122 research outputs found
The dynamics of eruptive prominences
This chapter discusses the dynamical properties of eruptive prominences in
relation to coronal mass ejections (CMEs). The fact that eruptive prominences
are a part of CMEs is emphasized in terms of their physical association and
kinematics. The continued propagation of prominence material into the
heliosphere is illustrated using in-situ observations. The solar-cycle
variation of eruptive prominence locations is discussed with a particular
emphasis on the rush-to-the-pole (RTTP) phenomenon. One of the consequences of
the RTTP phenomenon is polar CMEs, which are shown to be similar to the
low-latitude CMEs. This similarity is important because it provides important
clues to the mechanism by which CMEs erupt. The nonradial motion of CMEs is
discussed, including the deflection by coronal holes that have important space
weather consequences. Finally, the implications of the presented observations
for the modeling CME modeling are outlined.Comment: 28 pages, 15 figures, Chapter 15 of the book Solar Prominences,
edited by J.-C. Vial & O. Engvold, Springer, in press (2014
Factors Affecting The Intensity of Solar Energetic Particle Events
This paper updates the influence of environmental and source factors of
shocks driven by coronal mass ejections (CMEs) that are likely to influence the
solar energetic particle (SEP) events. The intensity variation due to CME
interaction reported in [1] is confirmed by expanding the investigation to all
the large SEP events of solar cycle 23. The large SEP events are separated into
two groups, one associated with CMEs running into other CMEs, and the other
with CMEs running into the ambient solar wind. SEP events with CME interaction
generally have a higher intensity. New possibilities such as the influence of
coronal holes on the SEP intensity are also discussed. For example, the
presence of a large coronal hole between a well-connected eruption and the
solar disk center may render the shock poorly connected because of the
interaction between the CME and the coronal hole. This point is illustrated
using the 2004 December 3 SEP event delayed by about 12 hours from the onset of
the associated CME. There is no other event at the Sun that can be associated
with the SEP onset. This event is consistent with the possibility that the
coronal hole interaction influences the connectivity of the CMEs that produce
SEPs, and hence the intensity of the SEP event.Comment: 6 pages, 2 figures, 2 table
Solar Activity Studies using Microwave Imaging Observations
We report on the status of solar cycle 24 based on polar prominence eruptions
(PEs) and microwave brightness enhancement (MBE) information obtained by the
Nobeyama radioheliograph. The north polar region of the Sun had near-zero field
strength for more than three years (2012 to 2015) and ended only in September
2015 as indicated by the presence of polar PEs and the lack of MBE. The
zero-polar-field condition in the south started only around 2013, but it ended
by June 2014. Thus the asymmetry in the times of polarity reversal switched
between cycle 23 and 24. The polar MBE is a good proxy for the polar magnetic
field strength as indicated by the high degree of correlation between the two.
The cross-correlation between the high- and low-latitude MBEs is significant
for a lag of ~5.5 to 7.3 years, suggesting that the polar field of one cycle
indicates the sunspot number of the next cycle in agreement with the
Babcock-Leighton mechanism of solar cycles. The extended period of near-zero
field in the north-polar region should result in a weak and delayed sunspot
activity in the northern hemisphere in cycle 25.Comment: 4 pages, 6 figures, invited paper to the URSI Asia-Pacific Radio
Science Conference in Seoul, August 21-25, 201
Observations of CMEs and Models of the Eruptive Corona
It is now realized that coronal mass ejections (CMEs) are the most energetic phenomenon in the heliosphere. Although early observations (in the 1970s and 19805) revealed most of the properties of CMEs, it is the extended and uniform data set from the Solar and Heliospheric Observatory (SOHO) mission that helped us consolidate our knowledge on CMEs. The Solar Terrestrial Relations Observatory (STEREO) mission has provided direct confirmation of the three-dimensional structure of CMEs. The broadside view provided by the STEREO coronagraphs helped us estimate the width of the halo CMEs and hence validate CME cone models. Current theoretical ideas on the internal structure of CMEs suggest that a flux rope is central to the CME structure, which has considerable observational support both from remote-sensing and in-situ observations. The flux-rope nature is also consistent with the post-eruption arcades with high-temperature plasma and the charge states observed within CMEs arriving at Earth. The quadrature observations also helped us understand the relation between the radial and expansion speeds of CMEs, which were only known from empirical relations in the past. This paper highlights some of these results obtained during solar cycle 23 and 24 and discusses implications for CME models
The Solar Origins of Severe Space Weather
Solar cycle 23 witnessed an unprecedented array of space- and ground-based instruments observing the violent eruptions from the Sun that had huge impact on the heliosphere. Coronal mass ejections (CMEs) contribute to space weather by producing geomagnetic storms and accelerating energetic particles, the two aspects that concern the space weather community. This paper discusses the kinematic and solar-source properties of these CMEs and how they vary with the solar activity cycle with particular emphasis on the following issues. Intense geomagnetic storms are caused by the out-of-the-ecliptic component of the magnetic field in CMEs and/or their sheath. Geoeffective CMEs originate close to the disk center of the Sun. Geoeffective CMEs are more energetic (average speed approx.1000 km/s, mostly halo CMEs or partial halo CMEs). CMEs producing solar energetic particles are the fastest (average speed approx. 1600 km/s) of all CME populations and have very high halo CME fraction. The source location requirement is different for Geoeffective and SEP-producing CMEs because of the different paths taken by CME plasma and energetic particles
Global Cooperation in the Science of Space Weather
The international space science community had recognized the importance of space weather more than a decade ago, which resulted in a number of international collaborative activities such as the Climate and Weather of the Sun Earth System (CAWSES) by SCOSTEP and the International Space Weather Initiative (ISWI). The ISWI program is a continuation of the successful International Heliophysical Year (IHY) program. These programs have brought scientists together to tackle the scientific issues behind space weather. In addition to the vast array of space instruments, ground based instruments have been deployed, which not only filled voids in data coverage, but also inducted young scientists from developing countries into the scientific community. This paper presents a summary of CAWSES and ISWI activities that promote space weather science via complementary approaches in international scientific collaborations. capacity building. and public outreach
Aspects of Coronal Mass Ejections Related to Space Weather
Solar cycle 23 witnessed an unprecedented array of space- and ground-based instruments observing the violent eruptions from the Sun that had huge impact on the heliosphere. It was possible to characterize corona) mass ejections (CMEs) that cause extreme solar energetic particle events and geomagnetic storms, the two aspects that concern the space weather community. In this paper I discuss the special populations of CMEs that have significant interplanetary consequences: shock-driving CMEs identified based on their association with type 11 radio bursts and in-situ shocks, SEP-producing CMEs, and geoeffective CMEs (those that produce geomagnetic storms). I discuss the kinematic and solar-source properties of these populations and how they vary with the solar activity cycle. I also compare their properties with the general population of CMEs, so one can recognize when and where these events occur on the Sun
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