Étude hydrodynamique du grand jet coronal ne observé à l'éclipse du 7 Mars 1970

Abstract

A Hydrodynamical Study of the Large NE Coronal Streamer Observed during the 7th March Eclipse.

The photometry of the large coronal streamer located on the N-E limb of the Sun observed on the 7th March 1970 in Mexico has been performed using compensated plates in unpolarized light as well as in tangentially and radially polarized light. The measured polarizations permit us to locate the streamer in space using a generally used method. The density distribution in the core of the streamer and for r > 1.5 R _⊙ is given as well as the half-widths of the density distribution perpendicular to the axis of the streamer. Densities n(r) in the 1(R _⊙) < r < 1.5(R _⊙) region are obtained assuming hydrostatic equilibrium (4) for 1.5 < r < 2.

The axial values of n(r) are given which agree with those of others models. The values of parameters for the model given are tabulated.

The variation of the expansion velocity has been derived from the hydrodynamical continuity equation. This velocity becomes supersonic [v > 150(km s⁻¹)] above the height of minimum cross section of the streamer, r = 3.5 (R _⊙). This result is verified by a simple calculation based on the observed curvature of the streamer's ‘stalk’. The velocity corresponding to the garden hose effect considered has a lower value equal to 60(km s⁻¹). The radial distribution of the expansion velocity is shown. Our model allows us to extrapolate in order to obtain the value of v(r) at the Sun's surface. This value, v ≈ 0.07 (km s⁻¹) can be compared with the value of the differential rotation velocity of the ‘foot’ of the streamer. The values of the corpuscular flux of the streamer are calculated [F=2.4 × 10³⁴(ℯ s^-1] and agree with the value of the flux corresponding to the density enhancements of the solar ‘wind’, measured in situ. This shows the importance of large streamers for the coronal expansion processus.