Michael J. Rycroft

A suggested model for the IRI plasmapheric distribution

Abstract A model has been constructed which grafts IRI topside profiles to field-aligned diffusive equilibrium profiles at a “reference level” near 650 km altitude. For different values of geographic latitude, longitude, sunspot number, season and time, the properties of the plasma distribution in the equatorial plane are investigated. These are compared with observations made by satellite (particularly GEOS and ISEE) and also with deductions made from whistler observations.

Modelling the plasmasphere for the international reference ionosphere

Abstract The paper discusses how profiles of electron and/or ion distributions that are produced by two different computer models can be smoothly coupled together. The first of these models is the empirical International Reference Ionosphere which produces a vertical profile of ionospheric parameters up to an altitude of 1000 km. The second is a physically-based, diffusive equilibrium model of the plasmasphere based upon the theoretical work of Angerami and Thomas /1/, in which plasma is constrained to move parallel to the Earths magnetic field lines. Some problems associated with this work are considered, as are some initial results.

Studies of the radiation budget anomalies over Antarctica during 1974–1983, and their possible relationship to climatic variations

Abstract We present the results of a study of anomalies, which are defined as differences of seasonal means from the data set seasonal means, in the Earths radiation budget from the analysis of nine years of ten day mean observations derived from the NOAA polar orbiter satellites for the period, 1974–1983. We estimate that the standard deviation in the outgoing longwave flux for this period is less than 12 Wm −2 and typically 7 Wm −2 . The results show that there are several geographical areas for which the standard deviation is in excess of 20 Wm −2 ; in such regions the radiation budget anomalies exceeded these due to natural atmospheric variability. In this paper we discuss the relationship of these anomalies with climatic change.

Quo vadimus re the springtime antarctic ozone depletion

Abstract As part of a Workshop on the springtime Antarctic ozone depletion, a Panel Discussion was held; the panel members were C.B. Farmer (Jet Propulsion Laboratory), G.M. Keating (NASA Langley), M.P. McCormick (NASA Langley) and R.S. Stolarski (NASA Goddard), with M.J. Rycroft in the chair. Some of the points that were made are reported here. The discussion focussed on the needs for future experimental programmes and for future theoretical and modelling studies. The aim of these is to improve understanding of the formation of the springtime Antarctic ozone depletion, which is a completely unexpected phenomenon of considerable environmental concern.

Modelling studies of ionospheric convection in northern and southern polar regions

Abstract The realistic model of Quegan et al. has been used to investigate the convection paths of ionospheric plasma at 300 km altitude, for different polar cap radii and in both hemispheres. Taking the Northern magnetic dip pole to be at a co-latitude of 11° and the Southern magnetic dip pole at a co-latitude of 23°, these paths are presented in a Sun-Earth frame, with the position of the Earths axis fixed as it is on 21 March, as polar plots centred on the magnetic pole. There are marked hemispheric differences between 13 and 23 L.T., particularly near the stagnation region at 18 to 21 L.T., but only minor differences between 00 and 12 L.T., when the radius of the polar cap exceeds 12°. For a smaller polar cap, the differences between the hemispheres are small at all local times. The time taken to perform a complete circuit is most dependent on the polar cap radius, and most variable - between 15 and 36 h - for convection paths starting near 60° latitude. The time that plasma convecting from noon to near midnight across the Northern polar cap spends within the 10° co-latitude circle increases from 6 h, for a polar cap radius of 10°, to 11.5 h at 17°. These results are compared and contrasted with other model calculation results and with some ground-based and satellite observations of plasma densities at high latitudes.

Proposed international facility in Antarctica

An international workshop was held at Stanford University, Stanford, Calif., April 24–28, to define the scientific and engineering requirements for a new international ELF/VLF wave injection facility to be placed in Antarctica. The workshop was sponsored by the U.S. National Science Foundation, and more than 25 scientists from five countries attended. Discussions covered recent scientific results of wave injection experiments, outstanding questions that lie ahead, and opportunities for international collaboration. Considerations agreed upon by workshop participants follow.

Energetic charged particle and electromagnetic wave injections into space

Man’s first, and most dramatic, activities in this field were to conduct high altitude (400...500 kin) nuclear explosions in the late 1950s and early 1960s. The Argus experiment created charged particles which affected the Van Allen trapped radiation belts. The Starfish experiment of 9 July 1962 had. a higher yield (l.L~Megaton (Mt)) than the Argus explosions (~1 kt); an intense artificial radiation belt was created, and this lasted longer (many years) since the source was at a lower latitude (Johnson Island, Pacific Ocean) than that used for the earlier Argus shots (South Atlantic). Three Soviet explosions in October and November 1962 made artificial radiation belts which were less intense than that due to Starfi~h. Because their source was at a higher latitude (Siberia) these belts decayed rather rapidly. Interesting effects have been observed in the VLF and ELF radio bands after high—altitude nuclear explosions. At the instant of detonation of Starfish, electromagnetic signals were radiated; a whistler was received in the opposite hemisphere. Only seconds after the explosion, artificial aurorae were observed in New Zealand and the absorption of cosmic radio noise by the Alaskan ionosphere was increased. The peak absorption occurred within one minute, with recovery to normal conditions taking a few hours. After a few minutes the ionosonde in Jamaica indicated greater absorption in the lower ionosphere. Also some minutes after the explosion the Q value of the resonant (8 Hz) earth-ionosphere cavity decreased; after about three hours it returned to its normal value. The change may be explained, not only by the enhancement of ionisation below the explosion, but also by the world—wide (low-latitude) ionisation produced by the trapped energetic electrons, arising from neutron decay, drifting eastwards in longitude. Synchrotron radiation from the ~ 2 million electron volt (MeV) electrons produced by the explosion was detected by radioastronomy observatories at low latitudes.