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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Ice Nucleation Processes in Upper Tropospheric Wave-Clouds Observed During SUCCESS

We have compared in situ measurements near the leading-edges of wave-clouds observed during the SUCCESS experiment with numerical modeling of ice nucleation. Observations of high supersaturations with respect to ice (\geq 150\%) near the leading edge of a very cold wave cloud (T < --60^\circC) are consistent with recent theoretical and laboratory studies suggesting that large supersaturations are required to homogeneously freeze sulfate aerosols. Also, the peak ice crystal number densities observed in this cloud (about 4cm -3/sup>) are consistent with the number densities calculated in our model. The consistency between model results (using homogeneous freezing and the observations indicates that the number density of effective heterogeneous ice nuclei must be no more than about 2 cm -3 . In the warmer wave-cloud (T (approx.)eq --37^\circC) relatively large ice number densities were observed (20--40 cm -3 . Our model calculations suggest that these large number densities are only possible if liquid droplets were activated at the cloud leading-edge, followed by subsequent homogeneous freezing. If sulfate aerosols had frozen before liquid droplets could be activated, then the peak ice crystal number density should have been less than 10 cm -3 .

Jensen, E. J.↗
NASA NTRS1981

A molecular model for ice nucleation and growth

The semi-empirical quantum mechanical approach and the central field empirical pair potential model are applied to the development of molecular models for ice nucleation and growth.

Source record↗
NASA NTRS2022

The impacts of immersion ice nucleation parameterizations on Arctic mixed-phase stratiform cloud properties and the Arctic radiation budget in GEOS-5

The influence of four different immersion freezing parameterizations on Arctic clouds and the top-of-the atmosphere (TOA) and surface radiation fluxes is investigated in the fifth version of the National Aeronautics and Space Administration (NASA) Goddard Earth Observing System (GEOS-5) with sea surface temperature, sea ice fraction and aerosol emissions held fixed. The different parameterizations were derived from a variety of sources, including classical nucleation theory, field and laboratory measurements. Despite the large spread in the ice-nucleating particle (INP) concentrations in the parameterizations, the cloud properties and radiative fluxes had a tendency to form two groups, with the lower INP concentration category producing larger water path and low-level cloud fraction during winter and early spring, whereas the opposite occurred during the summer season. The stability of the lower troposphere was found to strongly correlate with low-cloud fraction, and along with the effect of ice nucleation, ice sedimentation and melting rates, appears to explain the spring-to-summer reversal pattern in the relative magnitude of the cloud properties between the two categories of simulations. The strong modulation effect of the liquid phase on immersion freezing led to the successful simulation of the characteristic Arctic cloud structure, with a layer rich in supercooled water near cloud top and ice and snow at lower levels. Comparison with satellite retrievals and in situ data suggest that simulations with low INP concentrations more realistically represent Arctic clouds and radiation.

Arctic↗
NASA NTRS1978

Rocket effluent: Its ice nucleation activity and related properties

To investigate the possibility of inadvertent weather modification from rocket effluent, aerosol samples were collected from an instrumented aircraft subsequent to the Voyager 1 and 2 launches. The aerosol's morphology, concentration, and size distribution were examined with an electron microscope. The elemental compositions of individual particles were analyzed with an X-ray energy spectrometer. Ice nucleus concentration was measured with a thermal diffusion chamber. The particles' physical and chemical properties were related to their ice nucleation activity. A laboratory experiment on rocket propellant exhaust was conducted under controlled conditions. Both laboratory and field experimental results indicated that rocket propellant exhaust can produce active ice nuclei and modify local weather in suitable meteorological conditions.

Parungo, F. P.↗
NASA NTRS1978

Rocket effluent - Its ice nucleation activity and related properties

To investigate the possibility of inadvertent weather modification from rocket effluent, aerosol samples were collected from an instrumented aircraft subsequent to the Voyager I and II launches. The aerosol's morphology, concentration and size distribution were examined with an electron microscope. The elemental compositions of individual particles were analyzed with an X-ray energy spectrometer. Ice nucleus concentration was measured with a subfreezing thermal diffusion chamber. The particles' physical and chemical properties were related to their ice nucleation activity. A laboratory experiment on rocket propellant exhaust was conducted under controlled conditions. Both laboratory and field experimental results indicated that rocket propellant exhaust can produce active ice nuclei. Their consequences for potential inadvertant weather modification demand additional study.

Parungo, F. P.↗
NASA NTRS1980

Comments on 'Rocket effluent - Its ice nucleation activity and related properties'

Parungo and Allee (1978) reported ice nucleus (IN) measurements made from an aircraft in stabilized ground clouds from Titan III launches at KSC. They concluded from the measurements that the SGC contained IN. After an examination of the data the present authors (Hindman and Lala) argue that the filter devices were unable to detect IN in the SGC. In a reply Parungo and Allee attempt to refute this conclusion.

Hindman, E. E., II↗
NASA NTRS1982

Contact ice nucleation by submicron atmospheric aerosols

An apparatus designed to measure the concentrations of submicron contact ice nuclei is described. Here, natural forces transfer nuclei to supercooled sample drops suspended in an aerosol stream. Experimental measurements of the scavenging rate of the sample drops for several humidities and aerosol sizes are found to be in agreement with theory to within a factor of two. This fact, together with the statistical tests showing a difference between the data and control samples, is seen as indicating that a reliable measurement of the concentrations of submicron contact ice nuclei has been effected. A figure is included showing the ice nucleus concentrations as a function of temperature and assumed aerosol radius. For a 0.01 micron radius, the average is 1/liter at -15 C and 3/liter at -18 C. It is noted that the measurements are in fair agreement with ice crystal concentrations in stable winter clouds measured over Elk Mountain, WY (Vali et al., 1982).

Deshler, T.↗
NASA NTRS1981

A molecular model for ice nucleation and growth, attachment 1

The quantum mechanical technique is used to study ionic, configurational, and impurity defects in the ice surface. In addition to static calculations of the energetics of the water monomer-ice surface interactions, molecular dynamics studies were initiated. The calculations of the monomer-ice surface interaction, molecular dynamics studies were initiated. The calculations of monomer-ice surface interactions indicate that many adsorption sites exist on the ice surfaces and that the barriers between bonding sites are relatively low. Bonding on the prism face of ice is preferentially above lattice sites.

Plummer, P. L. M.↗
NASA NTRS2017

Dynamical Conditions of Ice Supersaturation and Ice Nucleation in Convective Systems: A Comparative Analysis Between in Situ Aircraft Observations and WRF Simulations

Occurrence frequency and dynamical conditions of ice supersaturation (ISS, where relative humidity with respect to ice (RHi) greater than 100%) are examined in the upper troposphere around convective activity. Comparisons are conducted between in situ airborne observations and the Weather Research and Forecasting model simulations using four double-moment microphysical schemes at temperatures less than or or equal to -40degdegC. All four schemes capture both clear-sky and in-cloud ISS conditions. However, the clear-sky (in-cloud) ISS conditions are completely (significantly) limited to the RHi thresholds of the Cooper parameterization. In all of the simulations, ISS occurrence frequencies are higher by approximately 3-4 orders of magnitude at higher updraft speeds (greater than 1 m s(exp -1) than those at the lower updraft speeds when ice water content (IWC) greater than 0.01 gm(exp -3), while observations show smaller differences up to approximately 1-2 orders of magnitude. The simulated ISS also occurs less frequently at weaker updrafts and downdrafts than observed. These results indicate that the simulations have a greater dependence on stronger updrafts to maintain/generate ISS at higher IWC. At lower IWC (less than or equal or 0.01 gm(exp -3), simulations unexpectedly show lower ISS frequencies at stronger updrafts. Overall, the Thompson aerosol-aware scheme has the closest magnitudes and frequencies of ISS greater than 20% to the observations, and the modified Morrison has the closest correlations between ISS frequencies and vertical velocity at higher IWC and number density. The Cooper parameterization often generates excessive ice crystals and therefore suppresses the frequency and magnitude of ISS, indicating that it should be initiated at higher ISS (e.g.,lees than or equal to 25%).

D’Alessandro, John J.↗
NASA NTRS2012

A FIRE-ACE/SHEBA Case Study of Mixed-Phase Arctic Boundary Layer Clouds: Entrainment Rate Limitations on Rapid Primary Ice Nucleation Processes

Observations of long-lived mixed-phase Arctic boundary layer clouds on 7 May 1998 during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE)Arctic Cloud Experiment (ACE)Surface Heat Budget of the Arctic Ocean (SHEBA) campaign provide a unique opportunity to test understanding of cloud ice formation. Under the microphysically simple conditions observed (apparently negligible ice aggregation, sublimation, and multiplication), the only expected source of new ice crystals is activation of heterogeneous ice nuclei (IN) and the only sink is sedimentation. Large-eddy simulations with size-resolved microphysics are initialized with IN number concentration N(sub IN) measured above cloud top, but details of IN activation behavior are unknown. If activated rapidly (in deposition, condensation, or immersion modes), as commonly assumed, IN are depleted from the well-mixed boundary layer within minutes. Quasi-equilibrium ice number concentration N(sub i) is then limited to a small fraction of overlying N(sub IN) that is determined by the cloud-top entrainment rate w(sub e) divided by the number-weighted ice fall speed at the surface v(sub f). Because w(sub c)< 1 cm/s and v(sub f)> 10 cm/s, N(sub i)/N(sub IN)<< 1. Such conditions may be common for this cloud type, which has implications for modeling IN diagnostically, interpreting measurements, and quantifying sensitivity to increasing N(sub IN) (when w(sub e)/v(sub f)< 1, entrainment rate limitations serve to buffer cloud system response). To reproduce observed ice crystal size distributions and cloud radar reflectivities with rapidly consumed IN in this case, the measured above-cloud N(sub IN) must be multiplied by approximately 30. However, results are sensitive to assumed ice crystal properties not constrained by measurements. In addition, simulations do not reproduce the pronounced mesoscale heterogeneity in radar reflectivity that is observed.

Fridlin, Ann↗
NASA NTRS2013

Ice Nucleation and Dehydration in the Tropical Tropopause Layer

Optically thin cirrus near the tropical tropopause regulate the humidity of air entering the stratosphere, which in turn has a strong influence on the Earth's radiation budget and climate. Recent highaltitude, unmanned aircraft measurements provide evidence for two distinct classes of cirrus formed in the tropical tropopause region: (i) vertically extensive cirrus with low ice number concentrations, low extinctions, and large supersaturations (up to approx. 70%) with respect to ice; and (ii) vertically thin cirrus layers with much higher ice concentrations that effectively deplete the vapor in excess of saturation. The persistent supersaturation in the former class of cirrus is consistent with the long time-scales (several hours or longer) for quenching of vapor in excess of saturation given the low ice concentrations and cold tropical tropopause temperatures. The low-concentration clouds are likely formed on a background population of insoluble particles with concentrations less than 100 L−1 (often less than 20 L−1), whereas the high ice concentration layers (with concentrations up to 10,000 L−1) can only be produced by homogeneous freezing of an abundant population of aqueous aerosols. These measurements, along with past high-altitude aircraft measurements, indicate that the low-concentration cirrus occur frequently in the tropical tropopause region, whereas the high-concentration cirrus occur infrequently. The predominance of the low-concentration clouds means cirrus near the tropical tropopause may typically allow entry of air into the stratosphere with as much as approx. 1.7 times the ice saturation mixing ratio.

dehydration↗
NASA NTRS1998

Analysis of Ice Nucleating Aerosol Measurements during SUCCESS: April, May 1996

This section describes our research activities during year three of this effort. In the second year, preliminary archive data sets were submitted to the SUCCESS archive. After additional analyses, final versions were prepared and submitted. These are included on the SUCCESS CD-ROM data editions that were recently released by NASA Ames. Over the range of temperature and supersaturation conditions of our measurements (15 to -40 C, and from ice saturation to approximately 15% water supersaturation), IN concentrations ranged from less than 0.1 to approximately 500 per liter, being generally greater at colder temperatures and higher supersaturations. To estimate the potential of aircraft exhaust as a source of IN, we examined data from six days of the field project when the DC-8 was following closely behind other humidity conditions of our measurements. In April 1997, a microphysical workshop was convened at NCAR to select cases for in depth analyses and to address questions about the consistency of cloud ice crystal measurements (size distributions and mass concentrations) and aerosol size distributions. We attended this meeting and contributed to the discussions. A particular concern was identified in the CN measurements. On the DC-8, CN measurements were obtained by four different investigator groups, using commercially available instrumentation. The DC-8 SUCCESS CN data showed long periods where the measurements were in substantial agreement, but there were also periods with large discrepancies. Several possible factors were identified that could help explain these discrepancies, including minimum detectable particle size, response at reduced pressures, and location of sample inlet on the aircraft.

Rogers, D. C.↗
NASA NTRS1977

Molecular model of ice nucleation

Two complementary techniques, semi-empirical quantum mechanical calculations and empirical central field pair potential calculations were used in developing a model of the interaction of water with simple surfaces.

Plummer, P. L. M.↗
NASA NTRS1981

A molecular model for ice nucleation and growth, attachment 2

The central field empirical pair potential model is applied to studying the effects of kinks, ledges, and vacancies on the absorption of water molecules from the vapor. Molecular dynamics simulations indicate that cluster and/or surface modes play a primary role in the absorption process, the flexibility of the hydrogen bond serves to decrease the energy required for structural interconversion, and the rapid distribution of added energy in a hydrogen bonded system lead to aggregate stability which greatly exceeds that predicted by static energy calculations.

Hale, B. N.↗
NASA NTRS1997

Measurements of Ice Nucleating Aerosols in the Upper Troposphere and Lower Stratosphere

Our major accomplishments during Year 1 were: Development of aerosol and crystal collection techniques. Development of single-particle chemical characterization techniques. Modification of system design for DC-8 and initial testing. Our major accomplishments during Year 2 were: Completion of system design and proof-of-concept experiments. Participation in SUCCESS mission. Reporting of theoretical and laboratory findings in the scientific literature. Reporting of initial SUCCESS results at scientific meetings. Our major accomplishments during Year 3 were: Data reduction and submission of all SUCCESS data to the archive. Participation in SUCCESS data comparison workshops. Reporting of SUCCESS results at the AEAP Meeting. Organization of CN counter intercomparison workshop. Preparation of three manuscripts submitted to the GRL SUCCESS Special Issue.

Kreidenweis, S. M.↗