TIMED Doppler interferometer (TIDI) observations of migrating diurnal and semidiurnal tides

Abstract

Based on zonally averaged TIDI meridional wind data from one yaw period (March 19–May 19, 2004) near equinox, we examine the latitudinal and altitudinal distribution of the migrating diurnal and semidiurnal tides using least-squares fitting method to provide a global view of these tidal waves. The TIDI results are compared with Global Scale Wave Model 00 output for the month of April. The diurnal tide amplitude distribution are in a good agreement in the northern hemisphere and differ in amplitude in the southern hemisphere. The TIDI results show a lower peak altitude (97 km), while GSWM00 peaks at 102 km.The peak latitudes for the diurnal tide are at 20°N and 20°S for both the TIDI data and GSWM00 model. The TIDI data seem to show that the amplitude of the diurnal tide stronger in the northern hemisphere than in the southern hemisphere based on least-squares fitting results over the yaw period. The visually estimated vertical wavelength from the TIDI is about 20 km, while least-square fit results over the yaw period provided longer vertical wavelengths in northern (∼40 km) and southern hemisphere (∼30 km). We suspect that the seasonal change in the tide may cause the larger vertical wavelength. The GSWM00 provides a vertical wavelength of ∼26 km for the two hemispheres. Both model and TIDI data show semidiurnal tide peak amplitudes at 45° latitude. The measured semidiurnal tide peaked at lower altitudes (102 km in the southern hemisphere and 105 km in the northern hemisphere), whereas the GSWM00 shows peak altitudes at 110 km or above. The phases for the semidiurnal tide show a good agreement between the data and the GSWM00 model. The TIDI meridional winds are compared with ground based meteor radar measurements at Maui. The meteor data show smaller diurnal tide amplitude than that shown in the TIDI data. The phases of the diurnal tide appear to be consistent between the two data sets.