The relationship between significant wave height and Indian Ocean Dipole in the equatorial North Indian Ocean     

Chen Fu  Dongxiao Wang  Lei Yang  Yao Luo  Fenghua Zhou  Tilak Priyadarshana  Jinglong Yao 《Ocean Dynamics》2018,68(6):689-699

Based on reanalysis data, we find that the Indian Ocean Dipole (IOD) plays an important role in the variability of wave climate in the equatorial Northern Indian Ocean (NIO). Significant wave height (SWH) in the equatorial NIO, especially over the waters southeast to Sri Lanka, exhibits strong interannual variations. SWH anomalies in the waters southeast to Sri Lanka correlate well with dipole mode index (DMI) during both summer and autumn. Negative SWH anomalies occur over the oceanic area southeast to Sri Lanka during positive IOD events and vary with different types of IOD. During positive prolonged (unseasonable) IOD, the SWH anomalies are the strongest in autumn (summer); while during positive normal IOD, the SWH anomalies are weak in both summer and autumn. Strong easterly wind anomalies over the southeast oceanic area of Sri Lanka during positive IOD events weaken the original equatorial westerly wind stress, which leads to the decrease in wind-sea waves. The longer wave period during positive IOD events further confirms less wind-sea waves. The SWH anomaly pattern during negative IOD events is nearly opposite to that during positive IOD events.  相似文献   

斯里兰卡近岸风暴潮模拟中风暴潮-潮汐相互作用特征分析:一个个例研究     

R. K. K. A. S. N. KODITHUWAKKU  李毅能  彭世球  朱宇航  李少钿  Tilak P. D. GAMAGE  付莉莉 《南京气象学院学报》2018,10(3):342-352

利用三维普林斯顿海洋模型（POM）以及逐时水位观测数据,研究印度洋北部斯里兰卡北部海岸风暴潮-潮汐相互作用特征.选择了2008年的"Nisha"台风作为台风风暴潮个例进行研究,并进行了3个数值敏感性试验.经验证,该风暴潮模型可以很好地再现该台风期间研究区域内的潮汐和总海水水位.试验结果表明,沿斯里兰卡西北海岸的风暴潮-潮汐相互作用显著,其强度与台风的强度和轨迹相关.当TC在42 h达到较大强度时,可以得到风暴潮-潮汐相互作用导致的最大增水值TSI （0.6 m）和从印度洋外海向斯里兰卡西北部浅滩流入的最大相互作用流场.在TC强度较弱的第30小时,得到最大负TSI （-0.6 m）和向南流出西北部浅水区域的较弱的相互作用流场.在整个台风期间,强TSI都发生在斯里兰卡西北部海滩到对岸的印度洋近岸区域.  相似文献   

Instruments of RT-2 experiment onboard CORONAS-PHOTON and their test and evaluation II: RT-2/CZT payload     

Tilak B. Kotoch  Anuj Nandi  D. Debnath  J. P. Malkar  A. R. Rao  M. K. Hingar  Vaibhav P. Madhav  S. Sreekumar  Sandip K. Chakrabarti 《Experimental Astronomy》2011,29(1-2):27-54

Cadmium Zinc Telluride (CZT) detectors are high sensitivity and high resolution devices for hard X-ray imaging and spectroscopic studies. The new series of CZT detector modules (OMS40G256) manufactured by Orbotech Medical Solutions (OMS), Israel, are used in the RT-2/CZT payload onboard the CORONAS-PHOTON satellite. The CZT detectors, sensitive in the energy range of 20 to 150 keV, are used to image solar flares in hard X-rays. Since these modules are essentially manufactured for commercial applications, we have carried out a series of comprehensive tests on these modules so that they can be confidently used in space-borne systems. These tests lead us to select the best three pieces of the ??Gold?? modules for the RT-2/CZT payload. This paper presents the characterization of CZT modules and the criteria followed for selecting the ones for the RT-2/CZT payload. The RT-2/CZT payload carries, along with three CZT modules, a high spatial resolution CMOS detector for high resolution imaging of transient X-ray events. Therefore, we discuss the characterization of the CMOS detector as well.  相似文献   

An international program on Silk Road Disaster Risk Reduction——a Belt and Road initiative (2016-2020)     

Lei Yu  Cui Peng  Amar Deep Regmi  Virginia Murray  Alessandro Pasuto  Giacomo Titti  Muhammad Shafique  Tilak Priyadarshana D. G 《山地科学学报》2018,15(7):1383-1396

Belt and Road Initiative (BRI) is a Chinese national strategy which calls for cooperative economic, political and cultural exchange at the global level along the ancient Silk Road. The overwhelming natural hazards located along the belt and road bring great challenges to the success of BRI. In this framework, a 5-year international program was launched to address issues related to hazards assessment and disaster risk reduction (DRR). The first workshop of this program was held in Beijing with international experts from over 15 countries. Risk conditions on Belt and Road Countries (BRCs) have been shared and science and technology advancements on DRR have been disseminated during the workshop. Under this program, six task forces have been setup to carry out collaborative research works and three prioritized study areas have been established. This workshop announced the launching of this program which involved partners from different countries including Pakistan, Nepal, Russia, Italy, United Kingdom, Sri Lanka and Tajikistan. The program adopted the objectives of Sendai Framework for Disaster Risk Reduction 2015–2030 and United Nation Sustainable Development Goals 2030 and was implemented to assess disaster risk in BRCs and to propose suitable measures for disaster control which can be appropriate both for an individual country and for specific sites. This paper deals with the outcomes of the workshop and points out opportunities for the near future international cooperation on this matter.  相似文献   

Improved Determination of Ethane (C₂H₆) Abundance in Titan's Stratosphere     

Timothy A. Livengood  Tilak Hewagama  Theodor KostiukKelly E. Fast  Jeffrey J. Goldstein 《Icarus》2002,157(1):249-253

Ethane spectral lines were observed in emission from Titan in August 1993, October 1995, and September 1996, at a spectral resolution of λ/Δλ≈10⁶, at wavelength 11.7−11.9 μm using the Goddard Infrared Heterodyne Spectrometer at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. The ethane mole fraction is determined to be (8.8±2.2)×10⁻⁶ (68.3% confidence limits, “1σ”), averaging the retrievals from each observing run obtained using the “recommended” thermal profile of R. V. Yelle, D. Strobel, E. Lellouch, and D. Gautier (1997, in Huygens: Science, Payload, and Mission (J.-P. Lebreton, Ed.), pp. 243-256, European Space Agency SP-1177).  相似文献   

Modification of Jupiter’s stratosphere three weeks after the 2009 impact     

Kelly E. Fast  Theodor Kostiuk  Timothy A. Livengood  Tilak Hewagama  John Annen 《Icarus》2011,213(1):195-200

Infrared spectroscopy sensitive to thermal emission from Jupiter’s stratosphere reveals effects persisting 23 days after the impact of a body in late July 2009. Measurements obtained on 2009 August 11 UT at the impact latitude of 56°S (planetocentric), using the Goddard Heterodyne Instrument for Planetary Wind and Composition mounted on the NASA Infrared Telescope Facility, reveal increased ethane abundance and the effects of aerosol opacity. An interval of reduced thermal continuum emission at 11.744 μm is measured ∼60-80° towards planetary east of the impact site, estimated to be at 305° longitude (System III). Retrieved stratospheric ethane mole fraction in the near vicinity of the impact site is enhanced by up to ∼60% relative to quiescent regions at this latitude. Thermal continuum emission at the impact site, and somewhat west of it, is significantly enhanced in the same spectra that retrieve enhanced ethane mole fraction. Assuming that the enhanced continuum brightness near the impact site results from thermalized aerosol debris blocking contribution from the continuum formed in the upper troposphere and indicating the local temperature, then continuum emission by a haze layer can be approximated by an opaque surface inserted at the 45-60 mbar pressure level in the stratosphere in an unperturbed thermal profile, setting an upper limit on the pressure and therefore a lower limit on the altitude of the top of the impact debris at this time. The reduced continuum brightness east of the impact site can be modeled by an opaque surface near the cold tropopause, which is consistent with a lower altitude of ejecta/impactor-formed opacity. The physical extent of the observed region of reduced continuum implies a minimum average velocity of 21 m/s transporting material prograde (planetary east) from the impact.  相似文献   

Large Area X-Ray Proportional Counter (LAXPC) Instrument on AstroSat and Some Preliminary Results from its Performance in the Orbit     

P. C. Agrawal  J. S. Yadav  H. M. Antia  Dhiraj Dedhia  P. Shah  Jai Verdhan Chauhan  R. K. Manchanda  V. R. Chitnis  V. M. Gujar  Tilak Katoch  V. N. Kurhade  P. Madhwani  T. K. Manojkumar  V. A. Nikam  A. S. Pandya  J. V. Parmar  D. M. Pawar  Jayashree Roy  B. Paul  Mayukh Pahari  Ranjeev Misra  M. H. Ravichandran  K. Anilkumar  C. C. Joseph  K. H. Navalgund  R. Pandiyan  K. S. Sarma  K. Subbarao 《Journal of Astrophysics and Astronomy》2017,38(2):30

Large area X-ray propositional counter (LAXPC) instrument on AstroSat is aimed at providing high time resolution X-ray observations in 3–80 keV energy band with moderate energy resolution. To achieve large collecting area, a cluster of three co-aligned identical LAXPC detectors, is used to realize an effective area in access of \({\sim }6000\,\hbox {cm}^{2}\) at 15 keV. The large detection volume of the LAXPC detectors, filled with xenon gas at \({\sim }\)2 atmosphere pressure, results in detection efficiency greater than 50%, above 30 keV. In this article, we present salient features of the LAXPC detectors, their testing and characterization in the laboratory prior to launch and calibration in the orbit. Some preliminary results on timing and spectral characteristics of a few X-ray binaries and other type of sources, are briefly discussed to demonstrate that the LAXPC instrument is performing as planned in the orbit.  相似文献   

Peat depth as a control on moss water availability under evaporative stress          下载免费PDF全文

Simon J. Dixon  Nicholas Kettridge  Paul A. Moore  Kevin J. Devito  Amey S. Tilak  Richard M. Petrone  Carl A. Mendoza  James M. Waddington 《水文研究》2017,31(23):4107-4121

Northern peatlands are a vital component of the global carbon cycle, containing large stores of soil organic carbon and acting as a long‐term carbon sink. Moss productivity is an important factor in determining whether these wetlands will retain this function under future climatic conditions. Research on unsaturated water flow in peatlands, which controls moss productivity during periods of evaporative stress, has focused on relatively deep bog systems. However, shallower peatlands and marginal connective wetlands can be essential components of many landscape mosaics. In order to better understand factors influencing moss productivity, water balance simulations using HYDRUS‐1D were run for different soil profile depths, compositions, and antecedent moisture conditions. Our results demonstrate a bimodal distribution of peatland realizations, either primarily conserving water by limiting evapotranspiration or maximizing moss productivity. For sustained periods of evaporative stress, both deep water storage and a shallow initial water table delay the onset of high vegetative stress, thus maximizing moss productivity. A total depth of sand and peat of 0.8 m is identified as the threshold above which increasing peat depth has no effect on changing vegetative stress response. In contrast, wetlands with shallow peat deposits (less than 0.5 m thick) are least able to buffer prolonged periods of evaporation due to limited labile water storage and will thus quickly experience vegetative stress and so limit evaporation and conserve water. With a predicted increase in the frequency and size of rain events in continental North America, the moss productivity of shallow wetland systems may increase, but also greater moisture availability will increase the likelihood they remain as wetlands in a changing climate.  相似文献   

Thermospheric/mesospheric temperatures on Venus: Results from ground-based high-resolution spectroscopy of CO2 in 1990/1991 and comparison to results from 2009 and between other techniques     

Guido Sonnabend  Peter Krötz  Frank Schmülling  Theodor Kostiuk  Jeff Goldstein  Manuela Sornig  Dušan Stupar  Timothy Livengood  Tilak Hewagama  Kelly Fast  Arnaud Mahieux 《Icarus》2012,217(2):856-862

We report temperatures in Venus’ upper mesosphere/lower thermosphere, deduced from reanalyzing very high resolution infrared spectroscopy of CO₂ emission lines acquired in 1990 and 1991. Kinetic temperatures at ～110 km altitude (0.15 Pa) are derived from the Doppler width of fully-resolved single line profiles measured near 10.4 μm wavelength using the NASA GSFC Infrared Heterodyne Spectrometer (IRHS) at the NASA IRTF on Mauna Kea, HI, close to Venus inferior conjunction and two Venus solstices. Measured temperatures range from ～200 to 240 K with uncertainty typically less than 10 K. Temperatures retrieved from similar measurement in 2009 using the Cologne Tuneable Heterodyne Infrared Spectrometer (THIS) at the NOAO McMath Telescope at Kitt Peak, AZ are 10–20 K lower. Temperatures retrieved more recently from the SOIR instrument on Venus EXpress are consistent with these results when the geometry of observation is accounted for. It is difficult to compare ground-based sub-mm retrievals extrapolated to 110 km due to their much larger field of view, which includes the night side regions not accessible to infrared heterodyne observations. Temperature variability appears to be high on day-to-day as well as longer timescales. Observed short term and long term variability may be attributed to atmospheric dynamics, diurnal variability and changes over solar activity and seasons. The Venus International Reference Atmosphere (VIRA) model predicts cooler temperatures at the sampled altitudes in the lower thermosphere/upper mesosphere and is not consistent with these measurements.  相似文献   

High spectral resolution infrared studies of Titan: Winds, temperature, and composition     

Theodor Kostiuk  Tilak Hewagama  Kelly E. Fast  John Annen  Guido Sonnabend  Juan D. Delgado  Richard Achterberg 《Planetary and Space Science》2010,58(13):1715-1723

The Cassini Huygens mission provides a unique opportunity to combine ground-based and spacecraft investigations to increase our understanding of chemical and dynamical processes in Titan’s atmosphere. Spectroscopic measurements from both vantage points enable retrieving global wind structure, temperature structure, and atmospheric composition. An updated analysis of Titan data obtained with the NASA Goddard Space Flight Center’s Infrared Heterodyne Spectrometer (IRHS) and Heterodyne Instrument for Planetary Wind and Composition (HIPWAC) prior to and during the Cassini Huygens mission is compared to retrievals from measurements with the Cassini Composite Infrared Spectrometer (CIRS). IRHS/HIPWAC results include the first direct stratospheric wind measurements on Titan, constraints on stratospheric temperature, and the study of atmospheric molecular composition. These results are compared to CIRS retrievals of wind and temperature profile from thermal mapping data and ethane abundance at 10-15° South latitude, near the equatorial region. IRHS/HIPWAC wind results are combined with other direct techniques, stellar occultation measurements, and CIRS results to explore seasonal variability over nearly one Titan year and to provide an empirical altitude profile of stratospheric winds, varying from ∼50 to 210 m/s prograde. The advantage of fully resolved line spectra in species abundance measurements is illustrated by comparing the possible effect on retrieved ethane abundance by blended spectral features of other molecular constituents, e.g., acetylene (C₂H₂), ethylene (C₂H₄), allene (C₃H₄), and propane (C₃H₈), which overlap the ν₉ band of ethane, and are not resolved at lower spectral resolution. IR heterodyne spectral resolution can discriminate weak spectral features that overlap the ν₉ band of ethane, enabling ethane lines alone to be used to retrieve abundance. Titan’s stratospheric mean ethane mole fraction (8.6±3 ppmv) retrieved from IRHS/HIPWAC emission line profiles (resolving power λ?Δλ∼10⁶) is compared to past values obtained from lower resolution spectra and from CIRS measurements (resolving power λ?Δλ∼2×10³) and more compatible recent analysis. Results illustrate how high spectral resolution ground-based studies complement the spectral and spatial coverage and resolution of moderate spectral resolution space-borne spectrometers.  相似文献