Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity

Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kVm-1 to 100 kVm-1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m-1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ measurements

The global atmospheric electrical circuit and climate

Evidence is emerging for physical links among clouds, global temperatures, the global atmospheric electrical circuit and cosmic ray ionisation. The global circuit extends throughout the atmosphere from the planetary surface to the lower layers of the ionosphere. Cosmic rays are the principal source of atmospheric ions away from the continental boundary layer: the ions formed permit a vertical conduction current to flow in the fair weather part of the global circuit. Through the (inverse) solar modulation of cosmic rays, the resulting columnar ionisation changes may allow the global circuit to convey a solar influence to meteorological phenomena of the lower atmosphere. Electrical effects on non-thunderstorm clouds have been proposed to occur via the ion-assisted formation of ultra-fine aerosol, which can grow to sizes able to act as cloud condensation nuclei, or through the increased ice nucleation capability of charged aerosols. Even small atmospheric electrical modulations on the aerosol size distribution can affect cloud properties and modify the radiative balance of the atmosphere, through changes communicated globally by the atmospheric electrical circuit. Despite a long history of work in related areas of geophysics, the direct and inverse relationships between the global circuit and global climate remain largely quantitatively unexplored. From reviewing atmospheric electrical measurements made over two centuries and possible paleoclimate proxies, global atmospheric electrical circuit variability should be expected on many timescale

Energetic particle influence on the Earth's atmosphere

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

Water vapour changes and atmospheric cluster ions

Properties of small ions in atmospheric air have been investigated using a modern ion spectrometer with co-located meteorological and atmospheric electrical measurements, in urban air at Reading during May and June, (days 147-154) 2005. The ion spectrometer's programmed measurement sequence determined the mean ion currents and their variability, permitting derivation of positive and negative ion number concentrations, and their associated mean mobilities, on a ∼ 30 min cycle. The ion measurements were validated by comparing the derived air conductivity with the nearby atmospheric electrical potential gradient, and both these independently measured parameters correlated closely under fair weather conditions. Histograms of the mean mobility for positive (μ+) and negative (μ-) ions across the 7 days of measurement showed μ- > μ+, i.e. that the negative ion mass was less than that of positive ions. Adjacent air humidity measurements were used to analyse the mobility data. Using the median water vapour pressure of 4.1 hPa as a threshold, the mean μ+ was found to be significantly lower when vapour pressures were above the threshold, but there was no significant change in μ- with vapour pressure. As the effect on positive ions remains present in strong sunlight, weak sunlight, and darkness, it is unlikely to be solely of photochemical origin but, more probably, related to changes in ion hydration. There is therefore an asymmetric response of positive and negative ions to water vapour. This will influence the aerosol electrification in fogs and clouds, and modify the radiative response of hydrated ion clusters. © 2007 Elsevier B.V. All rights reserved

Nineteenth century Parisian smoke variations inferred from Eiffel Tower atmospheric electrical observations

Atmospheric electrical measurements provide proxy data from which historic smoke pollution levels can be determined. This approach is applied to infer autumnal Parisian smoke levels in the 1890s, based on atmospheric electric potential measurements made at the surface and the summit of the Eiffel Tower (48.7°N, 2.4°E). A theoretical model of the development of the autumn convective boundary layer is used to determine when local pollution effects dominated the Eiffel Tower potential measurements. The diurnal variation of the Eiffel Tower potential showed a single oscillation, but it differs from the standard oceanic air potential gradient (PG) variations during the period 09-17UT, when the model indicates that the Eiffel Tower summit should be within the boundary layer. Outside these hours, the potential changes closely follow the clean air PG variation: this finding is used to calibrate the Eiffel Tower measurements. The surface smoke pollution concentration found during the morning maximum was 60±30μgm-3, substantially lower than the values previously inferred for Kew in 1863. A vertical smoke profile was also derived using a combination of the atmospheric electrical data and boundary layer meteorology theory. Midday smoke concentration decreased with height from 60μgm-3 at the surface to 15μgm-3 at the top of the Eiffel Tower. The 19th century PG measurements in both polluted and clean Parisian air present a unique resource for European air pollution and atmospheric composition studies, and early evidence of the global atmospheric electrical circuit. © 2003 Elsevier Ltd. All rights reserved

Absorption of infra-red radiation by atmospheric molecular cluster-ions

Protonated water clusters are a common species of atmospheric molecular cluster-ion, produced by cosmic rays throughout the troposphere and stratosphere. Under clear-sky conditions or periods of increased atmospheric ionisation, such as solar proton events, the IR absorption by atmospheric ions may affect climate through the radiative balance. Fourier Transform Infrared Spectrometry in a long path cell, of path length 545m, has been used to detect IR absorption by corona-generated positive molecular cluster-ions. The column concentration of ions in the laboratory spectroscopy experiment was estimated to be ~10^13 m-2; the column concentration of protonated atmospheric ions estimated using a simple model is ~10^14 m-2. Two regions of absorption, at 12.3 and 9.1 um are associated with enhanced ion concentrations. After filtering of the measured spectra to compensate for spurious signals from neutral water vapour and residual carbon dioxide, the strongest absorption region is at 9.5 to 8.8 um (1050 to 1140 cm-1) with a fractional change in transmissivity of 0.03 plus/minus 0.015, and the absorption at 12.5 to 12.1 um (800 to 825 cm-1) is 0.015 plus/minus 0.008.Comment: In press at Journal of Atmospheric and Solar-Terrestrial Physic