An investigation of the relationship between sub‐Saharan rainfall and global sea surface temperatures

Abstract

The relationship between sea surface temperature (SST) and rainfall index anomalies over sub‐Saharan Africa for the 15‐year period, 1970–84, has been examined. The objectively analysed monthly mean SST data were used for the global oceans between 40°S and 60°N. The rainfall data consist of annual mean rainfall indices for the Sahel and Soudan belts over north Africa.

An Empirical Orthogonal Function analysis of the SST data has been carried out for the Atlantic, Indian and global ocean regions. The results show that the most dominant eigenmode, EOF1, is characterized by warming over the central eastern Pacific, cooling over the eastern mid‐latitude Pacific and warming over the entire Atlantic and Indian ocean basins. The second EOF for the Atlantic Ocean SST analysis shows a dipole (north‐south see‐saw) pattern. The third EOF for the Atlantic SST analysis has the same sign over the entire Atlantic basin. Global SST EOF2 and EOF3 correspondió Atlantic SST EOF3 and EOF2, respectively.

The correlation between the sub‐Saharan annual rainfall index, which mainly represents the summer season rainfall from June to September, and SST EOFs shows that EOF1 has statistically significant monthly correlations for the Sahel and Soudan regions and that the warm El Niño‐like phases of SST EOF1 correspond to drought conditions. This result suggests that the large‐scale SST anomalies may be responsible for a significant component of the observed vacillation of sub‐Saharan rainfall. Some preliminary GLA GCM simulation results that support the above findings are also presented.     

Tectonic Evolution of the Southern Part of Aravalli Mountain Belt and its Environs: Possible Causes and Time Constraints

Structural studies on Proterozoic rocks belonging to the Lunavada Group, Southern Aravalli Mountain Belt (SAMB), India, have shown that they underwent three episodes of deformation which have led to the formation of various regional scale interference patterns. Whilst the northern parts of the SAMB underwent brittle-ductile deformation, the southern portion underwent more ductile deformation. On the basis of structural as well as metamorphic studies it has been established earlier that the region was subjected to uplift orogenesis during its evolutionary history. In the present paper an attempt is made to visualize the possible causes that led to deformation of the SAMB, the structural geology of which has been established by the authors, and to constraint the timing of these events on the basis of already available geochronological data. A “working-hypothesis” is proposed according to which it is suggested that deformation of the SAMB is a result of the accretion of the three protocontinents viz. Aravalli, Dharwar and Singhbhum during the Mesoproterozoic. It is envisaged that the accretion of Aravalli and Singhbhum Protocontinents occurred between 1600 and 1400 Ma along the NE-SW trending Son Suture and this event led to development of NE-SW trending structures in the SAMB. Suturing of Aravalli and Dharwar Protocontinents between 1400 and 935 Ma along the E-W Narmada Suture was responsible for the E-W to NW-SE trending D₃ structures of the SAMB. It is postulated that the Satpura orogeny which resulted in deformation of rocks in Satpura mountain range lying to the south of Narmada Suture was coeval with the accretion of Aravalli and Dharwar Protocontinents.     

Estimation of radioactive leakages into the Pacific Ocean due to Fukushima nuclear accident

High concentrations of several radionuclides were reported in the sea near the Fukushima Daiichi Nuclear Power Station (FDNPS) in Japan due to the nuclear accident that occurred on 11 March 2011. The main source of these concentrations was leakage of highly radioactive liquid effluent from a pit in the turbine building near the intake canal of Unit-2 of FDNPS through a crack in the concrete wall. In the immediate vicinity of the plant, seawater concentrations reached 68 MBq m^?3 for ¹³⁴Cs and ¹³⁷Cs, and exceeded 100 MBq m^?3 for ¹³¹I in early April 2011. These concentrations began to fall as of 11 April 2011 and, at the end of April, had reached a value close to 0.1 MBq m^?3 for ¹³⁷Cs. Following the nuclear accident, the Tokyo Electric Power Company (TEPCO) had initiated intense monitoring of the environment including the Pacific Ocean. Seawater samples were collected and the concentrations of few radionuclides were measured on a wide spatial and temporal scale. In this study, the measured concentrations of different radionuclides near the south discharge canal of the FDNPS were used to estimate their leakages into the Pacific Ocean. The method is based on estimating the release rates that reproduce the concentration of radionuclides in seawater at a chosen location using a two-dimensional advection–dispersion model in an iterative manner. The radioactive leakages were estimated as 5.68 PBq for ¹³¹I, 2.24 PBq for ¹³⁴Cs and 2.25 PBq for ¹³⁷Cs. Leakages were also estimated for ^99mTc, ¹³⁶Cs, ¹⁴⁰Ba and ¹⁴⁰La and they range between 0.02 PBq (^99mTc) and 0.53 PBq (¹⁴⁰Ba). It was estimated that about 11.28 PBq of radioactivity in total was leaked into the Pacific Ocean from the damaged FDNPS. Out of this, ¹³¹I constitutes 50.3 %; ¹³⁴Cs 20 %; ¹³⁷Cs 20 %; ¹⁴⁰Ba 4.6 %; ¹³⁶Cs 2.6 %; ¹⁴⁰La 2.3 % and ^99mTc 0.2 % of the total radioactive leakage. Such quantitative estimates of radioactive leakages are essential prerequisites for short-term and local-scale as well as long-term and large-scale radiological impact assessment of the nuclear accident.     

A computer program for the determination of finite strain using fry method

Fry method enables rapid estimate of finite strain from deformed aggregates such as clastic grains, fossil colonies, oolitic or pisolitic aggregates, prophyroblastic minerals or phenocrysts. It has an advantage over the other methods of finite strain analysis in its very quality of enabling rapid estimation with a reasonable degree of accuracy. Details of the software to prepare a plot using Fry method are outlined. This program has an advantage over other computer based programs on the world wide web in its aesthetic getup, small size, user friendliness and a help file.     

Analytical models for the groundwater tidal prism and associated benthic water flux

The groundwater tidal prism is defined as the volume of water that inundates a porous medium, forced by one tidal oscillation in surface water. The pressure gradient that generates the prism acts on the subterranean estuary. Analytical models for the groundwater tidal prism and associated benthic flux are presented. The prism and flux are shown to be directly proportional to porosity, tidal amplitude, and the length of the groundwater wave; flux is inversely proportional to tidal period. The duration of discharge flux exceeds the duration of recharge flux over one tidal period; and discharge flux continues for some time following low tide. Models compare favorably with laboratory observations and are applied to a South Atlantic Bight study area, where tide generates an 11-m³ groundwater tidal prism per m of shoreline, and drives 81 m³ s?^?1 to the study area, which describes 23% of an observational estimate. In a marine water body, the discharge component of any oscillatory benthic water flux is submarine groundwater discharge. Benthic flux transports constituents between groundwater and surface water, and is a process by which pollutant loading and saltwater intrusion may occur in coastal areas.     

Determining Field Correlations Produced by Stars from the Study of Spectral Changes in Double Slit Experiment

Experiments are performed to determine the coherence properties of wave fields, produced by the broadband stellar sources on the earth surface, from the study of spectral changes produced on interference in the Young's double slit experiment. The spectral degree of coherence obtained experimentally in this study for four bright stars in the wavelength range from 325 nm to 660 nm is in close agreement with the value that is expected theoretically from the known angular diameter of the stars. It is shown that the spectral degree of coherence obtained experimentally by this spectral interferometric technique could be used to determine the angular diameter of stars. This revised version was published online in July 2006 with corrections to the Cover Date. This revised version was published online in July 2006 with corrections to the Cover Date.     

Penrose Conference — 2011 on Deformation Localization in Rocks: New Advances — Manish A. Mamtani (IIT,Kharagpur; Email: mamtani@gg.iitkgp.ernet.in)

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Penrose Conference — 2011 on Deformation Localization in Rocks: New Advances — Manish A. Mamtani (IIT, Kharagpur; Email: mamtani@gg.iitkgp.ernet.in)