The three-dimensional plasma structures and flows of the Earth's upper atmosphere due to the Moon's gravitational force

The semidiurnal (12.42 h) and semimonthly (14.76 days) lunar tides have been well-known by fishermen for several centuries. The gravitational force of the relative positions between the Sun, the Moon, and the Earth results in two symmetrical tidal bulges (double bulges) appearing at equatorial latitudes directly under and opposite the Moon. We utilize ionospheric GNSS (Global Navigation Satellite System) radio occultation soundings to show the global three-dimensional structures and dynamics of the double bulges of ionospheric lunar tides for the first time. The double-bulge amplitude of ionospheric F2-peak height hmF2, lagging the sublunar or antipodal point by about 2-3 h, is about 3-5 km at the equator and 1.5-2.0 km at ± 35° magnetic latitude. The electron density further depicts global three-dimensional plasma flows in the ionosphere.

Polar cap mesosphere wind observations: comparisons of simultaneous measurements with a Fabry-Perot interferometer and a field-widened Michelson interferometer

Polar cap mesospheric winds observed with a Fabry-Perot interferometer with a circle-to-line interferometer optical (FPI/CLIO) system have been compared with measurements from a field-widened Michelson interferometer optimized for E-region winds (ERWIN). Both instruments observed the Meinel OH emission emanating from the mesopause region (approximately 86 km) at Resolute Bay, Canada (74.9 degrees N, 94.9 degrees W). This is the first time, to our knowledge, that winds measured simultaneously from a ground-based Fabry-Perot interferometer and a ground-based Michelson interferometer have been compared at the same location. The FPI/CLIO and ERWIN instruments both have a capability for high temporal resolution (less than 10 min for a full scan in the four cardinal directions and the zenith). Statistical comparisons of hourly mean winds for both instruments by scatterplots show excellent agreement, indicating that the two optical techniques provide equivalent observations of mesopause winds. Small deviations in the measured wind can be ascribed to the different zenith angles used by the two instruments. The combined measurements illustrate the dominance of the 12-h wave in the mesopause winds at Resolute Bay, with additional evidence for strong gravity wave activity with much shorter periods (tens of minutes). Future operations of the two instruments will focus on observation of complementary emissions, providing a unique passive optical capability for the determination of neutral winds in the geomagnetic polar cap at various altitudes near the mesopause.