Radiation balance at Ottawa during the snow-melt period

Observations were made with two commerically available radiometers on the net radiation absorbed by an exposed snow surface during the snow-melt period at Ottawa, Ontario, Canada. Although a considerable difference was found between the net radiation recorded by the two instruments, no decision could be made as to their relative accuracy. Using the mean of the values of net radiation obtained for each observation period, the components of the energy balance at the surface were calculated. Although it was difficult to assess the accuracy of the estimates obtained for these components, these calculations indicated that evaporation during the observation periods was a large percentage of the net radiation, and amounted to between 20 and 25 per cent of the snow that was dissipated. During 1959 and 1960, the Snow and Ice Section of the Division of Building Research, National Research Council of Canada, has been making observations on the radiation at various surfaces, including snow. The purpose of these observations has been two-fold: 1. to evaluate under field conditions various commercially available instruments for measuring net radiation, and 2. to determine the net radiation as one component of the total energy balance at the surface. The purpose of this paper is to explain some of the difficulties that were encountered in the use of two commercially available net radiometers, to compare observations made with them, and to present the components of the heat balance calculated from the observations made during the snow-melt period at Ottawa.On s'est servi de deux radiom\ue8tres commericaux pour mesurer exactement la quantit\ue9 de radiations absorb\ue9es par une surface enneig\ue9e \ue0 ciel ouvert, au cours de la fonte des neiges, \ue0 Ottawa (Ontario). Malgr\ue9 l'\ue9norme diff\ue9rence constat\ue9e entre les niveaux de radiations nets relev\ue9s par les deux appareils, on n'a pas pu se prononcer quant \ue0 leur pr\ue9cision relative. On a calcul\ue9 les composantes de l'\ue9 quilibre energ\ue9tique \ue0 la surface en utilisant la moyenne des niveaux de radiations nets relev\ue9s pour chaque p\ue9riode d' observations. Il n'\ue9tait pas facile de v\ue9rifier les \ue9 valuations obtenues pour ces composantes; mais, d'apr\ue8s les calculs, l'\ue9vaporation produite au cours des p\ue9riodes d' observation correspondait \ue0 un pourcentage notable du niveau de radiations net, et atteignait entre 20 et 25 pour cent de la neige dissip\ue9e. Au cours des ann\ue9es 1959 et 1960, la section des \ue9tudes sur la neige et la glace de la Division des recherches en b\ue2timent (Conseil national de recherches Canada) a \ue9tudi\ue9 les niveaux de radiations capt\ue9s par diverses surfaces, y compris la neige. Ces observations avaient une double but: 1) \ue9valuer sur le terrain divers appareils commerciaux concus pour mesurer le niveau de radiations net, et 2) d\ue9terminer le niveau de radiations net, c'est-\ue0-dire l'une des composantes de l'\ue9quilibre energ\ue9 tique total \ue0 la surface \ue9tudi\ue9e. Ce m\ue9moire vise \ue0 expliquer certaines des difficult\ue9s rencontr\ue9es dans l' utilisation de deux radiom\ue8tres commerciaux concus pour l'\ue9 tude des niveaux de radiations nets, \ue0 comparer les relev\ue9s effectu\ue9s avec ces deux appareils, et \ue0 pr\ue9senter les composantes de l'\ue9quilibre thermique calcul\ue9es d'apr\ue8s les observations effectu\ue9es au cours de la fonte des neiges, \ue0 Ottawa.Peer reviewed: NoNRC publication: Ye