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Title: Modeling Expansion of Particle Clouds

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Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
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Conference: Presented at: 26th ICDERS, Boston, MA, United States, Jul 30 - Aug 04, 2017
Country of Publication:
United States

Citation Formats

Kuhl, A, and Grote, D. Modeling Expansion of Particle Clouds. United States: N. p., 2017. Web.
Kuhl, A, & Grote, D. Modeling Expansion of Particle Clouds. United States.
Kuhl, A, and Grote, D. Thu . "Modeling Expansion of Particle Clouds". United States. doi:.
title = {Modeling Expansion of Particle Clouds},
author = {Kuhl, A and Grote, D},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jan 12 00:00:00 EST 2017},
month = {Thu Jan 12 00:00:00 EST 2017}

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  • A single-cell Lagrangian model has been developed for calculating the ionization and expansion dynamics of high-density clouds in magnetic fields or in magnetically confined plasmas. The model was tested by means of data from magnetospheric barium cloud experiments and approximately reproduced such global characteristics as expansion rate, stopping radius, stopping time, and magnetic cavity lifetime. Detailed calculations were performed for hydrogen clouds associated with the injection of frozen hydrogen pellets into tokamak plasmas. The dynamic characteristics of the cloud expansion, such as ionization radius, stopping time, lifetime, oscillation frequencies, and amplitudes, etc., are computed as functions of the magnetic fieldmore » strength, the background plasma temperature, and the cloud mass. The results are analyzed and compared with experimental observations.« less
  • The goal of this study is to determine the upper tropospheric moisture budget associated with convective events and, in particular, to extend process models to higher altitudes than have been achieved previously. Although upper tropospheric moisture concentrations are several orders of magnitude lower than those near the surface, upper tropospheric moisture exerts an important influence on climate. On a per-molecule basis, greenhouse absorption due to water vapor is about one hundred times more effective at high altitudes than at low altitudes. Several one-dimensional radiative convective models have been used to demonstrate the importance of upper tropospheric moisture on climate. Thesemore » models show that for a given fractional increase in water vapor at a given altitude, the response or change in surface temperature is qualitatively the same. Figure 1 shows the change in surface temperature for a 50% increase of the specific humidity in a 40-mbar layer in clear skies. At present, considerable controversy exists over the nature of the vertical redistribution of water vapor in a changing climate, particularly the distribution of water vapor in the upper troposphere. Because suitable data are lacking, this controversy is also reflected in the cumulus parameterization schemes currently used in models. Understanding upper tropospheric moistening processes is therefore of prime importance in addressing the water vapor feedback question.« less
  • A substantial portion of the disagreement in cloud feedback among various general circulation models (GCMs) can be traced to the models differing representations of the optical thickness of low-level clouds. Implicit cloud optical thickness feedback arises when the optical properties are prescribed as a function of height, because cloud height typically increases in model simulations of a warming climate. If the optical thickness decreases with height, a positive low cloud optics feedback results. Diagnostic parameterizations, in which optical thickness is assumed to increase with temperature based on, e.g., a calculation of the adiabatic liquid water content of a moist liftedmore » air parcel, produce a negative cloud optics feedback because the albedo effect dominates the greenhouse effect for low-level clouds. Prognostic schemes, in which cloud liquid/ice water is predicted as a function of time based on a cloud water budget and the optical properties diagnosed from the cloud water content, can produce either positive, neutral, or negative cloud optics feedbacks because such schemes incorporate both sources and sinks of cloud water. To date, no observational or theoretical consensus has emerged on the temperature dependence of the optical thickness of low clouds. Aircraft observations over the former Soviet Union indicate that the liquid water content of low and middle clouds increases with temperature except perhaps at the warmest temperatures. Researchers used this indication as the basis of an optical thickness feedback simulation in a one-dimensional radiative-convective (1DRC) model, illustrating the potentially large negative cloud optics feedback. Others used simple thermodynamic arguments to calculate the temperature dependence of adiabatic liquid water content, with similar implications for low cloud optical thickness feedback. There is no obvious liquid water path dependence on temperature in satellite microwave measurements over the North Atlantic.« less
  • Counterstreaming plasma expansion occurs in a variety of saturations ranging from laboratory devices to plasma in space. It was established that the processes of collisionless interaction of plasma flows play a decisive role in dynamics of such nonstationary astrophysical phenomena as Supernova burst, and Solar flares, and active experiments in space (AMPTE). As a result of such interaction in the surrounding background the waves and shock are generated. The deceleration of the plasma by the external magnetic field produces the flute modes observed on the surface of the expanding plasma cloud. These field-aligned structures appeared as ripples on the surfacemore » near the time of maximum expansion.« less
  • The entrainment of warm dry air from above the inversion into a stratocumulus deck may play an important role in the dissipation of the cloud. A quantitative understanding of radiatively induced convection at cloud top is necessary in order to produce accurate entrainment rates and predictions of the diurnal evolution of a cloud layer. A three dimensional numerical model is used to study such convection. The model has been used extensively to study Rayleigh-Benard convection in an approximate geophysical setting. Here the authors model an idealized, non-sheared, nocturnal marine boundary layer to investigate the development of convection generated by cloudmore » radiative cooling. Cloud forcing rather than surface forcing is investigated.« less