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C. T. Russell, Z. J. Yu, K. K. Khurana, S. P. Joy, M. G. Kivelson (IGPP, UCLA)
Singular value decomposition has been applied to the magnetic measurements obtained from the Galileo orbiter over the period from 1995 to 2001. This analysis is used to determine both the best values of the Legendre coefficients as well as which coefficients can be accurately determined. The Galileo measurements are available early in the mission only outside 9 RJ. Beginning in mid-1999 they are available to 5.9 RJ. Galileo orbits Jupiter close to the rotational equator. The secular variation of the jovian magnetic field during the period 1995 to 2001 is too small to be detected just as the secular variation could not be detected in the interval between Pioneer II and Voyager I [Connerney and Acuna, 1982]. However, comparison of the Galileo and Pioneer/Voyager data shows a significant change in the period between 1977 and the present. Using the 06 model of Connerney [1992] we find a 0.3 degree increase in the tilt of the dipole and an increase of the dipole moment of about 1.5%. Using the data obtained on orbits whose perijove radius was close to the orbit of Io we can obtain estimates of the secular variation of the quadrupole coefficients. Of the five quadrupole coefficients four of them appear to have changed significantly. The octupole secular variation cannot be measured at this time.