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Solid Precipitation Instrumentation, Monitoring and Evaluation in the USDANRCS and the USA CRREL

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Title: Solid Precipitation Instrumentation, Monitoring and Evaluation in the USDANRCS and the USA CRREL


1
Solid Precipitation Instrumentation, Monitoring
and Evaluation in the USDA-NRCS and the USA CRREL
Greg Johnson and Garry Schaefer, USDA-NRCS
National Water and Climate Center, Portland
Oregon Rick McClure, USDA-NRCS, Alaska State
Office, Anchorage, Alaska Jerome Johnson, USA
CRREL, Fort Wainwright, Alaska
Solid Precipitation Measurement in Alaska Shown
below are locations of the 15 Wyoming shielded
precipitation gauges in Alaska. Of the 15, 6 are
telemetered through SNOTEL (SNOw TELemetry), 6
are on automated site recorders and 3 are read
monthly. The 6 SNOTEL sites sending hourly data,
available on the web site ambcs.org, are Atigun
Pass, Imnaviat Creek, Gobbler's Knob, Eagle
Summit, Rocky Point, and Pargon Creek. The 6
automated sites are Nuka Glacier, Middle Fork
Bradley, Rhoads Creek, Sagwon, Barrow, and Red
Dog. Red Dog data are collected by John
Martinisko of Teckcominco Corporation (formerly
Cominco Alaska), through which monthly data are
published. New Barrow gauge data are collected
by Daqing Yang, Water and Environmental Research
Center, UAF. The three sites read monthly are
Chandalar Camp, Atigun Camp and Prudhoe Bay.
Atigun Pass, Atigun Camp, Chandalar Camp, Sagwon,
Barrow, Prudhoe Bay, and Imnaviat Creek (formerly
Toolik River) are sites with records back to the
late 1970s. They were initially installed
through a cooperative effort with the UAF
Geophysical Institute, CRREL, BLM, USGS and NRCS
(formerly SCS).
NRCS SNOTEL Climate Monitoring Network, and
Manual Snow Courses The SNOTEL (SNOwpack
TELemetry) network is a collection of automated
climate stations in the western U.S. and Alaska,
and is managed by the U.S. Department of
Agricultures Natural Resources Conservation
Service (NRCS). SNOTEL began operation in the
late 1970s with the objective of providing near
real-time snowpack information, and to automate
many of the manually collected snow measurements,
under the older Manual Snow Course network (see
below). SNOTEL uses meteor burst communication
technology to transmit locally collected data to
the National Water and Climate Center (NWCC)
central computer system in Portland, who then
distribute the data. SNOTEL collects, at a
minimum, daily SWE, accumulated water year
precipitation, current, maximum, minimum, and
average daily air temperature at all sites. SWE
is estimated using snow pillow technology, and
precipitation is measured with an all-season
(rocket) precipitation gauge. About 15 of the
SNOTEL system have additional sensors, measuring
wind speed and direction, soil moisture and soil
temperature, and other elements. 200 of the 665
operational SNOTEL stations have nearly 25 years
of record at present. Daily time increment
SNOTEL data are fairly thoroughly quality
controlled, while hourly data receive a much
lower level of quality control at present.
Approximately 50 of the total potential metadata
for all SNOTEL stations has been digitized and
can be made available upon request. Details of
station moves, instrumentation changes, detailed
location information, and other metadata are less
likely to be availableat least not in a readily
available format. The manual network of snow
courses consist of approximately 1205 locations,
also in the western U.S. and including Alaska.
Some snow courses have more than 90 years of
record, and many have at least 30 years. The
manual snow course network is a transect that is
made up of 5 to 50 measurement points that are
measured using a federal snow sampler. The
distance between each sample point is consistent
with most being five to fifty feet apart. Most
manual snow courses have 5 to 10 sample points.
Manual snow courses are typically measured on a
monthly basis from January through May. Snow
depth, water content, and snow density are
averaged for each snow course. Nearly 900
additional snow courses have from 1 to 60 years
of historical record but have now been
discontinued. Of the 1205 operational courses,
approximately 50 of the available metadata has
been digitized and can be made available to those
requesting information.
Wind Shield Precipitation Gauge Comparison Tests
at Barrow, AK A study of the windshield
alternatives, at a staffed location, under the
unique conditions of Alaska's Arctic coastal
region has been conducted since August of 1989 at
the Barrow(BRW) National Weather Service office
to answer the following questions. Will the
Canadian standard Nipher shield operate under
these conditions? What will be the comparison of
the Nipher shield record against the longer-term
records of the unshielded and Wyoming shielded
gauges? What is the significance of rime and its
effect on the various windshields? The snowfall
catch/snow water equivalent from five storage
precipitation gauges were compared for the first
several years, three shielded and two unshielded
1) Wyoming shielded 2) Nipher shielded 3) Alter
shielded 4) unshielded and serviced on an event
basis, the same as the three shielded gauges and
5) unshielded but treated as if it were a remote
gauge, allowing rime to build up and dissipate
naturally to see what effects it has on the
overall catch. All storage cylinders are 20.3 cm
diameter x 100 cm tall, mounted with the orifice
2 m above the normal ground surface. The Wyoming
shielded gauge had a blockage in the plumbing the
1991-92 year and the shield was blown over in a
unique wind event in August of 1994 and not
rebuilt. Measurements are for total
precipitation in the October 1 to June 1 period
each year. Results For the 3 years with the
Wyoming shield the Nipher catch averaged 92 of
the Wyoming, ranging from 69 to 106. The Alter
shield catch ranged from 37 to 68 of the Nipher,
with an average of 53. There was no significant
difference between the unshielded maintained and
unmaintained gauges--both caught between 10 to 36
percent of the Nipher shield, and both averaged
27. Gauge riming did seem to affect catch at
certain times in the unmaintained gauge, but had
no affect in long-term averages. The 13 year
average Nipher gauge total precipitation, Oct. 1
to June 1 at Barrow is 7.99 mm (3.15
in.). Acknowledgement. Appreciation is
expressed to Dan Endress, Station Chief, BRW, who
has serviced the precipitation gauges and
collected the data for this study.
Map of SNOTEL stations in the 11 states in the
continental Western U.S., and a typical SNOTEL
site configuration
Electronic Snow Water Equivalent Pressure Sensor
Development
Since 1997, the NRCS and the Armys Cold Regions
Research and Engineering Lab (CRREL) have
conducted a collaborative effort to develop an
electronic Snow Water Equivalent (SWE) pressure
sensor to replace fluid-filled sensors. The
primary source of error has been identified as a
thermal incompatibility between the SWE pressure
sensor and the soil around the sensor. By
modifying the SWE pressure sensor design to
reduce thermal incompatibilities three electronic
sensors have been produced that accurately
measure SWE during the winter. SWE measurement
errors do occur during the winter/spring
transition period due to the different time of
arrival for the 0 C isotherm over the soil and
sensor (please see graphs to the right), but
improve after this transition (Johnson, this
conference). Currently, the CRREL is modifying
and testing the electronic SWE sensor to
eliminate these winter to spring transition
errors. (Left) SWE pressure sensor B is 1 m
square and sensor C is 0.55 m square. They are
water permeable to allow soil wetting under the
sensors and more uniform thermal conditions with
the surrounding soil. (Right) Graphs of SWE
measurements for sensor A (a), sensor B (b), and
sensor C (C) for the 2001/2002 winter at the
Reynolds Mountain Snowpillow Test Site (2070 m
elevation at the USDA-ARS Reynolds Creek
Experimental Watershed in the Owyhee Mountains of
southwest Idaho). SWE pressure sensor A (not
shown) is a 1 m diameter sensor with a 0.46 m
center plate that is load sensitive. The sensor
annulus is inert and is designed to accommodate
sensor edge effects. The sensor was installed
under 5 cm of soil covered by a 3 m square
plastic sheet.
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