Intensity of the Fe XV emission line corona, the level of geomagnetic activity, and the velocity of the solar wind

Abstract

The average solar wind velocity and the level of geomagnetic activity (Kp) following central meridian passage of coronal weak and bright features identified from Oso 7 isophotograms of Fe XV (284 Å) are determined by the method of superposed epochs. Results are consistent with the concept that bright regions possess magnetic fields of closed configuration, thereby reducing particle escape, while coronal holes possess open magnetic field lines favorable to particle escape or enhanced outflow of the solar wind. Coronal holes are identified with Bartels' M regions not only statistically but by linking specific long‐lived holes with individual sequences of geomagnetic storms. In the study of bright regions a subdivision by brightness temperature (Tb) of associated 9.1‐cm radiation was found to be significant, with the regions of higher Tb having a stronger inhibiting power on the outflow of the solar wind when they were located in the solar hemisphere on the same side of the solar equator as the earth. Regions of highest Tb most strongly depress the outflow of solar wind but are also the most likely to produce flare‐associated great storms.

EUV analysis of polar plumes

“…Knowledge of the physical conditions in polar coronal holes and features such as polar plumes, which are contained in these areas, is critical to the development of theories accounting for the association of high spccd solar wind streams with coronal holes (cf. Kriegcr et al, 1974;Ncupcrt and Pizzo, 1974;Bell and Noci, 1976;Nolte et al, 1976;Sheelcy et al, 1976). Bccause polar plumes appear to be associatcd with open field lines, they may contribute a significant amount of material to thc solar wind originating from polar coronal holes.…”

The relation of open magnetic structures to solar wind flow

“…Although there is strong evidence that the sources of recurrent high-speed solar wind streams are coronal holes [Krieger et al, 1973;Neupert and Pizzo, 1974;Bell and Noci, 1975;Nolte et al, 1976;Sheeley et al, 1977], more general questions concerning the connection of other regions of the lower solar atmosphere to interplanetary space have received less attention. Recently developed techniques have resulted in models of the structure of the lower corona, and these models are being used to study the conn6ction between the solar magnetic field and various parts of the heliosphere, particularly the ecliptic plane at 1 AU [Levine et al, 1977a, b;Pneuman, 1976;Burlaga et al, 1978].…”

Recurrent Forbush decreases and the relationship between active regions and M regions

“…Alternatively, it would be implied from our analysis that the open magnetic field structure of an M region has a closed field structure of a long-lasting active region to its east and not to its Skylab could be formed from the decaying of a long-lasting active region and that the eastern boundary of the hole was dominated by active region formations. Although Neupert and Pizzo [1974] and Bell and Noci [1976] have established a oneto-one relationship of M type magnetic disturbances to coronal holes, such a relationship has not been confirmed with Forbush decreases as yet [Duggal and Pomerantz, 1977].…”