Ashwin Seshadri

Indian Institute of Science Bangalore | IISC · Centre for Atmospheric and Oceanic Sciences (CAOS)

Understanding the climate response to interhemispheric differences in imposed radiative forcing is crucial for solar radiative modification (SRM) investigations. While previous studies have shown that climate sensitivity to solar insolation changes imposed in the Northern (NH) versus the Southern Hemisphere (SH) is different, the underlying mechani...

In assessing responsibility for climate change, conventional metrics like cumulative and per-capita emissions do not capture the consequences of evolution of affluent lifestyles. Our study introduces a novel framework to assess the global mean surface warming that would have resulted if the historical lifestyles of individual countries had been the...

Exploring cost-effective wind-solar-storage combinations to replace conventional fossil-fuelled power generation without compromising grid reliability becomes increasingly important in a steadily decarbonizing electricity system. For a renewable energy-rich state in Southern India (Karnataka), we systematically assess various wind-solar-storage ene...

Understanding controls on convection on various timescales is crucial for improved monsoon rainfall forecasting. Although the literature points to vertically homogeneous vorticity signatures preceding rainfall during the Indian summer monsoon, we show using reanalysis data that, for rainfall associated with northward propagating intraseasonal oscil...

Low-order models obtained through Galerkin projection of several physically important systems (e.g., Rayleigh-B\'enard convection, mid-latitude quasi-geostrophic dynamics, and vorticity dynamics) appear in the form of coupled gyrostats. Forced dissipative chaos is an important phenomenon in these models, and this paper considers the minimal chaotic...

In the geosciences, a recurring problem is one of estimating spatial means of a physical field using weighted averages of point observations. An important variant is when individual observations are counted with some probability less than one. This can occur in different contexts: from missing data to estimating the statistics across subsamples. In...

Previous studies have shown that climate sensitivity, defined as the global mean surface temperature change per unit radiative forcing, is smaller for solar radiative forcing compared to an equivalent CO 2 radiative forcing. We investigate the causes for this difference using the NCAR CAM4 model. The contributions to the climate feedback parameter,...

Smoothing of generation variability, i.e., reduction of variance in the aggregate generation is crucial for grid integration of large-scale wind power plants. Prior studies of smoothing have focused on geographical smoothing, based on distance. In contrast, we propose a novel concept “diurnal smoothing” that depends on spatial variations in the tim...

The low-level Somali jet is the primary mechanism of moisture transport for the South Asian monsoon. It precedes monsoon onset over India and shares its key characteristic features such as rapid intensification and slower retreat during seasonal evolution. This study analyzes the kinetic energy (KE) budget of Somali jet region using high-spatiotemp...

South Asian monsoon rainfall varies rapidly in the paleoclimate record, and this has been interpreted using simple models as arising from tipping points. This study explores a class of simple monsoon models, based on convective quasi-equilibrium, and the bifurcations permitted by their mathematical forms. Specifically, low-order models are derived...

In response to north‐south pressure gradients set by the annual march of the Sun, a cross‐equatorial flow that turns to become a low‐level Somali Jet at around 10°N is established in the lower troposphere over the Indian Ocean. This flow plays a fundamental role in the Indian monsoon. A mechanistic understanding of drivers of this flow is lacking....

Wind power growth makes it essential to simulate weather variability and its impacts on the electricity grid. Low-probability, high-impact weather events such as a wind drought are important but difficult to identify based on limited historical datasets. A stochastic weather generator, Imperial College Weather Generator (IMAGE), is employed to iden...

Increasing the share of weather-dependent renewables in the electricity grid is essential to deeply decarbonize the electricity system. Wind and solar “droughts” or low generation days can severely impact grid stability in a renewable-rich grid. This paper analyzes for the first time wind, solar, and hybrid energy-droughts in India using a stochast...

The model of the Volterra gyrostat (VG) has not only played an important role in rigid body dynamics but also served as the foundation of low-order models of many naturally occurring systems, including atmospheric dynamics. It is well known that VG possesses two invariants, or constants of motion, corresponding to kinetic energy and squared angular...

Cumulative emissions accounting for carbon-dioxide (CO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {CO}_{2}$$\end{document}) is founded on recognition that gl...

Sulfur dioxide is a radiatively and chemically important trace gas in the atmosphere of Venus and its abundance at the cloud tops has been observed to vary on interannual to decadal timescales. This variability is thought to come from changes in the strength of convection which transports sulfur dioxide to the cloud tops, although the dynamics behi...

Sulfur dioxide is a radiatively and chemically important trace gas in the atmosphere of Venus and its abundance at the cloud-tops has been observed to vary on interannual to decadal timescales. This variability is thought to come from changes in the strength of convection which transports sulfur dioxide to the cloud-tops, {although} the dynamics be...

Cumulative emissions accounting for carbon-dioxide (CO2) is founded on recognition that global warming in Earth System Models (ESMs) is roughly proportional to cumulative CO2 emissions, regardless of emissions pathway. However, cumulative emissions accounting only requires the graph between global warming and cumulative emissions to be approximatel...

Rain gauges are considered the most accurate method to estimate rainfall and are used as the “ground truth” for a wide variety of applications. The spatial density of rain gauges varies substantially and hence influences the accuracy of gridded gauge-based rainfall products. The temporal changes in rain gauge density over a region introduce conside...

Large-scale extraction of carbon dioxide (CO2) from Earth's atmosphere ("negative emissions") is important for stringent climate change mitigation scenarios, and we examine optimal (i.e. least-cost) pathways of negative emissions in the presence of learning by doing ("endogenous learning"). Optimal pathways solve a variational problem involving min...

We estimate statistics of spatial averages defined by linearly weighting available observations over a spatial domain, and derive an account of bias and variance in the presence of missing observations. With missing observations, the spatial average is a ratio of random variables, and estimators are derived by truncating Taylor series of functions...

Highlights: Air pollution and associated health impacts are rapidly rising in India, in contrast to declining trends in other major economies of the World. India can substantially reduce air-pollution from its power sector by reducing coal use (decarbonisation scenario) and by implementing strict air pollution control norms (pollution control scena...

Spatial averages occur frequently in the geosciences. We consider statistics of such averages obtained by weighting available observations recorded over an arbitrary spatial domain. Assuming that observations are made using identical and independent measuring devices and observational noise is additive, a distribution-independent account of bias, v...

Global warming from carbon dioxide (CO2) is known to depend on cumulative CO2 emissions. We introduce a model of global expenditures on limiting cumulative CO2 emissions, taking into account effects of decarbonization and rising global income and making an approximation to the marginal abatement costs (MAC) of CO2. Discounted mitigation expenditure...

The dynamics of a linear two-box energy balance climate model is analyzed as a fast–slow system, where the atmosphere, land, and near-surface ocean taken together respond within few years to external forcing whereas the deep-ocean responds much more slowly. Solutions to this system are approximated by estimating the system’s time-constants using a...

Precipitation is a large-scale, spatio-temporally heterogeneous phenomenon, with frequent anomalies exhibiting unusually high or low values. We use Markov Random Fields (MRFs) to detect spatio-temporally coherent anomalies in gridded annual rainfall data across India from 1901-2005. MRFs are undirected graphical models where each node is associated...

Precipitation is a large-scale, spatio-temporally heterogeneous phenomenon, with frequent anomalies exhibiting unusually high or low values. We use Markov Random Fields (MRFs) to detect spatio-temporally coherent anomalies in gridded annual rainfall data across India from 1901-2005. MRFs are undirected graphical models where each node is associated...

Observations and GCMs exhibit approximate proportionality between cumulative carbon dioxide (CO\(_{2}\)) emissions and global warming. Here we identify sufficient conditions for the relationship between cumulative CO\(_{2}\) emissions and global warming to be independent of the path of CO\(_{2}\) emissions; referred to as “path independence”. Our s...

Monsoons involve increases in dry static energy (DSE), with primary contributions from increased shortwave radiation and condensation of water vapor, compensated by DSE export via horizontal fluxes in monsoonal circulations. We introduce a simple box-model characterizing evolution of the DSE budget to study nonlinear dynamics of steady-state monsoo...

Economics has a well-defined notion of equilibrium. Unlike mechanics or thermodynamics, economics does not include explicit theories of dynamics describing how equilibria are reached or whether they are stable. However, even simple economics problems such as maximization of a welfare function might sometimes be interpreted as dynamics problems. Her...

Forecasts of monsoon rainfall for India are made at national scale. But there is spatial coherence and heterogeneity that is relevant to forecasting. This paper considers year-to-year rainfall change and annual extremes at sub-national scales. We use Data Mining techniques to gridded rain-gauge data for 1901-2011 to characterize coherence and heter...

Carbon-dioxide (CO2) is the main contributor to anthropogenic global warming, and the timing of its peak concentration in the atmosphere is likely to be the major factor in the timing of maximum radiative forcing. Other forcers such as aerosols and non-CO2 greenhouse gases may also influence the timing of maximum radiative forcing. This paper appro...

Tradeoffs are examined between mitigating black carbon (BC) and carbon dioxide (CO2) for limiting peak global mean warming, using the following set of methods. A two-box climate model is used to simulate temperatures of the atmosphere and ocean for different rates of mitigation. Mitigation rates for BC and CO2 are characterized by respective timesc...

Prediction markets are increasingly being used to estimate probabilities of future events, and market equilibrium prices depend on the distribution of subjective probabilities of underlying events. When each contract requires the payment of a dollar if the underlying event were to occur, equilibrium prices are usually used to estimate the mean prob...

This article contributes a case study of regulation of the design of India’s Prototype Fast Breeder Reactor (PFBR). This reactor is the first of its kind in India, and perceived by the nuclear establishment as critical to its future ambitions. Because fast breeder reactors can experience explosive accidents called core disruptive accidents whose ma...

Carbon-dioxide (CO2) is the main contributor to anthropogenic global warming, and the timing of its peak concentration in the atmosphere is likely to govern the timing of maximum radiative forcing. While dynamics of atmospheric CO2 is governed by multiple time-constants, we idealize this by a single time-constant to consider some of the factors des...

In systems with rotational symmetry, bending modes occur in doubly-degenerate pairs with two independent vibration modes for each repeated natural frequency. In circular plates, the standing waves of two such degenerate bending modes can be superposed with a 1/4 period separation in time to yield a traveling wave response. This is the principle of...

The state of Karnataka in India faces a shortfall in its electricity-generating capacity, which is higher during peak demand periods. To remedy this, the government has planned a large expansion of baseload capacity, mainly in the form of large coal based thermal power plants. In the study described here, we calculate the per-kilowatt hour costs of...

This article explores the safety capabilities of the 500 MWe Prototype Fast Breeder Reactor that is under construction in India, and which is to be the first of several similar reactors that are proposed to be built over the next few decades, to withstand severe accidents. Such accidents could potentially breach the reactor containment and disperse...

This work presents a numerical model for normal engagement of two rough surfaces in contact. In this study, the Johnson translator system with a linear filter is used to transform a Gaussian white-noise input to an output surface with prescribed moments and autocorrelation function. The rough surface contact model employs influence coefficients obt...