J.-P. Raulin

Observation of cosmic ray and electric field variations in the surface atmosphere

The results of cosmic ray observations by the CARPET instrument at CASLEO (El Leoncito, Argentina, Rc ≈ 11.8 GV) in 2006–2008 are reported. The main attention is paid to CR variations due to electric field variations in the surface atmosphere.

Solar Flare Observations at Submm-waves

First 405 GHz and 212 GHz solar flare observations were obtained during short campaigns while the new solar submillimeter-wave telescope (SST) was still undergoing adjustments at the CASLEO EI Leoncito observatory in the Argentina Andes. We show here preliminary results for a large X1.1 class X-ray event occurred on 2000 March 22, which exhibited a small submm-w continuum response to the slow (minutes) bulk flare emission, and numerous subsecond spikes (100-300 ms), the brightest spikes reaching about 180 and 50 s.f.u. at 405 and 212 GHz, respectively. Solar flare observations are nearly unknown in the submm-IR range of wavelengths. Few results limited to time resolution of about one minute have suggested brightness variations of 10-100 K in active regions without clear flare associations (Clark & Park 1970; Hudson 1975). The six SST beams (Kaufmann et al. 1994) are superimposed on a Kitt Peak solar magnetogram (NOAA 2000) shown in Figure 1 (left) at about the time of the event on 2000 March 22. The flare emission light-curves in compressed time scales are shown in Figure 1 (right) for different frequencies. The H-a telescope is described elsewhere (Bagala et al. 1999). The bottom plot of Figure 1 (right) shows the rate of submm-w brightest (~ 20 K) spikes incidence with time. An example of such a bright spike (labeled A in Figure 1 (right)) is shown in Figure 2 (A) in a five seconds time interval, compared to data obtained tracking a quiet solar region, near its center, in Figure 2 (B), labeled B in Figure 1 (right). The spiky incidence increases drastically after about 1730 UT approximately together with the soft X-ray level. There is a pronounced concentration of brightenings in correspondence to the bulk emissions at X-rays and H-a. Clusters of spikes seem to be added at about 1745 UT and 1820 UT coincident to flares occurring in AR

Comparison of 30 THz impulsive burst time development to microwaves, Hα, EUV, and GOES soft X-rays

The recent discovery of impulsive solar burst emission in the 30 THz band is raising new interpretation challenges. One event associated with a GOES M2 class flare has been observed simultaneously in microwaves, H α , EUV, and soft X-ray bands. Although these new observations confirm some features found in the two prior known events, they exhibit time profile structure discrepancies between 30 THz, microwaves, and hard X-rays (as inferred from the Neupert effect). These results suggest a more complex relationship between 30 THz emission and radiation produced at other wavelength ranges. The multiple frequency emissions in the impulsive phase are likely to be produced at a common flaring site lower in the chromosphere. The 30 THz burst emission may be either part of a nonthermal radiation mechanism or due to the rapid thermal response to a beam of high-energy particles bombarding the dense solar atmosphere.

Periodic and quiescent solar activity effects in the low ionosphere, using SAVNET data

Important results have been acquired using the measurements of VLF amplitude and phase signals from the South America VLF Network (SAVNET) stations. This network is an international project coordinated by CRAAM, Brazil in cooperation with Peru and Argentina. It started operating in April 2006, and now counts on eight stations (Atibaia, Palmas, Santa Maria and Estacao Antartica Comandante Ferraz in Brazil; Piura, Punta‐Lobos and Ica, in Peru; CASLEO, in Argentina). Researches, through the last decades, have demonstrated the versatility of the VLF technique for many scientific and technological purposes. In this work, we summarize some recent results using SAVNET data base. We have obtained daily maximum diurnal amplitude time series that exhibited behavior patterns in different time scales: 1) 1ong term variations indicating the solar activity level control of the low ionosphere; 2) characteristic periods of alternated slow and fast variations, the former being related to solar illumination conditions, and...

Analysis of cosmic ray variations observed by the CARPET in association with solar flares in 2011-2012

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.

The 2015 Summer Solstice Storm: One of the Major Geomagnetic Storms of Solar Cycle 24 Observed at Ground Level

We report on the 22 – 23 June 2015 geomagnetic storm that occurred at the summer solstice. There have been fewer intense geomagnetic storms during the current solar cycle, Solar Cycle 24, than in the previous cycle. This situation changed after mid-June 2015, when one of the largest solar active regions (AR 12371) of Solar Cycle 24 that was located close to the central meridian, produced several coronal mass ejections (CMEs) associated with M-class flares. The impact of these CMEs on the Earth’s magnetosphere resulted in a moderate to severe G4-class geomagnetic storm on 22 – 23 June 2015 and a G2 (moderate) geomagnetic storm on 24 June. The G4 solstice storm was the second largest (so far) geomagnetic storm of Cycle 24. We highlight the ground-level observations made with the New-Tupi, Muonca, and the CARPET El Leoncito cosmic-ray detectors that are located within the South Atlantic Anomaly (SAA) region. These observations are studied in correlation with data obtained by space-borne detectors (ACE, GOES, SDO, and SOHO) and other ground-based experiments. The CME designations are taken from the Computer Aided CME Tracking (CACTus) automated catalog. As expected, Forbush decreases (FD) associated with the passing CMEs were recorded by these detectors. We note a peculiar feature linked to a severe geomagnetic storm event. The 21 June 2015 CME 0091 (CACTus CME catalog number) was likely associated with the 22 June summer solstice FD event. The angular width of CME 0091 was very narrow and measured ∼56∘

Variations in cosmic rays and the surface electric field in January 2016

{\sim}\, 56^{\circ }

Analysis of cosmic ray variations recorded in October–December 2013

degrees seen from Earth. In most cases, only CME halos and partial halos lead to severe geomagnetic storms. We perform a cross-check analysis of the FD events detected during the rise phase of Solar Cycle 24, the geomagnetic parameters, and the CACTus CME catalog. Our study suggests that narrow angular-width CMEs that erupt in a westward direction from the Sun–Earth line can lead to moderate and severe geomagnetic storms. We also report on the strong solar proton radiation storm that began on 21 June. We did not find a signal from this SEP at ground level. The details of these observations are presented.

Cosmic ray variations recorded by the CARPET facility on March 7, 2011

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 Rc = 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.

Dynamics of coronal magnetic fields inferred from multi-frequency radio observations of a solar flare

Results from analyzing variations in cosmic ray and solar activities in October–November 2013 are described. Data from observations using a Kover/GCR cosmic ray detector (CERN, Switzerland) and the neutron monitor worldwide network are used. Solar flare activity is analyzed using results on Hα, X-ray, gamma, and radio emissions observed at ground-based installations and on board spacecraft (e.g., GOES and FERMI). Attention is focused on the cosmic ray increases detected by the Kover/GCR detector on October 15 and November 19, 2013. Features of these events are similar to increases detected earlier on March 7, 2011, and January 23, 2012, by the Kover/CASLEO detector at the CASLEO astronomical complex in Argentina. Possible correlations between the observed cosmic ray intensity increases and flare solar activity or processes in the Earth’s atmosphere are considered.