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Centrifugal trapping in the magnetotail

Particles leaving the neutral sheet in the distant magnetotail at times display adiabatic trajectory sequences characterized by an inflection toward the equator and subsequent mirroring in its vicinity. We demonstrate that this low-latitude mirroring results primarily from a centrifugal deceleration due to the fast direction-changing E×B drift. This effect which we refer to as "centrifugal trapping" appears both in guiding centre and full particle treatments. It thus does not directly relate to nonadiabatic motion. However, pitch angle scattering due to nonadiabatic neutral sheet interaction does play a role in reducing the parallel speed of the particles. We show that centrifugal trapping is an important mechanism for the confinement of the slowest (typically below the equatorial E×B drift speed) plasma sheet populations to the midplane vicinity.
High-speed correction factor to the O+-O resonance charge exchange collision frequency

The high-speed correction factor to the O+-O collision frequency, resulting from drift velocities between ions and neutrals, is calculated by solving the integral expression in this factor both numerically and analytically. Although the analytic solution is valid for either small or large drift velocities between ions and neutrals, for temperatures of interest and all drift velocities considered, agreement is found between analytic and detailed numerical integration results within less than 1% error. Let Tr designate the average of the ion and neutral temperatures in K, and u=vd/α, where vd is the relative drift velocity in cm s-1, and α=4.56×103√Tr cm s-1 is the thermal velocity of the O+-O system. Then, as u ranges from 0 to 2, the correction factor multiplying the collision frequency increases monotonically from 1 to about 1.5. An interesting result emerging from this calculation is that the correction factor for temperatures of aeronomical interest is to a good approximation independent of the temperature, depending only on the scaled velocity u.
Analysis of auroral infrared emissions observed during the ELIAS experiment

The ELIAS (Earth Limb Infrared Atmospheric Structure) experiment was flown from the Poker Flat Research Range, Alaska in 1983 and successfully monitored visible and infrared emissions from an IBC III+ aurora. Measurements were performed in both staring and scanning modes over several hundred seconds. The data for short- and mid-wave infrared regions have been analyzed in terms of auroral excitation of the NO and NO+ vibrational bands. Auroral excitation efficiencies and kinetic implications are presented.
Nighttime enhancements in ionospheric electron content: seasonal and solar cycle variation

Various characteristics of anomalous nighttime enhancement in ionospheric electron content (IEC) at Lunping (14.08°N geomagnetic), a station near the crest of the equatorial anomaly, have been presented by considering the IEC data for the 21st solar cycle. Out of a total of 1053 enhancements, 354 occur in pre-midnight and 699 occur in post-midnight hours, which indicates an overall dominance of post-midnight events at Lunping. The occurrence is more frequent during summer, less during the equinox and least during winter months. All the characteristics of the enhancements have seasonal dependencies and they reach their maximum values during summer months. The occurrence of the pre-midnight events show positive and post-midnight events show negative correlation with solar activity. The results have been discussed and compared with those at low-latitude stations in India and Hawaii and at the mid-latitude station, Tokyo.
Twilight anomaly, midday recovery and cutoff latitudes during the intense polar cap absorption event of March 1991

A study was made of the polar cap absorption (PCA) event on 23-24 March 1991 produced by the largest solar proton event at E>10 MeV since August 1972. This PCA event was related to a solar flare in the eastern hemisphere lasting only 2 days and exhibiting a long time delay between the flare and the increase of ionospheric absorption. Midday recovery occurred regularly each PCA day near the cut-off latitudes during the noontime hours and is attributed to the daily variation in the proton cut-off latitudes. The maximum absorption during the PCA event was observed at high latitudes or near the cut-off latitudes where ionization may be due to both solar protons and trapped particles. The minimum in the absorption values during the night-time hours would appear to be caused by the chemistry of the D-region as well as access of the solar protons into the polar cap area.
On effective conductivity of the ionosphere with random irregularities

The influence of stochastic irregularities of the ionosphere on its effective conductivity has been estimated. The study was carried out for large scale inhomogeneities and quasistationary electromagnetic fields. It is found, that Pedersen conductivity sharply increases in a strong geomagnetic field even for small stochastic ionospheric irregularities of the electron density. This peculiarity has to be taken into account during analysis of ionospheric and magnetospheric measurements.
Steep latitudinal gradients of thermospheric composition during magnetic storms: a possible formation mechanism

Mass spectrometer satellite observations show that a narrow region with steep latitudinal gradients of neutral composition is formed in the subauroral winter thermosphere during magnetic storms. In order to analyze the relative importance of individual terms in the continuity equation for atomic oxygen, a two-dimensional model was used to simulate the thermospheric disturbance formation in response to intense Joule heating imposed in the auroral oval. Such an approach allowed three characteristic zones to be distinguished in the high-latitude thermosphere at heights of about 250 km. It was shown that vertical transport is of greatest importance within the local heating region. Horizontal transport dominates at subauroral latitudes near the mid-night edge of the auroral oval. Propagation of the disturbances to middle latitudes is prohibited near the noon edge of the oval by a strong counteraction of a poleward meridional wind. Here is a "relaxation zone" defined as the region which is spread to the equator from the boundary between the local heating area and the subauroral zone in the noon sector LT. It is at this boundary that composition distributions with steep latitudinal gradient are formed within the first few hours of Joule heating source action. Perturbations transported to middle latitudes during the periods when the meridional wind is directed equatorward begin to relax in this zone with a characteristic time scale of about 7 h, independent of season. However, in winter, composition at subauroral latitudes recovers to unperturbed N2/O values before the wind again turns equatorward, giving rise to a distribution with steep latitudinal gradient recovering. In summer, a complete relaxation cannot be reached due to a shorter time interval with poleward wind and a larger disturbance amplitude. These two factors result in an effective smoothing of the initial steep gradient and a more regular latitudinal distribution of composition is observed in the summer thermosphere.
On the formation of a plasma pressure anisotropy in the dayside magnetosheath

We present a numerical solution for the momentum equation of the magnetosheath particles that describes the distribution of the pressure anisotropy of the magnetosheath plasma in the midday meridian plane. The pressure anisotropy is a maximum near the magnetopause subsolar point (p⊥/pVert ≌ 10). The pressure anisotropy is caused by two factors: particles with small pitch angles (VVert>V⊥) which travel along the magnetic field lines away from the equatorial plane of the magnetosheath; and particles, after crossing the bowshock, which reach the bulk velocity component directed along the magnetic field lines again, away from the magnetosheath equatorial plane. This velocity increases with increasing distance from the subsolar point of the bowshock, and does not permit particles with large pitch angles (V⊥>VVert) to move toward the equatorial plane.
Observations of long-lived solar wind streams during 1990-1993

Interplanetary scintillation (IPS) can be used to identify changes in solar wind parameters over a wide range in heliographic latitude and elongation and constrain models of its large-scale structure, velocity and density. This paper reviews the scintillation density mapping method specifically, and presents over three years of data taken between March 1990 and September 1993 with the 3.6 hectare array in Cambridge. A novel form of synoptic plot that is particularly sensitive to corotating structures is introduced, and low-density streams are identified by their unequivocal signatures within it. Stable corotating structures are evident throughout - even during the active phase of the solar cycle - and specific periods are examined. Density measurements inferred from scintillation are compared with IMP-8 data for the same period and are shown to be in good agreement, giving further support to the scintillation/density relationship determined by Tappin (1986).
The onset of the Little Ice Age in Andalusia (southern Spain): detection and characterization from documentary sources

In this work the onset of the "Little Ice Age" period in Andalusia (southern Spain) is analysed from documentary data, focusing attention on the evolution of the climate during the 16th and 17th centuries. It is shown that changes in the rainfall regime have been more important than those in the temperature in studying the Andalusian climate change. Analysis of the total annual precipitation is carried out by codifying the documentary data and establishing an ordinal index. Several statistical methods are used to detect and characterize climate changes in the region. The results suggest a fluctuating evolution, without trends or abrupt changes, with a prevailing wet period from 1550 to 1650 AD. Cycles of ~17, 3.5 and 2.1 years are detected. Some possible causal mechanisms are suggested.