Nonmigrating semidiurnal tide over the Arctic determined from TIMED Doppler Interferometer wind observations

The TIMED Doppler Interferometer (TIDI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite has been measuring horizontal winds in the mesosphere and lower thermosphere (MLT) since 2002. Because of the high inclination of the TIMED orbit, TIDI measures the horizontal winds from pole to pole every orbit. This paper presents the first assessment of the spatial structure and temporal evolution of the nonmigrating semidiurnal tides over the Arctic determined from the TIDI wind measurements and a comparison of the structure of the nonmigrating semidiurnal tide between the Arctic and Antarctic. The nonmigrating semidiurnal tides were determined as a 60 day average based on the yaw cycles of the spacecraft. The nonmigrating semidiurnal tidal wind field over the Arctic comprises mainly the westward-propagating zonal wave numbers 1 (W1) and 3 (W3) and standing zonal wave number 0 (S0) modes. The W1 mode is the most prominent, maximizing above 90 km poleward of 60°N during the yaw interval ranging from mid-March to mid-May. While this mode exhibits a slight amplitude increase toward the North Pole during this interval, its phase is nearly constant with latitude. The S0 mode is enhanced over two yaw intervals ranging from mid-January to mid-May, but its amplitude decreases toward the North Pole. Compared to the W1 semidiurnal tide over the Antarctic, that over the Arctic is smaller in amplitude, of less extended duration, achieves maximum amplitudes at higher altitudes by ~10 km, and exhibits a weaker amplitude increase toward the pole. These differences likely result from differences in excitation mechanisms and efficiency and/or in propagation conditions in the two responses for the nonmigrating semidiurnal tides between the Arctic and Antarctic.