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 dependant 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variability to prior studies of nitrate in snow from Greenland and Antarctica (Hastings et al., 2004; Jarvis et al., unpublished data).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 dependant 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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