting satellites (POES) focus on climate. For example, infrared sensors on these satellites provide data on vegetation and deforestation. These sensors provide temperature profiles that can be used to help determine the pattern of global climate change. Also ultraviolet sensors provide information about ozone levels in the atmosphere and are able to detect the ozone hole in Antarctica. Two satellites make up the POES system that provides global coverage four times each day.
AWIPS is the Advanced Weather Interactive Processing System that is the new communication nerve center of operations at all the Weather Forecast Offices and River Forecast Centers. It combines information from ASOS and NEXRAD.
The newest satellites also serve as platforms for collecting and disseminating a wide variety of data from ground-based observational platforms. Buoys on the ocean surface, along with other automated devices, transmit the data to the satellite, which then relays that to land-based receiving stations. Wave heights, sea-surface temperatures, and seismic information can be sent around the world from remote locations along with standard weather data.
The array of remote sensing devices, used separately and in conjunction with satellites, is dazzling. Across the United States, more than 800 Automated Surface Observing Stations (ASOS) were installed during the 1990s. The ASOS program is a joint effort of several federal agencies, including the National Weather Service. The number of automated stations doubles the number of full-time surface weather observing sites. A much greater network of data is available. ASOS even provides computer-generated voice observations directly to aircraft in the vicinity of airports. Such messages are even available from automatic buoys placed out on the ocean. Of course, there's no substitute for human observers. For example, ASOS doesn't measure snow depth, it provides cloud information just up to 12,000 feet, and thunderstorms can't be directly determined. But it does provide a wealth of data over a vast area across a very dense network.