R.G. Roper

Semidiurnal tide in the 80–150 km region: an assimilative data analysis

Abstract A set of tabulated functions called ‘Hough Mode Extensions’ (HMEs), which represent numerical extensions of classical Hough modes into the viscous regime of the thermosphere, are used to least-squares fit a climatological data base of tidal measurements. The data base consists of monthly average vertical profiles of semidiurnal amplitudes and phases at 17 radar sites accessing some part of the 80–150 km height region. The radars are distributed between 78 S and 70 N latitude, and each one provides measurements of one or more of the following: eastward wind, southward wind, perturbation temperature. As a result of the fitting process, a single complex normalizing coefficient is derived for each month and for each of the four HMEs, designated (2,2), (2,3), (2,4) and (2,5) after their classical Hough function designations. Once the complex coefficients are derived, reconstruction by weighted superposition of the HMEs results in globally continuous specifications of semidiurnal horizontal and vertical wind, temperature, pressure, and density throughout the 80–150 km height region. The tidal variations in density, in particular, provide greater accuracy for several aerospace applications. The methodology developed here can also be utilized to derive tidal lower boundary conditions for Thermospheric General Circulation Models (TGCMs), or as a basis for future empirical model development. Comparisons are also made with HME coefficients and global tidal fields from the Forbes and Vial [(1989) J. atmos. terr. Phys. 51 , 649] numerical tidal model.

Preliminary results from the URSI/IAGA cooperative tidal observations program (CTOP)

Abstract This paper presents an overview of the results of the first three intervals of the Cooperative Tidal Observation Program (CTOP). The program has been undertaken as a collaborative effort by the incoherent scatter radar network, and the Global Radio Meteor Wind Studies Project (GRMWSP) under joint URSI/IAGA sponsorship to provide input to global models of the atmospheric circulation in the upper mesosphere and lower thermosphere. The data contributing to this overview are published in detail in nine companion papers in this issue.

The diurnal and semidiurnal oscillations in meteor winds over Atlanta

Abstract The wind data collected over Atlanta during the period August 1974–February 1978 using the Georgia Tech Radio Meteor Wind Facility, is analyzed to yield an average picture of the seasonal behavior of its diurnal tides. Both the zonal and meridional components are studied. The vertical structures of these oscillations over Atlanta are compared with similar studies over Garchy, Urbana and Adelaide. For the semidiurnal tide: the vertical structure during winter appears to have a strong latitude dependence, with vertical wavelength increasing with decreasing latitude; in spring, the (2, 4) and (2, 6) modes appear to dominate at all stations; in summer, the behavior is the same at all four locations, characterized by the apparent domination of the (2,2) mode; in autumn, both the Garchy and Atlanta results indicate the presence of a (2,2) mode, while the (2,4) mode appears to dominate over Urbana. The behavior of the diurnal tide is less well defined: during winter, as latitude decreases from Garchy to Atlanta, evanescent and higher order propagating modes seem to dominate; both spring and summer are characterized by a gradual decrease in observed vertical wavelengths as latitude decreases; in northern hemisphere autumn, the fundamental (1, 1) mode appears to dominate, but at Adelaide in southern hemisphere autumn, predominatly evanescent modes are observed.

Winds from the Atlanta (34°N, 84°W) radio meteor wind facility

Abstract A brief description of the Georgia Tech radio meteor wind facility is followed by a tabular presentation and discussion of winds measured over Atlanta (34°N, 84°W) for the first three intervals of the URSI/IAGA Cooperative Tidal Observations Program (CTOP). The pervailing zonal wind measured during August 1974, being easterly, is significantly different from that measured during October 1975 and January 1976, and is not typical of winds measured in August 1975 and August 1976, when westerlies predominated. The complicated tidal picture is detailed, but is not easily summarized.

Interdisciplinary atmospheric research featured at IUGG Meeting

In spite of the general climate of uncertainty that exists almost world-wide about future funding for atmospheric research, the International Association of Meteorology and Atmospheric Sciences (IAMAS) continues to serve as a focal point and clearinghouse for both fundamental and applied research, principally through its sponsorship of meetings and symposia. At the recent International Union of Geophysics and Geodesy Assembly in Boulder, Colo., IAMAS jointly sponsored a number of symposia and sessions spanning the breadth and depth of the IAMAS involvement in science. Ranging from ocean and atmosphere-global change through clouds, convection and large scale flows, radiation budget studies and land surface process modeling, to remote sensing algorithms in hydrology, the effects of Pinatubo, equatorial atmosphere and ionosphere interactions, middle atmosphere dynamics and chemistry, and climate variability and forcing, the interdisciplinary nature of IAMAS involvement is obvious. Even the “IAMAS only” sponsored sessions, on such topics as tropospheric ozone, atmospheric electrodynamics, the boundary layer and its mesoscale impact, stratospheric processes and their role in climate, and atmosphere-ocean behavior have interdisciplinary complexities and are of major importance to humanity and the sustainability of the environment.