This review is an overview of progress in understanding the theory and observation of the global atmospheric electric circuit, with the focus on its dc aspects, and its short and long term variability. The effects of the downward ionosphere-earth current density, Jz, on cloud microphysics, with its variability as an explanation for small observed changes in weather and climate, will also be reviewed. The global circuit shows responses to external as well as internal forcing. External forcing arises from changes in the distribution of conductivity due to changes in the cosmic ray flux and other energetic space particle fluxes, and at high magnetic latitudes from solar wind electric fields. Internal forcing arises from changes in the generators and changes in volcanic and anthropogenic aerosols in the troposphere and stratosphere. All these result in spatial and temporal variation in Jz.Variations in Jz affect the production of space charge in layer clouds, with the charges being transferred to droplets and aerosol particles. New observations and new analyses are consistent with non-negligible effects of the charges on the microphysics of such clouds. Observed effects are small, but of high statistical significance for cloud cover and precipitation changes, with resulting atmospheric temperature, pressure and dynamics changes. These effects are detectable on the day-to-day timescale for repeated Jz changes of order 10%, and are thus second order electrical effects. The implicit first order effects have not, as yet, been incorporated into basic cloud and aerosol physics. Long term (multidecadal through millennial) global circuit changes, due to solar activity modulating the galactic cosmic ray flux, are an order of magnitude greater at high latitudes and in the stratosphere, as can be inferred from geological cosmogenic isotope records. Proxies for climate change in the same stratified depositories show strong correlations of climate with the inferred global circuit variations.The theory for electrical effects on scavenging of aerosols in clouds is reviewed, with several microphysical processes having consequences for contact ice nucleation; effects on droplet size distributions; precipitation and cloud lifetimes. There are several pathways for resulting macroscopic cloud changes that affect atmospheric circulation; including enhanced ice production and precipitation from clouds in cyclonic storms, with latent heat release affecting cyclone vorticity; and cloud cover changes in layer clouds that affect the atmospheric radiation balance. These macroscopic consequences of global circuit variability affecting aerosols–cloud interactions provide explanations for the many observations of short term and long term changes in clouds and climate that correlate with measured or inferred Jz and cosmic ray flux changes due to external or internal forcing, and lead to predictions of additional effects.

https://iopscience.iop.org/article/10.1088/0034-4885/71/6/066801/pdf

The global atmospheric electric circuit and its effects on cloud microphysics

This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere.

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Energetic Particle Influence on the Earth's Atmosphere

A quasi-steady model of global lower atmospheric electricity is presented. The model considers thunderstorms as dipole electric generators that can be randomly distributed in various regions and that are the only source of atmospheric electricity and includes the effects of orography and electrical coupling along geomagnetic field lines in the ionosphere and magnetosphere. The model is used to calculate the global distribution of electric potential and current for model conductivities and assumed spatial distributions of thunderstorms. Results indicate that large positive electric potentials are generated over thunderstorms and penetrate to ionospheric heights and into the conjugate hemisphere along magnetic field lines. The perturbation of the calculated electric potential and current distributions during solar flares and subsequent Forbush decreases is discussed, and future measurements of atmospheric electrical parameters and modifications of the model which would improve the agreement between calculations and measurements are suggested.

A quasi-static model of global atmospheric electricity 1. The lower atmosphere

Atmospheric electrical processes may help explain statistical findings indicating that variable solar activity, such as solar flares or the Earth's position in the extended solar magnetic field, affects the weather. An atmospheric electrical mechanism bypasses difficulties associated with solar heating mechanisms. Understanding Sun–weather relationships offers a basis for long range weather forecasting.

Solar modulation of atmospheric electrification and possible implications for the Sun–weather relationship

The atmospheric global electric circuit : An overview

Recordings of potential gradient and air-earth current in fair-weather conditions were made at high-elevation mountain stations; the latter were generally above the vertical-mixing layer and not disturbed by local sources. Both electrical quantities increased significantly from the day of appearance of a solar flare (or a maximum incidence of flares) till the fourth day after the event. Peak potential gradient and air-earth current exceed the ‘normal levels’ measured during quiet-sun conditions by 50–60% in terms of averages. This result was compared with sferics incidence data and daily geomagnetic coefficients grouped around the selected (flare) dates. Both of the latter quantities show time histories (for the days preceding and following the selected dates) closely correlated with the atmospheric-electrical histories of the same intervals. We may conclude from these results that the total potential between the ground and the upper atmosphere increases for several days after solar flares. The results obtained by previous studies on Mauna Loa confirm this inference. The cause of the phenomenon is presumed to be enhanced thunderstorm activity attendant on solar disturbances.

Solar flares and their impact on potential gradient and air-earth current characteristics at high mountain stations

For the period February 1967–May 1969, a period of increasing solar activity, unrestricted substantiation was obtained of earlier results which had indicated that subsequent to Hα-flares potential gradient and air-earth current will increase significantly. A presupposition of this result is that the atmospheric electrical elements are recorded at stations with only minimal local climatic and aerosol physical disturbance factors, and that only meteorologically undisturbed days are used. It was ascertained that the exclusive use of fine weather days is of no influence on the results. The confirmed solar-terrestrial relation is even more pronounced when measurements are based on flares in the vicinity of the central meridian of the sun. It was further substantiated that the frequency of sferics pulses is significantly increased from the flare day on. As the cause for this a solar-triggered increase in thunderstorm frequency is suggested which, in turn, leads to an increase of the potential gradient and earth current. Proton flares have an effect analogous to that of Hα-flares. If Hα-flare key days are used on which significant changes were observed in the distribution of pressure over the northern hemisphere, a significant increase of potential gradient and air-earth current is found even with these flare key days. Thus for the first time a connection is made between solar-caused atmospheric electrical effects and synchronous global meteorological changes.

Further evidence for impact of solar flares on potential gradient and air-earth current characteristics at high mountain stations

From the years of 1968 and 1969, five periods were selected which are distinguished by the fact that at the recording site for potential gradientE and air earth currentI (at 3000 m a.s.l.), pure fine weather prevailed for 7 up to 20 days, and the site was persistently situated above the exchange layer. Thus, favorable conditions existed for the investigation of solar impact on the behavior ofE andI. The following parameters were compared withE andI during said periods: solar flares bursts of very high frequency waves,X and proton bursts, solar wind velocity, geomagnetic disturbances and storms, and solar 10 cm radiation flux. It became very apparent that a maximum of 10 cm flux was followed, after a few days, by a maximum ofE xI. This correlation is more pronounced than that existing betweenE xI and solar flares. The correlation ofE xI with other geophysical and astrophysical parameters is loose by comparison. The investigations have revealed that fine analyses such as have been attempted here, might be suited for clearing up, step by step, the actual causal relationship between a solar event and the behavior of the atmospheric electrical parameters.

Case study concerning the impact of solar activity upon potential gradient and air earth current in the lower troposphere

Vertical mixing and transport processes are studied, and their variation as influenced by atmospheric fine-structure conditions investigated, using data gathered from simultaneous measurements of RaB and RaC concentration in the ambient air at three mountain stations located close to each other horizontally, but at markedly differing levels (730, 1780 and 2960 m). RaB was used as a tracer on account of the high sensitivity to variations of vertical-mixing activity evidenced by RaB abundance figures. Strong inversions between 700 and 2500 m a.s.l. create a ‘zero condition’ at the higher level, where only 0.1% of the low-level RaB reading obtains; active turbulent mixing, on the other hand, leads to nearly equal RaB readings at the two levels. The vertical gradient of concentration of RaB is used to compute mean vertical-mass-exchange coefficients; the latter are studied in their relation to atmospheric structure characteristics. Statistical studies indicate that the barring effect of inversions is related solely to the magnitude of the inverse temperature gradient. Problems of radioactive equilibrium RaB-RaC are discussed, and the significance of aerosol particle size taken into consideration.

Upward flux of RaB and RaC in the planetary boundary layer as controlled by atmospheric microstructure

If needle-shaped ice crystals are grown in an atmosphere containing traces of nitrous gases, the amount of electrical charge generated when sharp crystal points break away, is between 10 and 50 times as high as in the case of crystals grown in absence of nitrous gases A definite relation has been found to exist between the NO3′ ion concentration of the ice crytals and the amount of charge (average value 2.7×10−8, maximum value 13×10−8 coulombs per gram of ice splinters) generated upon fragmentation. The relation found is possibly of importance with respect to thunderstorm electricity generation.

Reinhold Reiter

Papers

Solar flares and their impact on potential gradient and air-earth current characteristics at high mountain stations

Further evidence for impact of solar flares on potential gradient and air-earth current characteristics at high mountain stations

Case study concerning the impact of solar activity upon potential gradient and air earth current in the lower troposphere

Upward flux of RaB and RaC in the planetary boundary layer as controlled by atmospheric microstructure

Traces of NO{ 3 / ' } ions contained in ice crystals influence charge separation upon crystal fragmentation