On the cause of ‘fram’ type seasonal change in diurnal amplitude of air temperature in polar regions

Abstract

AbstractThe cause of Fram' type seasonal trend of diurnal amplitude of air temperature is investigated from the viewpoint of the surface energy balance. First, the cause of diurnal amplitude of the surface temperature is examined. Then, the effect of the atmosphere between the surface and the screen‐level on the amplitude of air temperature is evaluated.The data of the energy balance used in this work were collected at the base camp of the Axel Heiberg Island Expedition (79°25′N, 90°45′W, 200 m) in the Queen Elizabeth Islands, N.W.T., Canada. This site shows a typical ‘Fram’ type trend of diurnal amplitude with annual maximum in April, the summer minimum in June and a secondary peak in August.The April maximum is due to extremely slow sublimation and heat conduclion in the subsurface. The decrease in the amplitude during the later dry snow period in May and early June is due to a gradual increase in sublimation which is induced by the temperature increase. During the melt in June, the diurnal amplitude of the surface temperature is effectively reduced owing to the diurnal change of the latent heat of fusion. After the snow melt, the diurnal amplitude of absorbed global radiation is tripled compared with April. The temperature amplitude remains small, however, owing to the rapid increase in the diurnal amplitudes of energy sinks. The cause of the slight recovery of the diurnal temperature amplitude in August is the decrease in the sensible heat flux.Throughout the entire period, the result of the heat exchange is reflected in a larger temperature variation under lower temperature due to the Stefan‐Boltzmann law. This effect contributes to a larger diurnal amplitude in spring.