Abstract. This study examines solar wind plasma and magnetic field observations from Ulysses' first full polar orbit in order to characterize the high-latitude solar wind under conditions of decreasing and low solar activity. By comparing observations taken over nearly all hellolatitudes and two different intervals covering the same radial distances, we are able to separate the radial and latitudinal variations in the solar wind. We find that once the radial gradients are removed, none of the high-latitude solar wind parameters show much latitudinal variation, indicating that the solar wind emanating from the polar coronal holes is extremely uniform. In addition, by examining nearly 6 years of data starting in the declining phase of the last solar cycle and extending through the most recent solar minimum, we are able to address hemispheric asymmetries in the observations. We find that these asymmetries are most likely driven by differences in the solar wind source over the solar cycle and indicate that more energy goes into the polar solar wind during the declining phase of the solar cycle than around minimum. Because the mass flux is larger in the declining phase while the speeds are very similar, we conclude that this energy is introduced at an altitude below the solar wind acceleration critical point. Finally, we provide details of the statistics of over 20 solar wind parameters so that upcoming observations from Ulysses' second polar orbit, during much more active times on the Sun, can be readily compared to the quieter first orbit results. IntroductionThe Ulysses spacecraft recently completed its first full, nearly polar orbit of the Sun. This orbit allowed Ulysses to measure directly the solar wind plasma and field properties of the high-latitude heliosphere for the first time. Ulysses data have already led to a host of new discoveries which defied our pre-Ulysses understanding of the heliosphere and have al- As an addition to Plate 1, we have superposed a trace of the logarithm of the proton density (green line) on the original polar plot. Owing to the large variability in the solar wind density, we smoothed the density observations for this summary plot using a one-half solar rotation-long running boxcar average. In addition, because of the large variation in radial distance, R, from the Sun over Ulysses' orbit, we have scaled the densities to their 1 AU values by multiplying by R 2, where R is in AU. Plate 1 clearly shows that the density is higher at 10,419

[1] Observations of solar wind from both large polar coronal holes (PCHs) during Ulysses' third orbit showed that the fast solar wind was slightly slower, significantly less dense, cooler, and had less mass and momentum flux than during the previous solar minimum (first) orbit. In addition, while much more variable, measurements in the slower, in-ecliptic wind match quantitatively with Ulysses and show essentially identical trends. Thus, these combined observations indicate significant, long-term variations in solar wind output from the entire Sun. The significant, long-term trend to lower dynamic pressures means that the heliosphere has been shrinking and the heliopause must be moving inward toward the Voyager spacecraft. In addition, our observations suggest a significant and global reduction in the mass and energy fed in below the sonic point in the corona. The lower supply of mass and energy may result naturally from a reduction of open magnetic flux during this period. Citation: McComas, D.

The term "magnetic hole" has been used to denote isolated intervals when the magnitude of the interplanetary magnetic field drops to a few tenths, or less, of its ambient value for a time that corresponds to a linear dimension of tens to a few hundreds of proton gyro-radii. Data obtained by the Ulysses magnetometer and solar wind analyzer have been combined to study the properties of such magnetic holes in the solar wind between 1 AU and 5.4 AU and to 23 ø south latitude. In order to avoid confusion with decreases in field strength at interplanetary discontinuities, the study has focused on linear holes across which the field direction changed by less than 5 ø . The holes occurred preferentially, but not without exception, in the interaction regions on the leading edg es of highspeed solar wind streams. Although the plasma surrounding the holes was generally stable against the mirror instability, there are indications that the holes may have been remnants of mirror-mode structures created upstream of the points of observation. Those indications include the following:(1) For the few holes for which proton or alpha-particle pressure could be measured inside the hole, the ion thermal pressure was always greater than in the plasma adjacent to the holes. (2) The plasma surrounding many of the holes was marginally stable for the mirror mode, while the plasma environment of all the holes was significantly closer to mirror instability than was the average solar wind. (3) The plasma containing trains of closely spaced holes was closer to mirror instability than was the plasma containing isolated holes. (4) The near-hole plasma had much higher ion [5 (ratio of thermal to magnetic pressure) than did the average solar wind. (5) Near the holes, T.•/T• • tended to be either >1 or larger than in the average wind. (6) The proton and alpha-particle distribution functions measured inside the holes occasionally exhibited the flattened phase-space-density contours in space found in some numerical simulations of the mirror instability. 130 s, with a median of 50 s, corresponding to thickness in the solar radial direction of-200 proton gyro radii. Nine of the holes showed large angle changes with evidence for sub-Alfv6nic instreaming and field reconnection. Eight of the 28 Paper number 94JA01977. 0148-0227/94/94JA-01977 $05.00 holes, however, exhibited little or no directional change; such structures were named linear holes. The linear holes were observed in regions of high plasma I• = nkT/(B2/8•), and all but one of them occun'ed on or near the leading edges of high-speed streams in the solar wind. Turner et al. suggested that the linear holes, which could not have been caused by reconnection, resulted from the diamagnetic response of the field to local plasma inhomogeneities, but the cause of the inhomogeneities remained an open question. In a follow-on study, Fitzenreiter and Burlaga [1978] analyzed magnetic holes observed by both the IMP 5 and IMP 6 spacecraft. Combination of the data from the two spacecraft demonstrated consisten...

[1] We report an analysis of the proton temperature anisotropy evolution from 0.3 to 2.5 AU based on the Helios and Ulysses observations. With increasing distance the fast wind data show a path in the parameter space (b kp , T ?p /T kp ). The first part of the trajectory is well described by an anticorrelation between the temperature anisotropy T ?p /T kp and the proton parallel beta, while after 1 AU the evolution with distance in the parameter space changes and the data result in agreement with the constraints derived by a fire hose instability. The slow wind data show a more irregular behavior, and in general it is not possible to recover a single evolution path. However, on small temporal scale we find that different slow streams populate different regions of the parameter space, and this suggests that when considering single streams also the slow wind follows some possible evolution path. Citation: Matteini, L., S. Landi, P. Hellinger,

[1] Ulysses is now completing its second solar polar orbit, dropping back down in latitude as the Sun passes through its post-maximum phase of the solar cycle. A mid-sized circumpolar coronal hole that formed around solar maximum in the northern hemisphere has persisted and produced a highly inclined CIR, which was observed from $70°N down to $30°N. We find that the speed maxima in the high-speed streams follow the same slow drop in speed with decreasing latitude observed in the large polar coronal holes around solar minimum. These results suggest a solar wind acceleration effect that is related to heliolatitude or solar rotation. We also find that the solar wind dynamic pressure is significantly lower in the post-maximum phase of this solar cycle than during the previous one, indicating that while the heliosphere is larger than near solar minimum, it should be smaller than during or after the previous maximum.