Computer Science – Sound
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsa44a..02p&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SA44A-02
Computer Science
Sound
2411 Electric Fields (2712), 2439 Ionospheric Irregularities, 2443 Midlatitude Ionosphere, 2471 Plasma Waves And Instabilities (2772)
Scientific paper
Electric field and plasma density data gathered on sounding rockets launched in the presence of sporadic-E layers and QP radar echoes reveal a complex electrodynamics including both DC parameters and plasma waves detected over a large range of scales. We present results from two different sounding rocket experiments equipped with similar instrumentation which were conducted in the presence of intense QP radar echoes: a NASA sporadic-E investigation launched from Wallops Island, Va., in 1999 and the Japanese "SEEK-2" rocket launched from Uchinoura, Japan in 2002. Electric field data from both experiments reveal the presence of km-scale waves as well as well-defined packets of broadband (10's of meters to meters) irregularities. What is surprising is that in both experiments, neither the large scale nor short scale waves appear to be distinctly organized by the sporadic-E density layer. Data from the NASA rocket revealed large scale structures with wavelengths of 2-4 km and amplitudes of 1-2 mV/m that were most intense in the region of 90-110 km during the downleg trajectory of this flight. The waves were oriented in the NE-SW quadrants. On the other hand, during the SEEK-2 experiment, the electric field data above the sporadic-E layer on the upleg, from 110 km to the rocket apogee of 151 km, revealed a continuous train of distinct, large scale, quasi-periodic structures with wavelengths of 10-15 km that also propagated between the NE-SW quadrants. The electric field structures had typical amplitudes of 3-5 mV/m with some excursions to 8-9 mV/m, and had associated perturbations in the plasma density. The electric field waveforms showed evidence for steepening and/or convergence effects and may have mapped upwards along the magnetic field from the sporadic-E region below. Candidate mechanisms to explain the origin of these structures include the Kelvin-Helmholtz instability and the Es Layer instability. In both cases, the same shear that formed the sporadic-E layer would presumably provide the energy to generate the km-scale structures. Other possibilities include a gravity wave explanation or a combination of these processes. The data suggest that these structures were associated with the lower altitude density striations that were the seat of the QP radar echoes observed simultaneously. The SEEK-2 structures may also have been associated with the mechanism responsible for a well-defined pattern of "whorls" in the neutral wind data that were revealed in a chemical trail released by a second sounding rocket launched 15 minutes later. Well-defined packets of higher frequency (shorter scales < 100 m) broadband waves were also observed in-situ on both rockets, consistent with the observations of intense radar backscatter during the times of each launch. The linear gradient drift instability involving the DC electric field and the vertical plasma gradient is shown to be incapable of driving most, although not all, of the short scale waves observed during each flight. The data suggest that other sources of free energy may have been important factors for wave growth, and we conclude that drift waves associated with winds and horizontal plasma density gradients, as well as thermal or other instabilities, are necessary to explain the short-scale wave generation observed during these sporadic-E encounters.
Freudenreich Henry
Kudeki Erhan
Larsen Mark
Pfaff Robert F.
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