Quality Assessment of the First Measurements of Tropospheric Water Vapor and Temperature by the HAMSTRAD Radiometer Over Concordia Station, Antarctica

Abstract

International audienceThe HAMSTRAD microwave instrument operates at 60 and 183 GHz and measures temperature and water vapor, respectively, from 0- to 10-km altitude with a time resolution of 7 min. The radiometer has been successfully deployed at Dome C (Concordia Station), Antarctica (75°06' S, 123°21' E, 3233 m amsl) during the first summertime campaign for 12 days in January-February 2009. The radiometer has been continuously running since January 2010, hosted within a dedicated shelter. We have used the very first set of HAMSTRAD data, recorded when the instrument was outdoors, to assess its potential to sound the troposphere over Dome C, from the planetary boundary layer (PBL) up to the tropopause ( ~ 6 km above surface, ~ 9 km amsl). We have compared the HAMSTRAD measurements to several sets of measurements performed at the Dome-C station or in its vicinity: meteorological radiosondes, in situ PT100 and Humicap sondes along the vertical extent of a 45-m tower, meteorological sensor attached to the HAMSTRAD instrument, and the spaceborne Infrared Atmospheric Sounding Interferometer (IASI) instrument onboard the EUMETSAT MetOp-A satellite in polar orbit. The variability of integrated water vapor (IWV) observed by HAMSTRAD with extremely low values of 0.5 kg *m-2 was also measured by the radiosondes (very high HAMSTRAD versus radiosonde correlation of 0.98), whereas IASI cloud-free measurements did not reproduce well the HAMSTRAD IWV variation (weak HAMSTRAD versus IASI correlation of 0.58). The measurements of absolute humidity (H2O) from HAMSTRAD at Dome C cover a large vertical extent from the surface to about 6 km above surface with a high sensitivity in the free troposphere. The strong diurnal variation of H2O observed by the in situ sensors in the PBL is not well detected by the radiometer. In the free troposphere, the HAMSTRAD versus radiosonde H2O correlation can reach 0.8-0.9. Around the tropopause, HAMSTR- D shows the same variability as IASI and radiosondes but with a dry bias of 0.01 g *m-3. HAMSTRAD tends to show a wetter atmosphere by 0.1-0.3 g *m-3 compared with radiosondes from the surface to ~ 2-km altitude and a drier atmosphere above by ~ 0.1g *m-3. The sensitivity of the temperature profiles from HAMSTRAD is very high in the PBL and in the free troposphere but degrades around the tropopause. The strong diurnal signal measured above the surface by HAMSTRAD (3-6 K) is consistent with all the other in situ data sets. The temporal evolution over the 12-day period in the PBL is also consistent with all other data sets (radiosondes, IASI, in situ sondes, and meteorological sensors). In the free troposphere and around the tropopause, the HAMSTRAD temporal evolution is consistent with that observed by radiosondes and IASI, although a cold bias exists compared with IASI and radiosondes around the tropopause. For heights less than 4 km above surface, HAMSTRAD correlates very well with radiosondes and in situ sensors (correlation better than 0.8) but less well with IASI (0.4). Below the tropopause, th...

Genesis of diamond dust, ice fog and thick cloud episodes observed and modelled above Dome C, Antarctica

“…In the present study, the vertical profiles of temperature and humidity were taken from RS92 radiosondes using the standard Vaisala evaluation routines without any correction of sensor heating or time lag effect. We recall that the corrections performed on the radiosonde data measured in 2009 according to Miloshevish et al (2006) shown a weak impact (with a maximum of +4 % on IWV) on the vertical profiles (Ricaud et al, 2013). Furthermore, considering the updated tools developed in Miloshevich et al (2009) and Tomasi et al (2011Tomasi et al ( , 2012 found that, between 630 and 470 hPa, the correction factor for humidity estimated by the radiosonde varied within 1.10-1.15 for daytime and within 0.98-1.00 for night-time.…”

“…It has been running automatically since January 2010. Science and validation studies using HAMSTRAD data are detailed in Ricaud et al (2012Ricaud et al ( , 2013Ricaud et al ( , 2014aRicaud et al ( -c, 2015. All the HAM-STRAD data measured since 2009 are freely available at the following address: http://www.cnrm.meteo.fr/spip.php?…”

Maïdo observatory: a new high-altitude station facility at Reunion Island (21° S, 55° E) for long-term atmospheric remote sensing and in situ measurements

“…Once these tunings provide a calibrated spectrum with reduced undulations, vertical profiles will be obtained using the analysis tool Microwave ODIN Line Estimation and Retrieval (MOLIERE) originally developed for the space mission ODIN (Urban et al, 2003). It is based on the Optimal Estimation Method (Rodgers, 2000) to retrieve vertical profiles and has been successfully adapted to the ground-based H 2 O instruments: (1) MobRa, stratospheric H 2 O measured at 22 GHz , and (2) HAMSTRAD, tropospheric H 2 O measured at 183 GHz (Ricaud et al, 2013). Theoretical calculations (Motte, 2008) show that the DODO radiometer will be able to measure vertical profiles of H 2 O from ∼ 15 to ∼ 75 km with a resolution of 7-12 km.…”

Variabilités de la vapeur d'eau et de la température troposphérique au Dôme C (station Concordia), Antarctique. Partie I : l'instrument Hamstrad

“…La précision sur les profils verticaux de H 2 O et de température du radiomètre Hamstrad pour un temps d'intégration de 7 minutes est présentée respectivement dans les tableaux 3 et 4, associée aux résolutions verticales dans la couche limite atmosphérique, la troposphère libre et la haute troposphère-basse stratosphère. Nous avons appliqué en parallèle la théorie de l'estimation optimale (Rodgers, 2000) aux mesures du radiomètre Hamstrad pour caractériser les résolutions verticales des profils de H 2 O et de température (Ricaud et al, 2013a). Les fonctions de balayage associées (ou noyaux moyens) permettent de caractériser la résolution verticale des mesures en calculant leur largeur à mi-hauteur.…”

“…Fonctions de balayage ou noyaux moyens de la température relatives aux mesures du radiomètre Hamstrad au Dôme C : à gauche de 3,2 à 4,2 km d'altitude (0-1 km au-dessus de la surface) ; à droite de 3,2 à 13,2 km d'altitude (0-10 km au-dessus de la surface). Les chiffres à droite de chaque graphe montrent, pour chaque fonction de balayage, 1) l'altitude du pic et 2) la résolution verticale estimée à partir de la largeur à mi-hauteur de la fonction de balayage (tiré de Ricaud et al, 2013a). de balayer à la fois l'absorbant à température ambiante (charge chaude pour l'étalonnage) et l'atmosphère à différentes élévations.…”