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High-frequency oscillations in a solar active region coronal loop

Mathioudakis, M.; Keenan, F. P.; Phillips, K. J. H. +6 more

The Solar Eclipse Corona Imaging System (SECIS) was used to record high-cadence observations of the solar corona during the total solar eclipse of 1999 August 11. During the 2min 23.5s of totality, 6364 images were recorded simultaneously in each of the two channels: a white light channel, and the Fexiv (5303Å) `green line' channel (T~2MK). Here w…

Solar-cycle variation of the sound-speed asphericity from GONG and MDI data 1995-2000

Howe, R.; Hill, F.; Schou, J. +3 more

We study the variation of the frequency splitting coefficients describing the solar asphericity in both GONG and MDI data, and use these data to investigate temporal sound-speed variations as a function of both depth and latitude during the period 1995-2000 and a little beyond. The temporal variations in even splitting coefficients are found to be…

The phenomenology of solar-cycle-induced acoustic eigenfrequency variations: a comparative and complementary analysis of GONG, BiSON and VIRGO/LOI data

Chaplin, W. J.; Elsworth, Y.; Appourchaux, T. +2 more

We use high-quality helioseismic data collected by three different observational programmes during the declining phase of activity cycle 22,Q7 and a substantial portion of the rising phase of the current cycle (23), to study the phenomenological nature of the cycle-induced (centroid) eigenfrequency variations. We have analysed the frequency depend…

Changes to low-ll solar p-mode frequencies over the solar cycle: correlations on different time-scales

Chaplin, W. J.; Elsworth, Y.; Isaak, G. R. +3 more

We have studied variations in the frequencies of low-l solar p modes through the analysis of nine years of helioseismic data collected by the Birmingham Solar Oscillations Network (BiSON)†. This is the first time that such a long data set has been explored with the extra accuracy afforded by fitting the modes to asymmetric profiles. The epoch cove…

The anomalous intensities of helium lines in a coronal hole

Jordan, C.; Macpherson, K. P.; Smith, G. R.

Observations made at the quiet Sun-centre with the Coronal Diagnostic Spectrometer (CDS) and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instruments on the Solar and Heliospheric Observatory (SOHO) have shown that the intensities of the resonance lines of HeI and HeII are significantly larger than predicted by emission measure dist…