There are at least three independent ways in which the solar wind modulates the flow of current density (Jz) in the global electric circuit. These are (A) changes in the galactic cosmic ray energy spectrum, (B) changes in the precipitation of relativistic electrons from the magnetosphere, and (C) changes in the ionospheric potential distribution in the polar caps due to magnetosphere-ionosphere coupling. The current density J
z flows between the ionosphere and the surface, and as it passes through conductivity gradients it generates space charge concentrations dependent on J
z and the conductivity gradient. The gradients are large at the surfaces of clouds and space charge concentrations of order 1000 to 10,000 elementary charges per cm3 can be generated at cloud tops. The charge transfers to droplets, many of which are evaporating at the cloud-clear air interface. The charge remains on the residual evaporation nuclei with a lifetime against leakage of order 1000 sec, and for a longer period the nuclei also retain coatings of sulfate and organic compounds adsorbed by the droplet while in the cloud. The charged evaporation nuclei become well mixed with more droplets in many types of clouds with penetrative mixing. The processes of entrainment and evaporation are also efficient for these clouds. The collection of such nuclei by nearby droplets is greatly increased by the electrical attraction between the charge on the particle and the image charge that it creates on the droplet. This process is called electroscavenging. Because the charge on the evaporation nuclei is derived from the original space charge, it depends on J
z, giving a rate of electroscavenging responsive to the solar wind inputs. There may be a number of ways in which the electroscavenging has consequences for weather and climate. One possibility is enhanced production of ice. The charged evaporation nuclei have been found to be good ice forming nuclei because of their coatings, and so in supercooled clouds droplet freezing can occur by contact ice nucleation, as the evaporation nuclei are electroscavenged. Although quantitative models for the all the cloud microphysical processes that may be involved have not yet been produced, we show that for many clouds, especially those with broad droplet size distributions, relatively high droplet concentrations, and cloud top temperatures just below freezing, this process is likely to dominate over other primary ice nucleation processes. In these cases there are likely to be effects on cloud albedo and rates of sedimentation of ice, and these will depend on J
z. For an increase in ice production in thin clouds such as altocumulus or stratocumulus the main effect is a decrease in albedo to incoming solar radiation, and in opacity to outgoing longwave radiation. At low latitudes the surface and troposphere heat, and at high latitudes in winter they cool. The change in meridional temperature gradient affects the rate of cyclogenesis, and the amplitude of planetary waves. For storm clouds, as in winter cyclones, the effect of increased ice formation is mainly to increase the rate of glaciation of lower level clouds by the seeder-feeder process. The increase in precipitation efficiency increases the rate of transfer of latent heat between the air mass and the surface. In most cyclones this is likely to result in intensification, producing changes in the vorticity area index as observed. Cyclone intensification also increases the amplitude of planetary waves, and shifts storm tracks, as observed. In this paper we first describe the production of space charge and the way in which it may influence the rate of ice nucleation. Then we review theory and observations of the solar wind modulation of J
z, and the correlated changes in atmospheric temperature and dynamics in the troposphere. The correlations are present for each input, (A, B, and C), and the detailed patterns of responses provide support for the inferred electrical effects on the physics of clouds, affecting precipitation, temperature and dynamics.

Influence of Solar Wind on the Global Electric Circuit, and Inferred Effects on Cloud Microphysics, Temperature, and Dynamics in the Troposphere

The ionization production by MeV-GeV particles (mostly galactic cosmic rays) in the lower atmosphere has-well defined variations on a day-to-day time scale related to solar activity, and on the decadal time scale related to the sunspot cycle. New results based on an analysis of 33 years of northern hemisphere meteorological data show clear correlations of winter cyclone intensity (measured as the changes in the area in which vorticity is above a certain threshold) with day-to-day changes in the cosmic ray flux. Similar correlations are also present between winter cyclone intensity, the related storm track latitude shifts, and cosmic ray flux changes on the decadal time scale. These point to a mechanism in which atmospheric electrical processes affect tropospheric thermodynamics, with a requirement for energy amplification by a factor of about 107 and a time scale of hours. A process is hypothesized in which ionization affects the nucleation and/or growth rate of ice crystals in high-level clouds by enhancing the rate of freezing of thermodynamically unstable supercooled water droplets which are known to be present at the tops of high clouds. The electrofreezing increases the flux of ice crystals that can glaciate midlevel clouds. In warm core winter cyclones the consequent release of latent heat intensifies convection and extracts energy from the baroclinic instability to further intensify the cyclone. As a result, the general circulation in winter is affected in a way consistent with observed variations on the interannual/decadal time scale. The effects on particle concentration and size distributions in high-level clouds may also influence circulation via radiative forcing.

Apparent tropospheric response to MeV‐GeV particle flux variations: A connection via electrofreezing of supercooled water in high‐level clouds?

Tornadoes, with measured wind speeds of 125 m s−1 to perhaps 140 m s −1, are the most violent of atmospheric storms (Fig. 5.1). A tornado is defined here as a violently rotating, narrow column of air, averaging about 100 m in diameter, that extends to the ground from the interior of a cumulonimbus (or occasionally a cumulus congestus) cloud and appears as a condensation funnel pendant from cloud base and/or as a swirling cloud of dust and debris rising from the ground. Significant damage can occur at the ground even when the condensation funnel does not reach the surface. A condensation funnel associated with a tornadic vortex that fails to contact the ground is called a funnel cloud. A waterspout is a tornado over a body of water.

Tornadoes and Tornadic Storms

The structure and behavior of multiple subtornadic-scale vortices in a tornado were examined and were compared with laboratory, conceptual, and numerical models. Unique radar observations of an exceptionally large and violent tornado obtained with a Doppler on Wheels mobile radar on 3 May 1999 in northern Oklahoma provided the opportunity, for the first time ever with quantitative radar measurements, to characterize the size, strength, motion, horizontal and vertical structure, and persistence of multiple vortices in a tornado. Doppler velocity, received power, and spectral-width data were used to study the vortices. The structures of the multiple subtornadic-scale vortices were similar to that of tornadic vortices in certain respects. They exhibited doughnut-shaped received power maxima and/or hooks surrounding comparatively clear central eyes. Doppler velocity differences across the vortices decreased with height. However, the vortices exhibited intense small-scale shears at their centers that ...

The Multiple-Vortex Structure of a Tornado

We analyze reported correlations between solar activity and weather and climate and show that in six independent data sets there is a correlation of measured changes in atmospheric dynamics with measured or inferred changes in vertical atmospheric air-earth current density. The current density changes are due to external modulation of the global electric circuit by the solar wind. We describe the several ways in which the solar wind modulates the global circuit, and the observations that support a simple model of the circuit, with two return paths in parallel. One return path is at low latitudes with relatively constant impedance and the other is at high latitudes and is responsive to solar wind modulation. The six independent data sets exhibiting the correlations include meteorological and air-earth current density changes on the 10 to 12-year solar cycle as well as on the day-to-day timescales of Forbush decreases of galactic cosmic ray flux and of heliospheric current sheet crossings. The geographic locations include northern and southern high latitudes as well as the tropics. In regions where these correlations arc found, there exists free energy in the form of supercooled water droplets near the tops of clouds that are unstable with respect to precipitation. Laboratory data and models suggest that electrostatic charge accumulating on supercooled droplets and aerosols near cloud tops affects the probability of ice nucleation and droplet freezing, enhancing the rate of growth and sedimentation of ice crystals. This proposed mechanism is also an explanation for another longstanding meteorological problem, the discrepancy between measurements at cloud tops of initial concentrations of ice and of concentrations of ice-forming nuclei. For light cloud cover the effect of increases in ice nucleation and sedimentation can he to reduce cloud opacity and albedo. For storm cloud systems the effect can be to enhance precipitation rates and latent heat release intensifying the storm. In several cases, measured or inferred storm intensification (or weakening) is directly related to measured or inferred increases (or decreases) of air-earth current density. Thus electrical effects on cloud microphysics may serve as connecting links between the observed or inferred increases in air-earth current density and the observed changes in atmospheric dynamics. In cases where thunderstorm electric fields are generated there are additional cloud microphysical effects that might contribute to the correlations. We discuss the present uncertainties regarding solar wind effects on the distribution of air-earth current density in the glohal electric circuit and regarding the relevant cloud microphysics. Much work is required to quantify these effects and evaluate their importance relative to competing processes.

Correlations of atmospheric dynamics with solar wind‐induced changes of air‐Earth current density into cloud tops

The primary goal of this paper is to diagnose, the “direct” and “indirect” effects of latent heat release on a synoptic-scale wave system containing an extratropical cyclone that developed over the eastern United States. To achieve this goal, comparisons are made between MOIST (full model physics) and DRY (latent heating removed) predictions of the wave system during the period 27–29 February 1984 using the National Meteorological Center's Limited-Area Fine Mesh (LFM) model. Both the MOIST and DRY models predict significant cyclone systems, suggesting that the background adiabatic forcing is quite important. However, the DRY model predict a weaker cyclone. The direct and indirect latent heating influences are diagnosed using eddy energy quantities and the extended height tendency equation. Direct effects are restricted to the diabatic generation of available potential energy and height tendencies forced by diabatic heating. Results show that latent heating exerts an important direct influence on ...

Direct and Indirect Effects of Latent Heat Release on a Synoptic-Scale Wave System

The roles of adiabatic and diabatic forcings in the development of a cyclone are examined. The two types of height tendency equations (classical quasi-geostrophic and extended forms) employed to solve for height tendency are described. The extended equation, in which geostrophic wind is replaced with observed wind, the effects of diabatic heating are added, and three-dimensional varying static stability is permitted, is utilized to analyze the evolution of the January 9-11, 1975 cyclone event. The analysis reveals that vorticity advection has a primary effect on the movement and propagation of the wave system; the differential thermal advection has a secondary, but significant role in wave development; latent heating effects are minimal; and the vertical advection of static stability slows the propagation and development of the wave.

Patricia M. Pauley

Papers

Direct and Indirect Effects of Latent Heat Release on a Synoptic-Scale Wave System

A Comparison of Adiabatic and Diabatic Forcing in an Intense Extratropical Cyclone System