A numerical study on amplitude characteristics of the terdiurnal tide excited by nonlinear interaction between the diurnal and semidiurnal tides
© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2007
Received: 23 August 2006
Accepted: 4 December 2006
Published: 7 May 2007
A fully nonlinear numerical tidal model has been developed with the aim of presenting amplitude features of the terdiurnal tide excited by nonlinear interaction between the diurnal and semidiurnal tides. Since the superposition of the migrating diurnal and semidiurnal tidal solutions from the GSWM-00 (Global Scale Wave Model 2000) is taken as the initial disturbance for this nonlinear model, the diurnal and semidiurnal tides are allowed to nonlinearly interact with each other. The analyses on the simulations show that the migrating terdiurnal tide can be significantly excited by the nonlinear interaction between the diurnal and semidiurnal tides in the mesosphere and lower thermosphere (MLT) region, especially above 90 km, and have pronounced amplitudes (wind speeds over 15 m s−1 and temperature over 10 K) in the lower thermosphere (90–110 km). In addition, its amplitudes vary strongly with season and maximize during equinoctial months at low and middle latitudes, and its zonal wind component is larger than the meridional wind component. Simultaneously, the diurnal and semidiurnal tides exhibit evident variations, indicating that the wave-wave and wave-mean flow interactions are the important cause of the tidal variability. Our calculations also illustrate the remarkable alteration of the background fields induced by the mean flow/tidal interaction, implying this interaction should be comprehensively considered in describing global atmospheric dynamic and thermal structures in the MLT region.