The STARTWAVE atmospheric water database

Abstract

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.

Technical Note: Harmonized retrieval of column-integrated atmospheric water vapor from the FTIR network – first examples for long-term records and station trends

“…As an example for a ground-based microwave instrument, we show the sonde-correlation data for TROWARA (taken from Morland et al, 2006) in the 5th row of Table 1. The slope is 0.88, the intercept 1.36 mm, and the bias 0.36 mm.…”

“…One valuable source of data has turned out to be groundbased microwave radiometry (e.g., Morland et al, 2006;Fiorucci et al, 2008). Such measurements are being carried out to some extent within the NDACC 1 network, which is dedicated to long-term, ground-based, atmospheric sounding observations at many stations around the globe.…”

“…This is a result of the large distance between TROWARA and the launching site of the sondes ( x=40 km), i.e., the observed stdv=2.02 mm is not an appropriate measure of the (certainly significantly better) precision of TROWARA. Morland et al (2006) report correlating GPS and sun photometer (PFR) data with sondes (6th and 7th row of Table 1). The PFR shows a smaller bias (0.08 mm) than the GPS (0.53 mm).…”

Middle atmosphere water vapour and dynamical features in aircraft measurements and ECMWF analyses

“…The data quality in version 2 has improved significantly. Compared to the AMSOS version 1 profiles which have been used in earlier studies (Morland et al, 2006;Vasić et al, 2005), the new version 2 provides roughly four times as many retrieved profiles over the same flight distance due to the more efficient integration scheme. It also suffers less from instrumental artifacts in the lower retrieval layers.…”

The Sofia University Atmospheric Data Archive (SUADA)

“…IWV from the radiosonde station Sofia in Bulgaria is also archived in SUADA (About SUADA, 2014). The envisaged applications include (1) cross-validation of ground-based and satellite observations, and derivation of systematic biases, (2) validation of numerical models used for research and numerical weather prediction (NWP), (3) a study of water vapour distribution in Bulgaria/southeastern Europe, (4) detection of long-term water vapour trends in Bulgaria/southeastern Europe and links to heatwaves, droughts and changes in the pathway of the Atlantic cyclones, and (5) (Morland et al, 2006a) was funded within the framework of the NCCR Climate project 2001-2013(NCCR, 2014. The STARTWAVE database was used for studies covering (1) validation of two operational NWP models used in MeteoSwiss (Guerova et al, 2003), (2) comparison with the 40 year reanalysis data (ERA40) of the European Centre for Medium Range Weather Forecasting (Morland et al, 2006b), and (3) evaluation of the ECHAM5 climate model.…”