Fine Structure of the Global Electric Circuit

An extensive database obtained after long-term ground-based aero-electrical and magnetic measurements at the Geophysical Observatory “Borok”, enables a unique insight into the main components of the global electric circuit and their interconnection from the middle-latitude observation point. Data analysis allows us to describe the global electric circuit as an aggregation of structures with different spatio-temporal scales, including aeroelectric structures, thunderstorms, and synoptic-scale structures. The results of simultaneous observation of aeroelectric and geomagnetic fields during magnetic storm conditions are presented to illustrate strong coupling of different-scale phenomena in the global circuit. INTRODUCTION Over the recent decade many efforts have been undertaken both in observation and theoretical modeling providing substantial progress in understanding the global circuit. According to its classical definition, the global electrical circuit represents the current contour formed by bottom ionosphere and terrestrial surface conducting layers, with thunderstorm generators as the basic electrical sources, and the areas of a free atmosphere as zones of returnable currents [Bering et al., 1998; Rycroft et al., 2000]. Recent knowledge has brought an essentially new approach to appreciate structure and dynamics of aero-electrical processes in the Earth’s electrical environment [Anisimov et al., 19992003]. In this paper we present typical examples of these processes observed at the mid-latitude point: fair-weather electric field and its variations, fog and deep convection, great-scale air mass front transition and thunderstorm, magnetic storm. Along with case-study importance they illustrate strong coupling of different-scale phenomena in the global electric circuit. EXPERIMENTAL RESULTS AND DISCUSSION Wind For investigation of fine structure of the global electric circuit, we used the extensive database of long-term ground-based aero-electrical measurements and the data of several special campaigns directed to the study of the surface-layer electrodynamics. Particularly, a database of the mid-latitude Borok Geophysical Observatory [58.03 N, 38.33 E; L =2.95] contributes substantially to the study of the Earth's electromagnetic environment (http://geobrk.adm.yar.ru:1352). The Borok Geophysical Observatory (BGO) remains a unique mid-latitude geophysical observatory, performing continuous observations of geomagnetic and aeroelectric fields, air electric current and telluric currents, atmospheric pressure pulsations and other meteorological parameters, Doppler sounding of the ionosphere. The electrostatic fluxmeter of a “field mill” type is used for precise long-term observatory measurements of the atmospheric electric field. The horizontal long-wire antenna (“current collector”) is mounted for measurements of vertical electric current density. The effective antenna area is 2500 m. The digital data of aeroelectrical observations since 1997 has been recently included into the BGO database [Anisimov et al., 2001]. The remote receiving of electric field variations has been applied for the study of electrodynamic properties of the lower atmosphere. For this method realization aeroelectric field was measured by means of aeroelectrical sensors synchronously. The sampling rate of the digital recording was equal to 10 Hz. An example of the layout chart of field mills sensors is shown in Fig.1. Remote receiving of electric field variations . Fig.1. Five summer-autumn seasons campaigns were conducted for the study of aeroelectrodynamics of the lower atmosphere since 1998 to 2002. The field mils and electrostatic induction sensors were used for aeroelectrical ground-based observations. According to the goals of particular experiments, space scales of remote receiving experiments were changed from 3 m to 1000 m. The database of convective season campaigns has compiled about 10 Gb of aeroelectrical, geomagnetic and thermodynamical data. Data processing included the spectra, structure, spectral-timing and structuretemporal analysis of electric-field pulsations, using time series from tens of minutes to daily files. In the global electrical circuit the atmospheric electricity can be considered as a superposition of a number of factors. So the atmospheric electric field with a mean value Ez0 may be represented as follows: Ez(φ,θ,h,t)=Ezo(φ,θ,h,tUT)+∆EzM(φ,θ,h,tUT,tMT)+∆EzL(φ,θ,h,tUT,tMT,tLT) (1) KHZ-EZ= 0. 63 Lag = 106 min KHX-EZ= 0.76 Lag = 0 min KHY-EZ= 0.7 Lag = 183 min KHZ-EZ= 0.77 Lag = 200 min 00:00 – 24:00 04:00 – 24:00 04:00 – 16:00 00:00 – 24:00 KHX-EZ= 0.67 Lag = 10 min KHY-EZ= 0.81 Lag = 60 min KHX-HZ= 0.81 Lag = 0 min KHY-HZ= 0.81 Lag = -140 min 28-Mar 29-Mar 30-Mar 31-Mar 1-Apr 2 4 0 0 2 6 0 0 2 8 0 0 3 0 0 0 3 2 0 0 3 4 0 0 3 6 0 0 0 . 4 0 . 0 0 . 4 0 . 8 1 . 2 n T