Analytical studies of sodar observations at Delhi

A monostatic sodar system has been operating at the National Physical Laboratory, New Delhi (28.6°N, 77.2°E) since December 1974. Echograms obtained up to May 1976 (operational period of approximately 1500 h) have been qualitatively analyzed with respect to their structural details. Layers are a general feature of the sodar echograms with their thickness lying mostly within 20 m. Their percentage occurrence reaches a maximum of 95% between 1600–2000 h and a minima of 40% between 1200–1400 h. The height of the layers has a primary maximum (average height 220 m and maximum height 350 m) between 0200–0400 h, a minimum (average height 175 m) between 0800–1000 h and a secondary maximum (average height 190 m) between 1100–1400 h. Turbulence is a very characteristic observation under stable conditions and is present for about 13% of the time. The turbulent as also the layer structures have been classified into various categories according to their typical features. Discernible thermal plume structures have been rarely seen over Delhi. The structure is mostly affected by the prevalent ambient wind. The convective activity is maximum around 1200–1400 h.