Study of the nonradial directional property of the rays of the streamer belt and chains in the solar corona

Abstract

Based on analyzing corona images taken by the LASCO C1, C2, and C3 instruments, a study is made of the behavior of the streamer belt spanning one half of the 1996-2001 cycle of solar activity, from minimum to maximum activity, in the absence of coronal mass ejections. It is shown that: (1) The position of the streamer belt relative to the solar equator is generally characterized by two angles: θ_o and θ_E, where θ_o is the latitudinal position (near the solar surface) of the middle of the base of the helmet, the top of which gradually transforms to a ray of the streamer belt with a further distance from the Sun, and θ_E is the latitude of this ray for R>5-6 R_⊙ from the Sun's center where the ray becomes radial. (2) Only rays lying at some of the selected latitudes θ_o retain their radial orientation (θ_o≈θ_E) throughout their extent. Namely: θ_o≈0° (equator), θ_o≈±90° (north and south poles), and the angle θ_o lying in the range ≈±(65°−75°) in the N- and S-hemispheres. (3) A deviation Δθ of rays from their radial orientation in the direction normal to the surface of the streamer belt occurs: for latitudes θ_o<|65°−75°| toward the equator (Δθ>0°) reaching a maximum in the N and S hemispheres, respectively, when θ_OM≈40°, and θ_OM≈−42° for latitudes θ_o>|65°−75°| toward the pole (Δθ<0°). The regularities obtained here are a numerical test which can be used to assess of the validity of the theory for describing the behavior of the Sun's quasi-stationary corona over a cycle of solar activity.