Impact of Doppler Radar Wind in Simulating the Intensity and Propagation of Rainbands Associated with Mesoscale Convective Complexes Using MM5-3DVAR System

Pre-monsoon rainfall around Kolkata (northeastern part of India) is mostly of convective origin as 80% of the seasonal rainfall is produced by Mesoscale Convective Systems (MCS). Accurate prediction of the intensity and structure of these convective cloud clusters becomes challenging, mostly because the convective clouds within these clusters are short lived and the inaccuracy in the models initial state to represent the mesoscale details of the true atmospheric state. Besides the role in observing the internal structure of the precipitating systems, Doppler Weather Radar (DWR) provides an important data source for mesoscale and microscale weather analysis and forecasting. An attempt has been made to initialize the storm-scale numerical model using retrieved wind fields from single Doppler radar. In the present study, Doppler wind velocities from the Kolkata Doppler weather radar are assimilated into a mesoscale model, MM5 model using the three-dimensional variational data assimilation (3DVAR) system for the prediction of intense convective events that occurred during 0600 UTC on 5 May and 0000 UTC on 7 May, 2005. In order to evaluate the impact of the DWR wind data in simulating these severe storms, three experiments were carried out. The results show that assimilation of Doppler radar wind data has a positive impact on the prediction of intensity, organization and propagation of rain bands associated with these mesoscale convective systems. The assimilation system has to be modified further to incorporate the radar reflectivity data so that simulation of the microphysical and thermodynamic structure of these convective storms can be improved.     

Experimental Seasonal Forecast of Monsoon 2005 Using T170L42 AGCM on PARAM Padma

As a part of the Experimental Extended Range Monsoon Prediction Experiment, ensemble mode seasonal runs for the monsoon season of 2005 were made using the National Centre for Environmental Prediction (NCEP), T170L42 AGCM. The seasonal runs were made using six initial atmospheric conditions based on the NCEP operational analysis and with forecast monthly sea-surface temperature (SST) of the NCEP Coupled forecast system (CFS). These simulations were carried out on the PARAM Padma supercomputer of Centre for Development of Advanced Computing (C-DAC), India. The model climatology was prepared by integrating the model for ten years using climatological SST as the lower boundary. The climatology of the model compares well with the observed, in terms of the spatial distribution of rainfall over the Indian land mass. The model-simulated rainfall compares well with the Tropical Rainfall Measuring Mission (TRMM) estimates for the 2005 monsoon season. Compared to the model climatology (7.81 mm/day), the model had simulated a normal rainfall (7.75 mm/day) for the year 2005 which is in agreement with the observations (99% of long-term mean). However, the model could not capture the observed increase in September rainfall from that of a low value in August 2005. The circulation patterns simulated by the model are also comparable to the observed patterns. The ensemble mean onset is found to be nearer to the observed onset date within one pentad.     

Interpretation of self potential data for vertical and nearly vertical sheets of infinite horizontal extension

Summary Quantitative interpretation of SP anomalies due to vertical and nearly vertical, thin sheets of infinite horizontal extension has been developed in this paper. The methods proposed utilise selective SP values at some selected points on the profile thus enabling us to get the different parameters of the causative body directly. Also, for the case of vertical sheet, an interpretation technique has been formulated when the base station is within the zone of influence of the potential field of the causative body.     

Associated and non-associated constitutive relations for undrained behaviour of isotropic soft clays

Incremental theory of plasticity has been used to derive associated and non-associated stress–strain relations for analysing the undrained stress-strain response of isotropic normally and lightly overconsolidated clays. A series of comparisons between the theoretical stress-strain-pore pressure response and laboratory test results for 3 in. × 6 in. samples of very high degree of repeatability and reproduceability have been described. From these comparisons it can be seen that both the associated and, non-associated Cam clay models appear to give consistently the best correlations between the theoretical results and the experimental observations.     

Sediment magnetic properties reveal holocene climate change along the Minnesota prairie-forest ecotone

We propose a model that explains variations in magnetic parameters of lake sediments as a record of Holocene climate change. Our model is based on records from 4 lakes and incorporates the effects of erosion, dust deposition, and the authigenesis and diagenesis of the magnetic component of the sediment. Once checked against high resolution multi proxy climate records, which are currently being established for some of our study sites, it will allow us to use magnetic proxies to establish high-resolution climate reconstructions on a regional scale.Our model utilizes a combination of concentration-dependent parameters (magnetic susceptibility, IRM) and grain-size-dependent parameters (ARM/IRM, hysteresis parameters). Magnetic mineralogy is characterized by a combination of low-temperature measurements and S-ratios, and our magnetic measurements are complemented by XRD, LOI and smearslide analyses.During periods of forest growth within the watershed, deposition of terrigenous material is low and the sediment magnetic properties are characterized by low concentrations of mainly authigenic minerals (low values of IRM, high ratios of ARM/IRM). During the early to mid-Holocene dry period, deposition of terrigenous material increased due to intensified dust deposition and the erosion of lake margins caused by lowered water levels. Concentration of magnetic minerals increases (high IRM, ) and so does the grain-size of the magnetic fraction (low ARM/IRM). During the late-Holocene, sediment magnetic properties depend on the varied position of the site with respect to the prairie–forest ecotone.     

Prime controls on Archaean–Palaeoproterozoic sedimentation: Change over time

Although the principle of uniformitarianism may be applied to the Precambrian sedimentary record as a whole, certain periods of the Archaean and Palaeoproterozoic witnessed a changing pattern of prime influences controlling the depositional systems. This paper examines the major controls on sedimentation systems and environments during the Archaean and Palaeoproterozoic within the broader perspective of Earth evolution. Earth's earliest sedimentary system (4.4?-3.7 Ga) was presumably comprised of deep oceanic realms and probably influenced primarily by bolide impacts, major tsunamis, localized traction and global contour current patterns, and bathymetry. As continental crust began to form, the impact-dominated, tsunami type sedimentation gave way to wider varieties of sedimentary environments, known from the oldest sedimentary records. During early continental crustal evolution (c. 3.7–2.7 Ga), sedimentation was essentially of greenstone-type. Volcanic and volcaniclastic rocks were the major components of the greenstone belts, associated with thin carbonates, stromatolitic evaporites, BIF, pelites and quartzites and lesser synorogenic turbidites, conglomerates and sandstones. Volcanism and active tectonism (reflecting dynamic depositional settings during island arc and proto-continental nucleus formation) were the predominant factors influencing sedimentation during this phase of Earth evolution. Transgressions and regressions under the combined influence of tectonics and eustasy are reflected in fining- and coarsening-upwards successions from the proto-cratonic settings; low freeboard enabled the transgression to affect large areas of the proto-cratons. As the earliest, relatively stable craton formed, through a combination of plate tectonic and mantle-thermal processes, continents and supercontinents with the potential for supercontinental cycles started to influence sedimentation strongly. Major controls on Neoarchaean–Palaeoproterozoic sedimentation systems (2.7–1.6 Ga) were provided by a combination of superplume events and plate tectonics. Two global-scale ‘superevents’ at c. 2.7 Ga and c. 2.2–1.8 Ga were accompanied by eustatic rise concomitant with peaks in crustal growth rates, and large epeiric seas developed. The operation of first-order controls leading to development of vast chemical sedimentary platforms in these epeiric seas and concomitant palaeo-atmospheric and palaeo-oceanic evolution combined to provide a second-order control on global sedimentary systems in the Neoarchaean–Palaeoproterozoic period. The supercontinental cycle had become well established by the end of the Palaeoproterozoic, with the existence of large cratons across broad spectrums of palaeolatitude enabling erg development. The entire spectrum of sedimentary systems and environments came into existence by c. 1.8 Ga, prime influences on sedimentation and depositional system possibly remaining essentially uniform thereafter.     

Luminescence investigation of loess and tephra from Halfway House section, Central Alaska

Infrared stimulated luminescence (IRSL) properties of the Old Crow tephra and bracketing loess from the Halfway House site in Central Alaska are investigated in order to test newly developed techniques, including SAR and recently proposed fading corrections. Loess samples investigated show a standard growth of luminescence with regenerative dose while the tephra sample is less sensitive by an order of magnitude and saturates at lower dose. The growth curves obtained using multiple-aliquots regeneration (MAR) saturate at a higher value than those with the single-aliquot regeneration (SAR) protocol. Fading rate determinations for these samples are shown to be imprecise and no noticeable difference was observed between loess and tephra materials. Anomalous fading corrections using an average g value of 5% are applied to the natural test dose signal intensity using the dose rate correction (DRC) method. IRSL ages obtained for loess are in agreement with the expected age while the tephra age is lower than expected, suggesting the measured fading rate is underestimated for this material.     

Waves in the solar transition region

The power spectra for line intensities of several lines formed in the upper transition region around 100000 to 250000 K are presented. A period of 5 min is clearly present in lines due to Oiii, Oiv, and Ov. In one dataset a period approaching 10 min is present for 40 min. The size of the emitting features is limited to 7 arc sec squared. In all datasets examined, there is excess power below 4 mHz everywhere along the slit, although the observed periods do not always come from the most intense regions. In 40% of instances clear periods are observable in the 2–5 mHz range with the largest power peak at 3.0 mHz. In all regions, the 5.0 mHz power peak is smaller. For the frequencies investigated there are no significant time delays in any of the datasets examined. This finding may not be entirely unexpected as the formation temperatures of Oiii (100000 K) and Ov (250000 K) may be too close in order to result in an observable phase shift.The observations are discussed in terms of trapped magnetic modes below the transition region and resonant absorption of MHD waves. For resonant absorption we derive from the observed period of 5 min and the observed extent of the structure a typical magnetic field strength of about 2 G. This value is in good agreement with results from MDI for quiet-Sun regions. Our results seem to imply that resonant waves can play a role in the heating of the quiet Sun. We discuss the effect of observing without tracking on the power spectrum and show that the effect is small.     

Coronal line-width variations

Line-width measurements of the coronal ion Siviii confirm earlier observations which show an increase in the non-thermal velocity above the solar limb. The present data, taken at the equatorial limb, show an increase from 24 km s^-1 at the limb to 28 km s^-1 some 25000 km above the limb. The electron density as measured from the Siviii line pair shows a decrease from 3.5 × 10⁸ cm^-3 to 1.8 × 10⁸ cm^-3 over the same distance. These data imply that the non-thermal velocity is inversely proportional to the quadratic root of the electron density, in excellent agreement with that predicted for undamped radially propagating Alfvén waves.     

A reconnaissance survey of the distribution of some trace elements in Indian bauxite

The results of spectrographic analysis of 500 bauxite samples from 25 deposits show that the distribution of Cr, V, Zr and Ga is completely randomised in accordance with the model of complex, polycyclic sequence of bauxite genesis, deduced by other workers on the basis of mineralogical and major element studies. The same process of residual weathering, which generates a systematic enrichment and fractionation of major insoluble elements causes a random dispersion, notwithstanding the overall enrichment, of the insoluble trace elements due to seasonal variations in pH and in direction of movement of the pore water.