Simulation of monsoon intraseasonal variability in NCEP CFSv2 and its role on systematic bias

We have evaluated the simulation of Indian summer monsoon and its intraseasonal oscillations in the National Centers for Environmental Prediction climate forecast system model version 2 (CFSv2). The dry bias over the Indian landmass in the mean monsoon rainfall is one of the major concerns. In spite of this dry bias, CFSv2 shows a reasonable northward propagation of convection at intraseasonal (30–60 day) time scale. In order to document and understand this dry bias over the Indian landmass in CFSv2 simulations, a two pronged investigation is carried out on the two major facets of Indian summer monsoon: one, the air–sea interactions and two, the large scale vertical heating structure in the model. Our analysis shows a possible bias in the co-evolution of convection and sea surface temperature in CFSv2 over the equatorial Indian Ocean. It is also found that the simulated large scale vertical heat source (Q1) and moisture sink (Q2) over the Indian region are biased relative to observational estimates. Finally, this study provides a possible explanation for the dry precipitation bias over the Indian landmass in the simulated mean monsoon on the basis of the biases associated with the simulated ocean–atmospheric processes and the vertical heating structure. This study also throws some light on the puzzle of CFSv2 exhibiting a reasonable northward propagation at the intraseasonal time scale (30–60 day) despite a drier monsoon over the Indian land mass.     

Analytical solutions of tracer transport in fractured rock associated with precipitation-dissolution reactions

Precipitation-dissolution reactions are important for a number of applications such as isotopic tracer transport in the subsurface. Analytical solutions have been developed for tracer transport in both single-fracture and multiple-fracture systems associated with these reactions under transient and steady-state transport conditions. These solutions also take into account advective transport in fractures and molecular diffusion in the rock matrix. For studying distributions of disturbed tracer concentration (the difference between actual concentration and its equilibrium value), effects of precipitation-dissolution reactions are mathematically equivalent to a “decay” process with a decay constant proportional to the corresponding bulk reaction rate. This important feature significantly simplifies the derivation procedure by taking advantage of the existence of analytical solutions for tracer transport associated with radioactive decay in fractured rock. It is also useful for interpreting tracer breakthrough curves, because the impact of a decay process is relatively easy to analyze. Several illustrative examples are presented, which show that the results are sensitive to fracture spacing, matrix diffusion coefficient (fracture surface area), and bulk reaction rate (or “decay” constant), indicating that the relevant flow and transport parameters may be estimated by analyzing tracer signals.     

Ferrobasalts from the Central Indian Ocean Basin

We report the occurrence of ferrobasalts recovered from the Central Indian Ocean Basin crust generated at the Southeast Indian Ridge during a phase of moderate to fast spreading accretion (～110–190?mm/yr, full rate).The rocks are rich in plagioclase, FeO* (13–19%), and TiO₂ (2.27–2.76%), poor in olivine and MgO (3.44–6.20%), and associated with topographic highs and increased amplitude magnetic anomalies corresponding to chrons A25 and A24. We suggest that secon dary eruptions from ancient N-MORB magma, which may have been trapped at a shallow depth in a horizon of neutral buoyancy, could have produced the ferrobasalts.     

Geomorphological analysis of paleo drainage systems and their environmental implications in the desert of Kuwait

 A well-developed drainage network is carved in the hard calcretized and gypcretized gravelly sand of the Pleistocene Dibdibba Formation in northern Kuwait. The present-day aridity suggests that these drainages were developed during pluvial episodes that took place in the post-Pleistocene time and, therefore, are considered as paleo-drainage. Detailed morphometrical analysis of the endoeric drainage systems was performed and the degree of correlation among their different morphometric parameters was investigated. Based on these parameters, the studied drainage basins are statistically grouped into three groups. Such grouping was confirmed by discriminant analysis. The categorical data analysis demonstrated the dependence of these groupings on the surface geology, regional topography, and local geomorphological settings. Infiltration measurements revealed that the drainage bedrocks have a low infiltration rate (<20 cm h^–1), whereas the drainage fill deposits have a relatively high infiltration rate (67–30 cm h^–1). The impact of the drainage system pattern and morphometry on the hydrological conditions is discussed and potential near-surface low salinity to freshwater aquifers is delineated. The role of the studied drainage systems in the occurrence of mobile sand and sand dunes, rainwater harvesting, and land capability are discussed. Received: 8 September 1995 · Accepted: 24 October 1995     

Statistical analysis on yearly seismic moment release data to demarcate the source zone for an impending earthquake in the Himalaya

Tectonism in the Himalayan fold-thrust belt had generated great earthquakes in the past and will spawn more in the future. Sequential cumulative moment release data of macroearthquakes (Mb ≥ 4.5) over the years 1964–2006 in four zones of the Himalaya was analysed by nonparametric RUD method. The Z values of RUD analysis had neither rejected nor supported the null hypothesis of randomness. However, the Hurst analysis and plot, a statistical procedure to identify clustering of low and high values in a time series, brought out a pattern for earthquake prognostication. The pattern was a negative sloping segment representing a sluggish moment release over years, followed by a positive sloping segment indicating a sudden high moment release with occurrence of medium/large size earthquake(s). In recent past, such a negative sloping has been found in Zones B (1992–2006) and D (1998–2006), indicating an impending moderate/mega earthquake event in near future.     

Variation of the gas and radiation content in the sub-Keplerian accretion disk around black holes and its impact to the solutions

We investigate the variation of the gas and the radiation pressure in accretion disks during the infall of matter to the black hole and its effect to the flow. While the flow far away from the black hole might be non-relativistic, in the vicinity of the black hole it is expected to be relativistic behaving more like radiation. Therefore, the ratio of gas pressure to total pressure (β) and the underlying polytropic index (γ) should not be constant throughout the flow. We obtain that accretion flows exhibit significant variation of β and then γ, which affects solutions described in the standard literature based on constant β. Certain solutions for a particular set of initial parameters with a constant β do not exist when the variation of β is incorporated appropriately. We model the viscous sub-Keplerian accretion disk with a nonzero component of advection and pressure gradient around black holes by preserving the conservations of mass, momentum, energy, supplemented by the evolution of β. By solving the set of five coupled differential equations, we obtain the thermo-hydrodynamical properties of the flow. We show that during infall, β of the flow could vary up to ∼300%, while γ up to ∼20%. This might have a significant impact to the disk solutions in explaining observed data, e.g. super-luminal jets from disks, luminosity, and then extracting fundamental properties from them. Hence any conclusion based on constant γ and β should be taken with caution and corrected.     

Does accelerating Universe permit varying speed of light?

We investigate the possible variation of c in the context of the present accelerating Universe as discovered through SN Ia observations and show that variability of c is not permitted under the variable Λ models.     

The Eastern Ghats Belt … A polycyclic granulite terrain

The Eastern Ghats Belt is a polycyclic granulite terrain along the east coast of India whose western boundary is marked by a shear zone along which the granulites are thrusted over the cratonic units of the Indian shield, and its northern margin is marked by the presence of a number of fault-bounded blocks. Recent work has convincingly brought out that there are domains within the belt having different evolutionary histories. The segment south of the Godavari Rift went through a high grade thermo-tectonic event at ∼1.6–1.7 Ga. North of the Godavari Rift in a narrow zone along the western boundary the last high-grade metamorphic event is of late Archaean age. A series of alkaline plutons along the western boundary zone testifies to a rifting episode at ∼1.3–1.5 Ga. In the major part of the EGB the metamorphism is broadly of Grenvillian age, with two major thermo-tectonic pulses at ∼1.1–1.2 Ga and ∼0.95–1.0 Ga. But high grade conditions persisted for a long period and younger thermal events of ∼0.65 Ga to ∼0.80 Ga are locally recorded. There are differences in the tectonometamorphic histories of different domains, but the tectonic significance of these differences remains uncertain. Pan-African (0.50–0.55) thermal overprints are common and become conspicuous along the western boundary zone. The thrusting of the Eastern Ghats granulites in a hot state over the cratons to the west is of Pan-African age. In the Rodinia assembly (∼0.9 Ga) the Eastern Ghats and the Rayner-Napier Complexes of Antarctica were contiguous, but the pre-Rodinia configuration of these terrains remains unclear. At ∼0.8 Ga during the Rodinia break up Greater India rifted apart from East Antarctica, and only later it docked with Australia-East Antarctica at 530–550 Ma. The continuation of the East Antarctic Pan-African orogenic belts into the Eastern Ghats is yet to be ascertained.     

Seismicity pattern in north Sumatra-Great Nicobar region: In search of precursor for the 26 December 2004 earthquake

We analyse the seismicity pattern including b-value in the north Sumatra-Great Nicobar region from 1976 to 2004. The analysis suggests that there were a number of significant, intermediate and short-term precursors before the magnitude 7.6 earthquake of 2 November 2002. However, they were not found to be so prominent prior to the magnitude 9.0 earthquake of 26 December 2004 though downward migration of activity and a 50-day short-term quiescence was observed before the event. The various precursors identified include post-seismic and intermediate-term quiescence of 13 and 10 years respectively, between the 1976 (magnitude 6.3) and 2002 earthquakes with two years (1990–1991) of increase in background seismicity; renewed seismicity, downward migration of seismic activity and foreshocks in 2002, just before the mainshock. Spatial variation in b-value with time indicates precursory changes in the form of high b-value zone near the epicenter preceding the mainshocks of 2004 and 2002 and temporal rise in b-value in the epicentral area before the 2002 earthquake.     

Clustering of Earthquake Events in the Himalaya - Its Relevance to Regional Tectonic Set-up

The earthquake events of Himalaya of magnitude ≥5.0 from the time window 1905–2000 are statistically analysed. The inter-event time between earthquakes shows Hurst phenomena of temporal clustering which are spatially located in five distinct domains along the Himalayan fold-thrust belt. Out of these, two domains, one around Uttaranchal-Nepal border and the other around Nepal-Sikkim border reveal maximum number of temporal clusters and thus considered as seismically most potential zones of the Himalaya. Both these zones are located at the interface of the orthogonally disposed major tectonic discontinuities of the Peninsular Shield and Himalayan fold-thrust belt. Such zones are geologically most favourable locales for strain accumulation during later-tectonic movement. Statistical analysis points towards a probability of recurrence of seismic events in near future in these two zones. However, validity of such statistical results can be ascertained by detailed geological and geophysical modelling of the terrain.