Hydrometeor structure of a composite monsoon depression using the TRMM radar

This paper addresses the use of a satellite-based radar for obtaining the composite structure (from several monsoon depressions) of the distribution of precipitation elements in the horizontal and the vertical. This composting is based on the use of a simple elliptical layout of coordinates along the major and minor axes of each storm as it passed over north central India. This satellite, called the Tropical Rainfall Measuring Mission (TRMM), carries onboard a microwave instrument known as the Precipitation Radar (PR). The vertical structure of hydrometeors provided by the radar is somewhat of the same quality as the ground-based Doppler radar units. The PR could identify many features such as the melting layers, height of convection, extent of anvils and types of precipitation over different sections of the composited monsoon depression. Furthermore, the asymmetric nature of surface rainfall that intensifies around the composited monsoon depression has also been mapped, which could provide several more details than was possible from other satellite-based estimates. It is found that the most intense precipitation occurs in the south-southwest region of the monsoon depression. The preponderance of stratiform rain and the coverage of fewer deep convective elements, especially over the orographic upslope region, are some other noticeable features obtained using the TRMM PR. The stratiform rain was noted to arise where the melting layers (in the radar reflectivity signatures) were located near 5 km. In those few occasions where tall rain clouds were discernible, the cloud tops were seen to extend all the way from 12 to 15 km. Rainfall amounts across the composite monsoon depression range from 10 to 100 mm d⁻¹. The 3–4 d passage time of one of those disturbances resulted in local rainfall totals of the order of 200–300 min d⁻¹.     

THE CORRELATION REFRACTION METHOD AS APPLIED TO WEATHERED ZONE STUDIES IN A GRANITE TERRAIN*

The combined observation of first and later arrivals in shallow seismic refraction surveys, particularly on hard rock terrains, is discussed. Details of experimental weathered-zone investigations by the correlation refraction method in a granite terrain (i.e. field procedure, seismograms obtained, plotting of the data, and identification of the waves are presented). Complete travel time data and interpreted subsurface sections of a few test refraction surveys are included. In one instance the interpreted results of normal and converted refracted wave data have been tested by drilling at three points along a 220 m long profile.     

Fine-scale responses of phytoplankton to freshwater influx in a tropical monsoonal estuary following the onset of southwest monsoon

In May of 2007, a study was initiated by the National Institute of Oceanography (NIO), Goa, India, to investigate the influence of monsoonal rainfall on hydrographic conditions in the Mandovi River of India. The study was undertaken at a location ∼2 km upstream of the mouth of this estuary. During the premonsoon (PreM) in May, when circulation in the estuary was dominated by tidal activity, phytoplankton communities in the high saline (35–37 psu) waters at the study site were largely made up of the coastal neritic species Fragilaria oceanica, Ditylum brightwellii and Trichodesmium erythraeum. During the later part of the intermonsoon (InterM) phase, an abrupt decline in salinity led to a surge in phytoplankton biomass (Chlorophyll a ∼14 mg m^− 3), of a population that was dominated by Thalassiosira eccentricus. As the southwest monsoon (SWM) progressed and the estuary freshened salinity and Chlorophyll a (Chl a) concentrations decreased during the MoN, Skeletonema costatum established itself as the dominant form. Despite the low biomass (Chl a <2 mg m^− 3), the phytoplankton community of the MoN was the most diverse of the entire study. During the postmonsoon (PostM), the increase in salinity was marked by a surge in dinoflagellate populations comprising of Ceratium furca, Akashiwo sanguinea, and Pyrophacus horologium.     

THE BLIND-ZONE PROBLEM IN MULTIPLE REFRACTION-LAYER OVERBURDEN SITUATIONS*

The blind zone problem is examined with a view to provide a simple means of solving the problem in the general case of arbitrary number of refraction layers constituting the overburden to the masked layers. Considering the first arrival refraction interval corresponding to the masked layer which reduces to zero under blind zone conditions, a method to solve the problem is presented. Derivation of the critical distance expression is also included and convenient solutions to compute the thicknesses of the blind zone and its immediate overlayer are worked out. Based on test calculations on some known instances, the efficacy of the method is illustrated. A Fortran program for use when large numbers of refraction layers are involved under the overburden or when more than one masked layer is encountered is available from the authors.     

AN ULTRASONIC PROFILING INVESTIGATION ON SOME FRESH AND WEATHERED GRANITES OF HYDERABAD,INDIA*

The ultrasonic profiling method of measuring the compressional and shear wave velocities in cylindrical rock samples is extended to measurements in some weathered and fresh granite blocks collected from the Hyderabad (India) region. This possibility of the method provides a means of investigating the elastic properties of the less compact rocks, of which the near-surface formations are particularly important. In this article the important parts of the ultrasonic profiling instrument developed are described and the relevant aspects of the seismic wave fields and identification of the individual waves in the wavetrain responses to longitudinal excitation are considered. Compressional, shear and surface (Rayleigh) wave velocities in some fresh and weathered granites are detailed. The compressional velocities range from 4.8 km/s to 5.5 km/s in fresh granites and lie between 1.1 km/s and 2.5 km/s in weathered granites. Young's modulus and Poisson's ratios computed from the measured velocities are also presented. An empirical relation of the form log E= 4.27 + 2.11 log V_p between Young's modulus E and compressional velocities V_p in the fresh granites studied is deduced. The versatility of the approach is thus demonstrated.