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

摘要

Middle atmospheric water vapour can be used as a tracer for dynamicalprocesses. It is mainly measured by satellite instruments and ground-basedmicrowave radiometers. Ground-based instruments capable of measuring middle-atmospheric water vapour are sparse but valuable as they complement satellitemeasurements, are relatively easy to maintain and have a long lifetime.MIAWARA-C is a ground-based microwave radiometer for middle-atmospheric watervapour designed for use on measurement campaigns for both atmospheric casestudies and instrument intercomparisons. MIAWARA-C's retrieval version 1.1(v1.1) is set up in a such way as to provide a consistent data set even if theinstrument is operated from different locations on a campaign basis. Thesensitive altitude range for v1.1 extends from 4 hPa (37 km) to 0.017 hPa(75 km). For v1.1 the estimated systematic error is approximately 10% forall altitudes. At lower altitudes it is dominated by uncertainties in thecalibration, with altitude the influence of spectroscopic and temperatureuncertainties increases. The estimated random error increases with altitudefrom 5 to 25%. MIAWARA-C measures two polarisations of the incidentradiation in separate receiver channels, and can therefore provide twomeasurements of the same air mass with independent instrumental noise. Thestandard deviation of the difference between the profiles obtained from thetwo polarisations is in excellent agreement with the estimated randommeasurement error of v1.1. In this paper, the quality of v1.1 data isassessed for measurements obtained at two different locations: (1) a total of25 months of measurements in the Arctic (Sodankyl?,67.37° N, 26.63° E) and (2) nine months of measurements atmid-latitudes (Zimmerwald, 46.88° N, 7.46° E). For bothlocations MIAWARA-C's profiles are compared to measurements from thesatellite experiments Aura MLS and MIPAS. In addition, comparisons to ACE-FTSand SOFIE are presented for the Arctic and to the ground-based radiometerMIAWARA for the mid-latitude campaigns. In general, all intercomparisons showhigh correlation coefficients, confirming the ability of MIAWARA-C to monitortemporal variations of the order of days. The biases are generally below13% and within the estimated systematic uncertainty of MIAWARA-C. Noconsistent wet or dry bias is identified for MIAWARA-C. In addition,comparisons to the reference instruments indicate the estimated random errorof v1.1 to be a realistic measure of the random variation on the retrievedprofile between 45 and 70 km.