| 1. |
- Banik, Trisanu, et al.
(författare)
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Understanding dynamics of tropical cyclones in the Bay of Bengal using lightning data
- 2021
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Ingår i: Meteorology and atmospheric physics (Print). - : Springer Nature. - 0177-7971 .- 1436-5065. ; 133:5, s. 1505-1522
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Tidskriftsartikel (refereegranskat)abstract
- In the present work, we are studying the dynamics of 11 tropical cyclones (TCs) over the Bay of Bengal (BoB) using the World Wide Lightning Location Network (WWLLN) lightning data during 2013–2017. Detailed investigation of Lightning Stroke Count (LSC) shows that the initial phase of the TC intensification over BoB is associated with high lightning activity both in the eye region and rainband region. The study of different category TCs shows the weak and moderate-intensity TCs during both in pre-monsoon and post-monsoon seasons are lightning populated (specifically inner bands) during and prior to the intensification phase. Peak Maximum Sustained Wind Speed (MSWS), which is linked to sea surface temperatures (SSTs), is preceded by the peak LSC with a time lag of 6–12 h. The LSC peaks in the eye region and rain band for different categories of TCs between small to moderate wind shear range. The present study highlights that the monitoring of real-time lightning activity could provide supportive information on the existing forecast techniques. But further analyses are required over BoB to quantify the relationship between TC intensification and lightning activity both in space and time.
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| 2. |
- Thandlam, Venugopal, Mr. 1987-
(författare)
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A sea-level monopole in the equatorial Indian Ocean
- 2020
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Ingår i: npj Climate and Atmospheric Science. - : Springer Science and Business Media LLC. - 2397-3722. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we show the relationship between sea-level anomalies (SLA) and upper-ocean parameters in the Equatorial Indian Ocean (EIO). This work also focuses on the variability of SLA obtained from satellite altimeter data in different spatial and temporal scales and its relationship with computed ocean heat content (OHC), dynamic height (DH), and thermocline depth (20 °C isotherm: D20) during 1993–2015. SLA showed low Pearson’s correlation coefficient (CC) with upper-ocean parameters over central EIO resembling a “Monopole” pattern. The Array for Real-time Geostrophic Oceanography (ARGO) in situ profile data in the central EIO also confirmed this. SLA over this monopole showed low correlations with all parameters as compared with eastern and western EIO. These findings show a clear signature of a persisting sea-level monopole in the central EIO. Oscillating SLA over western and eastern EIO during summer and winter monsoon months is found to be responsible for locking this monopole in the central EIO. Both SLA and OHC increased in EIO during 2006–2015 compared with 1993–2005. The month of January showed different east–west trends at different times. This trend during 1993–2015 is neutral, but it shifted from negative during 1993–2005 to positive during 2006–2015.
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| 3. |
- Thandlam, Venugopal, Mr. 1987-, et al.
(författare)
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Are We in the Right Path in Using Early Warning Systems?
- 2019
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Ingår i: Journal of Extreme Events. - : World Scientific. - 2345-7376 .- 2382-6339. ; 06:02
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Tidskriftsartikel (refereegranskat)abstract
- This paper focusses on the recent tsunami in Indonesia and the factors led to the mass killing. We also discussed the failure of early warning systems, steps, methods, and technologies, in general, to improve the early warning systems in the future to mitigate the loss of lives and property during these impending disasters. We believe that this paper is timely as Indonesia has seen one of the worst tsunamis in recent years and the threat is still on. Hence, we stress the importance of improving and strengthening the existing early warning systems.
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| 4. |
- Thandlam, Venugopal, Mr. 1987-, et al.
(författare)
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Evaluation of surface shortwave and longwave downwelling radiations over the global tropical oceans
- 2019
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Ingår i: SN Applied Sciences. - : Springer Science and Business Media LLC. - 2523-3963 .- 2523-3971. ; 1:10
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, daily downwelling shortwave (QS) and longwave radiation (QL) data from one satellite and two hybrid products have been evaluated using Global Tropical Moored Buoy Array during 2001–2009 in the tropical oceans. Daily satellite data are used from the Clouds and Earth’s Radiant Energy System (CERES) program. Data are obtained using Moderate Resolution Imaging Spectroradiometer (MODIS) (CM) aboard the Terra and Aqua satellites. Coordinated Ocean Research Experiments (CORE-II) and Tropical Flux data (TropFlux) are the other two hybrid products used in this study. The analysis shows that majority of QS observations as well as derived products lie in 200–300 Wm−2 range in all the three tropical oceans. Both QS and QL in all products overestimated the majority of the observations. Yet, they underestimated the lower (0–100 Wm−2) values in QS and higher (300–440 Wm−2) values in QL. Majority of the QL observations lie within 390–420 Wm−2 range, and CM slightly overestimated this observed distribution in the Pacific and the Atlantic Oceans. But, majority of the observations in the Indian Ocean lie within 420–450 Wm−2 range. This implies that the tropical Indian Ocean receives 30 Wm−2 more energy as compared to the tropical Pacific and the Atlantic in the form of downwelling longwave radiation. Daily observed QS shows dominant seasonal cycle over the central, the eastern Pacific and the eastern Atlantic. On the other hand, the western Pacific, the central Atlantic and the Indian Oceans show intraseasonal variations. All products show this variation with high root-mean-square error (RMSE) values (QS and QL) over the Indian Ocean than in the Pacific and the Atlantic Oceans. Downwelling radiation from CORE-II shows highest RMSE (for both QS and QL) with least correlation coefficient (CC), and TropFlux has lowest RMSE and highest CC among all products in all three tropical oceans. CM has intermediate values of standard deviation, CC and RMSE. These results are not seasonally dependent, since the seasonal statistics are consistent with seasonal changes. Assuming that the SST is only driven by the downwelling shortwave and longwave fluxes, the errors associated with monthly SST can be as large as 0.2–0.3 (0.1–0.2) °C associated with errors in QS (QL). Both QS and QL in CORE-II have lower spatial variability as compared to other datasets. QL in the tropical oceans shows seasonal spatial variability determined by intertropical convergence zone positions. This variability does not change significantly over the Pacific and the Atlantic Oceans. The summer and winter monsoon patterns in the Indian Ocean guide the QL variability. Opposite to QS, higher QL values have lower variability. Thus, this study aims at finding better radiation dataset to use in the numerical models and deduce that satellite data could be an alternative to existing reanalysis products.
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| 5. |
- Thandlam, Venugopal, Mr. 1987-, et al.
(författare)
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Quantifying the role of antecedent Southwestern Indian Ocean capacitance on the summer monsoon rainfall variability over homogeneous regions of India
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- The role of ocean variability is at a focal point in improving the weather and climate forecasts at different spatial and temporal scales. We study the effect of antecedent southwestern Indian Ocean mean sea level anomaly (MSLA) and sea surface temperature anomalies (SSTA) as a proxy to upper ocean heat capacitance on all India summer monsoon rainfall (AISMR) during 1993–2019. SSTA and MSLA over the southwestern Indian Ocean (SWIO) have been influenced by El Niño-Southern Oscillation (ENSO), the impact of ENSO-induced SWIO variability was low on rainfall variability over several homogeneous regions. Rainfall over northeast (NE) and North India (EI) has been modulated by ENSO-induced SSTA and MSLA over SWIO, thus effecting the total AISMR magnitude. The ENSO-induced changes in heat capacitance (SSTA and MSLA) over SWIO during antecedent months has less impact on west coast of India, central India and North India (NI) rainfall variability. The long-term trend in pre-monsoonal SSTA and MSLA over SWIO shows decreasing rainfall trend over NI, NE, and EI in the recent time. Furthermore, the cooler (warmer) anomaly over the western Indian Ocean affects rainfall variability adversely (favourably) due to the reversal of the wind pattern during the pre-monsoon period. While SSTA and MSLA are increasing in the SWIO, large-scale variability of these parameters during preceding winter and pre-monsoon months combined with surface winds could impact the inter-annual AISMR variability over homogeneous regions of India. Similarly, from an oceanic perspective, the antecedent heat capacitance over SWIO on an inter-annual time scale has been the key to the extreme monsoon rainfall variability.
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| 6. |
- Thandlam, Venugopal, Mr. 1987-, et al.
(författare)
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Quantifying uncertainties in CERES/MODIS Downwelling radiation fluxes in the global tropical oceans
- 2023
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Ingår i: Ocean-Land-Atmosphere Research. - : American Association for the Advancement of Science (AAAS). - 2771-0378. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- The Clouds and the Earth's Radiant Energy System program, which uses the Moderate Resolution Imaging Spectroradiometer (CM), has been updated with the launch of new satellites and the availability of newly upgraded radiation data. The spatial and temporal variability of daily averaged synoptic 1-degree CM version 3 (CMv3) (old) and version 4 (CMv4) (new) downwelling shortwave (QS) and longwave radiation (QL) data in the global tropical oceans spanning 30°S–30°N from 2000 to 2017 is investigated. Daily in situ data from the Global Tropical Moored Buoy Array were used to validate the CM data from 2000 to 2015. When compared to CMv3, both QS and QL in CMv4 show significant improvements in bias, root-mean-square error, and standard deviations. Furthermore, a long-term trend analysis shows that QS has been increasing by 1 W m−2 per year in the Southern Hemisphere. In contrast, the Northern Hemisphere has a −0.7 W m−2 annual decreasing trend. QS and QL exhibit similar spatial trend patterns. However, in the Indian Ocean, Indo-Pacific warm pool region, and Southern Hemisphere, QL spatial patterns in CMv3 and CMv4 differ with an opposite trend (0.5 W m−2). These annual trends in QS and QL could cause the sea surface temperature to change by −0.2 to 0.3 °C per year in the tropical oceans. These results stress the importance of accurate radiative flux data, and CMv4 can be an alternative to reanalysis or other model-simulated data.
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| 7. |
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| 8. |
- Thandlam, Venugopal, Mr. 1987-, et al.
(författare)
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Spatio-temporal variability of atmospheric rivers and associated atmospheric parameters in the Euro-Atlantic region
- 2022
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Nature. - 0177-798X .- 1434-4483. ; 147:1-2, s. 13-33
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Tidskriftsartikel (refereegranskat)abstract
- We study the spatio-temporal variability of Atmospheric Rivers (ARs) and associated integrated water vapor and atmospheric parameters over the Euro-Atlantic region using long-term reanalysis datasets. Winds, temperature, and specific humidity at different pressure levels during 1979–2018 are used to study the water vapor transport integrated between 1000 and 300 hPa (IVT300) in mapping ARs. The intensity of ARs in the North Atlantic has been increasing in recent times (2009–2018) with large decadal variability and poleward shift (~ 5° towards the North) in landfall during 1999–2018. Though different reanalysis datasets show similar spatial patterns of IVT300 in mapping ARs, bias in specific humidity and wind components led to IVT300 mean bias of 50 kg m−1 s−1 in different reanalysis products compared to ERA5. The magnitude of winds and specific humidity in the lower atmosphere (below 750 hPa) dominates the total column water vapor and intensity of ARs in the North Atlantic. Reanalysis datasets in the central North Atlantic show an IVT300 standard deviation of 200 kg m−1 s−1 which is around 33% of the ARs climatology (~ 600 kg m−1 s−1). Though ARs have a higher frequency of landfalling over Western Europe in winter half-year, the intensity of IVT300 in winter ARs is 3% lower than the annual mean. The lower frequency of ARs in the summer half-year shows 3% higher IVT300 than the annual mean. While ARs in the North Atlantic show a strong decadal change in frequency and path, the impact of the North Atlantic Oscillation (NAO) and Scandinavian blocking on the location of landfall of ARs are significant. Furthermore, there is a strong latitudinal dependence of the source of moisture flux in the open ocean, contributing to the formation and strengthening ARs.
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