Instabilities in pitch angle diffusion and their possible relation to a 3 Hz modulation in pulsating aurora

The Coroniti-Kennel theory of electron precipitation pulsations has been reviewed, and an additional restriction of differential relaxation time has been introduced, making the model unstable under most conditions. The solution to the model was found to be nonlinear, and a very crude numerical solution has been attempted. Although suffering from several nonrealistic approximations, this model has confirmed the idea that a 3 Hz modulation in pulsating auroral forms is related to short bursts of Coroniti-Kennel type strong pitch angle diffusion. Strong pitch angle diffusion will fill the loss cone and is therefore not consistent with a self-excited steady state diffusion, i.e. it must be of a transient nature. The repetition frequency of such bursts depends on the size of the diffusion region along the magnetic field line combined with the parallel velocity of precipitating particles. Estimates based on reasonable diffusion region and velocity give a modulation frequency comparable to observations. The suggested mechanism is consistent with self-excited pitch angle diffusion only; it excludes the possibility that the diffusion is parasitic.The numerical model also indicated that the abnormal pitch angle distribution generated as a result of a magnetic disturbance might survive for hundreds of seconds and thus acts as a ‘memory’ on the fieldline, making it more susceptible for further disturbances.     

Ionospheric absorption and Pc1-type micropulsations following enhanced geomagnetic activity

Data of Pc 1-type micropulsations and ionospheric absorption derived from measurements at mid-latitudes were analysed during and after geomagnetically disturbed periods. In comparison to the normal Pc 1 activity, a rather reduced one has been found during disturbed conditions. A distinct increase of Pc 1 activity occurred, however, after selected key days in the investigated interval between days ‘+2’ and ‘+7’. A clear after-effect could also be shown for ionospheric absorption, measured at three frequencies in Kühlungsborn (φ∼55°N) and a quite moderate one at somewhat lower geographic latitudes (φ ∼ 48°–49°N). In Kühlungsborn the ionospheric after-effect is particularly prominent at all investigated frequencies in case of a simultaneous after-effect in Pc 1 pulsations. It is restrained in the LF-range and missing in the MF-range when the after-effect is lacking in Pc 1 pulsations.     

Broad-band auroral VLF hiss and inverted-V electron precipitation in the polar magnetosphere

A polar map of the occurrence rate of broad-band auroral VLF hiss in the topside ionosphere was made by a criterion of simultaneous intensity increases more than 5 dB above the quiet level at 5, 8, 16 and 20 kHz bands, using narrow-band intensity data processed from VLF electric field (50 Hz–30 kHz) tapes of 347 ISIS passes received at Syowa Station, Antarctica, between June 1976 and January 1983.The low-latitude contour of occurrence rate of 0.3 is approximately symmetric with respect to the 10–22 MLT (geomagnetic local time) meridian. It lies at 74° around 10 MLT, and extends down to 67° around 22 MLT. The high-latitude contour of 0.3 lies at invariant latitude of about 82° for all geomagnetic local times. The polar occurrence map of broad-band auroral VLF hiss is qualitatively similar to that of inverted-V electron precipitation observed by Atmospheric Explorer.(AE-D) (Huffman and Lin, 1981, American Geophys. Union, Geophysics Monograph, No. 25, p. 80), especially concerning the low-latitude boundary and axial symmetry of the 10–22 h MLT meridian.The frequency range of the broad-band auroral VLF hiss is discussed in terms of whistler Aode Cerenkov radiation by inverted-V electrons (1–30 keV) precipitated from the boundary plasma sheet. High-frequency components, above 12 kHz of whistler mode Cerenkov radiation from inverted-V electrons with energy below 40 keV, may be generated at altitudes below 3200 km along geomagnetic field lines at invariant latitudes between 70 and 77°. Low-frequency components below 2 kHz may be generated over a wide region at altitudes below 6400 km along the same field lines. Thus, the frequency range of the downgoing broad-band auroral hiss seems to be explained by the whistler mode Cerenkov radiation generated from inverted-V electrons at geocentric distances below about 2 R_E (Earth's radius) along polar geomagnetic field lines of invariant latitude from 70 to 77°, since the whistler mode condition for all frequencies above 1 kHz of the downgoing hiss is not satisfied at geocentric distance of 3 r_e on the same field lines.     

Calculations and ground-based observations of pulsed proton events in the dayside aurora

A procedure is established to evaluate the Balmer excitation rates of Hα and Hβ to produce the corresponding volume emission rates versus height, using semi-empirical range relations of protons in air. The calculations are carried out with identified ion-energy particle spectra of the dayside aurora obtained by low altitude satellites. The calculated emission intensities of Hα and Hβ indicate that they are indeed observable by ground-based optical detection. Measurements of the dayside aurora from Nordlysstasjonen in Adventdalen, Svalbard, are discussed in relation to these calculations. Periodic bursts of auroral Hα and Hβ emissions are observed in the dayside aurora by ground-based photometers and spectrometers. The mean period between proton events is found to be 10 min on average. Furthermore, it is found that when the time between successive bursts decreases, the emission ratio of Hα and Hβ fluctuates indicating a step-like behaviour in the primary initial proton energy.     

Bridewealth,dowry, property,and economics

Jack Goody and S. J. Tambiah. Bridewealth and Dowry. Cambridge Papers in Social Anthropology 7. Cambridge, England: Cambridge University Press, 1973. ix + 169 pp. Tables, figures, notes, and bibliography. $11.50.     

Competence,representations, rules,and inquiry

Anderson, Stephen R. Phonology in the Twentieth Century: Theories of Rules and Theories of Representations. Chicago: University of Chicago Press, 1985. x + 373 pp. including references and name and subject indices. $40.00 cloth, $17.50 paper.

Paikeday, Thomas M. The Native Speaker is Dead! Toronto: Paikeday Publishers, 1985. xiv + 109 pp. including appendices, references, and name index. $7.50.     

Angels,Illusions, Hydras,and Chimeras: Violence and Humanity

Gibson, Kathleen R. and Tim Ingold, eds. Tools, Language and Cognition in Human Evolution. Cambridge: Cambridge University Press, 1993. xii + 483 pp. including index. $69.95 cloth.

Wallman, Joel. Aping Language. Cambridge: Cambridge University Press, 1992. xii + 191 pp. including notes, references, and indices. $44.95 cloth, $14.95 paper.