Meteorology factors causing fluctuations of tritium concentration in precipitation.

Values of the tritium concentration in precipitation collected at Ottawa in 1961 fluctuate by as much as a factor of 3 from one measurement to the next a few days later. The first attempt to determine what meteorological factors could be responsible for these fluctuations was to sort the storms for April and May 1961 into two categories; those predominantly continuous and those predominantly showery precipitation, using both constant altitude radar pictures and hourly precipitation records. There was a slight tendency for the higher tritium concentrations to occur in continuous precipitation. Height/time diagrams showing the positions of the various airmasses over Ottawa revealed that the highest tritium concentrations occurred when maritime arctic air extended from the ground to the tropopause. On occasions with mA air at the ground and other airmasses above it, the measured tritium concentration was approximately proportional to the depth of mA air traversed by the precipitation. The lowest tritium concentration was measured in a storm wholly contained in mT air. Air mass trajectories confirmed that the higher concentrations were measured in precipitation which had fallen through air of arctic origin with an arctic trajectory than through air of tropical origin