CEDAR: Intraseasonal and Interannual Variations in Diurnal Tropospheric Heating and in Mesospheric and Lower Thermospheric Tides

Northwest Research Associates, Incorporated, Seattle WA

Investigators

Abstract

This project addresses variability of the tropical diurnal tide in the mesosphere on timescales of the intraseasonal, or Madden-Julian Oscillation (MJO, approximately 30-60 days) and the El Nino-Southern Oscillation (ENSO, approximately 2-10 years). Low-latitude medium frequency (MF) radar wind measurements suggest that diurnal tide amplitudes are modulated on intraseasonal (IS) and interannual time scales. The propagating diurnal tides are a strong agent of coupling between the tropical troposphere and the upper atmosphere. Thus, if the forcing of tropospheric diurnal tides undergoes systematic, large-scale variations on MJO and ENSO time scales, such variability may be transmitted into the upper atmosphere by means of the tide's vertical propagation at low latitudes. The tropical radars at Kauai (22 degrees N, 159 degrees W) and at Rarotonga (22 degrees S, and 160 degrees W) are uniquely situated with almost perfect symmetry around the equator. These are key locations for monitoring the structure and temporal variability of the diurnal tide, since they are near the latitude where the tidal wind amplitude maximizes. In addition to supporting scientific analyses of tidal variability, this project will provide operational support for the tropical radars. The operational support includes maintenance, system upgrades, minor repairs and data archival. We anticipate that this support would allow the radars to operate continuously, reliably and with enhanced capability for the duration of the TIMED mission.