Abstract
Abstract. This study uses 55 years of hourly observations of air temperature, relative humidity, daily precipitation, snow cover and cloud cover from 15 climate stations across the Canadian Prairies to analyze biosphere-atmosphere interactions. We will provide examples of the coupling between climate, snow cover, clouds, and land use. Snow cover acts as a fast climate switch. With the first snow fall, air temperature falls by 10 °C, and a similar increase in temperature occurs with snow melt. Climatologically, days with snow cover are 10 °C cooler than days with no snow cover in Alberta. However the interannual variability has a larger range, so that for every 10 % decrease in days with snow cover, the mean October to April climate is warmer by 1.4 to 1.5 °C. Snow cover also transforms the coupling between clouds and the diurnal cycle of air temperature from a boundary layer regime dominated by shortwave cloud forcing in the warm season to one dominated by longwave cloud forcing with snow cover. Changing agricultural land use in the past thirty years, specifically the reduction of summer fallowing, has cooled and moistened the growing season climate and increased summer precipitation. These hourly climate data provide a solid observational basis for understanding land surface coupling, which can be used to improve the representation of clouds and land-surface processes in atmospheric models.
Highlights
This paper reviews the analysis of the diurnal climatology of the Canadian Prairies (Betts et al, 2013a, b, 2014a, b, 2015; Betts and Tawfik, 2016)
In January, which is representative of all the winter months with snow, mean air temperature increases with opaque cloud cover, and sunrise minimum temperatures plunge under clear skies
In July and all months with no snow cover, minimum temperatures vary little with cloud cover, and the diurnal range to the afternoon maximum is largest under clear skies
Summary
This paper reviews the analysis of the diurnal climatology of the Canadian Prairies (Betts et al, 2013a, b, 2014a, b, 2015; Betts and Tawfik, 2016). We have used snow cover and the daily mean opaque cloud cover, OPAQm, to stratify this large dataset (660 station-years), and study the diurnal and seasonal climate. Precipitation falls as snow and the highly reflective snow cover acts as a fast climate switch, which drops the mean surface temperature by 10 ◦C within days, and changes the climatology One result is the mean cold season temperature is linearly related to the fraction of days with snow cover. Another impact of snow cover is to transform the coupling of the diurnal cycle to cloud cover K. Betts et al.: The impact of clouds, land use and snow cover on climate in the Canadian Prairies. At the time of maximum temperature, Tx, typically in the afternoon in the warm season, we derived the mixing ratio, Qtx, and the corresponding equivalent potential temperature and pressure-height to the lifting condensation level (LCL), which is close to cloud-base in the warm season (Betts et al, 2013a)
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