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Period persistence of long period oscillations in sunspots  

Nicky Chorley   Submitted: 2011-04-06 04:12

Long period oscillations in the microwave radiation intensity generated over the sunspot of NOAA AR 10330 are studied with the Nobeyama Radioheliograph as the sunspot passes over the solar disk, over the course of 9 days (06−15 April 2003). Periodogram, Fourier and global wavelet analyses reveal the presence of a significant oscillatory component in the range P ≈  50−120 min over the course of the observations. The spectral amplitudes of five significant Fourier components in the range P = 50−150 min are also seen to be stable over the observations, when the data are not affected by changes in magnetic configuration in the region. The ground-based nature of the instrument naturally introduces long data gaps in such long duration observations and the presence of the gaps does not allow any conclusion as to the stability of the phases of the oscillations. As a model to explain the persistence of the dominant long periods, a simple oscillator with a nonlinear driving term is proposed. The spectral difference between distinct peaks within, e.g. the 3 min spectral band, is expected to be able to resonate with the long period one hour oscillations.


Authors: N. Chorley, C. Foullon, B. Hnat, V. M. Nakariakov & K. Shibasaki
Projects: Nobeyama Radioheliograph

Publication Status: A&A, 529, A123.
Last Modified: 2011-04-15 08:06
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Long period oscillations in sunspots  

Nicky Chorley   Submitted: 2010-02-11 03:46

Long period oscillations of the gyroresonant emission from sunspot atmospheres are studied. Time series data generated from the sequences of images obtained by the Nobeyama Radioheliograph operating at a frequency of 17 GHz for three sunspots have been analysed and are found to contain significant periods in the range of several tens of minutes. Wavelet analysis shows that these periods are persistent throughout the observation periods. The presence of the oscillations is confirmed by several methods (periodogram, wavelets, Fisher randomisation and empirical mode decomposition). Spatial analysis using the techniques of period, power, correlation and time lag mapping reveals regions of enhanced oscillatory power in the umbral regions. Also seen are two regions of coherent oscillation of about 25 pixels in size, that oscillate in anti-phase with each other. Possible interpretation of the observed periodicities is discussed, in terms of the shallow sunspot model and the leakage of the solar g-modes.

Authors: N. Chorley, B. Hnat, V. M. Nakariakov, A. R. Inglis and I. A. Bakunina
Projects: None

Publication Status: A&A, accepted
Last Modified: 2010-02-11 13:33
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Period persistence of long period oscillations in sunspots
Long period oscillations in sunspots

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