SUBLIMATION OF SNOW INTERCEPTED BY AN ARTIFICIAL CONIFER

An experiment tested predictions of sublimation from snow intercepted on conifer crowns, using an artificial tree to avoid errors from desiccation and needle loss. The prediction model approximated vaporization from the crystal fragments most exposed on a snow surface by sublimation of uniform ice spheres. Monitoring temperature, humidity, radiation and wind speed over four winter months in a cold, dry climate provided data to estimate sublimation rate, dm/dt, for a 1-mm diameter ice sphere during each 15-min period. Weighing interception on the 1-m high, artificial tree provided measures of sublimation rate, dM/dt. Periods with and without snowfall were analyzed separately. Proportionality factor, Z, in the hypothesis, dM/dt = Z(dm/dt), was a function of intercepted mass, M, that depended on the time since snowfall ceased. Parameter a in the equation Z = aM(b), decreased by a factor of 2 as time after snowfall increased to 8 h. This result could reflect an increase in size, and decrease in the number, of vapor sources on each unit area of snow surface exposed. Parameter b, describing the change in exposed area with mass, first increased then decreased as increasing interception bridged between branches. The experiment determined b = (0.7 - 5 x 10(-5) M) for the artificial tree.