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Pinnacles Wilderness Area |
Site Name
IMPROVE:
PINN1
CASTNET: PIN414
Region
California Coast Ranges
Terrain
Terrain is shown in the 2 km terrain
map and
the 20 km terrain
map.
The Pinnacles Wilderness Area comprises 12,952 acres within the
Pinnacles National
Monument, located in the southern portion of the Gabilan Mountains of
central California, one of a series of parallel northwest-southeast ridges
that make up the Central Coast Range. Within the National Monument,
elevations range from 251 m (824 ft) along South Chalone Creek to 1007 m
(3,304 ft) at North Chalone Peak. Much of the terrain is rolling hills. It
is about 65 km (40 mi) inland from the Pacific Ocean, with the Santa Lucia
Mountains between which modifies the Ocean’s influence. The Gabilan range is
bounded on the west by the Salinas Valley that provides a conduit to the
Pacific coast near Monterey, a distance of 60 km (40 mi) east, and on the
east by the San Benito Valley that is a southern extension of the Santa
Clara valley at the southern end of the San Francisco Bay area 100 km (60
mi) to the north and that provides a corridor thereto.
The IMPROVE site representing the Pinnacles Wilderness is PINN1, located in
the Chalone Creek drainage near the eastern Monument boundary at an
elevation of 317 m (1,038 ft). This is very near the lower end of Wilderness
elevations and some 600 m (2,000 ft) lower than the highest Wilderness
elevation. The Pinnacles
CASTNET site PINN414 is also located here.
Representativeness
The PINN1 IMPROVE site is probably quite representative of Pinnacles WA
locations in general, although it is in the Chalone Creek drainage at a
relatively low elevation with respect to most of the Wilderness. It may be
isolated from higher Wilderness elevations if separated by being below the
base of a summertime subsidence inversion that contains higher Wilderness
elevations, or by being within a low-level wintertime inversion that does
not extend to higher Wilderness elevations. These are probably relatively
infrequent conditions, given the modest range of Wilderness elevations that
extend about 750 m (2,500 ft) vertically.
Nearby Population/Industrial Centers and Local Sources
The Pinnacles WA is potentially influenced by three California source
regions: the San Francisco Bay area, to which it is linked via a transport
corridor from the south Bay through Hollister, the San Joaquin Valley of
central California to the east, and the Monterey Bay area to the west via
Salinas Valley. Aerosol concentrations in Pinnacles NM may be most closely
linked to Bay Area emissions during episodic conditions that lead to aerosol
accumulations.
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. The best site for relating aerosol data to
local meteorology is the
CASTNET site PIN414, at the same location. Wind directions at PIN414 may
not be regionally representative of transport flow however, since there is
evidence of local terrain effects in
Pinnacles wind roses. The
Pinnacles
California RAWS site is within Wilderness boundaries at an
elevation of 403 m (1,322 ft). Data from numerous other sites in the region
are available from the Western Regional
Climate Center. Data from Hollister California may be of particular
usefulness in relating Wilderness aerosol concentrations to transport flow
from the Bay Area, as discussed in Wind and Flow Patterns.
Twice daily upper air data is collected at the Vandenburg AFB RAOB site on
the coast ~ 150 to 200 km (100 to 120 mi) south of Pinnacles WA.
There is a current project to collect meteorological data at well-exposed
near-ridge crest locations in the Pinnacles area that includes hourly wind
data for analysis of wind and transport patterns. The program began in 1997
and is ongoing. More information on this program is available from
Pinnacles National
Monument.
Wind and Flow Patterns
Regional winds are generally from the north or northwest throughout the
year, a consequence of the semi-permanent high pressure that lies off the
Pacific Coast. Southerly and easterly winds occur during the winter,
especially in the morning. Upper-level winds from the south and east are
infrequent during the summer. This pattern is indicated in monthly
Santa
Maria Wind Roses, from Santa Maria
located on the coast ~ 180 km (110 mi) to the south. There are local and
seasonal phenomena that modify this overall pattern, resulting in transport
flow scenarios indicated from air pollution studies of the central
California coast and interior.
Sea breezes entering the interior from the San Francisco and Monterey Bay
areas may augment transport flow from these areas into the Pinnacles
Wilderness Area. Transport flow from the Bay Area may by enhanced by a weak
Bay Area sea breeze that flows southward through the south Bay and into the
Pinnacles area via Hollister and the San Benito River valley, an extension
of the Santa Clara Valley. This could show up as a diurnal effect as
emissions from the Bay Area during the day arrive at Pinnacles in the
evening. The daily sea breeze from the Monterey Bay area could also reach
the Pinnacles WA on the west side via the Salinas Valley, with the potential
for transporting Monterey Bay area emissions directly. This would be
manifested in the Pinnacles area by increased maritime components such as
sea salt.
In the summertime, thermal lows at the north and south ends of the San
Joaquin Valley result in airflow from the Bay area through the Carquinez
Straits into the San Joaquin Valley towards Sacramento, thence in a
bifurcated flow north and south into the ends of the San Joaquin Valley.
Commingled Bay Area and San Joaquin Valley emissions may then impinge on the
Pinnacles area through a so-called “back door” effect as they flow down the
back (east) side of the east bay hills and turn back westwards through
Pacheco Pass. Easterly flow may also carry San Joaquin Valley emissions
directly into the Pinnacles area from the southern San Joaquin Valley during
infrequent conditions when a east to west pressure gradient is present, as
can occur with low pressure aloft off the coast and/or interior high
pressure over the Great Basin.
In the immediate vicinity of the PINN1 IMPROVE site, wind patterns are
probably upslope/downslope winds, or channeled synoptic flow, steered by the
Chalone Creek drainage as indicated in seasonal and diurnal
Pinnacles wind roses, nighttime
downslope flow being from north to south and upslope daytime flow south to
north.
In addition to the transport scenarios described above, there may be impacts
in the Pinnacles area resulting from prescribed and wildfires locally.
Inversions/Trapping
The Pinnacles WA and National Monument are in a valley complex, and there
may be surface based radiation inversions typical of mountains and valleys
especially in the wintertime. In the extended summer months, May to October,
the more common inversion is a subsidence inversion associated with regional
stagnation. Summertime subsidence inversions in the region typically have
bases near 300 m (1,000 ft), near the lower range of Wilderness elevations,
with tops near 1,000 to 1,500 m (3,000 to 4,000 ft). Aerosols could be
trapped within either of these types of inversions, although the summer
condition is most likely to lead to significant buildups of aerosol
concentrations.
Climatological Statistics
Pinnacles NM
Climate Data should be representative of climate conditions within the
Pinnacles WA. More detailed information, including diurnal patterns of
temperature and humidity, are available at the
Pinnacles
California RAWS site.
Keywords
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Last updated 13 November 2004
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