From all-sky TV and meridian scanning photometer data, obtained at Poker Flat, Alaska, during the 1982/1983 winter, 12 nights with extensive displays of pulsating aurora were selected for analysis. The majority of the pulsations were located near the equatorward edge of the proton aurora as identified by the Hβ emission; however, on two nights, pulsating aurora was also observed embedded in the main region of the proton aurora. The period of the pulsations varied from 3 to 25 s and appeared to be correlated with the Hβ intensity. The short periods corresponded to weak Hβ emissions while no pulsations were observed above 80 R in Hβ. The change in period appeared to be caused mainly by a variation in the time between individual pulses.

Pulsating aurora and hydrogen emissions

The mammilated chert(MC)studied in this paper is a kind of silica-rich concretion(SiO_2 93%) occurring in the Upper Devonian argillaceous silicolites(SiO_2≈88%)in Mugui,Guangxi. Impurity components in the MC are relatively low and show systematic variations as compared with the country rocks.Abundances of Mg,Si,Ti,Fe,Mn,U and Th are characteristically similar to those of recent and fossil hot-water sediments.Moreover,the MC is also characterized by low REE abun- dance,LREEHREE,apparent negative Ce anomaly and moderate positive Eu anomaly.Oxygen isotope data show that the formation temperature of the MC is about 20℃,higher than that of the host rock.The results of geochemical,geological and lithological studies suggest that the MC may have been formed through metasomatism,filling and crystallization beneath the sedimentary basin during the Devonian period.

Geochemistry of Upper Devonian Hydrothermal Mammilated Chert Guangxi,Southwest China

The mammilated chert (MC) studied in this paper is a kind of silica-rich concretion (SiO2 93%) occurring in the Upper Devonian argillaceous silicolites (SiO2≈88%) in Mugui, Guangxi. Impurity components in the MC are relatively low and show systematic variations as compared with the country rocks. Abundances of Mg, Si, Ti, Fe, Mn, U and Th are characteristically similar to those of recent and fossil hot-water sediments. Moreover, the MC is also characterized by low REE abundance, LREE > HREE, apparent negative Ce anomaly and moderate positive Eu anomaly. Oxygen isotope data show that the formation temperature of the MC is about 20 °C, higher than that of the host rock. The results of geochemical, geological and lithological studies suggest that the MC may have been formed through metasomatism, filling and crystallization beneath the sedimentary basin during the Devonian period.

Geochemistry of Upper Devonian Hydrothermal Mammilated Chert Guangxi, Southwest China

Recent satellite observations1 have revealed details on the strength of the pulsing extremely low frequency (ELF) hiss in the equatorial region which maps down to the auroral zone. It is shown here to be insufficient to produce pitch–angle scattering of energetic electrons into the loss cone at a sufficiently high rate to explain the characteristics of the measured pitch-angle distributions in pulsating auroras, within the framework of the theory proposed by Coroniti and Kennel2. It is suggested that wave–particle interactions involving both broadband incoherent ELF waves and narrow band coherent very low frequency (VLF) waves may be able to produce a sufficiently high rate of pitch-angle scattering.

R. W. Thomas

Papers

Electron pitch-angle scattering by low frequency waves at the geomagnetic equator