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201.
The dynamic importance of the Southern Indian Ocean (SIO) lies in the fact that it connects the three major world oceans: the Pacific, Atlantic, and Indian Oceans. Modeling study has been used to understand the circulation pattern of this very important region. Simulation of SIO (10°N–60°S and 30°E–120°E) is performed with z-coordinate Ocean General Circulation Model (OGCM) viz; MOM3.0 and the results have been compared with observed ship drift data. It is found that except near coastal boundaries and in equatorial region, the simulated current reproduce most well known current pattern such as Antarctic Circumpolar Current (ACC), South Equatorial Current (SEC) etc. and bears a resemblance to that of the observed data; however the magnitude of the surface current is weaker in model than the observed data, which may be due to deficiency in the forcing field and boundary condition and problem with observed data. The annual mean wind stress curl computed over the oceanic domain reveals about ACC and its similar importance. The way in which the ocean responds to the windstress and vertically integrated transport using model output is fascinating and rather good. 相似文献
202.
Trans-equatorial loops (TLs) are one of the distinct magnetic structures in the solar corona and have a close relationship to solar activity. We present a systematic study of the origin of TLs linking with the Babcock?–?Leighton dynamo process based on the model of Chatterjee, Nandy, and Choudhuri (Astron. Astrophys. 427, 1019, 2004). We propose that TLs are visible signatures of poloidal field lines across the equator. The cycle variation of TL lengths obtained by the connectivities of poloidal field lines happens to be roughly in agreement with what one gets by considering the positions of sunspots. This explains why this cycle variation of TL lengths was found to be in conformity with Spörer’s law. The active regions always make the poloidal field configuration favorable to form TLs, which causes the conformity. The formation of TLs is a three-dimensional problem, which will require three-dimensional dynamo models for full investigation. 相似文献
203.
Sandeep Panda Anil Kumar Satyabrata Das Rahul Devrani Santosh Rai Kuldeep Prakash Pradeep Srivastava 《地球表面变化过程与地形》2020,45(11):2495-2511
This study explores paleoflood deposits of the Siang River, known as the Tsangpo in Tibet. The river that often experiences large floods brings down huge amount of sediment and water that adversely affect the downstream regions with large human populations in the states of northeast Himalaya and its foreland. Along it's ~300 km mountainous stretch we collected samples for sedimentological, petrographic and Sr–Nd isotopic study to explore sediment provenance and dated the paleofloods (via optically stimulated luminescence, OSL). Geomorphic indices including precipitation and a geomorphic swath profile across the Brahmaputra catchment were studied to understand the interplay of mountain relief and rainfall that determine potential zones of high erosion and sediment supply. The OSL technique indicated the Siang River experienced at least eight large floods between 7 and 1 ka, possibly under the influence of warm and wet climatic conditions. The petrographic and isotopic data suggests that the eastern Himalayan syntaxis, which has the highest uplift and exhumation rate in the area, is not always the highest sediment producing zone. In some instances, the Tibetan plateau produces higher fluxes of sediments via glacial and landslide lake outburst floods (GLOFs and LLOFs). © 2020 John Wiley & Sons, Ltd. 相似文献
204.
In this article we investigate the nonlinear dynamics of 3D kinetic Alfvén waves (KAWs) and quasi-transverse weak whistler waves in a magnetized plasma. We have studied the problem numerically to examine the transient evolution of localized structures of 3D KAWs and whistler waves. The nonlinearity arises as a result of ponderomotive effects associated with 3D KAWs; consequently, the background density modifies. The weak whistler waves propagating in this modified density are localized and amplified. To improve our insight into the basic physics behind the formation of these localized structures, we have also solved the system semi-analytically. The power spectra show a Kolmogorov scaling (with a power of \(-5/3\)) in the inertial range that lies above the ion gyroradius. Below this scale, dispersive effects start to appear, and the power spectrum follows a steeper scaling (?2 to ?4). Our results show the important role that KAWs and whistler waves play in the energy cascading from larger to smaller scales. The results are consistent with the solar wind observations by the Cluster spacecraft. 相似文献
205.
Nuzhat Q. Qazi L. Adrian Bruijnzeel Shive Prakash Rai Chandra P. Ghimire 《水文科学杂志》2017,62(7):1114-1130
Baseflows have declined for decades in the Lesser Himalaya but the causes are still debated. This paper compares variations in streamflow response over three years for two similar headwater catchments in northwest India with largely undisturbed (Arnigad) and highly degraded (Bansigad) oak forest. Hydrograph analysis suggested no catchment leakage, thereby allowing meaningful comparisons. The mean annual runoff coefficient for Arnigad was 54% (range 44–61%) against 62% (53–69%) at Bansigad. Despite greater total runoff Qt (by 250 mm year–1), baseflow at Bansigad ceased by March, but was perennial at Arnigad (making up 90% of Qt vs. 51% at Bansigad). Arnigad storm flows, Qs, were modest (8–11% of Qt) and occurred mostly during monsoons (78–98%), while Qs at Bansigad was 49% of Qt and occurred also during post-monsoon seasons. Our results underscore the importance of maintaining soil water retention capacity after forest removal to maintain baseflow levels.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR D. Gerten 相似文献
206.
Kossitse Venyo Akpataku Shive Prakash Rai Masamaéya Dadja-Toyou Gnazou Lallébila Tampo Limam Moctar Bawa Gbandi Djaneye-Boundjou 《水文科学杂志》2019,64(8):983-1000
Hydrochemical, inverse geochemical modelling and isotopic approaches are used to assess the hydrogeochemical evolution of groundwater from the basement aquifers in the southeastern part of the Plateaux Region, Togo. Groundwater originates from present-day rainwater infiltration and is mostly fresh and slightly acidic to neutral. Hydrochemical facies are predominantly mixed cations-HCO3 associated with Ca/Mg-Cl, Na-HCO3 and Na-Cl water types in equilibrium with kaolinite and Ca/Mg-smectites. They are related to silicates hydrolysis, anthropogenic contamination, nitrification/denitrification, mixing along flowpaths and dissolution/precipitation of secondary minerals. The pattern of flow paths is in accordance with an increasing trend in total dissolved solids (TDS) toward the potentiometric depression located in the central and southern parts of the aquifer system. Inverse geochemical modelling using the NETPATH-WIN model showed the relative importance of biotite, plagioclase and amphibole weathering and dissolution of secondary carbonate minerals along the flowpath, suggesting that an abundance of minerals is not necessarily the main factor controlling the groundwater chemistry evolution. 相似文献
207.
Particle precipitation in Brazilian geomagnetic anomaly during magnetic storms is investigated using riometer and VLF propagation data. It is found that during large storms the changes in the ionosphere caused by particle precipitation are detectable. There is a good correlation between the behavior of the absorption and the variations of the magnetic field intensity during different phases of a storm. In particular, there seems to be a close relationship between the precipitation of high energy particles and short-period fluctuations of the magnetic field intensity of the order of 5–6 min. During the main phase of the storm, when the field intensity reaches its minimum, the flux of soft electrons also plays a significant role in producing absorption. The nature of precipitation associated with a sudden commencement appears to be more complex; the predominance of low or high energy particle flux may depend on the magnitude of the field increase. The amplitude and phase records of VLF signals also show the effect of the disturbance, but it is difficult to correlate the changes in these records with the features observed on the magnetogram, because only a small part of the propagation path lies in the region of the anomaly. A more detailed analysis of riometer data from different stations and VLF phase and amplitude records for different paths will be helpful in understanding the mechanism of particle precipitation associated with magnetic disturbances. In future experiments it may also be fruitful to look for detectable radiation emitted by the precipitating electrons, for example, Cherenkov and synchrotron radiation. 相似文献