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Wednesday, 20 December 2006 05:00
SLAP: Solar Variability Linkages to Atmospheric ProcessesWritten by Administrator
In polar regions an additional atmospheric circuit generator is active. The interaction of the solar wind and the Earth's magnetic field, the process that also results in the generation of the aurora, maintains a variable, generally dawn-to-dusk directed, potential difference across the polar cap. This manifests as a vertical electric field at ground level. The solar wind generator contributes a variable average of up to ~20% to the atmospheric circuit in polar regions, dependent upon the magnetic latitude of the location.
The atmospheric electric circuit links weather and solar activity. Thunderstorms and electrified clouds are the main generators of the circuit and solar activity influences cosmic rays which are the principal source of atmospheric ionisation which modulates the current flowing through the circuit. Thunderstorms and electrified clouds maintain a time-varying electric potential of ~250 kV, directed downward, between the global equipotentials of the ionosphere (except where local generators directly link to the ionosphere, maintaining local potential differences) and the ground. In fair-weather regions this potential drives an air-Earth current ~3 pA m-2 but can be most readily measured as a vertical electric field of ~100V m-1 near ground level. Both these values are approximately doubled on the high (~3000 m) Antarctic polar plateau due to the combined influence of the decrease with altitude of atmospheric density and the increase with altitude of ionization due to cosmic rays. The time-constant of the circuit is ~20 minutes.
It remains an open and a scientifically achievable goal to determine whether or not the atmospheric circuit linkage between weather and solar activity is passive or involves active coupling i.e., whether the atmospheric circuit merely responds to both meteorological and solar variations, or whether there is an active input to weather and climate via electrically induced changes in cloud microphysics.
Present research indicates that the best place to measure the global circuit is the Antarctic plateau (high, dry, relatively meteorologically stable). The Greenland plateau provides a possible northern hemisphere site. We propose making simultaneous vertical electric field and air-earth current measurements at a range of polar sites (plans presently envisage measurements at Vostok, South Pole and Concordia, 78S 24W, 84S 26W and 75S 70W and Greenland Summit Station).
A model of the global circuit is being developed that incorporates spatially and temporally varying global ion production due to the solar wind modulation of galactic cosmic rays, globally varying tropospheric and stratospheric aerosol concentrations and ion production in the stratosphere from relativistic electron precipitation and solar energetic particle events. It is also planned to insert the polar-cap potential distribution driven by solar wind-magnetosphere-ionosphere coupling into this model. We propose to compare the model and measurements on both an individual event and averaged basis to confirm or refine our understanding of the processes involved.
Measurements indicate that the global atmospheric circuit is principally sustained by both thunderstorm activity and electrified clouds. Published evidence suggests that global thunderstorm activity has a multiplicative dependency on equatorial surface temperatures. Simultaneous measurements of the atmospheric circuit and of power in the lightning generated Schumann resonance bands may provide sensitive independent proxy monitors for both equatorially-weighted global temperature and rainfall. We propose to determine how accurately our measurements can be used as proxy monitors, and to provide an accurate reference measurement of the atmospheric circuit in the IPY era.
Ground-based atmospheric circuit instrumentation on the Antarctic Plateau has recently been used to confirm that broad-scale polar ionospheric convection potentials can be measured independent of the existence of small scale ionospheric irregularities. Our multiple polar-plateau geoelectric field measurements will contribute to understanding and monitoring polar-cap ionospheric convection.
The circumpolar vortex surrounding Antarctica is typical of the southern polar regions under winter conditions. This strong circumpolar vortex blocks lower latitude, ozone-rich air from reaching central Antarctica. In combination with the lack of solar insolation in winter, the total ozone content above the southern polar regions decreases dramatically. The depth of the so-called ozone hole and its rate of filling in spring depends on the previous state of the atmosphere and has been shown to be affected by external influences related to solar activity. The relative effects of the influences of short-term changes in cosmic ray intensity, variations of the interplanetary electric field on atmospheric parameters (temperature and pressure) in the southern winter polar regions, the dynamics of the ozone layer, the effects of solar UV radiation and the role of the global electric circuit on winter-spring Antarctic ozone concentrations will be examined.
A study of pulsed cosmophysical signals in the Arctic (Barentzburg) and in Antarctica (Novolazarevskaya) is proposed. Measurments at Novolazarevskaya have revealed the regular occurrence of pulsed signals in the solar spectrum. The most pronounced pulses have been detected 4 days ahead of solar flare proton events (SPE). Results of the analysis of the spatial-temporal anisotropy of the cosmological signals will be used for derivation of an empirical model and to study the solar sources and mechanism of the pulsed irradiation. Study of the effects of the pulsed radiation on biological and technogenic systems is also planned.
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