43 research outputs found
Development of a coronal mass ejection arrival time forecasting system using interplanetary scintillation observations
Coronal mass ejections (CMEs) cause disturbances in the environment of the
Earth when they arrive at the Earth. However, the prediction of the arrival of
CMEs still remains a challenge. We have developed an interplanetary
scintillation (IPS) estimation system based on a global magnetohydrodynamic
(MHD) simulation of the inner heliosphere to predict the arrival time of CMEs.
In this system, the initial speed of a CME is roughly derived from white light
coronagraph observations. Then, the propagation of the CME is calculated by a
global MHD simulation. The IPS response is estimated by the three-dimensional
density distribution of the inner heliosphere derived from the MHD simulation.
The simulated IPS response is compared with the actual IPS observations made by
the Institute for Space-Earth Environmental Research, Nagoya University, and
shows good agreement with that observed. We demonstrated how the simulation
system works using a halo CME event generated by a X9.3 flare observed on
September 5, 2017. We find that the CME simulation that best estimates the IPS
observation can more accurately predict the time of arrival of the CME at the
Earth. These results suggest that the accuracy of the CME arrival time can be
improved if our current MHD simulations include IPS data.Comment: 39 pages, 6 figures, accepted for publication in Earth, Planets and
Spac
Is the Polar Region Different from the Quiet Region of the Sun?
Observations of the polar region of the Sun are critically important for
understanding the solar dynamo and the acceleration of solar wind. We carried
out precise magnetic observations on both the North polar region and the quiet
Sun at the East limb with the Spectro-Polarimeter of the Solar Optical
Telescope aboard Hinode to characterize the polar region with respect to the
quiet Sun. The average area and the total magnetic flux of the kG magnetic
concentrations in the polar region appear to be larger than those of the quiet
Sun. The magnetic field vectors classified as vertical in the quiet Sun have
symmetric histograms around zero in the strengths, showing balanced positive
and negative flux, while the histogram in the North polar region is clearly
asymmetric, showing a predominance of the negative polarity. The total magnetic
flux of the polar region is larger than that of the quiet Sun. In contrast, the
histogram of the horizontal magnetic fields is exactly the same between the
polar region and the quiet Sun. This is consistent with the idea that a local
dynamo process is responsible for the horizontal magnetic fields. A
high-resolution potential field extrapolation shows that the majority of
magnetic field lines from the kG-patches in the polar region are open with a
fanning-out structure very low in the atmosphere, while in the quiet Sun,
almost all the field lines are closed.Comment: Accepted for publication in AP