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tokens: s) the high ionization region. Figure 5. Same as Figure 4 , but for and . 3.4. Parameter Study In Figure 6 , we show the dependence of the Balmer- α line energy flux on (a) the preshock velocity v 0 and (b) the total number density of hydrogen nuclei n H,0 , respectively. In the Appendix , we also show the dependences regarding other lines such as Balmer- β , Paschen- α , and Paschen- β . 5 5 Those profiles would be similar even at infinity except for Ly α , because hydrogen is in the form of H 2 and excited H rarely exists above the shock front. As for Ly α , absorption in the interstellar medium modifies the profiles. As seen in panel (a), for v 0 30 km s −1 , the Balmer- α line flux is quite low. This is because almost all the energy of shock heating is consumed for dissociation of hydrogen molecules. For v 0 ≥ 30 km s −1 , the energy flux is found to be nearly proportional to in panel (a) and to n H,0 in panel (b). Intuitively, however, the energy flux is proportional to , because the kinetic energy that the flowing gas has before shock is . This holds true for Ly α , but for other lines, we have to take into account the effect of absorption of radiation propagated from downstream, as described below. Figure 6. Energy flux of the Balmer- α line (H α ) radiation at the shock front (i.e., the surface of the circumplanetary disk) against the preshock velocity v 0 (panels (a) and (c)) and the total number density of atomic hydrogen (including all the hydrogen nuclei) n H,0 (panels (b) and (d)). The upper two panels are the same as the lower two, respectively, but the latter shows the energy flux relative to the total incoming energy flux at the shock front (i.e., where is the total number of particles and μ is the mean molecular weight). In the left two panels, each color shows each choice of 10 15 m −3 (black), 10 16 m −3 (red), 10 17 m −3 (blue), 10 18 m −3 (orange), 10 19 m −3 (purple), and 10 20 m −3 (brown). Also in the right two panels, each color shows each choice of v 0 ; (black), (red), (blue), (orange), (purple), (brown), and (green). Figure 7 shows the profiles of the spectral energy density of the Ly α and Balmer- α lines at the shock front. In the upper row of panels, those for different choices of n H,0 are presented for v 0 = 40 km s −1 , while in the lower panels, those for different choices of v 0 are presented for . The Gauss profile caused by the Doppler broadening is seen near the line center, while the Lorenz profile mainly caused by the natural broadening is seen far from the line center. The borders between them are at ∼121.48 nm and ∼121.53 nm for Ly α (in panel (a)) and ∼656.00 nm and ∼656.26 nm for Balmer- α (in panel (b)), respectively. In panel (b), for to , the energy density is found to be nearly proportional to n H,0 as a whole. Figure 7. Spectral energy density profile of hydrogen Ly α line (left panels) and Balmer- α line (right panels) emitted upward at the shock front. In panels (a) and (b), the preshock