Research Projects

Project at a Glance

Project Status: complete

Title: Atmospheric tracer experiments aimed at characterizing upslope/downslope flows along the southwestern region of the Sierra Nevada mountains.

Principal Investigator / Author(s): Shair, Fredrick H

Contractor: California Institute of Technology

Contract Number: A4-126-32


Research Program Area: Atmospheric Processes


Abstract:

During the summer, surface meteorological data within the western region of the Sequoia National Park, indicate the presence of four distinct diurnal wind patterns. These regimes are (i) the downslope flow regime which extends between 1.900 and 0500, (ii) the morning transition period which occurs from 0500 to 0900, (iii) the upslope flow regime which extends between 0900 to 1700, and (iv) the evening transition regime which extends from 1700 until 1900. These regimes are quite reproducible with respect to wind direction, standard deviation, and speed. Following a major thunderstorm, the time required for the surface wind to return to its normal pattern is about 24-hours.

Four SF6 tracer experiments were conducted to document the transport and dispersion of atmospheric pollutants from foothills, located at the eastern region of the San Joaquin Valley, into the Sequoia National Park. During the first experiment, the early portion of the upslope flow was tagged. During the second and third experiments, the latter portions of the upslope flow were tagged. During the fourth test, the early morning wind which blows from south to north along the foothills was tagged.

Nearly one thousand tracer data points were collected, from elevations ranging from 1,000 to 11,000 feet above mean sea level, during each test. These data can be useful in (i) developing a better conceptual model of the region, and (ii) providing a quantitative base against which models may be tested.

Hourly averaged data were collected at several stationary sites. Grab samples were collected (i) at stationary sites, (ii) along auto traverses, (iii) along airplane traverses and (iv) via airplane spirals. Special attention was given to the Marble Fork of the Kaweah River, and especially to Emerald Lake.

In each experiment the tracer was transported to the headwaters of the various forks of the Kaweah River drainage system; these headwaters are at least 25 miles (40 kilometers) from the release site and at altitudes of about 11,000 feet msl.

Aside from Test 1, the transit times predicted from the surface wind data at Elk Creek (at about 3000 ft. msl along the western slopes), were close to those observed at sites located from the foothills to the Great Western Divide. The results of Tests 1 and 4 suggest that the upslope flow does not begin uniformly along the foothills at the eastern edge of the San Joaquin Valley.


 

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