Empirical models of Total Electron Content based on functional fitting over Taiwan during geomagnetic quiet condition

Empirical models of Total Electron Content (TEC) based on functional fitting over Taiwan (120° E, 24° N) have been constructed using data of the Global Positioning System (GPS) from 1998 to 2007 during geomagnetically quiet condition (<I>D<sub>st</sub></I>>−30 nT). The models provide TEC as functions of local time (LT), day of year (DOY) and the solar activity (F), which are represented by 1–162 days mean of F10.7 and EUV. Other models based on median values have been also constructed and compared with the models based on the functional fitting. Under same values of F parameter, the models based on the functional fitting show better accuracy than those based on the median values in all cases. The functional fitting model using daily EUV is the most accurate with 9.2 TECu of root mean square error (RMS) than the 15-days running median with 10.4 TECu RMS and the model of International Reference Ionosphere 2007 (IRI2007) with 14.7 TECu RMS. IRI2007 overestimates TEC when the solar activity is low, and underestimates TEC when the solar activity is high. Though average of 81 days centered running mean of F10.7 and daily F10.7 is often used as indicator of EUV, our result suggests that average of F10.7 mean from 1 to 54 day prior and current day is better than the average of 81 days centered running mean for reproduction of TEC. This paper is for the first time comparing the median based model with the functional fitting model. Results indicate the functional fitting model yielding a better performance than the median based one. Meanwhile we find that the EUV radiation is essential to derive an optimal TEC

Daytime longitudinal structures of electron density and temperature in the topside ionosphere observed by the Hinotori and DEMETER satellites

International audienceDaytime longitudinal structures of the electron density (N e) and temperature (T e) in the topside ionosphere observed by Hinotori and DEMETER are examined under various conditions of solar flux, local time, and seasons. Results from both satellites show a similar longitudinal N e structure in the morning from July to October, although the value of N e observed by Hinotori is higher than that of DEMETER owing to higher solar flux. This result implies that the longitudinal structure of N e may appear in any solar cycle. Further, a negative correlation between N e and T e in the longitudinal structures appears in the morning when N e is low, while a positive correlation appears around the magnetic equator when N e is sufficiently enhanced during noontime in the high solar flux. A spectrum analysis performed on the DEMETER data reveals that wave numbers 1-2 for N e and T e are dominant and nondominant. The observed wave numbers 3-4 for N e are dominant during November-May and June-October, while they are dominant for T e during October-June and July-September. Both N e and T e show the largest power of wave number 3 in December and wave number 4 in September. Further, observed annual variations of wave numbers 3-4 for N e and T e also differ from wave numbers 3-4 generated by waves in the lower thermosphere. It can be interpreted as discrepancies between the longitudinal distributions of N e and T e caused by difference in the condition of zonal winds driving E region dynamo and meridional winds modulating the ionospheric plasma structures

Modeling of 3D trajectory of Hayabusa2 re-entry based on acoustic observations

On 2020 December 5 at 17:28 UTC, Japan Aerospace Exploration Agency's Hayabusa2 sample return capsule (SRC) re-entered Earth's atmosphere. The capsule passed through the atmosphere at supersonic speeds, emitting sound and light. The inaudible sound was recorded by infrasound sensors installed by Kochi University of Technology and Curtin University. Based on analysis of the recorded infrasound, the trajectory of the SRC in two cases, one with constant-velocity linear motion and the other with silent flight, could be estimated with an accuracy of 0° 5 in elevation and 1° in direction. A comparison with optical observations suggests a state of flight in which no light is emitted but sound is emitted. In this paper, we describe the method and results of the trajectory estimation