Synoptic observations from higher levels of the atmosphere. There is a worldwide network of about 500 stations that release radiosondes twice daily at 00:00 and 12:00 GMT. These ascend at a predetermined rate to altitudes of 30 000 m or more. Observations of pressure, temperature, and relative humidity are transmitted back to the surface station, which may track the balloons by radar or radio-theodolite. Some stations release radiosondes that use GPS or LORAN signals for position finding. In either case, the tracking information is used to determine wind speeds and directions throughout the ascent. In future, radiosonde observations may be supplemented by those from aerosondes.
Subjects: Meteorology and Climatology.