Effect of Troposphere and Ionosphere on C-Band Radar Track Data and Correction of Tracking Parameters

At any launch base radar tracking is critical for assessing the state of the launch vehicle for range safety function as well as for trajectory monitoring. Tracking data corrected for refraction effects is essential for estimating the flight performance. This paper presents the refraction effects of troposphere and ionosphere on the radio waves of C-Band radars in terms of errors in the measured tracking parameters. Application of mapping functions for correcting refraction errors in C-Band radar track data is studied and a comparison of the performance of mapping functions is presented. The mapping functions not only show good convergence at low elevations but also correct around 90 per cent of the refraction error in elevation.Defence Science Journal, 2012, 62(6), pp.420-426, DOI:http://dx.doi.org/10.14429/dsj.62.116

Development of a high resolution land surface dataset for the South Asian monsoon region

In this study, we report the development of a high resolution land surface dataset for the South Asian monsoon region for studies on land surface processes, and land and atmosphere coupling. The high resolu- tion land data assimilation system was used to develop the land surface dataset utilizing TRMM rainfall and ECMWF atmospheric variables as forcing parameters. The dataset was developed at a spatial resolution of 0.5° and temporal resolution of 1 h and spans a period of 6 years, i.e. 1 January 2005 to 31 December 2010. The major highlights in the development of the present dataset are higher spatial and temporal resolution of land surface parameters, use of sub-daily forcing parameters including rainfall, use of MODIS land-use data in lieu of USGS land-use data and weekly varying vegetation fraction instead of monthly vegetation climatology. A comparison of soil moisture and soil temperature with limited surface observations of the IMD suggests reasonable reliability of the land surface data. The model sensible heat flux data are compared with in situ measurements at Ranchi and MEERA reanalysis data. The sensitivity analysis shows that the land surface data are sensitive to rainfall and green vegetation cover data used as the forcing parameters. The dataset has been used to discuss the variations of land surface processes associated with active and break spells and a severe heat wave observed in 2009. The present dataset will be useful for many applications, including initializing numerical models for weather prediction. This high resolution land surface dataset is available for research on request

Studies on atmospheric gravity wave activity in the troposphere and lower stratosphere over a tropical station at Gadanki

MST radars are powerful tools to study the mesosphere, stratosphere and troposphere and have made considerable contributions to the studies of the dynamics of the upper, middle and lower atmosphere. Atmospheric gravity waves play a significant role in controlling middle and upper atmospheric dynamics. To date, frontal systems, convection, wind shear and topography have been thought to be the sources of gravity waves in the troposphere. All these studies pointed out that it is very essential to understand the generation, propagation and climatology of gravity waves. In this regard, several campaigns using Indian MST Radar observations have been carried out to explore the gravity wave activity over Gadanki in the troposphere and the lower stratosphere. The signatures of the gravity waves in the wind fields have been studied in four seasons viz., summer, monsoon, post-monsoon and winter. The large wind fluctuations were more prominent above 10 km during the summer and monsoon seasons. The wave periods are ranging from 10 min-175 min. The power spectral densities of gravity waves are found to be maximum in the stratospheric region. The vertical wavelength and the propagation direction of gravity waves were determined using hodograph analysis. The results show both down ward and upward propagating waves with a maximum vertical wave length of 3.3 km. The gravity wave associated momentum fluxes show that long period gravity waves carry more momentum flux than the short period waves and this is presented

Rainrate and rain attenuation statistics for different homogeneous regions of India

303-314Rain rate and rain attenuation predictions are one of the most important steps to be considered when analyzing satellite communication links at the Ku and Ka bands. Rain rate distributions are calculated from the global data sets of Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Climatology Project (GPCP) for six rainfall homogeneous regions of India. The rain rate distributions are estimated from the monthly accumulations of TRMM and GPCP for the years 1998-2010. The estimated rain rate distributions are compared with the standard ITU-R P.837-5 (International Telecommunication Union - for Radio wave propagation) and observed relative errors are presented. The specific rain attenuation calculated at 0.01% and 0.001% probabilities of exceedance in an average year for different frequencies are also presented for the six homogeneous regions of India. Observations indicate maximum specific attenuation in the NE region over Cheerapunji at 0.001% of the time, and minimum attenuation of 21.988 dB km-1 in Bikaner at 0.01% for 50 GHz frequency in the NW region. Rain attenuation and rain rate distribution are found to exhibit similar characteristics over six homogeneous regions of India

Vertical velocity, horizontal divergence and turbulence associated with tropical mesoscale convective system

91-97The MST radars have been used to measure directly the vertical motions above the radar site. Vertical velocity profiles and horizontal divergence/convergence derived from the vertical velocity using the mass continuity equation as well as eddy dissipation rate estimated under strong-to-moderate convection period are presented in the paper. Data obtained from the Indian MST radar located at Gadanki(13.5oN, 79.8°E) have been used. The height range of the study is from 4 km to 20 km. The aim of the present study is to calculate the horizontal divergence from the vertical velocity and then to find the extent of the enhancement in the vertical velocity and horizontal divergence as well as turbulence distribution during the well developed tropical mesoscale disturbances. Strong enhancement is observed in the vertical velocity and the horizontal divergence/convergence. Maximum turbulence has been observed near the top of the cloud and above. Eddy dissipation rate of the order of 0.007m2s-3 has also been observed

MST radar observations of the Leonid meteor storm during 1996-2007

67-71The Indian MST radar is a powerful atmospheric remote sensing instrument for ionospheric studies operating at 53 MHz frequency. Systematic observations of Leonids were carried out during 16–20 November every year from 1996 to 2007 with radar operating in meteor mode. It has been observed that the presence of strong background component which resulted from several apparitions of parent comet is the cause for the shower activity every year. The trail component that was left behind during each apparition is strong enough to cause the meteor shower for two consecutive years. In this regard, the detailed study of 2007 Leonids is presented in the paper, even though the shower activity was observed to be quite low, and interestingly it resulted in a double (multiple) broad peak rather than a single peak. The results show that the Leonid stream composed of several narrow dense trails existed simultaneously and the sharp meteor outbursts were observed when the Earth encountered a region of high spatial density of particles within the stream

Northeast monsoon rainfall variability over South peninsular India and its teleconnections

Rainfall over south peninsular India during the northeast (NE) monsoon season (Oct-Dec) shows significant interannual variation. In the present study, we relate the northeast monsoon rainfall (NEMR) over south peninsular India with the major oscillations like El Niño Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and Equatorial Indian Ocean Oscillation (EQUINOO) in the Indian and Pacific Oceans. For establishing the teleconnections, sea surface temperature, outgoing long wave radiation, and circulation data have been used. The present study reveals that the positive phase of ENSO, IOD, and EQUINOO favor the NEMR to be normal or above normal over southern peninsular India. The study reveals that the variability of NEMR over south peninsula can be well explained by its relationship with positive phase of ENSO, IOD, and EQUINOO

Analysis of variations of cloud and aerosol properties associated with active and break spells of Indian summer monsoon using MODIS data

Indian summer monsoon exhibits significant intra-seasonal variations with active and break monsoon spells. Using MODIS data of 8 years (2000-2007), variations of cloud and aerosol properties over the Indian region associated with the active and break spells were examined. The study shows statistically significant variations of cloud properties (cloud optical depth, cloud fraction and cloud top pressure) between active and break monsoon days over central and northeast India and the equatorial Indian Ocean. During the monsoon break spells, associated with the anomalous circulation, aerosol loading from the north Arabian Sea is transported to central India. This increase in aerosol content decreases the cloud effective radii, suggesting the indirect effect of aerosols on cloud properties. There is also an inverse relationship of cloud properties over the monsoon zone over central India and the southeast equatorial Indian Ocean, suggesting possible role of southeast equatorial Indian Ocean on the development of active-break cycles