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John
Muir Wilderness Area |
(Also see Kaiser Wilderness Area)
Site Name
IMPROVE:
KAIS1 (Kaiser Wilderness Area)
Region
Sierra Nevada Range
Terrain
Terrain is shown in the 2 km terrain
map and the 20 km terrain
map.
The 581,000 acre John Muir Wilderness Area extends for 100 mi along the
crest and on both sides of the Sierra Nevada. West of the crest, it includes
the headwaters of the South and Middle Forks of the San Joaquin River and
the North Fork of the Kings River, which flow westward into the San Joaquin
Valley ~ 50 km (30 mi) west of the western boundary and the nearest major
source region for emissions that could affect visibility in Wilderness areas
west of the Sierra Nevada crest. Western elevations extend from the Sierra
Nevada crest down to 1,200 m (4,000 ft) where the South Fork of the San
Joaquin exits the Wilderness. East of the crest, the Wilderness includes
eastern slopes of the Sierra Nevada roughly between Mammoth Lakes in the
north and Owens Lake in the south, a distance of nearly 150 km (100 mi), and
elevations between the highest elevation at Mt. Whitney (4,419 m, 14,495 ft)
and lowest elevations near 1,600 m (5,000 ft) on the west side of the Owens
Valley. Eastern portions are generally in the rain shadow of the Sierra
Nevada.
The IMPROVE site representing John Muir Wilderness Area is the Kaiser
Wilderness Area site, KAIS1. It is located 80 m (260 ft) below the crest of
Chinese Peak at an elevation of 2,573 m (8,439 ft), about 5 km (3 mi) west
of the western boundary of the John Muir Wilderness Area.
Representativeness
The KAIS1 IMPROVE site is in a well exposed location with an unobstructed
vista into the South Fork of Joaquin River headwaters. Data from KAIS1
should thus be representative of aerosol concentration and composition in
western portions of the John Muir Wilderness Area except at valley and
canyon bottom locations during valley inversion conditions. KAIS1 is much
less representative of John Muir Wilderness Area locations east of the
Sierra Nevada crest, which are probably more susceptible to local emissions
in the Owens Valley area, notably from Owens Dry Lake near the southern
Wilderness boundary and a major source of windblown alkali dust.
Nearby Population/Industrial Centers and Local Sources
The western John Muir Wilderness Area and vicinity are drained by the San
Joaquin River, which flows into the San Joaquin Valley, the nearest source
region. The San Joaquin River channel opens up into the San Joaquin Valley
30 to 35 km (20 to 25 mi) to the southwest, where the primary population
center is Fresno. The eastern John Muir Wilderness Area, on the eastern
slopes of the Sierra Nevada, comprises much of the west side of the Owens
Valley, the nearest local source region for emissions that could affect
visibility west of the Sierra Nevada crest. Owens Valley includes Owens Dry
Lake, a major source of windblown playa dust.
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. The
Mount Tom
California RAWS site is a mountain site, elevation 2,749 m (9,018
ft) located 5 km north. Hourly data from that site includes wind data that
should be regionally representative. The
High Sierra
California RAWS site is also representative of Wilderness elevations
west of the Sierra Nevada crest. East of the crest there are no high
elevation meteorological network sites. The
Owens Valley
California RAWS site is representative of meteorology in the Owens
Valley source region suitable for analysis of wind patterns in Owens Valley
that could generate and transport windblown dust into eastern Wilderness
locations.
Best sites for representative routine upper air data in John Muir Wilderness
are the Reno and Desert Rock RAOB sites.
Wind 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 Fresno California Wind Roses. KAIS1 is well exposed to regional winds and this pattern
should be generally consistent there as well. In the absence of synoptic
forcing, a diurnal mountain/valley flow pattern may be evident at KAIS1,
with easterly (from the east) drainage flows from higher slopes of the
Sierra Nevadas at night and westerly daytime upslope flow from the direction
of the San Joaquin Valley via the San Joaquin River. Although the site is
well above San Joaquin Valley elevations, transport and return of San
Joaquin Valley air at the KAIS1 IMPROVE site would be indicated by a diurnal
pattern of aerosol concentration during periods of stagnation over central
California.
Winds in Wilderness locations east of the Sierra Nevada crest are channeled
locally by Owens Valley. Worst visibility resulting from local sources is
likely to occur with high speed valley winds to generate and transport
surface dust from Owens Valley. At times, with high pressure over the Great
Basin and a strong east to west pressure gradient, Owens Valley emissions my
spill over into Wilderness locations west of the Sierra Nevada crest.
Potential local transport routes into the John Muir Wilderness Area include
San Joaquin Valley emissions transported directly via diurnal upslope/downslope
flow, mixed upwards with afternoon mixing, or trapped regionally under a
persistent subsidence inversion. Also, on the east side, from Owens Valley
emissions transported and/or mixed upwards to Wilderness locations east of
the Sierra Nevada crest.
Inversions/Trapping
Valleys on the west side of the Wilderness are subject to wintertime
trapping surface inversions, notably the headwaters of the South and Middle
Forks of the San Joaquin River. In the east, surface inversions over Owens
Valley may at times extend upwards to Wilderness elevations that are as low
as 350 m (1,200 ft) above the valley floor. Wintertime surface based
inversions are common in the San Joaquin Valley, the principal source region
for local emissions, although at heights typically below Wilderness
elevations.
In the summer, the relatively shallow nighttime San Joaquin Valley boundary
layer is generally mixed to heights of at least 1,000 m (> 3,000 ft) above
the ground on a typical summer day, still well below John Muir elevations.
Summer inversions on both sides of the Sierra Nevada crests are usually
larger scale subsidence inversions associated with the establishment of the
semi-permanent Pacific high-pressure system and can result in 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), in the range of
Wilderness elevations that are between 1,200 m (4,000 ft) and 4,300 m
(14,000 ft).
Climatological Statistics
Fresno
California Normals Means and Extremes are representative of climate
characteristics in San Joaquin Valley and lower elevations west of the
Sierra Nevada crest. Climate summaries available through the
Mount Tom
California RAWS sitel are representative of higher elevations west of
the crest, including most locations in the western John Muir Wilderness
Area. Bishop
California Normals Means and Extremes are representative of Owens Valley
climate characteristics.
Keywords
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Last updated 13 November 2004
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