Performance of the Vaisala RS80A/H and RS90 Humicap Sensors and the Meteolabor “Snow White” Chilled-Mirror Hygrometer in Paramaribo, Suriname

Abstract

In climate research there is a strong need for accurate observations of water vapor in the upper atmosphere. Radiosoundings provide relative humidity profiles but the accuracy of many routine instruments is notoriously inadequate in the cold upper troposphere. In this study results from a soundings program executed in Paramaribo, Suriname (5.8°N, 55.2°W), are presented. The aim of this program was to compare the performance of different humidity sensors in the upper troposphere in the Tropics and to test different bias corrections suggested in the literature. The payload of each sounding consisted of a chilled-mirror "Snow White" sensor from Meteolabor AG, which was used as a reference, and two additional sensors from Vaisala, that is, either the RS80A, the RS80H, or the RS90. In total 37 separate soundings were made.For the RS80A a clear, dry bias of between Ϫ4% and Ϫ8% RH is found in the lower troposphere compared to the Snow White observation, confirming the findings in previous studies. A mean dry bias was found in the upper troposphere, which could be effectively corrected. The RS80H sensor shows a significant wet bias of 2%-5% in RH in the middle and upper troposphere, which has not been reported before. Comparing observations with RS80H sensors of different ages gives no indication of sensor aging or sensor contamination. It is therefore concluded that the plastic cover introduced by Vaisala to avoid sensor contamination is effective. Finally, the RS90 sensor yields a small but significant wet bias of 2%-3% below 7-km altitude.The time-lag error correction from Miloshevich et al. was applied to the Vaisala data, which resulted in an increased variability in the relative humidity profile above 9-(RS80A), 8-(RS80H), and 11-km (RS90) altitude, respectively, which is in better agreement with the Snow White data.The averaged Snow White profile is compared with the average profiles of relative humidity from the European Centre for Medium-Range Weather Forecasts (ECMWF). No significant bias is found in either the analyses or the forecasts. The correlation coefficient for the Snow White and ECMWF data between 200 and 800 hPa was 0.66 for the 36-h forecast and 0.77 for the analysis.

Convective Cells in Altocumulus Observed with a High-Resolution Radar

“…Additional instrumentation used in the experiment included the Sigma Space Micro Pulse lidar, the METEK Micro Rain Radar (Peters et al 2005), an in-house developed all-sky camera, the Meteolabor Snow White rawinsonde (Verver et al 2006), and a Cessna Cheyenne research aircraft operated by Weather Modification, Inc., that was equipped with a forward scattering spectrometer probe (FSSP) (Baumgardner 1983), a two-dimensional optical array imaging probe (2D-C) (Knollenberg 1981;Korolev et al 2011), a Commonwealth Scientific and Industrial Research Organisation (CSIRO) King liquid water probe for measuring the LWC (King et al 1978), as well as additional sensors for measuring the state variables of temperature (Rosemount 102 deiced series), dewpoint temperature, pressure, and the GPS location and altitude (Schmidt et al 2012). A video camera was also placed on the aircraft and was found useful in corroborating rapid fluctuations evident in the measured aircraft parameters during its flight into and out of the individual turrets within the cloud layer.…”

Accuracy assessment of water vapour measurements from in situ and remote sensing techniques during the DEMEVAP 2011 campaign at OHP

“…A number of studies documented the lower detection limit of Vaisala RS92 capacitive humidity sensors and Snow White chilled-mirror hygrometer (Vömel et al, 2003;Fujiwara et al, 2003;Vaughan et al, 2005;Verver et al, 2006). These studies were mainly focused on the upper troposphere.…”

Cirrus clouds, humidity, and dehydration in the tropical tropopause layer observed at Paramaribo, Suriname (5.8°N, 55.2°W)

“…Daily radiosonde launches provided temperature, pressure and wind profiles and occasionally during night time, a frost point hygrometer of the type “Snow White” was launched that allows a precise determination of the water vapor profile. The behavior of this sonde in the cold upper tropical troposphere has been studied by Vömel et al [2003], Fujiwara et al [2003b], and Verver et al [2006], who have found good performance up to at least 16 km altitude. This study uses the Snow White data up to 18 km that have passed the quality check suggested by Fujiwara et al [2003b].…”