Highly structured electron densities in the E and F regions over Puerto Rico during the night of February 20/21, 1999 were accompanied by intense coherent VHF radar backscatter from the E region and perturbations in neutral sodium in the mesosphere. Simultaneous observations of the event were made with the VHF Cornell University Portable Radar Interferometer (CUPRI) located near Isabela, PR, the University of Illinois VHF radar located at Salinas, PR, the Arecibo incoherent scatter radar, and the sodium lidar located at the Arecibo Observatory. On this geomagnetically quiet night, regions of very different electron concentrations moved through the region. The F-region peak altitudes of the low density regions differed by about 100 km from the high-density region altitudes. The E region also exhibited an unusual enhancement with a vertical extent of about 6 km and caused intense VHF backscatter. The echoing E regions seen by both VHF radars were highly structured with multiple filaments and Doppler shifts exceeding 300 m/s (directed north and upward) some of the time. The Arecibo incoherent scatter radar recorded a large eastward component of the velocity (~200 m/s) during the early portion of the event, which then switched to strongly westward (peaking over 500 m/s and averaging perhaps 400 m/s for about half an hour) before returning eastward. The meridional velocity components were also variable. The Arecibo lidar showed an intense sodium layer that maintained a constant altitude until the strongest VHF echoes began. Then the layer fell 2 km over a time span of about half an hour and the lidar echoes intensified. Because (1) the timing of the events at the different locations is well correlated with the F-region drifts as measured with the Arecibo radar, and (2) because the Pedersen conductivity falls precipitiously at the start of the event, we conclude there was strong coupling between the E and F regions, perhaps even reaching the mesosphere, during this event. However, major problems may remain. How can the E-region cloud track the F-region blob when supposedly it is coupled to the neutrals? Does the neutral wind track the F-region ion velocity? We do not think so, but this is the easiest solution.
|Number of pages
|Journal of Atmospheric and Solar-Terrestrial Physics
|Published - Aug 2002
All Science Journal Classification (ASJC) codes
- Atmospheric Science
- Space and Planetary Science