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Hoover Wilderness Area |
Site Name
IMPROVE:
HOOV1
Region
Sierra Nevada Range
Terrain
Terrain is shown in the 2 km terrain
map and the 20 km terrain
map.
The Hoover Wilderness is an area of approximately 48,000 acres in the Sierra
Nevada range, east of the crest hence primarily in the rain shadow of the
Sierra Nevada. It is sandwiched between Mono Lake and the eastern portion of
Yosemite National Park. Elevations within the wilderness range from about
2,500 m (8,000 ft) on lower slopes to over 3,600 m (12,000 ft) on the crest.
Streams flow eastward into Bridgeport Valley from the northern Wilderness
and into Mono Valley from the southern Wilderness. Mono Lake, in Mono
Valley, is a terminal lake with no outlet. Mono Lake and Owens Lake 150 km
to the south are major sources of windblown alkali dust that may impact
visibility in the Wilderness.
The IMPROVE site representing the Hoover Wilderness Area is the HOOV1,
located about 10 km (6 mi) east of the Wilderness boundary on the ridge that
separates Bridgeport and Mono Valleys. The site elevation is 2,566 m (8,416
ft).
Representativeness
The HOOV1 IMPROVE site is in a well-exposed location with an unobstructed
vista into the Hoover Wilderness Area to the west. Its elevation is near the
lower end of the range of Wilderness elevations and is some 500 to 600 m
(1,600 to 2,000 ft) above the Bridgeport and Mono Valley floors. HOOV1 data
should be generally representative of aerosol characteristics in the Hoover
Wilderness. During episodes of windblown dust from the valley floors it
should represent worst visibility conditions at the most impacted lower
Wilderness elevations.
Nearby Population/Industrial Centers and Local Sources
The Hoover Wilderness Area is on the east slopes of the Sierra Nevada,
adjacent to Mono and Bridgeport Valleys. Mono Lake and Owens Lake 150 km to
the south are potential sources of alkali dust from these dessicated lake
beds. Dust from these sources can be transported larger distances because it
is unusually fine-grained compared to dust from other natural sources. The
largest anthropogenic source region is the California Central Valleys, which
could be a source for aerosols mixed upwards and transported across the
Sierra Nevada crest by prevailing westerly winds.
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
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 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 Tonopah Nevada Wind Roses. Locally winds will be channeled by terrain features such as
Mono and Bridgeport Valleys. In the absence of synoptic forcing Wilderness
locations will see typical mountain/valley circulations, with nighttime
drainage towards valley locations to the east and daytime upslope flow from
east to west generally. Strongest southerly winds with potential for dust
storm development in Mono and Owens Valleys and transport into Hoover
Wilderness Area
Inversions/Trapping
Surface inversions over Mono and Bridgeport Valleys may at times extend
upwards to Wilderness elevations that are as low as 350 m (1,200 ft) above
the valley floor. 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
Bishop normals
means and extremes are representative of climate characteristics at
lower elevations east of the Sierra Nevada crest
Keywords
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Last updated 13 November 2004
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