More than 110 nations signed the Comprehensive (Nuclear) Test Ban Treaty (CTBT) during the first week after the Treaty opened for signature in September at the United Nations in New York. This means that a start will now be made during the coming year on the construction of an International Monitoring System (IMS) which will be used to ensure compliance with the terms of the Treaty. The International Monitoring System represents the largest effort ever undertaken on a global scale to detect and locate explosions in all physical environments. The establishment of the IMS has special significance for Australia because nearly ten per-cent of all IMS facilities will to be located on Australian territory.
The Warramunga Seismic (WRA) and Infrasonic (WRAI) Arrays at Tennant Creek have been included explicitly in the Treaty as primary alpha stations. These stations played a pivotal role in the negotiations for the Treaty at the Conference on Disarmament in Geneva. Data from both of these stations is currently being transmitted on-line via satellite to the International Data Center in Washington. The seismic array at Warramunga continues to be regarded as one of the most important installations in the global seismic network for monitoring purposes. At the present time, data from WRAI is still the only infrasonic data which is being received at the International Data Center from a designated CTBT infrasound station. The data from this station is therefore being used as the primary test data for much of the initial development work on detection, location and discrimination algorithms for the global infrasound monitoring system. The upgrading of the infrasonic array has continued during the past year with the addition of improved noise-reducing space filters and low-noise electronics. Further improvements are planned for the coming year which will significantly improve both the detection and location capability of the infrasonic array at Warramunga.
A very extensive co-operative experimental program involving the Australian National University, Monash University, the University of New South Wales and the University of Munich was carried over Central and Northern Australia in September and October of this year. A large network of microbarograph stations and automated weather stations was deployed over the region between the Simpson Desert and the Gulf of Carpentaria (see Figure 12). This experiment served as an initial test of the ultra-low power high capacity solid-state portable experiments. The performance of these recorders during this experiment has proven to be exceptional with a data recovery rate of greater than 97%. One of the primary objectives of this exercise is to determine the dynamical mechanism which gives rise to southerly Morning Glory waves. This is still an open question. It seems very likely that some of these disturbances are excited by advancing mid-latitude cold frontal systems, but the origin of other observed disturbances remains obscure. It is anticipated that the present experiment will provide observations with sufficient resolution to determine with certainty the origin of these unusual disturbances. The experiment has also been designed to study the complete evolution pattern of northeasterly Morning Glory waves and the interaction of these waves with southerly disturbances. It has been known for some time that some northeasterly Morning Glories propagate over great distances while others propagate only over very short distances. It is hoped that detailed studies of the evolution patterns measured during this experiment will reveal the mechanisms which influence the propagation of Morning Glory wave disturbances.
It has become increasingly clear that many of the observed anomalous evolution properties of highly nonlinear solitary waves in the lower atmosphere can be attributed to spatial and temporal variations in waveguide properties along the path of the disturbance. The atmospheric boundary layer is never stationary. The nocturnal boundary layer which provides the necessary stable waveguide layer for wave propagation over inland Australia continues to increase in depth and intensity with time after sunset. At dawn, this layer is subject to erosion from the surface under the influence of daytime convection which leads to a slowly disintegrating elevated inversion. Solitary waves have been observed on this elevated inversion waveguide. Another good example of a temporally and spatially heterogeneous waveguide is the layer of cold air which is created at the surface by an intense thunderstorm outflow density current. The complicated evolution pattern of thunderstorm-generated waves has been observed as they propagate along the slowly dissipating waveguide created in the outflow from an earlier storm. The creation and subsequent propagation of solitary waves has also been observed in the collision of density currents in the thunderstorm environment.
A very high resolution numerical model, which is based on an integration of the fully nonlinear nonhydrostatic primitive ensemble-averaged equations, has been developed to study wave propagation in temporally and spatially varying waveguides. Realistic boundary conditions have been developed which prevent reflections at all lateral boundaries and the upper boundary. This model is being used initially to study the formation, evolution and decay of solitary waves on a time-varying density current and solitary waves which are created in the head-on collision of density currents. Further studies of nonlinear atmospheric wave motions in other evolving waveguide systems will be carried out during the coming year.