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Sequoia National Park |
(Also, see Kings Canyon
National Park Meteorological Characterization Page)
Site Name
IMPROVE:
SEQU1
CASTNET: SEK402
Region
Sierra Nevada Range
Terrain
Terrain is shown in the 2 km terrain
map and the 20 km terrain
map.
Sequoia National Park consists of 386,642 acres of the western slopes of the
southern Sierra Nevada range. Sequoia and
Kings Canyon National Parks share a long boundary and are managed as one
park, with Kings Canyon NP to the north of Sequoia NP. Elevations range from
around 500 m (1,500 ft) where westward flowing streams exit the Park on the
west side, to over 4,000 m (13,000 ft) along the Sierra Nevada crest that
forms the eastern boundary and culminates at the peak of Mt. Whitney,
elevation 4,417 m (14,491 ft). Essential topographic features include the
North, Middle, and East Forks of the Kaweah River that flow out of the Park
on the west side and the Kern River that flows southward out of the eastern
Park area. These drainages connect the Park with central and southern
portions of the San Joaquin Valley, the source for most local emissions that
affect visibility within the Park.
The IMPROVE site representing Sequoia and Kings Canyon National Parks is
SEQU1, located in the Middle Fork of the Kaweah River drainage near its exit
from the Park. At an elevation of 535 m (1,755 ft) it is about 65 m (210 ft)
above the river. There is a CASTNET
site, SEK402, with meteorological monitoring, located at elevation 1,225 m
(4,018 ft) in the lower East Fork of the Kaweah River, also near the western
Park boundary and about 15 km (10 mi) south of SEQU1 across the ridge that
separates the two forks.
Representativeness
SEQU1 is situated near the bottom of one of the valleys that drain the Park
on the west side, and is at the very lowest end of elevation ranges within
the Park. It is well located for observing San Joaquin Valley emissions at
the Parks western boundary, and emissions from more local sources, and may
represent highest aerosol concentrations and most severe visibility impacts
within Park boundaries. During inversion conditions it may not be as
representative of aerosol concentration and composition at higher Park
elevations that could be impacted by emissions from more distant source
regions on a synoptic to global scale
Nearby Population/Industrial Centers and Local Sources
Kaweah River drainages open up into the central San Joaquin Valley near the
cities of Fresno and Visalia 50 km (30 mi) west of SEQU1 and the western
Park boundary. Lower Park elevations below 1,000 m (3,000 ft) are
susceptible to Valley emissions mixed upwards to this height on typical
summer afternoons.
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
Milk Ranch
California RAWS site is located near the ridge top southeast of SEQU1 at
an elevation of 1,898 m (6,225 ft) and may provide useful data on mesoscale
winds concurrent with SEQU1 aerosol monitoring. The Sequoia NP
CASTNET site, SEK402, is located
near the East Fork of the Kaweah River. Although it is not collocated with
SEQU1 it may provide hourly wind data that can be used to correlate SEQU1
data with the timing of upslope/drainage flow. It is 690 m (2,263 ft) higher
in elevation. Sequoia National Park wind roses (attached jpg files with
prefix SEK) from 5 years of data collected at SEK402 show the pronounced
seasonal and diurnal channeling pattern.
Upper air data is collected twice daily at the Oakland RAOB site.
Wind Patterns
Synoptic winds are influenced by the orientation of the San Joaquin Valley
and at the mesoscale are generally northwesterly (from the northwest), with
a high frequency of southeast winds in the winter. This pattern is evident
in monthly Fresno California Wind Roses. Locally and in the absence of synoptic forcing, winds at the SEQU1 site
should have a bimodal pattern as a result of steering by the Middle Fork of
the Kaweah valley including a significant diurnal mountain/valley component,
with easterly (from the east) nighttime drainage flow and westerly daytime
upslope flow from the direction of Fresno and Visalia in the San Joaquin
Valley. This pattern is evident in Sequoia National Park wind roses from the Sequoia NP
CASTNET site, SEK402, located at a
similar location close to the East Fork of the Kaweah River, the next
drainage to the south. Upslope/downslope flow could transport San Joaquin
Valley air to the IMPROVE site during the afternoon and evening, with return
flow at night and early morning.
Potential local transport routes into Sequoia National Park include San
Joaquin Valley emissions transported directly via diurnal upslope/downslope
flow, mixed upwards with afternoon mixing, or trapped regionally under a
persistent subsidence inversion. Transport corridors for San Joaquin Valley
emissions are primarily the Kaweah River from the direction of Fresno and
Visalia into western Park regions and the Kern River from the direction of
Bakersfield to the south into eastern Park regions. Synoptic westerly flow
could also cause transport into the National Park, including into higher
elevations near the crest of the Sierra Nevada range. During infrequent east
wind conditions, with high pressure over the Great Basin and low pressure
off the California Coast, emissions from Owens Valley and Owens Lake east of
the Sierra Nevada crest may be mixed upwards and impact highest elevations
on the west side of the National Park. At times this may spill over into
headwater areas west of the Sierra Nevada crest, though probably not
discernible at the SEQU1 monitoring site.
Inversions/Trapping
The upper Kern River valley in eastern Sequoia NP may be subject to surface
inversions and trapping of pollutants during periods of regional high
pressure and stagnation, especially in the winter. Wintertime surface based
inversions are also common in the San Joaquin Valley, although at heights
typically below National Park elevations. In the summer, the relatively
shallow nighttime San Joaquin Valley boundary layer is generally mixed to
heights of at least 1,000 m (> 3,000 ft) above the ground on a typical
summer day. This can result in valley emissions being mixed upwards to Park
locations. Summer inversions are usually larger scale subsidence inversions
associated with the establishment of the semi-permanent Pacific
high-pressure system and can result in aerosol buildup over periods of days.
Subsidence inversion heights are typically at elevations of 2,000 to 3,000 m
(6,000 to 10,000 ft). Both types of inversions, surface radiation and
elevated subsidence, can occur during the fall.
Climatological Statistics
Fresno
California Normals Means and Extremes are representative of climate
characteristics in San Joaquin Valley. Climate data from the Sequoia NP
CASTNET site, SEK402, and from the
Milk Ranch
California RAWS site are representative of lower Park elevations on the
west side. Other
Northern 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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