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Author: Per Even Sandholt
Publisher: Springer Science & Business Media
ISBN: 0306479699
Category : Science
Languages : en
Pages : 301
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Book Description
The auroral emissions in the upper atmosphere of the polar regions of the Earth are evidence of the capture of energetic particles from the Sun, streaming by the Earth as the solar wind. These auroral emissions, then, are a window to outer space, and can provide us with valuable information about electrodynamic coupling processes between the solar wind and the Earth's ionosphere and upper atmosphere. Studying the physics of these phenomena extends our understanding of our plasma universe. Ground-based remote-sensing techniques, able to monitor continuously the variations in the signatures of aurorae, in combination with in-situ satellite and rocket measurements, promise to advance dramatically our understanding of the physical processes taking place at the interface of the atmospheres of the Earth and the Sun. Decoding their complexity brings us closer to reliable prediction of communication environments, especially at high latitudes. This understanding, in turn, will help us resolve problems of communication and navigation across polar regions.
Author: Per Even Sandholt
Publisher: Springer Science & Business Media
ISBN: 0306479699
Category : Science
Languages : en
Pages : 301
Get Book Here
Book Description
The auroral emissions in the upper atmosphere of the polar regions of the Earth are evidence of the capture of energetic particles from the Sun, streaming by the Earth as the solar wind. These auroral emissions, then, are a window to outer space, and can provide us with valuable information about electrodynamic coupling processes between the solar wind and the Earth's ionosphere and upper atmosphere. Studying the physics of these phenomena extends our understanding of our plasma universe. Ground-based remote-sensing techniques, able to monitor continuously the variations in the signatures of aurorae, in combination with in-situ satellite and rocket measurements, promise to advance dramatically our understanding of the physical processes taking place at the interface of the atmospheres of the Earth and the Sun. Decoding their complexity brings us closer to reliable prediction of communication environments, especially at high latitudes. This understanding, in turn, will help us resolve problems of communication and navigation across polar regions.
Author: Boyi Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 205
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Book Description
This dissertation presents a comprehensive study of the dayside auroral dynamics and remote sensing of coupled magnetosphere-ionosphere system responses to various upstream disturbances, which include interplanetary magnetic field (IMF) discontinuities, foreshock transients, and magnetosheath high speed jets (HSJs). Recent studies have shown that these disturbances have significant impacts on coupled magnetosphere-ionosphere system, changing the particle transportation and energy budget. However, it has been difficult to find spatial structure and evolution of the interaction processes using a limited number of in-situ measurements. This dissertation aims to understand how dayside aurora and airglow respond to upstream disturbances, and to utilize auroral imaging to determine how the magnetosphere-ionosphere system responds to the upstream disturbances. Our study takes a unique approach by taking advantage of high-resolution 2D imaging to vastly increase community's understanding of magnetosphere-ionosphere responses to upstream disturbances, through tracing location, size and propagation of optical structures. We first examine the role of IMF southward turnings as the trigger of Poleward Moving Auroral Forms (PMAFs), which are thought to be an ionospheric signature of dayside magnetic reconnection. While PMAFs are more likely to occur when the IMF is southward, how often PMAFs are triggered by changes in solar wind parameters is still a major open question and has only been poorly understood due to the use of solar wind monitors far away from the bow shock. This dissertation addresses this question with the conjunction between the all-sky imager (ASI) at Automatic Geophysical Observatories (AGO) P1 station in Antarctica and the Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C satellites, which provide much more accurate solar wind conditions than the solar wind monitors at the L1 point. In a statistical study using 60 PMAF events, 70% of the events show a reduction of IMF Bz before PMAF onset, which indicates that IMF southward turning plays an important role in triggering a majority of PMAFs. Those PMAFs were further found to evolve to polar cap airglow patches. This dissertation investigates how often polar cap patches originate in PMAFs and are associated with flow channels, using the conjunction between the ASI at the AGO P1 station and DMSP satellites. Our 50-event statistical study shows that in a majority (45) of events, longitudinally narrow flow enhancements directed anti-sunward are found to be collocated with the patches, have velocities (up to a few km/s) substantially larger than the large-scale background flows (~500 m/s) and have widths comparable to patch widths (~400 km). The patches emanated out of PMAFs and were found to have a large IMF By dependence on the MLT of patches entering the polar cap. Through investigation of dayside aurora, we noticed that auroral brightenings can occur even without substantial changes in the IMF Bz or dynamic pressure. We examined whether disturbances generated in the foreshock and magnetosheath can contribute to dayside auroral brightening. Studies of the impact of foreshock and magnetosheath transients on the magnetosphere-ionosphere system are very limited, and it has been difficult to find how the transients interact in individual events due to limited in-situ and space-based imaging observations. In this dissertation, the conjunction between the ASI at South Pole and the THEMIS satellites during 2008 through 2011 is utilized to determine the magnetosphere-ionosphere responses to foreshock transients and magnetosheath HSJs in a 2D perspective. In situ observation by the THEMIS satellites showed that a foreshock transient during 1535-1545 UT on 25 June 2008 was associated with magnetospheric compression. The ASI at South Pole observed that both diffuse and discrete aurora brightened locally soon after the appearance of this foreshock transient. With the advantage of the high-resolution 2D imaging, we were able to determine that the diffuse auroral brightening corresponds to a localized azimuthal extent of a few Re size on the equatorial plane, and propagated duskward with an average speed of ~100 km/s. Similarly, we for the first time show a nearly one-to-one relationship between the HSJs and individual localized discrete/diffuse auroral brightenings using eight HSJ events. The azimuthal size of HSJ-related diffuse auroral signatures is ~800 km at 230-km altitude in the ionosphere and ~3.7 Re in the magnetosphere, which is slightly larger but of the order of the cross-sectional diameter of HSJs (~1 Re). Furthermore, most of those auroral signatures have azimuthal motions, whose magnitude and direction agree with magnetosheath background flows. In addition to magnetospheric compression, foreshock transients were also found to cause Pc5-band (150-600s) ultra-low frequency (ULF) waves, which are important in transporting mass, energy and momentum in the coupled magnetosphere-ionosphere system. Although it is difficult to find spatial structure of dayside Pc5 waves by a small number of satellites or ground magnetometers, we have successfully determined the 2D structure and motion of ULF waves in the ionosphere using optical imagers. This dissertation reports two series of foreshock-driven Pc5 waves, which are found to be field line resonances (FLRs). The ground-based ASI at South Pole shows that periodic poleward moving east-west arcs are the ionospheric signature of FLRs. The azimuthal distribution, including dawn-dusk symmetricity and azimuthal wavenumbers, of the FLRs in the magnetosphere, are further determined by 2D imaging. The fine structure embedded in the large-scale arcs indicates a wave with high toroidal wavenumber (m ~ 140) was coupled with the FLRs. Based on these works, a likely scenario revealed from the satellite-imaging coordinated observations is as follows: Foreshock transients and magnetosheath HSJs drive compressions of the magnetopause at a few RE, much more localized than global compression by shocks. The compressions launch fast-mode waves and FLRs, which create localized electron precipitation and auroral brightenings. The auroral responses found in this study can highlight structure and evolution of the magnetospheric and ionospheric responses, and signify the geoeffectiveness of localized and transient upstream energy input.
Author: Qiugang Zong
Publisher: John Wiley & Sons
ISBN: 1119509629
Category : Science
Languages : en
Pages : 320
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Book Description
Exploring the processes and phenomena of Earth’s dayside magnetosphere Energy and momentum transfer, initially taking place at the dayside magnetopause, is responsible for a variety of phenomenon that we can measure on the ground. Data obtained from observations of Earth’s dayside magnetosphere increases our knowledge of the processes by which solar wind mass, momentum, and energy enter the magnetosphere. Dayside Magnetosphere Interactions outlines the physics and processes of dayside magnetospheric phenomena, the role of solar wind in generating ultra-low frequency waves, and solar wind-magnetosphere-ionosphere coupling. Volume highlights include: Phenomena across different temporal and spatial scales Discussions on dayside aurora, plume dynamics, and related dayside reconnection Results from spacecraft observations, ground-based observations, and simulations Discoveries from the Magnetospheric Multiscale Mission and Van Allen Probes era Exploration of foreshock, bow shock, magnetosheath, magnetopause, and cusps Examination of similar processes occurring around other planets The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals.
Author: Carl Stephen Andersen
Publisher:
ISBN:
Category : Auroras
Languages : en
Pages : 216
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Book Description
"Two meridian scanning photometers, one located in Alaska and one in Svalbard, are used to examine the behavior of the dayside aurora just before the onset of the expansion phase of 61 substorms. In a strong majority of cases (80%), a poleward movement of the dayside aurora is seen in the minutes preceding sub storm onset. For the cases examined where a poleward movement of the dayside aurora is seen, a northward turning of the (generally southward) IMF is usually, but not always, seen. This suggests that for a majority of substorms, the 'trigger' is, or is related to, a northward turning of the IMF which can be seen by the motions of the dayside aurora. The observed movements of the dayside aurora and supposed onset triggers begin, on average, 12 minutes before substorm onset, which is the period before on-set during which nightside 'auroral fading' is known to happen. Two opposite but not necessarily exclusive behaviors of ionospheric convection have also been reported to occur during this period before onset, namely a decrease and/or an increase in polar cap convection velocities. Radar measurements of ionospheric convection are examined for these events but do not show an easily identifiable characteristic behavior"--Leaf iii.
Author: David J. Knudsen
Publisher: Springer
ISBN: 9789402421217
Category : Science
Languages : en
Pages : 409
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Book Description
This volume surveys our current scientific understanding of the terrestrial aurora. It is organized into eleven reviews detailing theoretical and observational aspects of characteristic auroral morphologies, and how these in turn are organized according to local time, latitude, and activity level. Popular descriptions often attribute the aurora to the interaction of charged particles from the solar wind with atoms in the upper atmosphere. In fact, most auroras are not the result of direct entry of solar wind particles. Rather, as detailed in this volume, auroral particle acceleration and generation of auroral forms occur primarily within the magnetosphere. Importantly, many key aspects of the aurora – most notably, the physical mechanisms responsible for the generation of discrete arcs – are still unexplained, and auroral physics continues to be an active area of scientific research. Each review chapter therefore includes a summary of open questions for further investigation. Providing the first comprehensive review of the terrestrial aurora in two decades, this book will aid both active researchers and newcomers interested in understanding the current state of the field. Previously published Space Science Reviews in the Topical Collection "Auroral Physics”
Author: Jøran Moen
Publisher: Springer Science & Business Media
ISBN: 9401152144
Category : Science
Languages : en
Pages : 446
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Book Description
These proceedings are based on the invited talks and selected research reports presented at the NATO Advanced Study Institute (ASI) on "POLAR CAP BOUNDARY PHENOMENA" held at Longyearbyen, Svalbard, June 4 - 13, 1997. The role of the polar cap and its boundary is very substantial in solar-terrestrial physics. At this NATO AS! a major change in thinking on the "cusp" precipitation region in the high-latitude days ide upper atmosphere was reflected, at least for intervals when the interplanetary magnetic field (IMF) is directed southward. It is likely that this has implications for northward IMF as well. The change comes from the now almost complete acceptance of the concept of magnetosheath particle entry along open magnetic field lines and the evolution of the precipitation into the upper atmosphere with time elapsed since magnetic reconnection which opened the field line. A key prediction of this view is that the low-latitude boundary layer (LLBL) is on open field lines.
Author: Yongliang Zhang
Publisher: John Wiley & Sons
ISBN: 1118978706
Category : Science
Languages : en
Pages : 324
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Book Description
The aurora is the most visible manifestation of the connection of the Earth to the space environment and has inspired awe, curiosity, and scientific inquiry for centuries. Recent advances in observing techniques and modeling and theoretical work have revealed new auroral phenomena, provided a better understanding of auroral dynamics, and have led to an enhanced capability for auroral forecasts. This monograph features discussions of: New auroral phenomena due to the ring current ion and polar rain electron precipitation Various auroral forms and hemispheric asymmetry Auroral model development and MHD simulations Application of the auroral observations for radio absorption and scintillation Aurora nowcast and forecast for space weather operations Auroral Dynamics and Space Weather is a valuable contribution for scientists, researchers, space weather operators, and students of Earth's space environment.
Author: Per Even Sandholt
Publisher: Springer Science & Business Media
ISBN: 9400909799
Category : Science
Languages : en
Pages : 468
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Book Description
Proceedings of the NATO Advanced Research Workshop, Lillehammer, Norway, September 20-24, 1988
Author: Glenn Allen Berg
Publisher:
ISBN:
Category : Auroras
Languages : en
Pages : 234
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Book Description
Author: J.A. Holtet
Publisher: Springer Science & Business Media
ISBN: 9400952953
Category : Science
Languages : en
Pages : 427
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Book Description
These proceedings are based upon introductory talks, research reports and discussions from the NATO Advanced Workshop on the "Morphology and Dynamics of the Polar Cusp", held at Lillehammer, Norway, 7-12 May, 1984. The upper atmosphere at high latitudes is called the "Earth's win dow to outer space". Through various electrodynamic coupling process es as well as through direct transfer of particles many geophysical effects displayed there are direct manifestations of phenomena occurring in the deep space. The high latitude ionosphere will also exert a feedback on the regions of the magnetosphere and atmosphere to which it is coupled, acting as a momentum and energy source and sink, and a source of particles. Of particular interest are the sections of the near space known as the Polar Cusp. A vast portion of the earth's magnetic field envelope is electrically connected to these regions. This geometry results in a spatial mapping of the magnetospheric pro cesses and a focusing on to the ionosphere. In the Polar Cusps the solar wind plasma has also direct access to the upper atmosphere. The polar regions are thus of extreme importance when it comes to under standing the physical processes in the near space and their effect on our environment. The Introductory Talks given at this workshop provided a common background for discussing and understanding the physics of the Polar Cusp. By this book we will make the information which thus was provid ed to the participants of the workshop accessible to a wider audience.
