Projected future changes in the contribution of Indo-Pacific sea surface height variability to the Indonesian throughflow     

Shilimkar  Vivek  Abe  Hiroto  Roxy  Mathew Koll  Tanimoto  Youichi 《Journal of Oceanography》2022,78(5):337-352

The Indonesian throughflow (ITF) transports a significant amount of warm freshwater from the Pacific to the Indian Ocean, making it critical to the global climate system. This study examines decadal ITF variations using ocean reanalysis data as well as climate model simulations from the Coupled Model Inter-comparison Project Phase 5 (CMIP5). While the observed annual cycle of ITF transport is known to be correlated with the annual cycle of sea surface height (SSH) difference between the Pacific and Indian Oceans, ocean reanalysis data (1959–2015) show that the Pacific Ocean SSH variability controls more than 85% of ITF variation on decadal timescales. In contrast, the Indian Ocean SSH variability contributes less than 15%. While those observed contributions are mostly reproduced in the CMIP5 historical simulations, an analysis of future climate projections shows a 25–30% increase in the Indian Ocean SSH variability to decadal ITF variations and a corresponding decrease in the Pacific contribution. These projected changes in the Indian Ocean SSH variability are associated with a 23% increase in the amplitudes of negative zonal wind stress anomalies over the equatorial Indian Ocean, along with a 12º eastward shift in the center of action in these anomalies. This combined effect of the increased amplitude and eastward shift in the zonal wind stress increases the SSHA variance over the Indian Ocean, increasing its contribution to the ITF variation. The decadal ITF changes discussed in this study will be crucial in understanding the future global climate variability, strongly coupled to Indo-Pacific interactions.

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Sensitivity of precipitation to sea surface temperature over the tropical summer monsoon region—and its quantification   总被引：1，自引：0，他引：1  

Mathew Roxy 《Climate Dynamics》2014,43(5-6):1159-1169

Over the tropical oceans, higher sea surface temperatures (SST, above 26 °C) in summer are generally accompanied by increased precipitation. However, it has been argued for the last three decades that, any monotonic increase in precipitation with respect to SST is limited to an upper threshold of 28–29.5 °C, and beyond this, the relationship fails. Based on this assessment it has often been presumed that, since the mean SSTs over the Asian monsoon basins (Indian Ocean and north-west Pacific) are mostly above the threshold, SST does not play an active role on the summer monsoon variability. It also implies that increasing SSTs due to a changing climate need not result in increasing monsoon precipitation. The current study shows that the response of precipitation to SST has a time lag, that too with a spatial variability over the monsoon basins. Taking this lag into account, the results here show that enhanced convection occurs even up to the SST maxima of 31 °C averaged over these basins, challenging any claim of an upper threshold for the SST-convection variability. The study provides us with a novel method to quantify the SST-precipitation relationship. The rate of increase is similar across the basins, with precipitation increasing at ~2 mm day^?1 for an increase of 1 °C in SST. This means that even the high SSTs over the monsoon basins do play an active role on the monsoon variability, challenging previous assumptions. Since the response of precipitation to SST variability is visible in a few days, it would also imply that including realistic ocean–atmosphere coupling is crucial even for short term monsoon weather forecasts. Though recent studies suggest a weakening of the monsoon circulation over the last few decades, results here suggest an increased precipitation over the tropical monsoon regions, in a global warming environment with increased SSTs. Thus the signature of SST is found to be significant for the Asian summer monsoon, in a quantifiable manner, seamlessly through all the timescales—from short-term intraseasonal to long-term climate scales.  相似文献   

Performance evaluation of environmentally compatible stormwater filtration systems     

M. P. Samuel  S. Senthilvel  A. C. Mathew 《International Journal of Environmental Science and Technology》2014,11(5):1327-1342

A horizontal flow multimedia stormwater filter was developed and tested for hydraulic efficiency and pollutant removal efficiency. Suitability of different natural fibres such as jute, sisal, hemp, coir and oil palm was studied as filter media. Furthermore, the efficacy of different fabric filter screens made up of both woven and nonwoven textiles was also assessed. A new terminology, Universal Performance Index, was introduced. Analysis of these indices showed that jute medium, nonwoven sisal screen and media proportion 1:1:1 performed better. All of the filter combinations exhibited 100 % sediment removal at lower sediment concentration in the inflow. Percentage of discarded flow versus reference flow for the stormwater filter combinations showed that the device performed better at lower flow rates. It was also observed that the hydraulic efficiency was directly proportional to the slope and inversely proportional to the cross-sectional area of the filter. Hydraulic efficiency showed a diminishing trend as the sediment level in inflow increases. By using matrix ranking method, the gravel–coir fibre–sand filter in 1:1:1 proportion with woven sisal hemp screens was selected as the best filter combination. The field evaluation of the filter showed 97.24 % efficiency in normalizing pH and 13.27 % efficiency in reducing electrical conductivity. The removal percentages of magnesium and sodium were 32 and 34 %, respectively. But higher removal efficiencies above 70 % were recorded for total solids, nitrates and sulphates.  相似文献   

Intraseasonal SST-precipitation relationship and its spatial variability over the tropical summer monsoon region   总被引：1，自引：1，他引：0  

Mathew Roxy  Youichi Tanimoto  B. Preethi  Pascal Terray  R. Krishnan 《Climate Dynamics》2013,41(1):45-61

The SST-precipitation relationship in the intraseasonal variability (ISV) over the Asian monsoon region is examined using recent high quality satellite data and simulations from a state of the art coupled model, the climate forecast system version 2 (CFSv2). CFSv2 demonstrates high skill in reproducing the spatial distribution of the observed climatological mean summer monsoon precipitation along with its interannual variability, a task which has been a conundrum for many recent climate coupled models. The model also exhibits reasonable skill in simulating coherent northward propagating monsoon intraseasonal anomalies including SST and precipitation, which are generally consistent with observed ISV characteristics. Results from the observations and the model establish the existence of spatial variability in the atmospheric convective response to SST anomalies, over the Asian monsoon domain on intraseasonal timescales. The response is fast over the Arabian Sea, where precipitation lags SST by ~5 days; whereas it is slow over the Bay of Bengal and South China Sea, with a lag of ~12 days. The intraseasonal SST anomalies result in a similar atmospheric response across the basins, which consists of a destabilization of the bottom of the atmospheric column, as observed from the equivalent potential temperature anomalies near the surface. However, the presence of a relatively strong surface convergence over the Arabian Sea, due to the presence of a strong zonal gradient in SST, which accelerates the upward motion of the moist air, results in a relatively faster response in terms of the local precipitation anomalies over the Arabian Sea than over the Bay of Bengal and South China Sea. With respect to the observations, the ocean–atmosphere coupling is well simulated in the model, though with an overestimation of the intraseasonal SST anomalies, leading to an exaggerated SST-precipitation relationship. A detailed examination points to a systematic bias in the thickness of the mixed layer of the ocean model, which needs to be rectified. A too shallow (deep) mixed layer enhances (suppress) the amplitude of the intraseasonal SST anomalies, thereby amplifying (lessening) the ISV and the active-break phases of the monsoon in the model.  相似文献   

High resolution facies architecture and digital outcrop modeling of the Sandakan formation sandstone reservoir,Borneo:Implications for reservoir characterization and flow simulation     

Numair A.Siddiqui  Mu.Ramkumar  Abdul Hadi A.Rahman  Manoj J.Mathew  M.Santosh  Chow W.Sum  David Menier 《地学前缘(英文版)》2019,10(3):957-971

Advances in photogrammetry have eased the acquisition of high-resolution digital information from outcrops, enabling faster, non-destructive data capturing and improved reservoir modeling. Geocellular models for flow dynamics with in the virtual outcrop in siliciclastic deposits at different sets of sandstone facies architecture remain, however, a challenge. Digital maps of bedding, lithological contrast, spatial-temporal variations of bedding and permeability characteristics make it more easy to understand flow tortuosity in a particular architecture. An ability to precisely model these properties can improve reservoir characterization and flow modeling at different scales. Here we demonstrate the construction of realistic 2 D sandstone facies based models for a pragmatic simulation of flow dynamics using a combination of digital point clouds dataset acquired from LiDAR and field investigation of the Sandakan Formation, Sabah, Borneo.Additionally, we present methods for enhancing the accuracy of outcrop digital datasets for producing high resolution flow simulation. A well-exposed outcrop from the Sandakan Formation, Sabah, northwest Borneo having a lateral extent of 750 m was chosen in order to implement our research approach. Sandstone facies and its connectivity are well constrained by outcrop observations, data from air-permeability measurements, bilinear interpolation of permeability, grid construction and water vector analysis for flow dynamics.These proportions were then enumerated in terms of static digital outcrop model(DOM) and facies model based on sandstone facies bedding characteristics. Flow simulation of water vector analysis through each of the four sandstone facies types show persistent spatial correlation of permeability that align with either cross-bedded orientation or straight with more dispersion high quality sandstone(porosity 21.25%-41.2%and permeability 1265.20-5986.25 mD) and moderate quality sandstone(porosity 10.44%-28.75% and permeability 21.44-1023.33 mD). Whereas, in more heterolithic sandstone(wavy-to flaser-bedded and bioturbated sandstone), lateral variations in permeability show spatially non-correlated patterns over centimeters to tens of meters with mostly of low quality sandstone(porosity 3.4%-12.31% and permeability < 1 mD to 3.21 mD). These variations reflect the lateral juxtaposition in flow dynamics. It has also been resulted that the vertical connectivity and heterogeneities in terms of flow are mostly pragmatic due to the interconnected sandstone rather than the quality of sandstone.  相似文献   

FT-IR Spectroscopic Investigation of Hydrous Components in Sillimanite from Eastern Ghat Granulite Belt, India     

R.V. Karanth  George Mathew  T.K. Gundu Rao 《Gondwana Research》1999,2(1):89

FT-IR spectra of sillimanite samples from high grade regionally metamorphosed rocks belonging to the granulite terrain (amphibolite to pyroxene granulite facies) deciphers prominent OH features. Heating experiments indicate growth of prominent band at 3161cm⁻¹. Heating above 1000°C all OH features disappear in intensity into broad features with slight shift of bands towards lower energies. Complete dehydration requires temperatures above 1000°C. Coexistence of boron and OH features are also observed in all sillimanite samples. The high temperature behaviour of sillimanite from the granulite terrain discerns that the hydrous species in sillimanite were incorporated much below 700°C, however, secondary hydration due to pegmatite activity, retrograde metamorphism and migmatisation is not ruled out. Thus a near anhydrous condition were probably not achieved during the granulite facies metamorphism in Eastern ghat granulite terrain.  相似文献   

Emerging Technologies and Synergies for Airborne and Space-Based Measurements of Water Vapor Profiles     

Amin R. Nehrir  Christoph Kiemle  Mathew D. Lebsock  Gottfried Kirchengast  Stefan A. Buehler  Ulrich Löhnert  Cong-Liang Liu  Peter C. Hargrave  Maria Barrera-Verdejo  David M. Winker 《Surveys in Geophysics》2017,38(6):1445-1482

A deeper understanding of how clouds will respond to a warming climate is one of the outstanding challenges in climate science. Uncertainties in the response of clouds, and particularly shallow clouds, have been identified as the dominant source of the discrepancy in model estimates of equilibrium climate sensitivity. As the community gains a deeper understanding of the many processes involved, there is a growing appreciation of the critical role played by fluctuations in water vapor and the coupling of water vapor and atmospheric circulations. Reduction of uncertainties in cloud-climate feedbacks and convection initiation as well as improved understanding of processes governing these effects will result from profiling of water vapor in the lower troposphere with improved accuracy and vertical resolution compared to existing airborne and space-based measurements. This paper highlights new technologies and improved measurement approaches for measuring lower tropospheric water vapor and their expected added value to current observations. Those include differential absorption lidar and radar, microwave occultation between low-Earth orbiters, and hyperspectral microwave remote sensing. Each methodology is briefly explained, and measurement capabilities as well as the current technological readiness for aircraft and satellite implementation are specified. Potential synergies between the technologies are discussed, actual examples hereof are given, and future perspectives are explored. Based on technical maturity and the foreseen near-mid-term development path of the various discussed measurement approaches, we find that improved measurements of water vapor throughout the troposphere would greatly benefit from the combination of differential absorption lidar focusing on the lower troposphere with passive remote sensors constraining the upper-tropospheric humidity.  相似文献   

Observed year-to-year sea surface salinity variability in the Bay of Bengal during the 2009–2014 period     

Akurathi Venkata Sai Chaitanya  Fabien Durand  Simi Mathew  Vissa Venkata Gopalakrishna  Fabrice Papa  Matthieu Lengaigne  Jerome Vialard  Chanda Kranthikumar  R. Venkatesan 《Ocean Dynamics》2015,65(2):173-186

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Erratum to: Observed year-to-year sea surface salinity variability in the Bay of Bengal during the 2009–2014 period     

Akurathi Venkata Sai Chaitanya  Fabien Durand  Simi Mathew  Vissa Venkata Gopalakrishna  Fabrice Papa  Matthieu Lengaigne  Jerome Vialard  Chanda Kranthikumar  R. Venkatesan 《Ocean Dynamics》2015,65(3):467-467

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Landslide susceptibility zonation mapping and its validation in part of Garhwal Lesser Himalaya, India, using binary logistic regression analysis and receiver operating characteristic curve method   总被引：12，自引：4，他引：8  

John Mathew  V. K. Jha  G. S. Rawat 《Landslides》2009,6(1):17-26

A landslide susceptibility zonation (LSZ) map helps to understand the spatial distribution of slope failure probability in an area and hence it is useful for effective landslide hazard mitigation measures. Such maps can be generated using qualitative or quantitative approaches. The present study is an attempt to utilise a multivariate statistical method called binary logistic regression (BLR) analysis for LSZ mapping in part of the Garhwal Lesser Himalaya, India, lying close to the Main Boundary Thrust (MBT). This method gives the freedom to use categorical and continuous predictor variables together in a regression analysis. Geographic Information System has been used for preparing the database on causal factors of slope instability and landslide locations as well as for carrying out the spatial modelling of landslide susceptibility. A forward stepwise logistic regression analysis using maximum likelihood estimation method has been used in the regression. The constant and the coefficients of the predictor variables retained by the regression model have been used to calculate the probability of slope failure for the entire study area. The predictive logistic regression model has been validated by receiver operating characteristic curve analysis, which has given 91.7% accuracy for the developed BLR model.  相似文献