Spatial variation of the solar wind speed in 1976 and 1977

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Spatial variations of the solar wind speed with respect to angular distance from the heliospheric current sheet (HCS) reported by ZHAO and HUNDHAUSEN (J. Geophys. Res., 88,451,1983) and by HAKAMADA and MUNAKATA (J. Geophys. Res., 89,357,1984) are re-examined. During the period considered here, the solar wind reaches higher speeds in magnetic northern higher latitudes than in magnetic southern higher latitudes, as shown by ZHAO and HUNDHAUSEN, although the solar wind speed in magnetic southern middle latitudes has a steeper gradient than in magnetic northern middle latitudes. Further, the solar wind speed is minimum on the HCS. This situation of the solar wind speed can be approximated by a simple functional form of V(km/s)=V_αtanh^2 (C(λ-λ_m))+V_m, where λ is an angular distance of the earth from the HCS, which is measured perpendicular to the HCS. V_α, C, V_m and λ_m are constants determined by the least squares method. V_α and C are 225km/s and 0.032 for λ>0,and 134km/s and 0.061 for λ<0,respectively. V_m and λ_m are equal to 390km/s and 0 degree, respectively.
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