Simultaneous observation of auroral substorm onset in Polar satellite global images and ground-based all-sky images

Substorm onset has originally been defined as a longitudinally extended sudden auroral brightening (Akasofu initial brightening: AIB) followed a few minutes later by an auroral poleward expansion in ground-based all-sky images (ASIs). In contrast, such clearly marked two-stage development has not been evident in satellite-based global images (GIs). Instead, substorm onsets have been identified as localized sudden brightenings that expand immediately poleward. To resolve these differences, optical substorm onset signatures in GIs and ASIs are compared in this study for a substorm that occurred on December 7, 1999. For this substorm, the Polar satellite ultraviolet global imager was operated with a fixed filter (170 nm) mode, enabling a higher time resolution (37 s) than usual to resolve the possible two-stage development. These data were compared with 20-s-resolution green-line (557.7 nm) ASIs at Muonio in Finland. The ASIs revealed the AIB at 2124:50 UT and the subsequent poleward expansion at 2127:50 UT, whereas the GIs revealed only an onset brightening that started at 2127:49 UT. Thus, the onset in the GIs was delayed relative to the AIB and in fact agreed with the poleward expansion in the ASIs. The fact that the AIB was not evident in the GIs may be attributed to the limited spatial resolution of GIs for thin auroral arc brightenings. The implications of these results for the definition of substorm onset are discussed herein

Current circuit connecting the polar and equatorial region deduced by a global ionospheric potential solver (GEMSIS-POT)

第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月27日（火） 国立極地研究所 2階大会議

Acceleration of the lower-thermospheric wind measured with a Fabry-Perot interferometer around substorm onsets at Tromsø, Norway

第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月26日（月）、27日（火） 国立極地研究所 2階ラウン

Effect of R2-FAC development on the ionospheric electric field pattern deduced by a global ionospheric potential solver

Toward the understanding of the effect of the magnetosphere originated disturbances on the global ionospheric electric field and current system, we developed a two-dimensional ionospheric potential solver based on the so-called "thin shell model." The important extension from the previous studies is that our model covers the pole-to-pole ionosphere without placing any boundary at the equator. By using this solver, we investigate how the ionospheric electric field changes from undershielding condition to overshielding condition as the field aligned current (FAC) distribution changes. Calculations are performed by changing IR2/IR1 (the ratio of current intensities of region 2 (R2) and region 1 (R1) FACs) and by moving R2-FAC relative to the fixed R1-FAC. The results are summarized as follows: (1) The turning point, at which the ionosphere turns from undershielding to overshielding is IR2/IR1 = 0.7 ∼ 0.8. (2) With increasing the local time deference between the R1 and R2-FAC peaks, the efficiency of the shielding by R2-FAC increases but the associated potential skews to the nightside. (3) At the same time the shielding effect is weakened around noon, where the R1-potential intrudes to the low latitude region instead, but the R2-potential remains dominant at other local times. The result suggests that the overshielding or undershielding should be identified by observations not only in a limited local time sector but also in the overall ionosphere as much as possible. In order to accurately describe the ionospheric condition, we suggest new classification terms, "complete-overshielding" and "incomplete-overshielding.

Observed correlation between pulsating aurora and chorus waves at Syowa Station in Antarctica: A case study

A high correlation between a pulsating auroral patch and grouped chorus waves was observed on 17 April 2006 at Syowa Station in Antarctica. The spatial distribution of aurora–chorus correlation coefficients is evaluated in order to determine the source region. A pulsating patch at the highest-correlation pixel shows a one-to-one correspondence with the intensity variation of the grouped chorus waves, consisting of successive rising-tone elements with a duration and spacing of 2–3 s and 20–30 s, respectively. The generation region of the chorus waves is estimated from the latitude and longitude dependence of the equatorial electron gyrofrequencies using the IGRF geomagnetic field model. The extent of the estimated latitude and longitude is consistent with the spatial distribution of the high-correlation aurora–chorus region. The time difference between the chorus waves and the scattered electrons is also evaluated to discuss the validity of the source region. It shows that electrons reached the ionosphere sooner than the associated chorus waves by ∼1 s, consistent with the theoretical value for conjugate pulsating aurora generated at the equator. These results support the hypothesis that pulsating aurora is caused by pitch angle scattering of high-energy electrons by whistler mode chorus waves, via a cyclotron resonance at the equator. These results are the first ground-based observations of high correlations between a spatially extended aurora and chorus waves

Visualization tool for three-dimensional plasma velocity distributions (ISEE_3D) as a plug-in for SPEDAS

Abstract This paper introduces ISEE_3D, an interactive visualization tool for three-dimensional plasma velocity distribution functions, developed by the Institute for Space-Earth Environmental Research, Nagoya University, Japan. The tool provides a variety of methods to visualize the distribution function of space plasma: scatter, volume, and isosurface modes. The tool also has a wide range of functions, such as displaying magnetic field vectors and two-dimensional slices of distributions to facilitate extensive analysis. The coordinate transformation to the magnetic field coordinates is also implemented in the tool. The source codes of the tool are written as scripts of a widely used data analysis software language, Interactive Data Language, which has been widespread in the field of space physics and solar physics. The current version of the tool can be used for data files of the plasma distribution function from the Geotail satellite mission, which are publicly accessible through the Data Archives and Transmission System of the Institute of Space and Astronautical Science (ISAS)/Japan Aerospace Exploration Agency (JAXA). The tool is also available in the Space Physics Environment Data Analysis Software to visualize plasma data from the Magnetospheric Multiscale and the Time History of Events and Macroscale Interactions during Substorms missions. The tool is planned to be applied to data from other missions, such as Arase (ERG) and Van Allen Probes after replacing or adding data loading plug-ins. This visualization tool helps scientists understand the dynamics of space plasma better, particularly in the regions where the magnetohydrodynamic approximation is not valid, for example, the Earth’s inner magnetosphere, magnetopause, bow shock, and plasma sheet

Theory, modeling, and integrated studies in the Arase (ERG) project

Abstract Understanding of underlying mechanisms of drastic variations of the near-Earth space (geospace) is one of the current focuses of the magnetospheric physics. The science target of the geospace research project Exploration of energization and Radiation in Geospace (ERG) is to understand the geospace variations with a focus on the relativistic electron acceleration and loss processes. In order to achieve the goal, the ERG project consists of the three parts: the Arase (ERG) satellite, ground-based observations, and theory/modeling/integrated studies. The role of theory/modeling/integrated studies part is to promote relevant theoretical and simulation studies as well as integrated data analysis to combine different kinds of observations and modeling. Here we provide technical reports on simulation and empirical models related to the ERG project together with their roles in the integrated studies of dynamic geospace variations. The simulation and empirical models covered include the radial diffusion model of the radiation belt electrons, GEMSIS-RB and RBW models, CIMI model with global MHD simulation REPPU, GEMSIS-RC model, plasmasphere thermosphere model, self-consistent wave–particle interaction simulations (electron hybrid code and ion hybrid code), the ionospheric electric potential (GEMSIS-POT) model, and SuperDARN electric field models with data assimilation. ERG (Arase) science center tools to support integrated studies with various kinds of data are also briefly introduced