AEROSOL OPTICAL DEPTH OVER CANADA AND THE LINK WITH SYNOPTIC AIR-MASSTYPES

Aerosol optical depth measurements acquired through the Canadian sunph otometer network were statistically analyzed for the 1987-1992 period in order to investigate spatial and temporal commonalities between the member stations. Four stations were chosen to yield a spatially repre sentative sampling of atmospheric optical conditions across Canada (Ea st Coast, eastern continental, western continental, and West Coast), A ll the stations were located in rural, local pollution free areas. The results of aerosol optical depth measurements showed significant diff erences between eastern and western Canadian stations. The effect of t he Pinatubo volcanic eruption was clearly seen in the measurements acq uired at Sable Island, Nova Scotia, Air mass relationships for the fou r stations sampled demonstrated the relevance of applying air mass cla ssification criteria to the analysis and discrimination of atmospheric optical depth. Knowledge of the seasonal trend combined with informat ion concerning air mass type enables a coarse a priori estimation of a erosol optical depth in the absence of traditional optical data, Synop tical air mass analysis facilitates the understanding of the mechanism s involved in the seasonal variations of aerosol optical depth and yie lds useful information about the atmospheric optical state, The releva nce of the synoptical air mass approach was demonstrated in one partic ular case: a seasonal aerosol optical depth trend for Arctic air masse s was observed for the three sunphotometer stations which regularily e xperience this type of air mass.