Lidar observation of aerosol stratification in the lower troposphere over Pune during pre-monsoon season of 2006     

P. Ernest Raj  S. K. Saha  S. M. Sonbawne  S. M. Deshpande  P. C. S. Devara  Y. Jaya Rao  K. K. Dani  G. Pandithurai 《Journal of Earth System Science》2008,117(1):293-302

Lidar observations of aerosol vertical distributions in the lower troposphere along with observations of horizontal and vertical winds from collocated UHF radar (Wind Profiler) over a tropical Indian station, Pune during the pre-monsoon season (March–May) of 2006 as part of an ISRO-GBP national campaign (ICARB) have been examined. Lidar vertical profiles showed high aerosol concentrations in the surface layers and a subsequent gradual decrease with height. Results showed the presence of an elevated stratified aerosol layer around 2000–3500m height which persisted throughout the months of March and April. Observed strong vertical gradients in both horizontal and vertical winds in the lower troposphere seem to be a possible cause for the formation of elevated aerosol layers. Further, high daytime temperatures accompanied by dry conditions at the surface help to enhance the aerosol loading in the lower layers over this location.  相似文献   

Short-term effects of changes in water management on the limnological characteristics and zooplankton of a eutrophic Mediterranean coastal lagoon (NE Iberian Peninsula)     

Badosa A  Boix D  Brucet S  López-Flores R  Quintana XD 《Marine pollution bulletin》2007,54(8):1273-1284

The Ter Vell (NE Iberian Peninsula) is a eutrophic coastal lagoon which has been flooded by the excess irrigation water and the agricultural runoff during the last decades. Between 1999 and 2003, restoration measures were applied to improve its water quality. At the same time, but independently, agricultural water management drastically reduced the freshwater inflow. The short-term effects of these management actions on the limnological characteristics of the lagoon were analysed by comparing two hydrological cycles, one before (1999/2000) and the other one after (2002/2003) the actions. The two cycles are illustrative of opposite situations in the hydrological functioning of coastal wetlands. In the first, the lagoon was exorheic, with prolonged flooding periods and a low residence time; in the second, it had a more endorheic character, with scarce water inputs and prolonged periods of confinement. Consequently, nitrogen inputs diminished and organic load and salinity increased as the internal loading and the accumulation effects became more relevant. These effects were actually caused by the drastic reduction in the freshwater inflow which prevented, in turn, the success of the restoration measures. The zooplankton community of the Ter Vell lagoon was not significantly altered by the hydrological change, at least in the short-term, and rotifers and cladocerans, mainly those species indicative of eutrophy, dominated the community.  相似文献   

Fractures,hydrothermal alterations and permeability in the Soultz Enhanced Geothermal System     

Béatrice Ledésert  Ronan Hebert  Albert Genter  Danièle Bartier  Norbert Clauer  Céline Grall 《Comptes Rendus Geoscience》2010,342(7-8):607-615

Borehole studies of the Soultz-sous-Forêts granite are dedicated to deep geothermics. The hydraulic properties of the reservoir are mainly controlled by the occurrence of some altered cataclastic shear zones showing a low natural permeability characterized by the occurrence of brines. Those zones show a fracture cluster organisation with sealed fractures of various types (post-filled joints, sheared fractures, veins). The main hydrothermal deposits observed within the permeable zones are geodic quartz, carbonates, illite and more locally sulphides. The fracture wall–rocks are intensely transformed: dissolution of igneous minerals, crystallization of new minerals, porosity and permeability increase. It is important to characterize the newly-formed minerals in order to choose the reagents used to improve the permeability of the exchanger by chemical stimulations. This article represents a synthesis of the studies completed by the authors between 1990 and 2008 on the fracture networks, hydrothermal alterations and mineral crystallizations they induced and data about the flow pathways in the exchanger.  相似文献   

Erratum to: A study of lightning activity over land and oceanic regions of India     

Asha Nath  G. K. Manohar  K. K. Dani  P. C. S. Devara 《Journal of Earth System Science》2009,118(6):735

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Jurassic uplift and erosion of the northeast Queensland continental margin: evidence from (U–Th)/He thermochronology combined with U–Pb detrital zircon age spectra     

Y. Cheng  M. Danišík  F. Sahlström  Z. Chang 《Australian Journal of Earth Sciences》2020,67(4):591-604

Abstract

The Jurassic–Cretaceous Great Artesian Basin is the most extensive, and largest volume, sedimentary feature of continental Australia. The source of its mud-dominated Cretaceous infill is attributed largely to contemporary magmatism along the continental margin to the east, but the source of its Jurassic infill, dominated by quartz sandstone, remains unconstrained. This paper investigates the question of a Jurassic sediment source for the northern part of the basin. Jurassic uplift and exhumation of the continental margin crustal sector to the east provided the primary Jurassic sediment source. (U–Th)/He data are presented for zircon and apatite from Pennsylvanian to mid Permian granitoids of the Kennedy Igneous Association distributed within the northern Tasmanides between the Townsville and Cairns regions and for coeval granites of the Urannha batholith from the Mount Carlton district (N Bowen Basin), also within the northern Tasmanides. The data from zircon indicate widespread Jurassic exhumation of a crustal tract located to the east of the northern Great Artesian Basin and largely occupied by rocks of the Tasmanides. Detrital zircon age spectra for samples of the Jurassic Hutton and Blantyre sandstones from the northeastern margin of the Great Artesian Basin show their derivation to be largely from rocks of the northern Tasmanides. In combination, the detrital age spectra and (U–Th)/He data from zircon indicate exhumation owing to uplift generating appreciable physiographic relief along the north Queensland continental margin during the Jurassic, shedding sediment westward into the Great Artesian Basin during its early development. A portion of (U–Th)/He data for zircon are consistent with late Permian–mid Triassic exhumation within the Tasmanides, attributable to the influence of the Hunter--Bowen Orogeny. Evidence of Cretaceous and Paleocene exhumation episodes is also indicated for some samples, mainly by apatite (U–Th)/He analysis, consistent with data previously published from fission track studies. Overall, new data from the present study reveal that the exhumation related to Jurassic regional uplift and the subsequent erosional reworking of the northeast Australian continental margin is critical for the evolution and development of the northern side of the Great Artesian Basin in eastern Australia. Apart from this, another two previously suggested Permian–Triassic and Cretaceous exhumation and uplift episodes along the northeast Australian continental margin are also confirmed by the dataset of this study.

1. KEY POINTS

2. U–Pb detrital zircon ages of sandstone samples from the northeastern Eromanga Basin reveal Paleozoic (480–280 Ma) and Proterozoic (1800–1400 Ma) age clusters.

3. (U–Th)/He zircon and apatite dating results of granitoids samples from Cairns, Townsville and the Mount Carlton districts are dominated by Jurassic (198–164 Ma) and Permian–Triassic (272–238 Ma) age clusters.

4. Combination of above two datasets proves the regional uplift-driving Jurassic exhumation episode in the northeast Australian continental is vital for the development of the northern Great Artesian Basin.

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Advances in atmospheric, hydrographic and vegetation remote sensing with lidar     

P C S Devara  P E Raj  G Pandithurai  R S Maheskumar  K K Dani 《Journal of the Indian Society of Remote Sensing》1997,25(4):225-238

Lidar has evolved as one of the powerful and versatile techinqne for atmospheric monitoring and geophysical and hydrographic studies from different observational platforom. This paper discusses the recent advances that have taken place in the lidar technology for rnulti-dimensional atmospheric, hydragraphic and vegetation monitoring together with the results of some specific atmospheric studies carried our for the past ten years using the lider systems built at the Indian Institute of Tropical Meteorotogy (IITm) Pune.  相似文献   

Temperatures and winds over tropical middle atmosphere during two contrasting summer monsoons, 1975 and 1979     

B.K. Mukherjee  C.P. Kulkarni  K. Indir  K.K. Dani 《大气科学进展》1989,6(3):325-334

Using the monthly geopotential heights and winds for 700 and 200 hPa for India during July and August, and the weekly M-100 Soviet rocketsonde temperature and wind data for Thumba (8.5oN, 76.9oE) during the last week of June and the first week of September for the two contrasting summer monsoon years 1975 (a very strong monsoon year) and 1979 (a very weak monsoon year), a study has been made to examine the mean circulation features of the troposphere over India, and the structures of the temperatures and the winds of the middle atmosphere over Thumba. The study suggested that the axis of the monsoon trough (AMT) at 700 hPa shifted southward in 1975 and northward towards the foothills of the Himalayas in 1979, from its normal position. Superimposed on the low-pressure area (AMT) at 700 hPa, a well-defined divergence was noticed at 200 hPa over the northern India in 1975.The mean temperatures, at 25,50 and 60 km (middle atmosphere) over Thumba were cooler in 1975 than in 1979. While a cooling trend in 1975 and warming trend in 1979 were observed at 25 and 50 km, a reversed picture was noticed at 60 km. There was a weak easterly/ westerly (weak westerly phase) zonal wind in 1975 and a strong easterly zonal wind in 1979. A phase reversal of the zonal wind was observed at 50 km. A tentative physical mechanism was offered, in terms of upward propagation of the two equatorially trapped planetary waves i.e. the Kelvin and the mixed Rossby-gravity waves, to explain the occurrence of the two spells of strong warmings in the mesosphere in 1975.  相似文献   

Study of total column atmospheric aerosol optical depth,ozone and precipitable water content over Bay of Bengal during BOBMEX-99     

K. K. Dani  R. S. Maheskumar  P. C. S. Devara 《Journal of Earth System Science》2003,112(2):205-221

The spatial and temporal variations in aerosols and precursor gases over oceanic regions have special importance in the estimation of radiative forcing parameters and thereby in the refinement of general circulation models. Extensive observations of the columnar aerosol optical depth (AOD), total column ozone (TCO) and precipitable water content (PWC) have been carried out using the on-line, multi-band solar radiometers onboard ORV Sagar Kanya (Cruise # SK 147B) over Bay of Bengal during 11th–28th August 1999. Aerosol optical and physical properties (optical depth and angstrom parameter) have been estimated at six wavelengths covering from UV to NIR (380–1020 nm) while TCO and PWC have been determined using the UV band around 300 nm and NIR band around 940 nm, respectively. Added, concurrent meteorological and satellite observations during this field phase of BOBMEX-99 have been utilized to investigate spectral-temporal variations of AOD, TCO and PWC in marine environment. The results indicate lower AODs (around 0.4 at characteristic wavelength of 500 nm) and size distributions with abundance of coarse-mode particles as compared to those aerosols of typical land origin. An interesting result that is found in the present study is the significant reduction in AOD at all wavelengths from initial to later part of observation period due to cloud-scavenging and rain-washout effects as well as signature of coastal aerosol loading. The clear-sky daytime diurnal variation of TCO shows gradual increase during post-sunrise hours, broad maximum during afternoon hours and gradual decrease during pre-sunset hours, which is considered to be due to photochemical reactions. The diurnal variation curve of PWC showed maximum (~ 4 cm) during morning hours and gradual decrease (~ 3.5 cm) towards evening hours, which are found to be greater as compared to typical values over land. Another interesting feature observed is that although the PWC values are very high, there was no proportionate or appreciable enhancement in AOD—a feature that can be utilized to infer composition of aerosols over the study region.  相似文献   

Apatite fission track and (U-Th)/He thermochronology of the Rochovce granite (Slovakia) – implications for the thermal evolution of the Western Carpathian-Pannonian region     

Martin Danišík  Milan Kohút  István Dunkl  L’ubomír Hraško  Wolfgang Frisch 《Swiss Journal of Geoscience》2008,101(1):225-233

The thermal evolution of the only known Alpine (Cretaceous) granite in the Western Carpathians (Rochovce granite) is studied by low-temperature thermochronological methods. Our apatite fission track and apatite (U-Th)/He ages range from 17.5 ± 1.1 to 12.9 ± 0.9 Ma, and 12.9 ± 1.8 to 11.3 ± 0.8 Ma, respectively. The data thus show that the Rochovce granite records a thermal event in the Middle to early Late Miocene, which was likely related to mantle upwelling, volcanic activity, and increased heat flow. During the thermal maximum between ~17 and 8 Ma, the granite was heated to temperatures ? 60 °C. Increase of cooling rates at ~12 Ma recorded by the apatic fission track and (U-Th)/He data is primarily related to the cessation of the heating event and relaxation of the isotherms associated with the termination of the Neogene volcanic activity. This contradicts the accepted concept, which stipulates that the internal parts of the Western Carpathians were not thermally affected during the Cenozoic period. The Miocene thermal event was not restricted to the investigated part of the Western Carpathians, but had regional character and affected several basement areas in the Western Carpathians, the Pannonian basin and the margin of the Eastern Alps.  相似文献   

Analysis of karst hydrodynamics through comparison of dissolved and suspended solids' transport     

Danièle Valdes  Jean-Paul Dupont  Nicolas Massei  Benoît Laignel  Joël Rodet 《Comptes Rendus Geoscience》2005,337(15):1365-1374

In karst systems, rain events often result in a decrease of the conductivity (a tracer of dissolved phase transport) and an increase in turbidity (a tracer of suspended solids transport) at wells and springs. This study shows that the comparison of suspended solids and solute transport by the coupled approach of $T\text{–}C$ curves (Turbidity–Conductivity) and autocorrelations gives evidence of the transport processes in the karst network and allows understanding the karst hydrodynamics. To cite this article: D. Valdes et al., C. R. Geoscience 337 (2005).  相似文献