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A. Gannet Hallar, Ian B. McCubbin, and Jennifer M. Wright

Curriculum in High Altitude Environments for Teaching Global Climate Change Education (CHANGE) uses place-based education to teach middle school students about meteorology and climate as a basis to improve climate science literacy. The curriculum provides in-school and out-of-school instruction and connects students with scientists at Storm Peak Laboratory, a high-elevation atmospheric research facility above Steamboat Springs, Colorado. Following an initial 2-h classroom lesson, students record their own measurements of temperature, pressure, wind speed, and particle concentrations while traveling up the mountain to Storm Peak Laboratory. After returning to the classroom, students graph these data and analyze their results. Evaluation of this program showed that students improved their knowledge of key concepts pertaining to climate literacy. The hands-on, place-based format of CHANGE can be used as a model for middle school students in alpine communities to teach lessons in weather and climate and can be further refined by improved lesson plans, increased feedback to students, and an independent evaluation.

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Linnea M. Avallone, A. Gannet Hallar, Heather Thiry, and Laura M. Edwards
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Sean M. Davis, A. Gannet Hallar, Linnea M. Avallone, and William Engblom

Abstract

The University of Colorado closed-path tunable diode laser hygrometer (CLH), a new instrument for the in situ measurement of enhanced total water (eTW, the sum of water vapor and condensed water enhanced by a subisokinetic inlet), has recently been flown aboard the NASA DC-8 and WB-57F aircrafts. The CLH has the sensitivity necessary to quantify the ice water content (IWC) of extremely thin subvisual cirrus clouds (∼0.1 mg m−3), while still providing measurements over a large range of conditions typical of upper-tropospheric cirrus (up to 1 g m−3). A key feature of the CLH is its subisokinetic inlet system, which is described in detail in this paper. The enhancement and evaporation of ice particles that results from the heated subisokinetic inlet is described both analytically and based on computational fluid dynamical simulations of the flow around the aircraft. Laboratory mixtures of water vapor with an accuracy of 2%–10% (2σ) were used to calibrate the CLH over a wide range of water vapor mixing ratios (∼50–50 000 ppm) and pressures (∼100–1000 mb). The water vapor retrieval algorithm, which is based on the CLH instrument properties as well as on the spectroscopic properties of the water absorption line, accurately fits the calibration data to within the uncertainty of the calibration mixtures and instrument signal-to-noise ratio. A method for calculating cirrus IWC from the CLH enhanced total water measurement is presented. In this method, the particle enhancement factor is determined from an independent particle size distribution measurement and the size-dependent CLH inlet efficiency. It is shown that despite the potentially large uncertainty in particle size measurements, the error introduced by this method adds ∼5% error to the IWC calculation. IWC accuracy ranges from 20% at the largest IWC to 50% at small IWC (<5 mg m−3).

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Roger Marchand, Gerald G. Mace, A. Gannet Hallar, Ian B. McCubbin, Sergey Y. Matrosov, and Matthew D. Shupe

Abstract

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 roughly equivalent to a relative error in IWC of 43%. Of the radar scans examined, 25% had a zenith-enhanced backscattering exceeding 3.5 dB (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 also sometimes likely a result of horizontally oriented nonspherical irregularly shaped particles. The analysis also shows there is a strong correlation (about −0.79) between the change in slant 45° 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.

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Douglas Lowenthal, A. Gannet Hallar, Ian McCubbin, Robert David, Randolph Borys, Peter Blossey, Andreas Muhlbauer, Zhiming Kuang, and Mary Moore

Abstract

The Isotopic Fractionation in Snow (IFRACS) study was conducted at Storm Peak Laboratory (SPL) in northwestern Colorado during the winter of 2014 to elucidate snow growth processes in mixed-phase clouds. The isotopic composition (δ 18O and δD) of water vapor, cloud water, and snow in mixed-phase orographic clouds were measured simultaneously for the first time. The depletion of heavy isotopes [18O and deuterium (D)] was greatest for vapor, followed by snow, then cloud. The vapor, cloud, and snow compositions were highly correlated, suggesting similar cloud processes throughout the experiment. The isotopic composition of the water vapor was directly related to its concentration. Isotopic fractionation during condensation of vapor to cloud drops was accurately reproduced assuming equilibrium fractionation. This was not the case for snow, which grows by riming and vapor deposition. This implies stratification of vapor with altitude. The relationship between temperature at SPL and δ 18O was used to show that the snow gained most of its mass within 922 m above SPL. Relatively invariant deuterium excess (d) in vapor, cloud water, and snow from day to day suggests a constant vapor source and Rayleigh fractionation during transport. The diurnal variation of vapor d reflected the differences between surface and free-tropospheric air during the afternoon and early morning hours, respectively. These observations will be used to validate simulations of snow growth using an isotope-enabled mesoscale model with explicit microphysics.

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Elisabeth Andrews, Patrick J. Sheridan, John A. Ogren, Derek Hageman, Anne Jefferson, Jim Wendell, Andrés Alástuey, Lucas Alados-Arboledas, Michael Bergin, Marina Ealo, A. Gannet Hallar, András Hoffer, Ivo Kalapov, Melita Keywood, Jeongeun Kim, Sang-Woo Kim, Felicia Kolonjari, Casper Labuschagne, Neng-Huei Lin, AnneMarie Macdonald, Olga L. Mayol-Bracero, Ian B. McCubbin, Marco Pandolfi, Fabienne Reisen, Sangeeta Sharma, James P. Sherman, Mar Sorribas, and Junying Sun

Abstract

To estimate global aerosol radiative forcing, measurements of aerosol optical properties are made by the National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL)’s Global Monitoring Division (GMD) and their collaborators at 30 monitoring locations around the world. Many of the sites are located in regions influenced by specific aerosol types (Asian and Saharan desert dust, Asian pollution, biomass burning, etc.). This network of monitoring stations is a shared endeavor of NOAA and many collaborating organizations, including the World Meteorological Organization (WMO)’s Global Atmosphere Watch (GAW) program, the U.S. Department of Energy (DOE), several U.S. and foreign universities, and foreign science organizations. The result is a long-term cooperative program making atmospheric measurements that are directly comparable with those from all the other network stations and with shared data access. The protocols and software developed to support the program facilitate participation in GAW’s atmospheric observation strategy, and the sites in the NOAA/ESRL network make up a substantial subset of the GAW aerosol observations. This paper describes the history of the NOAA/ESRL Federated Aerosol Network, details about measurements and operations, and some recent findings from the network measurements.

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A. Gannet Hallar, Steven S. Brown, Erik Crosman, Kelley C. Barsanti, Christopher D. Cappa, Ian Faloona, Jerome Fast, Heather A. Holmes, John Horel, John Lin, Ann Middlebrook, Logan Mitchell, Jennifer Murphy, Caroline C. Womack, Viney Aneja, Munkhbayar Baasandorj, Roya Bahreini, Robert Banta, Casey Bray, Alan Brewer, Dana Caulton, Joost de Gouw, Stephan F.J. De Wekker, Delphine K. Farmer, Cassandra J. Gaston, Sebastian Hoch, Francesca Hopkins, Nakul N. Karle, James T. Kelly, Kerry Kelly, Neil Lareau, Keding Lu, Roy L. Mauldin III, Derek V. Mallia, Randal Martin, Daniel L. Mendoza, Holly J. Oldroyd, Yelena Pichugina, Kerri A. Pratt, Pablo E. Saide, Philip J. Silva, William Simpson, Britton B. Stephens, Jochen Stutz, and Amy Sullivan

Abstract

Wintertime episodes of high aerosol concentrations occur frequently in urban and agricultural basins and valleys worldwide. These episodes often arise following development of persistent cold-air pools (PCAPs) that limit mixing and modify chemistry. While field campaigns targeting either basin meteorology or wintertime pollution chemistry have been conducted, coupling between interconnected chemical and meteorological processes remains an insufficiently studied research area. Gaps in understanding the coupled chemical–meteorological interactions that drive high-pollution events make identification of the most effective air-basin specific emission control strategies challenging. To address this, a September 2019 workshop occurred with the goal of planning a future research campaign to investigate air quality in western U.S. basins. Approximately 120 people participated, representing 50 institutions and five countries. Workshop participants outlined the rationale and design for a comprehensive wintertime study that would couple atmospheric chemistry and boundary layer and complex-terrain meteorology within western U.S. basins. Participants concluded the study should focus on two regions with contrasting aerosol chemistry: three populated valleys within Utah (Salt Lake, Utah, and Cache Valleys) and the San Joaquin Valley in California. This paper describes the scientific rationale for a campaign that will acquire chemical and meteorological datasets using airborne platforms with extensive range, coupled to surface-based measurements focusing on sampling within the near-surface boundary layer, and transport and mixing processes within this layer, with high vertical resolution at a number of representative sites. No prior wintertime basin-focused campaign has provided the breadth of observations necessary to characterize the meteorological–chemical linkages outlined here, nor to validate complex processes within coupled atmosphere–chemistry models.

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