THE STRUCTURE, WATER-BUDGET, AND RADIATIONAL FEATURES OF A HIGH-LATITUDE WARM-FRONT

On 30 September 1994 an Arctic low pressure system passed over the sou thern Beaufort Sea area of northern Canada and research aircraft obser vations were made within and around the warm front of the storm. This study is unique in that the warm front contained subzero centigrade te mperatures across the entire frontal region. The overall structure of the warm front and surrounding region was similar to midlatitude storm s; however, the precipitation rates,liquid water content magnitudes, h orizontal and vertical winds, vertical wind shear, turbulence, and the rmal advection were very weak. In addition, a low-level jet and cloud bands were aligned parallel to the warm front, near-neutral stability occurred within and around the front, and conditional symmetric instab ility was likely occurring. A steep frontal region resulted from stron g Coriolis influences that in turn limited the amount of cloud and pre cipitation ahead of the system. The precipitation efficiency of the st orm was high (60%) but is believed to be highly dependent on the stage of development. The mesoscale frontogenetic forcing was primarily con trolled by the tilting of isentropic surfaces with confluence/converge nce being the secondary influence. Sublimation contributions may have been large in the earlier stages of storm development. Satellite and a ircraft radiometers underestimated cloud top heights by as much as 4 k m and this was mostly due to the near transparency of the lofted ice l ayer in the upper portion of the storm. Maximum surface solar radiatio n deficits ranged between 91 W m(-2) and 187 W m(-2) at two surface ob serving sites. This common type of cloud system must have a major impa ct on the water and energy cycles of northern Canada in the autumn and therefore must be well accounted for within climate models.