Project: Statistical detection of propagating waves in the Solar Atmosphere
Background:
Evidence for waves in the solar atmosphere comes from
meaurements of intensities in a wide range of electromagnetic spectrum
including visible, ultraviolet, X-ray, and radio in addition to Doppler
oscillations in visible and ultraviolet light given off by
different solar structures at chromospheic, transition region and
coronal temperatures.
Results:
Using the temopral series data from the SUMER/SoHO, we studied
the oscillation found in transition region (N IV 765) and lower coronal
(Ne VIII 770) lines in on-disk both polar regions. We have
identified the compressional waves in network and internetwork regions
of both the pCHs. Measurements of phase delay between those two line
pairs reveals that the measured phases tend to line up along diagonal
lines corresponding to fixed time delays. From the orientation of the
slops of these diagonal lines, we can conclude the direction of
propagation of these waves. Here in this case, we have reported the
upward progating waves in network region and in internetwork region we
have reported the both upward and downword propagation waves refer
fig.1. From the estimate of the formation heights of the lines, and
using the measured time delays, we had estimated the propagation speed
for the line pair. The estimated speed indicates that the waves
producing these observed phase delays are slow magneto-acoustic waves
propagating at speed very less than the sound speed. By comparing with
the previous studies, here we have hypothesise that as waves propagates
upward it's speed increases with height in the solar atmosphere.
Figure 1: Phase delays measured between the oscillations in the
spectroscopic line pair for the dark locations of pCH. The phases in radiant flux
oscillations are shown in the grey circle symbols while that in LOS velocities are
shown as the black circle symbols. Overplotted on each figure are black
parallel lines, corresponding to fixed time delays. The inclined parallel
straight lines indicate the presence of both upwardly and downwardly propagating waves. Representative errors are indicated by the error bars.