The Heliospheric Magnetic Field and the Solar Wind during the Current

Unusual Solar MinimumL. A. Fisk

University of Michigan

The argument for a floor in the heliospheric magnetic field

A single heliospheric current sheet throughout the solar cycle.

Disconnections of open flux can only occur at current sheet; inside Alfven point.

But no observed heat flux dropouts (at time of original theories).

The argument for a floor in the heliospheric magnetic field

The heliospheric magnetic field increases at solar maximum, as seen in first figure, due to CMEs.

The CME magnetic flux does not build up due to interchange reconnection.

CMEs are less common during solar minimum. Heliospheric magnetic field reverts to the component that is not being disconnected at current sheet.

The solar wind from the region of the streamer belt stalks appears to have a distinctive composition; a higher O7 O6

ratio.The wind from the streamer belt comes from a noticeably narrower region in this solar minimum, compared to last solar minimum.Thus, region outside the belt of streamer belt wind is larger in this minimum than in the previous minimum.

The magnetic field strength is down in the current minimum, the area outside the streamer belt wind is up.The total magnetic flux from the region outside the streamer belt is approximately the same in the two minima.

Original concept for transport of open magnetic flux

Revised concept

The transport of magnetic flux through closed field regions by reconnection with loops inherently releases mass into the corona, which can determine the solar wind mass flux.

ρswuswS =Ml Nl

φ34δh2

δt⎛⎝⎜

⎞⎠⎟

BrS

Here, ρsw is the solar wind mass density;usw is the solar wind flow speed;Ml is the mass released from a loop;Nl is the surface number density of loops;φ is the magnetc flux in an independent flux element;δh2 2δt is the diffusion coefficient for random convective motions in the photo-sphere;Br is the radial magnetic field strength ofopen magnetic flux on surface S.

Note linear correlation between mass flux and radial field strength.

The transport of magnetic flux through closed field regions by reconnection with loops inherently displaces the open flux; the relaxation to equilibrium deposits energy in the corona, which can accelerate the solar wind.

usw2

2=

φMl

BorSun

8π⎛⎝⎜

⎞⎠⎟−

GMo

rSun

If we assume that the mass of a loop is proportional to its temperature --the density scale length of a loop is proportional to temperature T. And the loop temperatures determine the coronal electron temperatures -- electron heat flux is large.

Here Bo is the average value of open magnetic flux on the Sun; it is proportional to Brr2 .

usw2

2=

φMl ,ref

Tref

T⎛⎝⎜

⎞⎠⎟

BorSun

8π⎛⎝⎜

⎞⎠⎟−

GMo

rSun

We derive the Gloeckler, et al. (2003) relationship.

Summary

•As far as we can tell from this type of analysis, the solar wind is behaving in the current solar minimum just like in the previous one.

•Carried to the extreme (and unwise to do so), the only difference between the two minima, as far as the solar wind and the heliospheric magnetic field are concerned, is that the streamer belt, and the solar wind and magnetic field connected to it, occurs in a narrower region.

•This lowers the open magnetic field strength in regions outside the narrow streamer belt region, but otherwise the solar wind and the heliospheric magnetic field behave the same in the two minima.