Time filter

Source Type

Silverton, CO, United States

Chen Y.,Columbia University | Naud C.M.,Columbia University | Rangwala I.,University of Colorado at Boulder | Rangwala I.,National Oceanic and Atmospheric Administration | And 2 more authors.
Environmental Research Letters

Among the potential reasons for enhanced warming rates in many high elevation regions is the nonlinear relationship between surface downward longwave radiation (DLR) and specific humidity (q). In this study we use ground-based observations at two neighboring high elevation sites in Southwestern Colorado that have different local topography and are 1.3 km apart horizontally and 348 m vertically. We examine the spatial consistency of the sensitivities (partial derivatives) of DLR with respect to changes in q, and the sensitivities are obtained from the Jacobian matrix of a neural network analysis. Although the relationship between DLR and q is the same at both sites, the sensitivities are higher when q is smaller, which occurs more frequently at the higher elevation site. There is a distinct hourly distribution in the sensitivities at both sites especially for high sensitivity cases, although the range is greater at the lower elevation site. The hourly distribution of the sensitivities relates to that of q. Under clear skies during daytime, q is similar between the two sites, however under cloudy skies or at night, it is not. This means that the DLR-q sensitivities are similar at the two sites during daytime but not at night, and care must be exercised when using data from one site to infer the impact of water vapor feedbacks at another site, particularly at night. Our analysis suggests that care should be exercised when using the lapse rate adjustment to infill high frequency data in a complex topographical region, particularly when one of the stations is subject to cold air pooling as found here. © 2014 IOP Publishing Ltd. Source

Skiles S.M.,University of California at Los Angeles | Painter T.H.,University of California at Los Angeles | Painter T.H.,Jet Propulsion Laboratory | Deems J.S.,National Snow and Ice Data Center | And 3 more authors.
Water Resources Research

Here we present the radiative and snowmelt impacts of dust deposition to snow cover using a 6-year energy balance record (2005-2010) at alpine and subalpine micrometeorological towers in the Senator Beck Basin Study Area (SBBSA) in southwestern Colorado, USA. These results follow from the measurements described in part I. We simulate the evolution of snow water equivalent at each station under scenarios of observed and dust-free conditions, and +2°C and +4°C melt-season temperature perturbations to these scenarios. Over the 6 years of record, daily mean dust radiative forcing ranged from 0 to 214 W m-2, with hourly peaks up to 409 W m-2. Mean springtime dust radiative forcings across the period ranged from 31 to 49 W m-2 at the alpine site and 45 to 75 W m-2 at the subalpine site, in turn shortening snow cover duration by 21 to 51 days. The dust-advanced loss of snow cover (days) is linearly related to total dust concentration at the end of snow cover, despite temporal variability in dust exposure and solar irradiance. Under clean snow conditions, the temperature increases shorten snow cover by 5-18 days, whereas in the presence of dust they only shorten snow duration by 0-6 days. Dust radiative forcing also causes faster and earlier peak snowmelt outflow with daily mean snowpack outflow doubling under the heaviest dust conditions. On average, snow cover at the towers is lost 2.5 days after peak outflow in dusty conditions, and 1-2 weeks after peak outflow in clean conditions. © 2012. American Geophysical Union. All Rights Reserved. Source

Painter T.H.,Jet Propulsion Laboratory | Painter T.H.,University of California at Los Angeles | Skiles S.M.,University of California at Los Angeles | Deems J.S.,National Snow and Ice Data Center | And 3 more authors.
Water Resources Research

Dust in snow accelerates snowmelt through its direct reduction of snow albedo and its further indirect reduction of albedo by accelerating the growth of snow grains. Since the westward expansion of the United States that began in the mid-19th century, the mountain snow cover of the Colorado River Basin has been subject to five-fold greater dust loading, largely from the Colorado Plateau and Great Basin. Radiative forcing of snowmelt by dust is not captured by conventional micrometeorological measurements, and must be monitored by a more comprehensive suite of radiation instruments. Here we present a 6 year record of energy balance and detailed radiation measurements in the Senator Beck Basin Study Area, San Juan Mountains, Colorado, USA. Data include broadband irradiance, filtered irradiance, broadband reflected flux, filtered reflected flux, broadband and visible albedo, longwave irradiance, wind speed, relative humidity, and air temperatures. The gradient of the snow surface is monitored weekly and used to correct albedo measurements for geometric effects. The snow is sampled weekly for dust concentrations in plots immediately adjacent to each tower over the melt season. Broadband albedo in the last weeks of snow cover ranged from 0.33 to 0.55 across the 6 years and two sites. Total end of year dust concentration in the top 3 cm of the snow column ranged from 0.23 mg g1 to 4.16 mg g1. These measurements enable monitoring and modeling of dust and climate-driven snowmelt forcings in the Upper Colorado River Basin. © 2012. American Geophysical Union. All Rights Reserved. Source

Raleigh M.S.,U.S. National Center for Atmospheric Research | Landry C.C.,Center for Snow and Avalanche Studies | Hayashi M.,University of Calgary | Quinton W.L.,Wilfrid Laurier University | Lundquist J.D.,University of Washington
Water Resources Research

Snow surface temperature (Ts) is important to the snowmelt energy balance and landatmosphere interactions, but in situ measurements are rare, thus limiting evaluation of remote sensing data sets and distributed models. Here we test simple Ts approximations with standard height (2-4 m) air temperature (Ta), wet-bulb temperature (Tw), and dew point temperature (Td), which are more readily available than Ts. We used hourly measurements from seven sites to understand which Ts approximation is most robust and how Ts representation varies with climate, time of day, and atmospheric conditions (stability and radiation). Td approximated Ts with the lowest overall bias, ranging from 22.3 to 12.6°C across sites and from 22.8 to 1.5°C across the diurnal cycle. Prior studies have approximated Ts with Ta, which was the least robust predictor of Ts at all sites. Approximation of Ts with Td was most reliable at night, at sites with infrequent clear sky conditions, and at windier sites (i.e., more frequent turbulent instability). We illustrate how mean daily T d can help detect surface energy balance bias in a physically based snowmelt model. The results imply that spatial Td data sets may be useful for evaluating snow models and remote sensing products in data sparse regions, such as alpine, cold prairie, or Arctic regions. To realize this potential, more routine observations of humidity are needed. Improved understanding of Td variations will advance understanding of T s in space and time, providing a simple yet robust measure of snow surface feedback to the atmosphere. © 2013. American Geophysical Union. All Rights Reserved. Source

Lawrence C.R.,University of Colorado at Boulder | Painter T.H.,University of Colorado at Boulder | Painter T.H.,Jet Propulsion Laboratory | Landry C.C.,Center for Snow and Avalanche Studies | Neff J.C.,University of Colorado at Boulder
Journal of Geophysical Research: Biogeosciences

Dust deposition in the Rocky Mountains may be an important biogeochemical flux from upwind ecosystems. Seasonal (winter/spring) dust mass fluxes to the San Juan Mountains during the period from 2004 to 2008 ranged from 5 to 10 g m-2, with individual deposition events reaching as high as 2 g m -2. Dust deposited in the San Juan Mountains was primarily composed of silt- and clay-sized particles, indicating a regional source area. The concentrations of most major and minor elements in this dust were similar to or less than average upper continental crustal concentrations, whereas trace element concentrations were often enriched. In particular, dust collected from the San Juan Mountain snowpack was characterized by enrichments of heavy metals including As, Cu, Cd, Mo, Pb, and Zn. The mineral composition of dust partially explained dust geochemistry; however, based on results of a sequential leaching procedure it appeared that trace element enrichments were associated with the organic-, and not the mineral-, fraction of dust. Our observations show that the dust-derived fluxes of several nutrients and trace metals are substantial and, because many elements are deposited in a mobile form, could be important controls of vegetation, soil, or surface water chemistry. The flux measurements reported here are useful benchmarks for the characterization of ecosystem biogeochemical cycling in the Rocky Mountains. Copyright 2010 by the American Geophysical Union. Source

Discover hidden collaborations