ESTIMATING THE LONG-TERM VARIATIONS OF THE MAGNETOTAIL PRESSURE

Semiannual values of the dynamic pressure and the static pressure in t he solar wind are calculated for 1965-1988. Using the statistical rela tionship between the tail lobe magnetic field and solar wind parameter s, variations of the magnetic field pressure in the magnetic lobe at X = -20 R(E) are predicted. This prediction is compared with various sa tellite observations of the total pressure, although systematic observ ations were not available on a continuous basis. It is predicted that the semiannual value of the magnetotail total pressure exhibits the va riation with a period of approximate to 11 years in close conjunction with the solar cycles. The magnetotail total pressure tends to be mini mum at the maximum epoch of the sunspot number.