Comparisons of temperature, pressure and humidity measurements by balloon-borne radiosondes and frost point hygrometers during MOHAVE-2009

摘要

We compare coincident, in situ, balloon-borne measurements of temperature(T) and pressure (P) by two radiosondes (Vaisala RS92, Intermet iMet-1-RSB)and similar measurements of relative humidity (RH) by RS92 sondes and frostpoint hygrometers. Data from a total of 28 balloon flights with at least onepair of radiosondes are analyzed in 1-km altitude bins to quantifymeasurement differences between the sonde sensors and how they vary withaltitude. Each comparison (T, P, RH) exposes several profiles of anomalouslylarge measurement differences. Measurement difference statistics, calculatedwith and without the anomalous profiles, are compared to uncertaintiesquoted by the radiosonde manufacturers. Excluding seven anomalous profiles,T differences between 19 pairs of RS92 and iMet sondes exceed theirmeasurement uncertainty limits (2 σ) 31% of the time and reveal astatistically significant, altitude-independent bias of 0.5 ± 0.2 °C.Similarly, RS92-iMet P differences in 22 non-anomalous profiles exceedtheir uncertainty limits 23% of the time, with a disproportionate 83%of the excessive P differences at altitudes >16 km. The RS92-iMetpressure differences increase smoothly from ?0.6 hPa near the surface to0.8 hPa above 25 km. Temperature and P differences between all 14 pairs ofRS92 sondes exceed manufacturer-quoted, reproducibility limits (σ)28% and 11% of the time, respectively. About 95% of theexcessive T differences are eliminated when 5 anomalous RS92-RS92 profilesare excluded. Only 5% of RH measurement differences between 14 pairs ofRS92 sondes exceed the manufacturer's measurement reproducibility limit(σ). RH measurements by RS92 sondes are also compared to RH valuescalculated from frost point hygrometer measurements and coincident Tmeasurements by the radiosondes. The influences of RS92-iMet Tand Pdifferences on RH values and water vapor mixing ratios calculated from frostpoint hygrometer measurements are examined.