Neutral Atmosphere Dynamics Research Articles

The Ramfjordmoen MF radar (69°N, 19°E): application development 1990–2000

The partial reflection experiment (“PRE”) in northern Norway (69°N, 19°E), an MF radar system, has been operating for 25 years. During that time many improvements have been made to both hardware and software and the aspects of atmospheric physics that have been addressed have also changed. We find it not only timely to provide a “silver jubilee” short history of the instrument, but also to review the various applications to atmospheric science. In particular, we discuss parameterisation of turbulence. The radar may be applied to the study of how neutral atmosphere dynamics at scales from planetary waves down to turbulence may be affected by space weather, exotic concepts that would have seemed very foreign at the time of inception of the system. The reference list is intended to include every refereed publication hitherto using “PRE” data.

Middle atmosphere electrical structure, dynamics and coupling

The ram current to ion traps and the insensitivity of ion conductivity to compressibility provide the basis of robust techniques for middle atmosphere measurements. Gerdien condensers are more difficult to implement but provide more information. Mesospheric electrical conductivity shows many orders of magnitude variability, with depressions below gas phase model values indicating dominance by aerosol particles. The mobility of these ions has been directly measured and indicates particles of thousands of AMU. Large mesospheric fields have come into question, and diagnostic measurements show that many such measurements may be artifacts. However, some measurements of V/m fields with symmetrical and redundant sensors appear to be real. These fields complicate the “mapping” picture of electrical coupling and may also modulate the transport of aerosol particles. They are probably related to neutral atmosphere dynamics and/or the aerosol particles. Lightning couples much more energy to the middle atmosphere and above than previously suspected, primarily in the ELF-ULF range. There are many important unanswered questions in this relatively unexplored frontier area which may be answered with low cost balloon and sounding rocket experiments.

The vertical wave number spectrum of topside equatorial spread F: Estimates of backscatter levels and implications for a unified theory

A wave number spectrum for plasma density fluctuations in decaying equatorial spread F covering 5 orders of magnitude in spatial scale and 12 orders of magnitude in spectral power is presented. The outer scale is found, as is the spectral transition between a shallow spectral form (slope < 2) at intermediate scales and a steep spectrum at smaller scales. The characteristic features of the spectrum are discussed and related to the physical processes operating in several regimes. A unified model is discussed involving aeronomic effects and neutral atmospheric dynamics at the largest scales, a generalized Rayleigh‐Taylor plasma instability at intermediate scales, and a cascade of wave energy involving drift waves at transitional wavelengths. Open questions still remain concerning free energy sources near 1 km wavelength and at wavelengths less than a meter. Estimates of backscatter levels using the plasma density fluctuation spectra are consistent with Jicamarca and Altair radar observations except in topside regions of low plasma density, where in situ data at very short wavelengths are needed.

Concluding remarks, session 4: Atmospheric dynamics

Meteorologists used to criticize those who described themselves as aeronomers or ionospheric physicists, pointing out their neglect of neutral air motions in calculating ionospheric behavior. This situation has changed dramatically in the last few years. At this meeting, the effects of neutral air motions were considered either implicitly or explicitly in over one third of the papers presented. Some of the topics that explicitly touched on neutral atmosphere dynamics are described in the following paragraphs.

Neutral upper atmosphere structure

This review summarizes major contributions by the United States during the period 1967 to 1970 that deal with the structure of the neutral atmosphere above 90 km (the thermosphere and exosphere). An effort has been made to minimize possible overlap with the other reviews presented here, i.e., neutral atmosphere dynamics, hydrogen in the upper atmosphere, aurora and airglow, and various reviews in meteorology. Comprehensive reviews of recent results have been given by Champion [1968, 1969, 1970] on the lower thermosphere and by Jacchia [1968, 1969, 1970b] on the thermosphere and lower exosphere.