[P-EM04_28PO1] New Perspectives on Earth's Inner Magnetosphere

[PEM04-P01] Retrieval of plasmaspheric He+ density field-aligned distributions from EUV imaging data

*Kunihiro KEIKA¹, Pontus C. BRANDT², Anthony TOIGO², Demajistre ROBERT² (1.Solar-Terrestrial Environment Laboratory, Nagoya University, 2.The Johns Hopkins University Applied Physics Laboratory)

Keywords:Plasmasphere, Helium ion density, Inner magnetosphere, Plasma refilling, Forward modeling

We retrieve the spatial distributions of He+ density (n_He+) in the Earth’s plasmasphere from EUV imaging data, by using a forward modeling technique. We use a parametric model for the density distribution to simulate line-of-sight integrated He+ densities (i.e., EUV images), and then find parameters that give the best fit to real EUV images. The parametric model used in this study is described as a function of L and magnetic latitude (λ): n_He+ = n₀ (L₀/L)^alpha_L × (r₀/L₀ cosλ²)^alpha_f, where n₀ and L₀ are He⁺ density and L value at the inner boundary of this model (i.e., the topside ionosphere), and α_L and α_f are parameters that represent L and field-aligned dependence of He⁺ density, respectively. In this paper, we evaluated how well our forward model can retrieve the He⁺ density spatial distribution, by performing the following analysis. (1) EUV emission intensities were simulated through the EUV camera response function, given a vantage point of the IMAGE satellite. (2) EUV images were simulated for a large number of (α_L, α_f) pairs: α_L was chosen from 4.0 to 6.0 with 0.1 increment, and α_f was from 0.0 to 2.0 with 0.1 increment. (3) The EUV image corresponding to the (α_L, α_f)=(5.0, 1.0) pair was chosen as our synthetic EUV image. After noise was added to the synthetic image, the forward modeling was applied to all simulated images made in (2). The reduced χ² (χ_r²) was used to determine how well simulated image data fit to the synthetic image. The results of this analysis confirm that the He⁺ density distributions can be retrieved with good certainty within |40 deg.| MLAT. However, beyond this magnetic latitude it is difficult to determine the L dependence or field-aligned dependence of plasmaspheric He⁺ density. Next, in order to decouple the synthetic data from the parametric formula, we will use density distributions provided by physics-based ionosphere/plasmasphere models as our synthetic data. We will also apply our forward simulation model to real EUV image data from the EUV imager onboard the IMAGE spacecraft.