ARIS-Campaign: intercomparison of three ground based 22 GHz radiometers for middle atmospheric water vapor at the Zugspitze in winter 2009

Abstract

Abstract. This paper presents the Alpine Radiometer Intercomparison at the Schneefernerhaus (ARIS), which took place in winter 2009 at the high altitude station at the Zugspitze, Germany (47.42 • N, 10.98 • E, 2650 m). This campaign was the first direct intercomparison between three new ground based 22 GHz water vapor radiometers for middle atmospheric profiling with the following instruments participating: MIRA 5 (Karlsruhe Institute of Technology), cWASPAM3 (Max Planck Institute for Solar System Research, Katlenburg-Lindau) and MIAWARA-C (Institute of Applied Physics, University of Bern). Even though the three radiometers all measure middle atmospheric water vapor using the same rotational transition line and similar fundamental set-ups, there are major differences between the front ends, the back ends, the calibration concepts and the profile retrieval. The spectrum comparison shows that all three radiometers measure spectra without severe baseline artifacts and that the measurements are in good general agreement. The measurement noise shows good agreement to the values theoretically expected from the radiometer noise formula. At the same time the comparison of the noise levels shows that there is room for instrumental and calibration improvement, emphasizing the importance of low elevation angles for the observation, a low receiver noise temperature and an efficient calibration scheme.The comparisons of the retrieved profiles show that the agreement between the profiles of MIAWARA-C and cWAS-PAM3 with the ones of MLS is better than 0.3 ppmv (6 %) at all altitudes. MIRA 5 has a dry bias of approximately 0.5 ppm (8 %) below 0.1 hPa with respect to all otherCorrespondence to: C. Straub (corinne.straub@iap.unibe.ch) instruments. The profiles of cWASPAM3 and MIAWARA-C could not be directly compared because the vertical region of overlap was too small. The comparison of the time series at different altitude levels show a similar evolution of the H 2 O volume mixing ratio (VMR) for the ground based instruments as well as the space borne sensor MLS.

Transport of mesospheric H<sub>2</sub>O during and after the stratospheric sudden warming of January 2010: observation and simulation

“…Here, data from 10 January to 31 March 2010 is considered and analyzed to yield daily estimates of water vapor profiles in an altitude range between 10 and 0.02 hPa (approximately 30 to 75 km) with a vertical resolution of approximately 12 km. The uncertainty on MIAWARA-C's profiles is typical for ground based 22-GHz water vapor radiometers as shown in Straub et al (2010Straub et al ( , 2011. The simulated accuracy (determined as the 2-σ systematic error arising from uncertainties in a priori temperature, in calibration and in spectroscopy) is below 16 % at all altitudes, while the simulated precision (determined by propagation of 1-σ measurement noise) degrades from 5 % at altitudes up to 50 km to 18 % between 50 and 75 km.…”

“…It can be operated as a standalone instrument as it maintains its own weather station and a calibration scheme that does not rely on other instruments nor the use of liquid nitrogen. Water vapor profiles are retrieved from measured spectra of the pressure broadened 22 GHz rotational emission line (see Straub et al, 2010Straub et al, , 2011 for details on MIAWARA-C). Here, data from 10 January to 31 March 2010 is considered and analyzed to yield daily estimates of water vapor profiles in an altitude range between 10 and 0.02 hPa (approximately 30 to 75 km) with a vertical resolution of approximately 12 km.…”

Validation of middle-atmospheric campaign-based water vapour measured by the ground-based microwave radiometer MIAWARA-C

“…Recent validation efforts (e.g. Haefele et al, 2009;Nedoluha et al, 2011;Straub et al, 2011) have demonstrated the reliability of this technique. Validation studies are an important tool to assess the data quality of an instrument.…”

Development of a 22 GHz ground-based spectrometer for middle atmospheric water vapour monitoring

“…Moreover, it was shown that changes in middle atmospheric water vapour on time scales longer than the on time scales longer than the duration of a satellite mission can be successfully observed by ground-based instruments [Nedoluha et al, 2009]. Several other ground-based spectrometers have been developed in the last decades to detect the water vapour rotational emission line at 22.235 GHz with detect the water vapour rotational emission line at 22.235 GHz with heterodyne microwave receivers [e.g., Nedoluha et al, 2009;Straub et al, 2011]. Due [e.g., Nedoluha et al, 2009;Straub et al, 2011].…”