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Mount
Zirkel Wilderness Area |
Site Name
IMPROVE: MOZI1 beginning 7/30/94
STPE1 (Storm Peak) 12/1/93 – 7/27/94
CASTNET: Centennial CNT169 (Wyoming)
Region
Southern Rocky Mountains
Terrain
Terrain is shown in the 2 km terrain
map and the 20 km terrain
map.
The Mount Zirkel Wilderness is located in north-central Colorado near the
Wyoming border and abreast the Continental Divide at its most northern
extreme within the Southern Rockies. It is characterized by rivers flowing
from high glacial lakes and includes two major wilderness rivers, the
Encampment River that flows north out of the Wilderness, and the North and
South Forks of the Elk River which flows west from the Wilderness. Mount
Zirkel Wilderness is generally above the Yampa River drainage basin
extending to the west. Terrain is high peaks and valleys with elevations
ranging from 2,100 m (7,000 ft) to 3,713 m (12,180 ft) at the top of Mt. Zirkel.
Although it straddles the Continental Divide, it is separated from east
slopes of the Rockies by a long east-west stretch of the Divide and by the
North Park area of northern Colorado. It is thus probably more influenced by
meteorology and emission sources west of the Divide than are other Class I
areas on the Continental Divide in the Southern Rockies.
The Mount Zirkel IMPROVE site, MOZI1, is located on the crest of the Divide
just outside the southern Wilderness boundary. An earlier IMPROVE site,
STPE1, was located at the summit of Storm Peak, elevation 3,220 m (10,562 ft),
10 km (6 mi) south of the southern Wilderness boundary. A high elevation CASTNET, CNT169, is located in southern Wyoming 60 km (40 mi)
north-northeast of the Wilderness at an elevation of 3,178 m (10,424 ft).
Data Representativeness
Aerosol data from MOZI1 should be very representative of aerosol
concentration and composition at similar high elevations within the Mt.
Zirkel Wilderness. It may not be as representative of lower valley
elevations during periods when they are isolated within lower level
radiation inversions.
The CASTNET site CNT169, should provide meteorological data, including wind
data, uniquely representative of high elevations near the Continental Divide
in the region of Mt. Zirkel Wilderness.
Nearby Population/Industrial Centers and Local Sources
Nearby Meteorological 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.
The Centennial CASTNET site should provide meteorological data
representative of high elevation locations near the Continental Divide. This
data is available at the CASTNET
website. The Dry
Lake RAWS site where data collection started in 1985 is located 7 km (4
mi) south of the Wilderness boundary at an elevation of 2,537 m (8,320 ft) and
should be representative of climate at similar elevations within the
Wilderness west of the Divide. The
Willow Creek
RAWS site 20 km (12 mi) east of the Wilderness at an elevation of 2,963 m
(9,720 ft) should provide similar representation for Wilderness locations
east of the Divide.
Wind Patterns
Centennial wind roses are based on surface meteorological data collected at
the Centennial CASTNET site,
CNT169, for the period 1995 – 2001 and indicate annual and seasonal wind
direction (direction from which the wind is blowing) frequencies. The
Centennial site in southern Wyoming is at a location that is well exposed to
prevailing synoptic wind patterns driven by regional pressure gradients.
These show the predominance of westerly winds at high elevations, excluding
local terrain effects
More locally, wind patterns in the Mount Zirkel Wilderness Area are typical
upslope/downslope patterns, both at a local scale in the valleys and canyons
within the Park, as well as at a mesoscale, influenced by up/down flow from
the Yampa Valley to the west. Night time downvalley winds in the Yampa
Valley can be mixed upwards, then transported to the east towards Mount
Zirkel Wilderness during the day with upper level westerly flow, with the
potential for bringing Yampa Valley emissions into the Wilderness.
Transport pathways into the Mount Zirkel Wilderness Area are primarily via
upslope transport and upper level transport of emissions from the Yampa
Valley, as well as more regional flow from distant source regions in
Colorado, southern Wyoming, and Utah. Results from the
Mt. Zirkel Visibility Study include a conceptual model of
visibility impairment within the Mt. Zirkel Wilderness Area based findings
from an intensive measurement program conducted in 1994-1995.
Inversions/Trapping
The canyons and valleys of the Wilderness Area are subject to diurnal
radiation temperature inversions that could trap aerosols locally,
especially during wildland fire episodes. Inversions within the Yampa Valley
to the west may similarly isolate surface emissions in that area from
Wilderness locations while the inversion persists, but those surface
emissions may be mixed upward and transported into the Wilderness, as
described in the Wind Patterns section. Regional stagnation and subsidence
inversions could occur, especially during summer months. From May to
October, long term records show an average of 1 to 1.5 air stagnation event
per month during this period in north central 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 trapped local transported
haze as well as above regional haze trapped below large-scale subsidence
inversions and surface-based radiation inversions.
Climatological Statistics
Regional normals means and extremes are compiled for the
Grand Junction
NWS station Climate data representative of Eagles Nest Wilderness
Area are also collected at the
Dry Lake RAWS
site and the
Willow Creek RAWS site.
Meteorological Indicators for Local Sources
Keywords
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Updated 30 April 2004
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