Behaviour of the F1-region, and Esand spread-F phenomena at European middle latitudes, particularly under geomagnetic storm conditions

Knowledge of the ionospheric electron density distribution and its fluctuations is essential for predicting ionospheric characteristics for radio wave propagation and for other applications such as satellite tracking, navigation, etc. Geomagnetic storm is the most important source of the ionisation density perturbatio ns. Recent studies of the F1-region electron density distribution revealed systematic seasonal and latitudinal differences in the F1-layer response to geomagnetic storm. At European higher middle latitudes no significant effect has been observed in summer and spring at heights of 160-190 km, whereas well-pronounced depression appears in winter and late autumn at least at 180- 190 km. A brief interpretation of this finding will be presented. On the other hand, the pattern of the response of the ionosphere at F1-layer heights does not seem to depend on the type of response of F2-layer (foF2) or on solar activity. Concerning the main types of ionospheric irregularities sporadic E and spread-F, it has been found that considering sporadic E-layers as thin diffraction screen, it may be modelled for propagation of radio-waves by the determination of the temporal variation of foEs representing in ionograms the mean ion density of «patches» of increased ion density embedded in the Es-layer. Spectrum of these variations indicates the mean period of the variations, which multiplied by the wind velocity gives the mean distance of patches, that is, the mean distance between the screen points. In case of spread-F, it has been found that irregularities causing spread-F are mostly due to plasma instabilities, though the role of travelling ionospheric disturbances may be not entirely neglected

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

Study on atmospheric electric parameters considering condensation nuclei and local meteorological factors

Evening data of two atmospheric electric parameters (positive air conductivity and potential gradient) measured at Świder (Poland) between 1965 and 1995 have been investigated around days with low number of condensation nuclei (NCN). Based on the measure of the NCN decrease, two groups of days were distinguished, (days with moderate decrease: from -30% to -50% and days with strong decrease: below -50%, as related to the corresponding monthly average of the NCN).  These days have been applied as key days for two independent superposed epoch analyses. Air conductivity significantly increased both on days with moderate and strong NCN decreases.  For the strong events the conductivity increase was about the double of that found for the moderate ones. In accordance with Ohm's Law, the potential gradient showed its lowest value (in relation to the corresponding monthly average) on these key days. The response of this atmospheric electric parameter is also significant, however, it is less impressive than in the case of air conductivity. For checking the influence of meteorological changes on atmospheric electric parameters, the departures of air conductivity and potential gradient from corresponding monthly average have been tabulated according to the observed wind speed and wind direction, both for moderate and strong NCN events. Air conductivity generally showed a distinct increase with increasing wind speed in the case of both kinds of NCN events. A dependence on wind direction was also found.  The potential gradient responded in a proper sense to wind changes, even if the responses were less convincing than those of air conductivity

Changes in sporadic E parameters observed at Juliusruh during a period following solar activity maximum

Using data of Es parameters obtained at a high mid-latitude station in Germany (Juliusruh; geogr. lat.: 54º 38' daily and seasonal variations were derived and certain characteristics of these variations have been analysed during a period of changing solar activity. It has been confirmed that diurnal maxima appearing both in foEs and fbEs are generally higher around solar activity maximum than around the minimum. Seasonal maxima appearing in summer are also higher around solar activity maximum than towards the minimum. The daily variation of h'Es showed two maxima: one in the morning and another in the afternoon. The seasonal maximum of h'Es generally appeared in April or May while the minimum in October or November. All these results confirm earlier findings derived for a station in Hungary (Békéscsaba). The present study particularly intends to show changes in the diurnal variation of Es parameters associated with geomagnetic disturbances. The difference between foEs and fbEs might  be used as indicator of the transparency of the Es layer, and this quantity seems to increase on days with strong geomagnetic storms. Analysing the transparency based on the maximum values appearing in the daily variations of foEs and fbEs, a rather high quantity has been derived for stormy days in the year 1971. Actually, in this year, the daily variation of h'Es was also characterised by an extremely high afternoon maximum. The wind-shear theory is generally suitable for explaining the generation of sporadic E layer at mid-latitude. The present results are not inconsistent with the points of this theory

Long-term changes in atmospheric electricity and the multivariate ENSO index

Based on continuous measurements of the atmospheric electric potential gradient (PG) in the Geophysical Observatory at Nagycenk (Hungary), selected data of the interval 1993-2003 have been analysed. The analyses were particularly aimed at the confirmation of global signatures found by a previous study using PG data of a shorter period. The present results have proved that the seasonal variation of PG (generally showing a winter maximum and a summer minimum at land stations) might really be modified at Nagycenk by a secondary maximum appearing in summer-time of certain years. Further analyses have also been carried out by using data derived from measurements with two different apparatus, however, covering a shorter period. Moreover, a  connection between the occasional summer peaks of PG and the occurrences of warm El Niño periods might also be suggested on the basis of results derived from selected PG data and appropriate MEI Indices showing the time history of the ENSO phenomenon for the interval 1993-2003

Variations in Schumann resonances and their relation to atmospheric electric parameters at Nagycenk station

The present study is based on simultaneous measurements of the atmospheric electric potential gradient (PG) and Schumann resonances at Nagycenk station (Hungary) from 1993 to 1996. Annual and semi-annual variations detected previously in the relative amplitudes of Schumann resonances (SR) in the first three modes are confirmed by the extended data series applied here. The regular annual variation found in the PG (with winter maximum and summer minimum) is in the opposite phase, compared to that of the SR amplitudes. Nevertheless, even the PG (being a parameter of the DC global circuit) occasionally shows a distinct secondary peak in summer as indicated by the results of the present analysis (and corresponding to a recent study on further parameters of the DC global circuit). In spite of the presumed dominance of local influence over the global one, a suitable PG parameter correlates well with SR (representing the AC global circuit) on the annual time scale. It also became evident that a semi-annual variation (with spring and autumn maxima and winter and summer minima) is generally present in SR. Certain signatures of a semi-annual variation have also been revealed in the PG, however, the phase of this semi-annual variation does not fit the pattern shown by SR (and tropical surface air temperature, respectively). The representativeness of the PG data has also been checked by means of a single day's diurnal variations displaying a phase corresponding to that of the `Carnegie Curve'. Additionally, the coincidence of short-term changes (lasting some hours) both in the SR and the PG parameter is also demonstrated on a day disturbed by local factors. The results are discussed in the context of correlations between surface air temperature and parameters of the atmospheric electric global circuit shown by previous studies