Evaluating regional atmospheric water vapour estimates derived from GPS and short-range forecasts of the Canadian Global Environmental Multiscale model in southern Alberta

• Published in: Atmosphere-ocean 2008-12, Vol.46 (4), p.455-471
• Main Authors: Smith, C. D., Nicholson, N., Skone, S., Strong, G.S.
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Geophysics. Techniques, methods, instrumentation and models; Meteorology; Water in the atmosphere (humidity, clouds, evaporation, precipitation)
• ISSN: 0705-5900; 1480-9214
• DOI: 10.3137/ao.460406

Integrated atmospheric moisture has been derived from a network of Global Positioning System (GPS) receivers established in southern Alberta. GPS receivers and post-processing techniques provide the ability to estimate integrated precipitable water vapour (PWV) at temporal and spatial scales not usually available using conventional observational techniques and without costly expendables. GPS-derived PWV was evaluated during the Alberta GPS Atmospheric Moisture Evaluation (A-GAME) using nearby radiosonde observations from the Airdrie, Olds-Didsbury and Sundre airports during field campaigns in the summers of 2003 and 2004. For the 2004 A-GAME period, the regional (15 km) Global Environmental Multiscale model (GEM)-modelled PWV was compared to the GPS derived PWV using a distance weighting approach. GEM model performance was assessed with regards to prognosis time (from 0 to 9 hours), grid cell elevation, location and the presence of storms in the study region. The results show that there is good agreement between radiosonde-derived PWV and PWV derived from nearby GPS sites with correlations (r 2 ) ranging from 0.76 to 0.84; the GPS-derived PWV showed a small dry bias averaging 0.6 mm. When compared to GPS-derived PWV, GEM model performance was found to be favourable out to the hour-3 prognosis with an overall correlation (r 2 ) of 0.63. Performance decreased with increasing prognosis time and as a result of the presence of storm activity in the study region but did not decrease with increasing grid cell elevation.