Simultaneous observations of the atmospheric electric potential gradient (PG) at Bharati and Maitri stations were studied from 2014 to 2016. A new regional diurnal pattern of fair-weather PG for the coastal Antarctic region, perhaps the ubiquitous characteristics of the PG for the coastal Antarctic region, has been identified. This pattern has a significant broad minimum around noon hours. It is around this time the wind speed is also maximum. The PG data of past years of Syowa, Vostok, and Carnegie Cruise were also used in this study. The surface wind distorts the fair-weather diurnal pattern of PG over Bharati more intensely than at Maitri. The katabatic wind effect on the PG at Bharati appears to be more intense than at Maitri. The topography and katabatic winds associated with the Lambert glacier could be the reason. The observation of Bipolar Air Ion Concentration (BAIC) suggests that the wind speed significantly affects the concentration by accumulation and dispersion. The concentration is maximum when the wind speed is minimum. As the air ion concentration controls the conductivity, the PG is expected to be minimum during these hours to produce an anomalous diurnal pattern in the PG at Bharati. Data quality is improved by measuring the PG with a field monitor at the surface level instead of at an elevated position. This study provides new hope in pursuing globally representative data of the PG for further investigations on the global thunderstorm activity and the solar-terrestrial weather relationship.

Atmospheric electricity parameters (AEP) measurements from Antarctica predominantly feature either the potential gradient (PG) and/or air‐Earth current (AEC) density. We report for the first time simultaneous measurements of the bipolar ions concentration/conductivity, PG, and AEC density. AEP measurements were carried out at Maitri (70.8°S, 11.8°E) from December 2018 to November 2019. We formulated a few criteria, irrespective of the weather conditions, to select the electrically quiet days and some additional criteria based on the conductivity measurements to discern globally representative data (GRD) from such days. The measurements of the PG and AEC density over the Antarctic plateau demonstrated the diurnal curves similar to the Carnegie pattern, which represents the global thunderstorms and electrified shower clouds (ESCs) occurring on different continents and oceans, we regard the data having such trend as GRD. We found significant variability in the concentration of small bipolar ions/conductivity in the austral summer which in turn affects GRD. However, the concentration of bipolar ions is nearly consistent at ∼250 negative ions cm −3 and ∼300 positive ions cm −3 in winter and enhances the probability of GRD. Such differences can arise out of the prevalent planetary boundary layer processes in the two seasons. When the PG varied between ∼50 Vm −1 and ∼150 Vm −1 and the maximum range of conductivity variations was ∼0.2 × 10 −14 ℧ m −1 , the AEPs represented the signatures of the global thunderstorm and ESC activities.

The role of antennas in the detection of atmospheric conduction current has been discussed since the beginning of the 20th century. Propriety of the antenna design needs to be reviewed from time to time as the measurements experience different problems on various terrains. The present work deals with such issues and brings out a suitable antenna design to detect the conduction current observed at the Indian Scientific Research Station at Maitri (70.8 degrees 5 11.7 degrees E), Antarctica. Two long wire antennas and two plate antennas are simultaneously used to monitor the air-Earth current in the open space at this station. The experiments reveal that the currents recorded by the long-wire antenna and plate antenna display similar characteristics but differ in the magnitude and the response to the varying current. On a fair-weather day the mean current density obtained by 41 m long-wire antenna is similar to 0.4 pA m(-2), 10 m long-wire antenna is 2.5 pA m(-2), 0.25 m(2) plate antenna is 3.5 pA m(-2,) and 1 m(2) plate antenna is 4.2 pA m(-2). The current sensed by 1 s and 1000 s R-C time constant do not show any significant difference in the hourly mean diurnal variation as well as in the magnitude. The study reveals that a plate antenna is a better option for the long term monitoring of air-Earth current. The simultaneously monitored potential gradient at this station and Vostok (78.4 degrees 5, 106.8 degrees E) are used to identify the local and global electric signals.

This paper studies the effects of galactic cosmic rays on clouds and snow-fall rates in Antarctica using nine years of data (2001-2009) covering the long deep solar minimum (2007-2009) for the first time. Measurements of the fair-weather air earth current (Jz) at the Indian Antarctic station Maitri (70 degrees 45'S, 11 degrees 43' E), and equivalent galactic cosmic ray (GCR) flux from the neutron monitor measurements made at the American station McMurdo (77 degrees 51'S, 166 degrees 40'E) are used for the study. Meteorological data from the Antarctic stations Maitri, Vostok (78 degrees 27'S, 106 degrees 52'E), Scott Base (77 degrees 51'S, 166 degrees 46'E) and Antarctic Data base are also used. The results show that low level cloud coverage (pressure > 680 hPa) is positively correlated to GCR flux with the maximum correlation (31%) being at the long solar minimum (2007-2009) when snow-fall increased by 14%. The observed link between cosmic rays and climate in Antarctica is discussed in terms of ion-aerosol clear-sky hypothesis and ion-aerosol near-cloud hypothesis. GCR enhanced the cloud formation, and the increased low level clouds have invigoration to reflect more heat back to space.

The scope of this paper is to explore the mechanisms operating over Maitri (70.76 degrees S, 11.74 degrees E, 117m above mean sea level), a coastal Antarctic station, that produce an anomalous fair-weather diurnal pattern of the atmospheric electric potential gradient (PG) and air-Earth current density (AEC). The anomaly in the diurnal variations of AEC and the PG is displaying an ostensible minimum at similar to 10 UT and a diminished response to the thunderstorm over the African continent in the 14-16 UT time frame. The data sets (2005-2014, except 2012) of the PG, and to some extent, AEC, from Maitri, are used to explore this anomaly. It follows that the fair-weather electrical phenomena over Maitri can be ascribed to global electrified convection on the one hand and to regional phenomena like convection due to the replacement of warm air by katabatic winds on the other hand. The katabatic winds originate on the polar plateau and blow from similar to 130 degrees at Maitri which are likely to transport various elements from the mountain slopes, and space charge from the polar plateau is expected to produce various disturbances in the PG and AEC monitored over the coastal Antarctica. This mechanism may be responsible for peaks in the early UT hours and also for the anomalous behavior of atmospheric electrical parameters observed at Maitri. Maitri data are compared with that of Carnegie cruise and Vostok to explain the source of anomaly.

Cosmic noise absorption (CNA) at high latitudes is a typical manifestation of enhanced precipitation of energetic charged particles during the course of a magnetospheric substorm. Present analysis demonstrates the energetic particles precipitate to the high latitude ionosphere during substorms, affecting upper and lower regions of the ionosphere simultaneously. Previous studies have reported that intense and short-lived CNA events associated with substorms are mostly observed in the midnight sector of the auroral oval. In the current study, we have examined such type of CNA events predominantly occurring during 0000–0600UT (2300–0500MLT) at an Indian Antarctic station Maitri (corrected geomagnetic (CGM) coordinates 62.59°S, 53.59°E), which is located at the equatorward edge of the auroral oval. Absorption events related to isolated substorm and storm-time substorms exhibit distinct features in terms of their intensity and extent in latitude and longitude. Our study suggests that the maximum intensity of CNAs depends on the interplanetary conditions, such as, the solar wind speed, southward component of IMF Bz, and duskward component of IEF Ey. Moreover, the role of duskward component of IEF Ey is more noteworthy than other interplanetary parameters.

Schumann resonances (SRs) are the AC components of the global electric circuit and are excited by the lightning activity within the Earth-ionosphere waveguide. An induction magnetometer, which was operated from the Indian Antarctic station, Maitri (70.8 degrees S, 11.7 degrees E), served to examine the SR parameters, namely the amplitude and frequency, in the north-south (HNS) and east-west (H-EW) magnetic components. The analysis for the first resonant mode presented in this work reveals a strong UT variation in its amplitude in seasonal as well as yearly timescales. The NS amplitude reveals a semi-diurnal variation with peaks at similar to 1000 and similar to 2100 UT, whereas the EW amplitude exhibits a strong diurnal variation with a pronounced peak at 1600 UT. The diurnal curves for the frequency for both components are similar in nature to those for the amplitude, but for a time shift. The diurnal trend in the amplitude is retained irrespective of seasons, whereas significant difference are noticed in the frequency behaviour between the summer and winter seasons, especially in the EW component. The observed diurnal variation in the SR intensity is explained in terms of the dominant thunderstorm activity centred over the three convectively active regions: Asia/Maritime Continent (Indonesia), South America and Africa. The diurnal variation in frequency depends not only on the location of the thunderstorm region with respect to the observer, but also on the ionospheric day/night conditions and the Earth-ionosphere cavity thickness.

Scintillation observations are used to study the evolution of intermediate scale (similar to 100m-few kilometers) irregularities through growth of the Rayleigh-Taylor (R-T) instability on the bottom side of the post-sunset equatorial F region during magnetically quiet periods. Amplitude scintillations on a VHF signal from a geostationary satellite, recorded by spaced receivers at an equatorial station, are used to compute as a function of local time: (1) the coherence scale length for spatial variations of intensity in the ground scintillation pattern, which is linked with the spectrum of the intermediate scale irregularities near the peak of the equatorial F region that contribute the most to the observed scintillations; and (2) the random velocity, which accounts for the de-correlation of the spaced receiver signals. The relationship between the coherence scale length and the random velocity for saturated scintillations at different local times suggests that (1) the random velocity is linked with fluctuations in the drift velocity of the irregularities caused by the perturbation electric fields associated with the R-T instability rather than structural changes in the intermediate scale irregularities, (2) the spectrum of intermediate scale irregularities in the equatorial F peak region tends to be shallowest after the decay of the perturbation electric fields associated with the R-T instability, and (3) evolution of intermediate-scale irregularity spectrum in the equatorial plasma bubble near the equatorial F region peak depends on season and solar flux. These have implications for observation of low-latitude L-band scintillations.

Simultaneous measurements of atmospheric Maxwell current and electric field, using horizontal long wire antenna and passive horizontal wire antenna system at 1 m above the Earth’s surface, were carried out at Tirunelveli (8.7°N, 77.8°E), India, during January/February 2002. The objectives of the present work have been to understand the nature of the measured atmospheric electrical parameters and explore the possibility of detecting the signature associated with the global thunderstorm activity. As the measurements indicate, the atmospheric electrical parameters at Tirunelveli are severely masked by the locally induced current components during disturbed weather conditions, for example, severe convective activity. During the selected fair weather conditions, the hourly averaged diurnal variation curves of Maxwell current and electric field are characterized by two peaks: The first peak is the local “sunrise effect” and the second peak occurs at times close to 1900 UT, the time of maximum global thunderstorm activity as noted in the famous “Carniege curve”. The correlation coefficient between the measured Maxwell current and electric field has a high value (more than 0.8) for all the fair weather days. These results support our view that this site is free from local pollution during the fair weather conditions and is suitable for long-term measurements of atmospheric electrical parameters.

The global component of fairweather electricity is subject to special attention to watch the solar-terrestrial effects and secular changes in climate. It is generally considered that the diurnal variation of atmospheric electricity parameters, if they are not following the Carnegie pattern, are not representative of the global thunderstorm activity. Some of the results obtained from Maitri (70°45′54″S, 11°44′03″), are discussed here in context with global thunderstorm activity and space weather influences. The diurnal pattern of the Potential Gradient and current density strongly deviate from the Carnegie curve. We have showed that this deviation is not due to the local electrical influence but due to the global thunderstorm activity. During fairweather condition the parameters are representing the global thunderstorm activity and to some extent they respond to the upper atmospheric electro dynamic phenomenon. The mean value of the potential gradient (77.7 V/m) and current density (2.13 pA/m2) well below the expected global mean but close to the value reported from the same location and season in the past years. The mean conductivity, 3.34 × 10−14 mhom−1, is slightly at higher side and they exhibit a different diurnal trend comparing to the past measurements at this location.

During the month of March 2006, a short campaign was conducted to measure fair-weather atmospheric electricity parameters in Tripura, Northeast India (23.50°N, 91.25°E). The campaign was the first of its kind in this region of the globe. The main objective of the campaign was to characterize the diurnal variation of three parameters namely vertical potential gradient (E), vertical air-earth current density (J z ) and atmospheric electrical conductivity (σ) in fair-weather conditions. The diurnal variation of E and J z over sixteen fair-weather days shows two distinct maxima around 14UT and 20UT and a minimum around 03UT. The average vertical potential gradient is found to be 108V·m−1 and air-earth current density 1.85 pA·m−2. The average bipolar atmospheric electrical conductivity at the ground level is found to be 19.6 fS·m−1. An excellent positive correlation between E and J z is found, with a correlation coefficient of 0.96. A comparative study with Carnegie universal variation shows 70% correlation with observed variation of vertical potential gradient during the period of the campaign. The results are discussed in view of difficulty as well as possibility of getting global signatures in atmospheric electricity measurements made from tropical land stations.

We have developed an experimental set-up to measure the atmospheric air-earth current (conduction current). Data obtained with the continuous measurements of Wilson’s plate are used to study of air-earth current density, with the aim of gaining an understanding of the experimental set-up’s response to different meteorological conditions, including fair-weather days. This paper is a part of the on-going Global Electric Circuit (GEC) studies from Tirunelveli (8.7°N, 77.8°E), a measurement site in the tropical and southern tip of the Indian peninsula. Attempts have been made in past few years to obtain the global signature in this region with this sensor, but on most of the occasions it has been impossible to obtain the global signature during fair-weather days. The data used for February–April, 2007 have the well-defined nature of this global signature, which is in agreement with the well-established classical Carnegie curve of GEC. This paper also deals with very important observations made at sunrise and during those hours when fog existed. It is noted that the resistivity of the atmosphere increased significantly with the onset of fog and later decreased as the fog disappeared, based on the measured value of conduction current density when compared with the electric field measured by horizontal passive wire antenna. Also, during fair-weather conditions, conduction current and electric field variations are similar because the conductivity during this period is more or less constant at this site. Observations made during different meteorological conditions, such as different wind speeds, humidities, and temperatures, are also discussed.

Surface measurements of the atmospheric electrical parameters like Maxwell current, electric field and conductivity studied at the Indian station, Maitri (70.75° S, 11.75° E, 117 m above mean sea level), Antarctica, during austral summer have been analyzed for the years 2001 to 2004. A total of 69 days were selected which satisfied the ‘fairweather’ conditions, i.e., days with absence of high winds, drifting or falling snow, clouds, and fog effects. The diurnal variation curve of electric field and vertical current averaged for 69 fairweather days is a single periodic with a minimum at 03:00 UT and a maximum near 19:00 UT, which is very similar to the Carnegie curve. The correlation coefficient between these measured parameters has a high value (more than 0.9) for all the days. During fairweather days the measured current and field variations are similar and hence it is clear that the conductivity is more or less stable. During magnetically disturbed days, the dawn-dusk potential drop has clear influences on the diurnal variation and it modifies the conductivity. Apart from the day-to-day variation in low latitude thunderstorm activity, there are diurnal, seasonal, inter-annual variations in the electric potential and the currents, as well as solar influences on the measured parameters. This study will help us to examine the impact of solar and geophysical phenomena like solar flares, geomagnetic storms and substorms on the global electric circuit.

Observations of atmospheric Maxwell current from the low-latitude continental station, Tirunelveli (8.7°N, 77.8°E), over a period of 8 years are presented in this study. The horizontal long-wire antenna is used as a sensor for picking up charges from the atmosphere. The objectives of the present work have been to understand the antenna system in response to different meteorological conditions and on fairweather days. We define a fairweather day as a day when there is no snowfall/rainfall at the measuring site, when there are high clouds less than 3 octas throughout the day, and when the wind speed is less than 10 m s−1. A sunrise effect is observed in the measured Maxwell current during fairweather days in all seasons. The measured current exhibits an increase that commences about 30 min before sunrise and lasts for nearly 1.5 h. The sunrise effect is found to be inhibited on days when there is pre-dawn convection and during the presence of rain, haze, or cloud cover. Barring the sunrise effect, the rest of the variations on fairweather day appear to follow a trend typical of the Carnegie curve. On clear cloudless conditions, reasonably good data are obtained during equinox and winter months but not in summer when strong winds associated with the onset of the southwest monsoon make the measurement of Maxwell current difficult and limited data are available.

Results derived from a statistical study of the generation of equatorial spread F (ESF) irregularities as a result of magnetic activity based on spaced receiver ionospheric scintillation data recorded at a dip equatorial station is reported here. For a study of this nature it is essential to establish whether the observed scintillations are caused by freshly generated irregularities or by irregularities generated earlier, which later drift onto the signal path. It has been observed in the past that the maximum cross‐correlation between the spaced receiver signals is significantly less than 1 during the initial phase of development of ESF irregularities due to the presence of perturbation electric fields associated with the Rayleigh‐Taylor (R‐T) instability that produces equatorial plasma bubbles (EPBs), whereas in the later phase, when these perturbation electric fields die down, the correlation between the two signals increases rapidly. This feature is used in the present study to identify freshly generated ESF irregularities associated with EPBs using spaced receiver scintillation data. Magnetically disturbed days are chosen by using three hourly geomagnetic activity index ap, daily index Ap, and also AE index to study the cases of prompt penetration of high‐latitude electric field to the equatorial ionosphere. Disturbed time statistical occurrence pattern of freshly generated irregularities shows seasonal variation for all three types of magnetic disturbances: disturbance dynamo, prompt penetration, combination of disturbance dynamo and prompt penetration. However, it is found that fresh generation of the irregularities due to magnetic activity is most likely to occur around midnight hours in all seasons. Suppression of generation of irregularities immediately after sunset due to inhibition of the growth of the R‐T instability on the bottomside of the equatorial F region is clearly seen in vernal equinox (March and April) and solstice months but is not observed for autumnal equinox (September and October).

Effect of magnetic activity, caused by complex interaction of solar wind and magnetosphere, on night time equatorial F region plasma drifts is studied using scintillation data recorded using spaced receivers at Tirunelveli (dip 0.40), for a 251 MHz signal transmitted from a geostationary satellite. Once the perturbation electric field associated with plasma bubbles are eroded, about two hours after the initiation of bubble growth, the irregularities simply drift across the signal path along with background plasma. Hence irregularity drift speed estimated from spaced receiver scintillation data is very close to the drift speed of the background plasma during this period. In order to obtain monthly average quiet time plasma drift pattern in the nighttime equatorial F region, the drifts estimated from scintillation data are averaged after 22LT for all quiet days (Ap < 18) of a month. Quantitative estimate of the effect of a disturbance dynamo produced by enhanced geomagnetic activity, on the nighttime equatorial F region plasma drift is obtained by removing monthly quiet time plasma drift pattern from disturbed time plasma drift pattern. The maximum effect of disturbance dynamo on equatorial F region plasma drift is observed around midnight for most of the magnetically disturbed days considered in the present study. An attempt is made here, (i) to relate the maximum deviation of the disturbed nighttime equatorial F region plasma drifts from quiet time pattern, with an empirical measure of the Joule energy input at high latitudes during magnetically active periods (ii) to investigate the time delays, which are required for obtaining the maximum disturbance dynamo effects observed in the night time equatorial F region plasma drifts, based on AE and Kp indices.

The coherence scale length, defined as the 50% decorrelation scale length along the magnetic east-west direction, in the ground scintillation pattern obtained at a dip equatorial location, due to scattering of VHF radio waves by equatorial spread F (ESF) irregularities, is calculated, using amplitude scintillation data recorded by two spaced receivers. The average east-west drift of the ground scintillation pattern, during the pre- and post-midnight periods, also calculated from the same observations, shows an almost linear increase with 10.7-cm solar flux. In the present paper the variability of the drift is automatically taken into account in the calculation of the coherence scale length of the ground scintillation pattern. For weak scintillations, the coherence scale depends on the Fresnel scale, which varies with the height of the irregularity layer, and also on the spectral index of the irregularity power spectrum. It is found that for weak scintillations, the coherence scales are much better organized according to the 10.7-cm solar flux, during the pre-midnight period, than during the post-midnight period, with a general trend of coherence scale length increasing with 10.7-cm solar flux except for cases with F 10.7-cm solar flux <100. This indicates that, during the initial phase of ESF irregularity development, the irregularity spectrum does not have much variability while further evolution of the spatial structure in ESF irregularities is controlled by factors other than the solar flux.

The Indian Antarctic station Maitri (geog. 70‡45’S, 11‡45’E, geom. 66‡.03S, 53‡.21E) occupies a sub-auroral location during magnetically quiet conditions (Σκρ < 10), but attains an auroral position when the auroral oval shifts equatorwards with increasing strength of magnetic disturbance. At the latter times, triangulation with 3 fluxgate magnetometers located at the vertices of a suitable triangle provides a means of monitoring mobile auroral ionospheric current systems over Maitri. The spacing between the magnetometers is typically kept at 75–200 km, keeping in mind the scale-sizes of ∼ 100 km for these mobile current systems. This work reports the results of two triangulation experiments carried out around Maitri in January 1992 and January 1995, both during Antarctic summer. The velocities estimated for pulsations of the Pc4 and Pc5 type were about 0.59 km/sec in the direction 102‡.7 east of due north, in the first case, and about 1–3 km/sec in the second case in the east-west direction. While several magnetometer arrays exist in the northern auroral regions (e.g., the Alberta array in Canada, the Alaskan array in the U.S. and the IMS Scandinavian array), there is no report in literature of triangulation through arrays in Antarctica, except for a one-day study by Neudegg et al 1995 for ULF pulsations of the Pc1 and Pc2 type. The velocities obtained for the Pi3 type of irregular pulsations over Antarctica in the present study tally well with those obtained for northern auroral locations.

studied from ACE satellite data during the last phase of the 23 rd solar cycle. Such solar ejections consist of hot electrons, protons and helium ions embedded in magnetic fields of various intensities and which travel with velocities greater than supersonic speed towards the earth and breach terrestrial magnetic fields (under favourable conditions) and cause geomagnetic storms. Contemporary data of geoelectrical measurements made at the high latitude Indian Antarctic Research Station, Maitri (70.45°S, 11.44°E) have also been used to investigate the electrical processes during, before and after the above events. The study leads to the conclusion that CMEs enhance the population of the multi-ion plasma species, which paves the way for an increase in the overhead ionospheric electric potential during the onset or even up to the main phase of the magnetic disturbance. The near earth electrical environment is besieged with magnetic disturbance at the high latitude.