85th AMS Annual Meeting

Wednesday, 12 January 2005
Trends in cloud types and diurnal changes in cloudiness in Canada 1953-2003
Ewa J. Milewska, MSC, Toronto, ON, Canada
Clouds play an important role in water and energy flux; they directly affect surface temperature and precipitation. Fifty-one years (1953-2003) of hourly observations of cloud amounts, opacities, types, and layers from the Canadian airports are used to study changes in the incidences of different cloud types, e.g. low and high clouds, stratiform and convective, etc. on the annual, monthly, daytime, nighttime, and diurnal scale. The results might be indicative of whether we see more or less convective type weather activities under changing climate scenario (some climate models predict more convective clouds), or more or less low or high clouds. These are important questions, as, for example, increasing convective clouds could produce more extreme precipitation. High clouds are more effective in trapping long-wave radiation than low clouds, which are more effective in reflecting shortwave radiation, so changes in either type might enhance or dampen warming now observed in daily temperature minimums and maximums. In the assessment of the energy budget, not only cloud height and structure but also cloud opacity is likely to play a role even more critical than cloud amounts, so opacity is also analyzed. Unfortunately the information regarding cloud types have lately been irreversibly lost at some observing stations with recent automation.

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