Modelling for Science, for a better future - some recent outcomes
Subsurface imaging of brown coal bearing Tertiary sedimentaries - Deccan Trap interface using microtremor method
by Dhananjay A.Sant, Imtiyaz A.Parvez, Govindan Rangarajan, Satish J.Patel, T.A.Sanoop Salam and Madhuri N.Bhatt
We propose an application of the microtremor (ambient noise) H/V spectral ratio technique to identify significant rheological boundaries at shallow depths, estimate thickness of both lignite bearing Tertiary sedimentary sequence and late Cretaceous Deccan basalt flows and comprehend basinal geometry of Umarsar Basin (Babia syncline). Forty-six stations were gauged in a grid format at ~250 m resolution during the microtremor survey. The microtremor H/V spectral ratio technique takes into account the frequency of the ratio between the horizontal (NS + EW) and vertical components of persistent Rayleigh waves in the area. Depth estimates are made using Mean_Vs (433.69 m/s) from three borehole records (MMA_Vs (431.6 m/s), MMB_Vs (406.86 m/s) and MMC_Vs (462.6 m/s) using standard relationship between depth and velocity. In the present study, we recognize three rheological interfaces viz., L1 interface (0.2328 Hz to 0.3862 Hz), L2 interface (0.7843 Hz to 2.5123 Hz) and L3 interface (6.2477 Hz to 27.1119 Hz). The geology and stratigraphic records supplement correlation for L1, L2 and L3 interfaces with Mesozoic–Deccan Trap (M-DT) boundary, Deccan Trap-Tertiary (DT-T) boundary, and boundaries between shale‑carbonate hardpans within sediment sequence belonging to Naredi Formation respectively. The estimated depth range for M-DT boundary (L1) is 281–466 m and for DT-T boundary (L2) is 43–138 m. The subsurface image acquired from the frequency records advocates for a palaeo high in SE portion that retains its entity over the present landscape. The frequency records advocate for 369 m to 206 m thick Deccan basalt and 85 m to 18 m thick lignite bearing Naredi Formation. The ambient noise seismic study further suggests NW-SE trending basin geometry of Babia syncline comprising three distinct depressions having six local depocenters. Finally, we propose the microtremor H/V spectral ratio technique as a tool to develop economical borehole plan with realistic reserve estimate and a step forward towards rapid economical assessment covering large mining lease areas complementary to local geological studies.
Source: https://www.sciencedirect.com/science/article/pii/S0926985117310078#!
Comparative Evaluation of the skill of a Global Circulation Model and a Limited Area Model in simulating Tropical Cyclones in the North Indian Ocean
by G N Mohapatra, V Rakesh, P K Mohanty and S Himesh
Considerable improvement has taken place in forecasting tropical cyclones at 24‐48 hour leads; however, improving accuracy of tropical cyclones forecasts at longer leads is still a major scientific challenge. The major bottleneck in accurate tropical cyclone forecast using limited area models (LAM) comes from the use of artificial lateral boundary conditions, especially at longer leads. Although, global circulation models (GCM) still cannot match the horizontal resolution that can be implemented in a LAM over a smaller domain, it is possible that better representation of scales and thus scale interactions in a global domain can lead to better simulation of tropical cyclones with a GCM even with relatively coarser resolution. This hypothesis is tested in the present work with a GCM and LAM configuration. We consider 30 cyclones over the north Indian Ocean (NIO) that represents different seasons and intensity during 1999‐2012. Analysis of forecast skills at 3 leads (24‐hour, 48‐hour and 96 hour) show that while LAM has better skill compared to GCM at shorter lead (< 48 hour), GCM has significantly higher skill at longer lead (96 hour). The two configurations are found to exhibit somewhat complementary skills in terms of forecast lead and the severity of the cyclones. Therefore, it is suggested that a methodology combining both LAM and GCM can provide more reliable forecasts.
Source: https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/met.1718?af=R
Monsoon Climate Change Projection for the Orographic West Coast of India Using High‐Resolution Nested Dynamical Downscaling Model
by Jayasankar, C. B., Rajendran, K. & Sajani Surendran
An efficient, reliable very high resolution dynamical downscaling model, a regional climate model (Weather Research and Forecasting‐Advanced Research Weather Research and Forecasting) one‐way nested into skillful general circulation model (National Center for Atmospheric Research‐Community Climate System Model version 4), is configured and implemented for ecologically sensitive, densely populated west coast of India encompassing Western Ghats (WG) having complex, meridionally oriented orography and wide biodiversity. This model with 3 km resolution resolves orographic features enabling realistic simulation of physical and dynamical characteristics of present‐day Indian summer monsoon (ISM) and extreme events, particularly recent trends in ISM rainfall over WG as observed. Marked skill of this model provides confidence in its future climate projection at regional scale. Future ISM rainfall projection shows significant increase (reduction) over 50.7% (5.8%) of Indian grid points. Significant reduction (10–20% of mean) over WG is due to upper‐tropospheric warming effect that stabilizes the atmosphere. Projected changes in extreme events show overall increase in warm days and warm nights over India with maximum increase over South India. Projected changes show widespread increase in wet days over most of India and reduction over WG. Projection of consecutive dry days implies wetter future for most parts of India but strengthened drought conditions for WG. Wind extreme projection shows strengthened (weakened) low (high) winds probability over WG and increase (decrease) in very high (low) winds over central India. This study establishes the importance of (i) employing sufficiently high‐resolution model, (ii) using bias‐corrected boundary data, and (iii) configuring model for realistic present‐day climate over complex topographic coastlines such as the west coast, in order to obtain useful climate change information for adaptation measures.
Link: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JD028677
Citation:
Jayasankar, C. B., Rajendran, K., & Sajani Surendran, (2018). Monsoon climate change projection for the orographic west coast of India using high-resolution nested dynamical downscaling model. Journal Geophysical Research: Atmospheres, 123, 7821–7838. https://doi.org/10.1029/2018JD028677
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