2023 Fiscal Year Research-status Report
Investigating the conditions of ELF/VLF wave propagation from space to the ground.
| Project/Area Number |
22K14083
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| Research Institution | Nagoya University |
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Principal Investigator |
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| Project Period (FY) |
2022-04-01 – 2025-03-31
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| Keywords | VLF waves / conjugated events / bursty-patches / VLF propagation / multi-point observations |
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| Outline of Annual Research Achievements |
We analyzed data from the VLF receiver at OUJ (installed in Oct. 2022) and compared to KAN, focusing on statistical results and conjugated events. VLF waves were more easily detected at KAN (occ. rate of 58%) than at OUJ (38%). Waves at L=5.5 are 20% more likely to reach the ground than at L=4.5. Occurrence rate of conjugated events was quite similar (OUJ 10% vs KAN 12%). 20-26% of waves at OUJ and KAN come from the same source region in the magnetosphere. Ionospheric exit point was on the East-West axis. Latitudinal extent of conjugated events was 1 L-shell, meaning latitudinal propagation can reflect source region size. Occurrence rate of bursty-patches were x10 lower at OUJ, even if their source region should be at those L-shells. We will continue to investigate this point further.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
We have analyzed OUJ data for short-term statistics and multiple conjugated events between OUJ and KAN. We have also compared with other PWING data to find general results for overall VLF wave properties. A collaboration with F. Nemec (Charles U., Czechia) used OUJ and other PWING data to asses VLF wave intensities on the ground and in space (paper under revision). The polarization code used to pinpoint ionospheric exit angles has been implemented and validated. We have also started developing a sferics filter to help with VLF bursty-patches characteristics. A paper with some of our results is currently being written. The current difficulty is processing large amounts of data, for statistics and case selection, as it has to be done by eye.
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| Strategy for Future Research Activity |
Currently, the most interesting question is that of bursty-patch propagation to the ground. To investigate this properly we will set up a PHLR and sferics filter to all PWING stations, including OUJ. We hope to have a working code by Fall 2024 and validation by the end of the year (publication expected). This will increase our chances at detecting conjugated events between KAN, OUJ, and Arase. These results will be presented at the VERSIM workshop. For selected events, we will do ray tracing analysis and triangulation of the ionospheric exit point. We hope these results will result in another paper.
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| Causes of Carryover |
Increase of travel expenses plus the very low yen value have made travel out of Japan quite expensive. Moving the leftover money to the next year would allow me to participate in two major conferences next year: (1) VERSIM workshop where I have been given an invited talk. The participants of this workshop are experts in the field of VLF waves and their properties, allowing me to get excellent feedback on my data and results. (2) AGU 2024, the biggest geophysical conference in the USA, allowing me to share my results and introduce OUJ data to a wide range of participants.
Should AGU prove too expensive, a 2-week trip to UCLA to discuss ray tracing procedures and precipitation data will be done instead. Leftover money will be used to cover publication fees or other data/receiver-related expenses.
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