Investigator’s Annual Reports (IAR’s) for Crater Lake National Park

Spatial, Temporal and Depth Distribution of Snow Properties in the Crater Lake Snowpack

 

Report Number: 33788

Permit Number: CRLA-2005-SCI-0001

Current Status: Checked in

Date Received: Dec 28, 2005

Reporting Year: 2005

Principal Investigator: Ms Lora Koenig, University of Washington, Department of Earth and Space Sciences, Seattle, WA

Additional investigator(s): Julia C. Jarvis

Park-assigned Study Id. # CRLA-00004

Permit Expiration Date: Jun 30, 2005

Permit Start Date: Jan 01, 2005

Study Starting Date: Jan 01, 2005

Study Ending Date: Jun 30, 2005

Study Status: Completed

Activity Type: Research

Subject/Discipline: Glaciers

Objectives: There are three main purposes of this study:

a) to investigate the changes of snow’s thermal conductivity with depth

b) to create a highly spatially sampled snow grain size dataset

c) to create an in-situ dataset that can be used with a variety of space-borne sensors

d) to determine the temporal variability of nitrate (NO3-) isotopes in snow at Crater Lake

e) to test field methods for later use in Antarctica

General Purpose:

Remote sensing of snow properties is the future of snow science. Satellites have the ability to determine spatially distributed snow properties on a daily basis in inhospitable areas (Dozier and Painter, 2004). However there is a dearth of in-situ measurements collected specifically for satellite ground tracks. This research will begin to fill in this void of information by collecting a spatial and depth distributed ground dataset for sensor calibration. This dataset will include depth dependent information on thermal conductivity and snow grain size. This depth component is important for satellite sensors, such as passive microwave sensors, that record emission some distance into the snow. The deep snow pack at Crater Lake National Park is an ideal location for studying changes in snow parameters with depth.

A specific focus on the changes in thermal conductivity in snow will elucidate how snow properties affect a new model developed by Winebrenner (et al., 2004). Winebrenner developed a new relationship between microwave brightness temperatures and physical surface temperature over Antarctica. This relationship depends on a characteristic time scale of emission, which is defined as the inverse of the microwave extinction coefficient and the thermal diffusivity of snow. Using this relationship Koenig (et al., 2004) showed that the characteristic time scale of emission co-varied with accumulation rate near Byrd Station, Antarctica. In order to understand why the characteristic time scale co-varies with accumulation rate more needs to be known about the changes in thermal conductivity, an unknown variable in thermal diffusion. Sturm (et al., 1997) has summarized work to date on thermal conductivity of seasonal snow. This work neglects changes in thermal conductivity with depth. The investigators want to use the deep Crater Lake snow pack to look at depth dependent thermal conductivity profiles. The study will also allow for testing of field techniques that will eventually be conducted in Antarctica.

Snow grain size scatters microwave emissions and can affect the extinction coefficient. Multiple space-borne sensors are being used to estimate snow grain size (Painter et al., 2003). Collecting grain size data will allow investigators to evaluate current grain size retrieval methods and analyze their applicability in Antarctica. The relationship between grain size and thermal conductivity will also be studied.

In addition to the snow properties study, snow samples will also be collected to determine the temporal variability of nitrate (NO3-) isotopes in snow at Crater Lake. Nitrate deposition in snow and rainwater is the dominant sink for nitrogen oxides (NOx = NO + NO2) in the atmosphere, the sources of which include fossil fuel combustion, biomass burning, soil emissions, and lightning. Previous studies suggest that nitrate isotopes may contain information as to the sources of NOx to a region (e.g. Hastings et al., 2003). Collection of fresh snow at Crater Lake, where heavy snowfall likely removes all of the atmospheric nitrate and nitric acid in the region, and subsequent isotopic analysis of nitrate will add spatial variability to prior studies of nitrate in snow from Greenland and Antarctica (Hastings et al., 2004; Jarvis et al., unpublished data).

Findings and Status:  The 2004-2005 winter snowpack at Crater Lake National Park was used to study spatial and depth dependent changes in snow thermal conductivity. This research was used to test equipment and methodology to be used in 2006 on the Greenland and Antarctic ice sheets. Over large portions of the Antarctic ice sheet a link has been established between passive microwave emission, accumulation rate and thermal conductivity (Koenig et al., in prep). The link to accumulation rate, which influences sea level change, motivates studies of thermal conductivity changes over space and with depth.

Eleven snow pits were dug within skiing distance of the plowed road connecting Crater Lake lodge to Oregon Highway 62. The following methodology was used for all snow pits. The pits were sampled every 10 cm for snow thermal conductivity, density, grain size, hardness, temperature and crystal type. Thermal conductivity was measured directly in the snowpack using a transient-state probe (Jackson and Taylor, 1986). The probe heats the snow and then measures the cooling curve to obtain a thermal conductivity measurement. In order to take a thermal conductivity measurement the snowpack must be below -3 degrees Celsius to prevent a phase change during the heating cycle. Temperature was measured with a dial thermometer. Density was measured with a 1000 cc density cutter. A hand hardness test was used to measure the grain bonding and the crystal type was recorded using the International Classification for Seasonal Snow on the Ground (Colbeck et al., 1990).

In total 77 good thermal conductivity measurements were obtained. According to a published review article by Sturm et al. (1997), the 77 thermal conductivity measurements from Crater Lake National Park comprise the second largest thermal conductivity dataset from a specific location. Preliminary results show that that there was no significant change in thermal conductivity with depth or space. The spatial result was expected because to the homogeneous nature of the Cascade snowpack. The mean thermal conductivity of all measurements was .161 W/m K, the minimum .047 W/m K, the maximum .392 W/ m K and the standard deviation was .07. The mean thermal conductivity of 842 previous published measurements in seasonal snow is .215 W/m K; the mean thermal conductivity of the snowpack at Crater Lake, .161 W/m K, is less than the previous measurements (Sturm et al., 1997). The mean density of the snowpack was 296 Kg/m3. The majority of the snow crystals were well rounded with a grain size larger than .5 mm.

Sterile snow samples were taken directly after and during snow storms to sample for nitrate concentrations. Approximately 10 samples were taken during the Crater Lake field season. These samples are waiting to be processed in the lab and results are expected by the end of 2006.

For this study, were one or more specimens collected and removed from the park but not destroyed during analyses? No

Funding provided this reporting year by NPS: 0

Funding provided this reporting year by other sources: 500

Full name of college or university:  n/a

Annual funding provided by NPS to university or college this reporting year: 0

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