NOTE ON LOW-LEVEL GEOMAGNETIC RING-CURRENT EFFECTS
Low-level geomagnetic ring-current effects and radiation intensity measurements within the inner van allen belt
VAN ALLEN BELT↗
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The interplanetary magnetic field, solar origin and terrestrial effects
Observations related to large-scale structure of interplanetary magnetic field, solar origin, and geomagnetic effects
Wilcox, J. M.↗
Solar Influences on Geomagnetic and Related Phenomena
A discussion of the geomagnetic effects of streams of electromagnetic and particular radiation from the sun. The interplay of forces between the geomagnetic field and solar streams is outlined; and the theoretical relationship between these, the solar storms, the trapped Van Allen radiations, the polar aurora, and geomagnetic field distortion are presented.
Vestine, E. H.↗
International Cosmic Ray Conference, 13th, University of Denver, Denver, Colo., August 17-30, 1973, Proceedings. Volumes 1 & 2
Topics discussed include diffuse gamma rays, gamma ray sources (in particular, the Crab Nebula and Crab Pulsar), X-ray sources, isotopic and nuclear composition, spectra of nuclei, searches for antinuclei, studies of VH and VVH nuclei, measurements of electrons and positrons, the spectra of high-energy electrons, cosmic gamma rays, cosmic ray sources, interplanetary radial gradients, the theory and observation of electron modulation, short-period cosmic ray intensity variations, atmospheric and coupling effects on neutron monitors and muon telescopes, secondary particles and photons in the atmosphere, harmonics of diurnal variations, geomagnetic effects and cutoffs, planetary and interplanetary effects, solar particle access observations, long-term cosmic ray intensity modulation by solar activity and interplanetary effects, Forbush decreases, modulation and anisotropy of low-energy particles, the theory and models of solar particle propagation, solar flare particle composition, and relativistic solar particles. Individual items are announced in this issue.
Source record↗
Discontinuities and shock waves in the interplanetary medium and their interaction with the magnetosphere.
The discontinuous structure of the solar wind is described with emphasis on properties related to geomagnetic impulses. Some of the discontinuities are clearly hydromagnetic shocks and tangential discontinuities, and can produce a significant change in the momentum flux at the magnetosphere boundary. Such a change generates an impulse which propagates through the magnetosphere to the earth where it is observed world-wide as an impulse in magnetograms. The propagation process is not reviewed here, but the relation between the initial cause (discontinuity) and the final effect (geomagnetic impulse) is reviewed in detail. The various types of impulses are examined, and are related qualitatively to the various types of discontinuities. The magnitude of an impulse is related to the change in the momentum flux. The propagation time and the rise time depend on the propagation process rather than on the initial state.
Burlaga, L. F.↗
Major Geomagnetic Storms (Dst less than or equal to -100 nT) Generated by Corotating Interaction Regions
Seventy-nine major geomagnetic storms (minimum Dst less than or equal to -100 nT) observed in 1996 to 2004 were the focus of a Living with a Star Coordinated Data-Analysis Workshop (CDAW) in March, 2005. In 9 cases, the storm driver appears to have been purely a corotating interaction region (CIR) without any contribution from coronal mass ejection-related material (interplanetary coronal mass ejections, ICMEs). These storms were generated by structures within CIRs located both before and/or after the stream interface that included persistently southward magnetic fields for intervals of several hours. We compare their geomagnetic effects with those of 159 CIRs observed during 1996 - 2005. The major storms form the extreme tail of a continuous distribution of CIR geoeffectiveness which peaks at Dst approx. -40 nT but is subject to a prominent seasonal variation of - 40 nT which is ordered by the spring and fall equinoxes and the solar wind magnetic field direction towards or away from the Sun. The O'Brien and McPherron [2000] equations, which estimate Dst by integrating the incident solar wind electric field and incorporating a ring current loss term, largely account for the variation in storm size. They tend to underestimate the size of the larger CIR-associated storms by Dst approx. 20 nT. This suggests that injection into the ring current may be more efficient than expected in such storms. Four of the nine major storms in 1996 - 2004 occurred during a period of less than three solar rotations in September - November, 2002, also the time of maximum mean IMF and solar magnetic field intensity during the current solar cycle. The maximum CIR-storm strength found in our sample of events, plus additional 23 probable CIR-associated Dst less than or equal to -100 nT storms in 1972 - 1995, is (Dst = -161 nT). This is consistent with the maximum storm strength (Dst approx. -180 nT) expected from the O'Brien and McPherron equations for the typical range of solar wind electric fields associated with CIRs. This suggests that CIRs alone are unlikely to generate geomagnetic storms that exceed these levels.
Richardson, I. G.↗
Time variations of geomagnetic H and D at disturbed stations.
Cylindrical coordinate system describing geomagnetic field analyzed, noting consequences in magnetic cartography when going from field to time gradients
TIME FACTOR↗
Magnetic declination and solar control of the topside ionosphere
Effects of magnetic declination and solar control on topside ionospheric electron density distribution
SOLAR EFFECT↗
The physics of the neutral upper atmosphere.
Particular attention is given to models of the upper atmosphere that deal with the diurnal variation and the latitudinal density dependence. The upper atmosphere is considered as essentially an ideal gas, or rather a weakly ionized plasma, where physical and chemical processes of considerable complexity take place. The final goal for the theoretical models of the upper atmosphere is to derive the time and space dependence of the physical quantities density, composition, temperature, pressure, and state of motion by theoretical considerations from basic physical assumptions. Questions of the dynamics of the upper atmosphere are discussed together with one- and two-dimensional models of the upper atmosphere, three-dimensional models, the geomagnetic effect, and the semiannual density variation.
Blum, P.↗
The relation between the polarity of the interplanetary magnetic field and the polar geomagnetic field
The relation between the azimuthal component of the interplanetary magnetic field and the polar cap geomagnetic field is discussed. The geomagnetic effects can be described as produced by an ionospheric current system encircling the magnetic pole. The sense of the current is clockwise during toward-sectors and reversed during away-sectors. The importance of this very direct solar-terrestrial relation is stressed. A recent magnetic sunspot cycle model is discussed as inferred from this relationship, the basic feature being that the sun reproduces the same sector pattern during every sunspot cycle.
Svalgaard, L.↗
SAS 2 observations of the earth albedo gamma radiation above 35 MeV
The earth albedo gamma radiation above 35 MeV in the equatorial region is investigated using observations from the second Small Astronomy Satellite. The zenith angle distribution of the gamma radiation has a peak toward the horizon which is about an order of magnitude more intense than the radiation coming from the nadir, and nearly two orders of magnitude more intense than the gamma radiation from most parts of the sky. The gamma radiation originating from the western horizon is a factor of four more intense than the radiation from the eastern horizon and a factor of three more intense than that from the northern and southern directions. This reflects the geomagnetic effects on the incident cosmic rays whose interactions produce the albedo gamma rays. The variation of the upcoming gamma ray intensity with vertical cutoff rigidity is consistent with the empirical relationship found by Gur'yan et al. (1979).
Thompson, D. J.↗
Measurement of neutrino oscillations in MACRO experiment
The possibility of investigating neutrino oscillations in the proposed MACRO experiment are considered. Its sensitivity taking into account the theoretical uncertainties coming from flux calculations, geomagnetic effects and propagation through matter, and the experimental limitations.
Musser, J.↗
Comparison of the calibration of ionospheric delay in VLBI data by the methods of dual frequency and Faraday rotation
When both S-band and X-band data are recorded for a signal which has passed through the ionosphere, it is possible to calculate the ionospheric contribution to signal delay. In Very Long Baseline Interferometry (VLBI) this method is used to calibrate the ionosphere. In the absence of dual frequency data, the ionospheric content measured by Faraday rotation, using a signal from a geostationary satellite, is mapped to the VLBI observing direction. The purpose here is to compare the ionospheric delay obtained by these two methods. The principal conclusions are: (1) the correlation between delays obtained by these two methods is weak; (2) in mapping Faraday rotation measurements to the VLBI observing direction, a simple mapping algorithm which accounts only for changes in hour angle and elevation angle is better than a more elaborate algorithm which includes solar and geomagnetic effects; (3) fluctuations in the difference in total electron content as seen by two antennas defining a baseline limit the application of Faraday rotation data to VLBI.
Scheid, J. A.↗
Interplanetary shock collisions - Forward with reverse shocks
When one interplanetary shock overtakes another, the structure that results depends upon the nature of the interacting shocks. The results of collisions of forward with reverse shocks, in two dimensions, are numerically examined, and it is shown that the results depend primarily upon shock strength. It is also noted that such interactions could explain why many energy outburst on the sun that would be expected to cause geomagnetic effects at the earth, do not.
Smith, Z. K.↗
On the statistics of El Nino occurrences and the relationship of El Nino to volcanic and solar/geomagnetic activity
El Nino is conventionally defined as an anomalous and persistent warming of the waters off the coasts of Ecuador and Peru in the eastern equatorial Pacific, having onset usually in Southern Hemispheric summer/fall. Some of the statistical aspects of El Nino occurrences are examined, especially as they relate to the normal distribution and to possible associations with volcanic, solar, and geomagnetic activity. With regard to the very strong El Nino of 1982 to 1983, it is noted that, although it may very well be related to the 1982 eruptions of El Chichon, the event occurred essentially on time (with respect to the past behavior of elapsed times between successive El Nino events; a moderate-to-stronger El Nino was expected during the interval 1978 to 1982, assuming that El Nino occurrences are normally distributed, having a mean elapsed time between successive onsets of 4 years and a standard deviation of 2 years and a last known occurrence in 1976). Also, although not widely recognized, the whole of 1982 was a record year for geomagnetic activity (based on the aa geomagnetic index, with the aa index registering an all time high in February 1982), perhaps, important for determining a possible trigger for this and other El Nino events. A major feature is an extensive bibliography (325 entries) on El Nino and volcanic-solar-geomagnetic effects on climate. Also, included is a tabular listing of the 94 major volcanic eruptions of 1835 to 1986.
Wilson, Robert M.↗
The Earth's Middle Atmosphere: COSPAR Plenary Meeting, 29th, Washington, DC, 28 Aug.-5 Sep., 1992
The conference presented the results from the Upper Atmosphere Research Satellite (UARS) in the areas of wind, temperature, composition, and energy input into the upper atmosphere. Also presented is the current status of validation of the UARS temperature and wind instruments measuring at and above the menopause. The two UARS instruments involved were the High Resolution Doppler Imager (HRDI) and the WIND Imaging Interferometer (WINDII). Papers are presented covering almost all aspects of middle atmospheric science, including dynamics, layering in the middle atmosphere, atmospheric composition, solar and geomagnetic effects, electrodynamics, and the ionosphere.
Grosse, W. L.↗
Solar Activity Forecasting for use in Orbit Prediction
Orbital prediction for satellites in low Earth orbit (LEO) or low planetary orbit depends strongly on exospheric densities. Solar activity forecasting is important in orbital prediction, as the solar UV and EUV inflate the upper atmospheric layers of the Earth and planets, forming the exosphere in which satellites orbit. Geomagnetic effects also relate to solar activity. Because of the complex and ephemeral nature of solar activity, with different cycles varying in strength by more than 100%, many different forecasting techniques have been utilized. The methods range from purely numerical techniques (essentially curve fitting) to numerous oddball schemes, as well as a small subset, called 'Precursor techniques.' The situation can be puzzling, owing to the numerous methodologies involved, somewhat akin to the numerous ether theories near the turn of the last century. Nevertheless, the Precursor techniques alone have a physical basis, namely dynamo theory, which provides a physical explanation for why this subset seems to work. I discuss this solar cycle's predictions, as well as the Sun's observed activity. I also discuss the SODA (Solar Dynamo Amplitude) index, which provides the user with the ability to track the Sun's hidden, interior dynamo magnetic fields. As a result, one may then update solar activity predictions continuously, by monitoring the solar magnetic fields as they change throughout the solar cycle. This paper ends by providing a glimpse into what the next solar cycle (#24) portends.
Schatten, Kenneth↗
The Formation of CIRs at Stream-Stream Interfaces and Resultant Geomagnetic Activity
Corotating interaction regions (CIRs) are regions of compressed plasma formed at the leading edges of corotating high-speed solar wind streams originating in coronal holes as they interact with the preceding slow solar wind. Although particularly prominent features of the solar wind during the declining and minimum phases of the 11-year solar cycle, they may also be present at times of higher solar activity. We describe how CIRs are formed, and their geomagnetic effects, which principally result from brief southward interplanetary magnetic field excursions associated with Alfven waves. Seasonal and long-term variations in these effects are briefly discussed.
Richardson, I. G.↗