High‐energetic charged particles, such as solar protons, and phenomena such as Forbush decreases are eligible candidates to affect the global electric circuit. These effects have been studied by analyzing disturbances of the potential gradient in ground‐based measurements in fair weather regions. In this paper, we investigate deviations in the potential gradient diurnal curve, during solar proton events, and Forbush decreases, from the mean values obtained in fair weather conditions. In each situation, we select only events which are not accompanied or followed by the other. Using the superposed epoch analysis, in order to enhance the visualization of small effects, we study the potential gradient data recorded between January 2010 and December 2019 at two stations located at low and middle‐latitudes, and at two different altitudes: the Complejo Astronómico El Leoncito (CASLEO), Argentina: 31.78°S, 2550 m a.s.l., and the Geophysical Observatory in Świder (SWIDER), Poland: 52.12°N, 100 m a.s.l., respectively. For intense solar proton events (>100 MeV) we found a statistically significant increase of the potential gradient after solar proton events recorded at CASLEO and no such deviation in the potential gradient recorded at SWIDER. For Forbush decrease events (greater than 4%), no significant deviation of the potential gradient after the start of the event was found in both stations, however for very intense Forbush decreases (>7%) we found an increase of the potential gradient recorded at CASLEO.

The study of the global atmospheric electric circuit is important to understand the climate system and this can be done by monitoring the atmospheric electric field worldwide. In this way, continuous measurements of atmospheric electric field are being recorded by the Atmospheric electric FIeld Network in South America (AFINSA). The main objective of this network is to obtain the daily curve of atmospheric electric field variations under fair weather conditions for each station, through monthly, seasonal and annual averages. These curves are called 'standard curves'. In this paper, we compare and analyze the monthly, seasonal and annual standard curves for each sensor location. The results indicate significant similarities and differences between the annual standard curve and the Carnegie curve. The similarities, with correlation r >= 0.9 for most stations, are associated with a global representation of the global electrical circuit and the differences due to local effects, such as 'Austausch' effect and pollution.

Continuous measurements of the potential gradient are being recorded at the CASLEO astronomical observatory near to the Andes Mountain of Argentina, since 2010 (Latitude: 31 degrees 47.88 ' S, Longitude: 69 degrees 17.7 ' W, Altitude: 2552 masl). This study aims to use the potential gradient diurnal variation in fair weather conditions, which we named 'standard curve', to examine its correlation with the 'universal' Carnegie curve and to investigate its dependence with aerosol amount and lightning occurrences. In addition, a spectral analysis was performed to our data. The aerosol optical depth is recorded by an AERONET station at CASLEO, while the lightning occurrences was obtained from the STARNET network. For the analysis, the average of monthly, seasonal and annual electric field curves was determined. We found that the shape of these curves is preserved from year to year indicating their high reliability. The correlation between the standard curve for CASLEO and the Carnegie curve was found to be high (r = 0.94). However, some significant local effects were also found. We determined that these local effects in the standard curve may be associated to the convective process, which is more predominant during summertime than wintertime. The inspection of the seasonal variation of the potential gradient and the lightning occurrences showed a high similarity only after removing the effects of aerosols. Apart from this, the spectral analysis exposed a daily, annual and 165-day oscillation in the potential gradient.

Solar phenomena such as flares and solar energetic particles events are potential candidates to affect the global atmospheric electric circuit. One can study these effects using measurements of the atmospheric electric field in fair weather regions. In this paper, we investigate deviations of the atmospheric electric field daily curve during solar disturbances (solar flares and solar proton events) from mean values obtained in fair weather conditions. Using the superposed epoch analysis, in order to enhance the visualization of small effects, we study the atmospheric electric field data observed between January 2010 and December 2015 at the Complejo Astronómico El Leoncito, San Juan, Argentina. The results show no deviation of the atmospheric electric field after solar flares, and an increase of about 10 V/m after solar proton events. The last result suggests possible ionization effects above thunderstorm in disturbed weather regions, which alters the global atmospheric electric circuit. On the other hand, we analyze the variation of the atmospheric electric field during a ground level enhancement on 17 May 2012, which was capable to produce changes on the surface electric field.

Three units of neutron detectors and four blocks of gamma-ray spectrometers have been installed and started operation at Complejo Astronomico El Leoncito, CASLEO (San Juan, Argentina; coordinates 31 S, 69 W; height of 2550 m; the rigidity of geomagnetic cutoff of R c = 9.7 GV) in May 2015 as part of the scientific cooperation between the Lebedev Physical Institute, Russian Academy of Sciences (Moscow, Russia), Universidade Presbiteriana Mackenzie (San Paulo, Brazil) and Complejo Astronomico El Leoncito, CASLEO (San Juan, Argentina). Measurements with the new detectors greatly supplement the experimental data on variations in the charged component of cosmic rays obtained by the CARPET ground-based cosmic ray detector in 2006. The first results from a joint analysis of new experimental data are presented. Particular attention is given to growing cosmic ray fluxes associated with changes in the surface electric field. The main characteristics of the events recorded in January 2016 are presented.

Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012 – 2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5 – 40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena.

We analyze a large set of 17 solar radio bursts observed at sub-THz (0.2 and 0.4 THz) in 2012-2014 together with the new solar patrol radio telescopes (45 and 90 GHz), operated at El Leoncito, in the Argentinean Andes, allowing the derivation of complete burst spectra in this unexplored range of frequencies. We discuss the uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission. The burst spectra were completed with microwave bursts data obtained by the Radio Solar Telescope Network-RSTN. The events selection was based on GOES soft X-rays burst reported for classes stronger then C. Nearly 50 percent of the bursts exhibited a frequency increasing sub-THz spectral component. The results suggest that the THz component might be always present, with the minimum turn-over frequencies shifting to higher frequencies for larger energies of the electrons producing the emissions.

A new system of two photometers was built to observe the Sun at 3 and 7 THz from space, named SOLAR-T. It has been flown coupled to U.C. Berkeley GRIPS experiment on a NASA stratospheric balloon flight over Antarctica, 19-30 January 2016. The mission was successfully accomplished. We describe the system performance, solar brightness determination and the first THz impulsive burst detected.

Impulsive 30 THz continuum bursts have been recently observed in solar flares, utilizing small telescopes with a unique and relatively simple optical setup concept. The most intense burst was observed together with a GOES X2 class event on October 27, 2014, also detected at two sub-THz frequencies, RHESSI X-rays and SDO/HMI and EUV. It exhibits strikingly good correlation in time and in space with white light flare emission. It is likely that this association may prove to be very common. All three 30 THz events recently observed exhibited intense fluxes in the range of 104 solar flux units, considerably larger than those measured for the same events at microwave and sub-mm wavelengths. The 30 THz burst emission might be part of the same spectral burst component found at sub-THz frequencies. The 30 THz solar bursts open a promising new window for the study of flares at their origin

Детектор космических лучей КОВЕР (CARPET) был установлен в 2006 г. в Аргентинских Андах на высоте 2550 м в Астрономическом комплексе Леонсито (Аргентина; S31.8, W69.3; Rc = 9.65 ГВ). Этот прибор был создан в ФИАНе им. П.Н. Лебедева в рамках договора о международном сотрудничестве между ФИАН, Университетом Маккензи (Бразилия) и Астрономическим комплексом Леонсито (Аргентина). В данной работе представлены результаты анализа вариаций интенсивности космических лучей, зарегистрированных детектором КОВЕР во время солнечного протонного события 7 марта 2011 г. В анализе также использованы экспериментальные данные, полученные на спутниках ГОЕС (GOES), ФЕРМИ (FERMI) и МКС (ISS) во время этой солнечной вспышки.

The CARPET cosmic ray detector was installed in 2006 in the Argentinean Andes at an altitude of 2550 m at the El Leoncito Astronomical Complex (CASLEO) in San Juan, Argentina (S31.8, W69.3; R c = 9.659.65 GV). This instrument was developed at the Lebedev Physical Institute (LPI) in Russia as part of an international collaboration between the LPI, Brazil’s Mackenzie Center for Radioastronomy and Astrophysics (CRAAM), and the CASLEO. This work presents the results from analyzing variations in cosmic ray intensity recorded by the CARPET facility during the solar proton event of March 7, 2011. Also used in our analysis were the experimental data obtained by the GOES, FERMI, and ISS spacecraft during this solar event.

We present a new system of two circular polarization solar radio telescopes, POEMAS, for observations of the Sun at 45 and 90 GHz. The novel characteristic of these instruments is the capability to measure circular right- and left-hand polarizations at these high frequencies. The two frequencies were chosen so as to bridge the gap at radio frequencies between 20 and 200 GHz of solar flare spectra. The telescopes, installed at CASLEO Observatory (Argentina), observe the full disk of the Sun with a half power beam width of 1.4∘, a time resolution of 10 ms at both frequencies, a sensitivity of 2 – 4 K that corresponds to 4 and 20 solar flux unit (=104 Jy), considering aperture efficiencies of 50±5 % and 75±8 % at 45 and 90 GHz, respectively. The telescope system saw first light in November 2011 and is satisfactorily operating daily since then. A few flares were observed and are presented here. The millimeter spectra of some flares are seen to rise toward higher frequencies, indicating the presence of a new spectral component distinct from the microwave one.

The CARPET cosmic ray detector was installed on April 2006 at CASLEO (Complejo Astronmico El Leoncito) at the Argentinean Andes (31.8S, 69.3W, 2550 m, Rc=9.65 GV). This instrument was developed within an international cooperation between the Lebedev Physical Institute RAS (LPI; Russia), the Centro de Radio Astronomia e Astrofsica Mackenzie (CRAAM; Brazil) and the Complejo Astronmico el Leoncito (CASLEO; Argentina). In this paper we present results of analysis of cosmic ray variations recorded by the CARPET during increased solar flare activity in 2011-2012. Available solar and interplanetary medium observational data obtained onboard GOES, FERMI, ISS, as well as cosmic ray measurements by ground-based neutron monitor network were also used in the present analysis.

Ground- and space-based observations of solar flares from radio wavelengths to gamma-rays have produced considerable insights but raised several unsolved controversies. The last unexplored wavelength frontier for solar flares is in the range of submillimeter and infrared wavelengths. Here we report the detection of an intense impulsive burst at 30 THz using a new imaging system. The 30 THz emission exhibited remarkable time coincidence with peaks observed at microwave, mm/submm, visible, EUV, and hard X-ray wavelengths. The emission location coincides with a very weak white-light feature, and is consistent with heating below the temperature minimum in the atmosphere. However, there are problems in attributing the heating to accelerated electrons. The peak 30 THz flux is several times larger than the usual microwave peak near 9 GHz, attributed to non-thermal electrons in the corona. The 30 THz emission could be consistent with an optically thick spectrum increasing from low to high frequencies. It might be part of the same spectral component found at sub-THz frequencies whose nature remains mysterious. Further observations at these wavelengths will provide a new window for flare studies.