Task 3

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Contents

How does short-term solar variability affect the geospace environment?

Co-Leaders of Task Group 3

  • Kazunari Shibata (Kyoto University, Japan)
  • Joseph E. Borovsky (Los Alamos National Laboratory, USA)

Scientific Issues & Organization Structure

The scientific issues of the Task Group 3 are as follows.

(1) Origin and emergence of solar magnetism

The ultimate origin of the solar activity is sub-surface magnetic field which is probably created near the base of the convection zone of the Sun. No one has observed magnetic field in the solar interior, so that we do not have firm observational basis for this issue. However, recent development of the helioseismology enables us to see the emergence of magnetic flux tube just below the photosphere. The 3D MHD simulation is also a useful tool to explore the sub-surface dynamics of magnetic field in the solar convection zone.

Chair: A. S. Brun (CEA, France)

(2) Shock formation in the solar atmosphere

When a solar flare occurs, various types of shock waves occur. For example, Moreton waves observed in H alpha images are chromospheric counter part of coronal MHD fast mode shocks emitted from flares. Type II radio bursts are also related to such coronal MHD fast mode shocks propagating from flares. It is interesting to note that the origin of these coronal MHD fast mode shocks directly emitted from flares has not yet been solved. The prominence eruption is one candidate of the origin of coronal shocks, but should be studied in more detail. EIT waves are closely associated with flares and CMEs, but it has not yet been clarified whether these waves are real MHD shocks/waves or not. In large scale, there is now increasing observational evidence that MHD fast mode shocks are formed just ahead of fast CMEs. On the other hand, in small scale, there are also possibilities that slow mode MHD shocks are associated with Petschek type reconnection and fast mode MHD shocks (termination shocks) are formed just ahead of reconnection jet/outflow. These shocks are important site for particle acceleration, especially for SEP (solar energetic particles), which are important for space weather.

Chair: Y. Yan

(3) CME-ICME connection

Coronal mass ejections (CMEs) are associated with flares and/or prominence eruptions, and ultimate cause of geomagnetic storm. Historically, there were controversies whether CMEs are physically different from flares or not, but now many solar physicists consider that both simply show different manifestation of the same MHD explosive phenomena in the solar atmosphere; that is, the part related to electromagnetic emission is called flares, while the part related to mass ejections is called CMEs. Interplanetary coronal mass ejections (ICMEs) are interplanetary counter part of CMEs, and are observed with in-situ instruments. Hence the relation between CMEs and ICMEs are not trivial. There are a lot of remaining puzzles, such as kinematics, magnetic flux and magnetic helicity, and charge state in CME-ICME connection.

Chair: K. Kusano (Nagoya University, Japan)

(4) Coronal hole and high speed solar wind

The high speed solar wind from coronal hole is another important agent that causes geomagnetic storms. Hence the acceleration mechanism of high speed solar wind is one of the most important subjects in space weather research. Recently, soft X-ray telescope (XRT) aboard Hinode satellite revealed that there are ubiquitous tiny X-ray jets in polar coronal holes and also that these jets often show helical motion or Alfvenic motion (i.e., evidence of propagating Alfven waves). These Alfven waves may be the origin of high speed solar wind and also may be related to solar wind turbulence which ultimately lead to geomagnetic storm through the occurrence of CIR (corotating interaction region).

Chair: M. Shimojo (Nobeyama Solar Radio Observatory, Japan)

(5) 3D structure of ICME and solar wind

The three dimensional structure of interplanetary coronal mass ejection (ICMEs) and solar wind is the fundamental subject in space weather research, and has been extensively studied using radio observations of interplanetary scintillation (IPS) as well as Thomson scattered light observations with interplanetary missions such as SMEI (solar mass ejection imager). and STEREO. Excellent time dependent tomography movies are developed through these observations, which are quite useful to reveal the 3D structure of solar wind and ICMEs.

Chair: B. Jackson (University of California, San Diego, USA)

(6) Solar wind - magnetosphere interface

The solar wind with a southward magnetic field is the primary driver of geomagnetic activity. 3D MHD simulations are an important tool to understand the interaction of the solar wind with the magnetosphere and the resulting dynamics of the magnetosphere. There remain several fundamental problems, including the detailed nature of the reconnection coupling of the solar wind to the magnetosphere, the boundary-layer coupling between the solar wind and the magnetosphere, the mechanisms behind mass transport from the solar wind into the magnetosphere, and the dynamical behavior of the magnetosphere ionosphere system. The system behavior includes a number of plasma-physics problems such as the formation of the ring current, the creation and heating of the radiation belts, and the dynamics of the cold plasmasphere. Computer simulations that involve MHD and beyond will be important to understand these problems.

Chair: T. Ogino (Nagoya University, Japan)

(7) Substorm variability and radiation belts

Two longstanding problems in magnetospheric physics are the (1) the dynamics of magnetospheric substorms and (2) the origin and evolution of the outer electron radiation belt. Magnetospheric substorms are driven by the solar wind. Undoubtedly, substorms play an important role in the origin and evolution of the radiation belt. One candidate for the source population of the electron radiation belt are medium-energy electrons injected into the dipolar magnetosphere from the magnetotail during substorm expansion phases. Some of the magnetospheric plasma waves (such as ulf oscillations and whistler-mode chorus) deemed important for the energization of the radiation-belt electrons are believed to be driven by substorm-injected populations of particles. Exploring the interactions between solar-wind driving and substorm dynamics and between substorm dynamics and radiation-belt physics is an avenue for future understanding of the radiation belts.

Chair: B. T. Tsurutani (Jet Propulsion Laboratory, USA)

Current Activity

The blog for Task Group 3

Latest news and information of the task group are published on the following blog page.

Continuous H-Alpha Imaging Network (CHAIN) Project

Upcoming Scientific Meetings Related to Task 3

  • IAU Symposium 286: Comparative magnetic minima: characterizing quiet times in the Sun and stars

Past Scientific Meetings

  • CAWSES II Half-Day Meeting "The 3-D structure of CMEs in the Solar Wind"
    • July 15, 2010 @ Seminaris CampusHotel, Berlin
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