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Evidence of solar dipole rotation during the reversal in polar cap field polarities. The upper panel shows the latitude of Ulysses during the five years surrounding the recent solar maximum (the year is shown along the top scale). The middle panel contains estimates of the dipole tilt angle obtained from magnetic field measurements by comparing the relative duration of positive and negative sectors during successive Carrington rotations (numbered along the lower scale). The angle...

Solar wind magnetic field and the current sheet

Apart from the diffusion coefficients all cosmic ray transport models also require knowledge of the global structure and geometry of the heliosphere, the heliospheric magnetic field, the current sheet, and the solar wind velocity. Observations by the Pioneer, Voyager, Ulysses and other spacecraft have contributed significantly to understanding the spatial dependence and time evolution of these features. A major contribution was the confirmation that V is not uniform over all latitudes but that...

The Ulysses Picture The Solar Wind In Four Dimensions

When Ulysses was launched some 17 years ago our picture of the solar wind in the heliosphere was that of a ballerina skirt frilled, flapping up and down, complex, yet limited to the vicinity of the ecliptic and the solar equatorial planes. We had very little understanding of the solar wind from polar regions. With Ulysses now on its third polar orbit (and still going strong) this has changed profoundly, and in a way it has become simpler. The structure of the heliosphere, shaped by the solar...

The transport equation

The transport of cosmic rays in the heliosphere is described by Parker's (1965) transport equation. If (r, P, t) is the cosmic ray distribution function with respect Figure 6.9. In comparison with Figure 6.7, the count rate of > 70MeV protons onboard Voyager 1 is inserted. Although Voyager 1 was farther away from the Sun than Voyager 2 in 1987, the intensity is higher at Voyager 2. Since Voyager 1 was at about 30 N and Voyager 2 still close to the ecliptic, the figure illustrates the...

Coronal mass ejections

Coronal mass ejections are spectacular events when seen in white light (e.g., with the LASCO coronagraph on SoHO). But the identification of their interplanetary counterparts, termed ICMEs, is less than a trivial matter and is still something of an art'' (Gosling, 1997). Zurbuchen and Richardson (2006) have compiled a comprehensive table of 23 ICME signatures subdivided into 5 classes magnetic field, plasma dynamics, plasma composition, plasma waves, and energetic particle signatures an image...

Rotation Axis

The current sheet in the heliosphere. In contrast to Figure 4.9, this three-dimensional figure shows the HCS at large distances from the Sun. Two sectors and two solar rotations are shown and the warped current sheet extends out to about 15 AU. The tilt angle between the HCS and the Sun's rotation axis is about 30 a value characteristic of solar minimum. (Jokipii and Thomas, 1981) Figure 4.10. The current sheet in the heliosphere. In contrast to Figure 4.9, this three-dimensional...

The Parker field model

Parker Spiral Equation

Parker has a specific theoretical point of view. He avoids electric fields, E, and currents, j, preferring to work with only the plasma velocity, V, and the magnetic field, B. The rationale is that E can always be derived afterward, if necessary, from E V x B and j can be obtained from j V x B. This approach is basically magnetohydrodynamic (MHD) theory and is widely used by other plasma theorists. It is sometimes referred to as the VB paradigm (Parker, 1996). This approach will be used...

Bt and the Parker spiral angle

Qualitatively, the Parker spiral results from having one end of the open field line being attached to the rotating Sun while the other end is carried off in the solar wind. In a frame of reference that corotates with the Sun, the solar wind streamlines form Archimedes spirals and the magnetic field lines are parallel to the streamlines. In a non-rotating or inertial frame of reference, the solar wind streamlines become radial but the field lines continue to follow an Archimedes spiral....

Hmf At Solar Maximum And Its Solar Cycle Variation

4.7.1 Introduction to solar maximum and the Hale cycle The state of the heliosphere at solar maximum involves profound changes. The simple dipole-like structure is replaced by a more complex structure that is also time-dependent. The solar magnetic dipole gradually weakens and disappears then reappears with the opposite magnetic polarity. This event designates the solar cycle as lasting 22 years, the so-called Hale cycle. The solar field is dominated by smaller scale but much stronger magnetic...

Northsouth Asymmetry Of The Solar Dipole And Its Solar Cycle Variation

Ulysses observations at solar minimum during the first Fast Latitude Scan provided convincing evidence of a significant north-south asymmetry in heliospheric structure. The asymmetry was first seen in measurements of the latitude gradients in galactic and anomalous cosmic rays (Simpson, Zhang, and Bame, 1996 McKibben et al., 1996 Heber et al., 1996). Both data sets revealed flux minima, not on the solar equator, but displaced southward by about 10 . The observations implied a corresponding...