Proceedings with Extended Abstracts (single PDF file) - Radio ...

latitudes, arguing that the former can be explained in terms of a secondary wave gradientdrift mechanism and, occasionally, by neutral atmospheric turbulence.The first presentation of the second day of the session was an invited paper by E. Kudekiwho addressed the enigmatic echoes detected at equatorial latitudes and ~150 kilometeraltitudes during the daytime. These echoes are very aspect sensitive and exhibit virtually nozonal structuring, suggesting a possible role for meridionally propagating gravity waves inforcing their characteristic periodicity. Next, D. Farley presented results from F. Lu, D.Farley, and W. E. Swartz concerning the aspect sensitivity of equatorial electrojetirregularities. In their experiments, type 2 echoes exhibited relatively uniform RMS aspectwidths between about 0.2°-0.25° and decreasing with altitude while strong type 1 echoeshad considerably smaller widths approaching 0.1°. The type 2 widths were smaller thanthose reported by Kudeki and Farley, [1989], a fact Farley attributed to recentimprovements to the experimental apparatus and configuration at Jicamarca. A paper by J.Y. Liu, C. C. Hsiao, S. Fukao, et al. then compared plasma densities measured by the MUradar and with a collocated sounder and endeavored to extract gravity wave parametersfrom the measurements. The paper by C. L. Chen and C. J. Pan that followed returned thesession to the topic of mid-latitude sporadic E layers with a discussion of QP echoesobserved with the Chung Li radar. Using interferometry, they associated the echoes withdrifting quasi-point targets, reverberating the theme from the previous day's session. On thebasis of data from the Gadanki radar in India, the next paper by R. K. Choudhary, J. P. St.Maurice, L. Kagan, et al. parsed sporadic E layer echoes into two varieties arriving fromabove and below 110 km altitude, respectively. The dichotomy was reminiscent of the oneproposed earlier by J. Urbina et al. However, the assignment of irregularity altitude on thebasis of range alone was challenged in the paper by D. L. Hysell, M. F. Larsen, and J. L.Chau which introduced aperture synthesis imaging to the session. Common volumeimaging radar experiments with Arecibo again indicated that QP echoes arise frompolarized, patchy sporadic E layers drifting horizontally and descending slowly. On severaloccasions, radar imaging also revealed large-scale electrostatic waves propagating to thesouthwest in the E region over Arecibo, further highlighting the importance of E/F regioncoupling. The paper by Y. H. Chu and C. Y. Wang that followed analyzed beambroadening effects associated with spectral measurements of sporadic E layer echoes usinga formalism similar to that applied to MST radar data. Finally, the first portion of sessionI.2 concluded with an invited presentation by F. D. Lind, J. C. Foster, and P. E. Erickson.This paper described observations of auroral-zone Farley-Buneman waves made through asidelobe of the Millstone Hill radar as incoherent scatter drifts were measured through themain beam on a common flux tube. Such experiments directly address the saturationmechanism of Farley Buneman waves. The paper concluded with an ambitious proposal todeploy a multi-purpose passive coherent scatter radar network over North America.PMSE: The last part of Session I.2 was devoted to studies of coherent echoes from thesummer mesopause region and was chaired by R. Palmer and M. Sarango. The first paperwas an invited contribution by M. Rapp, F. Lübken, and W. Singer. Dr. Singer presentedthe paper where the underlying cause of Polar Mesosphere Summer Echoes (PMSE) wasinvestigated. In particular, the source of electron density irregularities at scales of λ/2 wasscrutinized. Important characteristics of PMSE were presented including layering andobserved differences in upper and lower regions of PMSE. The role of charged ice particles21