X-ray emission characteristics of flares associated with CMEs

We present the study of 20 solar flares observed by “Solar X-ray Spectrometer (SOXS)” mission during November 2003 to December 2006 and found associated with coronal mass ejections (CMEs) seen by LASCO/SOHO mission. In this investigation, X-ray emission characteristics of solar flares and their relationship with the dynamics of CMEs have been presented. We found that the fast moving CMEs, i.e., positive acceleration are better associated with short rise time (< 150 s) flares. However, the velocity of CMEs increases as a function of duration of the flares in both 4.1–10 and 10–20 keV bands. This indicates that the possibility of association of CMEs with larger speeds exists with long duration flare events. We observed that CMEs decelerate with increasing rise time, decay time and duration of the associated X-ray flares. A total 10 out of 20 CMEs under current investigation showed positive acceleration, and 5 of them whose speed did not exceed 589 km/s were associated with short rise time (< 150 s) and short duration (< 1300 s) flares. The other 5 CMEs were associated with long duration or large rise time flare events. The unusual feature of all these positive accelerating CMEs was their low linear speed ranging between 176 and 775 km/s. We do not find any significant correlation between X-ray peak intensity of the flares with linear speed as well as acceleration of the associated CMEs. Based on the onset time of flares and associated CMEs within the observing cadence of CMEs by LASCO, we found that in 16 cases CME preceded the flare by 23 to 1786 s, while in 4 cases flare occurred before the CME by 47 to 685 s. We argue that both events are closely associated with each other and are integral parts of one energy release system.     

Glacier inventory in Himachal Pradesh using satellite images

A total of 125 glaciers covering an area of 1896 sq. km. were mapped on 1:250,000 scale in Himachal Pradesh using satellite images. The areal extent obtained from satellite images was found to be comparable with that from field estimates for eight glaciers for which data are available. This suggests that remote sensing can provide glacial areal extent similar to ground-based methods. Depth of an individual glacier was inferred indirectly by using its relationship with areal extent and geomorphological characteristics, as suggested by Muller (1970). These characteristics were estimated by using satellite images. The analysis suggests that the water equivalent of the glaciers in Himachal Pradesh is about 165 cu km. It is seventeen times more than the storage capacity of the Govind Sagar. This estimate will get revised when other snow/ice features as permanent snow field, ice apron, hanging glaciers and rocky glaciers are mapped. Mapping on larger scale, say 1:50,000, will lead to a further revision as many smaller glaciers and other features will get mapped.     

Snow and glacier melt runoff model to estimate hydropower potential

Himalayan region has high concentrations of mountain glaciers. Large extent of this region is covered by seasonal snow during winter. Runoff generates from melting of these snow and glaciers is one of the important sources of water for the Himalayan Rivers. Glaciers and snowfields are distributed throughout the Himalayas and form a source of numerous streams. Due to steep slopes, all such streams have potential sites for hydropower generation. If this potential is fully utilized, it will help in generating power from environmentally friendly Run-of-River (RoR) hydropower stations. Considering these aspects, a stream flow simulation model was developed for small streams. This will help in estimation of average seasonal unrestricted hydropower potential of snow and glaciated streams for winter, summer, monsoon and autumn seasons. Information generated through remote sensing technique as glacier, permanent snow cover, seasonal snow cover, altitude of snow and glaciers were used in conjunction with daily maximum and minimum temperature, rainfall and discharge. The model was developed for Malana nala located in Parbati River basin near Kullu in Himachal Pradesh. It was validated at adjacent Tosh nala in the same basin. Seasonal runoff computed from the model is comparable with observed data for all seasons except Monsoon. Good results in autumn, winter and summer seasons demonstrates usefulness of runoff model to assess hydropower potential of snow and glaciated streams and therefore, the model was applied to ungauged Sorang Gad and Kirang Khad. In winter runoff was estimated as 1.8 and 1.69 cumecs for Kirang Khad and Sorang Gad, respectively. This is important, as viability of hydropower station depends upon winter stream runoff. These results suggest that the model is useful tool to assess initial estimate of hydropower potential for large number of snow and glaciated streams, for which no hydrological data is available.     

Knowledge discovery from multispectral satellite images

A new approach to extract knowledge from multispectral images is suggested. We describe a method to extract and optimize classification rules using fuzzy neural networks (FNNs). The FNNs consist of two stages. The first stage represents a fuzzifier block, and the second stage represents the inference engine. After training, classification rules are extracted by backtracking along the weighted paths through the FNN. The extracted rules are then optimized by use of a fuzzy associate memory bank. We use the algorithm to extract classification rules from a multispectral image obtained with a Landsat Thematic Mapper sensor. The scene represents the Mississippi River bottomland area. In order to verify the rule extraction method, measures such as the overall accuracy, producer's accuracy, user's accuracy, kappa coefficient, and fidelity are used.     

Impact of climatic parameters on statistical stream flow sensitivity analysis for hydro power

Large area of Himalayas covered with seasonal snow during winter are rapidly changing during summer, significantly affects the stream flow of many rivers originating from Himalayas. This necessitates the efficient time series monitoring of seasonal snow cover in the rugged mountainous region throughout the winter and summer periods for weekly/monthly as well as seasonal forecast of stream run-off for water management and other developmental activities.     

Sandstone diagenesis and porosity modification during basin evolution

The properties of sandstones as potential reservoirs and shales as source rocks depend on primary facies relationships and diagenesis. Porostiy loss due to mechanical compation and pressure solution is essentially a function of grain parameters (sorting, packing and composition) and net overburden stress. The porosity loss can be predicted to a certain extent. The importance of secondary porosity caused by dissolution of framework grains and cements has been fully recognized. The discussion has focused on the processes causing such dissolution and to what extent it can cause net increase in porosity.The most critical factor in clastic diagenesis is the nature of porewater flow and the degree of mass transfer taking place as a result of this. In the North Sea reservoir rocks, petrographic and geochemical evidence suggest that most of the leaching of feldspar and mica resulting in the formation of kaolinite occurred early during fresh wather flushing. Recent calculations indicate that »acids« derived from source rocks are inadequate to explain the secondary porosity observed in reservoir rocks. Mathematical modelling suggests that thermal convection is of limited importance in sedimentary basins, except where there are high lateral changes in geothermal gradients. Evidence from porewater geochemistry suggests that porewaters in sedimentary basins are often stratified or compartmentalized in a way which is inconsistent with large scale convection or compactional flow, making it necessary to assume that diagenetic reactions are relatively isochemical during deeper burial.A better understanding of the diagenetic reactions will help us to improve our predictions about porosity/depth relations, pore size, and pore geometry distribution in reservoir rocks.Porosity depth trends from offshore Norway and published data from other basins are discussed. Empirical linear best fit lines are found to illustrate the relationship quite well for depths between one and five km. Within a specific region, the linear porosity gradient is a function of mineral composition and of temperature and pressure gradients. Primary porosity tends to be best preserved in sandstones with high proportions of stable grains (e. g. in quartz arenites) down to about 3 or 4 km. At greater depth, porosity loss is accelerated due to increased pressure solution. Secondary and primary porosity adjacent to feldspar grains then tends to be selectively preserved relative to primary pores between quartz grains.

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Zusammenfassung Die bestimmenden Faktoren von Sandsteinen als mögliche Speichergesteine und von Schiefern als Bildungsort von Kohlenwasserstoffen liegen in den Verhältnissen der primären Fazieausbildungen der Gesteine und deren Diagenesegeschichte. Korn-Parameter (Sortierung, Pakkungsdichte und Zusammensetzung) und Netto-Auflast steuern mechanische Kompaktion und Drucklösung. Diese sind für Porositätsreduzierungen verantwortlich, die bis zu einem bestimmten Grad abgeschätzt werden können. Der Einfluß von Lösungserscheinungen für die Bildung sekundären Porenraums, der hier definiert werden konnte und die Vorgänge, die Lösungsphasen iniziieren, bilden den zentralen Punkt der Diskussion.Größte Bedeutung in der Diagenese klastischer Sedimente kommt dem Charakter der Grundwasserbewegungen und deren Eigenschaft im Bereich des Stofftransportes zu. Daten der Petrographie und der Geochemie ergeben für die Speichergesteine der Nordsee, daß der Hauptanteil der Lösung von Feldspat und Muskovit, ein Vorgang, der zur Bildung von Kaolinit führte, frühdiadenetisch unter Einfluß von Süßwasser stattfand. Aufgrund neuerer Kalkulationen kann die Bedeutung saurer Lösungen, die man von dem Bildungsgestein hergeleitet, für die sekundäre Porosität der Speichergesteine ausgeschlossen werden. Mathematische Berechnungen räumen dem Einfluß thermaler Konvektion in sedimentären Becken meist geringe Bedeutung zu, es sei denn es gibt große laterale Unterschiede des geothermischen Gradienten. Die geochemische Analyse des Porenwassers ergibt vertikale und horizontale Zonierungen im Chemismus des Wassers. Diese Tatsache widerspricht der These einer großräumischen Konvektion, da in diesem Fall die Diagenese-Prozesse unter Bedeckung bei relativ einheitlicher chemischer Zusammensetzung ablaufen würden.Ein besseres Verständnis der diagenetischen Vorgänge wird die Abhängigkeit des Verhältnisses von Porosität zur Tiefe, der Verteilung des Hohlraumvolumens und der Hohlraumgeometrie in Speichergesteinen erleichtern.Diskutiert werden Zusammenhänge von Porosität und Tiefe, die Daten an Stellen vor der Küste Norwegens und anderen Becken entnommen wurden. Für Tiefen zwischen einem und fünf Kilometern scheinen empirische, lineare Geraden am besten die Verhältnisse zu verdeutlichen. Regional begrenzt kann der lineare Porositätsgradient als eine Funktion der Gradienten von Mineralzusammensetzung, Temperatur und Druck beschrieben werden. Primäre Porosität ist am besten in Sandsteinen mit einem hohen Anteil an stabilen Komponenten (z. B. Quatzarenite) bis zu einer Tiefe von drei oder vier Kilometern erhalten.Drucklösungserscheinungen sind für die zunehmende Abnahme der Porosität in größeren Tiefen verantwortlich. Dabei scheinen sekundäre und intergranulare Porenräume zwischen Feldspatkörnern relativ zu primären Porenräumen zwischen Quartzkörnern stabiler zu sein.

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Résumé Les facteurs qui caractérisent des grès en tant que réservoirs potentiels d'hydrocarbures et des shales en tant que roches-mères sont les relations facielles primaires et la diagenèse. La perte de porosité due à la compaction mécanique et aux impressionnements («pressure-solution») est fonction essentiellement des paramètres des grains (classement, ordonnance et composition) et des contraintes dues à la surcharge. La perte de porosité peut être prévue dans une certaine mesure. On connaît l'importance de la porosité secondaire provoquée par la dissolution des grains et des ciments. La discussion est centrée sur les processus responsables de cette dissolution et sur leur incidence dans l'accroissement net de la porosité.Le facteur le plus critique dans la diagenèse des élastiques est la nature du flux d'eau intersticielle et le degré de transfert de matière qui en résulte. Dans les roches-magasins de la Mer du Nord, les observations pétrographiques et géochimiques montrent que la plus grande partie de l'altération en kaolin du feldspath et du mica s'est produite lors du lessivage par de l'eau douce. Selon des calculs récents, les «acides» dérivés des roches-mères ne peuvent expliquer la porosité secondaire des roches-magasins. La modélisation mathématique suggère que la convection thermique ne joue qu'un rôle subordonné dans un bassin de sédimentation, sauf aux endroits de forte variation latérale du gradient géothermique. L'étude géochimique des eaux intersticielles montre que dans les bassins sédimentaires, elles sont souvent stratifiées ou compartimentées d'une manière qui est incompatible avec une convection à grande échelle car un tel phénomène impliquerait des réactions diagénétiques relativement isochimiques.Une meilleure compréhension des réactions diagénétiques doit nous aider à améliorer nos prévisions relatives à la relation porosité/profondeur, et à la répartition de la taille et de la forme des pores dans les roches-magasins.Une discussion est présentée à propos de la relation porosité/profondeur, à partir des données recueillies off-shore en Norvège et de données publiées provenant d'autres bassins. Il apparaît qu'entre 0 et 5 km de profondeur, des courbes empiriques linéaires rendent le mieux compte de ces relations. Dans une région donnée, le gradient linéaire de porosité est fonction de la composition minéralogique et des gradients de pression et de température. La porosité primaire tend à être bien préservée dans les grès riches en grains stables (p. ex. dans les arénites quartziques) jusqu'à une profondeur de 3 à 4 km. Plus bas, la perte de porosité s'accélère en raison des phénomènes d'impressionnement. Dans ces conditions profondes, les pores primaires et secondaires adjacents aux grains de feldspath semblent relativement plus stables que les pores primaires situés entre les grains de quartz.

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Impacts of sea-level rise on coastal zones of Mauritius: insights following calculation of a coastal vulnerability index

Natural Hazards - Whilst climate change has been regarded as a growing concern in recent years due the disruptive and detrimental effects experienced across the globe, one of its most compelling...     

North-south asymmetry of the polar solar wind and some characteristics of solar magnetic field

We have found correlated variations of the yearly averaged north-south asymmetry in the polar solar wind speed (_sol) and the ratio of the zonal quadrupolar to the zonal dipolar contribution in the inferred coronal magnetic field during the declining phase of sunspot cycle 21. A physically meaningful association between _sol and some polar solar magnetic field proxies is also observed during the low sunspot activity periods of the above cycle.     

Do damped and sub-damped Lyman-alpha absorbers arise in galaxies of different masses?

We consider the questions of whether the damped Lyman-alpha (DLA) and sub-DLA absorbers in quasar spectra differ intrinsically in metallicity, and whether they could arise in galaxies of different masses. Using the recent measurements of the robust metallicity indicators Zn and S in DLAs and sub-DLAs, we confirm that sub-DLAs have higher mean metallicities than DLAs, especially at z ? 2. We find that the intercept of the metallicity-redshift relation derived from Zn and S is higher than that derived from Fe by 0.5–0.6 dex. We also show that, while there is a correlation between the metallicity and the rest equivalent width of Mg II λ2796 or Fe II λ2599 for DLAs, no correlation is seen for sub-DLAs. Given this, and the similar Mg II or Fe II selection criteria employed in the discovery of both types of systems at lower redshifts, the difference between metallicities of DLAs and sub-DLAs appears to be real and not an artefact of selection. This conclusion is supported by our simulations of Mg II λ2796 and Fe II λ2599 lines for a wide range of physical conditions. On examining the velocity spreads of the absorbers, we find that sub-DLAs show somewhat higher mean and median velocity spreads (Δv), and an excess of systems with Δv > 150 km s^?1, than DLAs. Compared to DLAs, the [Mn/Fe] vs. [Zn/H] trend for sub-DLAs appears to be steeper and closer to the trend for Galactic bulge and thick disk stars, possibly suggesting different stellar populations. The absorber data appear to be consistent with galaxy down-sizing. The data are also consistent with the relative number densities of low-mass and high-mass galaxies. It is thus plausible that sub-DLAs arise in more massive galaxies on average than DLAs.