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Steamboat Springs, CO, United States

Samy S.,Desert Research Institute | Mazzoleni L.R.,Michigan Technological University | Mishra S.,Desert Research Institute | Zielinska B.,Desert Research Institute | And 2 more authors.
Atmospheric Environment | Year: 2010

Water extracts of atmospheric particulate matter (PM2.5) collected at the Storm Peak Laboratory (SPL) (3210 MSL, 40.45° N, 106.74° W) were analyzed for a wide variety of polar organic compounds. The unique geographical character of SPL allows for extended observations/sampling of the free tropospheric interface. Under variable meteorological conditions between January 9th and January14th 2007, the most abundant compounds were levoglucosan (9-72 ng m-3), palmitic acid (10-40 ng m-3) and succinic acid (18-27 ng m-3). Of 84 analytes included in the GC-MS method, over 50 individual water extractable polar organic compounds (POC) were present at concentrations greater than 0.1 ng m-3. During a snow event (Jan. 11th-13th), the concentrations of several presumed atmospheric transformation compounds (dicarboxylic acids) were reduced. Lower actinic flux, reduced transport distance, and ice crystal scavenging may explain this variability. Diurnal averages over the sampling period revealed a higher total concentration of water extractable POC at night, 211 ng m-3 (105-265 ng m-3), versus day, 160 ng m-3 (137-205 ng m-3), which suggests a more aged nighttime aerosol character. This may be due to the increased daytime convective mixing of local primary emissions from the Yampa Valley. XAD resin extracts revealed a gas-phase partitioning of several compounds, and analysis of cloud water collected at this site in 2002 revealed a similar compound abundance trend. Levoglucosan, a wood smoke tracer was generally found to be the most abundant compound in both aerosol and cloud water samples. Variations in meteorological parameters and local/regional transport analysis play an important interpretive role in understanding these results. © 2010 Elsevier Ltd. All rights reserved.


Marchand R.,University of Washington | Mace G.G.,University of Utah | Hallar A.G.,Desert Research Institute | Hallar A.G.,Storm Peak Laboratory | And 4 more authors.
Journal of Atmospheric and Oceanic Technology | Year: 2013

Nonspherical atmospheric ice particles can enhance radar backscattering and attenuation above that expected from spheres of the same mass. An analysis of scanning 95-GHz radar data collected during the Storm Peak Laboratory Cloud Property Validation Experiment (StormVEx) shows that at a least a small amount of enhanced backscattering was present in most radar scans, with a median enhancement of 2.4 dB at zenith. This enhancement will cause an error (bias) in ice water content (IWC) retrievals that neglect particle orientation, with a value of 2.4 dB being roughlyequivalent to a relative error in IWC of 43%. Of the radar scans examined, 25% hada zenith-enhanced backscattering exceeding 3.5dB (equivalent to a relative error in IWC in excess of 67%) and 10% of the scans had a zenith-enhanced backscattering exceeding 6.4 dB (equivalent to a relative error in IWC in excess of 150%). Cloud particle images indicate that large enhancement typically occurred when planar crystals (e.g., plates and dendrites) were present, with the largest enhancement occurring when large planar crystals were falling out of a supercooled liquid-water layer. More modest enhancement was sometimes due to planar crystals, but it was alsosometimes likely a result of horizontally oriented nonspherical irregularly shapedparticles. The analysis also shows there is a strong correlation (about20.79) between the change in slant 458 depolarization ratio with radar scan elevation angle and the magnitude of the zenith-enhanced backscattering, suggesting that measurements of the slant depolarization ratio can be used to improve radar-based cloud microphysical property retrievals. © 2013 American Meteorological Society.


Matrosov S.Y.,University of Colorado at Boulder | Mace G.G.,University of Utah | Marchand R.,University of Washington | Shupe M.D.,University of Colorado at Boulder | And 4 more authors.
Journal of Atmospheric and Oceanic Technology | Year: 2012

Scanning polarimetric W-band radar data were evaluated for the purpose of identifying predominant ice hydrometeor habits. Radar and accompanying cloud microphysical measurements were conducted during the Storm Peak Laboratory Cloud Property Validation Experiment held in Steamboat Springs, Colorado, during the winter season of 2010/11. The observed ice hydrometeor habits ranged from pristine and rimed dendrites/stellars to aggregates, irregulars, graupel, columns, plates, and particle mixtures. The slant 45° linear depolarization ratio (SLDR) trends as a function of the radar elevation angle are indicative of the predominant hydrometeor habit/shape. For planar particles, SLDR values increase from values close to the radar polarization cross coupling of about 221.8 dB at zenith viewing to maximum values at slant viewing. These maximum values depend on predominant aspect ratio and bulk density of hydrometeors and also show some sensitivity to particle characteristic size. The highest observed SLDRs were around 28 dB for pristine dendrites. Unlike planar-type hydrometeors, columnar-type particles did not exhibit pronounced depolarization trends as a function of viewing direction. A difference in measured SLDR values between zenith and slant viewing can be used to infer predominant aspect ratios of planar hydrometeors if an assumption about their bulk density is made. For columnar hydrometeors, SLDRoffsets from the cross-coupling value are indicative of aspect ratios. Experimental data were analyzed for a number of events with prevalence of planartype hydrometeors and also for observations when columnar particles were the dominant species. Arelatively simple spheroidal model and accompanying T-matrix calculations were able to approximate most radar depolarization changes with viewing angle observed for different hydrometeor types. © 2012 American Meteorological Society.

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