This paper describes the phenomenon of the midlatitude red arc of September 29, 1967, through observations of the properties of the ionospheric plasma. The ion and electron temperatures, ion composition and density, and suprathermal electron flux during this period are measured by retarding potential analyzers near 900 km from Ogo 4 and near 2000 kra from Explorer 31. These parameters show the following changes in the region L • 2.3 to 3.0 during the red arc period, as compared with their values during normal periods: (1) Electron and ion temperatures increase to above 4000øK from a normal value of 2000øK at 900 km, while at 2000 km electron temperature increases to above 5000øK from a normal value of 2500øK. (2) At 900 km the ratio of O*/(H* • He*) changes from I to 5, while the total density remains approximately the same. (3) At 2000 km the ion density decreases by a factor of 10 with the composition remaining all H*. (4) There is no significant increase in the flux of 5-to 10-ev electrons. The relative importance of electric field heating, magnetospheric conduction, and the changes in the neutral composition in the lower atmosphere are examined in the light of these observations. It is concluded that the subauroral red arc is caused by a combination of thermal conduction of energy from the magnetosphere and changes in the neutral compositions in the lower atmosphere. Recent measurements of electron temperatures in the region of subauroral red arcs have given direct support to the concept that the arc is produced primarily by the thermal electron excitation of atomic oxygen [Norton and Findlay, 1969]. The mechanism exciting the arc is therefore related to the mechanism he.ating the ambient plasma. In recent years, a number of models for heating the electron gas have been proposed. These are (1) adc electric field [Megill et al., 1963]; (2) a precipitating flux of low-energy electrons [Dalgarno, 1964]; (3) the thermal conduction of energy from the magnetosphere in the ionosphere along the geomagnetic field lines [Cole, 1965, 1970]. Walker and Rees [1968] investigated the relative merits of the three processes in raising electron temperature to the point of exciting the 600-R red arc of June 21, 1961. They concluded that all satisfied the necessary criteria so far as ability to heat the ambient plasma was concerned.
The ionosonde data are studied for equatorial station, Thumba, to delineate various features of the evening height rise of F layer. Sharp increase of h'F and h_F2 is obß 13 served •n the postsunset period for high solar activity. Seasonal variation is observed in this increase of h'F and it is maximum for equinox months. For summer months, there is a delay of about an hour in the time of occurrence of h'F (peak) as compared to winter and equinox months. This delay is shown to be associated with the delay in sunset times in the conjugate E regions. As for magnetic activity dependence, it is found that this height increase is less pronounced for disturbed days for winter and equinox whereas for summer it is marginally higher over the quiet day values. Further, it is observed that the value of h'F (peak) during disturbed periods is almost at the same value of 350 km for all the three seasons. Thus the seasonal variation of magnetic activity effects appears to be mainly governed by the average seasonal variation for quiet times. The increase in F layer height is due to zonal eastward electric fields developed after sunset which is believed to be due to F region dynamo fields. While the main driving force for these fields is the zonal neutral winds, the development of these fields depend on the ratio of the F region to E region conductivity and the longitudinal gradient in the E region conductivity. Experimental observations of both the neutral winds and ionospheric conductivities are examined for their variation with solar activity, season and magnetic activity as both these factors will contribute for the various observed features of the height rise. Through model calculations it is shown that the E region density (conductivity) gradient in the postsunset period is higher by a factor of 2 for high solar activity compared to low solar activity and hence it is partly responsible for the observed solar activity variation of the postsunset height rise of the F layer. The importance of the studies using available ionosonde data for understanding the F region dynamo electric fields is emphasized.
The characteristic features of the equatorial F region are studied using the published ionospheric data. The study reveals some important differences in the Asian, African, and American zones. In the diurnal variation of foF2 there are two peaks, one in the forenoon and the other in the afternoon, in the Asian zone, whereas the afternoon peak is absent in the American zone during sunspot maximum. The width of the equatorial trough is smaller in the American than in the Asian zone. The location of the F‐region equator is examined; the results indicate that the F‐region equator does not correspond exactly to the magnetic dip equator but is shifted slightly toward the north in the Asian and American zones and slightly toward the south in the African zone.
In the transition region lying between the equatorial anomaly region and the middle latitudes a characteristic postsunset rise in foF2 is observed during years of high sunspot activity. This phenomenon is found to depend on the evening height rise in the equatorial region. The analysis presented in this paper substantiates the view that the ionization lifted over the equatorial region is transported along the magnetic lines of force to the transition region.
Developing advanced magnetic divertor configurations to address the coupling of heat and particle exhaust with impurity control is one of the major challenges currently constraining the further development of fusion research, and therefore has become the focus of extensive attention in recent years. In J-TEXT, several new divertor configurations, including the high-field-side single-null poloidal divertor and the island divertor, as well as their associated fundamental edge divertor plasma physics have recently been investigated. The purpose of this paper is to briefly summarize the latest progress and achievements in this relevant research field on J-TEXT in the past few years.
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