DOCSLIB.ORG

A Three-Dimensional Time-Dependent Model of the Polar Wind

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Three-Dimensional Time-Dependent Model of the Polar Wind JOURNAL OF G EOPHYSICAL RESE ARCH. VO L. 94 . NO . A7. PAG E 8973-8991 , J ULY I. 1989 A Three-Dimensional Time-Dependent Model of the Polar Wind R. W. SCHUNK AND J. J. SOJKA Center for Atmospheric and Space Sciences, Utah State University, Logan A time-dependent global model of the polar wind was used to study transient polar wind per­ turbations during changing magnetospheric conditions. The model calculates three-dimensional distributions for the NO+, ot, Nt, N+ and 0 + densities and the ion and electron tempera­ tures from diffusion and heat conduction equations at altitudes between 120 and 800 km. At altitudes above 500 km, the time-dependent nonlinear hydrodynamic equations for 0 + and H+ are solved self-consistently with the ionospheric equations. The model takes account of supersonic ion outflow, shock formation, and ion energization during a plasma expansion event. During the simulation, the magnetic activity level changed from quiet to active and back to quiet again over a 4.5-hour period. The study indicates the following: (1) Plasma pressure changes due to Te , Ti or electron density variations produce perturbations in the polar wind. In particular, plasma flux tube motion through the auroral oval and high electric field regions produces transient large-scale ion upflows and downflows. At certain times and in certain regions both inside and outside the auroral oval, H+-O+ counterstreaming can occur, (2) The density structure in the polar wind is considerably more complicated than in the ionosphere because of both horizontal plasma convec­ tion and changing vertical propagation speeds due to spatially varying ionospheric temperatures, (3) During increasing magnetic activity, there is an overall increase in Te , Ti and the electron density in the F-region, but there is a time delay in the buildup of the electron density that is . as long as five hours at high altitudes, (4) During increasing magnetic activity, there is an overall increase in the polar wind outflow from the ionosphere, while the reverse is true for declining activity, (5) In certain regions, however, localized ionospheric holes can develop during increasing magnetic activity, and in these regions the polar wind outflow rate is reduced, (6) During changing magnetic activity, the temporal evolution of the ion density morphology at high altitudes can be different from, and even opposite to, that at low altitudes. 1. INTRODUCTION Burch, 1985; Persoon et al., 1983] . Also, theoretical mod­ In the early 1960s, it was recognized that the interaction elling has shown that the polar \\' ind is collision-dominated of the solar wind with the Earth's dipole magnetic field acts at low altitudes (;5 2000 km) and collisionless at high al­ to significantly modify the magnetic field configuration in a titudes. The collision-dominated characteristics of the flow vast region close to the Earth [Axford and Hines, 1961] . The have been extensively studied with the aid of hydrodynamic dynamo action associated with the flow of solar wind plasma models [Banks and Holzer, 1968, 1969; Marubashi, 1970; across magnetic field lines generates an intense current sys­ Raitt et al., 1975, 1977; Schunk et al. , 1978]. When colli­ tem, which acts to compress the Earth's magnetic field on sions prevail, the temperature (or pressure) distribution is the dayside and stretch it into a long comet-like tail on the isotropic and the heat flow is proportional to the tempera­ nightside. The magnetic field lines that form the tail origi­ ture gradient. In the collisionless regime, on the other hand, nate in the Earth's polar regions, and since the pressure in the temperature distribution is anisotropic and the mathe­ ~he ionosphere is much greater than that in the distant tail, matical formulation of the polar wind is considerably more It was suggested that a continual escape of thermal plasma complicated. This collisionless regime has been modelled (H+ and He+) should occur along these 'open' field lines with hydromagnetic [Holzer et al., 1971] , kinetic [Lemaire, [Bauer, 1966; Dessler and Michel, 1966]. 1972; Lemaire and Scherer, 1970, 1973], and semi-kinetic The early suggestions of light ion outflow were based on a [Barakat and Schunk, 1983, 1984] equations. Also, gen­ t.hermal evaporation process. Via thermal evaporation, the eralized transport equations have been used that include ~~ht ions would escape the topside ' ionosphere with veloc­ both collision-dominated and collisionless characteristics of Ities close to their thermal velocities and then flow along the ion outflow, and hence, provide for continuity from the magnetic field lines to the magnetospheric tail. However, it collision-dominated to collisionless regimes [Schunk and was. Subsequently argued that the outflow should be super­ Watkins, 1981, 1982; Demars and Schunk, 1986, 1987; Gan­ BOme and it was termed the 'polar wind' in analogy to the guli, 1986; Ganguli and Palmadesso, 1987; Ganguli et al. , ~lar wind [Axford, 1968]. A simple hydrodynamic descrip­ 1987] . t~on was then used that emphasized the supersonic nature All of the above studies of the 'classical' polar wind were 0. the flow and the basic polar wind characteristics were elu­ for 'steady state' conditions, with the emphasis on elucidat­ Cl~ted [Banks and Holzer, 1968, 1969; Marubashi, 1970]. ing physical processes. As a result of these studies, signif­ I he supersonic nature of the polar wind has now been icant progress has been made in understanding the basic Cearly established by both direct and indirect methods [Hoff­ polar wind characteristics for a wide range of conditions [cf. man and Dodson, 1980; Nagai et al., 1984; Gurgiolo and Schunk, 1986, 1988] . More recently, attention has been fo­ cussed on studying the temporal characteristics of the polar wind. However, because of the severe numerical difficulties Copyright 1989 by the American Geophysical Union. associated with solving the more complicated sets of trans­ ~~per number 89JA00211. port equations [ef. Schunk, 1977; Demars and Schunk, 1979; 48-0227/89/89JA-00211$05.00 Barakat and Schunk, 1982], the initial time-dependent mod- 8973 8974 SCHUNK AND SOJKA: THREE· DIMENSIONAL POLAR WIND els of the classical polar wind were based on a hydrodynamic sumption that local heating and cooling processes dOminate formulation [Singh and Schunk, 1985; Gombosi et al., 1985 , (valid below 500 km). Flux tubes of plasma were followed 1986; Gombosi and Schunk, 1988]. as they moved in response to convect ion electric fields. A Singh and Schunk [1985] studied the temporal evolution further extension of the model to include the minor ions N+ of density perturbations in the supersonic collisionless polar and He+ , an updated photochemical scheme, and the mass wind, including extended density depletions and localized spectrometer/incoherent scatter (MSIS) atmospheric model density bumps and holes. For this study, the H+ continu­ is described in Schunk and Raitt [1980]. ity and momentum equations were solved without allowance The addition of plasma convection and particle precipita. for collisions and assuming constant, isotropic ion and elec­ tion models is described in Sojka et al. [1981a , b) . More re­ tron temperatures of 3560 K. Also, the effects of localized cently, the ionospheric model has been extended by SchUnk ion heating on the polar wind were studied by Gombosi et and Sojka [1982a] to include ion thermal conduction and al. [1985, 1986] and by Gombosi and Killeen [1987]. Both diffusion-thermal heat flow , so that the ion temperature is high-altitude and low-altitude ion heating events were con­ now rigorously calculated at all altitudes between 120-800 sidered. In these studies, the full hydrodynamic continuity, km. The adopted ion energy equation and conductivities are momentum, and energy equations for H+ , 0+, and electrons those given by Conrad and Schunk [1979]. Also, the electron were solved including collisional conductivities and assum­ energy equation has been included recently by Schunk et al. ing isotropic, but variable, ion and electron temperatures. [1986], and consequently, the electron temperature is now More recently, Gombosi and Schunk [1988] conducted a rigorously calculated at all altitudes. The electron energy comparative study of plasma expansion events in the polar equation and the heating and cooling rates were taken from wind. The temporal characteristics of the polar wind were Schunk and Nagy [1978], and the conductivities were taken studied with both a full set of hydrodynamic equations and from Schunk and Walker [1970]. a simplified set of collisionless equations that took account . of the extremely large ion temperature anisotropies that de­ 2.2. High-Altitude Hydrodynamic Model velop at high altitudes [ef. Holzer et al. , 1971; Lemaire and The high-altitude model is based on a numerical solution Scherer, 1973]. These temperature anisotropies were shown of the time-dependent coupled continuity and momentum to be stable with respect to the excitation of electrostatic equations for H+ and 0+ ions. The equations are solved waves by Barakat and Schunk [1987]. The two different po­ along a diverging 'open' magnetic flux tube with boundary lar wind models were solved with different numerical tech­ conditions specified at low altitudes and outflow conditions niques and the results were compared for a range of idealized imposed at high altitudes. The specific equations adopted expansion scenarios. The models were also used to study are as follows: the temporal response of the polar wind to varying electron temperature conditions. (1) All of the time-dependent polar wind studies described above were based on one-dimensional models applied to a single location, with the temporal variations driven by as­ sumed inputs. In this paper, we present a time-dependent, three-dimensional, multi-ion model of the polar wind. The model covers the altitude range of from 120 to 9,000 km and takes account of supersonic ion outflow, shock formation, +p·--+nCME ·k (IIT. -T....1.) --1aA \ r2 \ \ t A ar and ion energization during plasma expansion events.
Load more

Recommended publications
  • O + Escape During the Extreme Space Weather Event of 4-10 September
    O + Escape During the Extreme Space Weather Event of 4-10 September 2017 Audrey Schillings, Hans Nilsson, Rikard Slapak, Peter Wintoft, Masatoshi Yamauchi, Magnus Wik, Iannis Dandouras, Chris Carr To cite this version: Audrey Schillings, Hans Nilsson, Rikard Slapak, Peter Wintoft, Masatoshi Yamauchi, et al.. O + Es- cape During the Extreme Space Weather Event of 4-10 September 2017. Journal of Space Weather and Space Climate, EDP sciences, 2018, 16 (9), pp.1363-1376. 10.1029/2018SW001881. hal-02408153 HAL Id: hal-02408153 https://hal.archives-ouvertes.fr/hal-02408153 Submitted on 12 Dec 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. SPACE WEATHER, VOL. ???, XXXX, DOI:10.1002/, + 1 O escape during the extreme space weather event of 2 September 4–10, 2017 Audrey Schillings,1,2 Hans Nilsson,1,2 Rikard Slapak,3 Peter Wintoft,4 Masatoshi Yamauchi,1 Magnus Wik,4 Iannis Dandouras,5 and Chris M. Carr,6 Corresponding author: Audrey Schillings, Swedish Institute of Space Physics, Kiruna, Sweden. ([email protected]) 1Swedish Institute of Space Physics, Kiruna, Sweden. 2Division of Space Technology, Lule˚a University of Technology, Kiruna, Sweden.
    [Show full text]
  • Geomagnetic Disturbance Intensity Dependence on the Universal Timing of the Storm Peak
    Geomagnetic disturbance intensity dependence on the universal timing of the storm peak R.M. Katus1,3,2, M.W. Liemohn2, A.M. Keesee3, T.J. Immel4, R. Ilie2, D. T. Welling2, N. Yu. Ganushkina5,2, N.J. Perlongo2, and A. J. Ridley2 1. Department of Mathematics, Eastern Michigan University, Ypsilanti, MI, USA 2. Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA 3. Department of Physics and Astronomy, West Virginia University, Morgantown, WVU, USA 4. Space Sciences Laboratory, University of California, Berkeley, CA, USA 5. Finnish Meteorological Institute, Helsinki, Finland Submitted to: Journal of Geophysical Research Corresponding author email: [email protected] AGU index terms: 2730 Magnetosphere: inner 2788 Magnetic storms and substorms (4305, 7954) 4305 Space weather (2101, 2788, 7900) 4318 Statistical analysis (1984, 1986) 7954 Magnetic storms (2788) Keywords: Geomagnetic indices, ground-based magnetometers, Longitudinal dependence, magnetic storms, space weather Key points: • We statistically examine storm-time solar wind and geophysical data as a function of UT of the storm peak. • There is a significant UT dependence to large storms; larger storms occur with a peak near 02 UT. • The difference in storm magnitude is caused by substorm activity and not by solar wind driving. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/2016JA022967 This article is protected by copyright. All rights reserved.
    [Show full text]
  • Ionospheric Response to Traveling Convection Twin Vortices
    GEOPHYSICAL RESEARCH LETTERS, VOL. 21, NO. 17, PAGES 1759-1762, AUGUST 15,1994 JonoS heric response to traveling convection twin vortices It W. Schunk, L. Zhu, and J. J. Sojka Center for Atmo pheric and Space Sciences, Utah State University, Logan, Utah 84322-4405 Abstract. Traveling convection twin vortices have been move in the antisunward direction for a period of several hours, bserved for everal years. At ionospheric altitudes, the twin with about a 15-minute time interval between vortices. ~ortiCes correspond to spatially localized, transient structures Mounting evidence indicates that the twin vortices occur on embedded in large-scale background convection pattern. The closed magnetic field lines and most likely those field lines convection vortices are typically observed in the morning and that connect to the low-latitude boundary layers (LLBL) evening regions. They are aligned predominantly in the east­ [Heikkila et ai., 1989; McHenry et ai., 1990a]. At present, the west direction and have a horizontal extent of from 500-1000 prevailing view is that the twin vortices are not a result of flux km. Associated with the twin vortices are enhanced electric transfer events at the dayside magnetopause, but their exact fields, particle precipitation, and an upward/downward field­ cause is still controversial. Friis-Christensen et ai. [1988] aligned cu rrent pair. Once formed, the twin vortex structures suggested that the traveling vortices are due to sudden changes propagate in the tail ward direction at speeds of several km/s, in the solar wind dynamic pressure or the interplanetary but they weaken as they propagate and only last for about 10- magnetic field (lMF).
    [Show full text]
  • The Exosphere, Leading to a Much More Descriptive Science
    UNCLASSIFIED 1070 SSPPAACCEE EENNVVIIIRROONNMMEENNTT TTEECCHHNNOOLLOO GGIIIEESS GEOCORONA IN LYMAN Contract F19628 Contract Justin Technologies public distribution Notice: This document is released for May 2012 EXOSPHERIC HYDROGEN EXOSPHERIC J. J. OBSERVATIONS OF THE OF OBSERVATIONS Bailey ATOM DISTRIBUTIONS ATOM . THREE - 03 by by - C Space Space Environment - OBTAINED FROM OBTAINED 0076 SET TR 2012 - DIMENSIONAL - - 001 ALPHA THREE-DIMENSIONAL EXOSPHERIC HYDROGEN ATOM DISTRIBUTIONS OBTAINED FROM OBSERVATIONS OF THE GEOCORONA IN LYMAN-ALPHA by Justin J. Bailey A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (ASTRONAUTICAL ENGINEERING) May 2012 Copyright 2012 Justin J. Bailey for my wife, Natalie, a bona fide yogini who at times had to wrap her hands around my head to keep my brain from falling out ii Acknowledgements My opportunity to contribute in this field was established and supported by many different people. After finishing with an M.S. in Astronautical Engineering, I walked into Professor Mike Gruntman’s office hoping to learn more about space physics and aeronomy. He proceeded to draw the geocorona in assorted colors on a whiteboard, and it was then that the content of this dissertation was born. Of course, none of this research would have been possible were it not for his expertise and guidance. I would like to thank my advisory committee (Professors Daniel Erwin, Joseph Kunc, W. Kent Tobiska, and Darrell Judge) for their many insightful observations. I am especially indebted to Dr. Tobiska for numerous opportunities to learn more about the solar output and how it drives the exosphere, leading to a much more descriptive science discussion in the relevant sections.
    [Show full text]
  • On the Effect of the Background Wind on the Evolution of Interplanetary Shock Waves
    A&A 430, 1099–1107 (2005) Astronomy DOI: 10.1051/0004-6361:20041676 & c ESO 2005 Astrophysics On the effect of the background wind on the evolution of interplanetary shock waves C. Jacobs, S. Poedts, B. Van der Holst, and E. Chané Centre for Plasma Astrophysics, K.U. Leuven, Celestijnenlaan 200B, 3001, Leuven, Belgium e-mail: [email protected] Received 16 July 2004 / Accepted 20 September 2004 Abstract. The propagating shock waves in the solar corona and interplanetary (IP) space caused by fast Coronal Mass Ejections (CMEs) are simulated numerically and their structure and evolution is studied in the framework of ideal magnetohydrodynamics (MHD). Due to the presence of three characteristic velocities and the anisotropy induced by the magnetic field, the CME shocks generated in the lower corona can have a complex structure and topology including secondary shock fronts, over-compressive and compound shocks, etc. The evolution of these CME shocks is followed during their propagation in IP space up to r = 30 R. Here, particular attention is given to the effect of the background solar wind on the evolution parameters of the fast CME shocks, i.e. shock speed, deformation of the leading shock front and the CME plasma, stand-off distance of the leading shock front, direction, spread angle, etc. First, different “frequently used” solar wind models are reconstructed with the same numerical code, the same numerical technique on exactly the same numerical grid (and thus the same numerical dissipation), the same boundary conditions, and the same normalization. Then, a simple CME model is superposed on three different solar wind models, again using exactly the same initial conditions.
    [Show full text]
  • Validation for Global Solar Wind Prediction Using Ulysses Comparison: Multiple Coronal and Heliospheric Models Installed at the Community Coordinated Modeling Center
    Validation for Global Solar Wind Prediction Using Ulysses Comparison: Multiple Coronal and Heliospheric Models Installed at the Community Coordinated Modeling Center L.K. Jian (1,2), P.J. MacNeice (2), M.L. Mays (3,2), A. Taktakishvili (3,2), D. Odstrcil (4,2), B. Jackson (5), H.-S. Yu (5), P. Riley (6), I.V. Sokolov (7) 1. Department of Astronomy, University of Maryland, College Park, Maryland, USA 2. Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA 3. Department of Physics, Catholic University of America, Washington, District of Columbia, USA 4. School of Physics, Astronomy, and Computational Sciences, George Mason University, Fairfax, Virginia, USA 5. Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, California, USA 6. Predictive Science Inc., San Diego, California, USA 7. Department of Atmospheirc, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA Abstract The prediction of the background global solar wind is a necessary part of space weather forecasting. Several coronal and heliospheric models have been installed and/or recently upgraded at the Community Coordinated Modeling Center (CCMC), including the Wang- Sheely-Arge (WSA)-Enlil model, MHD-Around-a-Sphere (MAS)-Enlil model, Space Weather Modeling Framework (SWMF), and heliospheric tomography using interplanetary scintillation (IPS) data. Ulysses recorded the last fast latitudinal scan from southern to northern poles in 2007. By comparing the modeling results with Ulysses observations over seven Carrington rotations, we have extended our third-party validation from the previous near-Earth solar wind to mid-to- high latitudes, in the same late declining phase of solar cycle 23.
    [Show full text]
  • The Polar Wind Modulated by the Spatial Inhomogeneity of the Strength of the Earth's Magnetic Field
    Originally published as: Li, K., Förster, M., Rong, Z., Haaland, S., Kronberg, E., Cui, J., Chai, L., Wei, Y. (2020): The Polar Wind Modulated by the Spatial Inhomogeneity of the Strength of the Earth's Magnetic Field. - Journal of Geophysical Research: Space Physics, 125, 4, e2020JA027802. https://doi.org/10.1029/2020JA027802 RESEARCH ARTICLE The Polar Wind Modulated by the Spatial Inhomogeneity 10.1029/2020JA027802 of the Strength of the Earth's Magnetic Field Key Points: Kun Li1 , Matthias Förster2,3, Zhaojin Rong4,5 , Stein Haaland2,6, Elena Kronberg2,7 , • The density and the particle flux of 1,8 4,5 4,5 the polar wind are revealed to be Jun Cui , Lihui Chai , and Yong Wei anticorrelated with the strength of 1 the Earth's magnetic field Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun • The polar rain can be the main Yat‐sen University, Zhuhai, China, 2Max Planck Institute for Solar System Research, Göttingen, Germany, 3German energy source of the polar wind in Research Centre for Geosciences, Helmholtz Centre Potsdam, Potsdam, Germany, 4Institute of Geology and Geophysics, the southern hemisphere during Chinese Academy of Sciences, Beijing, China, 5College of Earth and Planetary Sciences, University of Chinese Academy of periods of high solar activity levels 6 7 • A strong magnetic field diminishes Sciences, Beijing, China, Birkeland Centre for Space Science, University of Bergen, Bergen, Norway, Department of energy depositions in the polar cap Earth and Environmental Sciences, Ludwig Maximilian University of Munich, Munich, Germany, 8Chinese Academy of and thus controls the density and Sciences, Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Beijing, China particle flux of the polar wind Abstract When the geomagnetic field is weak, the small mirror force allows precipitating charged fl Correspondence to: particles to deposit energy in the ionosphere.
    [Show full text]
  • Multiple Transpolar Auroral Arcs Reveal Insight About Coupling Processes in the Earth's Magnetotail
    Multiple transpolar auroral arcs reveal insight about coupling processes in the Earth’s magnetotail Qing-He Zhanga,1, Yong-Liang Zhangb, Chi Wangc, Michael Lockwoodd, Hui-Gen Yange, Bin-Bin Tangc, Zan-Yang Xinga, Kjellmar Oksavikf,g, Larry R. Lyonsh, Yu-Zhang Maa, Qiu-Gang Zongi, Jøran Idar Moenj,g, and Li-Dong Xiaa aShandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, Shandong, 264209, China; bThe Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723; cState Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, 100190, China; dDepartment of Meteorology, University of Reading, Reading, RG6 6BB, United Kingdom; eMinistry of Natural Resources Key Laboratory of Polar Science, Polar Research Institute of China, Shanghai, 200136, China; fDepartment of Physics and Technology, Birkeland Centre for Space Science, University of Bergen, Bergen, N-5020, Norway; gArctic Geophysics Department, The University Centre in Svalbard, Longyearbyen, N-9171, Norway; hDepartment of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095; iSchool of Earth and Space Sciences, Peking University, Beijing, 100871, China; and jDepartment of Physics, University of Oslo, Blindern, Oslo 0371, Norway Edited by Lennard A. Fisk, University of Michigan, Ann Arbor, MI, and approved May 26, 2020 (received for review January 11, 2020) A distinct class of aurora, called transpolar auroral arc (TPA) (in twisting of the magnetotail due to IMF variations (3, 21, 22). some cases called “theta” aurora), appears in the extremely high- These processes could result in plasma sheet bifurcation, fila- latitude ionosphere of the Earth when interplanetary magnetic mentary extent into the lobes, or hot plasma trapped in the tail field (IMF) is northward.
    [Show full text]
  • Solar Illumination Control of the Polar Wind 10.1002/2017JA024615 L
    Journal of Geophysical Research: Space Physics RESEARCH ARTICLE Solar Illumination Control of the Polar Wind 10.1002/2017JA024615 L. Maes1,2 , R. Maggiolo1 ,J.DeKeyser1,3 , M. André4 , A. I. Eriksson4 , Key Points: S. Haaland2,5 ,K.Li6,7 , and S. Poedts3 • Polar wind flux density exhibits a dependence on the solar zenith angle 1Royal Belgian Institute for Space Aeronomy, Brussels, Belgium, 2Max Planck Institute for Solar System Research, • Both density and velocity in the polar 3 4 wind show similar but weaker solar Göttingen, Germany, Center for Mathematical Astrophysics, KU Leuven, Leuven, Belgium, Swedish Institute for Space zenith angle dependence Physics, Uppsala, Sweden, 5Department of Physics and Technology, University of Bergen, Bergen, Norway, 6Key • Seasonal variations are observed in Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, the polar wind flux density China, 7State Key Laboratory of Space Weather, Chinese Academy of Sciences, Beijing, China Supporting Information: • Supporting Information S1 Abstract Polar wind outflow is an important process through which the ionosphere supplies plasma • Figure S1 to the magnetosphere. The main source of energy driving the polar wind is solar illumination of the ionosphere. As a result, many studies have found a relation between polar wind flux densities and solar EUV Correspondence to: intensity, but less is known about their relation to the solar zenith angle at the ionospheric origin, certainly L. Maes, at higher altitudes. The low energy of the outflowing particles and spacecraft charging means it is very [email protected] difficult to measure the polar wind at high altitudes.
    [Show full text]
  • Velocity Fluctuations in Polar Solar Wind
    Ann. Geophys., 27, 877–883, 2009 www.ann-geophys.net/27/877/2009/ Annales © Author(s) 2009. This work is distributed under Geophysicae the Creative Commons Attribution 3.0 License. Velocity fluctuations in polar solar wind: a comparison between different solar cycles B. Bavassano, R. Bruno, and R. D’Amicis Istituto di Fisica dello Spazio Interplanetario, Istituto Nazionale di Astrofisica, Roma, Italy Received: 8 October 2008 – Revised: 26 January 2009 – Accepted: 4 February 2009 – Published: 20 February 2009 Abstract. The polar solar wind is a fast, tenuous and steady a dominant feature of the high-latitude heliosphere. Its prop- flow that, with the exception of a relatively short phase erties have been extensively investigated by Ulysses, the first around the Sun’s activity maximum, fills the high-latitude spacecraft with a highly inclined orbital plane with respect to heliosphere. The polar wind properties have been exten- the ecliptic. Launched in October 1990, the Ulysses’ out-of- sively investigated by Ulysses, the first spacecraft able to per- ecliptic journey began in February 1992, with a Jupiter grav- form in-situ measurements in the high-latitude heliosphere. ity assist. Presently data extend till December 2008, though The out-of-ecliptic phases of Ulysses cover about seventeen the spacecraft operations were expected to end in July 2008 years. This makes possible to study heliospheric properties (due to technical problems arisen in January 2008). With an at high latitudes in different solar cycles. In the present in- orbital period of 6.2 years, during this period of time Ulysses vestigation we focus on hourly- to daily-scale fluctuations of has covered two complete out-of-ecliptic orbits and ∼78% the polar wind velocity.
    [Show full text]
  • Sudden Depletion of Alfv\'Enic Turbulence in the Rarefaction Region
    Sudden depletion of Alfvénic turbulence in the rarefaction region of corotating solar wind high speed streams at 1 AU: possible solar origin ? G. Carnevale1; 3, R. Bruno2, R. Marino3, E. Pietropaolo1, and J.M. Raines4 1 University of L’Aquila, Dept. of Physical and Chemical Sciences, Via Vetoio 48, 67100 Coppito (AQ) , Italy 2 INAF-Institute for Space Astrophysics and Planetology, Via del Fosso del Cavaliere 100, 00133 Rome, Italy 3 Laboratoire de Mécanique des Fluides et dÁcoustique, CNRS, École Centrale de Lyon, Université Claude Bernard Lyon 1, INSA de Lyon, F-69134 Écully, France 4 University of Michigan, Dept. of Climate and Space Sciences and Engineering, Ann Arbor[MI], United States ABSTRACT A canonical description of a corotating solar wind high speed stream, in terms of velocity profile, would indicate three main regions: a stream interface or corotating interaction region characterized by a rapid flow speed increase and by compressive phenomena due to dynamical interaction between the fast wind flow and the slower ambient plasma; a fast wind plateau characterized by weak compressive phenomena and large amplitude fluctuations with a dominant Alfvénic character; a rarefaction region characterized by a decreasing trend of the flow speed and wind fluctuations dramatically reduced in amplitude and Alfvénic character, followed by the slow ambient wind. Interesting enough, in some cases the region where the severe reduction of these fluctuations takes place is remarkably short in time, of the order of minutes, and located at the flow velocity knee separating the fast wind plateau from the rarefaction region. The aim of this work is to investigate which are the physical mechanisms that might be at the origin of this phenomenon.
    [Show full text]
  • Determine the Role of Nitrogen Ions in the Ionospheric Outflow
    Determine the Role of Nitrogen Ions in the ABSTRACT Knowledge of ion composition in the terrestrial ionosphere and magnetosphere is crucial to understand the plasma dynamics in the Earth’s magnetosphere-ionosphere system. The discovery of O+ and N+ in the ionosphere and Ionospheric Outflow: Tracking the Differential magnetosphere hinted to the connection between the ionospheric and magnetospheric plasma, suggesting that the ionosphere acts as a reservoir for the magnetospheric plasma. However, most instruments flying in space couldn’t + + distinguish between O+ and N+ due to their close masses, and therefore the contribution of N+ to the magnetosphere- Behavior of N and O Ions from the Outflowing ionosphere system has remained unknown. Idealized simulation results with the Hot Electron Ion Drift Integrator (HEIDI) point out the importance of N+ in the ring current. The presence of N+, even small amount of it, changes the magnetospheric dynamics and alters the ENA fluxes. In order to track the behavior and determine the role of N+ in magnetosphere- Ionosphere to the Inner Magnetosphere ionosphere system, we properly include N+ ions into the Polar Wind Outflow Model (PWOM). Preliminary simulation 1 1 2 results indicate that the presence of N+ in the ionospheric outflow can change ionospheric dynamics in the low altitudes Mei-Yun Lin ([email protected]), Raluca Ilie and Alex Glocer where chemical reaction and collision are dominated. Our initial simulation results suggest that N+ and O+ are required to 1Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign describe separately in the magnetosphere-ionosphere system, since they obey different chemical and physical reactions.
    [Show full text]