Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh13c..02g&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH13C-02
Astronomy and Astrophysics
Astrophysics
[7534] Solar Physics, Astrophysics, And Astronomy / Radio Emissions, [7536] Solar Physics, Astrophysics, And Astronomy / Solar Activity Cycle
Scientific paper
The 17 GHz microwave brightness temperature in coronal holes is typically enhanced by 500 to 2000 K with respect to the quiet Sun. This is considered to be a property of the upper chromosphere, where the plasma temperature is ~10000 K. We constructed a microwave butterfly diagram using the synoptic images obtained by the Nobeyama Radioheliograph and compared it with the magnetic butterfly diagram. We found a good correlation between the microwave brightness enhancement and the polar field strength. We also performed a rotation-by-rotation comparison between the two data sets to obtain the correlation between the magnetic field strength and the microwave brightness temperature. The microwave butterfly diagram covers part of cycle 22, whole of cycle 23, and part of cycle 24, thus enabling comparison between the cycle 23/24 and cycle 22/23 minima. The microwave brightness during the cycle 23/24 minimum was found to be lower than that during the cycle 22/23 minimum by ~250 K. The reduced brightness temperature is consistent with the reduced polar field strength during the cycle 23/24 minimum seen e.g., in the SOHO/MDI magnetic butterfly diagram. We suggest that the microwave brightness at the solar poles is a good indicator of the speed of the solar wind sampled by Ulysses at high latitudes.
Gopalswamy Nat
Makela P. A.
Shibasaki Kazuo
Yashiro Seiji
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