Earth's Space Environment Research Articles

The correspondence between thermospheric neutral densities and broadband measurements of the total solar soft X‐ray flux

While it is accepted that neutral densities in the thermosphere have a significant dependence on the solar soft X‐ray fluxes, until recently the only coincident measurements available for an extended time period were from the AE‐E satellite in the late 1970's. However, the Student Nitric Oxide Explorer (SNOE) satellite began measuring the solar soft X‐ray flux (full disk) in March of 1998. Photometers on SNOE measured the solar flux in broad bands from 2 to 20 nm, rather than having high spectral resolution like the AE‐E measurements. The SNOE measurements are coincident with high precision satellite orbit measurements, from which total neutral densities near 350 km can be derived, for the GeoForschungsZentrum (GFZ) satellite. The GFZ data ended on 1 June, 1999. A quantitative assessment of the relationship between densities and broad band measurements of solar soft X‐rays, such as those from SNOE, is needed to determine the usefulness of broad band solar measurements for space weather applications. We have conducted such an assessment for geomagnetically undisturbed times and find correlations of ∼0.74 between the daily variations in total neutral density and the soft X‐rays measured by SNOE. The correlation seen between F10.7 and the neutral densities is significantly lower, ∼0.60. These results indicate that broadband solar soft X‐ray measurements could significantly improve the specification and prediction of neutral densities in the Earth's space environment.

Modelers and Users Meet at CCMC Workshop

Descriptive and predictive models of the Earth's space environment, from the Sun to the Earth's surface, are critical for operational users. The large solar events during the last week of October 2003 coincided with the many stimulating presentations and vigorous discussions during the second biennial workshop for the Community Coordinated Modeling Center (CCMC) that was held at the Maui (Hawaii) High Performance Computing Center.

The use of far ultraviolet remote sensing to monitor space weather

This paper discusses the connection between changes in Earth's thermosphere and ionosphere induced by changes in the Earth's local space environment (or “space weather”) and the phenomena observed in far ultraviolet images of the Earth. Two new experiments, the Global Ultraviolet Imager (GUVI) and the Special Sensor Ultraviolet Imager (SSUSI), will provide a new capability for monitoring changes in thermospheric composition and ionospheric density as they change in response to space weather. These sensors provide a ten-fold improvement in spatial and temporal resolution and a greater than ten-fold improvement in sensitivity over that provided by sensors on the POLAR and IMAGE satellites. These sensors are expected to provide new insights into the mesoscale coupling between the ionosphere and thermosphere, as well as allowing us to develop a better specification of the high latitude convection electric field pattern.

Interaction between an interplanetary magnetic cloud and the Earth's magnetosphere: Motions of the bow shock

An interplanetary magnetic cloud (IMC) is an important solar‐terrestrial connection event. It is an ideal object for the study of solar‐terrestrial relations and space weather because the Earth's space environment can be affected considerably during an IMC passage. An IMC was observed to pass the Earth during October 18–20, 1995. Wind recorded its interplanetary characteristics at ∼ 175 RE upstream of the Earth's bow shock, and ∼ 45 min later, Geotail, being near the nominal location of the dawn bow shock, detected IMC‐related multiple bow shock crossings. Using simultaneous measurements from Wind and Geotail, we analyzed, with a semiempirical bow shock model with two parameters, the bow shock motion caused by the interaction of the IMC with the magnetosphere during the passage. We also compared the bow shock motion predicted by the model, and hence the predicted Geotail bow shock crossings, with Geotail observations of the actual crossings. The results showed that the observed multiple bow shock crossings, which were obviously due to temporal variations of the upstream solar wind, can be well explained by the model‐predicted bow shock motion.

High performance computer methods applied to predictive space weather simulations

Taking advantage of the advent of massively parallel computers, sophisticated solution-adaptive techniques, and recent fundamental advances in basic numerical methods the authors have developed a high performance, adaptive-scale MHD code capable of resolving many of the critical processes in the Sun-Earth system which range over more than nine orders of magnitude. The development of such models are of increasing importance as the impact of space weather on vulnerable technological systems increases, and too, as the severity of space weather increases with the approach of solar maximum. There is an increasing need to develop physics-based, high performance models of the Sun-Earth system from the solar surface to the Earth's upper atmosphere which can operate faster than real time and which can provide reliable predictions of the near Earth space environment based upon solar observations and upstream solar wind measurements. They report on the status of the Michigan adaptive-scale MHD model, which is one effort whose goal is the development of an operational predictive space weather model.

Electron Acceleration in the Aurora and Beyond

Charged particles that populate Earth's space environment span an enormous range of kinetic energies, from less than 1 eV in the ionosphere to millions of GeV in the spectrum of cosmic rays. Duncan Bryant's ambitious new book, Electron Acceleration in the Aurora and Beyond, spans approximately this range as well. This is a delightful book, in which the author uses mainly words and diagrams to provide clear explanations of a large variety of space plasma topics, all related in some way to charged particles in space.The scope of the book extends well beyond mechanisms of electron acceleration. It begins at a very elementary level by introducing the mass and charge of an electron, and it ends (apart from appendices) with careful discussions of first‐order and second‐order Fermi acceleration of galactic electrons to cosmic ray energies.

Catching the wave: ULF research in the U.S. since 1991

Variations in the ultra‐low frequency (ULF) range, with periods from 0.1 to 600 seconds, were noted in the Earth's magnetic field long before they were understood to be indicators of plasma processes in the Earth's space environment. They are now also recognized as a significant means of dissipating solar wind and/or magnetospheric energy and as a primary means of coupling magnetospheric and ionospheric processes. ULF waves also constitute the source field for electromagnetic induction studies of the structure and motions of conductive bodies in the Earth. Knowledge of the spatial and temporal variation of these waves thus can aid in our understanding of properties of both Earth's external plasma environment and its underlying oceans, crust, and mantle.

High frequency electromagnetic radiation in CRRES geostationary injections

It is shown that experiments with geostationary injections of dense barium plasma clouds after CRRES program presented a unique opportunity for investigation of Earth's space environment radiation generation mechanism at frequencies 100 to1000 times higher than the usual plasma frequency signal. We present electromagnetic noise or radiostorm data obtained in Havana in broad frequency bands 45–90 MHz, 235MHz and 280 MHz after Ba injection. It is proposed that signals appearing with 7 to 10 min delay after injection possibly caused a substorm initiated by the injection, during which the radiation is generated by local energetic particles flowing through the irregular barium cloud. Another possibility is connected with irradiation of the barium cloud by the Jicamarca radar. Modulation of radioburst at barium gyrofrequency is typical for both cases.

EURECA's exposure in the near earth space environment. Hyper velocity impact cratering distributions at a time of space debris growth

EURECA's exposure in the near earth space environment. Hyper velocity impact cratering distributions at a time of space debris growth

Solar wind-magnetosphere-ionosphere coupling and chaotic dynamics

Electromagnetic fields and currents connect various regions of the earth's near space environment extending upto the magnetopause. Realization of this fact has lead to the concept of Global Electric Circuit (GEC) to describe the electromagnetic environment of the earth's atmosphere. Solar wind - magnetosphere - ionosphere coupling forms a vital component of GEC. Magnetospheric substorms represent a global interaction between the solar wind, the magetosphere, and the ionosphere. This article gives an overview of the solar wind - magnetosphere- ionosphere coupling processes with emphasis on the nonlinear particle dynamics in the magnetotail. Those aspects of the substorm processes which involve the chaotic dynamics are highlighted. Various methods based on nonlinear particle dynamics, linear prediction filtering techniques, phase space reconstruction techniques, and dynamical anologue models of geomagnetic activity are reviewed. It is shown that the solar wind- magnetosphere - ionosphere system behaves as a strongly coupled nonlinear dynamical system which could be driven from regular to chaotic behavior with low dimensionality when the solar wind forcing is strong enough.

Solar breeze

With the assistance of the Moon's gravitational field, NASA will launch the Wind spacecraft November 1 to the forward libration point to study the physics of the solar‐terrestrial system. Eight instruments aboard the 1250‐kg satellite will measure various quantities in the solar wind about 1 hour before it reaches the Earth. The highly quantitative measurements will help scientists predict how changes in solar wind affect the Earth's atmosphere. “Extensive use has been made of ‘intelligent’ instruments, and they are able to operate in a wide variety of modes and productivity will be high,” says Keith Ogilvie, deputy project scientist. “It's pretty modern stuff,” Ogilvie says. Wind is the first of two missions of the Global Geospace Science (GGS) initiative, the U.S. component of the International Solar‐Terrestrial Physics program. The launch of Polar, the second GGS satellite, is slated for late 1995. Polar is designed to measure the flow of plasma within Earth's magnetosphere. Both craft, which together cost about $458 million to develop, are part of a larger project to provide simultaneous, interactive data on key regions of Earth's space environment, from beyond the Earth foreshock region to the magnetosphere to transient gamma ray events.

The Southern Hemisphere Auroral Radar Experiment (SHARE)

The near Earth space environment (known as Geospace) is dominated by the interaction between the solar wind and the geomagnetic field, which creates the magnetosphere. Considerable energy flows from the solar wind into the magnetosphere and ends up in the Earth's upper atmosphere (the thermosphere and ionosphere). The coupling of the geomagnetic field with that of the solar wind (known as the interplanetary magnetic field, or IMF) produces a variety of electro-dynamic responses with signatures such as electric fields and currents in the polar ionospheres. These produce, inter alia, motion of the ionospheric plasma (at altitudes between 100 and 1000kms) which can be monitored from the ground using radar techniques. Analysis of such plasma motion provides a very powerful means of investigating the nature of the interactions taking place at the boundaries between the magnetosphere and the solar wind. To do this effectively requires simultaneous measurements over as large an area (in latitude and longitude) as possible.

Satellite probes plasma processes in Earth orbit

The Combined Release and Radiation Effects Satellite (CRRES), launched on July 25, 1990, is a joint Department of Defense/NASA mission to provide better understanding of the physics of the Earth's near space environment including the radiation belts and the ionosphere. New data has already been obtained that will help spacecraft designers protect against radiation belt particles that adversely affect sensitive electronic parts in satellites, degrade solar panel arrays, and pose hazards to people living and working in space.

Particulate Detection in the Near Earth Space Environment Aboard the Long Duration Exposure Facility Ldef: Cosmic or Terrestrial?

AbstractExamination of surfaces exposed for more than five and a half years, from detectors with unique attitude stabilisation relative to the orbital velocity vector, offers scope for examining definitively the sources of hypervelocity space particulates. Surfaces reveal discrete crater morphologies, crater size distributions and incident flux distributions. Discrete crater studies will later also reveal the chemistry of residues which can, especially via the capture cell principle, lead to elemental analysis of micron dimensioned particles.First analyses of the flux data from the thin foil perforation experiments (MAP) involve a study of the statistics of the forward (ram) direction, the rear (trailing) direction and the space pointing direction. Modelling of the dynamics of geocentrically bound and unbound orbits yields evidence that the characteristics of the particles, and hence probably their source, change over the particle size range measured by the experiment. Smaller particles (< 1 μm diameter) have lower velocities which could include geocentrically bound particulates, whereas the larger particles (5-10 μm diameter) can be identified with “cosmic” particles of interplanetary or interstellar origin.

Spear — space power experiments aboard rockets

The SPEAR program was initiated by the Innovative Science and Technology Office of the Strategic Defence Initiative Organization to investigate the operation of high power electrical systems in the near earth space environment. SPEAR I was successfully launched on a suborbital sounding rocket on December 13, 1987. Its purpose was to investigate the current collection for theoretical validation of highly charged objects operating in the iononspheric plasma. SPEAR II is planned for an April, 1989, launch aboard another sounding rocket. Its mission will be to operate representative Strategic Defence electrical components at pulsed megawatt level peak powers while using little or no insulation other than the vacuum of space. Extensive ground testing and theoretical support have preceded these launches with new understanding of high voltage operation in the space environment.

An intercomparison of longwave measurements by ERBE radiometers on the NOAA-9 and ERBS satellites

Two instrument modules of each satellite on which ERBE is orbiting observe components of the earth radiation budget with three different scales of earth view. An intercomparison of longwave measurements by these instruments provides relative information concerning radiometric performance at satellite altitude, techniques of estimating upwelling exitances, and an end-to-end evaluation of the data processing system. Results indicate that the ERBE radiometers are mildly sensitive to varying thermal loads from the spacecraft and/or the earth-space environment. Radiometric variations at the satellite and methods of data interpretation contribute about equally to the uncertainty of radiant exitances from the earth. The RMS uncertainty of observed differences between instruments is about ±4 W/m 2 for irradiances at satellite altitude, ±7 W/m 2 for exitances at the top-of-the-atmosphere, and ±7 W/m 2 for monthly averages after time and space averaging. Overall, the longwave observational consistency is about ±3.0% for individual measurements and ±3.0 % for monthly estimates.

GOES‐4 failure investigated

The Visual Infrared Spin‐Scan Radiometer (VISSR) on board the western Geosynchronous Operational Environmental Satellite (GOES‐4), failed at 0445 UT, November 26, 1982, as a series of intense storms descended on the California coast. The VISSR maps the earth and its cloud cover day and night and allows the tracking and forecasting of severe storm systems. This failure of the VISSR on board GOES‐4 deprived weather forecasters of an important means of tracking the nighttime progress of life‐threatening storms as they moved across the Pacific.The cause o f this critical satellite failure is of great interest to the National Oceanic and Atmospheric Administration (NOAA), operators of the GOES network. A study now in progress should resolve the reason for failure and determine whether solar activity caused it. Figure 1 was prepared at the National Geophysical Data Center in Boulder, Colo., in response to a call for information about the earth's space environment at the time of the GOES‐4 failure.

Relationships of the characteristics of magnetohydrodynamic waves to plasma density gradients near L = 4

Important recent work, both experimental and observational, has provided exciting new results and understandings of the excitation and localization characteristics of magnetohydrodynamic waves ( ω ⪡ ion gyrofrequency) that exist in the Earth's magnetosphere. This paper reviews several of our recent contributions to this research area, with special emphasis on the importance of magnetospheric plasma density gradients in determining wave localizations. The observational results are discussed in the context of current theoretical ideas of hydromagnetic wave excitation in the Earth's space environment.

Can cosmic clouds cause climatic catastrophes?

SEVERAL authors1–3 have discussed whether past immersion of the Solar System in dense interstellar matter (ISM) might have left observable imprints on the Earth. Accretion cannot affect the solar constant significantly unless the surrounding ISM attains densities of 105–107 cm−3 (refs 2 and 3). We demonstrate here, however, that a much more modest ISM density of 102–103 cm−3 (a value typical of dense interstellar clouds in spiral arms) would prevent the solar wind from reaching the Earth, and propose that such a change in the Earth's space environment may trigger drastic climatic changes.

The Atmosphere above Earth's Surface

The earth's near space environment plays a significant role in maintaining a reliable long distance communication, carrying out astronomical research, space exploration with continuous link with space ships, making meteorological predictions etc. The paper presents the present day concept of the structure of the atmosphere above earth's surface.