Measurement of Upper Air Pressure, Temperature and Humidity

12.1.1 Definitions The following definitions from WMO (1992; 2003a) are relevant to upper air measurements using a radiosonde: Radiosonde: Instrument intended to be carried by a balloon through the atmosphere, equipped with devices to measure one or several meteorological variables (pressure, temperature, humidity, etc.), and provided with a radio transmitter for sending this information to the observing station. Radiosonde observation: An observation of meteorological variables in the upper air, usually atmospheric pressure, temperature and humidity, by means of a radiosonde. NOTE: The radiosonde may be attached to a balloon, or it may be dropped (dropsonde) from an aircraft or a rocket. Radiosonde station: A station at which observations of atmospheric pressure, temperature and humidity in the upper air are made by electronic means. Upper air observation: A meteorological observation made in the free atmosphere, either directly or indirectly. Upper air station, upper air synoptic station, aerological station: A surface location from which upper air observations are made. Sounding: Determination of one or several upper air meteorological variables by means of instruments carried aloft by balloon, aircraft, kite, glider, rocket, etc. This chapter will primarily deal with radiosonde systems. Measurements using special platforms, specialized equipment, or made indirectly by remote sensing methods will be discussed in various chapters of Part II of this Guide. Radiosonde systems are normally used to measure pressure, temperature and relative humidity. At most operational sites, the radiosonde system is also used for upper-wind determination (see Chapter 13 in this Part). In addition, some radiosondes are flown with sensing systems for atmospheric constituents, such as ozone concentration or radioactivity. These additional measurements are not discussed in any detail in this chapter.