[P-EM15] 太陽地球系結合過程の研究基盤形成

[PEM15-10] Feasibility study to estimate the ion velocity field in the F region from EISCAT_3D radar observations

*吹澤 瑞貴¹、小川 泰信¹、西村 耕司²、上野 玄太³、西山 尚典¹、橋本 大志¹、津田 卓雄⁴ (1.国立極地研究所、2.京都大学、3.統計数理研究所、4.電気通信大学)

キーワード：EISCAT_3D、電離圏、イオン速度、ベイズ推定

We conducted a feasibility study to estimate the horizontal ion velocity field in the ionospheric F region from ion velocities observed by the EISCAT_3D radar. We assumed a 27-beam configuration with a minimum elevation angle of 30 degrees. The ion velocity observation data from 200 km to 500 km altitude were projected to 200 km altitude, assuming that ions in this altitude range follow the E x B drift. Then, we reconstructed ion velocity vectors for ±250 km in the east-west direction and ±500 km in the north-south direction at 200 km altitude. The resolution in north-south and east-west directions was 25 km. The reconstruction was conducted by maximizing a posterior probability based on Bayes’ theorem. The constraints were set to minimize the L2 norms of the following four vectors in the horizontal plane: (1) the first and (2) the second derivative of three components of the ion velocity vector, (3) the divergence of the ion velocity perpendicular to the magnetic field lines, and (4) the ion velocity parallel to the magnetic field lines. We investigated which combination of the four constraints would reconstruct the shear flow field most correctly and found that the best combination was (2), (3), and (4). Weighting factors for each term were determined by the 5-fold cross-validation method.