The COSPAR Colloquium on Solar-Terrestrial Magnetic Activity and Space Environment (STMASE) was held in the National Astronomy Observatories of Chinese Academy of Sciences (NAOC) in Beijing, China in September 10-12, 2001. The meeting was focused on five areas of the solar-terrestrial magnetic activity and space environment studies, including study on solar surface magnetism; solar magnetic activity, dynamical response of the heliosphere; space weather prediction; and space environment exploration and monitoring. A hot topic of space research, CMEs, which are widely believed to be the most important phenomenon of the space environment, is discussed in many papers. Other papers show results of observational and theoretical studies toward better understanding of the complicated image of the magnetic coupling between the Sun and the Earth, although little is still known little its physical background. Space weather prediction, which is very important for a modern society expanding into out-space, is another hot topic of space research. However, a long way is still to go to predict exactly when and where a disaster will happen in the space. In that sense, there is much to do for space environment exploration and monitoring. The manuscripts submitted to this Monograph are divided into the following parts: (1) solar surface magnetism, (2) solar magnetic activity, (3) dynamical response of the heliosphere, (4) space environment exploration and monitoring; and (5) space weather prediction. Papers presented in this meeting but not submitted to this Monograph are listed by title as unpublished papers at the end of this book.
Front Cover 1
Solar-Terrestrial Magnetic Activity and Space Environment 4
Copyright Page 5
Contents 10
Preface 6
Section I: Solar Surface Magnetism 14
Chapter 1. Magnetic Reconnection in the Solar Lower Atmosphere 16
Chapter 2. Small-Scale Magnetic Structure in the Photosphere: Relevance to Space Weather Phenomena 22
Chapter 3. Sunspot Dynamics and Coronal Heating 32
Chapter 4. Solar Coronal Activity and Evolution of the Magnetic Field 40
Chapter 5. The Sun-as-a-Star Magnetic Field: Results of Stokesmeter Measurements in Different Spectral Lines 46
Chapter 6. Useful Aspects of Chromospheric Magnetic Field Data 50
Chapter 7. Configurations of Magnetic Fields in Solar Active Regions 54
Chapter 8. Reversed Polarity Structures and Powerful X5.7/3B Flare on July 14, 2000 58
Chapter 9. Properties of Twist of Solar Bipolar Magnetic Fields 64
Chapter 10. Helicity Evolution of a Spot 68
Chapter 11. The Distribution of Magnetic Shear of Active Regions From 1995 to 2000 72
Chapter 12. The Evolution Rate of Small Solar Active Regions and Its Temporal and Spatial Variations 76
Chapter 13. Correcting the Projection Effects of Solar Vector Magnetogram 80
Chapter 14. Applications of Magnetic Line Ratio Method to Magnetographic Observations of Large-Scale Solar Magnetic Fields 84
Chapter 15. The Primary Design of A 1-Meter Infrared Solar Telescope 88
Chapter 16. Huairou Data On Line 92
Section II: Solar Magnetic Activity 96
Chapter 17. Lower Energy Cutoff of Nonthermal Electrons Derived From Batse/CGRO Hard X-Ray 98
Chapter 18. Non-LTE Inversion of an Ha Flaring Loop 102
Chapter 19. Magnetic Flux Cancellation Associated with Coronal Mass Ejections 106
Chapter 20. Dip-Like Magnetic Field Structure Seen in Solar Prominences 116
Chapter 21. Common Characteristics of CMEs and Blobs: a New View of Their Possible Origin 122
Chapter 22. Statistical Studies of Filament Disappearances and CMEs 126
Chapter 23. Catastrophic Behavior of Coronal Magnetic Flux Ropes in Partially Open Magnetic Fields 130
Chapter 24. Coronal Response to the Emergence of New Magnetic Flux 138
Chapter 25. Initiation of Coronal Mass Ejections 142
Chapter 26. What Can We Learn From Constructing CME Models 150
Chapter 27. A Dual-Loop Initiation Model for Coronal Mass Ejections 158
Chapter 28. Coronal Mass Ejections From the Corona to the Interplanetary Medium 162
Chapter 29. Relation Between Coronal Mass Ejections and their Interplanetary Counterparts 170
Chapter 30. A Manifestation of Magnetic Fluxes in Microwave Emission of the Solar Corona 178
Chapter 31. Statistical Properties of Radio-Rich Coronal Mass Ejections 182
Chapter 32. The Broadening Cause of the CaXIX Resonace Line in Solar Flares 186
Chapter 33. Dynamical Features of the Dipole Magnetic Fields Generated Two X-Ray Coronal Mass Ejections and Type IVµ Burst 188
Chapter 34. S-Shaped Magnetic Field Generated an Extra Large Type IVµ Burst and Coronal Mass Ejection 192
Chapter 35. Solar Centimetric Type N and Type M Bursts 196
Chapter 36. Role of Hydrogen and Deuterium in Energy Release From the Solar Flare: Comment on Neupert Effect 202
Chapter 37. Analysis of the January 6-11, 1997, CME Event 206
Section III: Dynamical Response of the Heliosphere 212
Chapter 38. Analysis of Lasco Observations of Streamer Blowout Events 214
Chapter 39. The Geoeffectiveness of Frontside Full Halo Coronal Mass Ejections 222
Chapter 40. The Heliospheric Magnetic Field Probed with Fast Charged Particles 230
Chapter 41. Evolution of the Bastille Day High-Speed Stream 238
Chapter 42. Ensemble and Time Averages: the Missing Diamagnetic Effect 246
Chapter 43. The Global Significance of the CEP Events 252
Chapter 44. Effects of Electron Pressure Gradient in Magnetic Reconnection 264
Chapter 45. The Effect of Geomagnetic Disturbances on Ecosystem 268
Chapter 46. Relationship Between the Cumulative AL and Dst Indices During Magnetic Storms and the UT Variations of the Dst Index 272
Chapter 47. Solar Wind Density and the Auroral Electrojets During Geomagnetic Storms 276
Chapter 48. A Cone Model for Coronal Mass Ejections 280
Chapter 49. Injection of Intense Storm Ring Current Ions 284
Chapter 50. Heliospheric Magnetic Fields and Particle Transport 288
Chapter 51. Geomagnetic Disturbances as Probabilistic Nonlinear Processes 294
Chapter 52. Fine Structure of Sprites and Proposed Global Observations 300
Chapter 53. Night-Time Behavior of 630 Nm Emission in Mid-Latitude Auroras during Strong Magnetic Storms 308
Chapter 54. Doppler Effects in the High-Latitude Ionospere during Observations Geomagnetic Pulsations 312
Chapter 55. Time-Variation of Periodic Components of Yearly Sunspot Numbers 320
Chapter 56. A New Model for Evaluation of the Electromagnetic Energy Flux into an Open Night side Magnetosphere 324
Chapter 57. Numerical Modeling the High-Latitude Ionosphere 328
Chapter 58. Basic Cause of Solar Magnetic Activity Solar Motion or Gyromagnetic Effect 340
Section IV: Space Exploration and Environment 344
Chapter 59. Some Implications of the Interball Studies for Space Weather 346
Chapter 60. Solar Radio Bursts and Fine Structures in the Range of 1.0-7.6 GHz on 14 July 2000 358
Chapter 61. On the Solar Radio Spectro-Interferometry at Low Frequency 362
Chapter 62. Drift Shell Tracing and Secular Variation of inner Radiation Environment in the Saa Region 366
Chapter 63. Energetic Ions in the High Latitude Magnetosphere During the Leading Phase of Acme 372
Chapter 64. Space Environment Data Acquisition Equipment - Attached Payload on the International Space Station 378
Chapter 65. Space Environment Data Acquisition Equipment on Board Mission Demonstration Test Satellite-1 382
Section V: Space Weather Prediction 386
Chapter 66. Space Weather: The Scientific Forecast 388
Chapter 67. Space Weather Effects and how Soho has Improved the Warnings 398
Chapter 68. Implementation and Verification of the Chen Prediction Technique for Forecasting Large Nonrecurring Storms 406
Chapter 69. An Applicable Method for Long-Term Solar Cycle Predictions 410
Chapter 70. Real-Time Space Weather Forecasting Driven by Solar Observations 414
Chapter 71. A New Mechanism for Auroral Electron Acceleration by Nonlinear KAW 422
Chapter 72. Geomagnetic Activity and Solar-Cycle Dependence of the Ring Current Ions 434
Chapter 73. The Application of Non-Linear Filtering Methods to the Forecast of Geomagnetic Indices 440
Chapter 74. Prediction of Relativistic Electron Fluence Using Magnetic Observatory Data 452
Chapter 75. Space Weather Aspects of the ESA Solar Orbiter Mission 456
Chapter 76. Effects of Hysteresis in Solar Cycle Variations Between Flare Index and some Solar Activity 460
Author Index 466
List of Participants 470
List of Unpublished Papers 472
Magnetic Reconnection in the Solar Lower Atmosphere
C. Fang; P.F. Chen; M.D. Ding 1 Department of Astronomy, Nanjing University, Nanjing, 210093, China
ABSTRACT
There are many active phenomena, such as Ellerman bombs (EBs), Type II white-light flares (WLFs) etc, appear in the solar lower atmosphere. They have many common features despite of the large energy gap between them. They are considered to result from the local heating in the solar lower atmosphere. This paper presents the numerical simulations of magnetic reconnection occurring in such a deep atmosphere, with the aim to account for the common features of some of these active phenomena, especially EBs and Type II WLFs. Numerical results manifest the following two typical characteristics of the assumed reconnection process: (1) magnetic reconnection saturates in ~600–900 s, which is just the lifetime of the phenomena; (2) ionization in the upper chromosphere consumes quite a large part of the energy released through reconnection, leading to weak heating; On the contrary, in the lower chromosphere, the ionization and radiation have weak effect, resulting a strong heating in the lower chromosphere. The application of the reconnection model to the phenomena is discussed in detail.
INTRODUCTION
There are many active phenomena, such as Ellerman bombs (EBs), Type II white-light flares (WLFs), surges, spicules and Hα brightening (microflares etc.), which are related to the heating in the solar lower atmosphere and thought to be caused by the magnetic reconnection in the solar lower atmosphere.
Ellerman bombs, also known as moustaches, are small brightening events which are observed in Hα wings around sunspots or under arch filament systems (AFS). They have a typical space scale of ~1 arcsec (Kurokawa et al., 1982), and a typical upward flow of ~6 km s−1 in the chromosphere (Kitai, 1983). EBs are cospatial with bright features in the 3840Å network, as well as with continuum facular granule (cf. Rust and Keil, 1992), and are pushed away by expanding granules (Denker et al., 1995), where one polarity magnetic features may be driven to meet other opposite polarity features. It was suggested by many authors that the heating originates in the lower atmosphere (e.g., Kitai and Muller, 1984; Dara et al., 1997). Recent observations of EBs show that they are located at the boundaries of magnetic features and associated with heating in lower atmosphere (Dara et al., 1997; Qiu et al., 2000). Recently, we have proposed that EBs are caused by magnetic reconnection in the solar lower atmosphere, and typical EB line profiles can be reproduced by assuming that they are caused by the nonthermal electron bombardment originated in the lower chromosphere (Ding, Hénoux and Fang, 1998; Hénoux, Fang and Ding, 1998).
Solar white-light flares (WLFs) are among the strongest flaring events, with an increase in the visible continuum. They are of great importance in flare research because they are not only similar in many aspects to stellar flares, but also present a major challenge to the flare atmospheric models and energy transport mechanisms (Neidig. 1989). It was proposed that there are two types of WLFs which show distinctive emission features, i.e., Type I WLFs reveal a Balmer or Paschen jump, while Type II do not (Machado et al., 1986). Such a distinction results from different continuum radiation mechanisms: hydrogen free-bound transitions for Type I while negative hydrogen (H−) radiations for Type II. Mauas et al. (1990) first investigated the semi-empirical atmospheric models for WLFs, indicating that white-light emission may correspond to the heating of the lower layers in the atmosphere. Further systematic studies on both the spectral characteristics and the atmospheric models for WLFs by Fang and Ding (1995) indicated that the features for Type I WLFs (e.g., a good time correlation between the emission of hard X-ray and the continuum, etc.) can be well explained by the conventional flare picture: energy is initially released in the corona, and then transported into and heats the lower atmosphere. However, for Type II WLFs, since the known mechanisms of energy transport are no longer effective (see Neidig, 1989; Ding et al., 1999 for more references), an in situ heating mechanism deep in the chromosphere or the photosphere is required. Emslie and Machado (1979) and Mauas et al. (1990) suggested that the required in situ heating may be due to the local Joule dissipation of current. Recently, Li et al. (1997) proposed magnetic reconnection in a weakly ionized plasma as the in situ heating mechanism, by which they tried to account for the space scale and the lifetime of Type II WLFs. However, their work is based on a linear analysis.
Surges, spicules and Hα brightening (microflares etc.) are also thought to be related to the reconnection in the solar lower atmosphere (e.g., Dere et al., 1991). Recently, some authors have proposed and studied reconnection in the lower atmosphere. Wang and Shi (1991) provide some evidence of photospheric reconnection as the magnetic cancellation mechanism (see also Litvinenko, 1999). Karpen et al. (1995) made 2.5D simulations and indicated that chromospheric eruptions could be the results of shear-induced reconnection in the chromosphere. Sturrock et a1.(1999) proposed that the reconnection of flux tubes in the chromosphere could contribute to coronal heating. By use of two-component MHD equations, Ji et al. (2001) made 2D numerical simulation and their results support the idea that magnetic cancellation, Ellerman bombs, and type II white-light flares are due to magnetic reconnection in the solar lower atmosphere. In this paper, 2D numerical simulations are performed, with the effects of ionization and radiation included, to study the magnetic reconnection in the lower atmosphere, with the aim to account for some common features of EBs and Type II WLFs.
METHOD OF NUMERICAL SIMULATION
For the magnetic reconnection in the solar lower atmosphere, ionization and radiation become important, while heat conduction is negligible, contrary to the situation in the corona. For simplicity, in this paper the weakly ionized plasma is approximately described by the one-fluid model. Another difficulty in 2D simulations of the lower atmosphere is the strong density stratification, since the pressure scale height is 100–600 km in the chromosphere and photosphere, resulting in a difference of about 7 orders of magnitude for the density between the top of the chromosphere and the lower photosphere. Incorporating such a stratification needs a very fine numerical mesh which makes the computations impractical. Thus, we further neglect the gravity and assume a uniform atmosphere by considering three cases with different characteristic parameters.
The MHD equations we used are as follows:
ρ∂t+∇⋅ρv=0,
(1)
∂v∂t+ρv⋅∇v+∇P−j×B=0,
(2)
B∂t−∇×v×B+∇×η∇×B=0,
(3)
∂tPγ−1+neχH+ρv2/2+∇⋅Pγ−1+neχH+ρv2/2v−−∇⋅Pv−E⋅j+R−H=0,
(4)
where =∂∂xe^x+∂∂ye^y, v = (vx, vy, vz). The quantities ρ, v, B, and T have their usual meanings; E is the electric field, while j is the current density; R and H represent the radiative loss and the heating terms, respectively; the gas pressure P = (nH + ne)kT, k is the Boltzmann constant, nH and ne are the number density of hydrogen atoms and electrons, respectively; χH is the ionization potential, ne is deduced by a modified Saha and Boltzmann formula for pure hydrogen atmosphere:
e=ϕ2+4nHϕ−ϕ/2,T≤105K,nHT>105K,
(5)
Where =1b12πmekTh23/2e−χH/kT (cf. Gan and Fang 1990).
Radiation is important in the lower atmosphere. Strictly speaking, it should be solved by the non-LTE theory, which is too difficult to deal with in the present 2D simulations. Instead, it is substituted by an empirical formula given by Gan and Fang (1990):
=nHneαZf′T,
(6)
where α(Z) and f′(T) are functions of Z (the height from τ5000 = 1 of the photosphere) and T (the temperature), respectively. Since gravity is neglected, α is set to be uniform accordingly, which is done by fixing the value of Z. The pre-heating rate is given by H = nH , where = (neα f′) t=0...
| Erscheint lt. Verlag | 20.11.2002 |
|---|---|
| Sprache | englisch |
| Themenwelt | Sachbuch/Ratgeber |
| Naturwissenschaften ► Physik / Astronomie ► Astronomie / Astrophysik | |
| Naturwissenschaften ► Physik / Astronomie ► Elektrodynamik | |
| Technik ► Fahrzeugbau / Schiffbau | |
| Technik ► Luft- / Raumfahrttechnik | |
| ISBN-10 | 0-08-054143-7 / 0080541437 |
| ISBN-13 | 978-0-08-054143-3 / 9780080541433 |
| Haben Sie eine Frage zum Produkt? |
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