J. C. Cain

The magnetic field in the pile-up region at Mars, and its variation with the solar wind

[1] The magnetic measurements from the Mars Global Surveyor satellite are used to study the magnetic field on the Martian dayside, and its variation with the solar wind. Because of the lack of solar wind measurements near Mars, solar wind measurements near Earth during a period centered on a Mars-Earth conjunction are used. Concurrent variations atMarsandEarthrelatedtotheinterplanetarysector-structure and dynamic pressure variations are demonstrated. The study is confined to the northern hemisphere of Mars in regions where the crustal anomalies are weak. Here we find a close association between the solar wind dynamic pressure and the magnetic pressure in the pile-up region, and also a strong asymmetry with the Interplanetary magnetic field (IMF) By-component, probably related to solar wind pick-up of planetary ions. INDEX TERMS: 2780 Magnetospheric Physics: Solar wind interactions with unmagnetized bodies; 5443 Planetology: Solid Surface Planets: Magnetospheres (2756); 2134 Interplanetary Physics: Interplanetary magnetic fields; 6225 Planetology: Solar SystemObjects: Mars.Citation: Vennerstrom,

Geomagnetic secular variation 1995–2000

[1] A study was done to determine the difficulty of obtaining a field model for 1995 using magnetic observations taken since that epoch. Orsted vector data taken from 1999 to 2001 in conjunction with scalar data from all surface ship surveys and secular variation data from magnetic observatories taken since 1995 were utilized. Spherical harmonic models were constructed for the interval from 1995 through early 2001 using selected, magnetically quiet, nighttime intervals. Corrections were made for Dst variations assuming a constant, i.e., ratio (0.28). The data were corrected for magnetic anomalies using Magsat coefficients (m102389) above n = 21. In order to compute secular change data, some observatory hourly values were reduced to remove the annual variations, which ranged up to 40 nT at a few stations. Coefficients were adjusted up to n = 21 in spatial terms, n = 13 in linear secular variation terms, and n = 12 in parabolic secular variation terms. There was also a 30 nT, n = 1 external term. Component maps of this model (f052101) truncated to n = 10 were compared with the IGRF2000 and generally found to be within 20 nT at the surface except for a 110 nT difference in the northern polar region. The model agreed with the OIFM at satellite altitude to within a few nanoteslas except for a few tens of nanoteslas at the poles. Model differences at 1995 from the IGRF1995 peaked over 800 nT in the region west of South America. However, statistical estimates in this region and epoch show model errors up to several hundred nanoteslas. Use of a linear model or one truncated to lower degree is seen to reduce these differences and maximum errors at 1995, but at the expense of less accuracy elsewhere. Besides the large differences from the 1995 IGRF it was also noted that there are a number of areas where the field changes require parabolic coefficients, even over this short a time span.

A text for planetary geology

In this article I review my findings from a search for a suitable text to use in an introductory undergraduate course in planetary geology for nonscience students. I hope to elicit comments from others with a similar need. The books from which I have drawn material for my course are listed below. I first used Hamblin and Christiansen [1991] as the required text but had to switch to a simpler one and chose Wagners [1991] since it was the most recently published. Morrison and Owens 1987 edition was considered, but it would have required too much additional material to bring it up to date. (It is scheduled for a new revision in September 1993). There are many excellent older books that are not listed here, including those in astronomy, which include planetary science in some chapters.

The Magnetic Field of the Earth's Lithosphere: The Satellite Perspective

During the planning stages of the World Magnetic Survey in the early 1960s, geologists and geophysicists had no inkling that crustal magnetic anomalies might one day be observed from space. The appearance of The Magnetic Field of the Earths Lithosphere: The Satellite Perspective is a welcome testimony to how far that science has advanced. However, although much progress has been made in understanding features discovered by the several spacecraft that have measured geomagnetic fields in low-Earth orbit, the contents of this book make it clear that many mysteries are yet to be solved.

Taking a Look at Introductory Planetary Books

Introductory astronomy courses are far more popular with students than their planetary science counterparts. This is not surprising: astronomy instructors have access to several superb texts with color illustrations, while introductory planetary science books struggle to afford even a few pages of color plates. At present the most attractive and current text material for nonscience students remains the planetary chapters in the 1995 editions of Kalers Astronomy (Harper Collins); Morrison, Wolff, and Fraknois Abells Exploration of the Universe (Saunders College Publishing); and Chaisson and McMillans Astronomy (Prentice Hall). Even so, the few chapters in each of these texts cannot serve a complete course in planetary science. “Space” remains high on the list of student interest. There should be a good market for well-written texts for both the nonscience students meeting liberal studies science requirements and science majors interested in planetary geophysics or geology.

First SEDI Symposium

How should the seismic irregularities observed in the lowermost 100–200 km of the mantle (the D″ layer) be partitioned between thermal and chemical heterogeneity, anisotropy, and core-mantle boundary (CMB) topography? How smooth is the core-mantle boundary? Do mantle convection and the thickness of D″ regulate the core geodynamo? How large is the outward temperature fall across the D″ layer? What is the temperature within the core? At what depths, or range of depths, do the vigorous upwellings and downwellings, demanded by dynamo action, occur within the outer core? Are seismically excited internal oscillations of the outer core observationally detectable in surface superconducting gravimeter records? These constitute an illustrative sample of the questions discussed by almost 200 scientists at the first Study of the Earths Deep Interior (SEDI) symposium entitled “Structure and Dynamics of the Core and Adjacent Mantle,” held on the Costa Brava of Spain, at Blanes from June 23–25, 1988, in conjunction with the 17th International Conference of the Committee on Mathematical Geophysics. SEDI is a new committee of the International Union of Geodesy and Geophysics, created at the Vancouver General Assembly in August 1987. This symposium and the SEDI secretariat have been sponsored by the National Science Foundation with help from the National Aeronautics and Space Administration. The following is a report of the SEDI symposium, which consisted of 13 oral presentations, 48 posters, and 5 open discussion periods during which the posters and general issues were discussed.