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Great
Sand Dunes Wilderness Area |
Site Name
IMPROVE: GRSA1
Region
Southern Rockies
Terrain
Terrain is shown in the 2 km terrain
map and the 20 km terrain
map.
The Great Sand Dunes Monument and
Preserve is located in the San Luis Valley of south central Colorado, in
the upper reaches of the Rio Grande River. Specifically, it is located in an
easternmost part of the San Luis Valley that nests into the Sangre De Cristo
Mountains. The Wilderness Area is wholly contained within the Monument
boundaries, and comprises ~ 90% of the Monument area. The predominant
physical feature is the Sand Dunes, which were formed over time by
prevailing southwest winds forcing sand from the San Luis Valley up against
the Sangre de Cristo Mountains. Elevations within the Wilderness Area range
from ~2,380 m (~7,800 ft) to ~2,900 m (~9,500 ft), although most of the area
lies below ~2,750 m (~9,000 ft). By contrast, elevations of the Sangre de
Cristo Mountains rise to ~ 3,500 m (~11,500 ft) immediately east of the
Wilderness Area. The generally low relief terrain of the greater San Luis
Valley area to the west and southwest has elevations typically near 2,300 m
(~7,500 ft).
Although the elevation of the Wilderness and adjacent San Luis Valley are
lower than typical elevations representative of the Southern Rocky
Mountains, it is included in the Southern Rocky Mountain physiographic
region, surrounded as it is by the Sangre de Cristo and San Juan ranges of
the southern Rockies to the east and west, respectively. At its relatively
low-lying elevation it may be more subject to direct local source effects
than most higher elevation Class I areas of the Southern Rocky Mountain
region.
The Great Sand Dunes IMPROVE site, GRSA1, is located just within the
southeastern Monument boundary at an elevation of 2,504 m (8,213 ft), an
elevation near the lowest end of Wilderness elevations.
Representativeness
Aerosol data collected at GRSA1 should be very representative of conditions
within the Wilderness Area.
Nearby Population/Industrial Centers and Local Sources
Nearby Meteorological Data Stations
Nearby meteorological monitoring network stations are shown in the data
network map and at the
US Climate Archive and RAWS
station US Climate Archive sites. The Alamosa NWS station, a first order
meteorological station, is located about 35 km (22 mi) southwest of the
Wilderness boundary, with no intervening terrain. Alamosa should be very
representative of regional climate, including regional wind patterns. There
is a NWS COOP station, the
Great Sand Dunes
NM COOP site at the same site as the IMPROVE station. This site has
long-term precipitation and temperature data. High time resolution wind
speed and directions data with have been collected at this site unofficially
since 1996 for visitor information purposes.
Wind Patterns
Alamosa wind roses are representative of regional scale transport winds
within the San Luis valley. Wind directions are predominantly south to
southwesterly, with a slightly enhanced frequency of southeasterly winds
during the summer. Springtime winds can be particularly strong southwesterly
winds. With spring plowing in the agricultural areas of the San Luis valley
this results in frequent high dust concentrations in the Wilderness Area.
During wildland fires in the San Juan Mountains across the San Luis Valley
to the south and west, the prevailing southerly to southwesterly winds can
also bring particulate emissions into the Wilderness.
In the absence of strong regional pressure gradients the upslope/downslope
pattern in the San Luis valley would be generally drainage from the north at
night, upslope from the south during the daytime. At Wilderness area
locations, especially on the east side, the mesoscale pattern may be
modified by diurnal upslope/downslope flow that occurs near the mouths of
the canyons coming down from the crest of the Sangre de Cristo Mountains,
resulting in local easterly drainage at night.
Potential transport routes into Great Sand Dune Wilderness include low-level
transport into the area from the south and west via the San Luis valley and
upper Rio Grande drainage, and via upper air transport of emissions from
distant source regions.
Inversions/Trapping
The San Luis Valley is subject to frequent cold pooling with associated
strong occasionally persistent surface-based inversions that may trap
emissions locally. Great Sand Dune Wilderness locations may at times be
within this San Luis Valley cold pool, and this Wilderness area may be more
subject to local effects than Class I areas at higher elevations of the
Southern Rockies.
Regional stagnation and subsidence inversions can occur, especially during
summer months. From May to October, long-term records show an average of
about 0.5 to 1.0 air stagnation events per month during this period in south
central Colorado, where a stagnation event is defined as stagnation
conditions that persist for 4 days or longer (Wang
and Angell, 1999).
Climatological Statistics
Alamosa Apt Normals,
Means and Extremes should be representative of conditions within the
Great Sand Dunes Wilderness Area.
Meteorological Indicators for Local Sources
|
Updated 30 April 2004 |