7638 - Laserfiche WebLink

Home Browse Search

. . somewhat by local channeling of air flow through the Muddy Creek drainage, it showed representative seasonal wind patterns in the upper Colorado River drainage. Wind direction was predominantly from the north-northwest durinQ the winter and spring months, then shifts to the south-southwest 1n summer, and back to the northwest in the autumn. . . Slope and Valley Winds Slope and valley winds are one of the most common synoptic and mesoscale meteorological phenomena in Colorado Plateau riparian environments. During the daylight (especially the afternoon) hours, heated air on the floor and walls of canyons rises, creating an updraft and pulling air upstream. These up- canyon winds may also be driven by prevailing southwestern winds where stream courses flow southwest or northeast. At night, cool air on the mesa tops and mountains subsides, following drainage. Consequently, during periods of otherwise moderate weather, daytime winds in canyons often move upstream while night-time winds tend to move downstream. Diurnal, upslope winds are stronger at low elevations and nocturnal downslope winds are stronger at higher elevations. Valley winds are generally strongest during winter and spring seasons. Ecological Effects Winter winds may prevent snow accumulation in some alpine landscapes. Interactions between exposure and gopher (Thomomys talpoides) feeding activity limit the growth of Kobresla be17ardii, a tussock forming sedge in Rocky Mountain tundra habitats (Osburn 1958). Despite the low snowpack on exposed sites, melting late-winter snows contribute significant amounts of water to the soils. Humus accumulations of up to 15 cm increase soil moisture sufficiently in the A soil horizon to provide sufficient moisture for shallow rooted species, such as Kobresia, which qUickly come to dominate the alpine habitat. Slope and valley winds serve as important geomorphological and biological forces. These winds are sufficiently persistent to create high eolian dunes along rivers (e.g., the Colorado River in the Grand Canyon). Slope and valley winds aid in anemophilous pollination of grasses, cottonwood and alders. Such winds may aid raptors in their soaring along canyon cliffs, and may also serve or retard in the dispersal of aerial adult insects, such as fphemeroptera, Plecoptera, Odonata, and Diptera (e.g., chironomid midges and simuliid gnats), as well as in the migratory flights of monarch butterflies (Danaius plexippus), birds and bats. Slope, valley, and other winds may also serve as disturbance factors. The lack of duff accumulation under Salix exigua stands in the lower . . . . . . 19 .