A. K. De

On fine structure of dot echoes as observed by acoustic sounder

Abstract Sometimes in the lower atmospheric boundary layer, depending upon the prevailing micro-/meso-scale meteorological condition, ‘dot’ (also known as ‘lump’) type echo structures appear generally during night-time with light wind and stable stratifications. They are associated often with disturbed atmospheric boundary layer conditions like the occurrence of thunderstorms and/or of precipitation. Digitization and scanning of individual dot/lump echo structure can indicate a cluster of points with varying echo intensity levels. In the coastal region of Calcutta they are found to be spreading vertically and the size of the cluster depends on the vertical height of occurrence. Using image processing technique fine structures of these echoes have been processed, their statisticalnature has been analysed and reported in this paper.

VHF propagation characterization during atmospheric disturbances

Abstract The propagation of a television (TV) signal is usually perturbed during periods of atmospheric disturbance such as in thunderstorms. The region under investigation here is situated in the coastal area of the Bay of Bengal and has experienced frequent thunderstorm activities. An investigation to study their effects on VHF signal propagation transmitted from Satkhira in Bangladesh and received at the Indian Statistical Institute, Calcutta, has been undertaken. The depths of the atmospheric disturbances within a 1 km range have been recorded and measured by acoustic sounder (sodar) operated continuously at the receiving station. The inset of the storm is marked by the enhanced signal level with deep fluctuations characteristic during the periods of thunderstorms.

Sodar observation of elevated layers around Calcutta

Abstract Sodar (sound radar) echograms recorded at the Indian Statistical Institute, Calcutta, often exhibit stratified or elevated layers over the ground-based inversion. These have been noticed often after the occurrences of thunderstorms and rain. These layers may be single or multiple, continuous or intermittent and are associated with some perturbations even as gravity wavelike structures. All these features of the lower atmospheric structures over this coastal station, as detected by a sound radar, are discussed in this paper.

Cloud Characteristics by Using Doppler Radar over Kolkata

In present days radio communication scenario, three issues are considered to be the most important. These are reliability, directivity and regulation of transmitted power. All such issues can be taken care provided the characterization of our tropospheric medium is done with good degree accuracy. The radio wave propagating above 10 GHz is affected severely by rain and cloud. In case of rain, the attenuation of radio wave is the main concerned but for cloud along with attenuation, noise temperature generated by cloud is also another issue. Cloud attenuation and cloud noise temperature can be deduced if cloud morphology in terms of cloud coverage, cloud height, cloud thickness, cloud liquid water content etc. is available. The meteorologists of India have studied cloud morphology as well as cloud dynamics for the weather forecasting purposes. But in this paper, an attempt has been made to deduce results on cloud parameters for radio wave propagation studies by utilizing the observations taken by the sophist...