Outer-arc active tectonic deformation off the Nias – Nicobar Trench: Insights from lithospheric stress and seismic slip models
by K. Silpa and Anil Earnest
This study investigates the seismic behavior and deformation characteristics in the outer-arc region off the Nicobar trench using stress inversion and teleseismic finite-fault modeling. The spatial and depth-wise variations in stress field in this region indicate variations in post-seismic deformation scenarios along the arc. The lateral shear, similar to the north Wharton basin, is the major deformational field in the Nicobar segment, favoring earthquake faulting along ∼ESE or ∼NNE nodal planes here. Shallow oblique-normal faulting and deeper oblique-reverse regimes are observed in the Nias region. These observations suggest that the plate bending effects directly influence the ongoing tectonics in the Nias region. Moreover, variations in the stress fields across the arc could be indicative of an uncoupled plate interface. Our finite-fault modeling analysis indicates dominant ∼ESE-WNW fault plane orientations for selected events from this region. This suggests the possibility of faulting within similarly oriented active shear structures within the northern Wharton Basin, contrasting the prevailing ∼N-S faulting pattern in that area. Besides, the centroid depths of most of these earthquakes are typically within the 600°C isotherm. However, the seismic slip may extend deeper by rupturing the crust, occasionally reaching upper mantle depths.
A comprehensive study of atmospheric dynamics associated with cloudburst events in 2022 over Indian Himalayan Region
by Payoshni Samantray and Krushna Chandra Gouda
This comprehensive study aims to investigate the cloudburst events that occurred in the Indian Himalayan Region (IHR) during the year 2022, focusing on their characteristics, structure and dynamics. Cloudburst events have been observed in different states of the Himalayan region, with their unique geographical features, and are susceptible to extreme weather phenomena, which pose significant challenges to the local communities and infrastructure. A majority of cloudburst events occur within the folds of valleys of the Indian Himalayas, where elevations range from 325 to 4073 m. As the year 2022 witnessed frequent cloudburst events in the IHR (Himachal Pradesh recorded around 24 cloudburst events, Uttarakhand recorded 18 and Jammu and Kashmir recorded 24 events), an attempt is being made for the comprehensive analysis of the role of atmospheric dynamics to result in such extreme events in the valley region. The analysis clearly advocates that certain atmospheric phenomena, such as frontal boundaries like temperature, humidity, convective available potential energy, convective inhibition, or atmospheric disturbances, can act as triggers for cloud burst events. The spatial distribution of different thermodynamic parameters during the previous day, event day and the day after the cloudburst events are also analysed to quantify the role of atmospheric dynamics in the temporal distribution. This study has highlighted the importance of low-level jets and moisture transport in forming the convective systems that lead to cloudbursts over the Himalayan region due to wind patterns.
Morphology of Equatorial F-region Irregularities over the Indian Longitude sector using GPS-derived ROTI Observations
by Siva Sai Kumar Rajana, Sampad Kumar Panda, Sridevi Jade, Chiranjeevi G. Vivek
The occurrence characteristics of Equatorial F-region Irregularities (EFIs) along the Indian longitude sector are investigated using GPS-derived ROTI observations from 2010 to 2023, under both quiet and disturbed geomagnetic conditions. The analysis of the results emphasizes a strong dependence of EFIs occurrence on solar cycle variation. Additionally, the EFIs are more intense at the EIA regions under maximum solar activity periods attributed to the high ambient electron density in the F-layer. The occurrence of EFIs is found to be severe and frequently observed in equinox seasons in contrast to solstice seasons. Also, the occurrence of EFIs exhibits equinoctial asymmetry with more intense EFIs in the spring equinox than autumn equinox during the peak and declining periods of the solar cycle. Conversely, severe EFIs are observed during autumn equinox than spring equinox in the ascending phase of the solar cycle. The seasonal occurrence probability of EFIs is highest in the equinox seasons, following the winter solstice, and summer solstice in high solar activity conditions. Investigations of EFIs during two prominent geomagnetic storm events (17 March 2015 and 08 September 2017) during the study period show that the storm-induced Prompt Penetration Electric Fields (PPEFs) modulated the regular intensity of dusk time Pre-Reversal Enhancement (PRE), resulting in poleward expansion of ionospheric irregularities up to mid-latitude regions with spatial time lags. However, storm-induced westward electric fields and oscillating IMF Bz created Counter Electrojet (CEJ) like conditions, suppressing the dusk time ionospheric irregularities over dip equatorial and low-latitude regions on 17 March 2013. This study provides a comprehensive understanding of how ionospheric irregularities manifest under varying conditions, thereby supporting further research on substantiating the spatiotemporal EFIs characteristics and their predictions over the region.
Assessment of long-term spatio-temporal variability of hot extremes and associated physical mechanism over India
by Rani Devi, K. C. Gouda & Smrutishree Lenka
By exploring the multifaceted physical mechanisms underlying hot extreme events, the way for informed strategies to mitigate their impacts and enhance the nation's resilience in the wake of a changing climate can be paved. The long-term spatio-temporal variability of hot extremes analysis found an increasing trend (0.001 °C) of DMXT over whole Indian region except the eastern parts (Indo-Gangetic plains). The hot day is noted when DMXT > 40 °C, DMXT > 37 °C, DMXT > 35 °C and also DMXT is above the 90th percentile at each grid point in the plains, hilly, coastal region of India. The temperature tendency equation has been computed to identify the role of various physical processes driving the local extreme temperature changes in India. The analysis showed that the surface adiabatic warming found to be one of the prominent drivers of hot extreme events over India. The impact of El Niño-Southern Oscillation (ENSO) phases on the frequency of hot extreme days at local scale in India are quantified. The linear trend of hot days has been found increasing at a rate of 0.14/year, 0.08/year and 0.06/year in El Niño, La Niña and neutral years respectively. Similarly, the DMXT anomaly found to be 0.4 °C higher in El Niño phase as compared to La Niña phase. The results infers that the chances of hot days occurrence are increased (decreased) by 38% (16% and 8%) in El Niño (La Niña and neutral) period. The advection of hot air by westerlies into the Indian region leads to an increase in temperature. The composite elevated (dropped) geopotential height at 500 hPa showed the presence of high (low) pressure systems which leads to hot days occurrence over western, southern and central (northern, north western) India, where winds are westerlies (easterlies) in El Niño (La Niña) phase of ENSO. This reversal of wind is linked with the movement of warm sea surface temperature from western to eastern Pacific Ocean. Comprehending the dynamics of hot extremes in the India is vital for the development of strategies to mitigate the adverse impacts on various sectors, including agriculture, health, water resources, and infrastructure.
Source: https://doi.org/10.1007/s00477-024-02744-w
Homogeneity Adjustment of Surface Temperature Data and Study of the Climate Variability Over Coastal Odisha by a Climate Departure Index
by Bishnupada Sethi, Krushna Chandra Gouda, Sarat Chandra Sahu, Manas Kumar Mallick, Amrutanshu Panigrahi & Satish Kumar Samal
In the recent years, extreme temperature i.e. cold in winter and warm in summer has been observed in the coastal Odisha state in the east part of India. Hydro-meteorological disasters such as floods, droughts, heat waves and cold spells being experienced nowadays are unprecedented in living memory. In this work the climate variability over the coastal Odisha region is quantified considering the temperature parameter. A climate departure index (CDI) of three versions (simple, absolute and least-square) are calculated using monthly, annually and seasonally maximum, minimum as well as mean temperature form seven stations in the costal Odisha for the period 1969 to 2018 for assessing the degree of normal/unusual/extreme of a particular year in compared to the long-term average for the specific coast under consideration. Temperature time series data for the period 1969 to 2018 are homogenized by using the relative comparison between station observations and composite reference series by calculating CDI. Results indicates that CDI values of least-square on all cases are comparatively greater than simple and absolute CDIs. Least-square method is the appropriate method for determining the category of a year or a month or a season in terms of the temperature variation. Analysis based on mean temperature infers that only twenty extreme seasons are observed in monsoon season while three normal are observed during the month of October i.e., in post-monsoon season over the coastal Odisha. The relationship of climatic event including El Nino or La Nina feature of a particular year with respect to CDI is also investigated. The climatic variability is very high on some of the years based on analysis of index values of annual average of the temperatures (maximum, minimum and mean) over a region.
Source: https://doi.org/10.1007/s00024-024-03465-5
- Assessment of Country-Specific GHG Emissions from Road Transport Sector in India
- Decoding low-frequency climate variations: A case study on ENSO and ocean surface warming
- Intensity duration and frequency of Heat wave in different phases of MJO over India
- Impact of two severe geomagnetic storms on the ionosphere over Indian longitude sector during March-April 2023
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