timed

The primary mssion objective for TIMED is to investigate and quantitatively understand the energetics and dynamics of the Mesosphere and Lower Thermosphere-Ionosphere (MLTI) from ~50 - 200km. This is a region that is sometimes dubbed the "ignorosphere" because of the rudimentary nature of our understanding, caused by the lack of a comprehensive measurements base. It is a region where atmospheric motions are dominiated by poorly understood gravity waves and tides that both propagate through and dissipate in the region. Briefly, the mission goals are:

To determine the spatial and temporal variations of temperature, constituent densities, and winds.
To determine the importance of radiation, chemistry, and atmospheric motions for the energy balance.
To determine the source and magnitudes of atmospheric waves, tides, and their interactions.
To determine the spatial and temporal variations of minor species such as CO2, O3, NO, and H2O, which are important for the energy balance.
To determine the importance of electric fields, and winds for the atmosphere and ionosphere.
To investigate the processes responsible for the anthropogenic effects, and to establish a baseline set of observations for future investigations.

The MLTI is characterized as region of transition in which many important processes are known to change dramatically. For example, in the mesosphere the relative abundances of atmospheric species are primarily controlled by turbulent mixing and eddy diffusion and tend to be independent of altitude. In the thermosphere, however, molecular diffusion begins to be the dominant transport process, and the composition changes drastically with altitude such that the heavier species are concentrated lower down, while the light ones dominate at the higher altitudes. The process that induces turbulent mixing is probably related to the breaking of gravity waves, but it is not known where and how the transition from turbulent mixing to molecular diffusion occurs or how it varies globally, annually or on other time scales. This transition also profoundly affects the dynamics and energy balance of the region. The external energy sourses from the Sun that drives these processes also change dramatically throughout the region. In the mesosphere and stratosphere the absorbed radition is in the UV which varies somewhat with solar activity, and the primary absorber is ozone, strongly influenced by the chemical processes. But in the tenuous thermosphere at higher altitudes, the energy input arises primarily from the highly variable solar EUV radiation and the magnetospheric sources (due to auroral particles and electric fields) which dominate at high latitudes.