In this research, the focus is on examining the occurrence of localized Cloudburst events in the Indian Himalayan region (IHR). Specifically, in the year 2022, a total of 66 cloudburst cases were observed in the region, indicating a rise in the severity of extreme rainfall events (ERE) in recent times. Due to limited information and awareness, the mountainous hazards often go unnoticed. As the topographical feature has wider variation and because of the regional divergence there is also a variability in the intensity, duration and frequency of the EREs. Therefore, it is crucial to study the dynamics of the atmosphere during these events in order to enhance the understanding of researchers and facilitate the simulation of highly intense localized events in the future. Longitude-wise box (1ox1o ) was classified over the IHR in this research for a systematic analysis of the ERE dynamics. Furthermore, our study emphasized the statistical observational analysis of atmospheric dynamics in relation to observed rainfall across various boxes during the occurrence of the Cloudburst events. The temporal analysis is carried out by considering the atmospheric studies for the period starting 2 days before the event at the region. The relationship between major physical and thermodynamical atmospheric parameters and rainfall in different boxes has been comprehended and analysed. Understanding the intricate relationships between the atmosphere and land surface is crucial for making accurate predictions about the future. By delving into these complex interactions, researchers can gain valuable insights that can help improve forecasting models and enhance our understanding of the Earth's systems.
by Sambit Prasanajit Naik, Siva Sai Kumar Rajana, Sampad Kumar Panda, Chiranjeevi G. Vivek & Devanshu Ghildiyal
This study examines the Co-seismic Ionospheric Disturbances (CIDs) triggered by Mw 7.6 Cayman Islands earthquake along the transform fault setting in the Caribbean Sea on 8 February 2025 using the GNSS-based Total Electron Content (TEC) observations. The significance of characterizing the effects of this particular earthquake event through probing ionospheric perturbations lies in its occurrence under quiet solar and geomagnetic conditions. This provides unambiguous identification of ionospheric perturbations caused by lithospheric forcing from below, and valuable insights into solid Earth-ionosphere coupling mechanisms. The earthquake exhibited the two-stage rupture process, beginning with a slow initial sub-shear rupture phase followed by a rapid acceleration into the supershear regime. This rupture behavior facilitated the generation of strong ground motion and produced atmospheric acoustic-gravity waves (AGWs) that propagated upward and reached ionospheric altitudes. Notably, filtered TEC data exhibited distinct oscillations following the earthquake, which clearly showed the CIDs signatures with the amplitudes reaching up to 0.8 TECU. The filtered TEC values also exhibited the spatial asymmetry due to the atmospheric effects and the ambient geomagnetic field. Also, spectral analysis confirmed the dominant acoustic wave frequencies (2–4 mHz) and horizontal propagation velocities (~ 1.34 km/s) aligning with the theoretical acoustic wave speeds, which further confirmed the signatures of seismic origin ionospheric disturbances. These findings reinforce the role of CIDs as reliable indicators of seismic activity in transform plate boundary settings and highlight the potential use of GNSS networks for real-time earthquake monitoring.
We investigate the 3-D shear velocity (Vs) structure of the crust beneath the Kumaon Garhwal Himalaya using joint inversion of interpolated receiver functions from 57 seismic stations, and Rayleigh wave group velocity dispersion data in the period 2 to 100 s with significantly improved horizontal resolution of about 25 km. The velocity image reveals several important features. In the shallow crust, the Main Himalayan Thrust (MHT) is characterised as a flat-ramp-flat structure, inferred from the presence of low Vs of 3.1–3.4 km/s representing wet sediments dragged along the MHT and lying above the crystalline Indian crust of Vs ∼ 3.6 km/s. The MHT is at a depth of about 8 km beneath the southern edge of the Himalaya, dipping at 3○ to the north. At the front of the High Himalaya, the dip increases significantly to about 35○–40○ representing the ramp and reaching a depth of 24 km. Farther north beneath the High Himalaya, the MHT continues as a nearly flat structure. The middle crust (20–30 km) has reduced Vs (3.3–3.5 km/s) below the northern part of the Lesser Himalaya, possibly due to the presence of fluid released by metamorphism of the subducting Indian crust along with the presence of mica produced as a consequence of deformation. The thickness of the crust is ∼50 km beneath the sub and Lesser Himalaya and increases abruptly in the front of the High Himalaya to 60 km and remains so till the southern part of Tethys Himalaya. The observed thick crust with lower seismic velocity (and rigidity) beneath the High Himalaya could be responsible for its high topography. We report almost 6–8 km thinning of the crust in the eastern segment of Garhwal Himalaya adjoining Nepal.
by S K Sahoo, Krushna Chandra Gouda, S Himesh and R K Sahu
An unprecedented heat wave lasting approximately two weeks occurred in Odisha during the third and fourth weeks of May 2015, resulting in meteorological hazards. In this study, an extreme temperature event (ETE) occurred on 25-27th May 2015, with about 15 meteorological observation stations in the state of Odisha recording maximum temperatures exceeding 45 °C, resulting in an intense heat wave. The mesoscale modeling framework (WRF4.0) is configured and optimized to simulate ETE at the regional scale in this study using different land-use scenarios. The maximum temperature from a time-ensemble simulation using the current land-use scenario based on Indian Space Research Organization (ISRO) data is found to be more accurate than simulations based on US Geological Survey (USGS) data at India Meteorological Department (IMD) meteorological stations. The mean percentage errors of simulated maximum temperatures over Odisha with respect to IMD station-scale observations are 1.6% (ISRO) and 3% (USGS) on 25th May 2015, and 4.2% (ISRO) and 4.7% (USGS) on 26th May 2015, respectively. Compared with the simulation based on ISRO data (more urbanized), the simulated horizontal surface wind at the different locations in Odisha is generally higher in the simulation based on USGS data. Changes in land use increase the roughness length, reducing surface wind speed. The dynamical aspects are also explored by analyzing humidity, outgoing longwave radiation (OLR), Convective Available Potential Energy (CAPE), and Convective Inhibition (CIN), etc., from the model and validated with the reanalysis products, which support the model performance in capturing the conducive environment resulting in a regional heat wave. The land use analysis reveals that the state-wide increase in urbanization between 1992 and 2015 was about 0.4%, with the highest percentage increase occurring in cities like Bhubaneswar, Sambalpur, Jharsuguda, and Rourkela in the Sundergarh district, which regularly experience the heat wave in the month of May, and the same are accurately simulated by the optimized and calibrated model configuration. Land-use change, including urban expansion and shifting cropping patterns, along with increased anthropogenic activities, is directly linked to the rise in maximum temperatures.
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