| |
Desolation Wilderness Area |
(Also See Mokelumne Wilderness Area)
Site Name
IMPROVE:
BLIS1 (Bliss State Park, Tahoe Regional Planning Agency)
Region
Sierra Nevada Range
Terrain
Terrain is shown in the 2 km terrain
map and
the 20 km terrain
map.
The 63,500 acre Desolation Wilderness is located directly to the west of
Lake Tahoe. It is bisected by the Rubicon River that flows northward from
its source in the southern Wilderness to eventually flow into the headwaters
of the American Rivera and towards the San Joaquin Valley of central
California. Wilderness elevations range from around 2,000 m (6,500 ft) to
3,000 m (10,000 ft) at highest peaks. Lowest elevations are thus near Lake
Tahoe’s elevation of 1,897 m (6,225 ft). The nearest source of local
emissions is probably the Lake Tahoe basin, immediately east of the
Wilderness. However, most of the Wilderness is not part of the nearby Lake
Tahoe airshed, although easternmost east facing slopes are.
The IMPROVE site representing Desolation and Mokelumne Wilderness Areas is
BLIS1 (Bliss State Park) located near the western shore of Lake Tahoe at an
elevation of 2,116 m (6,940 ft), about 220 m (720 ft) above the shore of
Lake Tahoe and near lowest elevations on the eastern slopes of Desolation
Wilderness.
Representativeness
The BLIS1 IMPROVE site is close to and about 220 m (720 ft) above the shore
of Lake Tahoe, and near lowest Wilderness locations on slopes facing Tahoe
Basin. It is likely more susceptible to local and trapped emissions in the
Tahoe basin that do not extend to higher Desolation Wilderness elevations.
It is probably representative of Desolation Wilderness locations on lower
eastern slopes facing Lake Tahoe that may be worst case conditions overall,
and during conditions of uniform regional haze.
Nearby Population/Industrial Centers and Local Sources
The closest source region with emissions that could contribute to haze in
the Desolation Wilderness is the Lake Tahoe basin. The more distant central
valley of California near Sacramento, from which emissions could be
transported to Desolation Wilderness, is some 80 km (50 mi) southwest,
linked to Desolation Wilderness by the American River and Rubicon River. The
Reno Nevada area is about the same distance to the northeast but is
generally downwind for prevailing wind directions and in a distant airshed.
Nearby Meteorological Data Stations
Nearby meteorological monitoring network stations are shown in the data
network map
and at the RAWS station US
Climate Archive site. Data from the
South LT/Lake
Tahoe AP California SAO airport site are representative of the Tahoe
basin. The
Meyers California RAWS site may provide data that shows the timing of
drainage flow from slopes surrounding Tahoe Basin.
Upper air data is collected twice daily at the Reno Nevada RAOB site.
Wind and Transport Patterns
Synoptic winds in the region are generally northwesterly (from the
northwest), with an additional component of more southerly winds in the
winter with the weakening of the Pacific High Pressure System. This pattern
is evident in monthly Reno Nevada Wind Roses. Tahoe Basin is somewhat more sheltered, especially on the west side
where the BLIS1 IMPROVE site is located, and wind patterns near the BLIS1
IMPROVE site are likely more influenced by diurnal flows off the western
slopes of the Tahoe Basin. Within the central Desolation Wilderness, diurnal
patterns will be channeled by the upper Rubicon River valley, and there may
be some penetration into the area of San Joaquin Valley emissions via the
American and Rubicon Rivers that is not seen at BLIS1 which is more within
the Tahoe Basin airshed.
Potential local transport routes into the Desolation Wilderness include San
Joaquin Valley emissions transported directly via diurnal upslope/downslope
flow and valley flow in American and Rubicon River valleys, mixed upwards
with afternoon mixing and transported via prevailing upper level westerly
winds, or trapped regionally under a persistent subsidence inversion. This
transport condition, from source regions to the west in the California
central valley, occurs mainly in the summer. Locally, eastern Wilderness
locations may be predominantly influenced by emissions within the Tahoe
Basin. Highest summertime measured concentrations at BLIS1 are associated
with regional forest fire events. In the absence of such regional events
there is likely to be a significant contribution from vehicle traffic in
Tahoe basin to aerosol measurements at BLIS1. In the fall and winter there
may be woodsmoke impacts associated with prescribed burns and residential
burning in the Tahoe Basin.
Inversions/Trapping
The Lake Tahoe Basin, where BLIS1 is located, lies in a depression between
the crests of the Sierra Nevada range and the Carson range to the east. It
is subject to frequent trapping inversions that result from cooling of
surface air over the lake, a common winter condition, and from drainage of
cool air from surrounding slopes into the basin, a common summer condition.
Surface trapping inversions may at times extend upwards to the height of the
BLIS1 IMPROVE site that is about 220 m (720 ft) above lake level. Frequently
but especially in the winter a layer of wood smoke can be seen over the lake
in the morning, which could affect measurements at BLIS1. In the summer,
larger scale subsidence inversions during regional forest fire events can
result in wood smoke aerosol buildup over periods of days. Subsidence
inversion heights are typically at elevations of 2,000 to 3,000 m (6,000 to
10,000 ft), just above the Lake Tahoe level of 1,897 m (6,225 ft).
Climatological Statistics
Tahoe
California Climate data are representative of Lake Tahoe and BLIS1.
Other Northern
California Climate Summaries and
Nevada Climate
Summaries are available from the
Western Regional Climate Center.
Keywords
|
Last updated 13 November 2004
|