The heliospheric magnetic field and the solar wind during the solar cycle

Abstract

Abstract. The heliospheric magnetic field and the solar wind are behaving differently in the current solar minimum, compared to the previous minimum. The radial component of the heliospheric magnetic field, and thus the average value of the component of the solar magnetic field that opens into the heliosphere, the so-called open magnetic flux of the Sun, is lower than it was in the previous solar minimum; in fact, lower than in any previous solar minimum for which there are good spacecraft observations. The mass flux, the ram pressure, and the coronal electron temperature as measured by solar wind charge states are also lower in the current minimum compared to the previous one. This situation provides an opportunity to test some of the concepts for the behavior of the heliospheric magnetic field and the solar wind that have been developed; to improve these theories, and to construct a theory for the solar wind that accounts for the observed behavior throughout the solar cycle, including the current unusual solar minimum.

Nonzero azimuthal magnetic fields at the solar source surface: Extraction, model, and implications

“…They found that very deep minima in SSN are correlated with weak polar fields since the meridional plasma flow speed is around 20 m/s on average and therefore the polar field needs around 20 months to be transported to the equator, not inconsistent with the 20 month time lag between B r ( R s ) and SSN found here. The solar cycle variation of B r ( R s ) in Figure 10 appears to agree with the variation of the radial component of the heliospheric magnetic field measured by Ulysses [ Fisk and Zhao , 2009]. They found that the distance‐normalized radial component varies over the solar cycle, increasing by a factor of ∼2 near solar maximum and being smallest near solar minimum.…”

“…This field component is a measure of the Sun's open magnetic flux. The faster meridional plasma flow in the first half of solar cycle 23 and the slower flow in the second half in models 2001, Fisk andZhao, 2009;Nandy et al, 2011] are consistent with a larger average magnitude of B f (R s ) from solar minimum to just after solar maximum, and then a smaller average value for the rest of the cycle.…”

Nonzero azimuthal magnetic fields at the solar source surface: Extraction, model, and implications

“…They found that very deep minima in SSN are correlated with weak polar fields since the meridional plasma flow speed is around 20 m/s on average and therefore the polar field needs around 20 months to be transported to the equator, not inconsistent with the 20 month time lag between B r ( R s ) and SSN found here. The solar cycle variation of B r ( R s ) in Figure 10 appears to agree with the variation of the radial component of the heliospheric magnetic field measured by Ulysses [ Fisk and Zhao , 2009]. They found that the distance‐normalized radial component varies over the solar cycle, increasing by a factor of ∼2 near solar maximum and being smallest near solar minimum.…”

“…This field component is a measure of the Sun's open magnetic flux. The faster meridional plasma flow in the first half of solar cycle 23 and the slower flow in the second half in models 2001, Fisk andZhao, 2009;Nandy et al, 2011] are consistent with a larger average magnitude of B f (R s ) from solar minimum to just after solar maximum, and then a smaller average value for the rest of the cycle.…”

Modeling 1 AU solar wind observations to estimate azimuthal magnetic fields at the solar source surface

“…The solar cycle variation of B r ( R s ) appears to agree with the variation of the radial magnetic component measured by Ulysses [ Fisk and Zhao , 2009]. They found that the distance‐normalized radial component varies over the solar cycle, increasing by a factor of ≈2 near solar maximum and being smallest near solar minimum.…”

Association of solar wind proton flux extremes with pseudostreamers

“…The extreme‐high‐proton‐flux data (red) peak at a Br flux value greater than the rest of the solar wind (green). This is consistent with the theoretical argument that the amount of the open magnetic flux in a solar wind flux tube should be proportional to the solar wind mass flux along it [ Fisk and Zhao , ; Zhao and Fisk , ]. Also, this is probably the consequence of the pile‐up effect in the interface between fast and slow wind, i.e., corotating interaction regions, where fast wind pushes the slow wind in front of it, making both the plasma flux and B‐field compressed.…”

Nonzero azimuthal magnetic fields at the solar source surface: Extraction, model, and implications

“…They found that very deep minima in SSN are correlated with weak polar fields since the meridional plasma flow speed is around 20 m/s on average and therefore the polar field needs around 20 months to be transported to the equator, not inconsistent with the 20 month time lag between B r ( R s ) and SSN found here. The solar cycle variation of B r ( R s ) in Figure 10 appears to agree with the variation of the radial component of the heliospheric magnetic field measured by Ulysses [ Fisk and Zhao , 2009]. They found that the distance‐normalized radial component varies over the solar cycle, increasing by a factor of ∼2 near solar maximum and being smallest near solar minimum.…”

“…This field component is a measure of the Sun's open magnetic flux. The faster meridional plasma flow in the first half of solar cycle 23 and the slower flow in the second half in models 2001, Fisk andZhao, 2009;Nandy et al, 2011] are consistent with a larger average magnitude of B f (R s ) from solar minimum to just after solar maximum, and then a smaller average value for the rest of the cycle.…”

Modeling 1 AU solar wind observations to estimate azimuthal magnetic fields at the solar source surface

“…The solar cycle variation of B r ( R s ) appears to agree with the variation of the radial magnetic component measured by Ulysses [ Fisk and Zhao , 2009]. They found that the distance‐normalized radial component varies over the solar cycle, increasing by a factor of ≈2 near solar maximum and being smallest near solar minimum.…”

Association of solar wind proton flux extremes with pseudostreamers

“…The extreme‐high‐proton‐flux data (red) peak at a Br flux value greater than the rest of the solar wind (green). This is consistent with the theoretical argument that the amount of the open magnetic flux in a solar wind flux tube should be proportional to the solar wind mass flux along it [ Fisk and Zhao , ; Zhao and Fisk , ]. Also, this is probably the consequence of the pile‐up effect in the interface between fast and slow wind, i.e., corotating interaction regions, where fast wind pushes the slow wind in front of it, making both the plasma flux and B‐field compressed.…”

Nonzero azimuthal magnetic fields at the solar source surface: Extraction, model, and implications

“…They found that very deep minima in SSN are correlated with weak polar fields since the meridional plasma flow speed is around 20 m/s on average and therefore the polar field needs around 20 months to be transported to the equator, not inconsistent with the 20 month time lag between B r ( R s ) and SSN found here. The solar cycle variation of B r ( R s ) in Figure 10 appears to agree with the variation of the radial component of the heliospheric magnetic field measured by Ulysses [ Fisk and Zhao , 2009]. They found that the distance‐normalized radial component varies over the solar cycle, increasing by a factor of ∼2 near solar maximum and being smallest near solar minimum.…”

“…This field component is a measure of the Sun's open magnetic flux. The faster meridional plasma flow in the first half of solar cycle 23 and the slower flow in the second half in models 2001, Fisk andZhao, 2009;Nandy et al, 2011] are consistent with a larger average magnitude of B f (R s ) from solar minimum to just after solar maximum, and then a smaller average value for the rest of the cycle.…”

Modeling 1 AU solar wind observations to estimate azimuthal magnetic fields at the solar source surface

“…The solar cycle variation of B r ( R s ) appears to agree with the variation of the radial magnetic component measured by Ulysses [ Fisk and Zhao , 2009]. They found that the distance‐normalized radial component varies over the solar cycle, increasing by a factor of ≈2 near solar maximum and being smallest near solar minimum.…”

Association of solar wind proton flux extremes with pseudostreamers

“…The extreme‐high‐proton‐flux data (red) peak at a Br flux value greater than the rest of the solar wind (green). This is consistent with the theoretical argument that the amount of the open magnetic flux in a solar wind flux tube should be proportional to the solar wind mass flux along it [ Fisk and Zhao , ; Zhao and Fisk , ]. Also, this is probably the consequence of the pile‐up effect in the interface between fast and slow wind, i.e., corotating interaction regions, where fast wind pushes the slow wind in front of it, making both the plasma flux and B‐field compressed.…”