Ian B. McCubbin

Observations of Ice Crystal Habits with a Scanning Polarimetric W-Band Radar at Slant Linear Depolarization Ratio Mode

AbstractScanning 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 −21.8 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 w...

Sub‐3 nm particles observed at the coastal and continental sites in the United States

Direct measurements of atmospheric sub-3 nm particles are crucial for understanding the new particle formation mechanisms, but such measurements are very limited at present. We report measurements of sub-3nm particles at Brookhaven, New York (a coastal site in summer) and Kent, Ohio (a continental site in winter). During daytime, in approximately 80% of the observation days at both sites, sub-3nm particle events were observed with concentrations of 2800 ± 1600 cm-3, and they appeared with the elevated sulfuric acid concentrations. During the nighttime at the coastal site under the marine air mass influences, there were also substantial concentrations of sub-3nm particles (1500 ± 400 cm-3), but they did not grow larger. On the other hand, at the coastal Brookhaven site under the continental air mass influences and at the inland Kent site during the night, the sub-3nm particles were significantly lower (190 ± 130 cm-3). Our results indicate that sub-3nm particles were not always present, and their presence was rather closely associated with specific aerosol nucleation precursors: sulfuric acid and other unknown condensable chemical species likely present in the marine air masses. These findings are thus different from other studies conducted in the Finland boreal forest, which showed a persistent presence of high concentrations of sub-2nm particles and that these sub-2nm particles were more correlated to monoterpene oxidation products than to sulfuric acid. Therefore, different nucleation mechanisms, as opposed on to a universal mechanism, involving different nucleation precursors dominate in different atmospheric environments with different emissions and transported trace gases.

CHANGE: A Place-Based Curriculum for Understanding Climate Change at Storm Peak Laboratory, Colorado

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 b...

Enhanced Radar Backscattering due to Oriented Ice Particles at 95GHz during StormVEx

AbstractNonspherical 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 dendri...

Science in the Mountains: A Unique Research Experience to Enhance Diversity in the Geosciences.

Ethnic and racial minorities constitute an important part of the geosciences community because of their diverse perspectives and backgrounds. However, the geosciences have the poorest diversity record of all the science and engineering fields. Recruitment of minorities is important and numerous programs are focusing on engaging students in geosciences during their undergraduate schooling. The Geoscience Research at Storm Peak (GRASP) program provides a model for retaining students in the geosciences pipeline and encouraging students’ interest in geoscience careers. GRASP offers college age students research experiences in urban and rural environments, introduces students to a wide range of geosciences career options, and connects students to mentors and role models. The main challenge associated with the GRASP program in its first year was recruitment. This paper uses the Geoscience Pipeline Model as a framework for evaluating the program’s success. GRASP not only exposed the students to a variety of geosciences careers, but it also taught them skills used by geosciences professionals. Overall, GRASP participants demonstrated a positive change in knowledge, attitudes, and behaviors related to the pipeline indicators.

Large Contribution of Coarse Mode to Aerosol Microphysical and Optical Properties: Evidence from Ground-Based Observations of a Transpacific Dust Outbreak at a High-Elevation North American Site

AbstractThis work is motivated by previous studies of transatlantic transport of Saharan dust and the observed quasi-static nature of coarse mode aerosol with a volume median diameter (VMD) of approximately 3.5 μm. The authors examine coarse mode contributions from transpacific transport of dust to North American aerosol properties using a dataset collected at the high-elevation Storm Peak Laboratory (SPL) and the nearby Atmospheric Radiation Measurement (ARM) Mobile Facility. Collected ground-based data are complemented by quasi-global model simulations and satellite and ground-based observations. The authors identify a major dust event associated mostly with a transpacific plume (about 65% of near-surface aerosol mass) in which the coarse mode with moderate (~3 μm) VMD is distinct and contributes substantially to total aerosol volume (up to 70%) and scattering (up to 40%). The results demonstrate that the identified plume at the SPL site has a considerable fraction of supermicron particles (VMD ~3 μm) a...

Isotopic Fractionation in Wintertime Orographic Clouds

AbstractThe 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 (δ18O 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 δ18O was used to show...

Sub-3 nm particle observations in the atmosphere of two sites in Eastern United States

Direct measurement of sub-3 nm particles is crucial for understanding the new particle formation process and its contribution to cloud condensation nuclei (CCN) formation. Sub-3 nm particles measured at Long Island, New York (coastal site) and Kent, Ohio (inland continental site) show that high concentrations of nighttime sub-3 nm particles were present at the coastal site only with marine air masses, whereas nighttime sub-3 nm particle concentrations were significantly low in continental air masses and at the inland continental site. The coastal nighttime sub-3 nm particles did not grow larger. Measured sulfuric acid and Volatile Organic Compounds (VOCs) indicate that the potential source precursors of nighttime sub-3 nm particles may be unknown ocean-originated chemical species other than sulfuric acid and biogenic VOCs (isoprene and monoterpenes).