Main Objective:
To coordinate observations with the Venus-orbiting spacecraft, Akatsuki, as it transits behind the Sun.
Scientific Justification:
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 structures of the electron density as well as magnetic field by using Faraday rotation.
The solar conjunction of Akatsuki (Planet-C) in June 2016 provides an opportunity to perform such observation in coordination with Hinode. Akatsuki is Venus Climate Orbiter of JAXA. Although the injection to the Venus orbit in December 2010 was not successful, they succeeded in inserting Akatsuki in to the orbit on 7-Dec-2015. There will be a conjunction of Akatsuki and the Sun on Jun-2016. Akatsuki will transit behind the Sun near the solar equator and we have an opportunity to perform coordinated observation soon after Akatsuki will appear from the E-limb of the Sun.
The Akatsuki team plans to perform radio sounding observation of solar wind 11 times during May 30 - June 15, 2016. The observing time are from 02:30UT-07:00UT in each 11 days. It will provide the spectra of electron density fluctuation in the range of 0.0001-10Hz, corresponding to the spatial scale of about 30~300,000km (assuming solar wind speed of 300 km/s). In addition to that, they can measure Faraday rotation by using left and right handed polarized radio waves.
We propose coordinated observation of Hinode on June 8 when the probe passes above the E-limb near the solar equator. XRT and EIS observation, along with EUV and coronagraph images from SDO and STEREO can provide the information of steady structure in the corona/solar wind as well as of the occurrence of X-ray/EUV jets and CMEs. By comparison with these imaging observation we will be able to investigate the electron density fluctuation and magnetic field above E-limb, and, if they occur, in jets and CMEs. Moreover, spectroscopic observation by EIS may allow us to study the correlation 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 above the EIS field of view even in the observing duration. 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 above E-limb. |
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