Analysis of the Tsunami of December 26, 2004, on the Kerala Coast of India—Part II: Arrival Times

The Tsunami of December 26, 2004, in the Indian Ocean arrived on the coast of Kerala in southwest India some three hours after the tsunami was generated. The tsunami activity persisted throughout that day and, in some locations, even into the early morning of the next day. Based on interviews with eye witnesses, arrival times of tsunami waves are presented here followed by some preliminary analysis of the results.     

Research report—A geographical information system for oil spills sensitivity mapping in the Shetland Islands (United Kingdom)

Geographical Information Systems (GIS) have been making important contributions to environmental monitoring and management. This paper discusses their use in oil spill sensitivity mapping in the Brent System Pipeline Nearshore Section in the Shetland Islands. The study demonstrates the efficiency and effectiveness of the GIS approach in determining the critical areas that need to be protected in the event of an oil spill. It concludes with a discussion on the future development in this field.     

Dynamics of intensification of the boreal summer monsoon flow during IOD events

The present study focuses on understanding the dynamics of intensification of the boreal summer monsoon cross-equatorial flow generally observed during positive-Indian Ocean Dipole (IOD) events, by taking 1994 as a case study. In particular, the influence of the anomalous divergent motions during 1994 (i.e., east–west circulation over equatorial Indian Ocean and the monsoon Hadley-type circulation) on the intensification of summer monsoon cross-equatorial flow is investigated. This problem is examined using diagnostic analyses and simulation experiments from a multi-level global atmospheric model forced with observed diabatic heating. The results suggest that the transfer of kinetic energy (KE) from the divergent motions to the rotational flows can be very effective during IOD periods like 1994; and provides a plausible explanation for the increase of KE of the monsoon cross-equatorial flow over Bay-of-Bengal and adjoining areas. The study also investigates the enhanced activity of westward propagating disturbances observed during 1994 over the monsoon region.     

A first-order Markov model for assessing rainfall discontinuity in central Australia

Summary For six stations in central Australia daily rainfalls were combined over five-day intervals. The resulting pentads were classed as either wet or dry according to whether a total of at least 0.1 inch of rain had occurred. A first order Markov model and a simple random model were constructed for the distribution of runs of wet and dry pentads. A ² test showed that the random model gives a poor fit to the observed frequencies. With the Markov model, however, good agreement was obtained with the exception of a few cases. Although the Markov model could be further improved it seems to be a practical statistical tool for assessing the long-term incidence of runs of wet or dry weather in central Australia.

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Zusammenfassung Für sechs Stationen in Mittelaustralien wurden tägliche Niederschlagssummen zu Pentaden-Summen zusammengefaßt. Die resultierenden Pentaden wurden als naß oder trocken klassifiziert, je nachdem, ob wenigstens 2,5 mm Regen gefallen war oder nicht. Für die Verteilung von Folgen von trokken und nassen Pentaden wurden ein Markov-Modell 1. Ordnung und ein einfaches Zufallsmodell konstruiert. Ein ² zeigte, daß das Zufallsmodell die beobachteten Häufigkeiten nur schlecht wiedergibt. Mit dem Markov-Modell wurde dagegen, mit Ausnahme einiger Fälle, gute Übereinstimmung erzielt. Obwohl das Markov-Modell noch weiter verbessert werden könnte, scheint es eine praktische Möglichkeit zur Darstellung länger dauernder Folgen von nassen oder trockenen Pentaden in Mittelaustralien zu bieten.

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Résumé On a établi les sommes pentadaires des précipitations de six stations d'Australie centrale. Les groupes de cinq jours ainsi établis sont répartis en deux classes, humides ou secs selon que la dite somme dépasse 2,5 mm de pluie ou non. Pour l'étude de la répartition de successions de pentades humides ou sèches on a construit un modèle de Markov du premier ordre et un modèle aléatoire simple. Un examen au mogen du teste ² a montré que lemodèle aléatoire ne reflète que très mal fréquences observées. On obtient par contre, quelques cas exceptés, une assez bonne coïncidence avec le modèle de Markov. Bien que ce dernier puisse encore être amélioré, il semble présenter une possibilité pratique pour la représentation de successions importantes de pentades humides ou sèches en Australie centrale.

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With 2 Figures     

Efficient encoding and decoding algorithms for distributed resampling

This paper discusses algorithms for compressing floating point data which is encountered while performing resampling algorithm for rectifying geometric distortions on the images transmitted by the remote sensing satellite on a distributed computing environment. Two efficient algorithms for encoding and decoding floating point data compression, (i) 3-byte packing and (ii) 3-byte + 2-bit packing have been proposed. Both algorithms are tested to execute resampling algorithm on radiometrically corrected for IRS- LISS-III 4 bands data on a distributed system. First algorithm compresses 4-byte floating point data to 3-byte obtaining 25% compression while later one compresses 4-byte floating point data to 3-byte + 2-bit achieving about 18.75% compression. The computational time is reduced by 22% as compared to the distributed resampling algorithms without compression. Further it is found that in lossy compression algorithm only 220 pixels out of 37.4 MB pixels have utmost one Gray count difference, which will not pose any issues for digital classification or any other methods that will be employed in the corrected image by Image Analysts.     

Mapping the liquefaction induced soil moisture changes using remote sensing technique: an attempt to map the earthquake induced liquefaction around Bhuj, Gujarat, India

The Bhuj earthquake (Mw = 7.9) occurred in the western part of India on 26th January 2001 and resulted in the loss of 20,000 lives and caused extensive damage to property. Soil liquefaction related ground failures such as lateral spreading caused significant damage to bridges, dams and other civil engineering structures in entire Kachchh peninsula. The Bhuj area is a part of large sedimentary basin filled with Jurassic, Tertiary and Quaternary deposits. This work pertains to mapping the areas that showed sudden increase in soil moisture after the seismic event, using remote sensing technique. Multi-spectral, spatial and temporal data sets from Indian Remote Sensing Satellite are used to derive the Liquefaction Sensitivity Index (LSeI). The basic concept behind LSeI is that the near infrared and shortwave infrared regions of electromagnetic spectrum are highly absorbed by soil moisture. Thus, the LSeI is herein used to identify the areas with increase in soil moisture after the seismic event. The LSeI map of Bhuj is then correlated with field-based observation on Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR), depth to water table, soil density and Liquefaction Severity Index (LSI). The derived LSeI values are in agreement with liquefaction susceptible criteria and observed LSI (R ² = 0.97). The results of the study indicate that the LSeI after calibration with LSI can be used as a quick tool to map the liquefied areas. On the basis of LSeI, LSI, CRR, CSR and saturation, the unconsolidated sediments of the Bhuj area are classified into three susceptibility classes.     

Volume 52

Volume Contents

Volume 52     

Pacific decadal oscillation and variability of the Indian summer monsoon rainfall

Recent studies have furnished evidence for interdecadal variability in the tropical Pacific Ocean. The importance of this phenomenon in causing persistent anomalies over different regions of the globe has drawn considerable attention in view of its relevance in climate assessment. Here, we examine multi-source climate records in order to identify possible signatures of this longer time scale variability on the Indian summer monsoon. The findings indicate a coherent inverse relationship between the inter-decadal fluctuations of Pacific Ocean sea surface temperature (SST) and the Indian monsoon rainfall during the last century. A warm (cold) phase of the Pacific interdecadal variability is characterized by a decrease (increase) in the monsoon rainfall and a corresponding increase (decrease) in the surface air temperature over the Indian subcontinent. This interdecadal relationship can also be confirmed from the teleconnection patterns evident from long-period sea level pressure (SLP) dataset. The SLP anomalies over South and Southeast Asia and the equatorial west Pacific are dynamically consistent in showing an out-of-phase pattern with the SLP anomalies over the tropical central-eastern Pacific. The remote influence of the Pacific interdecadal variability on the monsoon is shown to be associated with prominent signals in the tropical and southern Indian Ocean indicative of coherent inter-basin variability on decadal time scales. If indeed, the atmosphere–ocean coupling associated with the Pacific interdecadal variability is independent from that of the interannual El Niño-Southern Oscillation (ENSO), then the climate response should depend on the evolutionary characteristics of both the time scales. It is seen from our analysis that the Indian monsoon is more vulnerable to drought situations, when El Niño events occur during warm phases of the Pacific interdecadal variability. Conversely, wet monsoons are more likely to prevail, when La Niña events coincide during cold phases of the Pacific interdecadal variability.