THE NEAR-EARTH MAGNETIC FIELD FROM MAGNETOSPHERIC AND QUIET-DAY IONOSPHERIC SOURCES AND HOW IT IS MODELED

Abstract Early attempts to model fields from sources in the magnetosphere during magnetically quiet times were unsuccessful. This is attributed to the presence of fields from lithospheric sources and to deficiencies in the data distribution. The availability of data from the Magsat satellite allowed definitive determination of the first-degree field from magnetospheric sources. Temporal variation of those fields on time scales of hours to a few years was implemented by use of a proxy function thought to mimic that variation. The Dst index was chosen as the proxy function. Extension of determination of the first-degree magnetospheric field to earlier times, namely to 1900, is accomplished first by use of the annual average of the aa index as a proxy function and then by use of cubic B-splines as temporal basis functions. The model first-degree field is well correlated with the annual sunspot number, both in its general level changes and in its detailed year-to-year variation. The correlation coefficient of the year-to-year variation of the first-degree, zero order, external term with the annual sunspot number is 0.77 when the external term lags the sunspot number by 2 years. Another extension of the results made possible by the Magsat data is simultaneous determination of a model of the fields from the magnetosphere, the ionosphere, and internal to the Earth. In this case, data from the Magsat and POGO satellites and magnetic observatory hourly mean and annual mean data were analyzed together. Though still in an experimental stage, these models are shown to fit all the data closely and to be able to readily isolate the fields according as the source is in the magnetosphere, ionosphere, or Earth.

[1]  T. Sabaka,et al.  Uncertainty estimates in geomagnetic field modeling , 1989 .

[2]  L. A. Bauer.  Chief results of a preliminary analysis of the Earth's magnetic field for 1922—No. 1. , 1923 .

[3]  R. Langel,et al.  Geodynamics branch data base for main magnetic field analysis , 1991 .

[4]  Fischbach,et al.  New geomagnetic limits on the photon mass and on long-range forces coexisting with electromagnetism. , 1994, Physical review letters.

[5]  G. Rangarajan.  Indices of geomagnetic activity. , 1989 .

[6]  G. L. Trigg,et al.  Encyclopedia of Applied Physics , 1994 .

[7]  W. H. Campbell.  The regular geomagnetic-field variations during quiet solar conditions. , 1989 .

[8]  T. Sabaka,et al.  The geomagnetic field 1900-1995, including the large-scale field from magnetospheric sources, and the NASA candidate models for the 1995 revision of the IGRF , 1997 .

[9]  D. Stern,et al.  Are existing magnetospheric models excessively stretched , 1993 .

[10]  P. Mayaud,et al.  Derivation, Meaning, and Use of Geomagnetic Indices , 1980 .

[11]  D. Barraclough.  Spherical harmonic models of the geomagnetic field , 1978 .

[12]  R. H. Estes,et al.  Large‐scale, near‐field magnetic fields from external sources and the corresponding induced internal field , 1983 .

[13]  J. Cain.  MODELS OF THE EARTH'S MAGNETIC FIELD. , 1966 .

[14]  J. Cain.  Geomagnetic models from satellite surveys. , 1971 .

[15]  R. Langel,et al.  Comparisons of magnetic anomalies of lithospheric origin measured by satellite and airborne magnetometers over western Canada , 1980 .

[16]  T. Rikitake.  Electromagnetism and the earth's interior , 1966 .

[17]  R. E. Sweeney,et al.  Asymmetric ring current at twilight local time , 1971 .

[18]  J. Cain,et al.  Geomagnetic survey by the polar-Orbiting Geophysical Observatories. , 1971 .

[19]  N. Olsen.  Magnetospheric contributions to geomagnetic daily variations , 1996 .

[20]  A. T. Price,et al.  The Electric and Magnetic State of the Interior of the Earth, as Inferred from Terrestrial Magnetic Variations , 1930 .

[21]  P. Mayaud,et al.  The aa indices: A 100-year series characterizing the magnetic activity , 1972 .

[22]  Robert A. Langel,et al.  The near‐Earth magnetic field at 1980 determined from Magsat data , 1985 .

[23]  John Tyndall,et al.  Scientific memoirs, selected from the transactions of foreign academies of science and learned societies, and from foreign journals , 1837 .

[24]  T. Speiser,et al.  The neutral sheet in the geomagnetic tail - Its motion, equivalent currents, and field line connection through it. , 1967 .

[25]  G. D. Mead,et al.  Initial geomagnetic field model from Magsat vector data , 1980 .

[26]  R. Langel.  Processing of the total field magnetometer data from the OGO-2 satellite , 1967 .

[27]  Robert A. Langel,et al.  A Proposed Model for the International Geomagnetic Reference Field-1965 , 1967 .

[28]  G. D. Mead,et al.  Some new methods in geomagnetic field modeling applied to the 1960-1980 epoch. , 1982 .

[29]  Christopher T. Russell,et al.  GEOPHYSICAL COORDINATE TRANSFORMATIONS , 1971 .

[30]  Robert A. Langel,et al.  A geomagnetic field spectrum , 1982 .

[31]  B M McCormac,et al.  Radiation Trapped in Earth's Magnetic Field. , 1965, Science.

[32]  N. Tsyganenko.  A magnetospheric magnetic field model with a warped tail current sheet , 1989 .

[33]  R. Langel.  Near‐Earth magnetic disturbance in total field at high latitudes 1. Summary of data from Ogo 2, 4, and 6 , 1974 .