Bulk flow velocities in the solar corona |
| |
| Authors: | D J Lewis G M Simnett |
| |
| Institution: | School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT |
| |
| Abstract: | We present velocity estimates of bulk motions in the solar corona using data from the Large Angle Spectrometric Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory spacecraft ( SOHO ). We describe a new technique which automatically provides a mass-weighted mean velocity profile in an entirely objective fashion without the need for individual event identification. A weighted velocity profile of this kind reflects the motion of the energetically dominant component of the coronal mass ejection (CME) mass spectrum and is of particular interest in consideration of the overall energy budget of the CME process. We consider the mean motion within three latitudinal bands centred at 0°, 20° and 40° over a one-year period around the time of solar minimum. We find terminal velocities within the LASCO field of around 300 km s?1 in all latitude bands but note a latitudinal dependence in CME evolution through the low corona prior to reaching these velocities. We find evidence that ejections in the equatorial zone undergo continuous acceleration whilst at higher latitudes a discrete burst of acceleration is seen to occur at around 4 R⊙ from the Sun's centre with relatively little acceleration thereafter. We also consider the energy deposition rates necessary to generate these profiles. |
| |
| Keywords: | Sun: corona solar–terrestrial relations solar wind |
|
|
