Accession Number : ADA263028


Title :   The Detection and Characterization of High Frequency and High Wavenumber Solar Oscillations


Descriptive Note : Doctoral thesis


Corporate Author : STANFORD UNIV CA DEPT OF PHYSICS


Personal Author(s) : Fernandes, David N


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a263028.pdf


Report Date : Jun 1992


Pagination or Media Count : 131


Abstract : Doppler shift measurements of the Na D1 absorption line have revealed solar oscillations in a new regime of frequency and wavenumber. Oscillations of vertical velocities in the temperature minimum and low chromosphere of the Sun are observed with frequencies ranging up to 9.5 mHz. There is no evidence for chromospheric modes of 3 minute period. This indicates that the chromosphere does not form a good cavity for acoustic waves. The fundamental-modes appear with wavenumbers up to 5.57/Mn (equivalent spherical harmonic degree, 3877). The frequencies lie below the predicted values at wavenumbers above 1/Mn. The values are in agreement with previous measurements that exist for wavenumbers up to 2. 67/Mn. Spatial maps of velocity power show that high wavenumber oscillations are suppressed in active regions. The shape of the power depression indicates that wave motion is affected in the layer of atmosphere where the measurement is made. The f-modes are suppressed in the same way as p-modes, indicating that the mechanism for wave suppression affects velocity fluctuations. Mode frequencies are not affected by the magnetic fields by more than 50 microHz, the precision of the measurement.


Descriptors :   *ATMOSPHERIC DISTURBANCES , *SOLAR ACTIVITY , *SUN , *SOLAR PHYSICS , VELOCITY , MEASUREMENT , TEMPERATURE , MAGNETIC FIELDS , POWER SPECTRA , OSCILLATION , CHROMOSPHERE , MAGNETOMETERS , ZEEMAN EFFECT , TELESCOPES , ERRORS , SPECTRA , HIGH FREQUENCY , SURFACE WAVES , ACOUSTIC WAVES , THESES


Subject Categories : Astrophysics
      Acoustics
      Electricity and Magnetism


Distribution Statement : APPROVED FOR PUBLIC RELEASE