qs015.watari02 Posted: 26-Jan-92 Updated: 05-May-92, 05-Dec-92, 31-Jul-93, 08-Mar-94, 20-Nov-94, 22-Aug-95, 18-May-96 Events specified: N/A
Collaboration: S. Watari, K. T. Strong Motivation: The high speed solar winds from coronal holes are associated with recurrent geomagnetic storms. A coronal hole is a dark region in soft X-ray observations and a bright region in He 10830 observations. Ground-based He 10830 observations started just after the SKYLAB era. Soft X-ray and He 10830 data have a good correlation about high latitude coronal holes. On the contrary, the correlation between soft X-ray and He 10830 images is not good for low latitude coronal holes. Hence, correspondence between He 10830 coronal holes and soft X-ray coronal holes should be reexamined. The characteristics (latitude, area, latitudinal extension, and darkness, etc.) of soft X-ray coronal holes may influence the strength of the resulting geomagnetic disturbances.
To analyze long term variations of coronal holes and to compare coronal holes with recurrent magnetic storms associated with high speed solar winds, soft X-ray solar images need to be taken by the SOLAR-A SXT for a long term. The SOLAR-A SXT data permits a new study of the relationship between the characteristics (latitude, area, latitudinal extension, and darkness, etc.) of soft X-ray coronal holes and geomagnetic storms associated with high speed streams from coronal holes. These analyses make clear why coronal holes blow high speed solar winds.
Required Observations/Analysis Techniques:
Update 18-May-96
One paper was published about this subject.
Journal : J.Geomag.Geoelectr., 47, pp.1063-1071, 1995.
Title : Soft X-ray Coronal Holes Observed by the Yohkoh SXT
Authors : S. Watari (Communications Research Laboratory)
Y. Kozuka and M. Ohyama (Solar-Terrestrial Laboratory)
T. Watanabe (Ibaraki Univ.)
Abstract :
Many coronal holes have been observed by the Yohkoh Soft X-ray Telescope (SXT). These holes appear as dark regions in the soft X-ray images. It is now widely accepted that coronal holes are sources of high-speed solar wind. However, the size of coronal holes has not been clearly defined in previous works, and the relationship between soft X-ray coronal holes and high-speed solar wind is still not fully understood. In this paper we check the results from Skylab observations against the Yohkoh SXT data. We examined the boundaries of soft X-ray coronal holes imaged by the SXT. We then analyzed the characteristics of coronal holes associated with high-speed solar wind at 1 AU and compared the results with Skylab data. Faster solar wind seems to blow from larger and darker coronal holes. Coronal holes at relatively high latitudes (more than 30 degree), which extend from polar coronal holes, also produce high-speed streams, as coronal holes located around the solar equator. The manifestation of coronal and the sudden changes in their boundaries are frequently associated with large-scale coronal disturbances (LCDs) such as filament eruptions or flares. LCDs may be a possible source of non-recurrent interplanetary disturbances, and transit holes suggest the formation of open magnetic fields related to these events.
Now I am writing a paper about the coronal holes and solar wind during the declining phase of the solar cycle.
I am also analyzing about the coronal holes and solar wind during the solar minimum.
Update 22-Aug-95
1. The coupling between solar wind and the Earth's magnetosphere make it to difficult to predict an effect of coronal holes even if coronal holes emanaite high-speed stream.
2. The sector structure changed from 2-sector to 4 sector during September-November 1995. This was confirmed by solar coronal holes.
3. Cycle evolution of coronal holes
Small isolated coronal holes were observed near equator around solar maximum.
During the declining phase, large well-established coronal holes recurred for several rotations.
Around the solar minimum (now), cronal holes tend to shrink towards both poles.
We can expect to observe change of coronal holes during the ascending phase.
Update 20-Nov-94
1. The interplanetary disturbance with large longitudinal extent (about 50 degree) was observed associated with the transient hole on 11 November 91.
Update 8-Mar-94
It was found that the birth of coronal holes and sudden extension of coronal hole boundaries during the SKY lab. era. However, their effects for solar wind were not mentioned. I found that drastic change of corona producing holes (e.g. 91-11-12) are responsible for high speed solar wind and produce geomagnetic storms. This result may explain unknown sources of geomagnetic storms.
It is said that coronal holes located in low latitude (less than 30 degrees) are most effective for geomagnetic storms and latitudinal expansion of high speed stream is small. It is found that relatively high latitude (more than 30 degrees) coronal holes, which extend from polar region, have also important roles for high speed stream if there are not active regions around equator.
Update 31-Jul-93
Solar wind associated with coronal holes has been analized by using IMP-8 solar wind data. It takes long time to get IMP-8 data and to get many examples.
Update 05-Dec-92
The characteristics (darkness, area and latitudinal distribution) of coronal holes associated with high speed solar winds have been examined by IMP-8 solar wind data.
Update (5 May 1992): Abstract:
APPLICATION OF THE YOHKOH SOFT X-RAY TELESCOPE (SXT) TO SOLAR TERRESTRIAL PREDICTION Shin-ichi Watari, Nariaki Nitta, Saku Tsuneta, Maki Akioka, Jun Nishikawa, Fumihiko Tomita, .......................
Hiraiso Solar Terrestrial Research Center
Communication Research Laboratory
Ministry of Posts and Telecommunication
3601 Isozaki, Nakaminato, Ibaraki, 311-12 JAPAN
The YOHKOH was launched on 30 August 1991. Soft X-ray images
taken by the YOHKOH Soft X-ray Telescope (SXT) are daily
transmitted to the Hiraiso Solar Terrestrial Research Center, Japan
via network for solar forecasting purpose. The
SXT are producing many impressive images. We mainly
use the SXT data to identify coronal holes as a source
of recurrent geomagnetic storms.
Active regions which produce intense flares have
large, bright, and complex feature in soft X-rays, and can be
easily identified as flare producing regions
for forecasting purpose.
Suggested working group: 1, Solar Working Group Poster: Yes