A review on far-infrared brightness-temperature maps of the solar atmosphere is presented. They have been taken with the aid of a 60 cm-diameter balloon-borne telescope at a height of 39 km in France. Three bandpass filters at the wavelengths 50 μm, 80 μm and 200 μm of 6 to 10 % bandwidth have been applied. The filters as well as the Au-doped Ge bolometer were cooled by liquid He. An
observation on 30.4.83 represents the active sun, while one on 28.9.84 shows the quiet sun. The observations at the three wavelengths correspond to three different heights in the solar atmosphere at the transition of the photosphere and chromosphere. Over active regions, average temperature enhancements of 75 K to 250 K are observed relative to the inactive regions depending of the height in the solar atmosphere.
We consider the general problem of linear Alfvèn waves propagating in a dissipative atmosphere Cl], and obtain an exact solution of the wave equation with double diffusion, i.e., by fluid viscosity and electrical resistance. This solution includes, as particular cases, nondissipative Alfvèn waves in an isothermal atmosphere, with a vertical [2,3] or oblique [4] magnetic field, and the case when resistive dissipation alone is present C5,6]. This solution may be relevant to a variety of solar atmospheric problems in which dissipation is an essential element, e.g., atmospheric heating C7] or resonances [81, which have been modelled using the undamped solutions of the Alfvèn wave equation. The present, exact solution, can be used to assess the domain of validity of the RLC-analogy C9],and of the phase mixing approximation [10-11]. An exhamination of the effects, on wave amplitude and phase, of changing wave frequency, horizontal wavenumber, magnetic field inclination and viscous and resistive damping scales (Figures 2 to 6), shows that intense, localized dissipation can occur generally at an intermediate altitude; this mechanism of atmospheric heating by propagation-diffuse coupling is a spatial analogue of some properties [12] unsteady magnetic fields.
During the maximum activity year 1980, chromospheric mass ejections were observed with the Multichannel Subtractive Double Pass Spectrograph operating at Mcudon (MSDP), while the UV and X ray emissions were observed respectively with Ultra Violet Spectrograph (UVSP) and HXIS instruments on board the SMM satellite. These ejections are not related directly to flares but are located in active regions near sunspots. As the magnetic field is frozen in the matter, the study of the velocity field leads to the geometry of the magnetic structures and to the temporal evolution
of the magnetic field lines. Ejections of matter recur often with a period of 10 to 20 minutes. In CIV, the bright loops colncide with the Hα surge but are more extended. Associated with the events are either X ray emission or type III bursts. We interprete these signatures by invoking, respectively closed or open structures. The estimate of the energy involved gives constraints on the mechanism responsible for the surge.