View Full Version : Solar Wind analog of luminosity

2009-Nov-29, 10:53 PM
The Sun's luminosity is typically given as around 3.839 1026 W.

Is there a power equivalent term for the Solar Wind, and would this include, and/or be affected buy, the Sun's magnetic field? Is it meaningful to talk about a "solar wind flux", an overall "solar wind energy"?

2009-Nov-30, 03:14 AM
I can't claim expertise on this subject, but I believe hour to hour variation in the solar wind flux are at up to 2 to 1, while luminosity variation are perhaps 01%. The Sun's magnetic field, CME = coronal mass ejections and sun spots are three reasons for the solar wind variations.
I can think of no reason total solar wind output can not be expressed as a percent of the luminosity and in watts. I'll await eagerly some numbers.
My guess is: not appropriate to express the average magnetic field in watts, nor to add it to the solar wind watts, but it does appear that a qualified comparison can be made, even though the magnetic field does not typically decrease as the square of the distance. Neil

2009-Nov-30, 03:05 PM
I can't imagine how any total wattage value could be calculated given so very few satellites around the Sun.

The flux important to Earth can be found at various web sites like www.spaceweather.com

2009-Nov-30, 05:00 PM
I would think that different researchers would find different measurements to be useful: mass, momentum, and energy fluxes could each have their uses, although I suspect that many researchers would be more concerned with the flux that is measured in the plane of the ecliptic or the flux in the locale of the Earth than with average over a sphere of some radius.

2009-Nov-30, 06:02 PM
Ah, iantresman, always good for some difficult questios!

There is the solar wind, at the moment at ~300 km/s and a density of ~0.2 cm-3, basically protons (also to keep it simple). Naturally, we can calculate the kinetic energy of 1 these protons:

Ek(p) = 0.5 mp (300e3)2

This only holds for the "equatorial" solar wind. We all remember this figure by Ulysses (http://science.nasa.gov/headlines/y2008/images/northpole/swoops_wind.jpg), so the wasp-hips of the solar wind in the topleft panel. With that we can define a surface, e.g. at the Earth's orbit through which this solar wind blows.

Basically we can then calculate the kinetic energy flux of the solar wind through this surface. A similar thing can be done for the top and the bottom part of the fast solar wind.

Similarly one can calculate the magnetic energy of the solar wind, for which one has to take a constant average value Bsw and the energy is given by Bsw2/4μ0, or another approach could be to take the Poynting vector of the solar wind (E x B) in the Earth's frame and then do the same thing once more as with the kinetic energy flux.

Just a way I think one could calculate this.