Drainage Flow Characteristics and Inversion Breakup in Two Alberta Mountain Valleys

Abstract

Wind and temperature profiles and corresponding acoustic sounder data collected in September 1982 are presented for nocturnal drainage flow and inversion breakup in two Alberta mountain valleys. The results show that the diurnal amplitude of average valley air temperatures for the Canyon Creek Valley is greater than the Elbow River Valley for four case days. The two-dimensional topographic amplification factors for both valleys show that this difference can be explained on the basis of differing valley geometry. The bottom half of the Canyon Creek Valley drainage flow had a weak inversion (1?2 K/100 m) with the top half of much greater strength (7 K/100 m). The Elbow River Valley drainage flow had an inversion strength of 2.9 K/100 m which was invariant with height. In the Canyon Creek Valley when the ridgetop winds had an up-valley component, the maximum down-valley wind speed occurs at 30%?40% of the drainage depth as opposed to 50%?60% when there is no up-valley component. There is also a linear relationship between surface inversion strength and the maximum down-valley wind speed. Cross-valley wind components in the Canyon Creek Valley drainage flow are indicative of a sloshing behavior as the flow adjusts to the sharp 90° bend in the valley. The mechanism for inversion breakup in both valleys is different from that associated with flat terrain. Inversion descent occurs in the Canyon Creek Valley, and evidence from two case days suggests that it results from a thermodynamically driven process.