Geomagnetic effects on cosmic ray propagation under different conditions for Buenos Aires and Marambio, Argentina

The geomagnetic field (Bgeo) sets a lower cutoff rigidity (Rc) to the entry of cosmic particles to Earth which depends on the geomagnetic activity. From numerical simulations of the trajectory of a proton using different models for Bgeo (performed with the MAGCOS code), we use backtracking to analyze particles arriving at the location of two nodes of the net LAGO (Large Aperture Gamma ray burst Observatory) that will be built in the near future: Buenos Aires and Marambio (Antarctica), Argentina. We determine the asymptotic trajectories and the values of Rc for different incidence directions, for each node. Simulations were done using several models for Bgeo that emulate different geomagnetic conditions. The presented results will help to make analysis of future observations of the flux of cosmic rays done at these two LAGO nodes.Comment: 9 page

Are There Different Populations of Flux Ropes in the Solar Wind?

Flux ropes are twisted magnetic structures, which can be detected by in situ measurements in the solar wind. However, different properties of detected flux ropes suggest different types of flux-rope population. As such, are there different populations of flux ropes? The answer is positive, and is the result of the analysis of four lists of flux ropes, including magnetic clouds (MCs), observed at 1 AU. The in situ data for the four lists have been fitted with the same cylindrical force-free field model, which provides an estimation of the local flux-rope parameters such as its radius and orientation. Since the flux-rope distributions have a large dynamic range, we go beyond a simple histogram analysis by developing a partition technique that uniformly distributes the statistical fluctuations over the radius range. By doing so, we find that small flux ropes with radius R<0.1 AU have a steep power-law distribution in contrast to the larger flux ropes (identified as MCs), which have a Gaussian-like distribution. Next, from four CME catalogs, we estimate the expected flux-rope frequency per year at 1 AU. We find that the predicted numbers are similar to the frequencies of MCs observed in situ. However, we also find that small flux ropes are at least ten times too abundant to correspond to CMEs, even to narrow ones. Investigating the different possible scenarios for the origin of those small flux ropes, we conclude that these twisted structures can be formed by blowout jets in the low corona or in coronal streamers.Comment: 24 pages, 6 figure

Global axis shape of magnetic clouds deduced from the distribution of their local axis orientation

Coronal mass ejections (CMEs) are routinely tracked with imagers in the interplanetary space while magnetic clouds (MCs) properties are measured locally by spacecraft. However, both imager and insitu data do not provide direct estimation on the global flux rope properties. The main aim of this study is to constrain the global shape of the flux rope axis from local measurements, and to compare the results from in-situ data with imager observations. We perform a statistical analysis of the set of MCs observed by WIND spacecraft over 15 years in the vicinity of Earth. With the hypothesis of having a sample of MCs with a uniform distribution of spacecraft crossing along their axis, we show that a mean axis shape can be derived from the distribution of the axis orientation. In complement, while heliospheric imagers do not typically observe MCs but only their sheath region, we analyze one event where the flux-rope axis can be estimated from the STEREO imagers. From the analysis of a set of theoretical models, we show that the distribution of the local axis orientation is strongly affected by the global axis shape. Next, we derive the mean axis shape from the integration of the observed orientation distribution. This shape is robust as it is mostly determined from the global shape of the distribution. Moreover, we find no dependence on the flux-rope inclination on the ecliptic. Finally, the derived shape is fully consistent with the one derived from heliospheric imager observations of the June 2008 event. We have derived a mean shape of MC axis which only depends on one free parameter, the angular separation of the legs (as viewed from the Sun). This mean shape can be used in various contexts such as the study of high energy particles or space weather forecast.Comment: 13 pages, 12 figure

Causes and Consequences of Magnetic Cloud Expansion

Context. A magnetic cloud (MC) is a magnetic flux rope in the solar wind (SW), Which, at 1 AU, is observed ∼2–5 days after its expulsion from the Sun. The associated solar eruption is observed as a coronal mass ejection (CME). Aims. Both the in situ observations of plasma velocity distribution and the increase in their size with solar distance demonstrate that MCs are strongly expanding structures. The aim of this work is to find the main causes of this expansion and to derive a model to explain the plasma velocity profiles typically observed inside MCs. Methods. We model the flux rope evolution as a series of force-free field states with two extreme limits: (a) ideal magnetohydrodynamics (MHD) and (b) minimization of the magnetic energy with conserved magnetic helicity. We consider cylindrical flux ropes to reduce the problem to the integration of ordinary differential equations. This allows us to explore a wide variety of magnetic fields at a broad range of distances to the Sun. Results. We demonstrate that the rapid decrease in the total SW pressure with solar distance is the main driver of the flux-rope radial expansion. Other effects, such as the internal over-pressure, the radial distribution, and the amount of twist within the flux rope have a much weaker influence on the expansion. We demonstrate that any force-free flux rope will have a self-similar expansion if its total boundary pressure evolves as the inverse of its length to the fourth power. With the total pressure gradient observed in the SW, the radial expansion of flux ropes is close to self-similar with a nearly linear radial velocity profile across the flux rope, as observed. Moreover, we show that the expansion rate is proportional to the radius and to the global velocity away from the Sun. Conclusions. The simple and universal law found for the radial expansion of flux ropes in the SW predicts the typical size, magnetic structure, and radial velocity of MCs at various solar distances.Fil: Démoulin, Pascal. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Dasso, Sergio Ricardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Global and local expansion of magnetic clouds in the inner heliosphere

Observations of magnetic clouds (MCs) are consistent with the presence of flux ropes detected in the solar wind (SW) a few days after their expulsion from the Sun as coronal mass ejections (CMEs). Both the \textit{in situ} observations of plasma velocity profiles and the increase of their size with solar distance show that MCs are typically expanding structures. The aim of this work is to derive the expansion properties of MCs in the inner heliosphere from 0.3 to 1 AU.We analyze MCs observed by the two Helios spacecraft using \textit{in situ} magnetic field and velocity measurements. We split the sample in two subsets: those MCs with a velocity profile that is significantly perturbed from the expected linear profile and those that are not. From the slope of the \textit{in situ} measured bulk velocity along the Sun-Earth direction, we compute an expansion speed with respect to the cloud center for each of the analyzed MCs. We analyze how the expansion speed depends on the MC size, the translation velocity, and the heliocentric distance, finding that all MCs in the subset of non-perturbed MCs expand with almost the same non-dimensional expansion rate ($\zeta$). We find departures from this general rule for $\zeta$ only for perturbed MCs, and we interpret the departures as the consequence of a local and strong SW perturbation by SW fast streams, affecting the MC even inside its interior, in addition to the direct interaction region between the SW and the MC. We also compute the dependence of the mean total SW pressure on the solar distance and we confirm that the decrease of the total SW pressure with distance is the main origin of the observed MC expansion rate. We found that $\zeta$ was $0.91\pm 0.23$ for non-perturbed MCs while $\zeta$ was $0.48\pm 0.79$ for perturbed MCs, the larger spread in the last ones being due to the influence of the environment conditions on the expansion

Forecast of solar ejecta arrival at 1 AU from radial speed

Las eyecciones transitorias de masa solar (EMS) pueden producir cambios en el campo geomagnético. Cuando la polaridad magnética de la EMS es adecuada, puede disparar intensas tormentas geomagnéticas. La predicción de la llegada de EMS desde el Sol al geoespacio tiene una importancia crucial para poder predecir el clima espacial. En este trabajo implementamos un modelo simple, desarrollado por Gopalswamy et al., 2000 para estimar el tiempo de llegada de EMS a una Unidad Astronómica. Este modelo requiere sólo un parámetro de entrada: la velocidad radial de la EMS en el momento de su expulsión desde el Sol. Cuando la velocidad de la EMS es medida desde una posición dentro de la línea Sol-Tierra, sólo la componente de la velocidad en el plano del cielo puede ser obtenida. Debido a que la predicción del modelo depende de la velocidad inicial de la EMS observada remotamente, es muy importante obtener esta velocidad lo más exactamente posible. Una de las mayores incertezas cuando se mide la velocidad inicial de la EMS es el efecto de proyección. El objetivo de este trabajo es corregir efectos de proyección a partir de la localización en la superficie solar de la erupción y del tamaño de apertura de la EMS. Encontramos que la corrección desarrollada acuerda con un modelo obtenido en observaciones estereoscópicas en el pasado.Solar ejecta produce changes in the interplanetary magnetic field of the terrestrial environment. When the magnetic polarity of the ejecta is suitable, it may trigger intense geomagnetic storms. Therefore, prediction of the arrival of solar ejecta in the geospace is of crucial importance for space weather applications. We implement a simple model, developed by Gopalswamy et al., (2000) to estimate the time of arrival for solar ejecta at 1AU. This model requires just one input parameter: the radial speed of the associated coronal mass ejection (CME) at the moment of its expulsion from the Sun. When the speed of the CME is measured from a location on the Sun-Earth line, only the plane of the sky speed can be obtained. Since the prediction model depends on the initial speed of the CMEs observed remotely, it is important to obtain this speed as accurately as possible. One of the major uncertainties in the measured initial speed is the extent of projection effects. We attempt to correct for projection effects using the solar surface location of the eruption and assuming a width to the CME. We found that the correction is in agreement with a model obtained from stereoscopic observations from the past.Fil: Dasso, Sergio Ricardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Gopalswamy, N.. National Aeronautics And Space Administration. Goddart Institute For Space Studies; Estados UnidosFil: Lara, A.. Universidad Nacional Autónoma de México; Méxic

Coronal Transient Events During Two Solar Minima: Their Solar Source Regions and Interplanetary Counterparts

In the frame of two coordinated observational and research efforts, two full solar rotations were investigated in the times of two distinct solar minima. These two campaigns were dubbed Whole Sun Month (WSM; 10 August – 8 September 1996) and Whole Heliosphere Interval (WHI; 20 March – 16 April 2008). The nearly uninterrupted gathering of solar coronal data since the beginning of the Solar and Heliospheric Observatory (SOHO) era offers the exceptional possibility of comparing two solar minima for the first time, with regard to the coronal transient aspect. This study characterizes the variety of outward-traveling transients observed in the solar corona during both time intervals, from very narrow jet-like events to coronal mass ejections (CMEs). Their solar source regions and ensuing interplanetary structures were identified and characterized as well, toward a global-scale description of their role in determining the heliosphere’s conditions. Multi-wavelength images provided by the space missions SOHO, Yohkoh (only WSM), and Solar-Terrestrial Relations Observatory (STEREO; only WHI) and ground-based observatories were analyzed for coronal ejecta and their solar sources, while data registered by the Advanced Composition Explorer (ACE) spacecraft were inspected for interplanetary CMEs and magnetic clouds. Notable differences arise from the analysis of the detailed survey of events: more (fewer) ejecta during WHI (WSM), 12% (40%) were produced by active regions during WHI (WSM), and nearly no (high) deflection from the radial direction was observed during WHI (WSM). Instrumental aspects such as dissimilar resolution, cadence, and fields of view are considered in order to discern instrumentally driven disparities from inherent differences between solar minima.Fil: Cremades Fernandez, Maria Hebe. Universidad Tecnologica Nacional; ArgentinaFil: Mandrini, Cristina Hemilse. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Dasso, Sergio Ricardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Analysis of large scale MHD quantities in expanding magnetic clouds

Magnetic clouds (MCs) transport the magnetic flux and helicity released by the Sun. They are generally modeled as a static flux rope traveling in the solar wind, though they can present signatures of expansion. We analyze three expanding MCs using a self-similar free radial expansion model with a cylindrical linear force-free field (i.e., Lundquist solution) as the initial condition. We derive expressions for the magnetic fluxes, the magnetic helicity and the magnetic energy per unit length along the flux tube. We find that these quantities do not differ more than 25% when using the static or expansion model.Fil: Nakwacki, Maria Soledad. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Dasso, Sergio Ricardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Mandrini, Cristina Hemilse. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Démoulin, Pascal. Centre National de la Recherche Scientifique. Observatoire de Paris; Franci

Calibration of the operative cosmic ray detector at Marambio Base in the Antarctic Peninsula

During 2019 an Antarctic Space Weather Laboratory was deployed at Marambio base in the Antarctic Peninsula. The main instrument installed was a cosmic ray detector based on water Cherenkov radiation (WCD). This detector is the first permanent Antarctic node of the LAGO (Latin American Giant Observatory) Collaboration. Long-term calibrated observations of the WCD will be presented here. Finally, the global galactic cosmic rays variability observed with the WCD will be compared with observations of a neutron monitor with similar rigidity cut off than the Marambio site