Task 3

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The scientific issues of the Task Group 3 are as follows.
The scientific issues of the Task Group 3 are as follows.
-
=== ===
+
===[[Task 3-1|(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: S. Brun
 +
 
 +
===[[Task 3-2|(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
 +
 
 +
===[[Task 3-3|(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
 +
 
 +
===[[Task 3-4|(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

Revision as of 05:24, 26 November 2010

Contents

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

Introduction

Scientific Issues

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: S. Brun

(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

(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

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