MASS FLUX IN THE ECLIPTIC-PLANE AND NEAR THE SUN DEDUCED FROM DOPPLERSCINTILLATION

During the late declining phase of the solar cycle, the tilt of the so lar magnetic dipole with respect to the Sun's rotation axis leads to l arge-scale organization of the solar wind, such that alternating regio ns of high- and low-speed solar wind are observed in the ecliptic plan e. In this paper, we use Doppler scintillation measurements to investi gate mass flux of these two types of solar wind in the ecliptic plane and inside 0.3 AU, where in situ measurements have not been possible. To the extent that Doppler scintillation reflects mass flux, we find t hat mass flux in high-speed streams: (1) is lower (by a factor of appr oximately 2.2) than the mass flux of the average solar wind in the hel iocentric distance range of 0.3-0.5 AU, (2) is lower still (by as much as a factor of about 4) than the mass flux of the slow solar wind ass ociated with the streamer belt, and (3) appears to grow with heliocent ric distance. These Doppler scintillation results are consistent with the equator to pole decrease in mass flux observed in earlier spectral broadening measurements, and with trends and differences between high - and low-speed solar wind observed by in situ measurements in the ran ge of 0.3-1.0 AU. The mass flux results suggest that the solar wind fl ow in high-speed streams is convergent towards the ecliptic near the S un, becoming less convergent and approaching radial with increasing he liocentric distance beyond 0.3 AU. The variability of mass flux observ ed within equatorial and polar high-speed streams close to the Sun is strikingly low. This low variability implies that, as Ulysses currentl y ascends to higher latitudes and spends more time in the south polar high-speed stream after crossing the heliospheric current sheet, it ca n expect to observe a marked decrease in variations of both mass flux and solar wind speed, a trend that appears to have started already.