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436 records · Page 25

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NASA NTRS1990

Measurements of condensation nuclei in the Airborne Arctic Stratospheric Expedition - Observations of particle production in the polar vortex

The ER-2 Condensation Nucleus Counter (ER-2 CNC) was operated in the Airborne Arctic Stratospheric Expedition (AASE) in January and February 1989. The ER-2 CNC measures the mixing ratio of particles, CN, with diameters from approximately 0.02 to approximately 1 micron. The spatial distribution of CN in the Arctic polar vortex was found to resemble that measured in the Antarctic in the Spring of 1987. The vertical profile of CN in the vortex was lowered by subsidence. At altitudes above the minimum in the CN mixing ratio profile, CN mixing ratios correlated negatively with that of N2O, demonstrating new particle production. CN serve as nuclei in the formation of Polar Stratospheric Clouds (PSCs) and the concentration of CN can affect PSC properties.

Wilson, J. C.↗

NASA NTRS1984

Temperature measurements during the CAMP program

The Cold Arctic Mesopause Program (CAMP) was conducted at ESRANGE, Sweden, in July/August 1982. During the time period of several weeks, the temperature was monitored by ground-based OH emission spectrometers and by satellite radiance measurements. Rocket launchings occurred on the nights of 3/4 and 11/12 August. On 3/4 August, seven rocket payloads were launched during a period of noctilucent cloud sighting over ESRANGE. The presence of the NLC was confirmed by several rocket-borne photometer profiles. The temperature measurements showed that the temperature profiles in the stratosphere and lower mesosphere were near the expected values of high latitude summer models. A large amplitude wave structure with three temperature minima of 139K, 114K and 111K were observed at altitudes between 83 and 94 km. The temperature minimum at 83 km was the location of the observed NLC. The temperature minima caused by the growth of the gravity wave amplitude in the highly stable mesosphere provide the regions for the growth of particles by nucleation to optical scattering size, as well as regions where the nuclei for condensation can be formed through ion chemistry paths.

Philbrick, C. R.↗

DOE OSTI2021

Impacts of long-range-transported mineral dust on summertime convective cloud and precipitation: a case study over the Taiwan region

As one of the most abundant atmospheric aerosols and effective ice nuclei, mineral dust affects clouds and precipitation in the Earth system. Here numerical experiments are carried out to investigate the impacts of dust aerosols on summertime convective clouds and precipitation over the mountainous region of Taiwan by acting as ice-nucleating particles. We run the Weather Research and Forecasting model (WRF) with the Morrison two-moment and spectral-bin microphysics (SBM) schemes at 3 km resolution, using dust number concentrations from a global chemical transport model (GEOS-Chem-APM). The case study indicates that the long-range-transported mineral dust, with relatively low number concentrations, can notably affect the properties of convective clouds (ice and liquid water contents, cloud top height, and cloud coverage) and precipitation (spatial pattern and intensity). The effects of dust are evident during strong convective periods, with significantly increased ice water contents in the mixed-phase regime via the enhanced heterogeneous freezing. With both the Morrison and SBM schemes, we see the invigoration effects of dust aerosols on the convective intensity through enhanced condensation and deposition latent heating. The low-altitude dust particles are uplifted to the freezing level by updrafts, which, in turn, enhance the convective cloud development through immersion freezing and convective invigoration. Compared to the Morrison scheme, the SBM scheme predicts more realistic precipitation and different invigoration effects of dust. The differences are partially attributed to the saturation adjustment approach utilized in the bulk scheme, which leads to a stronger enhancement of condensation at midlatitudes to low altitudes and a weaker deposition increase at the upper level.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2022

Lithium and boron isotopic compositions of olivine in chondrules from carbonaceous and ordinary chondrite meteorites: Implications for the origin of solar 11 B/ 10 B ratio

We report the origin of solar 11 B/ 10 B ratio ~4 remains an open question. It has been thought that a significant portion of boron in the Solar System was derived from continuous spallation nucleosynthesis during interactions between Galactic Cosmic Rays and C—N—O nuclei in the interstellar medium. However, because GCR-produced boron is characterized by 11 B/ 10 B ~2.5, an endmember with 11 B/ 10 B > 4 is required to account for the solar 11 B/ 10 B ratio. Two leading hypotheses for the sources of 11 B-rich components include low energy spallation in the Sun’s parental molecular cloud and the neutrino process during the supernova explosions. In this study, lithium and boron elemental and isotopic compositions of seven porphyritic olivine chondrules and one isolated olivine crystal from four meteorites (Allende, Yamato 81020, Asuka 12236, and QUE 97008) were determined in-situ to help constrain which of the two nucleosynthetic mechanisms has most likely supplied the forming Solar System with extra 11 B. Apparent isotopic variations in Li/Si, B/Si, δ 7 Li and δ 11 B were found in chondrule olivine crystals, but only three chondrules exhibit statistically resolved δ 11 B heterogeneities. Using these three chondrules as a basis for discussion, we evaluated the processes that could potentially cause elemental and isotopic variations of Li and B. We argue that the data can be best understood in the context of condensation of lithium-boron-rich material onto chondrule precursors in (an) initially heterogeneous gaseous reservoir(s), which could be realized if the Solar System derived 11 B-rich components from a supernova or supernovae.

58 GEOSCIENCES↗