Ainda existem muitas lacunas sobre a geração do vento solar e, o que se sabe,é fundamentado principalmente em observações. Isso se deve principalmenteà sua complexa origem eà falta de medidas in situ nas regiões onde o mesmoé acelerado. Porém, naórbita da Terra suas características são muito bem conhecidas e constantemente monitoradas. A interação do vento com o campo magnético terrestre levaà criação de diversas regiões distintas da magnetosfera e, uma vez que as condições sejam favoráveis, leva tambémàs chamadas atividades geomagnéticas. O estudo das variações na atividade geomagnética controlada pelas condições do vento solar se faz totalmente justificado do ponto de vista acadêmico. Do ponto de vista prático, tais variações podem, por exemplo, prejudicar o funcionamento de sistemas de solo e a bordo de satélites devido ao aumento das correntes atmosféricas e da radiação que chega até o planeta, aumentando assim a importância desse tipo de pesquisas. Esse artigo apresenta uma breve revisão de alguns dos principais efeitos da interação entre o vento solar e a magnetosfera terrestre. Palavras-chave: física espacial, vento solar, atividade geomagnética.Nowadays, there are a lot of doubts about solar wind generation and most of what is known comes from observations. This is because its generation is too complex and the non-existence of observations in the regions where the wind is accelerated. However, near the Earth its features are well known and always measured. Solar wind interaction with the Earth magnetosphere leads to the formation of several magnetospheric regions. If the conditions are favorable such interaction leads also to geomagnetic activity. Studying geomagnetic activity variations caused by solar wind conditions is a main topic in space physics. For practical and technological aplications such variations can, for instance, damage ground and onbord satellites sistems because of the enhancement in atmospheric currents and levels of radiation, making this kind of research so important. This paper presents a brief revision about some of the main effects of solar wind and Earth's magnetosphere interaction. Keywords: space physics, solar wind, geomagnetic activity. IntroduçãoAs pesquisas em física espacial se concentram principalmente nas interações entre partículas energéticas carregadas e campos eletromagnéticos no espaço interplanetário. Próximoà Terra, a energia da maior parte dessas partículas provém diretamente do Sol ou da interação do vento solar com a magnetosfera terrestre.Na primeira metade do século XX os cientistas já acreditavam que as auroras fossem causadas por partículas vindas do Sol. Para tanto, essas partículas deveriam viajar até nosso planeta de alguma forma, surgindo assim o primeiro modelo para o que hoje chamamos de vento solar. Primeiramente foi suposto que o vento solar era intermitente. Posteriormente, em 1943, o astrônomo alemão Cuno Hoffmeister notou que as caudas dos cometas não permaneciam na direção oposta a seus movimentos, mas sim em uma direção levemente desviada para...

Abstract. Magnetic reconnection can be a continuous or a transient process. Global magnetohydrodynamics (MHD) simulations are important tools to understand the relevant magnetic reconnection mechanisms and the resulting magnetic structures. We have studied magnetopause reconnection using a global 3-D MHD simulation in which the interplanetary magnetic field (IMF) has been set to large positive B y and large negative B z components, i.e., a south-duskward direction. Flux tubes have been observed even during these constant solar wind conditions. We have focused on the interlinked flux tubes event resulting from time-dependent, patchy and multiple reconnection. At the event onset, two reconnection modes seem to occur simultaneously: a timedependent, patchy and multiple reconnection for the subsolar region; and, a steady and large-scale reconnection for the regions far from the subsolar site.

Magnetic reconnection permits topological rearrangements of the interplanetary and magnetospheric magnetic fields and the entry of solar wind mass, energy, and momentum into the magnetosphere. Thus, magnetic reconnection is a key issue to understand space weather. However, it has not been fully understood yet under which interplanetary/magnetosheath conditions magnetic reconnection takes place more effectively at the dayside magnetopause. In the present study 25 dayside magnetopause reconnection events are investigated using the "Time History of Events and Macroscale Interactions during Substorms" (THEMIS) satellite observations in order to find its dependence on solar wind and magnetosheath conditions. It is found that the reconnection electric field is proportional to the interplanetary electric field and inversely proportional to the solar wind-Alfvén Mach number and that the reconnection outflow speed is proportional to the solar wind Alfvén speed and inversely proportional to the magnetosheath plasma beta. It is also shown that the range of magnetic shear angles for which magnetic reconnection should occur is restricted to large shears as the magnetosheath flow direction becomes more perpendicular to the direction of the local magnetopause normal vector. Since these results refer to fairly typical solar wind-Alfvén Mach number condition, they may not necessarily apply to more extreme cases.

The coupling response between solar wind structures and the magnetosphere is highly complex, leading to different effects in the outer radiation belt electron fluxes. Most Coronal Mass Ejections cause strong geomagnetic storms with short recovery phases, often 1–2 days. By contrast, High‐Speed Solar Wind Streams lead to moderate and weak storms often with much longer recovery phases, from several to ∼10 days. The magnetosphere receives energy for a long time under the influence of the HSSs, considerably changing its dynamics. This in turn has an effect on the charged particles trapped in the outer radiation belt. Although the high‐energy electron flux enhancements have received considerable attention, the high‐energy electron flux enhancement pattern (L > 4) has not. This paper identifies 37 events with this enhancement pattern in the high‐energy electron flux during the Van Allen Probes era. We find the enhancements coincident with HSS occurrence. The interplanetary magnetic field (IMF) exhibits north/south Bz fluctuations of Alfvénic nature with moderate amplitudes. The high‐energy electron flux enhancements also correspond to long periods of auroral activity indicating a relationship to magnetotail dynamics. However, the AE index only reaches moderate values. Ultra‐Low Frequency waves were present in all of the events and whistler‐mode chorus waves were present in 89.1% of the events, providing a convenient scenario for wave‐particle interactions. The radial gradient of the ULF wave power related to the L, under the influence of the HSSs, is necessary to trigger the physical processes responsible for this type of high‐energy electron flux enhancement pattern.

The dynamics of the electron population in the Earth’s radiation belts affect the upper atmosphere’s ionization level through the low-energy Electron Precipitation (EP). The impact of low-energy EP on the high-latitude ionosphere has been well explained since the 1960’s decade. Conversely, it is still not well understood for the region of the South American Magnetic Anomaly (SAMA). In this study, we present the results of analysis of the strong geomagnetic storm associated with the Interplanetary Coronal Mass Ejection (May 27-28, 2017). The atypical auroral sporadic E layers (Esa) over SAMA are observed in concomitance with the hiss and magnetosonic wave activities in the inner radiation belt. The wave-particle interaction effects have been estimated, and the dynamic mechanisms that caused the low-energy EP over SAMA were investigated. We suggested that the enhancement in pitch angle scattering driven by hiss waves result in the low-energy EP (≥10 keV) into the atmosphere over SAMA. The impact of these precipitations on the ionization rate at the altitude range from 100 to 120 km can generate the Esa layer in this peculiar region. In contrast, we suggested that the low-energy EP (≤1 keV) causes the maximum ionization rate close to 150 km altitude, contributing to the Esa layer occurrence in these altitudes.

We use a global magnetohydrodynamics simulation to analyze transient magnetic reconnection processes at the magnetopause. The solar wind conditions have been kept constant, and an interplanetary magnetic field with large duskward BY and southward BZ components has been imposed. Five flux transfer events (FTEs) with clear bipolar magnetic field signatures have been observed. We observed a peculiar structure defined as interlinked flux tubes (IFTs) in the first and fourth FTE, which had very different generation mechanisms. The first FTE originates as an IFTs and remains with this configuration until its final moment. However, the fourth FTE develops as a classical flux rope but changes its 3‐D magnetic configuration to that of IFTs. This work studies the mechanism for generating IFTs. The growth of the resistive tearing instability has been identified as the cause for the first IFTs formation. We believe that the instability has been triggered by the accumulation of interplanetary magnetic field at the subsolar point where the grid resolution is very high. The evidence shows that two new reconnection lines form northward and southward of the subsolar region. The IFTs have been generated with all the classical signatures of a single flux rope. The other IFTs detected in the fourth FTE developed as a result of magnetic reconnection inside its complex and twisted magnetic fields, which leads to a change in the magnetic configuration from a flux rope of twisted magnetic field lines to IFTs.

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The particle dynamics in the outer radiation belt are very complex. The Earth's magnetic field geometry traps energetic charged particles, and their motion can be described by combining the gyration around the magnetic field lines, bounce motion along the magnetic field lines between the mirror points, and azimuthal drift at a radial distance above the Earth's surface, or L-shell (McIlwain, 1961;Roederer, 1970;Ukhorskiy & Sitnov, 2013). Each of these three movements is associated with adiabatic invariants (Baumjohann & Treumann, 2012;Schulz & Lanzerotti, 1974), which can be violated, causing electron acceleration or scattering from the outer radiation belt, and resulting in enhancements or reduction in the electron differential flux (