What coronal parameters determine solar wind speed? M. Kojima, M. Tokumaru, K. Fujiki, H. Itoh and...
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Transcript of What coronal parameters determine solar wind speed? M. Kojima, M. Tokumaru, K. Fujiki, H. Itoh and...
What coronal parameters determine solar wind speed?
M. Kojima, M. Tokumaru, K. Fujiki, H. Itoh and T. MurakamiSolar-Terrestrial Environment Laboratory, Nagoya University
K. HakamadaDepartment of Natural Science and Mathematics, Chubu University
In order to model the solar wind acceleration it is important to find a universal relation between the global properties of the solar wind and corona holes. However most coronal holes are at high latitudes where spacecraft cannot access, with the exception of the Ulysses.
In this study we identify the relation between the wind velocity and
the coronal magnetic condition using the IPS tomographic measurements, which can derive an unbiased solar wind velocity map over all latitudinal ranges,.
Interplanetary scintillation measures an integration of the solar wind speed V and density turbulent level △Ne distributed along a line of sight.
Earth
☆Radio source
Computer Assisted Tomography analysis
This technique can retrieve not only unbiased solar wind parameters but also provides high spatial resolution.
The IPS los integrations provide us with perspective views of 3D SW structures at various different view angles using both the solar rotation and solar wind outward motion.
• Nolte et al. (1976) the velocity depends on the coronal hole sc
ale size.
• Wang and Sheeley (1990) the flux expansion rate is inversely proport
ional to the solar wind speed.
• Fisk et al. (1999) reconnection of emerging magnetic fields i
n supergranules supplies Poynting flux to accelerate the solar wind.
We investigate the relation between the solar wind velocityand the coronal magnetic condition for various kinds of coronal holes, which have different properties of magnetic field intensity B and flux expansion rate f.
We make correlation analysis between the velocity V and a) the inverse of an expansion rate 1/f, b) photospheric magnetic field intensity B, and c) the ratio between these two parameters B/f.
V-map on the source surface from IPS tomography
Coronal holes on the photosphereHeI, open B region
Data from the National Solar Observatory (NSO) at Kitt Peak
Potential magnetic field lines
Although the polar coronal hole extended to lower latitudes than 60 degrees, we examine the coronal hole area at latitudes higher than 60 degrees because the boundary region has a complex structure. If there is a extension from a polar coronal hole toward the equator beyond a latitude of 40 degrees, it is treated as an independent mid-latitude coronal hole.
1. CR1830 : Jun. 11.4556, 1990. 2. CR1844 : Jun. 28.2611, 1991. 3. CR1855 : Apr. 23.4361, 1992 4. CR1870 : Jun. 6.4778, 1993. 5. CR1887 : Sep. 12.9590, 1994. 6. CR1898 : Jul. 10.0910, 1995. 7. CR1901 : Sep. 29.8104, 1995. 8. CR1909 : May 5.2840, 1996. 9. CR1925 : Jul. 15.5059, 1997. 10. CR1939 : Aug. 1.3214, 1998.11. CR1950 : May 28.5213, 1999. 12. CR1964 : Jun. 13.3296, 2000.13. CR1976 : May 6.7222, 2001.
Analysis 3Data period: 1990-2001
Mesh size:
11
2
,
,
Flux expansion rate r photosphere source surface
r source surface photosphere
B R
B R
Physical meaning of the parameter B/f
• Energy supply ー B
• Efficiency ー Flux expansion f
slow
fast slower slower
CH size
What is the role of the coronal hole size in determining the solar wind speed ?