Studying of solar-terrestrial connections in the dynamics of the surface atmospheric electric field

The paper presents the results of the analysis of variations in the electric field intensity of the surface atmosphere obtained in highlatitude, high-altitude and lowland observation points, together with the parameters of solar and geomagnetic activity.


Introduction
At present, in the conditions of global and regional climate changes, solar-terrestrial connections have an undeniable influence on the weather and climate of the Earth. The problem of studying the relationship of solar activity with weather events and climate, both in the short and long term, is the mechanisms of its effects on the atmosphere that are not fully understood. One of these mechanisms that can explain the influence of solar activity on meteorological and climatological processes can be the atmospheric global electrical circuit, whose characteristics are related to the parameters of solar activity, planetary indices, and the intensity of galactic cosmic rays.
The solar effect on the electrical state of the atmosphere is caused by short-wave and xray radiation, the action of solar cosmic rays and solar wind. At the same time, the impact of these factors is largely determined by the cycle of solar activity, the rotation of the Sun and Earth, and the variability of the solar atmosphere. Current research shows that the impact of solar activity on the state of the surface atmosphere is manifested in different time ranges

Theoretical bases
The influence of solar activity on the state of the lower atmosphere may be related to variations in the parameters of the global electric circuit (GEC). First, the high layers of the atmosphere are ionized mainly by ultraviolet and x-ray radiation from the Sun. Second, variations in cosmic ray flows can have a sufficient effect on the conductivity of the atmospheric column and modulate the intensity of the electric current in the planetary circuit, as well as the electric field in the "fair weather" regions. The electric field intensity is modulated by the rate of atmospheric ionization and changes in the ionospheric potential [1,2]. Galactic cosmic rays (GCR), solar protons, and electrons of the Earth's radiation belts change the rate of atmospheric ionization, and changes in the ionospheric potential can occur due to geomagnetic disturbances. Note that the variations of the GCR flow are in the opposite phase with the 11-year cycle of solar activity: at the minimum of solar activity, the interplanetary medium is weakly disturbed and the cosmic ray flows are maximum. In turn, there is a connection between the atmospheric electric field and the intensity of cosmic radiation: the atmospheric electric field decreases almost immediately after the Forbush effect in the GCR and is restored within a few days [3].

Experimental studies
Observations of the atmospheric electric field strength at the stations (Verkhne Dubrovo, Tiksi) of the network of Federal service for hydrometeorology and environmental monitoring (Roshydromet) were made by automated meters "POLE-2M" [4]. The electric field meter EFM 550 (Vaisala company) was used to register the electric field strength at the high-altitude station Peak Cheget (High-mountain geophysical Institute, Roshydromet) [5].
The high-altitude station Peak Cheget is characterized by the absence of strong sources of radioactive radiation and a low content of aerosol particles in the atmosphere [6,7]. The Tiksi polar station is located far from major industrial centers, which, in turn, also excludes strong anthropogenic influence [8]. Verkhne Dubrovo station is one of the typical continental stations. The distance from major industrial centers allows us to exclude the anthropogenic component in the formation of the electrical state of the surface layer. The main characteristics and a brief description of the observation points are shown in table 1. The station is located in the polar region, on the coast of the Arctic ocean (on the shore of the bay of the same name) Peak Cheget 43,2 42,3 3050 The station (3040 m above sea level) is located on the Northern slope of Cheget mountain in the Elbrus region The behaviour of the atmospheric electric field near the earth depending on the dynamics of solar activity is studied in this paper. The values of solar activity characteristics are obtained using the Geostationary Operational Environmental Satellite (GOES15 and GOES14) [9].
At present, the dynamics of solar activity can be expressed not only by the number of sunspots (wolf numbers), but also by the density of the radio emission stream at a wavelength of 10.7 cm. The analysis of observations shows that the relationship between these characteristics is quite strong and stable [10]. The radio emission flux density (p) is measured in solar units of flux (1 s.u.f.=10 -22 W/m 2 ) and varies widely from 50 to 300 s.u.f.
To estimate the reaction of the Earth's magnetic field to the activity of the Sun, the planetary index (A p ) is used, which represents the average level of geomagnetic activity. Values of the A p -index (in nTl): from 0 to 7 -a calm state of the ionosphere, from 15 to 20an unstable, active state, and values greater than 35 correspond to a magnetic storm.
This work is a continuation of the research started earlier. The results presented below are in good agreement and support the conclusions indicated in [11,12].

Results and discussion
In 2020, the next cycle of solar activity is coming to an end, the maximum of which was in 2014, and the minimum was in 2019. Table 2 shows some characteristics of solar activity for the summer season (June-August) for 2014 (maximum) and 2017 (closer to the minimum). On the basis of experimental data, the features of characteristic values and variations of the atmospheric electric field intensity for the periods of maximum and minimum solar activity are studied. Figure 1 shows graphs of atmospheric electric field intensity values for different numbers of spots on the Sun's surface in the year of active Sun (2014), and the values for 2017 are indicated by an asterisk. Number of sunspots presented earlier [12]. For the Tiksi polar station, on the contrary, there is a slight increase in the electric field, while for the Verkhne Dubrovo continental station, the values of the field strength practically do not change relative to the average value.
A similar behavior of the electric field is observed when comparing its values with the flux density (p) of solar radio radiation at a wavelength of 10.7 cm figure 2 shows the change in the electric field strength at different p values for the summer season of 2014. Previously, the influence of the number and power of solar flares on the values of the atmospheric electric field strength was studied [11]. This study used experimental data for periods when powerful solar flares were observed. The main characteristics of class X outbreaks observed during the summer season are shown in table 3.  Based on the experimental data for summer seasons in 2014 and 2017, obtained at the Peak Cheget mountain station, the dependence of the distribution of the electric field of the atmosphere "fair weather" from the index (Index) flare activity up to 7.5. Figure 3 shows the dependence of the electric field from the index values of flare activity.
The regression line equations approximating the experimental distributions have the form: , for 2014 data, , for 2017 data. Thus, the values of the electric field strength of the atmosphere in the year of the active Sun (2014) are greater, and the tendency to decrease the electric field is more significant when the Sun is calmer (2017). This is due to the large number of days characterized by low outbreak activity: days with Index values less than 1 are equal to 69% of the total number of cases in 2017 and, respectively, 21% in 2014. Next, we will consider some features of variations in the electric field strength of the surface atmosphere when observing powerful solar flares of class X and for calm Sun conditions. Figure 4 shows the daily variations of the atmospheric electric field averaged for periods when there were no outbreaks of class C or higher (the index of flash activity is zero) for 2014 and 2017. In addition, for comparison, the variations in the electric field on the day when the class X flash was observed are given. Based on the results of earlier studies, the dependence of the electric field strength values on the value of the Ap-index for a high-altitude observation point in the summer months was obtained, and the distribution of electric field values for different States of the geomagnetic field at stations of the Roshydromet network was considered. So, for the alpine and polar observation points there is a decrease in the intensity of the atmospheric electric field with increasing activity of the geomagnetic field [11].
In this study, the nature of daily variations of the atmospheric electric field under different geomagnetic activity is investigated. The average daily variations in the atmospheric electric field strength (in % relative to the average value) for two points (highaltitude and continental) for 2014 are shown in figure 5 at different levels of geomagnetic activity: less than 5 nTl -calm state (dotted line) and 20÷30 nTl -unstable state (solid line). Note the following characteristic features: at high values of the Ar index, the values of the electric field strength during the day for a high-altitude point are consistently higher than the average, and for a continental station, on the contrary.

Conclusions
Thus, data from atmospheric-electrical observations at continental stations in high-latitude, high-altitude and flat zones showed the influence of solar and geomagnetic activity indices on the values and variations of the surface electric field.