सीएसआईआर-राष्ट्रीय डेटा विज्ञान एवं कृत्रिम बुद्धिमत्ता संस्थान

by Arya V. B., Sajani Surendran and Kavirajan Rajendran

Abstract
Association of higher (lower) rainfall with lower (higher) Aerosol Optical Depth (AOD) is consistent with the understanding that increased washout (build-up) and shorter (longer) life-time of aerosols occur in wetter (drier) conditions. Given the life-time of aerosols, it is imperative to examine how aerosols impact active/break (wetter/drier than normal) spells, the prominent intraseasonal variability (ISV) of Indian summer monsoon (ISM), through their composite analysis using recent satellite observations of aerosols and cloud properties, circulation and rainfall. Dust aerosols can act as CCN and participate efficiently in cloud processes during active phase. During breaks, build-up of desert dust transported by prevalent circulation, is associated with lower cloud effective radius implying aerosols’ indirect effect where they can inhibit cloud growth in the presence of reduced moisture and decrease precipitation efficiency/rainfall. Correspondingly, correlation albeit small, between intraseasonal anomalies of AOD and rainfall is negative, when AOD leads rainfall by 3–5 days implying that indirect aerosols impact is effective during breaks, though it is not the dominant responsible factor. During breaks, lower shortwave flux at top of atmosphere hints at dust-induced semi-direct effect. As breaks are permanent features of ISM, incorporation of dust-induced feedbacks in models, is essential for improved ISV simulation and ISM prediction.

Citation: Arya V. B., Sajani Surendran and Kavirajan Rajendran. On the build-up of dust aerosols and possible indirect effect during Indian summer monsoon break spells using recent satellite observations of aerosols and cloud properties. J. Earth Syst. Sci., 130, 42 (2021).

Source: https://doi.org/10.1007/s12040-020-01526-6

by Kantha Rao Bhimala, Krushna Chandra Gouda & S. Himesh 

The present study evaluates the skill of the Weather Research and Forecasting (WRF) model to simulate high-resolution rainfall, 2-m air temperature (T2m), and 2-m relative humidity (RH2m) over the metropolitan city of Bangalore, India. The novelty of the present study is that the WRF model simulations were carried out for ten different rain intensities during the monsoon season and compared with in situ observations from a high-density rain gauge network (81 rain gauge stations) and automatic weather stations (AWS) located over Bangalore. Our analysis shows that the model underestimated (bias score < 1) rainfall for most (87%) of the stations, and the model accuracy in the forecasting of rainfall was more than 70% for 16% of stations in the city. The RMSE values ranged between 18 and 28 mm/day for most of the rainfall events. Our analysis also found that the underestimation of the convective available potential energy (CAPE < 2000 J/kg) may be a possible reason for the simulation of low-intensity rainfall (< 10 mm/day) in most of the stations in Bangalore. In the case of T2m and RH2m simulations, the model closely matched the observed values [bias: T2m (−1 °C to 1 °C), Rh2m (0–10%)] for most of the AWS, while the model showed cold (−4.5 °C) and moist bias (19%) for the industrial area of Begur station. Proper representation of the urban morphology, air pollution, and anthropogenic heat data in the WRF modeling system may improve the model skill to capture the spatial variability in rainfall, T2m, and RH2m over highly urbanized cities in India.

Source: https://doi.org/10.1007/s00024-021-02676-4

by Jagat Dwipendra Ray, M. Sithartha Muthu Vijayan,  and Walyeldeen Godah

The area of North-East India and Nepal Himalaya undergoes seasonal deformations due to the variation of surface mass loads induced mainly by annual monsoon precipitation. The present study focuses on comparing seasonal horizontal deformations of the Earth’s surface obtained over the area of North-East India and Nepal Himalaya using Global Positioning System (GPS) and the corresponding ones obtained from Gravity Recovery and Climate Experiment (GRACE) satellite mission data. Seasonal deformations of the Earth’s surface in horizontal components were determined using daily observations from 36 GPS stations located in North-East India and Nepal Himalaya and Release-05 GRACE-based Global Geopotential Models (GGMs). The consistency between these seasonal horizontal deformations was investigated using three statistical metrics, namely: the correlation, Weighted Root Mean Square (WRMS) reduction and Nash–Sutcliffe model Efficiency (NSE). The results obtained indicate that at nearly 89% of GPS stations investigated, positive correlation can be determined between seasonal deformations of the Earth’s surface in the north component obtained from GPS and the corresponding ones from GRACE data. The percentage of WRMS reductions computed from seasonal horizontal deformations of the Earth’s surface obtained using GPS and GRACE data reach ~ 18% and 0.71% in north and east components, respectively. Moreover, we obtain the median value of NSE almost 0.28 for north and − 0.01 for east components. The study finds that seasonal horizontal deformations in the area investigated are controlled by local tectonics, and realizes the need of a realistic Earth model comprising local crustal inhomogeneities and tectonic features for better constraining the surface deformations in this region.

Source: https://link.springer.com/article/10.1007/s40328-020-00331-3

by V Anil Kumar and Debabrata Das

Multipath Transmission Control Protocol (MPTCP) is an innovative next-generation transport protocol standardized by the Internet Engineering Task Force (IETF) to overcome the single path limitation of the Transmission Control Protocol (TCP). MPTCP augments TCP with a new set of signaling options for seamless transmission and reception of application data across multiple interlinked TCP connections called subflows. In this paper, we focus on a new security concern associated with the signal exchanging process of MPTCP. To the best of our knowledge, for the first time, this paper exposes that MPTCP signal exchange scheme is vulnerable to a sophisticated packet spoofing technique, which we name as Data Sequence Signal (DSS) manipulation. We implement the vulnerability, create attack scenarios in Linux Kernel and conduct experiments over emulated testbed to demonstrate the existence of the vulnerability and means of exploiting it for powerful attacks. Our results show that DSS manipulation can be tactically exploited, on top of TCP optimistic ACKing, to generate non-responsive traffic like Denial-of-Service (DoS) attack flood. Particularly, we demonstrate two new adverse scenarios, where a MPTCP sender is forced to: (a) transmit at a rate significantly higher than the bottleneck link bandwidth, and (b) induce high intensity and harmful packet bursts at line-rate called Maliciously-induced-Bursts (MiBs). We also show that the non-responsive traffic resulting from the attack can suppress genuine congestion controlled traffic to the extent of causing DoS attack. We capture and analyze the dynamics of important MPTCP parameters, like send buffer occupancy of meta and subflow sockets, congestion window and flightsize to highlight the attack impact. DSS manipulation originates from a fundamental protocol design limitation rather than from any implementation flaw. We also propose a novel technique called data sequence map skipping for detection and countermeasure against DSS manipulation based attacks.

Source: https://doi.org/10.1016/j.cose.2021.102180