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Size distribution of radar echoes from convective clouds around Delhi during monsoon season

Sat, 01 Jun 1996 00:00:00 GMT

Title: Size distribution of radar echoes from convective clouds around Delhi during monsoon season Authors: Chatterjee, R N; Ali, K; Prakash, Prem; Majumdar, S C Abstract: The size distributions of radar echoes from convective clouds observed in Delhi region during each monsoon season of the 6-year period from 1967 to 1972 have been investigated. It has been found that the size distribution of about 99 per cent of the total echoes in each monsoon season and covering echoes up to diameter 35 km (30 km in 1972) are well represented by the exponential distribution N_D = a exp (-b), where N_D is the number of echoes in the diameter interval D to D + D, is the mid-value of the interval, i.e. D + D/2, and a and b are the coefficients to describe the exponential distribution. The possibility of using these results in connection with the estimation of rain attenuation for millimeter wave propagation has been discussed. Page(s): 124-128

Hall and Pedersen conductivities in the auroral ionosphere of Jupiter

Sun, 01 Dec 1996 00:00:00 GMT

Title: Hall and Pedersen conductivities in the auroral ionosphere of Jupiter Authors: Singhal, R P Abstract: Hall and Pedersen conductivities in the auroral ionosphere of Jupiter have been calculated. Conductivity profiles are presented for three characteristic energies 10, 30 and 100 keV of the Maxwellian distribution of precipitating particles (electrons). Calculations are performed for three values of the magnetic fields, i.e. for 6, 10 and 14 G. Height integrated conductivities are tabulated. Results are compared with previous estimates. God qualitative agreement is found. It is found that that the major contribution to the conductivities comes from the heavy hydrocarbon ions and not H+ as assumed in some earlier works. Page(s): 361-366

Implication of the ionosphere in low latitude micropulsations

Sun, 01 Dec 1996 00:00:00 GMT

Title: Implication of the ionosphere in low latitude micropulsations Authors: Roy, Manashi Abstract: The low frequency hydromagnetic waves in the terrestrial magnetosphere, known as geomagnetic micropulsations, have to propagate through the ionosphere before they are detected on the ground. It is generally argued that the polarization suffers a 90° rotation while it crosses the ionosphere. All ground data are analysed on this premise. The arguments put forward to this theory have been briefly reviewed and it has been shown that this is not always true, certainly not in the low latitude ionosphere. A general expression is then derived for the low latitude ionospheric effects demonstrating that the rotation angle is substantially different from /2. Moreover, the amount of rotation is a function of the direction of the wave field. Since the transformation matrix is a complex quantity the ionosphere also introduces phase change among the two horizontal components. Thus the nature of polarization also changes as the wave penetrates the ionosphere. Page(s): 356-360

Wave-particle interactions and charged particle precipitation

Sun, 01 Dec 1996 00:00:00 GMT

Title: Wave-particle interactions and charged particle precipitation Authors: Singh, U P; Singh, Ashok K; Singh, D P; Singh, R P; Singh, R N Abstract: The lightning-generated electric field produces ducted whistler mode waves. These short-duration electric fields penetrate to the equator and alter the dynamics of cyclotron resonant interactions between trapped energetic electrons and whistler mode waves. The electric field also enhances pitch angle diffusion which results into enhanced precipitation of charged particles in the upper atmosphere. Numerical results for the precipitation of electrons into different regions of the magnetosphere are discussed. The enhanced precipitating fluxes produce pimples of different sizes in the ionization density at the bottom of the ionosphere which may result in various changes in radio signals propagating in the earth-ionosphre waveguide. Page(s): 351-355