A Comparative Study of the Atmospheric Layers below First Lifting Condensation Level for Instantaneous Pre-Monsoon Thunderstorm Ocurence at Agartala(23°30′N,91°15′E) and Ranchi(23°14′N,85°14′E) of India

ＡＣｏｍｐａｒａｔｉｖｅＳｔｕｄｙｏｆｔｈｅＡｔｍｏｓｐｈｅｒｉｃＬａｙｅｒｓｂｅｌｏｗＦｉｒｓｔＬｉｆｔｉｎｇＣｏｎｄｅｎｓａｔｉｏｎＬｅｖｅｌｆｏｒＩｎｓｔａｎｔａｎｅｏｕｓＰｒｅ－ＭｏｎｓｏｏｎＴｈｕｎｄｅｒｓｔｏｒｍＯｃｕｒｅｎｃｅａｔＡｇａ...     

THE RETREAT OF THE FOREST IN SOUTHEAST ASIA: A CARTOGRAPHIC ASSESSMENT

Rapid deforestation is a major problem throughout the tropical world. The conditions and the pace under which societies and economies of the Third World are currently evolving and growing, combined with the specificities of tropical forests, render the latter increasingly vulnerable. Among the major tropical areas of the world, Southeast Asia is perhaps the one where these conditions have had the most impact on the retreat of the forest cover over the last quarter of this century. This is illustrated through the presentation of two maps of the distribution of five basic forest formations in Southeast Asia circa 1970 and circa 1990. The maps are examined and compared, as well as confronted with statistical assessments of deforestation. Finally, the complex causes behind the retreat of the tropical forests as well as the implications of this retreat are briefly discussed.     

Primary minerals of Zn-Pb mining and metallurgical dumps and their environmental behavior at Plombières,Belgium

The primary phases and minerals of the Plombières dumps include typical smelting furnace products such as metallic Fe, Pb, Cu, Zn, Fe-Zn alloys, carbides, phosphides, sulfides of Fe, Zn, Pb, Cu, Mn (alabandite), and FeAs. Spinels, mainly of Fe and Al, are common constituents of the primary assemblage; substitution by Zn, V, Cr, Ti, Mg, and Ca occurs. Primary phases also include the most common Zn-rich fayalite, Zn-rich Ca-Fe silicates, melilite, corundum, and apatite. Most of the Zn is incorporated in iron silicates, ZnO and ZnS. Lead occurs mainly as PbS, metallic lead, and is also present in coal residues. Cadmium is found mainly in metallic zinc and its alloys and in ZnO. The dumps also contain mining wastes composed of pyrite, melnikovite, and iron oxides produced by natural weathering of Zn-Pb ores. Melnikovite and iron oxides are rich in As, Pb, and Zn and possess an increased content of Tl. Leaching tests carried out on the surfaces of polished sections indicate that acid rain (solutions I and II) will mobilize mainly Zn and Cd and, to a much smaller extent, Pb and Sb. Leaching of metals by sulfate-chloride fluids present in the pore network of dumps (solutions III, IV, and V) depends on the pH, which in the dumps is controlled by the proportion of carbonates to sulfides. The more acid fluids leach both sulfides and silicates.     

Evolution of sand waves in the Messina Strait, Italy

In the present paper the morphodynamics of sand waves in the Messina Strait, Italy, is analysed by comparing data gathered during two different surveys carried out in 1991 and 2001, respectively. In particular, a morphometric analysis on the most recent data and a qualitative analysis of the differences between bottom bedform patterns, are carried out. At locations characterised by greater depths, only minor changes to the planimetric configuration of the field, i.e. crest orientation (which is seen to be orthogonal to the direction of net gross sand transport) and wave length are observed, while differences in wave length and crest direction are more evident in more shallow areas. On the other hand, wave height has significantly increased in the whole field. A possible explanation of such a change, based on the previsions of a theory which relates sand-wave growth and migration to the main components of the tidal ellipse, is provided.Responsible Editor: Jens Kappenberg     

Assessing land use/cover changes: a nationwide multidate spatial database for Mexico

A nationwide multidate GIS database was generated in order to carry out the quantification and spatial characterization of land use/cover changes (LUCC) in Mexico. Existing cartography on land use/cover at a 1:250,000 scale was revised to select compatible inputs regarding the scale, the classification scheme and the mapping method. Digital maps from three different dates (the late 1970s, 1993 and 2000) were revised, evaluated, corrected and integrated into a GIS database. In order to improve the reliability of the database, an attempt was made to assess the accuracy of the digitalisation procedure and to detect and correct unlikely changes due to thematic errors in the maps. Digital maps were overlaid in order to generate LUCC maps, transition matrices and to calculate rates of conversion. Based upon this database, rates of deforestation between 1976 and 2000 were evaluated as 0.25 and 0.76% per year for temperate and tropical forests, respectively.     

Weathering: Toward a Fractal Quantifying

Weathering occurs over a wide range of scales. To link features through these scales is a major challenge for interdisciplinary weathering studies. Fractal approach seems to be specially useful for this purpose. We introduce a multistep fractal weathering assessment scheme devoted to extract fractal weathering classifiers from texture analysis of the mineral's image. Our scheme enables to quantitatively estimate the global and local information about the geometry of the weathering pattern. This information is basic to develop geometrical indices of weathering, which can significantly enrich the common qualitative and semiquantitative weathering assessment schemes. To justify the fractal approach, a strong statistical self-similarity has been documented for both the weathering and fresh features of two common silica minerals: quartz and biogenic A-opal (phytolith) over four orders of length scales. The procedure is fast, drastically reduces thresholding bias, promises to be universal, it is valid for genetically different minerals and rock types, scale independent, and specially useful for monitoring the changes in the mineral's roughness during the alteration. Two of the proposed classifiers seem to be potentially useful for direct application in the field and be used by nonspecialist.     

Meteorological Office, Pune-411 005

Natural disasters like floods, tornadoes, tropicalcyclones, heat and cold wavewreak havoc and cause tremendous loss ofproperty all over the world. Most ofthe natural disasters are either dueto weather or are triggered due toweather related processes.Extreme weather events claimed thousands oflives and caused damage on vastscale. Recent super cyclone which affectedOrissa in 1999, Bangladesh cyclone of1970 and Hurricane Andrew in 1992 areexamples of some of the more damagingtropical cyclones which affected developingas well as the developed world. Heatand cold waves are also extreme events,which cause enormous losses in terms oflives lost and human discomfort and ailmentsarising out of them. The heat waveof 1995 and 1998 are still fresh in the mindof the Indian public. The estimated lossof human lives due to heat wave in 1998 was morethan 15,000. Economic losses asa result of these disasters and in particular inassociation with tropical cyclones haveincreased enormously over the last three decades.During 1961–1991, total loss oflives from drought alone was 1,333,728 overthe whole world. In terms of economiclosses, there is 8–10 fold increase from thebase figure of 1960. The socio-economicimpact of natural disaster is complex dependingupon the vulnerability of the placeand mitigation strategies that are put in place.Meteorology plays a crucial role in forewarningpeople about the severe/extremeweather systems and a constant endeavour by themeteorological services worldover has gone a long way towards minimizing thelosses caused by natural disasters.The paper summarises the natural disasterstatistics over south Asia and the possibleprediction strategies for combating theirsocio-economic impacts.     

Seismic activity at the MCT in Sikkim Himalaya

A microearthquake survey in the Sikkim Himalaya raised a question whether the north–south segment of the Main Central Thrust (MCT) in this part of the Himalaya is seismically active(?). Fault-plane solution of a cluster of events occurred below this segment of the MCT shows right-lateral strike-slip motion. The seismic observations and the geological evidences suggest that a NNE–SSW trending strike-slip fault, beneath this segment, caused right lateral movement on the MCT, and is seismically active.