Contrary to the prevalent belief that tropical region is characterized by convective clouds rather than by layer clouds, we have suggested that deep convective clouds occur on meso-scale, but layer clouds occur on larger synoptic-scale with a relatively small region of deep convective clouds. Sustenance of deep convective clouds is inhibited by the presence of inertio-gravity waves, which have alternating layers of upward and downward motion in the vertical. We have also shown that inertio-gravity waves generate regions of relatively strong horizontal velocity, vertically separated by layers of relatively weak horizontal velocity. Layers of strong horizontal velocity are created by inertio-gravity wave system through convergence of vertical flux of horizontal momentum. We have also suggested that horizontal convergence/divergence of moisture flux is generated by inertio-gravity waves, giving rise to vertically alternating layers of high/low humidity, and visible or sub-visible clouds. Layers of high humidity become layers of strong radar reflectivity at frequency of 53 MHz at which MST Radar at Gadanki, near Tirupati, India, operates. These observations, more than 2,50,000 in number, for vertical grid points, spread over all the months of the year, have helped us, among other observations, to arrive at these conclusions. Further, the analysis suggests that the main source of strong MST radar reflectivity is not mechanical turbulence as is commonly believed.

VHF and UHF Doppler radars provide a unique database to estimate the refractivity structure constant Cn2, eddy dissipation rate ∈, and vertical flux of horizontal momentum. Using the data collected from the Indian MST radar, these parameters are studied at a tropical latitude. The refractivity turbulence structure constant is estimated from the backscattered power of the received echoes. Cn2 (radar) and Cn2 (model), derived from radiosonde observations, are compared, and a fairly good agreement is seen. Diurnal and seasonal variations of Cn2 are also presented. The eddy dissipation rate is estimated from the radar echoes employing the power and spectral width methods. A fairly good agreement is seen between the two methods. Values of ε are found to vary from 10−6 to 10−3 m2 s−3 in a height range of 4–19 km. Cn2 and ε are observed to be minimum during a moderate jet stream wind of 50–60 m s−1. Vertical flux of horizonal momentum is computed using the symmetrical two‐beam method. Significant fluxes of westward and northward momentum are observed, and the values lie in the range of −1 to +1 m2 s−2. The implied accelarations are also estimated. The results presented are largely consistent with the results available in the literature.

Thermodynamic stabilities of the ordered structures in Pd3Mn have been theoretically evaluated, both in the presence and absence of hydrogen. The internal energies of the L12 and L12−s structures of Pd3Mn were found to be the same. The Ll2−s phase is the stable phase at all temperatures, both in the presence and absence of hydrogen, according to the statistical thermodynamic calculations indicating that the hydrogen-induced ordering phenomenon from the Ll2−s to the Ll2 structure could be due to stress-assisted motion of atoms as a result of hydrogen occupying interstitial sites in the Ll2−s form. The difference in stabilities between the Ll2 and Ll2−s structures is small for both of the cases. The difference in configurational entropies between the two ordered forms of Pd3Mn decreases with increasing hydrogen concentration. The effect of configurational entropy on the stability of the Ll2 and Ll2−s phases has been addressed.