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[1] We present a validation study for the ground-based Middle Atmospheric Water Vapour Radiometer (MIAWARA) operating at 22 GHz. MIAWARA measures the water vapor profile in the range of 20-80 km. The validation was conducted in two phases at different geographical locations. During the first operational period the radiometer was operated at middle latitudes in Bern, Switzerland, and the measured water vapor profiles were compared with the HALOE satellite instrument. The agreement between HALOE and MIAWARA was for most altitudes better than 10%. The agreement between the balloon instruments and MIAWARA was better than 2% for a total number of 10 comparable flights. This showed the potential of MIAWARA in water vapor retrieval down to 20 km. In addition, the northern Finland MIAWARA profiles were compared with POAM III water vapor profiles. This comparison confirmed the good agreement with the other instruments, and the difference between MIAWARA and POAM was generally less than 8%. Finally, the tipping curve calibration was validated with tipping curve measurements of the All-Sky Multi Wavelength Radiometer (ASMUWARA) which was operated 10 months side by side with MIAWARA. The agreement of the tropospheric opacity derived from these tipping curves agree within 1%.

Abstract. The STARTWAVE (STudies in Atmospheric Radiative Transfer and Water Vapour Effects) project aims to investigate the role which water vapour plays in the climate system, and in particular its interaction with radiation. Within this framework, an ongoing water vapour database project was set up which comprises integrated water vapour (IWV) measurements made over the last ten years by ground-based microwave radiometers, Global Positioning System (GPS) receivers and sun photometers located throughout Switzerland at altitudes between 330 and 3584 m. At Bern (46.95 • N, 7.44 • E) tropospheric and stratospheric water vapour profiles are obtained on a regular basis and integrated liquid water, which is important for cloud characterisation, is also measured. Additional stratospheric water vapour profiles are obtained by an airborne microwave radiometer which observes large parts of the northern hemisphere during yearly flight campaigns. The database allows us to validate the various water vapour measurement techniques. Comparisons between IWV measured by the Payerne radiosonde with that measured at Bern by two microwave radiometers, GPS and sun photometer showed instrument biases within ±0.5 mm. • E, 366 m), which is located on the south side of the Alps, the bias is +1.9 mm. The sun photometer at Locarno was found to have a bias of −2.2 mm (13% of the mean annual IWV) relative to the data from the closest radiosonde station at Milano. This result led to a yearly rotation of the sun photometer instruments between low and high altitude stations to improve the calibrations. In order to demonstrate the caCorrespondence to: J. Morland (june.morland@mw.iap.unibe.ch) pabilites of the database for studying water vapour variations, we investigated a front which crossed Switzerland between 18 November 2004 and 19 November 2004. During the frontal passage, the GPS and microwave radiometers at Bern and Payerne showed an increase in IWV of between 7 and 9 mm. The GPS IWV measurements were corrected to a standard height of 500 m, using an empirically derived exponential relationship between IWV and altitude. A qualitative comparison was made between plots of the IWV distribution measured by the GPS and the 6.2 µm water vapour channel on the Meteosat Second Generation (MSG) satellite. Both showed that the moist air moved in from a northerly direction, although the MSG showed an increase in water vapour several hours before increases in IWV were detected by GPS or microwave radiometer. This is probably due to the fact that the satellite instrument is sensitive to an atmospheric layer at around 320 hPa, which makes a contribution of one percent or less to the IWV.

Microwave radiometer observations are compared with various radiative transfer model calculations based on simultaneous radiosondes. This analysis uses observations from Payerne, Switzerland, in cloud free conditions during the Temperature Humidity and Cloud (TUC) experiment in winter 2003/04. The results show a systematic bias in the brightness temperatures measured by the Radiometrics profiler at 55-59 GHz, which has since been corrected in the control software. Observations at lower frequencies (22-30 GHz) in these cold conditions do not support recent proposed changes to the width of the 22.235 GHz water vapour line, although this is subject to the assumption of no residual bias in the radiosonde humidity. At intermediate frequencies (51-54 GHz), the absorption models produce large differences, which may be due to differences in oxygen line coupling and highlight the need for further laboratory measurements at low temperatures. Zusammenfassung Bodengestützte Mikrowellen-Radiometer Messungen der troposphärischen Helligkeitstemperatur werden mit Strahlungstransfer-Berechnungen verglichen, die auf gleichzeitigen Radiosondierungen beruhen. Im Vergleich werden Daten der Temperature Humidity and Cloud (TUC) Kampagne verwendet, die im Winter 2003/04 in Payerne, Schweiz, gewonnen wurden. Die Resultate zeigen systematische Fehler in den Helligkeitstemperaturen des Profilers von Radiometrics zwischen 55 und 59 GHz, die in der weiteren Datenverarbeitung berücksichtigt wurden. Im Gegensatz zu aktuellen Vorschlägen zeigen die Messungen zwischen 22 und 30 GHz bei tiefen Lufttemperaturen keinen Bedarf einer Änderung der Breite der Wasserdampf-Absorptionslinie bei 22,235 GHz. Zwischen 51 und 54 GHz gibt es große Unterschiede zwischen den geprüften Modellen, was mit Unterschieden in der Kopplung der Sauerstoff-Linien erklärt werden kann. Die Unterschiede legen weitere Labormessungen bei tiefen Temperaturen nahe.

The retrieval of tropospheric water and temperature with the ground-based and automatically operating radiometer system ASMUWARA (All-Sky MUlti WAvelength RAdiometer) is described. This instrument operates simultaneously at microwave and IR channels. Integrated water vapour (IWV) and integrated liquid water (ILW) are retrieved with a newly developed linear algorithm to an accuracy of 0.014 kgm −2 (ILW) and 0.41 kgm −2 (IWV), thanks to the inclusion of a channel at 151 GHz. These measurements are made for the whole hemisphere and therefore provide information about the spatial distribution of water in the troposphere. With an optimal estimation algorithm, tropospheric temperature and humidity profiles are retrieved. The results are quasi bias free with a mean error of less than 2.5 K for the temperature (less than 1 K in the lowest km above ground), and less than 1 gm −3 for the humidity. Examples of all measurements are shown. Zusammenfassung Die Bestimmung von Wasser und Temperatur der Troposphäre mit dem bodengestützten und automatischen Radiometersystem ASMUWARA (All-Sky MUlti WAvelength RAdiometer) wird beschrieben. Dieses Instrument arbeitet gleichzeitig im Mikrowellen-und Infrarotbereich. Integrierter Wasserdampf und integriertes Flüssigwasser werden durch einen neu entwickelten linearen Algorithmus mit einer Genauigkeit von 0,014 kgm −2 (ILW) und 0,41 kgm −2 (IWV) gemessen, dank der Einbeziehung eines Kanals bei 151 GHz. Diese Messungen werden auf die gesamte Hemisphäre angewandt und bieten deshalb Informationen über die örtliche Verteilung des Wassers in der Troposphäre. Mittels eines Optimal Estimation Algorithmus werden sodann Temperatur-und Feuchteprofile bestimmt. Die Profile werden ohne nennenswerten systematischen Fehler und mit einem mittleren Fehler von weniger als 2,5 K (1 K im untersten Kilometer über Boden), resp. weniger als 1 gm −3 gemessen. Beispiele aller Messungen werden gezeigt.