Abstract
Abstract. 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 frost point hygrometers. Data from a total of 28 balloon flights with at least one pair of radiosondes are analyzed in 1-km altitude bins to quantify measurement differences between the sonde sensors and how they vary with altitude. Each comparison (T, P, RH) exposes several profiles of anomalously large measurement differences. Measurement difference statistics, calculated with and without the anomalous profiles, are compared to uncertainties quoted by the radiosonde manufacturers. Excluding seven anomalous profiles, T differences between 19 pairs of RS92 and iMet sondes exceed their measurement uncertainty limits (2 σ) 31% of the time and reveal a statistically significant, altitude-independent bias of 0.5 ± 0.2 °C. Similarly, RS92-iMet P differences in 22 non-anomalous profiles exceed their uncertainty limits 23% of the time, with a disproportionate 83% of the excessive P differences at altitudes >16 km. The RS92-iMet pressure differences increase smoothly from −0.6 hPa near the surface to 0.8 hPa above 25 km. Temperature and P differences between all 14 pairs of RS92 sondes exceed manufacturer-quoted, reproducibility limits (σ) 28% and 11% of the time, respectively. About 95% of the excessive T differences are eliminated when 5 anomalous RS92-RS92 profiles are excluded. Only 5% of RH measurement differences between 14 pairs of RS92 sondes exceed the manufacturer's measurement reproducibility limit (σ). RH measurements by RS92 sondes are also compared to RH values calculated from frost point hygrometer measurements and coincident T measurements by the radiosondes. The influences of RS92-iMet Tand P differences on RH values and water vapor mixing ratios calculated from frost point hygrometer measurements are examined.
Highlights
Vertical profile measurements of essential climate variables T, P and relative humidity (RH) have been made around the globe for decades
We have rigorously compared coincident, in situ, balloonborne measurements of T and P by RS92 and iMet-1-RSB radiosondes, and measurements of RH by RS92 sondes with RH values calculated from frost point hygrometer measurements
Profiles of median differences in 1-km altitude bins were constructed for each sensor pair, and for every comparison we identified several anomalous difference profiles that do not conform to the majority of profiles (e.g., Fig. 2)
Summary
Vertical profile measurements of essential climate variables T , P and RH have been made around the globe for decades. We examine differences between RH measurements by Vaisala RS92 radiosondes and two frost point hygrometers, the cryogenic frost point hygrometer (CFH; Vomel et al, 2007a) and the NOAA frost point hygrometer (FPH; Mastenbrook and Oltmans, 1983; Hurst et al, 2011). These balloon-borne measurements were made as part of the MOHAVE-2009 campaign, 11–27 October 2009 (Leblanc et al, 2011). We compare only measurements made from the same balloons, eliminating any concerns about spatial and temporal differences between the measurements by different sensors
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