Does Adding Solar Wind Poynting Flux Improve the Optimum Solar Wind‐Magnetosphere Coupling Function?. Issue 7 (22nd July 2019)

• Record Type: Journal Article
• Authors: Lockwood, Mike
• Is Part Of: Journal of geophysical research. Volume 124:Issue 7(2019)
• Page Start: 5498
• Page End: 5515
• Publication Date: 2019-07-22
• Subjects: solar wind -- energy flow -- geomagnetic disturbance -- Poynting flux -- coupling function; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2019JA026639
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: We study the contribution of the solar wind Poynting flux S → sw to the total power input into the magnetosphere. The dominant power delivered by the solar wind is the kinetic energy flux of the particles, which is larger than S sw by a factor of order M A 2, where M A is the Alfvén Mach number. The currents J → flowing in the bow shock and magnetosheath and the electric field E → of the solar wind give regions where J → . E → < 0, which are sources of Poynting flux, generated from the kinetic energy flux. For southward interplanetary magnetic field, E → is duskward and the currents in the high‐latitude tail magnetopause are also sources of Poynting flux. We show transfer of kinetic energy into the magnetosphere is less efficient than direct entry of S → sw by a factor M A . Because M A is typically of order 10, this means that although the power density in the solar wind due to S → sw is typically only 1%, it is responsible for of order 10% of the energy input to the magnetosphere. To investigate the effect of this, we add a term to the solar wind‐magnetosphere energy coupling function that allows for S → sw and that increases the correlation with the geomagnetic am index for 1995–2017 (inclusive) from 0.908 to 0.924 for 1‐day averages and from 0.978 to 0.979 for annual means. The increase for means on daily or smaller timescales is a small improvement but is significant (at over the 3 σ level), whereas the improvement for annual or Carrington rotation means is not significant. Plain Language Summary: Space weather is caused by energy extracted from the solar wind by the magnetosphere, the volume of space surrounding the Earth that is dominated by Earth's magnetic field. That energy arrives in two main forms in the solar wind: the kinetic energy of the particle flow and an electromagnetic energy flux. The most successful predictors of space disturbances have considered only the kinetic energy flux. The paper shows typically 10% of the power input comes from the electromagnetic energy flux in the solar wind and allowing for this can make a small, but significant, improvement to our ability to predict terrestrial space weather disturbances. Key Points: Solar wind Poynting flux is about 1% of the total solar wind energy flux but provides typically 10% of the power entering the magnetosphere Equations for adding solar wind Poynting flux to kinetic energy flux are presented Allowing for solar wind Poynting flux gives correlations with geomagnetic activity that are slightly but significantly raised