Upper Air Soundings
Low Resolution Upper Air Sounding Data (AMPS Low)
High Resolution Upper Air Sounding Data (AMPS High)
Upper Air Sounding Systems – The Eastern and Western Ranges use a weather balloon system called the Automated Meteorological Profiling System (AMPS). AMPS balloons come in two types: low resolution (lo-res) and high resolution (hi-res). Wind measurements from balloons assume the balloon follows the wind and derives the horizontal wind vector from the time derivative of the balloon’s horizontal position. Thermodynamic measurements are made in-situ using sensors carried by the balloon. The lo-res AMPS uses a standard latex weather balloon with a GPS-tracked expendable sonde or “flight element” that contains sensors for temperature (thermistor) and relative humidity (carbon film hygristor). Altitude is directly measured from the GPS data and pressure is calculated from the hydrostatic equation using the altitude and thermodynamic data for the trajectory of the sonde as it rises. The balloon rise rate is about 1000 ft/min (5.5 m/s) and the maximum altitude usually exceeds 100 kft (33 km). The wind measurement accuracy is about 1 m/s RMS with a vertical resolution of about 350m. The air temperature and RH RMS accuracies are respectively 0.2° C and 5%. The barometric pressure accuracy is about 0.5 hPa (mb). Data are downlinked from the sonde on one of 16 channels near a frequency of 403 MHz GPS and meteorological data are transmitted separately. At the ground, the received signals are processed in an AMPS signal processing system and the results are provided to an Upper Air Systems Controller who can perform manual quality control before the data are released to MIDDS (see description in section A8.5.1 below) for dissemination to the users. The hi-res AMPS uses a special balloon which is identical to radar tracked “Jimsphere” balloons except that they are clear because they do not have the aluminized coating used for radar tacking. The balloon is 2m in diameter with surface roughness elements that control boundary layer separation to reduce self-induced balloon motions. It rises at about 1000 ft/minute to a maximum altitude of between 55 and 60 kft (17 – 18 km). The flight element for these sondes is smaller and lighter because it does not carry thermodynamic sensors. The wind measurement accuracy and vertical resolution of the AMPS hi-res balloons is about the same as that of Jimspheres (a radar-tracked predecessor to the hi-res AMPS), less than 1 m/s RMS and 150m respectively (Eastern Range Handbook, rev July 2005; Wilfong et al., 1997). Data transmission and processing uses the same system as the AMPS lo-res packages.