Projects per year
Abstract
Context. In transverse coronal loop oscillations, two periodicities have been measured simultaneously and are interpreted as the fundamental kink mode (with period P1) and the first harmonic ( with period P2). Deviations of the period ratio P1/2P(2) from unity provide information about the extent of longitudinal structuring within the loop.
Aims. Here we develop an analytical approximation that describes the shift in P1/2P(2) in terms of the ratio L/Lambda(c) of the length 2L of a coronal loop and the density scale height Lambda(c).
Methods. We study the MHD wave equations in a low beta plasma using the thin tube approximation. Disturbances are described by a differential equation which may be solved for various equilibrium density profiles, obtaining dispersion relations in terms of Bessel functions. These dispersion relations may be used to obtain analytical approximations to the periods P1 and P2. We also present a variational approach to determining the period ratio and show how the WKB method may be used.
Results. Analytical approximations to the period ratio P1/2P(2) are used to shed light on the magnitude of longitudinal structuring in a loop, leading to a determination of the density scale height. We apply our formula to the observations in Verwichte et al. (2004) and Van Doorsselaere et al. (2007), obtaining the coronal density scale height.
Conclusions. Our simple formula and approximate approaches highlight a useful analytical tool for coronal seismology. We demonstrate that P1/2P(2) is linked to the density scale height, with no need for estimates of other external parameters. Given the accuracy of current observations, our formula provides a convenient means of determining density scale heights.
Original language  English 

Pages (fromto)  819825 
Number of pages  7 
Journal  Experimental Astronomy 
Volume  481 
DOIs  
Publication status  Published  Apr 2008 
Keywords
 Sun : corona
 Sun : oscillations
 stars : coronae
 MAGNETICFLUX TUBE
 LOOP OSCILLATIONS
 TRANSVERSE OSCILLATIONS
 DENSITY STRATIFICATION
 PROMINENCE FIBRILS
 VERTICAL MOTIONS
 FLARE
 EQUATIONS
 WAVES
 FIELD
Fingerprint
Dive into the research topics of 'Analytical determination of coronal parameters using the period ratio P1/2P(2)'. Together they form a unique fingerprint.Projects
 1 Finished

Solar&Magnetospheric Plasma Theory PP/E1: Solar and Magnetospheric Plasma Theory
Neukirch, T., Hood, A. W., Parnell, C. E., Priest, E., Roberts, B. & Wright, A. N.
1/04/07 → 31/03/12
Project: Standard