TIDI Measurements of Upper Atmosphere Dynamics

The TIDI instrument collects upper atmosphere wind velocity data as the TIMED satelite orbits the globe. The data shown on the surface of the globe is a hyperslice in time and space depicting upper atmosphere wind speeds. As you move around the globe to the west you move forward through time. i.e. data to the west is more recent than data to the east. The cutting plane that passes through the globe shows approximately one day's data and approximates the orbit of the satelite. The instrument collects data along two paths: the cold side and the warm side. Each animation shows either data from the "cold" side or "warm" side of the Earth. The meridional and zonal winds are compared in the animations. The color scheme represents wind speed from -150 to 150 KM/hour, with red indicating negative values and blue positive.

On December 7, 2001, the TIMED satellite was launched into a near circular orbit with 625 km altitude, 74.1° inclination, and a 3° per day precession rate. Approximately every 60 days, a 180° yaw maneuver of the satellite is performed to avoid the sunlight shining onto the cold side of the spacecraft. There are four instruments onboard TIMED.

The instrument designated to study lower thermosphere and mesosphere dynamics is TIDI. TIDI simultaneously measures the neutral winds on two sides of the spacecraft. The dynamics of the observed region are dominated by atmospheric tides. The strongest tides are the migrating tides, which are induced by the absorption of solar radiation by water molecules in the lower atmosphere and ozone in the middle atmosphere. In addition to tides, planetary waves and gravity waves also play important roles in upper atmosphere dynamics.

TIDI’s four telescopes are oriented orthogonal to each other, allowing the instrument to measure neutral wind vectors on both sides of the satellite track. The two telescopes viewing the same side of the track observe the same locations with a time delay of a few minutes as the spacecraft moves forward. The viewing directions of these two telescopes are perpendicular to one another. Assuming that the neutral winds do not change much during the short time period, the samplings at the two directions can then be used to form the neutral wind vector in terms of the meridional and zonal components.

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