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Saguaro Wilderness Area |
Site Name
IMPROVE:
SAGU1 (Saguaro National Monument)
SAWE1 (Saguaro West)
Region
Southwest Deserts
Terrain
Terrain is shown in the 2 km terrain maps,
east and
west, and the
20 km
terrain map.
The Saguaro Wilderness comprises most, 71,400 acres, of
Saguaro National Park, broken into
two units by the city of Tucson: Saguaro National Park West and Saguaro
National Park East. The Saguaro West unit, also called the Tucson Mountain
Unit, has its eastern boundary a few km from the western Tucson city limit.
It is essentially a westerly extension of the Tucson Mountains, with
elevations ranging from about 720 m (2,350 ft) at lower elevations of the
surrounding flatland to the west to 1,429 m (4,687 ft) at the top of Wasson
Peak. The IMPROVE site representing the West Saguaro Wilderness is
SAWE1,
located at relatively low elevation of 718 m (2,355 ft) on the gentle west
slope. The Saguaro West unit including
SAWE1 is isolated from the Tucson
urban area by the Tucson Mountains that present a barrier between them.
The eastern unit, also called the Rincon Mountain Unit, is much larger and
more mountainous, consisting of slopes of Mica Mountain that crests at 2,642
m (8,666 ft) at the eastern edge of the Wilderness. It has its western
boundary a few km from the eastern Tucson city limit. Within the Wilderness,
two ridges extend west and south from the peak of Mica Mountain. Lowest
elevations are near 900 m (3,000 ft) at the western edge of the Wilderness.
The IMPROVE site representing the East Saguaro Wilderness is SAGU1, located
at a relatively low elevation of 933 m (3,060 ft) near the base of the
mountains on the west side and very close to eastern Tucson city limits.
Unlike the west Saguaro Wilderness, the east Saguaro Wilderness including
SAGU1 is likely to be influenced by Tucson urban emissions as there are no
terrain obstructions between.
Representativeness
The two IMPROVE sites SAWE1 and SAGU1 should be quite representative of
aerosol characteristics within their respective Saguaro Wilderness units
except when contained in surface inversions that do not extend to higher
Wilderness elevations, most likely on winter nights. Note that the elevation
range between the IMPROVE site and highest Wilderness elevations is 711 m
(2,332 ft) for the west Wilderness and 1,709 m (5,606 ft) for the east
Wilderness.
Nearby Population/Industrial Centers and Local Sources
Nearby Meteorological Data Stations
Nearby meteorological monitoring network stations are shown in the data
network maps and at the RAWS
station US Climate Archive sites. The
Rincon Arizona
RAWS Site is located at an elevation of 2,512 m (8,240 ft) near the
crest of Mica Mountain and should be very representative of meteorological
conditions at higher elevations of the East Saguaro Wilderness. For lower
elevations of the Saguaro Wilderness, east and west, representative
long-term and current data is available from the
Tucson WSO AP.
The Tucson RAOB site conducts atmospheric soundings twice daily that
provides the best possible representation of upper air structure of the
area.
Wind Patterns
Wind patterns of the region are characterized by
Tucson wind roses that show
prevailing east to southeasterly wind directions, with some strong westerly
winds during the spring. There may be some orographic influence on wind
directions shown in these wind roses. The Tucson area including Saguaro
Wilderness is well within the influence of the
North American
Monsoon that typically establishes itself in early July and persists
through mid- September. During this period moisture bearing winds move into
the region from the southwest at the surface, from the Gulf of California,
and aloft from the southeast, from the Gulf of Mexico.
Locally, in the absence of strong regional pressure gradients, flows in the
eastern Saguaro Wilderness will be dominated by the upslope/downslope winds
typical of mountainous areas. Nighttime drainage flow will be towards lower
terrain away from the crest of Mica Mountain.
Potential transport routes into the Saguaro Wilderness Area include long
distance transport via upward mixing from more distant source regions and
transport into the region via upper level flow. Possible source regions
include areas to the south, southwest, and southeast, including northern
Mexico. The Tucson area and the Phoenix area about 150 km (100 mi)
northwest, with emissions typical of urban areas, are also significant
potential source regions.
Inversions/Trapping
Wang and Angell,
1999 describe two regions of the U.S. with high frequencies of regional
stagnation events in the southwest and south-central U.S. that include the
Saguaro Wilderness. According to long term data the region typically has one
to two stagnation episodes per month from May to October, where an air
stagnation episode is defined as stagnation conditions that persist for 4
days or longer. During this period, pressure and temperature gradients in
the region are weakest, and wind circulations weakest. Subsidence inversions
during these conditions may trap regional haze with buildup over periods of
several days.
The Tucson area is subject to surface-based radiation inversions especially
in the winter. During inversion episodes the SAGU1 site may be within the
inversion at times when higher elevations of the Saguaro east Wilderness are
above the inversion. The west Saguaro Wilderness IMPROVE site, SAWE1, is
separated from the Tucson area by the Tucson Mountains that may present a
barrier to urban Tucson emissions. Consequently, there may be significant
differences in aerosol characteristics between the two sites during
surface-based inversion episodes.
Climatological Statistics
Tucson Normals
Means and Extremes are representative of regional climatology at lower
elevations.
Meteorological Indicators for Local Sources
Keywords
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Last updated 17 December 2004
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