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Cucamonga Wilderness Area |
(also, see San Gabriel
Wilderness Area)
Site Name
IMPROVE:
SAGA1 (San Gabriel Wilderness Area)
Region
Southern California Ranges
Terrain
Terrain is shown in the 2 km terrain
map and the 20 km terrain
map.
The Cucamonga Wilderness Area occupies 12,981 acres on the eastern end of
the San Gabriel Mountains, one of the Transverse Ranges that lie along an
east-west axis from the Santa Barbara coast to the Mojave Desert creating a
natural barrier between central and southern California. Wilderness
elevations range from about 1,300 m (4,300 ft) to 2,500 m (8,200 ft), with
highest elevations at the crests of Telegraph Peak (2,739 m, 8,984 ft) and
Cucamonga Peak (2,701 m, 8,859 ft). Cucamonga and Deer Canyons drop south
from Cucamonga Peak to the southern Wilderness boundary, thence south 8 to
10 km (4 to 6 mi) into the Los Angeles basin near the cities of Pomona,
Ontario, and Rancho Cucamonga, forming the most direct route for low
elevation urban pollution transport into the Wilderness.
The IMPROVE site representing the Cucamonga Wilderness is SAGA1 (San Gabriel
Wilderness), is located just outside the western boundary of the San Gabriel
Wilderness and ~ 35 km (20 mi) west of the Cucamonga Wilderness, with
mountainous intervening terrain. It is a well-exposed ridge-top site at an
elevation of 1,701 m (5,874 ft), near the lower end of the range of
elevations within the Cucamonga Wilderness.
Also see San Gabriel Wilderness Area.
Representativeness
The SAGA1 IMPROVE is separated from the Cucamonga Wilderness by ~ 35 km (20
mi) of intervening complex mountainous terrain. It should be representative
of aerosol composition and concentration at Cucamonga Wilderness locations
when the atmosphere is well mixed and haze is uniform over the region. It
should also be representative of the impact of Los Angeles basin emissions
on the San Gabriel Mountains generally. Lowest Wilderness elevations are
probably above the regional marine layer that frequently overlies over the
Los Angeles basin and that typically thickens and advances inland during the
night and early morning hours, before burning off around midday. It will be
less representative of Cucamonga Wilderness locations when impacted by local
sources.
Also see San Gabriel Wilderness Area.
Nearby Population/Industrial Centers and Local Sources
The Cucamonga Wilderness is within 10 km of the sprawling and heavily
populated and industrialized South Coast Air Basin and is very subject to
its influence. Nearest Los Angeles area communities are Pomona, Ontario, and
Rancho Cucamonga.
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. There are numerous RAWS and other
network sites shown in the data network map although none of them are
strictly within Cucamonga Wilderness Area boundaries. The nearest RAWS site
at an elevation representative of the relatively high Cucamonga Wilderness
elevations is the
Sunset
California RAWS site, elevation 1,693 m (5,553 ft). The
Mt. Wilson No. 2
California COOP site, elevation 1,741 m (5,710 ft) has long-term data
from a well-exposed regionally representative site for higher elevations.
There are also numerous meteorological monitoring sites in the Los Angeles
basin that should provide data that is regionally representative for lower
elevations, including
Ontario
International Airport SAO about 15 km (10 mi) within the Los Angeles
basin at an elevation of 248 m (944 ft).
The Cucamonga Wilderness Area is roughly midway between the San
Diego/Miramar and Vandenburg AFB RAOB sites in southern California both of
which conduct atmospheric soundings twice daily. Data from these sites is
regionally representative for upper air structure.
Wind Patterns
Overall, the prevailing wind direction in the region around the Cucamonga
Wilderness is south to southwesterly. This is evident in
Los Angeles wind
roses. There are seasonal phenomena
that modify this overall pattern. In the summer a thermal low develops over
the Mohave Desert. During the winter, higher pressure over the Mohave Desert
results in winds blowing from the desert towards the California south coast.
Locally and in the absence of synoptic forcing, wind patterns in the
Cucamonga Wilderness should be characteristic of mountain/valley upslope/downslope
circulation. Within the Cucamonga Canyon that exits into the LA basin near
Rancho Cucamonga, upslope flow will be from the basin towards the
Wilderness, with the potential for transporting urban aerosols into the
Wilderness. Nighttime downslope will be the reverse. Note that transport due
to such local canyon winds may not be manifested in observations at the
SAGA1 IMPROVE site.
Potential local transport routes into the Wilderness include Los Angeles
Basin emissions transported directly via upslope winds, mixed upwards with
afternoon mixing, or trapped regionally under a persistent subsidence
inversion. There is also a potential for particulate matter associated with
regional and local wildland fires common in the region.
Also, see San Gabriel Wilderness Area
Inversions/Trapping
San Gabriel Wilderness valleys are subject to inversion and trapping of
pollutants during periods of high pressure and stagnation over southern
California. Under some conditions there may be a diurnal pattern to
extinction in the Wilderness, when afternoon vertical upward mixing results
in pollutants being transported into the Wilderness, followed by return
drainage transport at night and decrease in light extinction. A diurnal
pattern could also occur in conjunction with the daily advent of the marine
layer, which typically thickens and advances over the Los Angeles basin
during the night and early morning hours, before retreating to the sea or
"burning off" to hazy sunshine around midday. Such a pattern could persist
until the region is scoured of visibility degrading particulate matter by
synoptic events. Most likely to occur during summer, when strong surface
heating results in afternoon upward mixing to valley elevations. This
phenomenon may not always be seen in data from the SAGA1 IMPROVE site
located near a ridge crest some 35 km (20 mi) to the west.
Wang and Angell,
1999 describe a region of the U.S. with high frequency of regional
stagnation events centered over the southern California Mojave Desert.
According to long term data the region typically has two or more 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. These
buildup periods should be evident in data from the SAGO1 IMPROVE site.
Climatological Statistics
The Mt. Wilson
No. 2 California COOP site, elevation 1,741 m (5,710 ft) has long-term
data from a well-exposed regionally representative site for higher
elevations. Data from the
Pasadena
California COOP site is representative of lower elevation locations
within the LA basin. These and other
Southern California
Climate Summaries are available from the
Western Regional Climate Center.
Keywords
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Last updated 13 November 2004
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