A case study on multiple self-interactions of MSTID bands: New insights
by Dipjyoti Patgiri, Rahul Rathi, Virendra Yadav, Sumanta Sarkhel, Dibyendu Chakrabarty, Subarna Mondal, M.V. Sunil Krishna, Arun K. Upadhayaya, Chiranjeevi G. Vivek, Suresh Kannaujiya, Surendra Sunda
Abstract
In this study, we report a special event of nighttime southwestward propagating medium scale traveling ionospheric disturbances (MSTIDs) observed in O(1D) 630.0 nm airglow images from an all-sky imager at Hanle (32.7°N, 78.9°E; Mlat. ∼ 24.1°N), Leh Ladakh, India on a geomagnetically quiet (Ap = 7) night of 15 September 2018. The time sequence of airglow images unveiled two dynamic interactions between multiple dark bands of MSTID. Following the first interaction, one of the interacting bands decayed possibly due to the entrance of plasma from the ambient higher plasma density region. Shortly after this interaction, the other interacting dark band was involved in the second interaction with a third dark band which resulted in the co-alignment of the two interacting bands. Following this co-alignment, one of the bands started rotating prominently that led to further separation of these two co-aligned bands. These changes in the MSTID phase fronts (bands) are explained based on the development of the polarization electric fields arising out of the interactions. This investigation combines the all-sky 630.0 nm airglow imaging observations with TEC maps constructed, for the first time over the Indian sector, from 67 Global Navigation Satellite System (GNSS) measurements to capture the MSTID over this region. The investigation reveals a few important features of self-interactions of MSTID bands over the geomagnetic low-mid latitude transition region which is important to assess their impact over low latitudes.
3-D Crustal structure in Kumaon–Garhwal Himalaya using joint inversion of receiver functions and surface wave group velocity
by Ashish, Gokul Saha and Shyam S Rai
Summary
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.
Atmospheric opacity using 220 GHz (1.36 mm) radiometer data and water vapor trends over Indian Astronomical Observatory (IAO), Hanle
by Shantikumar S.Ningombam, Sethulakshmy E.S, SrideviJade, T.S.Shrungeshwara, Chiranjeevi G.Vivek, Dorje Angchuk, T.P.Prabhu and Tashi Tshering Mahay
The present work reports atmospheric opacity at 220 GHz over Indian Astronomical Observatory (IAO)-Hanle during 2006 to 2018. The opacity data were derived from the radiometric measurement of sky-brightness temperature as a function of zenith angle for every 10 min during day and night. Since the operating frequency range is not completely opaque during rainfall or cloudy atmosphere, observations are performed even during rainfall or cloudy sky conditions. The minimum opacities observed at the site varied from 0.06-0.07 at 1st quartile and 0.08-0.09 at 2nd quartile during December-January. Opacity at Hanle is linearly correlated with high temporal resolution GPS (Global Positioning System) Precipitable Water Vapor (PWV) with a correlation coefficient of about 0.8. The observed median opacity at Hanle has increased by 44% during the best observing months (October–March) and 24% over the annual data (October-September) with reference to the opacity observed during 2000–2003. Such increasing opacity trends are apparently due to effects of the dynamics of the regional and global hydrological cycle. In order to assess the impacts of the regional and global hydrological cycle, PWV obtained from AErosol RObotic NETwork (AERONET), satellite and reanalysis data were studied at nine high-altitude astronomical observatories spread spatially across the globe such as Atacama desert in Chile, Mauna Loa Observatory in Hawaii, Hanle and Merak in India, Ali and Yangbajing Observatories in Tibet, LLAMA in Argentina, and Dome A and Dome C in the Antarctic Plateau during 2003-2018. On an average, PWV trend over Atacama desert is increasing by 0.01 to 0.03 mm per year and at IAO-Hanle, Merak and Ali by 0.01 to 0.05 mm per year, indicating non uniform dynamic hydrological cycles. Interestingly, there is no noticeable PWV trend for the sites located in the Antarctic Plateau. During the four best observing months, PWV observed at Hanle, Merak and Ali sites have values lower than the Mauna Loa observatory by 0.14 mm and 0.56 mm at 1st and 2nd quartiles, respectively.
Source: https://doi.org/10.1016/j.jastp.2020.105404
Simulation of flood associated with extreme rainfall events over the urban city, Bengaluru, India
Smrati Purwar, G. N. Mohapatra, and V. Rakesh
Urban flooding affects millions of people in Indian major cities during past decades and is expected to be severe in near future under the warming climate scenario. Rapid urbanization and demography changes in the Bengaluru city in the past has led to significant hydrological and environmental stress contributing to the severity of urban flooding. The whole Bengaluru city (Urban as well as Rural) consists of four watershed valley and here, we have chosen Koramangala-Challaghatta (KC) valley as our study area which is known for its low-lying topography and frequent flooding events. In this study, we selected four Extreme Rainfall Events (EREs), occurred on 07 September 2015, 1 June 2016, 15 August 2017, and 24 September 2018, for simulation using the Storm Water Management Model (SWMM). The digital elevation model (DEM) is examined to understand the topography of high and low-lying areas to assess the flood impacts of EREs in various regions. Based on the frequency distribution, the 99th percentile of daily rainfall intensity (39.5 mm/day) is considered as the threshold for defining EREs in the study region, and long-term rainfall data (1998–2024) revealed a clear increasing trend in frequency of EREs. Results indicate that rainfall exceeding 30 mm/day leads to flooding in more than half of the area in KC Valley, with flash floods occurring when rainfall surpasses 55 mm/day. The most flood-prone locations are those near historical natural lakes, where urban encroachment has diminished natural flood detention capacity. Evaluation using multiple statistical metrics demonstrates reliable performance of SWMM in flood simulation, particularly for high-intensity rainfall events. The bias in simulated stormwater discharge ranges from + 4 to −4 m3/s, indicating useful skill of the model. The reliable methodological framework to tackle hydrometeorological challenges presented in this study can be handy tools for designing integrated flood management strategies for urban cities.
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