Comparison of In Situ Humidity Data from Aircraft, Dropsonde, and Radiosonde

Abstract

Results are presented from the Measurement of Tropospheric Humidity (MOTH) Tropic and MOTH Arctic airborne field experiments, comparing a number of in situ humidity measurements. Good agreement is shown between the Total Water Content probe on board the C-130 aircraft, and the Vaisala RS90 and ''new'' Vaisala RS80 radiosondes; ''old'' Vaisala RS80 radiosondes and Vaisala RD93 dropsondes show the dry bias noted by others. An empirical correction for RD93 dry bias is presented and is shown to produce good results with both MOTH and non-MOTH data. It was concluded that the aircraft and corrected dropsonde data agree (1) to Ϯ1 g kg Ϫ1 ; these limits are due to atmospheric variability. The possibility of temperature measurement errors producing errors in RD93 relative humidities is not significant compared to atmospheric variability. Meteolabor Snow White radiosondes are shown to exhibit a wet bias at high and low mixing ratios and possible reasons are discussed. Intercomparisons between the RS90s and other instruments, partitioned by day-night and by experiment, suggest deficiencies in RS90 daytime radiation corrections.

The Spring-Time Boundary Layer in the Central Arctic Observed during PAMARCMiP 2009

“…The dropsonde system (Vaisala RD93 [2]) records air pressure, temperature, relative humidity, altitude, wind speed and wind direction along with GPS coordinates while descending to the ground. The vertical resolution is about 8 m. The accuracy for temperature is given by the manufacturer as 0.2 K, for pressure 0.4 hPa, for relative humidity 2%, and for horizontal wind speed 0.5 m s and the respective harsh landing do not allow quantifying the near-surface temperature.…”

“…Data are of special interest due to different feedback mechanisms, like the interaction of the Arctic atmospheric boundary layer (AABL) with surfaces dominated by open water and ice, which differ strongly in terms of skin temperature and albedo. Therefore, dropsonde observations performed by aircraft [2] and radiosonde data obtained from ship and ice surfaces (e.g., during the Surface Heat Budget of the Arctic Ocean, SHEBA campaign [3]) and the Russian North Pole Drifting stations [4] are of great value for Arctic climate research.…”

Evaluation of daytime measurements of aerosols and water vapor made by an operational Raman lidar over the Southern Great Plains

“…Previous comparisons of PWV from RS‐90 sondes and MWRs at the ARM SGP and TWP sites have found that the radiosonde PW is consistently 6–8% drier for daytime soundings than for nighttime soundings (L. M. Miloshevich, personal communication, 2004). Other comparisons have also found a daytime dry bias of about 3–4% in the RS‐90 sondes [ Vance et al , 2004] and that this bias is due to solar heating of the air stream inside these sondes (J. Nash et al, Progress in improving upper air moisture measurements over the UK, preprints of 12th Symposium on Meteorological Observations and Instrumentation, American Meteorological Society, Long Beach, California, 2003).…”

Aircraft validation of clear air absorption models at millimeter wavelengths (89–183 GHz)

“…This has been estimated as ±0.008 g/kg or ±8% (whichever is greater) for humidity mass mixing ratio, 0 < r < 20 g/kg, based partly on previous comparison with a cryogenically cooled mirror hygrometer [ Ström et al , 1994]. The aircraft humidity sensors were also compared with dropsonde and radiosonde sensors [ Vance et al , 2004]. Humidity profiles are derived from the Lyman‐α hygrometer throughout this study.…”