Information on the small-scale structures of plasma near the sun is important for understanding the mechanism of plasma heating and accelerating the solar wind. Phase and amplitude scintillation measurement of spacecraft radio signals during solar conjunctions can be used to obtain information of the small-scale strucutures of the electron density.
The solar conjunction of AKATSUKI in June 2011 provides an opportunity to perform such observation in coordination with Hinode. AKATSUKI (Planet-C) is Venus Climate Orbiter of JAXA. The injection to the the Venus orbit in December 2010 was not successuful and the space craft is now in solar orbit at around 0.7AU. There will be four close conjunction of Akatsuki and the Sun by the end 2015, and the one in June-July 2011 is the closest. The minimum sun-earth-probe (SEP) angle is 0.405 degree (=1458 arcsec ~ 1.54 R_sun) when the prove passes just above the north pole as seen from th Earth.
The Akatsuki team plans to perform radio sounding observation of solar wind on June 6 - July 8, 2011, when the SEP angle changes in the range of 0.4 ~ 5.4. It will provide the spectra of electron density fluctuation in the range of 0.0001-10Hz, corresponding to the spatial scale of about 30~300000km (assuming solar wind speed of 300km/s).
We propose coordinated observation of Hinode during June 23-27 when the prove passes above the north pole. XRT and EIS observation, along with EUV and coronagraph images from SDO, STEREO and SOHO, can provide the information of steady strucutre in the corona/solar wind as well as of the occurrence of polar jets and CMEs. By comparison with these imaging observation we will be able to investigate the difference of electron density fluctuation in and outside the coronal hole and plumes, and, if they occur, in jets and CMEs. Moreover, spectroscopic observation by EIS may allow us to study the correllation between the density fluctuation and other plasma parameters such as intensity in different lines (i.e., DEM), electron density, and line width (if there are enough counts). We note that the Akatsuki's position will be slightly (~20") above the EIS field of view even in the closed conjunction on 25th. However, EIS data is still useful because it provides unique information of plasma parameters between the solar surface and the height at with Akatsuki measurement is done. The vector magnetogram from SOT/SP can be used to model the magnetic fields in the coronal hole and plumes. We also plan to obtain some H-alpha images in the north pole region at the Hida observatory to monitor
the transient events. |
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