Vertical profiles of aerosol black carbon in the atmospheric boundary layer over a tropical coastal station: Perturbations during an annular solar eclipse     

S. Suresh Babu  V. Sreekanth  K. Krishna Moorthy  Mannil Mohan  N.V.P. Kirankumar  D. Bala Subrahamanyam  Mukunda M. Gogoi  Sobhan Kumar Kompalli  Naseema Beegum  Jai Prakash Chaubey  V.H. Arun Kumar  Ravi K. Manchanda 《Atmospheric Research》2011,99(3-4):471-478

Altitude profiles of aerosol black carbon (BC) in the atmospheric boundary layer (ABL) over a tropical coastal station, Trivandrum have been examined on two days using an aethalometer attached to a tethered balloon. One of these days (15th January, 2010) coincided with a (annular) solar eclipse, the longest of this century at this location, commenced at 11:05 local time and ended by 15:05, lasting for 7 min and 15 s (from 13:10:42), with its maximum contact occurring at ~ 13:14 IST with ~ 92% annularity, thereby providing an opportunity to understand the eclipse induced perturbations. Concurrent measurements of the ABL parameters such as air temperature, relative humidity and pressure were also made on these days to describe the response of the ABL to the eclipse. BC profiles, in general, depicted similar features up to an altitude of ~ 200 m on the eclipse day and control day, above which it differed conspicuously with profiles on eclipse day showing increasingly lower concentration as we moved to higher altitudes. Examination of the meteorological profiles showed that the altitude of maximum convection rapidly fell down during the eclipse period compared to that on control day indicating a rather shallow convection on eclipse day. Comparison of diurnal variations of BC at the surface level showed that the rate of decrease in BC during daytime on the eclipse day was smaller than that on the control day due to the reduced convection, shallow ABL and consequent reduction in the ventilation coefficient. Moreover the time of the nocturnal increase has advanced by ~ 1:30 h on the eclipse day, occurred at around 19:30 IST in contrast to all the other days of January 2010, where this increase usually occur well after 20:30 IST, with a mean value of 21:00 IST. This is attributed to the weak sea-breeze penetration during the eclipse day, which led to an early onset of the land breeze.  相似文献   

Against mono-consequentialism: Multiple outcomes and their drivers in social–ecological systems     

Arun Agrawal  Ashwini Chhatre   《Global Environmental Change》2011,21(1):1-3

  相似文献   

Reconstruction of Antarctic climate change using ice core proxy records from the coastal Dronning Maud Land,East Antarctica     

Meloth Thamban  C. M. Laluraj  Sushant S. Naik  Arun Chaturvedi 《Journal of the Geological Society of India》2011,78(1):19-29

Antarctic ice core records have provided unprecedented information on past climatic changes and forcing factors on decadal to millennial timescales. The glaciochemical and stable isotope records of a shallow ice core from the coastal Dronning Maud Land (East Antarctica) were used here to reconstruct the coastal Antarctic environmental variability during the past ∼470 years. Sea salt ion data indicate a significant additional contribution of chloride ions compared to sea water values, possibly through atmospheric scavenging. The nitrate (NO₃ ⁻) profile exhibit significant temporal shifts than that of the sulphate (SO₄ ²⁻), with a major shift around 1750 AD. The changes in NO₃ ⁻ record are synchronous with the proxy record of solar activity (¹⁰Be profile from a South Pole ice core), suggesting enhanced NO₃ ⁻ values during periods of reduced solar activity like the Dalton Minimum (∼1790–1830 AD) and Maunder Minimum (∼1640–1710 AD). The δ¹⁸O records reveal that the more negative δ¹⁸O values were coeval with several events of increased NO₃ ⁻ concentrations, suggesting enhanced preservation of NO₃ ⁻ during periods of reduced air temperatures. The δ¹⁸O and δD records of the core also suggest significant short-term and long-tem variability with more negative values indicating relatively lower air temperatures prior to 1715 AD. The δ¹⁸O records also revealed a significant warming of 2.7°C for the past 470 years, with a warming of ∼0.6°C per century.  相似文献   

Is there lower limit to velocity or velocity change?     

B. N. Sreenath  Kenath Arun  C. Sivaram 《Astrophysics and Space Science》2013,345(1):209-211

Here we explore the possibility of a lower limit to velocity or velocity change which is 20 orders of magnitude smaller than the speed of light and explore the various observable signatures including those in cosmic rays and gamma ray bursts.  相似文献   

Why were some La Niñas followed by another La Niña?     

Zeng-Zhen Hu  Arun Kumar  Yan Xue  Bhaskar Jha 《Climate Dynamics》2014,42(3-4):1029-1042

This paper investigates why some La Niña events are followed by another La Niña and some others are not. We propose two preconditions that result in continuation of a La Niña. The first one is that La Niña must be a strong event (a major La Niña). This ensures that the reflected Rossby wave signal at the eastern boundary of the Pacific has a strong westward propagating cold ocean temperature anomaly over the off-equatorial region. The off-equator cold anomaly may not be conducive to the equatorial recharge process, and as a result, may favor the persistence of cold ocean subsurface temperature anomaly and prevent the transition from La Niña to El Niño. The second precondition is whether there are eastward propagating downwelling Kelvin waves during the decay phase of a major La Niña. Eastward propagating downwelling Kelvin waves could lead to demise for a tendency for a follow-up La Niña. The equatorial Kelvin wave activities are associated with fluctuations of surface wind in the equatorial far-western Pacific. The analysis suggests that both the surface wind in the equatorial far-western Pacific and the recharge/discharge of the equatorial Pacific are indicators for occurrence or no occurrence of a follow-up La Niña event.  相似文献   

A Comparative Analysis on the Applicability of Entropy in Remote Sensing     

P. V. Arun 《Journal of the Indian Society of Remote Sensing》2014,42(1):217-226

Entropy is the measure of uncertainty in any data and is adopted for maximisation of mutual information in many remote sensing operations. The availability of wide entropy variations motivated us for an investigation over the suitability preference of these versions to specific operations. The popular available versions like Tsalli’s, Shannon’s, and Renyi’s entropies have been analysed in context of various remote sensing operations namely thresholding, clustering and registration. These methodologies have been evaluated with reference to the study area using different statistical parameters. Renyi’s entropy has been found to be suitable for image registration purpose followed by Tsalli’s and Shannon; whereas Tsalli’s entropy has been found preferable for thresholding and clustering.  相似文献   

Fuzzy Neural Network Models for Supervised Classification: Multispectral Image Analysis     

Arun D. Kulkarni  Kamlesh Lulla 《国际地球制图》2013,28(4):42-51

Abstract

It has been well established that neural networks provide a reasonable and powerful alternative to conventional classifiers. During the past few years there has been a large and energetic upswing in research efforts aimed at synthesizing fuzzy logic with neural networks. This combination of fuzzy logic and neural networks seems natural because two approaches generally attack the design of “intelligent” systems from quite different angles. Neural networks provide algorithms for learning, classification, and optimization whereas fuzzy logic deals with issues such as reasoning on a higher (semantic or linguistic) level. Consequently the two technologies complement each other. In this paper we propose two novel fuzzy‐neural network models for supervised learning. The first model consists of three layers, and the second model consists of four layers. In both models, the first two layers implement fuzzy membership functions and the remaining layers implement the inference engine. Both models use the gradient decent technique for learning. As an illustration, we have analyzed two Thematic mapper images using these models. Results are presented in the paper.  相似文献   

Observed and Forecasted Intraseasonal Activity of Southwest Monsoon Rainfall over India During 2010, 2011 and 2012     

D. R. Pattanaik  L. S. Rathore  Arun Kumar 《Pure and Applied Geophysics》2013,170(12):2305-2328

The monsoon seasons of 2010 and 2011, with almost identical seasonal total rainfall over India from June to September, are associated with slightly different patterns of intraseasonal rainfall fluctuations. Similarly, the year 2012, with relatively less rainfall compared to 2010 and 2011, also witnessed different intraseasonal rainfall fluctuations, leading to drought-like situations over some parts of the country. The present article discusses the forecasting aspect of monsoon activity over India during these 3 years on an extended range time scale (up to 3 weeks) by using the multimodel ensemble (MME), based on operational coupled model outputs from the ECMWF monthly forecasting system and the NCEP’s Climate Forecast System (CFS). The average correlation coefficient (CC) of weekly observed all-India rainfall (AIR) and the corresponding MME forecast AIR is found to be significant, above the 98 % level up to 2 weeks (up to 18 days) with a slight positive CC for the week 3 (days 19–25) forecast. However, like the variation of observed intraseasonal rainfall fluctuations during 2010, 2011 and 2012 monsoon seasons, the MME forecast skills of weekly AIR are also found to be different from one another, with the 2012 monsoon season indicating significant CC (above 99 % level) up to week 2 (12–18 days), and also a comparatively higher CC (0.45) during the week 3 forecast (days 19–25). The average CC between observed and forecasted weekly AIR rainfall over four homogeneous regions of India is found to be the lowest over the southern peninsula of India (SPI), and northeast India (NEI) is found to be significant only for the week 1 (days 5–11) forecast. However, the CC is found to be significant over northwest India (NWI) and central India (CEI), at least above the 90 % level up to 18 days, with NWI having slightly better skill compared to the CEI. For the individual monsoon seasons of 2010, 2011 and 2012, there is some variation in CC and other skill scores over the four homogeneous regions. Thus the slight variations in the characteristics of intraseasonal monsoon rainfall over India is associated with variations in predictive skill of the coupled models and the MME-based predictions of intraseasonal monsoon fluctuations for 2–3 weeks, providing encouraging results. The MME forecast in 2010 is also able to provide useful guidance, well in advance, about an active September associated with a delayed withdrawal of the monsoon and also the heavy rainfall over north Pakistan.  相似文献   

Geophysical Characterization of the Salna Sinking Zone, Garhwal Himalaya, India     

Rambhatla G. Sastry  Suman K. Mondal 《Surveys in Geophysics》2013,34(1):89-119

Infrastructure and communication facilities are repeatedly affected by ground deformation in Gharwal Himalaya, India; for effective remediation measures, a thorough understanding of the real reasons for these movements is needed. In this regard, we undertook an integrated geophysical and geotechnical study of the Salna sinking zone close to the Main Central Thrust in Garhwal Himalaya. Our geophysical data include eight combined electrical resistivity tomography (ERT) and induced polarization imaging (IPI) profiles spanning 144–600 m, with 3–10 m electrode separation in the Wenner–Schlumberger configuration, and five micro-gravity profiles with 10–30 m station spacing covering the study region. The ERT sections clearly outline the heterogeneity in the subsurface lithology. Further, the ERT, IPI, and shaliness (shaleyness) sections infer the absence of clayey horizons and slip surfaces at depth. However, the Bouguer gravity analysis has revealed the existence of several faults in the subsurface, much beyond the reach of the majority of ERT sections. These inferred vertical to subvertical faults run parallel to the existing major lineaments and tectonic elements of the study region. The crisscross network of inferred faults has divided the entire study region into several blocks in the subsurface. Our studies stress that the sinking of the Salna village area is presently taking place along these inferred vertical to subvertical faults. The Chamoli earthquake in March 1999 probably triggered seismically induced ground movements in this region. The absence of few gravity-inferred faults in shallow ERT sections may hint at blind faults, which could serve as future source(s) for geohazards in the study region. Soil samples at two sites of study region were studied in a geotechnical laboratory. These, along with stability studies along four slope sections, have indicated the critical state of the study region. Thus, our integrated studies emphasize the crucial role of micro-gravity in finding fine subsurface structure at deeper depth level; supported by ERT and IPI at shallow depth intervals, they can satisfactorily explain the Salna sinking zone close to Lesser Himalaya. The geotechnical studies also lend support to these findings. These integrated studies have yielded a better understanding of the mass-wasting mechanism for the study region.  相似文献   

Enigmatic aspects of entropy inside the black hole: what do falling comoving observers see?     

C. Sivaram  Kenath Arun 《Astrophysics and Space Science》2012,337(1):169-172

In a recent paper it was suggested that inclusion of mutual gravitational interactions can give a possible scenario for reversing gravitation collapse and averting a singular phase. We extend this idea to the still unsolved problem of matter collapsing beyond black hole event horizons. For a comoving observer there is no change in entropy as he goes through the horizon. Matter collapses to a minimum radius, and then can re-expand with the same entropy. It is shown that phase space inside a collapsing black hole is also invariant.  相似文献