Aeronomy is the study of the structure, dynamics, and chemistry of the ionosphere, thermosphere, and mesosphere. Yet the separation between magnetospheric topics and aeronomical topics is artificial; they are too closely coupled to separate sharply. Horwitz and Shelley's reports could have gone under aeronomy, and the first report under aeronomy could have gone under the magnetosphere. This is Larry Lyons's `The ionosphere as a screen for magnetospheric processes,' which might have been titled, `The magnetosphere as a source for ionospheric processes.' Lyons's choice exploits an asymmetry: the ionosphere is more accessible than the magnetosphere. This is a report on systematic efforts to interrogate the ionosphere as a way to answer questions about the magnetosphere. The message is that these efforts, epitomized by the Geospace Environment Modeling program (GEM), are starting to pay off handsomely.
Ed Szuszczewicz treats the ionosphere qua ionosphere in `Advances in ionospheric physics: Roles, relevance and predictions in the system of solar terrestrial plasmas.' His perspective is on `ionospheric weather and climatology and on the roles and limitations of data and models in developing a predictive capability.' Since the ionosphere is at the receiving end of processes initiated at the sun, in the magnetosphere, in the thermosphere, and in the lower atmosphere, to understand what takes place there researchers need the assimilating and integrating power of global computer codes and the testing function of comprehensive data bases. This report documents the comparatively advanced state, resulting from community cooperation in organized programs, of both the modeling and measuring efforts---though still not advanced enough for some essential applications. In `Thermospheric connections,' Maura Hagan develops further, indeed `celebrates,' the theme that to understand an environmental domain as interactive as the thermosphere---or the ionosphere---requires community cooperation in organized programs. To this end NSF's Coupling Energetics and Dynamics of Atmospheric Regions (CEDAR) program has been conspicuously successful. Hagan persuasively documents the enabling role of community cooperation in advancing thermospheric research. She also stresses the importance of such research. One reason aeronomical research is interesting is that the ionosphere, thermosphere, and mesosphere are strongly coupled. Coupling from below is dominated by waves---tidal, planetary, and gravitational---generated in the troposphere and stratosphere and propagated up to deposit their momentum and energy. For its bearing on coupling, it is appropriate to end this suite of aeronomical reviews with Tim Killeen and Roberta Johnson's survey `Upper atmospheric waves, turbulence, and winds: Importance for mesospheric and thermospheric studies.'
The whole SPA collection of reports ends on an ecumenical note
with Andy Nagy, Tom Cravens, and Hunter Waite's `All ionospheres are
not alike: Reports from other planets.' Earth-based remote sensing,
especially of emissions of tri-atomic hydrogen ions, gave most of the
data during this quadrennium, while model development evolved to squeeze more
information out of archived data sets. One concludes that the questions are
well posed and the computational tools are well honed for the coming return
visits to Mars, Jupiter, and
[4]
Saturn.