TOTAL ELECTRON-CONTENT AND SCINTILLATION STUDIES - CURRENT STATUS

Satellite beacon studies have contributed mainly in two areas of resea rch, namely, total electron content (TEC) and small scale structures o r irregularities, and both of these have important practical implicati ons in trans-ionospheric radio propagation. The current status of thes e two fields of research is summarized, and recent developments in the study of equatorial anomaly using US NNSS satellite signals, geomagne tic storm effects, travelling ionospheric disturbances, nighttime enha ncements, and slab thickness, which are of particular relevance to the equatorial and low latitudes, are reviewed. Recent initiatives on TEC modelling and comparison of existing models with observations are hig hlighted. New concepts like computerized ionospheric tomography are br iefly outlined. Recent advances in the understanding of scintillation morphology, particularly its longitude dependence and the variation of the width of the equatorial scintillation belt are summarized. Future directions in respect of multitechnique investigation of the low lati tude ionosphere and the mosphere, measurement of GHz scintillations, a nd spectral studies are pointed out. Important application areas of th is field are also included.