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161.
Level 3 (3A25) TRMM Precipitation Radar (PR) data are used for 13 years period (1998–2010) to prepare climatology of TRMM PR derived near surface rain (Total rain) and rain fractions for the 4-months duration of Indian Summer Monsoon season (June–September) as well as for individual months. It is found that the total rain is contributed mostly (99 %) by two rain fractions i.e. stratiform and convective rain fractions for the season as well as on the monthly basis. It is also found that total rain estimates by PR are about 65 % of the gauge measured rain over continental India as well as on sub-regional basis. Inter-annual variability of TRMM-PR rain estimates for India mainland and its sub-regions as well as over the neighboring oceanic regions, in terms of coefficient of variability (CV) is discussed. The heaviest rain region over north Bay of Bengal (BoB) is found to have the lowest CV. Another sub-region of low CV lies over the eastern equatorial Indian ocean (EEIO). The CVs of total rain as well as its two major constituents are found to be higher on monthly basis compared to seasonal basis. Existence of a well known dipole between the EEIO and the north BoB is well recognized in PR data also. Significant variation in PR rainfall is found over continental India between excess and deficit monsoon seasons as well as between excess and deficit rainfall months of July and August. Examination of rainfall fractions between the BoB and Central India on year to year basis shows that compensation in rainfall fractions exists on monthly scale on both the regions. Also on the seasonal and monthly scales, compensation is observed in extreme monsoon seasons between the two regions. However, much less compensation is observed between the north BoB and EEIO belts in extreme rain months. This leads to speculation that the deficit and excess seasons over India may result from slight shift of the rainfall from Central India to the neighboring oceanic regions of north BoB. Contribution of stratiform and convective rain fractions have been also examined and the two fractions are found to contribute almost equally to the total rain. Results are further discussed in terms of the possible impact of the two rain fractions on circulation based on possible difference is vertical profiles of latent heat of two types of rain. Substantial differences in the lower and upper tropospheric circulation regimes are noticed in both deficit and excess monsoon months/seasons, emphasizing the interaction between rainfall (latent heat) and circulation. 相似文献
162.
Samir M Zaid 《Journal of Earth System Science》2017,126(4):50
Texture, mineralogy, and major and trace element geochemistry of 26 coastal dune sand samples were studied to determine the provenance and tectonic environment of two dune fields close to the beaches of Safaga (SF) and Quseir (QS) at the Egyptian Red Sea coast. Onshore winds generate fine, moderate, moderately-well to well-sorted, coarse-skewed to near-symmetrical dune sands with mesokurtic distributions. Winds pick up and transport grains from nearby beach sands and alluvial deposits into a wide Red Sea coastal plain at the border of the beach. The mineralogical (Qt–Ft–Lt) and geochemical composition of the sands, indicate that SF and QS coastal dune sands are mature and influenced by quartz-rich sands. The average CIA values in SF and QS coastal dune sands are low relative to the range of the PAAS, suggesting an arid climate and a low intensity of chemical weathering. The SF and QS coastal dune sand samples are plotted in the recycled orogen and partly in craton interior fields suggesting recycled older sedimentary and partly metamorphic-plutonic sources. The high content of quartz with shell debris and carbonates in coastal dune sands support the recycled sedimentary beach and alluvial sand sources. The dominance of heavy minerals like amphiboles (hornblende) and biotite in the coastal dune sands also supports the effect of metamorphic-plutonic source rocks. The new tectonic discriminant-function diagrams suggest that the coastal dune sands were deposited in a passive margin of a synrift basin. The results provide a good evidence for the extension in the Red Sea rift system during Oligocene-post Pliocene, which is consistent with the general geology of Egypt. 相似文献
163.
Samir M Zaid 《Journal of Earth System Science》2017,126(7):103
Petrography and bulk rock geochemistry of the Middle Miocene sandstones of the lower and upper members of Gebel El Rusas Formation along the Egyptian Red Sea Coastal plain, have been investigated to determine the provenance, tectonic setting, and weathering condition of this formation. The Lower Member is formed mainly of sandstones and conglomerates with clay interbeds. The Upper Member is more calcareous and formed mainly of sandstones and limestones with marls and clays intercalations. Petrographically, the Lower Member sandstones are mostly immature and classified as arkoses with an average framework composition of \(\hbox {Q}_{66}\hbox {F}_{29}\hbox {R}_{5}\), and the Upper Member sandstones are partly submature (more quartzose, less feldspathic) and classified as subarkoses with an average framework composition of \(\hbox {Q}_{80}\hbox {F}_{17}\hbox {R}_{3}\). The Gebel El Rusas sandstones are enriched in Sr, Ba, Zr and Rb and depleted in Co and U, as compared to UCC. The chemical index of alteration (CIA) values suggest moderate weathering conditions. The geochemistry results revealed that the Gebel El Rusas sandstones were derived from felsic-granitic source rocks and deposited in a passive margin of a synrift basin. The inferred tectonic setting for Middle Miocene Gebel El Rusas sandstones in the study area is consistent with the regional geology of the Eastern Desert of Egypt during Middle Miocene. 相似文献
164.
Bachaer Ayed Ikram Jmal Samir Sahal Naziha Mokadem Salwa Saidi Emna Boughariou Salem Bouri 《Environmental Earth Sciences》2017,76(24):821
Worldwide, groundwater resources have been considered as the main sources of drinking, domestic uses, industrial and agriculture water demands, especially in arid and semiarid regions. Accordingly, the monitoring of the groundwater quality based on different tools and methods becomes a necessity. The aim of this study was to apply several approaches to assess the water quality and to define the main hydrochemical process which affect groundwater of the Maritime Djeffara shallow aquifer. In addition to the hydrochemical approach, two multivariate statistical analyses, hierarchical clusters analysis (HCA) and principal component analysis (PCA), were carried out to identify the natural and the anthropogenic processes affecting groundwater chemistry. Hydrochemical approach, based on 47 analyzed groundwater samples, shows that most of samples present a sulfate to mixed chloride, with sodi-potassic tendency facies. According to their chemically composition, the HCA revealed three different groups (C1, C2 and C3) according to their electrical conductivity (EC) values: C1 (average EC = 4500 µS/cm), C2 (average EC = 7040 µS/cm) and C3 (average EC = 9767 µS/cm). Furthermore, PCA results show two principal factors account 84.05% of the total variance: (1) F1 represents the natural component, and (2) F2 symbolizes the anthropic component. Moreover, the groundwater quality map of the Maritime Djeffara shows three categories: suitable, doubtful and unsuitable water for irrigation. These different results should be taken to protect water resources in arid and semiarid regions, especially at the alluvial coastal regions. Also, they help to make a suitable planning to manage and protect the groundwater resources. 相似文献
165.
166.
Chott El Jerid in the Zone of Chotts of Tunisia is one of the largest endorheic basins in the world. During the dry period, from May to August, it is generally covered by continental evaporites which result from the desiccation of the lake formed after a flooding event. This lake comprises runoff water from the surrounding relief and also water resurgence. In order to map and monitor these evaporitic surfaces (mineral composition and evolution in space and time), optical multisource, multispectral, and multidate satellite data have been used. Landsat 4–5 TM, Landsat 8 OLI, SPOT 6, and Landsat Surface Reflectance (LSR) constitute the main data set. The central part of the Chott, north and south of the road crossing the Chott over 70 km from Tozeur to Kebili, has been particularly studied, because it corresponds to the major evaporite accumulation zone. These evaporites precipitated as concentric layers (a relatively rare pattern), mainly north of the road, after several recent flooding events during the last 15 years. Winds can play a significant role in the development of the evaporite layers. Image interpretation associated with field data shows that after the final desiccation of the playa lake, the mineralogy of the salt crust comprised an assemblage dominated by halite south of the road and by gypsum north of the road. Halite and gypsum are the only minerals to be identified using satellite remote sensing data. Sulfates such as gypsum can be identified thanks to a drop in reflectance in the short-wave infrared (SWIR) range caused by vibrations of the SO4 group. Gypsum crusts are more widely distributed than halite crusts. LSR data are particularly suitable for multitemporal comparison because they are calibrated and atmospherically corrected. The classical bull’s eye pattern characterizing evaporitic deposits (from carbonates along the rims to halite, gypsum, and finally potassium-magnesium minerals in the center of the basin) is deeply disturbed by the road crossing Chott El Jerid. 相似文献
167.
Alzahraa Abo HABIBAH Kamal DAHAB Ashraf SHABANA Samir KAMH Hekmat IBRAHIM 《《地质学报》英文版》2022,96(3):1082-1097
The El Minia governorate lies within the Nile Valley, surrounded by calcareous plateaus to the east and west. The present study focuses on the hydrogeochemistry of the Eocene limestone aquifer at some wadis in the east El Minia governorate, Eastern Desert, Egypt. Hydrogeologically, two main aquifers are encountered in the study area, namely the Maghagha marly limestone and the Samalut chalky limestone aquifers. The Maghagha aquifer is composed of alternating layers of marly limestone and shale with thicknesses ranging from 3.49 m to 177.05 m and a groundwater depth ranging from 8.5 m to 59.27 m which reflects low groundwater potentiality. The groundwater salinity representing this aquifer ranges from 603.5 mg/L to 978.5 mg/L, reflecting fresh water type. Samalut aquifer is made up of chalky, cavernous and fractured limestone with thickness ranging from 30 m to 205 m and groundwater depth ranging from 9 m to 86.77 m, which indicates good groundwater potential. The groundwater salinity of the concerned aquifer ranges from 349.7 mg/L to 2043.9 mg/L, reflecting fresh to possibly brackish water types. Groundwater in the study area is of meteoric water origin; recent recharge is mainly controlled through the presence of fractures and their densities. The majority of groundwater samples in the study area are suitable for drinking and irrigation purposes. 相似文献