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Weminuche Wilderness Area |
Site Name
IMPROVE: WEMI1
Region
Southern Rocky Mountains
Terrain
Terrain is shown in the 2 km terrain
map and
the 20 km terrain
map.
The large (more than ½ million acres) Weminuche Wilderness is located in
southwestern Colorado and brackets both sides of the Continental Divide in
this region. It includes the headwaters of the eastward flowing Rio Grande
and the westward flowing San Juan Rivers. The high mountainous terrain
includes immense glacial valleys and high ridges of the Continental Divide.
Terrain elevations range from valley floors at 2,400 m (8,000 ft) to 4,300 m
(14,000 ft) at the highest peaks. The
Weminuche IMPROVE site, WEMI1, is located outside the Wilderness Area
boundary on the west side about 50 km (30 mi) from the western boundary at
an elevation of 2,765 m (9,069 ft). It is located on a bench on the slope of
Engineer Mountain. A second site is due to be installed in February, 2004
near Bayfield, Colorado, about 7 km (4 mi) south of the western edge of the
Wilderness area, at a lower elevation in rolling hills. The new site will
include meteorology monitoring.
Representativeness
Aerosol data collected at WEMI1 should be representative of conditions
within the Wilderness Area at similar elevations on the west side of the
Continental Divide. The Bayfield site, to be installed in February or March,
2004, is being installed to examine the hypothesis that it will be more
within the regional haze over the Four Corners region to the southwest. The
new site should be more representative of haze conditions at lower
elevations of the Wilderness Area, with the existing site, WEMI1, being more
representative of haze conditions at higher and ridge crest elevations.
These sites may be only marginally representative of aerosol concentration
and composition at Wilderness Area locations in northeaster portions of the
Wilderness Area located east of the Continental Divide.
Nearby Population/Industrial Centers and Local Sources
Nearby Data Stations
Nearby monitoring network stations are shown in the data network
map and at
the US Climate Archive
and RAWS station US Climate
Archive sites. There is a variety of Snotel sites around the region,
with temperature and precipitation data, including Beartown in the western
Wilderness Area. COOP sites, with temperature and precipitation data,
include Rio Grande Reservoir, representative of lower elevation sites on the
east side of the Divide. Meteorology data to be collected at the new IMPROVE
site near Bayfield should provide representative data, including humidity
data, for lower elevation sites west of the Divide. Wind direction data at
this site will likely be significantly influenced by terrain. Wind data from
the Grand Junction NWS station is probably most representative of wind
patterns at exposed ridge locations, and of upper air structure.
Wind Patterns
Mesa Verde wind roses are based on surface meteorological data collected at
the Mesa Verde CASTNET site, MEV405, for the period 1995 – 2001. These
should be reasonably representative of wind directions at exposed locations
in Weminuche Wilderness Area. These indicate annual and seasonal wind
direction (direction from which the wind is blowing) frequencies. Prevailing
wind directions are predominantly northerly, with additional southerly flow
in the summer. At most locations in the wilderness area local flow will show
a typical mountain/valley upslope/downslope pattern.
Potential transport routes into Weminuche Wilderness include low-level
transport into the area from the west via the Colorado and San Juan River
drainages, and from the east via the Rio Grande drainage, with upward
convective and upslope mixing to higher elevations. Encompassing the
Continental Divide in the region, the Wilderness Area is subject to upper
level transport from distant source regions to the west and east.
Inversions/Trapping
The deep canyons and valleys of the Wilderness Area are subject to frequent
diurnal radiation temperature inversions that could trap aerosols locally.
Regional stagnation and subsidence inversions could occur, especially during
summer months. From May to October, long term records show an average of
nearly one air stagnation event per month during this period in western
Colorado, where a stagnation event is defined as stagnation conditions that
persist for 4 days or longer (Wang
and Angell, 1999). Higher elevations may be above regional haze trapped
within large-scale subsidence inversions.
Climatological Statistics
Meteorological Indicators for Local Sources
Keywords
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Page last updated 30 April 2004
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