Up-valley Winds Research Articles

Average Diurnal Behavior of Surface Winds during Summer at Sites in Complex Terrain

Mean diurnal wind distributions from five surface stations in the rugged Geysers area of northern California were examined to determine how they were affected by the terrain. The one-dimensional slop-flow model of Garrett was abel to simulate the average diurnal wind distribution at the station with the simplest slope geometry and using only routine weather observations as input. Wind direction frequency distributions at the other four stations clearly could not be explained by a simple daytime upslope and nighttime downslope wind distribution. Winds blew perpendicular to canyon axes (simple katabatic and daytime upslope flow) or parallel to canyon axes (organized drainage and upvalley winds), depending on station location. Winds always blew upslope during the day, but at two stations the wind blen some night and downslope on the others. The upslope flow at night may have been caused by prevailing winds in one case, and by drainage winds flowing off an opposing slope and across the intervening riverbed in the other.

Summer daily circulation in the Po Valley, Italy

Abstract Surface wind data from a network of stations located in the Po Valley, Italy, have been analysed in order to investigate the features of the local circulation during summer, under synoptic conditions of weak pressure gradients. The up-valley wind appears to be closely coupled with the sea-land breeze in the eastern part of the valley. The nocturnal phase winds are almost completely absent in the central part of the valley. An anomalous nocturnal circulation in the northeastern part of the valley is tentatively related to the influence of a low-level jet developing in a near plain. Due to the differential heating of the mountain slopes and the valley floor, the flow is divergent and anticyclonic during the day and convergent and cyclonic at night.

Observations of vertical atmospheric structure in a deep mountain valley

A tethered balloon sounder was used to collect vertical temperature and wind structure data in the Gore River Valley of Western Colorado during December, 1975. Observations taken on a clear morning in which a deep inversion was initially present in the valley showed that the inversion top descended at a steady rate of ∼120 m hr−1. reaching the valley bottom after approximately 4 hours. Weak down-valley winds were present within the inversion layer while stronger up-valley winds prevailed above. A hypothesis is presented to account for these observations. A case study is presented for afternoon and evening cooling in which a ground-based inversion developed to a depth of 175 m in less than 2 hours. Winds within the inversion became decoupled from the synoptic-scale winds and remained very weak during the night. The effect of cloud cover during a morning heating cycle was to make the temperature soundings approach isothermal while sensible heating continued throughout the valley volume.

Slope and Valley Winds in the Columbia River Valley *

The behavior of slope and valley winds near the town of Trail in the Columbia River valley system in southern British Columbia was studied, and the results compared with those obtained from similar studies made in the Alps. The hourly wind velocities for two stations—one in the main valley, the other in a side valley—were resolved into components parallel to and at right angles to the valley. This procedure gives the valley and slope winds respectively. The usual diurnal wind pattern was found to prevail in most instances, with up-slope and up-valley winds during the day, and down-slope and down-valley winds at night. These systems were much better developed during the summer than in winter, and approximated the ideal pattern more closely on sunny days when the overall pressure gradient was weak.