Influence of Meteorological Variables on Atmospheric Electric Conductivity over an Urban Location

The measurements of atmospheric electric conductivity along with selected meteorological parameters was carried out at Bengaluru, an urban site in southern India (12.96° N, 77.56° E) during January-December 2015 to understand the electric nature of urban air. During the study period, well defined diurnal variation of conductivity was observed with higher values before sun rise and lower values during afternoon hours. For most of the fair weather days, variations in conductivity show a strong correlation with relative humidity and anti-correlation with ambient temperature. The monthly mean values of conductivity show highest values in winter and lowest in monsoon and interestingly a positive Pearson’s correlation coefficient of +0.5 was found between measured alpha ionization energy and atmospheric conductivity during the study period.

The Electrical Activity of Saharan Dust as perceived from Surface Electric Field Observations in Greece

We report on the electric field variations during Saharan dust advection over two atmospheric remote stations in Greece, using synergistic observations of the vertical atmospheric electric field strength (Ez) at ground and the lidar-derived particle backscatter coefficient profiles. Both parameters were monitored for the first time with the simultaneous deployment of a ground-based field mill electrometer and a multiwavelength lidar system. The field mill timeseries are processed to extract the diurnal variations of the Global Electric Circuit and remove fast field perturbations due to peak lightning activity. In order to identify the influence of the elevated dust layers on the ground Ez, we extract a Localized Reference Electric Field from the timeseries that reflects the local fair weather activity. Then, we compare it with the reconstructed daily average behaviour of the electric field and the Saharan dust layers' evolution, as depicted by the lidar system. Reported cases of enhanced vertical electric field for detached pure dust layers suggest the presence of in-layer electric charges. Although higher dust loads are expected to result in electric field enhancement, episodic cases that reduce the electric field are also observed. To quantitatively approach our results, we examine the dependency of Ez against theoretical assumptions for the distribution of separated charges within the electrified dust layer. Electrically neutral dust is approximated by atmospheric conductivity reduction, while charge separation areas within electrically active dust layers are approximated as finite extent cylinders. This physical approximation constitutes a more realistic description of the distribution of charges, as opposed to infinite extent geometries, and allows for analytical solutions of the electric field strength, so that observed electric field variations during the monitored dust outbreaks can be explained.

A plasmachemical axially symmetric self-consistent model of daytime sprite

The paper presents the results of self-consistent axially symmetric modelling of a daytime sprite. Perturbations of the concentrations of ions, neutral compounds, excited atoms and molecules along with disturbances of the atmospheric conductivity and electric field due to the initiation of a daytime sprite are studied. It is shown that in daytime conditions a sprite develops in the altitude range between 50 and 70 km, which is approximately 20 km lower than the range of a typical nighttime sprite. The uncompensated charge of a parent flash is typically characterized by the impulse charge moment (ICM) of several thousands of C · km; in the modelling of a daytime sprite ICM values are assumed to lie in the range of 2000–4000 C · km. It is shown that the behaviour of the system can be described by two scenarios, with and without a rapid increase in electron concentration, which are studied in detail by assuming ICM values of 3750 C · km and 2750 C · km respectively. During a discharge with an ICM of 2750 C · km, the decrease in the concentration of electrons in the electric field is caused by their attachment to molecular oxygen, and no sharp increase in electron concentration occurs; the concentrations of the most significant ions and electrons reach unperturbed values in less than a second. For an ICM of 3750 C · km, an initial decrease in the electron concentration is followed by the formation of an avalanche of electrons characterized by an increase in their concentration by more than an order of magnitude relative to the initial value. A slight decrease in the electric field leads to another sharp decrease in the electron concentration; then relaxation of the ion concentration makes the electron concentration increase, but it is not before about one second after the discharge that the latter once again reaches the maximum value attained during the avalanche, and then it does not change much for several tens of second. A rapid increase in electron concentration occurs in the central part of a sprite, leading to the conductivity disturbance and rapid displacement of the electric field. As a result of this study, the possibility of the initiation of a daytime sprite by an extremely intense lightning discharge leading to a significant long-term perturbation of atmospheric chemical balance is demonstrated.

A 3D Time-Dependent Model for the Study of the Electrification of Non Spherical Dust Particles due to Ion Attachment

<p>Electrical processes can be a potential key player in the lifecycle of desert dust. The dust particles can be charged during their transport, either by the attachment of atmospheric ions or by particle to particle collisions (triboelectric effect). Measurements indicate that, on average, larger particles become positively charged while the smaller ones become negatively charged [<em>Zhao, H. L.</em>, J. Electrostat, 55, 2002; <em>Lacks, D.J.</em>, et al., Phys. Rev. Lett., 100, 188305, 2008; <em>Merrison, J.P.</em>, Aeolian Res., 4, 2012; <em>Shinbrot, T. and Herrmann, H.J.</em>, Nature, 451, 2008]. During dust transportation, the larger and mainly positively charged particles separate from the smaller negatively charged particles due to the gravitational sedimentation, which sorts the dust particles by size. This process develops vertical electric fields within the dust cloud, enhancing the pre-existing field due to the depletion of atmospheric conductivity by the presence of the dust layer [<em>Gringel W. and Mulheisen. R.</em>, Beitr. Phys. Atmos., 51, 121–8, 1978]. Depending on its strength, the total electric field within the dust cloud can: (a) counteract the gravitational settling of large particles and (b) cause a preferential orientation of the non-spherical particles along the vertical direction affecting particle aerodynamics [<em>Ulanowski, Z., et al.</em>, Atmos. Chem. Phys., 7, 2007]. Therefore, electrical processes may alter dust removal processes, and thus the evolution of particle size during transport, affecting dust-radiation-cloud interactions and the associated air quality [<em>Sajani S.Z., et al.</em>, Occup. Environ. Med., 68(6), 2011], weather, and climate modeling [<em>Mahowald, N., et al.</em>, Aeolian Res., 15, 2014].</p><p>In the present work, we have developed a novel 3D Cartesian time-dependent model that takes into account several atmospheric processes, such as: (i) the ionization due to the galactic cosmic rays radiation, (ii) the ion-ion recombination, and (iii) the ion attachment to non spherical dust particles.  The model is able to self-consistently calculate the time dynamics of the atmospheric conductivity, and the atmospheric electric field, under the presence of a distribution of stationary non spherical dust particles. Additionally, the total charge density, dust particle charge and dust particle orientation are also quantified. The new 3D electrification formalism allows the study of dust layers without imposing any symmetry and  is valid for layers with any horizontal and vertical extend, as opposed to 1D models which are valid when the horizontal extend is much larger than the vertical, or to 2D models which assume a symmetry in the shape of the dust layer. The results are compared, in the limiting case that the horizontal extend is much larger than the vertical one, with those obtained from 1D models found in the past literature [e.g. <em>Zhou, L., Tinsley, B.A.</em>, Adv. Space Res. 50, 2012]. Moreover, the effect of the studied electrification process is assessed through a comparison with recent and unique electric field measurements within lofted dust layers, as performed with the use of novel low cost atmospheric electricity sensors in an experimental campaign of the D-TECT ERC project, in Cyprus the past November.</p>

Schumann Resonance on Titan : Huygens Observations Critically Re-Assessed and prospects for the Dragonfly Mission

<p>The Huygens probe to Titan in 2005 was the first planetary probe or lander to feature ELF electric field sensing and atmospheric conductivity measurements. The atmospheric electricity community showed great interest in the claimed detection of a Schumann resonance signal on another world (despite its unexpected dominant frequency of 36 Hz), and the planetary science community embraced an interpretation of the altitude dependence of the signal as evidence of a theoretically-anticipated internal water ocean beneath an ice crust many tens of km thick.</p><p>Quantitative scrutiny suggests that prospects of detecting a Schumann signal at Titan with the Huygens experiment were in fact very poor, due to short measurement time, a horizontal antenna orientation, a lack of lightning, and the likely presence of severe dynamical effects on the probe. Although the latter objections were considered, and arguments developed against them (notably the novel postulated Saturn-magnetospheric excitation of the resonance), we have re-examined the data in the light of a better understanding of the probe dynamics. The evolution of the 36Hz power shows a very strong correlation with accelerometer records of short-period motions of the probe under its small stabilizer parachute, suggesting that mechanical oscillations of the probe and/or the antenna booms were actually the cause. The ‘signal’ ramped up just as the probe accelerated from the much more quiescent main parachute, and ceased abruptly a couple of seconds after impact.</p><p>While the Huygens signal may therefore have been an artifact, this does not mean that a Schumann resonance does not occur on Titan. Most likely if it occurs, it may be very sporadic, responding to the infrequent rainstorms on Titan. A search for such signals should therefore be a long-duration monitoring exercise (not unlike listening for seismic events that could also probe Titan’s interior). The Dragonfly mission to Titan, recently selected for launch in 2026 with arrival planned in 2034 and over two years of surface operation, provides an opportunity to perform such monitoring.</p>

Hybrid-Vlasov modelling of nightside auroral proton precipitation during southward interplanetary magnetic field conditions

Particle precipitation plays a key role in the coupling of the terrestrial magnetosphere and ionosphere by modifying the upper atmospheric conductivity and chemistry, driving field-aligned currents, and producing aurora. Yet, quantitative observations of precipitating fluxes are limited, since ground-based instruments can only provide indirect measurements of precipitation while particle telescopes onboard spacecraft merely enable point-like in-situ observations with inherently coarse time resolution above a given location. Further, orbit time scales generally prevent the analysis of whole events. On the other hand, global magnetospheric simulations can provide estimations of particle precipitation with a global view and higher time resolution. We present the first results of auroral (~ 1–30 keV) proton precipitation estimation using the Vlasiator global hybrid-Vlasov model in a noon-midnight meridional plane simulation driven by steady solar wind with southward interplanetary magnetic field. We first calculate the bounce loss cone angle value at selected locations in the simulated nightside magnetosphere. Then, using the velocity distribution function representation of the proton population at those selected points, we study the population inside the loss cone. This enables the estimation of differential precipitating number fluxes as would be measured by a particle detector onboard a low-Earth-orbiting spacecraft. The obtained differential flux values are in agreement with a well-established empirical model in the midnight sector, as are also the integral energy flux and mean precipitating energy. We discuss the time evolution of the precipitation parameters derived in this manner in the global context of nightside magnetospheric activity in this simulation, and we find in particular that precipitation bursts of

AC and DC global electric circuit properties and the height profile of atmospheric conductivity

An apparent discrepancy is pointed out - at all heights, and by up to an order of magnitude - between the height profiles of atmospheric conductivity derived at AC using ELF propagation studies, especially from information on Schumann resonance of the Earth-ionosphere cavity, and using a model of the DC global atmospheric electric circuit. This serious issue is resolved by creating a hybrid profile of these two mid-latitude profiles, the first of which refers to conditions by day and the second by night. This hybrid profile is thus a first order attempt to represent globally averaged conditions. Close to the Earth’s surface, where the resistance of the atmosphere is largest, the properties of the DC global model exert the greatest influence, whereas in the middle atmosphere, at heights between 40 and 100 km, full wave computations show that the AC results are the more crucial. The globally averaged hybrid profile presented here has some limitations, and the physical reasons for these are addressed. They are due to the presence of aerosol particles of ice and/or of meteoric material which reduce the ionospheric D-region conductivity by an order of magnitude over only ~2 km of height, thereby causing ledges of ionisation. In the context of the globally averaged profile, published observations of the ionospheric effects of the giant gamma-ray flare from SGR 1806-20 (a neutron star having an enormously large magnetic field) occurring at 21:30 U.T. on December 27, 2004, are briefly discussed.