Observations and Models of the Long-Term Evolution of Earth’s Magnetic Field

The geomagnetic signal contains an enormous temporal range—from geomagnetic jerks on time scales of less than a year to the evolution of Earth’s dipole moment over billions of years. This review compares observations and numerical models of the long-term range of that signal, for periods much larger than the typical overturn time of Earth’s core. On time scales of 10⁵–10⁹ years, the geomagnetic field reveals the control of mantle thermodynamic conditions on core dynamics. We first briefly describe the general formalism of numerical dynamo simulations and available paleomagnetic data sets that provide insight into paleofield behavior. Models for the morphology of the time-averaged geomagnetic field over the last 5 million years are presented, with emphasis on the possible departures from the geocentric axial dipole hypothesis and interpretations in terms of core dynamics. We discuss the power spectrum of the dipole moment, as it is a well-constrained aspect of the geomagnetic field on the million year time scale. We then summarize paleosecular variation and intensity over the past 200 million years, with emphasis on the possible dynamical causes for the occurrence of superchrons. Finally, we highlight the geological evolution of the geodynamo in light of the oldest paleomagnetic records available. A summary is given in the form of a tentative classification of well-constrained observations and robust numerical modeling results.     

Microwave Radiometric Sensing for Air Navigation

This paper discusses the results of an analytic study of the feasibility of using microwave radiometry as a technique for navigation data sensing in Army aircraft. The study included a review of Army aircraft characteristics and navigation requirements. Various means of sensing passively aircraft velocity, altitude, and velocity-altitude ratio were considered. While there appears to be no practical method for direct measurement of either velocity or altitude separately, it does appear possible to measure velocity-altitude ratio by comparing radiometric signals received from the terrain along the aircraft ground track. When combined with a radar altimeter, such a sensor could yield navigation data compatible with Army aircraft requirements. Microwave radiometry may also be the basis for direction sensing (to known landmarks) in high-flying aircraft or satellites.     

The Orbiting Astronomical Observatories

A review is presented of the Orbiting Astronomical Observatories Program together with a detailed of the OAO spacecraft and the four astronomical instruments currently being developed for the first three observations.     

Pseudo-Noise Interferometer

This paper describes a radio interferometer that can be employed for beaming and attitude determination. It differs from conventional interferometers in that it employs a carrier modulated by a pseudonoise sequence. This enables it to provide an unambiguous angular resolution of the signal source.     

OLTARIS: On-line tool for the assessment of radiation in space

OLTARIS (On-Line Tool for the Assessment of Radiation In Space) is a space radiation analysis tool available on the World Wide Web. It can be used to study the effects of space radiation for various spacecraft and mission scenarios involving humans and electronics. The transport is based on the HZETRN transport code and the input nuclear physics model is NUCFRG. This paper describes the tools behind the web interface and the types of inputs required to obtain results. Typical inputs are mission parameters and slab definitions or vehicle thickness distributions. Radiation environments can be chosen by the user. This paper describes these inputs as well as the output response functions including dose, dose equivalent, whole body effective dose equivalent, LET spectra and detector response models.     

A molecular probe of dark energy

Many theoretical models of dark energy invoke rolling scaler fields which in turn predict time varying values of the fundamental constants. Establishing the value of the fundamental constants at various times in the universe can probe and test the various dark energy theories. One of the constants that is predicted to vary is the ratio of the electron to proton mass μ. It was established early on that molecular spectra are sensitive to the value of μ and can be used as probes of that value. This article describes the use of the spectrum of molecular hydrogen in high redshift Damped Lyman Alpha systems (DLAs) as a sensitive probe of the time evolution of μ.     

The interplanetary magnetic field. Solar origin and terrestrial effects

Many observations related to the large-scale structure of the interplanetary magnetic field, its solar origin and terrestrial effects are discussed. During the period observed by spacecraft the interplanetary field was dominated by a sector structure corotating with the sun in which the field is predominantly away from the sun (on the average in the Archimedes spiral direction) for several days (as observed near the earth), and then toward the sun for several days, etc. The average sector appears to be a coherent entity with internal structure such that its preceding portion is more active than its following portion. Cosmic rays corotate with the interplanetary field, and there are differential flows associated with the sector pattern. Profound effects on geomagnetic activity and the radiation belts are produced as the sector pattern rotates past the earth. The solar origin of the sector pattern is discussed. The solar source may be associated with the large-scale weak background photospheric fields observed with the solar magnetograph. It is suggested that there may be a rather continual relation between this solar structure and terrestrial responses, of which the recurring M-Region geomagnetic storms are just the most prominent example.