A new investigation of microbursts at meter-decameter wavelengths

We report on a new investigation of microbursts at meter-decameter wavelengths observed using the Broad Band Array at Gauribidanur Radio Observatory. This is an independent set of observations of microbursts: previous observations had been obtained only by the Clark Lake multifrequency radioheliograph. We confirm several properties of microbursts reported earlier. In addition, we have studied some new properties of microbursts such as time profile characteristics, flux density and energy spectra for comparison with the corresponding properties of normal type III bursts. The present study supports the idea that the microbursts and the normal type III bursts are generated by electron beams of similar characteristics. We interpret the low brightness temperature of microbursts as follows: plasma waves generated by the electron beams through beam-plasma instability are quickly isotropized as they scatter on the density fluctuations in the corona. The resulting low levels of plasma waves are converted into transverse radiation of low brightness temperature. One important consequence of the isotropization is that the second harmonic plasma emission dominates the fundamental and hence the microbursts are expected to be predominantly a harmonic plasma emission.     

Pulsating radio emission at decametre wavelengths from the sun

Observations on the pulsation pattern in the time profile of short duration solar radio bursts at decametre wavelengths are presented. The pulsations are found to be present predominantly in the saturation phase of the burst. A tentative physical model based on the non-linear development of the waves interacting in a turbulent medium is invoked to explain the origin of the pulsations.     

Storm surge vulnerability along Chennai–Cuddalore coast due to a severe cyclone THANE

A very severe cyclonic storm ‘Thane’ developed over the Bay of Bengal during 25–30 December 2011, crossed the Tamilnadu coast between Pondicherry and Cuddalore (southeast coast of India) in early hours of 30 December with a wind speed 120–140 km/h. The offshore tide record reveals that the surge started to generate around 1100 hours on 29 December 2011 with a height 0.4 m and later raised to 0.68 m at the time of land fall, that is, early hours (0000 hours) of 30 December 2011. Field reconnaissance survey on surge run-up and inundation distance at 15 selected locations of cyclone affected areas reveals that the vulnerability levels are highly variable along the coast. The inundation distance extended up to 30–230 m landward from the shoreline and run-up reached to 1.6–3.2 m above chart datum depending upon the cross-shore geometry of the location. In the areas (Verranampattinam, Chinamudaliyar kuppam and Silver beach) near cyclone landfall, the run-up was up to 2.5–3.2 m and the inundation distance extended up to a maximum of 230 m. However, in the areas located about 150 km north of cyclone landfall, the run-up limited from 1.6 to 1.7 m and the inundation distance extended up to only a maximum of 169 m. The inundation distance is mainly influenced by the slope of the beach. In the areas having beach slope between 1 in 135 and 1 in 220, the inundation distance was 210–230 m. However, in the areas having beach slope 1 in 17 to 1 in 34, the inundation distance is restricted between 35 and 50 m.     

Study of interacting CMEs and DH type II radio bursts

The subject of interaction between the Corona Mass Ejections (CMEs) is important in the concept of space-weather studies. In this paper, we analyzed a set of 15 interacting events taken from the list compiled by Manoharan et al. (in J. Geophys. Res. 109:A06109, 2004) and their associated DH type II radio bursts. The pre and primary CMEs, and their associated DH type II bursts are identified using the SOHO/LASCO catalog and Wind/WAVES catalog, respectively. All the primary CMEs are associated with shocks and interplanetary CMEs. These CMEs are found to be preceded by secondary slow CMEs. Most of primary CMEs are halo type CME and much faster (Mean speed = 1205 km?s^?1) than the pre CME (Mean speed = 450 km?s^?1). The average delay between the pre and primary CMEs, drift rate of DH type IIs and interaction height are found to be 211 min, 0.878 kHz/s and 17.87 Ro, respectively. The final observed distance (FOD) of all pre CMEs are found to be less than 15 Ro and it is seen that many of the pre CMEs got merged with the primary CMEs, and, they were not traced as separate CMEs in the LASCO field of view. Some radio signatures are identified for these events in the DH spectrum around the time of interaction. The interaction height obtained from the height-time plots of pre and primary CMEs is found to have correlations with (i) the time delay between the two CMEs and (ii) the central frequency of emission in the radio signatures in the DH spectrum around the time of interaction. The centre frequency of emission in the DH spectrum around the time of interaction seems to decrease when the interaction height increases. This result is compared with an interplanetary density model of Saito et al. (in Solar Phys. 55:121, 1977).     

High energy observations of June 1980 solar flares

The paper presents a detailed study of the high energy X-ray observation of the most unusual solar events observed on 4 and 7 June, 1980 with the Hard X-Ray Burst Spectrometer (HXRBS) on Solar Maximum Mission (SMM) satellite. The hard X-ray data of the events are also compared with the radio microwave fluxes.The X-ray time profiles of these flares are characterized by the occurrence of impulsive phase superposed with a number of narrow spikes before the occurrence of the main energetic events. Studies of the temporal and spectral properties of these events indicated a quasi-oscillatory nature of the sources. Various models for explaining the evolution of the events are considered and the sequential firing loop model seems to be consistent with the observations of the events.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Heavy metals distribution and fractionation in sediments of the Mahanadi River basin, India

Heavy metals distribution in core sediments, different size fractions of bed sediments (>212 urn, 90-212 jam, 63–90 urn, 53–63 urn, < 53 urn), and suspended sediments (>30 urn, 20–30 m, 10–20 urn, 2–10 urn, <2 m) have been discussed. Pb, Zn, and Cr have been accumulating in recent years in the sediments. Si, Al, Fe, Ca, and Mg dominate the bed and suspended sediment composition. Metals show increasing concentrations in finer sediments. Applying multivariate analysis to sediment composition, metals have been grouped into different factors depending upon their source of origin. Chemical fractionation studies on suspended and bed sediments show Fe, Zn, Cu, and Pb are associated with the residual fraction and Mn with the exchangeable fraction.     

Textural characteristics of the Krishna River sediments,India

To evaluate the magnitude of variation in grain size distribution in the Krishna river, bed sediments and suspended sediments collected along the length of the river have been studied. There are both temporal and seasonal variation in the grain size distribution of suspended sediments. The statistical parameters show the change along the river in a non-linear fashion which may be due to human interference and due to different types of sediments contributed by tributaries to the Krishna river. The suspended sediments are mostly fine silt (4 to 16m), poorly sorted, showing coarse to fine skewed and are platyto leptokurtic. The bed sediments are mostly medium sand (350m) showing moderate to well sorted, coarse to fine skewed and are platy- to leptokurtic. The CM diagram of Krishna river bed sediments suggests that deposition takes place by (1) rolling (2) rolling and suspension and (3) graded suspension. The suspended sediments represent deposits of uniform suspension.