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Brian A. Tinsley
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ABSTRACT: This note critically examines the relative importance of several effects which influence the diurnal variation of atomic hydrogen abundance near the critical level.It is pointed out that the neglect of exospheric hydrogen in a recent theoretical treatment causes an overestimation of the diurnal variation at high exospheric temperatures, and an underestimation at low exospheric temperatures. The fluxes due to lateral flow are large compared to other fluxes only to the extent that the actual diurnal variation is very different from the diurnal variation corresponding to zero net lateral flow, which does not seem to be the case in the real atmosphere. Two effects which are probably important are charge exchange reactions with thermal oxygen ions, resulting in a diurnal exchange with the plasmasphere; and charge exchange reactions with high velocity protons, resulting in enhanced escape and diurnal variation.
Planetary and Space Science. 05/1973;
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ABSTRACT: Using ion temperature and density data at specific points and times in June 1969 provided by the OGO 6 satellite, and altitude profiles of the ion and electron temperature and concentration provided by the Arecibo radar facility over the period February 1972–April 1974, the diurnal and solar cycle variation of the charge exchange induced hydrogen escape flux was investigated. It was calculated that for low to moderate solar activity at Arecibo, the diurnal ratio of the maximum-to-minimum charge exchange induced hydrogen escape flux was approximately 6 with a peak around noon and a minimum somewhere between 0100 and 0300 h L.T. This study of a limited amount of OGO 6 and Arecibo data seems to indicate that the charge exchange induced hydrogen escape flux increases as the F10.7 flux increases for low to moderate solar activity.
Planetary and Space Science.
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Brian A. Tinsley
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ABSTRACT: Measurements of the 2sP—23S emission of helium arising from resonant scattering of sunlight on upper atmosphere helium in the metastable 23S state have been made. Intensities from less than 200 R to greater than 1000 R (reduced to the zenith) were found for solar depression angles greater than 10°. A marked maximum in the emission rate was found in the winter of 1966–1967, and the emission rates looking north were significantly greater than those looking south during this period. The present results, obtained at latitude 34°, L parameter 2, are similar to those found by Federova at latitude 68°, L parameter 15, in 1960–3.Possible latitude variations in atmospheric constituents, and the effects of conjugate point photoelectrons, are discussed with regard to the north-south asymmetry and the winter maximum.A strong northerly emission accompanying a moderate magnetic storm was observed.
Planetary and Space Science.
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ABSTRACT: Electrical charges on aerosol particles and droplets modify the droplet–particle collision efficiencies involved in scavenging, and the droplet–droplet and particle–particle collision efficiencies involved in coalescence of droplets and particles, even in only weakly electrified clouds and aerosol layers. This work places electrically enhanced scavenging, and the electrical inhibition of scavenging in the context of the microphysics of weakly electrified clouds.Collision efficiencies are calculated by numerical integration to obtain particle trajectories, that are determined by the complex interplay of electrical, gravitational and phoretic forces together with inertia. These modify the trajectory of a particle as it is carried by flow around the falling droplet. Conversely, the flow around the particle also modifies the trajectory of the droplet. The flows are specified analytically, using a hybrid of the Proudman–Pearson stream function for that region close to the droplet or particle, where it is accurate, merging into the exact Oseen stream function for larger distances, where that becomes accurate. The effect of the flow around the particle on the motion of the droplet was simulated using Langmuir's superposition technique on the hybrid stream functions. The treatment of inertia in the present calculations allows an extension of the scope of our previous work by a factor of 10 larger in particle size (103 in mass). The coverage is extended to a wide range of atmospheric conditions and particle densities.The pressures and temperatures used in the models ranged from a representation of the lower troposphere at ∼ 1 km altitude (900 hPa, 10 °C) to that of the middle stratosphere at ∼ 30 km altitude (12 hPa, − 47 °C). The particles considered range from 0.1 μm to 10 μm radius; the droplet radii range from 4 μm to 50 μm; particle densities range from 300 kg m− 3 to 2500 kg m− 3; particle charges range from 2e to 100e with droplet charges of like sign of 100e; and relative humidities range from 10% to 100%.For the larger particles (radii greater than about 3 μm) interacting with the larger droplets (radii greater than about 15 μm) the effects of inertia increase with particle density and dominate at the larger densities. For particles with radii in the range 1–3 μm the ‘Greenfield Gap’ of very low collision efficiencies was found, and was determined to be due to the effects of the gravitational force causing a reduction of collisions of particles with the front of the droplet, and the effect of inertia overcoming the tendency for the weight to produce a collision in the slow velocity region in the rear. When the electrical or phoretic forces are sufficiently large the Greenfield Gap is closed.When the particles have radii < 3 μm inertial effects no longer dominate the collisions, although inertia modifies the weight effects for particles with radii down to about 0.5 μm. For charged aerosol particles with radii smaller than about 0.1 μm interacting with droplets or background aerosol particles smaller than a radius of about 15 μm, the long range electrical repulsive force is effective in opposing the phoretic forces and keeping the particle out of range of the short range attractive image force. Thus ‘electroscavenging’ gives way to ‘electroprotection’ against the scavenging or coagulation processes otherwise caused by Browninan diffusion or phoretic forces.In an atmosphere of temperature 10 °C and pressure 900 hPa the net phoretic force reduces to zero and becomes repulsive for particles with radii above about 2 μm (depending on particle conductivity). This enhances the development of the Greenfield Gap. However, the value of this radius (at which the net phoretic force is zero) increases strongly with decreasing temperature and pressure (increasing altitude) as expected from theory, and is about 5 μm in the middle troposphere and more than 10 μm in the stratosphere. Thus a net attractive phoretic force on particles extends into the 1–3 μm radius range in the upper troposphere; however, the weight and inertial effects can ensure the presence of the Greenfield Gap in that range for 2000 kg m− 3 particles up to the middle stratosphere.
Atmospheric Research.
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ABSTRACT: Monte Carlo models of the distribution of atomic hydrogen in the exosphere of Venus were computed which simulate the effects of thermospheric winds and the production of a “hot” hydrogen component by charge exchange of H+ and H and O in the exosphere, as well as classic exospheric processes. A thermosphere wind system that is approximated by a retrograde rotating component with equatorial speed of 100 m/sec superimposed on a diurnal solar tide with cross-terminator day-to-night winds of 200 m/sec is shown to be compatible with the thermospheric hydrogen distribution deduced from Pioneer Venus orbiter measurements.
Icarus.
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Brian A. Tinsley
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ABSTRACT: It is argued that there is a terrestrial loss of hydrogen as ions which includes the polar wind but extends effectively down to a latitude in the range 45–50° invariant. In daytime and for much of the night-time the flux is close to the limiting value for H+ flow through the topside ionosphere. It is argued that the flux decreases rapidly with increasing solar activity, following the decrease in neutral hydrogen concentration. It has been found that as solar activity increases the Jeans escape flux increases, and the charge exchange escape flux increases until moderate solar activity levels are reached. As solar activity increases from moderate to high levels, the charge exchange escape may decrease again. A new budget for terrestrial hydrogen loss over the solar cycle is given. The global flux of hydrogen ions outward from the ionosphere is comparable with estimates of the plasma sheet loss rates, and this flux, together with some solar wind plasma, is an attractive source for the plasma sheet.The energetic neutrals produced from the charge exchange of ring current ions with thermal-energy neutrals in the exosphere produce the optical emission of the equatorial aurora, which can be related to ion production rates near and above the E-region. The ionization production is adequate to explain the enhancements in ion production observed during magnetic storms at Arecibo.
Planetary and Space Science.
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ABSTRACT: Reports of a variety of short-term meteorological responses to changes in the global electric circuit associated with a set of disparate inputs are analyzed. The meteorological responses consist of changes in cloud cover, atmospheric temperature, pressure, or dynamics. All of these are found to be responding to changes in a key linking agent, that of the downward current density, Jz, that flows from the ionosphere through the troposphere to the surface (ocean and land). As it flows through layer clouds, Jz generates space charge in conductivity gradients at the upper and lower boundaries, and this electrical charge is capable of affecting the microphysical interactions between droplets and both ice-forming nuclei and condensation nuclei.Four short-term inputs to the global circuit are due to solar activity and consist of (1) Forbush decreases of the galactic cosmic ray flux; (2) solar energetic particle events; (3) relativistic electron precipitation changes; and (4) polar cap ionospheric convection potential changes. One input that is internal to the global circuit consists of (5) global ionospheric potential changes due to changes in the current output of the highly electrified clouds (mainly deep convective clouds at low latitudes) that act as generators for the circuit.The observed short-term meteorological responses to these five inputs are of small amplitude but high statistical significance for repeated Jz changes of order 5% for low latitudes increasing to 25–30% at high latitudes. On the timescales of multidecadal solar minima, such as the Maunder minimum, changes in tropospheric dynamics and climate related to Jz are also larger at high latitudes, and correlate with the lower energy component (∼1 GeV) of the cosmic ray flux increasing by as much as a factor of two relative to present values. Also, there are comparable cosmic ray flux changes and climate responses on millennial timescales. The persistence of the longer-term Jz changes for many decades to many centuries would produce an integrated effect on climate that could dominate over short-term weather and climate variations, and explain the observed correlations.Thus, we propose that mechanisms responding to Jz are a candidate for explanations of sun–weather–climate correlations on multidecadal to millenial timescales, as well as on the day-to-day timescales analyzed here.
Advances in Space Research.
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ABSTRACT: 1] The effects of electric charge on collision rate coefficients for scavenging of aerosol particles by droplets are evaluated, as appropriate to weak electrification conditions in clouds. Variations in charges on droplets and particles in clouds are proportional to the flow of current in the global electric circuit through gradients in resistivity, which are determined by gradients in droplet concentration and humidity. We obtain the collision rate coefficients by ''trajectory model'' calculations for spherical aerosol particles and droplets using the exact electrical force equation, with its long-range repulsion and short-range attraction, interacting with drag, inertia, and phoretic forces. The use of the exact electric force gives rate coefficients up to a factor of two greater than previous image charge calculations for particles in the ''Greenfield Gap''. Rate coefficients for scavenging by Brownian diffusion are obtained by the analytic expression for ''flux model'' calculations. Rate coefficients for combined effects of electric and phoretic scavenging are given, as appropriate for scavenging of droplets evaporating to residual particles while temporarily retaining the original droplet charge. For particles of radii below about 0.1 mm and with charges typical of residues of freshly evaporated droplets, the long-range repulsive electrical force reduces the collision rate coefficients below those for phoretic scavenging in subsaturated air and below the rates for Brownian scavenging. Time constants for scavenging of particles are given for selected values of droplet size, particle and droplet charges, and particle density, and the applications to observed effects in the atmosphere are discussed. Citation: Zhou, L., B. A. Tinsley, and A. Plemmons (2009), Scavenging in weakly electrified saturated and subsaturated clouds, treating aerosol particles and droplets as conducting spheres, J. Geophys. Res., 114, D18201, doi:10.1029/2008JD011527.
