CEDAR: Vertical Velocity Measurements in the Mesosphere: Biases and Possible Solutions Using Spatial Interferometry

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One of the most important parameters, which can be derived from atmospheric Doppler radars, is the vertical component of the neutral wind. This project will compare and contrast the various methods used in estimating the vertical velocity in the mesosphere. Mesosphere-stratosphere-troposphere (MST) and partial reflection drifts (PRD) radars will be used to achieve this goal. MST radars typically use either a vertically pointing beam or the velocity-azimuth-display (VAD) technique to estimate the vertical wind. The vertical beam technique can be biased by instrumental as well as atmospheric effects. The PIs propose that any instrumental bias can be removed using spatial interferometry (SI) to track a radio star such as Cygnus A. Differences between the astronomical position and that obtained from the SI measurements can be attributed to a systematic offset in the beam position. Any atmospheric bias, due to inhomogeneities in the reflectivity field, can also be removed using SI techniques. If implemented properly, the VAD technique can produce an unbiased estimate of the vertical wind. On the other hand, if not properly implemented, the resulting vertical velocity estimates will be biased by the divergence in the wind field. The PIs propose to implement both the VAD and SI techniques using the Middle and Upper (MU) Atmosphere radar in Shigaraki, Japan, in the 60-90 km range. Both these mesospheric measurements can be conducted essentially simultaneously. Most PRD measurements are restricted to the vertical position because of the configuration of typical systems. Therefore, the biases mentioned above, for the vertically pointing MST radar, are also applicable for PRD systems. Furthermore, the biases should be enhanced because of the typically wide beamwidths used with these radars. PRD radars are multiple-receiver systems operating at 2-3 MHz. As a result, the methods of eliminating the biases using SI techniques are very similar to the MST case. The PIs will make measurements using a PRD radar, which is planned for installation in Sondre Stromfjord, Greenland, by researchers at Clemson University and the University of Colorado.