| |
Denali National Park |
Site Name
IMPROVE:
DENA1 (Denali National Park)
CASTNET: DEN417
Region
Alaska Continental (Interior Region)
Terrain
Terrain in the area is depicted in detailed 20 km terrain map and 2 km
terrain map.
Denali National Park occupies just
over six million acres in the central interior of Alaska, removed from
oceanic influence. Terrain includes a vast plain in the north with
elevations of 250 m (800 ft) or less, and rugged mountains separating broad
river valleys in the south and east. The highest Park elevation is 6,195 m
(20,320 ft) at the summit of Mt. McKinley, part of the Alaska Range that
dominates the southern area of the Park.
The Denali National Park Improve site is DENA1, located at an elevation of
658 m (2,159 ft) near Hines Creek, some 125 km (78 mi) northwest from the
summit of Mount McKinley near the northeastern Park boundary. Surrounding
terrain is complex, but is generally a broad valley. Hines Creek drains into
the north-flowing Nenana River 1 to 2 miles east of the DENA1. To the west
of DENA1, elevation rises slightly, then drops gently into a broad valley
with drainages to the north. The immediate area is bounded on the north by
an east-west ridge with elevations near 1,500 m, some 800 m (2,500 to 2,600
ft) above the monitoring site. The Denali
CASTNET site DEN417 is within ½ km
and southwest of DENA1.
Ground cover near the site is forest.
Representativeness
DENA1 should be representative of haze conditions in Denali National Park
and in this remote region generally. It is near the bottom of the Hines and
Nenana River valleys that may be subject to surface inversions in the colder
months. Because of the vast area and wide range of Park elevations it may
also at specific times be decoupled from air at specific Park locations.
Nearby Population/Industrial Centers
The monitoring site is near the Park Headquarters complex (near water tank).
The small community of Healy is located some 15 km (9 miles) north via
Alaska Highway 3 along the Nenana River. The nearest major population area
is Fairbanks, 135 km (~85 mi) northeast. Highest aerosol concentrations at
DENA1 may occur in the spring as a result of regional wild and prescribed
vegetative burning or from Asian dust transported into the region. In any
case, Denali NP is one of the most pristine Class I areas.
Nearby Data Stations
This map shows the location of the
nearest air quality and meteorological monitoring sites, with respect to the
DENA1 IMPROVE site. The Denali National Park
CASTNET site DEN417 is close to
DENA1 and should provide the best representation of meteorological
conditions concurrent with aerosol monitoring. Another
CASTNET site, POF425, is located
at Poker Flats in the Yukon NM, 175 km north-northwest of DENA1 and
northwest of Fairbanks. The nearest RAWS site (97 km west of DENA1) is the
Wonder Lake
Alaska RAWS site established in July 1995. The closest (135 km northeast
from DENA1) long-term NWS meteorological monitoring station is the
Fairbanks Alaska NWSFO which is also the
nearest upper air sounding site.
Wind Patterns
On a global scale, Denali NP is near the northern edge of the zone of
midlatitude westerly flow, though at times in the spring it may be
influenced by polar easterlies and associated Arctic Haze incursions.
Probably more importantly with respect to visibility reducing pollutants,
there are times, especially in the spring, when the Pacific High over the
eastern Pacific Ocean intensifies and creates a ridge that diverts
midlatitude westerly flow from Asia towards Alaska. This can result in
transport of Asian dust to Alaska. Towards the end of summer, this ridge
weakens and midlatitude flow becomes more zonal (westerly). Winds in the
region are generally calm to light with seasonal storm outbreaks that bring
high winds and precipitation. Several times each winter, strong winds top
the Alaska Range from the south and raise temperatures in the Interior. Dry
chinook winds can raise temperatures to as high as 50 degrees above zero in
the dead of winter
Locally, DENA1 is situated in east-west elongated valley, and mountain
valley winds can affect local flow.
Denali National Park wind roses based on 1998-2001 data from the Denali
National Park CASTNET site DEN417
show local patterns. Annually, prevailing directions are northerly and
southerly, possibly linked to channeled flow in the Nenana River valley that
is oriented north to south just west of DENA1 although long term Fairbanks
Alaska wind roses (link to Fairbanks wind roses archived) show a similar
pattern. The highest frequency of southerly flow occurs in the spring and
may be associated with diverted synoptic westerly flow described above. At
this latitude the seasonal variation in solar insolation and surface heating
is much greater than at more southerly latitudes of the contiguous U.S.
There is still an evident diurnal flow pattern on an annual basis, with
nighttime flow off the mountain slopes to the north that border the Hines
Creek drainage. During the day the flow is predominantly southerly.
Inversions/Trapping
The valleys of the Hines and Nenana Rivers in the vicinity of DENA1 exit
through a narrow channel to the north and the area may be subject to
inversion and trapping of local pollutants, especially from September to May
when solar heating is least. In those cases, the monitoring site, located at
the bottom of the valley, would probably be contained within the trapped
stable layer.
Meteorological Indicators
Keywords
|
Last updated 22 September 2004
|