Already Registered? Please fill in your username and click the logon button.	Username:
Forgot your Login? Please fill in your e-mail address below and your registration details will be mailed to you.

TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics) is a two-year NASA Mission to study the energetics and dynamics of the Earth's mesosphere and lower thermosphere (MLT) in the altitude range from 60-180 km. Because the atmospheric density is still relatively high in this altitude regime, it cannot be studied with in situ instruments on orbiting spacecraft. Thus, our knowledge of the MLT has been limited to occasional sounding rocket measurements or remote sensing observations with instrumentation located on the ground or on higher altitude spacecraft. For this reason, the mesosphere and lower thermosphere are the least understood regions of the Earth's atmosphere. Nevertheless, they are important as they form the interface between the ionized and often energetic gases that permeate the Earth's magnetosphere and interplanetary space and the underlying bulk of the Earth's atmosphere. Energy is deposited in the MLT from above through solar radiation, energetic particle precipitation (aurora), and electric fields; and from below through upwelling waves and tides within the Earth's atmosphere and through upwelling gases that are, in part, created by human activity

Click on Figure to view a larger image

The goals of the TIMED Mission are to use a new generation of optical remote sensing instrumentation to understand how energy is deposited into the MLT on a global basis and to study the impact of this deposition on MLT global dynamics. To aid in this endeavor, the NSF CEDAR (Coupling, Energetics and Dynamics of Atmospheric Regions) Program has agreed to co-sponsor a number of ground-based investigations that will provide additional data to support the TIMED mission objectives and to study related CEDAR science topics. Particular emphasis has been given to high-latitude energy inputs associated with auroral particle precipitation and high-latitude electric fields. The latter arise from plasma processes that couple momentum and energy from the solar wind to the Earth's magnetosphere and thence to the Earth's high-latitude ionosphere. These electric fields drive currents that deposit momentum and energy into the lower thermosphere, heating the atmospheric gases and driving large-scale atmospheric circulation.

The SuperDARN radars are supporting the TIMED-CEDAR collaboration through their unique ability to provide direct global measurements of plasma circulation and electric fields in the high-latitude regions of both hemispheres. The radars operate continuously providing global maps of plasma convection every 2 minutes.

The figure to the right shows a polar view of the northern hemisphere on which one set of convection observations from SuperDARN are superposed. The solid and dashed contours represent the paths of plasma circulation. The colored lines represent velocity vectors in regions where SuperDARN measurements were available. Both the contours and the vectors are derived from the observations. In this example, yellow vectors represent velocities in excess of 1 km/s. Noon is toward the top of the plot and midnight is toward the bottom. The grayed portion of the map is in darkness. It can be seen that the velocity vectors have a generally antisunward orientation over the polar cap and are directed sunward at lower latitudes. This type of circulation is commonly referred to as a two-cell convection pattern.

The electric fields associated with this convection pattern may be obtained by rotating each velocity vector 90( clockwise and equating 1 km/s to 50 mV/m. The total electrical potential drop across the polar region was 104 kV at this time.

This site contains a continuous record of high-latitude convection patterns for the duration of the TIMED mission. A sample 2-minute snapshot is provided for each 10-minute interval. Plots may be downloaded as well as digital data files. Users of this data are requested to follow the rules regarding data usage. In the near future, similar data will be available from the southern-hemisphere SuperDARN radars.

SuperDARN radars are also sensitive to backscatter from meteor trails at a nominal altitude of 95 km. The trails drift with the ambient wind pattern at that altitude and Doppler radar data from these trails may be used to study the neutral winds patterns. These meteor wind observations will also be available from this site in the near future.