Success in visualizing the propagation path of electromagnetic waves
from space to ground

Date:
December 9, 2021
Source:
Kanazawa University
Summary:
Using data on electromagnetic (EM) waves and plasma particles
measured simultaneously via multiple satellites, an international
collaborative research group has discovered the existence of
invisible 'propagation path' of EM waves and elucidated the
mechanism by which EM waves propagate to the ground.



FULL STORY ==========================================================================
It is known that various kinds of EM waves occur naturally in geospace and cause variations in the plasma environment that surrounds the Earth via a physical process known as wave-particle interaction. In particular, when geospace storms occur due to disturbances of sun and solar wind, EM waves become more active, and variations of geospace environment sometimes,
may cause damage to spacecrafts, expose astronauts to radiation, and
cause terrestrial power grid failures. To understand variation in the
plasma environment caused by EM waves in space, in-situ measurement has
been performed in space using spacecrafts, such as the Japanese geospace satellite "Arase."

==========================================================================
As EM waves in space propagate far away from their origin, to correctly understand the effects of EM waves, it is crucial to understand where in
space the EM waves are generated and how they are propagated. However,
it has been difficult to unravel the origin of EM waves and the
mysteries of how EM waves spread spatially using only single-point
observation. "Electromagnetic ion cyclotron waves (EMIC waves)," which are
the focus of this study, are an important class of EM wave in geospace
that control variations in the geospace plasma environment. The source
region of ion mode waves has a finite spatial extent, and generated EMIC
waves are considered to propagate north to south along the geomagnetic
field lines. The specific spatial size of the EMIC wave source region
and the 3D aspect of how the propagation path is formed from space to
ground are yet to be elucidated.

The international collaborative research group, linking observations
from space using the Japanese "Arase" and US "Van Allen Probes,"
with observations from the Japanese "PWING Project" and Canadian
"CARISMA Magnetometer Array," has successfully performed simultaneous observations of EMIC waves from different locations. By comparing the observation data obtained from each location, it was clarified that
only waves that exist in a straw-shaped "propagation path" are able to
travel from space to ground. The Van Allen Probes near the geomagnetic
equator and the PWING and CARISMA magnetometer on the ground observed
the same EMIC waves, indicating the existence of a propagation path for
the EMIC waves between space and ground. Arase observed the EMIC waves
in the mid-latitudes and contributed to determining the spatial size of
the propagation path. Arase achieved high-quality EM wave measurements
with the Plasma Wave Experiment (PWE) and Magnetic Field Experiment (MGF) instruments aboard the spacecraft, and the value of the Arase observation
was significantly enhanced through the international collaboration.

The precise measurements of plasma particles obtained from "Arase"
and the "Van Allen Probes" have also shown that EMIC waves energize
thermal ions as they propagate along the "propagation path;" thus, they
cause changes to the ambient plasma environment. It is also known that
EMIC waves produce proton auroras, and the results of this study can
be interpreted as clarifying the path taken by the energy that is the
source of the proton aurora when propagating from space to the ground.

This study has clarified the "propagation path" for guiding EMIC waves
from space to ground. By understanding where EMIC waves occur in space
and how they propagate, it is possible to clarify the mechanism by which
the space plasma environment change occurs simultaneously in the vast
geospace. The findings of this study will contribute to improve the
accuracy of space weather forecast.

Further, members of the international collaborative research group are
in charge of developing wave instruments aboard the BepiColombo/Mio for
Mercury orbiter and the JUICE spacecraft (scheduled for launch in 2022)
for Jovian system. Based on these results, we aim to elucidate the
mechanism of EM wave generation and propagation on planets other than
Earth, as well as move forward, toward a comprehensive understanding of
space environment and contribute to space weather forecasting.

========================================================================== Story Source: Materials provided by Kanazawa_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. S. Matsuda, Y. Miyoshi, Y. Kasahara, L. Blum, C. Colpitts,
K. Asamura, Y.

Kasaba, A. Matsuoka, F. Tsuchiya, A. Kumamoto, M. Teramoto,
S. Nakamura, M. Kitahara, I. Shinohara, G. Reeves, H. Spence,
K. Shiokawa, T.

Nagatsuma, S. Oyama, I. R. Mann. Multipoint Measurement of
Fine‐Structured EMIC Waves by Arase, Van Allen Probe A,
and Ground Stations. Geophysical Research Letters, 2021; 48 (23)
DOI: 10.1029/ 2021GL096488 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211209095628.htm

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