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1.
This paper describes a wide-field survey made at 34.5 MHz using GEETEE,1 the low frequency telescope at Gauribidanur (latitude
13°36′12′′N). This telescope was used in the transit mode and by per forming 1-D synthesis along the north-south direction
the entire observable sky was mapped in a single day. This minimized the problems that hinder wide-field low-frequency mapping.
This survey covers the declination range of-50° to + 70° (- 33° to +61° without aliasing) and the complete 24 hours of right
ascension. The synthesized beam has a resolution of 26′ x 42′ sec (δ- 14°. 1). The sensitivity of the survey is 5 Jy/beam (1σ). Special care has been taken to ensure that the antenna responds
to all angular scale structures and is suitable for studies of both point sources and extended objects
This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore and the Roman Research Institute, Bangalore. 相似文献
2.
Seasonal evolution of surface mixed layer in the Northern Arabian Sea (NAS) between 17° N–20.5° N and 59° E-69° E was observed
by using Argo float daily data for about 9 months, from April 2002 through December 2002. Results showed that during April
- May mixed layer shoaled due to light winds, clear sky and intense solar insolation. Sea surface temperature (SST) rose by
2.3 °C and ocean gained an average of 99.8 Wm−2. Mixed layer reached maximum depth of about 71 m during June - September owing to strong winds and cloudy skies. Ocean gained
abnormally low ∼18 Wm−2 and SST dropped by 3.4 °C. During the inter monsoon period, October, mixed layer shoaled and maintained a depth of 20 to
30 m. November - December was accompanied by moderate winds, dropping of SST by 1.5 °C and ocean lost an average of 52.5 Wm−2. Mixed layer deepened gradually reaching a maximum of 62 m in December. Analysis of surface fluxes and winds suggested that
winds and fluxes are the dominating factors causing deepening of mixed layer during summer and winter monsoon periods respectively.
Relatively high correlation between MLD, net heat flux and wind speed revealed that short term variability of MLD coincided
well with short term variability of surface forcing. 相似文献
3.
K. Golap N. H. Issur R. Somanah R. Dodson M. Modgekar S. Sachdev N. Udaya Shankar Ch. V. Sastry 《Astrophysics and Space Science》1995,228(1-2):373-377
The Mauritius Radiotelescope (MRT) is a T-shaped array of helical antennas with a 2048 m EW arm and a 890 m South arm. The primary objective of the telescope is to produce a sky survey in the declination zone -15° to -65° with a point source sensitivity of 200 mJy and an angular resolution of 4'×4.6'cosec(z) at 151.6 MHz, z being the zenith angle . This paper describes the telescope and the present status 相似文献
4.
A technique to detect man-made interference in the visibility data of the Mauritius Radio Telescope (MRT) has been developed.
This technique is based on the understanding that the interference is generally ‘spiky’ in nature and has Fourier components
beyond the maximum frequency which can arise from the radio sky and can therefore be identified. We take the sum of magnitudes
of visibilities on all the baselines measured at a given time to improve detectability. This is then high-pass filtered to
get a time series from which the contribution of the sky is removed. Interference is detected in the high-pass data using
an iterative scheme. In each iteration, interference with amplitudes beyond a certain threshold is detected. These points
are then removed from the original time series and the resulting data are high-pass filtered and the process repeated. We
have also studied the statistics of the strength, numbers, time of occurrence and duration of the interference at the MRT.
The statistics indicate that most often the interference excision can be carried out while post-integrating the visibilities
by giving a zero weight to the interference points. 相似文献
5.
Effects of climate change on coastal fresh groundwater resources 总被引：1，自引：0，他引：1
This study evaluates the impacts of climate change on fresh groundwater resources specifically salinity intrusion in water resources stressed coastal aquifers. Our assessment used the Hadley Centre climate model, HadCM3 with high and low emission scenarios (SRES A2 and B2) for years 2000–2099. In both scenarios, the annual fresh groundwater resources losses indicate an increasing long-term trend in all stressed areas, except in the northern Africa/Sahara region. We also found that precipitation and temperature individually did not show good correlations with fresh groundwater loss. However, the relationship between the aridity index and fresh groundwater loss exhibited a strong negative correlation. We also discuss the impacts of loss of fresh groundwater resources on socio-economic activities, mainly population growth and per capita fresh groundwater resources. 相似文献
6.
The first set of full resolution images have been made using the Mauritius Radio Telescope (MRT) for the Right Ascension range
18:00 to 19:00 hours and the declination range -70° to -10°.This is a part of the southern sky survey at 151.5 MHz being carried out using the MRT. To minimise the effect of bandwidth
decorrelation, the images are made from the visibilities recorded with four different delay settings. This paper discusses
three key issues of data analysis for the survey: Selection of good data for the survey, detection and removal of interference
in the images and, preliminary analysis of these images.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Impacts of climate variability on water quality with best management practices in sub‐tropical climate of USA 
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下载免费PDF全文 Efficiency of non‐point source pollution control methods may be altered in future climate. This study investigated climate change impacts on sediment and nutrient transport, and efficiency of best management practices (BMPs), in the Upper Pearl River Watershed (UPRW) in Mississippi. The Soil and Water Assessment Tool was applied to the UPRW using observed flow, sediment and nutrient data. Water quality samples were collected at three US geological survey gauging stations. The model was successfully calibrated and validated for daily time steps (Nash Sutcliffe efficiency and coefficient of determination – R2 up to 0.7) using manual and automatic (sequential uncertainty fitting version 2) methods from February 2010 to May 2011. Future weather scenarios were simulated using the LARS‐WG model, a stochastic weather generator, with Community Climate System Model, global climate model, which was developed by the National Center for Atmospheric Research in the USA. On the basis of the Special Report on Emissions Scenarios A1B, A2 and B1 of the Intergovernmental Panel on Climate Change, climate change scenarios were simulated for the mid (2046–2065) and late (2080–2099) century. Effectiveness of four BMPs (Riparian buffer, stream fencing, sub‐surface manure applications and vegetative filter strips) on reducing sediment and nutrient were evaluated in current and future climate conditions. Results show that sediment, nitrogen and phosphorus loadings will be increased up to a maximum of 26.3%, 7.3% and 14.3%, respectively, in future climate conditions. Furthermore, the effectiveness of BMPs on sediment removal will be reduced in future climate conditions, and the efficiency of nitrogen removal will be increased, whereas phosphorus removal efficiency will remain unchanged. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
8.
Observed oceanic response to tropical cyclone Jal from a moored buoy in the south-western Bay of Bengal 总被引：1，自引：1，他引：0
M. S. Girishkumar K. Suprit Jayaram Chiranjivi T. V. S. Udaya Bhaskar M. Ravichandran R. Venkat Shesu E. Pattabhi Rama Rao 《Ocean Dynamics》2014,64(3):325-335
Upper oceanographic and surface meteorological time-series observations from a moored buoy located at 9.98°N, 88°E in the south-western Bay of Bengal (BoB) were used to quantify variability in upper ocean, forced by a tropical cyclone (TC) Jal during November 2010. Before the passage of TC Jal, salinity and temperature profiles showed a typical BoB post-monsoon structure with relatively warm (30 °C) and low-saline (32.8 psu) waters in the upper 30- to 40-m layer, and relatively cooler and higher salinity (35 psu) waters below. After the passage of cyclone, an abrupt increase of 1 psu (decrease of 1 °C) in salinity (temperature) in the near-surface layers (up to 40-m depth) was observed from buoy measurements, which persisted up to 10–12 days during the relaxation stage of cyclone. Mixed layer heat budget analysis showed that vertical processes are the dominant contributors towards the observed cooling. The net surface heat flux and horizontal advection together contributed approximately 33 % of observed cooling, during TC Jal forced stage. Analysis showed the existence of strong inertial oscillation in the thermocline region and currents with periodicity of ～2.8 days. During the relaxation stage of the cyclone, upward movement of thermocline in near-inertial frequencies played significant role in mixed layer temperature and salinity variability, by much freer turbulent exchange between the mixed layer and thermocline. 相似文献
9.
N. Vedachalam S. Ramesh P. Udaya Prasanth G. A. Ramadass 《Marine Georesources & Geotechnology》2018,36(8):966-973
Natural gas hydrates is considered as a strategic unconventional clean hydrocarbon resource in the energy sector. Understanding the behavior of the rising methane gas bubbles during production leaks from the deep marine gas hydrate reservoirs well head is essential for environmental impact studies and to design environmental monitoring systems. Numerical model for quantitatively characterizing the vertical dissolution pattern of the wellhead released methane gas bubbles is analyzed for three potential gas hydrate locations in India. Simulation results indicate that the methane bubbles with diameter of 10?mm can transport methane gas till 650, 800, and 750?m from the seabed in the Krishna–Godavari(KG), Mahanadi and Andaman basins respectively. Results brought out that potential well head damage during methane hydrate production at 1050?m water depth could release up to 28?m3 of methane gas, in which 50% of the molar mass shall get dissolved within 40?m of water column from the seafloor. 相似文献
10.
Priyantha Jinadasa Sinhalage Uday Pathirana Gayan Ranasinghe Pradeep Nalak Centurioni Lu Hormann Verena 《海洋学报(英文版)》2020,39(3):103-112
Monsoon driven water mass exchange between the Bay of Bengal(Bo B) and Arabian Sea(AS) is the common experience. However, it is not yet firmly confirmed that the exchange pathway is either passing through southern tip of Sri Lanka or Palk Strait. Local circulation patterns impact the pathways followed by the East Indian Coastal Currents(EICC) that drive exchange, thereby modulating mixing and water mass transformation in the Bay of Bengal around Sri Lanka. In this study, observations from surface drifters were incorporated with the satellite derived data to understand the monsoonal impact on circulation patterns in the Indian Ocean. This was the first multi-national scientific effort which was conducted in the Bo B and AS during 2013 to 2015 to understand the monsoonal impact on circulation patterns in the complex region. The results indicated that seasonally reversing monsoonal currents of southern Sri Lanka, traced by the wintertime freshwater export pathways of the EICC. The deflection of monsoon currents running along the east coast of Sri Lanka by forming cyclonic and anti-cyclonic eddies, which influence the mixing and stirring associated with these flows. Results further indicate the low salinity cold water flows from the Bo B to AS along the western boundary of the Bo B during northeast monsoon. In the same way, reverses the phenomena during southwest monsoon, transporting high salinity warm water from AS to the Bo B. This maintain the bay status which occurred due to freshwater influx from large rivers and high saline water from AS. However, no evidences were observed for the exchange through Palk Strait during the study.Also, there are some mis-matches in in-situ and remotely sensed measurements which imply the necessity of systematic observation system for the complex region as an alternative approach. 相似文献