[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P21] Estimating the extent of chorus wave source region: LAMP rocket and EMCCD all-sky camera observations

*Masaya Hirano¹, Keisuke Hosokawa¹, Yoshizumi Miyoshi², Kazushi Asamura³, Marc Lessard⁴, Matthew Mcharg⁵, Allison Jaynes⁶, Mykhaylo Shumko⁷, Vincent Ledvina⁸, Don Hampton⁸, Takeshi Sakanoi⁹, Takefumi Mitani³, Taku Namekawa¹⁰, Masahito Nose¹¹, Yasunobu Ogawa¹², Alexa Jean Halford¹³ (1.Graduate School of Informatics and Engineering, University of Electro-Communications, 2.Institute for Space-Earth Environement Research, Nagoya University, 3.Japan Aerospace Exploration Agency, 4.University of New Hampshire, 5.The United States Air Force Academy, 6.University of Iowa, 7.Johns Hopkins University Applied Physics Laboratory, 8.University of Alaska Fairbanks, 9.Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University, 10.The National Institute of Information and Communications Technology, 11.School of Data Science, Nagoya City University, 12.National Institute of Polar Research, 13.NASA Goddard Space Flight Center)

Keywords:rocket measurement, pulsating aurora

Aurorae observed in the nightside auroral zone are primarily classified into two broad categories: discrete aurorae, which have clear and distinct spatial structures, and diffuse aurorae characterized by vague and indistinct patchy shapes. It is known that most of diffuse aurorae exhibit quasi-periodic luminosity modulations on timescales of a few to a few tens of seconds, and these are referred to as pulsating aurora (PsA). The energy of the precipitating electrons causing PsA tends to be higher than that of those causing typical discrete aurorae, and we refer to these precipitating electrons here as “PsA electrons”. Such sub-relativistic electron precipitation can be explained by whistler-mode chorus waves, which are generated near the magnetospheric equatorial plane and propagate along magnetic field lines, scattering electrons through wave-particle interactions at high latitudes. It has been shown that the chorus wave source region can extend over spatial scales of hundreds to thousands of kilometers, but its exact shape and size remain unclear.
Regarding the relationship between PsA electrons and auroral emissions, simultaneous observations by the Reimei satellite, using an electron detector and a multi-spectral auroral camera, suggest that a flux modulation, whose of electrons energy is above a few keV, is the primary cause of the luminosity modulation of PsA. However, the duration of those earlier observations was as short as a minute and focused on a small area. As a result, the detailed correlation between the luminosity modulation of PsA and the energy spectrum of PsA electrons during relatively longer intervals has not yet been clarified. In addition, the spatial extent of region showing a strong correlation between PsA electrons and auroral emissions has not yet been visualized through actual observations.
To address these issues, this study conducted a correlation analysis between PsA electrons and auroral brightness over a period of several minutes and an area spanning more than 500 km. We used in-situ low-energy electron data obtained from the EPLAS onboard the LAMP sounding rocket and PsA emission intensity data obtained from an EMCCD all-sky camera in Alaska during the launch window. The launch window of the LAMP sounding rocket window was from 11:29 to 11:38 UT on March 5, 2022, and the EPLAS instrument covered an energy range from 5 eV to 15 keV. Meanwhile, the EMCCD all-sky camera in Venetie, Alaska, observed the region containing the magnetic footprint of the rocket during the launch window with a temporal resolution of 100 Hz. Visualization of the correlation coefficients between the two datasets showed that, for most of the observation period, higher correlation coefficients were confined to areas near PsA patches. We refer to these areas as “high-correlation regions.” It was also revealed that the correlation between PsA luminosity modulations and low-energy electron flux is not always high and can be unclear at certain times. Furthermore, the spatial extent of the high-correlation regions changed over time. By projecting these high-correlation regions onto the equatorial plane of the magnetosphere, we estimated the radial extent of the chorus wave source region driving PsA to be on the order of ~1,500–3,500 km and the azimuthal extent to be ~500–3,300 km. Comparison with estimates from previous studies suggests that the shape of the high-correlation regions in the ionosphere manifests the distribution of the chorus wave source region in the magnetosphere. This indicates that through PsA observations and the EPLAS particle measurements, an approach not achievable by satellites alone, we can visualize the two-dimensional spatial distribution of the chorus wave source region. In the presentation, we will demonstrate the spatial distribution of the correlation coefficients, where it changes with the motion of the rocket. We will then discuss the relationship between the several-minute long PsA luminosity variations and the temporal changes in the PsA electron energy spectrum during the launch window. Based on these results, we will discuss the factors that control the degree of correlation between PsA electrons and auroral emissions.