Ravi S. Nanjundiah

Ravi S. Nanjundiah
Indian Institute of Science | IISC · Centre for Atmospheric and Oceanic Sciences (CAOS)

About

182
Publications
34,991
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
2,963
Citations
Additional affiliations
July 1995 - present
Indian Institute of Science
Position
  • Professor

Publications

Publications (182)
Preprint
Full-text available
Deep Learning (DL) based downscaling has become a popular tool in earth sciences recently. Increasingly, different DL approaches are being adopted to downscale coarser precipitation data and generate more accurate and reliable estimates at local (few km or even smaller) scales. Despite several studies adopting dynamical or statistical downscaling o...
Preprint
Deep Learning (DL) based downscaling has become a popular tool in earth sciences recently. Increasingly, different DL approaches are being adopted to downscale coarser precipitation data and generate more accurate and reliable estimates at local (~ few km or even smaller) scales. Despite several studies adopting dynamical or statistical downscaling...
Article
The evaluation and usefulness of lightning prediction for Indian subcontinent are demonstrated. Implementation of the lightning parameterizations based on storm parameters, in Weather Research and Forecasting (WRF), with different microphysics schemes are carried out. With the availability of observed lightning measurements over Maharashtra from th...
Preprint
The formation of Middle Tropospheric Cyclones (MTCs) that are responsible for a large portion of annual precipitation and extreme rainfall events over western India is studied using an unsupervised machine learning algorithm and cyclone tracking. Both approaches reveal four dominant weather patterns that lead to the genesis of these systems; specif...
Poster
Western India, home to millions of people, and northeast Arabian sea, the entrance of monsoon jet to the Indian subcontinent, is a region that witnesses some of the world's heaviest rain spells. This region has been exhibiting a significant increase in frequency of extreme rainfall events and an increase in annual rainfall over the past few decades...
Preprint
Full-text available
This survey focuses on the current problems in Earth systems science where machine learning algorithms can be applied. It provides an overview of previous work, ongoing work at the Ministry of Earth Sciences, Gov. of India, and future applications of ML algorithms to some significant earth science problems. We provide a comparison of previous work...
Preprint
Full-text available
Accurate short range weather forecasting has significant implications for various sectors. Machine learning based approaches, e.g., deep learning, have gained popularity in this domain where the existing numerical weather prediction (NWP) models still have modest skill after a few days. Here we use a ConvLSTM network to develop a deep learning mode...
Article
The ensemble predictions were more skillful than the deterministic forecasts , as they were able to predict rainfall anomalies.
Article
Entrainment and mixing processes occur during the entire life of a cloud. These processes change the droplet size distribution, which determines rain formation and radiative properties. Since it is a microphysical process, it cannot be resolved in large scale weather forecasting models. Small scale simulations such as Direct Numerical Simulations (...
Article
Mid-Tropospheric Cyclones (MTCs) are moist synoptic systems with distinct mid-tropospheric vorticity maxima and weak signatures in the lower troposphere. Composites and statistics of tropical MTCs are constructed and compared with monsoon lows and depressions (together, lower troposphere cyclones; LTCs). We begin with South Asia, where tracking rev...
Article
During August 2018 and 2019 the southern state of India, Kerala received unprecedented heavy rainfall which led to widespread flooding. We aim to characterize the convective nature of these events and the large-scale atmospheric forcing, while exploring their predictability by three state of the art global prediction systems, the National Centre fo...
Article
Full-text available
This study reports a very high-resolution (400 m grid-spacing) operational air quality forecasting system developed to alert residents of Delhi and the National Capital Region (NCR) about forthcoming acute air pollution episodes. Such a high-resolution system has been developed for the first time and is evaluated during October 2019-February 2020....
Article
Thunderstorms source of lightning discharge is a major hazard to humans. In India, the loss of human life due to thunderstorms is high because of frequent lightning during pre-monsoon season (March-May). Therefore, simulation of lightning flash counts based on various lightning parameterization schemes and Lightning Potential Index (LPI) in Weather...
Article
Full-text available
We document the observed changes in the intraseasonal variability of precipitation and outgoing longwave radiation (OLR) associated with the Madden-Julian Oscillation (MJO) from 1998 to 2015 when reliable and simultaneous satellite-derived daily precipitation and OLR are available. Tropical Rainfall Measuring Mission (TRMM) observations show a stat...
Chapter
The Indian summer monsoon (ISM) variability impacts freshwater availability, agriculture, and livelihood of more than a billion people across South Asia. ISM rainfall variability is characterized by multiple spatial and temporal scales. Physical mechanisms for the variability are still under active research. This chapter provides a brief overview o...
Preprint
Mid-Tropospheric Cyclones (MTCs) are moist synoptic systems with distinct mid tropospheric vorticity maxima and weak signatures in the lower troposphere. Composites and statistics of MTCs over the tropics are constructed and compared with monsoon lows and depressions (together, lower troposphere cyclones; LTCs). We begin with South Asia, where trac...
Article
Full-text available
This paper examines the accuracy of Weather Research and Forecasting model coupled with Chemistry (WRF‐Chem) generated 72 hr fine particulate matter (PM2.5) forecasts in Delhi during the crop residue burning season of October‐November 2017 with respect to assimilation of the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical dept...
Article
Full-text available
Clear-sky, direct shortwave aerosol radiative forcing (ARF) has been estimated over the Indian region, for the first time employing multi-year (2009–2013) gridded, assimilated aerosol products, as an important part of the South West Asian Aerosol Monsoon Interactions (SWAAMI) which is a joint Indo-UK research field campaign focused at understanding...
Preprint
Full-text available
Elevated levels of fine particulate matter (PM2.5) during winter-time have become one of the most important environmental concerns over the Indo-Gangetic Plain (IGP) region of India, and particularly for Delhi. Accurate reconstruction of PM2.5, its optical properties, and dominant chemical components over this region is essential to evaluate the pe...
Technical Report
Availbale online at https://www.tropmet.res.in/~lip/Publication/Technical-Reports/TR-6.pdf
Article
Air quality has become one of the most important environmental concerns for Delhi, India. In this perspective , we have developed a high-resolution air quality prediction system for Delhi based on chemical data assimilation in the chemical transport model-Weather Research and Forecasting with Chemistry (WRF-Chem). The data assimilation system was a...
Preprint
Full-text available
Abstract. Clear-sky, direct shortwave Aerosol Radiative Forcing (ARF) has been estimated over the Indian region, for the first time employing multi-year (2009–2013) gridded, assimilated aerosol products. The aerosol datasets have been constructed following statistical assimilation of concurrent data from a dense network of ground-based observatorie...
Article
Full-text available
Customarily, the strength of the impact of El Niño–Southern Oscillation (ENSO) on Indian summer monsoon is evaluated with respect to the seasonal mean rainfall. As the rainfall occurring over the Indian subcontinent experiences strong variations intraseasonally, the impact of ENSO on these intraseasonal fluctuations are often more important for the...
Article
Full-text available
Climate model projections for the 21st century predict an elongated dry season in the Amazon basin, potentially reducing the discharge into the equatorial Atlantic Ocean. In order to understand the climatic role of Amazon runoff into the ocean, sensitivity experiments were carried out using the Community Earth System Model (CESM). Without Amazon ru...
Article
The study of climatic variables that govern the Indian summer monsoon has been widely explored. In this work, we use a non-linear deep learning-based feature reduction scheme for the discovery of skilful predictors for monsoon rainfall with climatic variables from various regions of the globe. We use a stacked autoencoder network along with two adv...
Article
A Winter Fog EXperiment (WiFEX) was conducted to study the genesis of the fog formation between winters 2016-2017 and 2017-2018 at Indira Gandhi International Airport (IGIA), Delhi, India. To support the WiFEX field campaign, the weather research and forecasting model (WRF) was used to produce real-time forecasts at 2 km horizontal grid spacing. Th...
Article
A multidecadal or ultra low‐frequency mode of variability in the Indian summer monsoon rainfall (ISMR) with a spectral peak at nearly 67‐years is identified using a non‐parametric approach, namely, singular spectrum analysis. This mode not only modulates the seasonal mean rainfall over India, but also frequent occurrences of excess or below normal...
Conference Paper
Full-text available
Water availability and food security in most of Asia’s major river basins are imperiled by climate change. Global warming is unequivocal and is mostly the primary cause for the recent increase in magnitude and frequency of extreme events. Recent consecutive floods in the Mahanadi River Basin (MRB) motivated us to analyze the impact of climate chang...
Article
Full-text available
Improving the accuracy of regional aerosol climate impact assessment calls for improvement in the accuracy of regional aerosol radiative effect (ARE) estimation. One of the most important means of achieving this is to use spatially homogeneous and temporally continuous datasets of critical aerosol properties, such as spectral aerosol optical depth...
Article
Full-text available
In spite of the summer monsoon’s importance in determining the life and economy of an agriculture-dependent country like India, committed efforts toward improving its prediction and simulation have been limited. Hence, a focused mission mode program Monsoon Mission (MM) was founded in 2012 to spur progress in this direction. This article explains t...
Article
Full-text available
Equatorial Indian Ocean Oscillation (EQUINOO) and El‐Niño Southern Oscillation (ENSO) are important climatic oscillation over the Pacific Ocean and Indian Ocean influencing the inter‐annual variation of the Indian monsoon. The study of these indices, including their relationship and influence over various climatic phenomena are mainly focused in li...
Article
Full-text available
With a view to improving the performance of WRF-Chem over the Indian region in simulating BC (black carbon) mass concentrations as well as its short-term variations, especially on a diurnal scale, a region-specific diurnal variation scheme has been introduced in the model emissions and the performance of the modified simulations has been evaluated...
Article
Full-text available
The strength of the simultaneous linear relationship between El Nino Southern Oscillation (ENSO) and Indian summer monsoon (ISM) precipitation show strong variations on a decadal timescale. While some studies attribute this to shift in the state of the climate and consequent teleconnection pattern, some other argue this as natural variability betwe...
Chapter
Monsoon spells are important climatic phenomenon modulating the quality and quantity of monsoon over a year. India being an agricultural country, identification of monsoon spells is extremely important to plan agricultural policies following the phases of monsoon to attain maximum productivity. Monsoon spells’ detection involve analyzing and predic...
Article
Full-text available
With a view to improving the performance of WRF-Chem over the Indian region in simulating BC (black Carbon) mass concentrations as well as its short-term variations, especially on diurnal scale, a region-specific diurnal variation scheme has been introduced in the model emissios and the performance of the modified simulations has been evaluated aga...
Article
Full-text available
Improving the accuracy of regional aerosol climate impact assessment calls for an improvement in the accuracy of regional aerosol radiative effects (ARE) estimation. One of the most important means of achieving this is to use spatially homogeneous and temporally continuous datasets of critical aerosol properties, such as spectral aerosol optical de...
Article
Full-text available
Improving the accuracy of regional aerosol cli- mate impact assessment calls for improvement in the accu- racy of regional aerosol radiative effect (ARE) estimation. One of the most important means of achieving this is to use spatially homogeneous and temporally continuous datasets of critical aerosol properties, such as spectral aerosol opti- cal...
Article
Synergizing satellite remote sensing data with vertical profiles of atmospheric thermodynamics and regional climate model simulations, we investigate the relative importance, transport pathways, and seasonality of contribution of dust from regional (Thar Desert and adjoining arid regions) and remote (southwest Asia and northeast Africa) sources ove...
Chapter
Relationship between convective available potential energy (CAPE) and precipitation is explored in a season-long cloud-resolving model (CRM) simulation of Indian summer monsoon. The location of maximum precipitation and CAPE does not always coincide in a CRM simulation. The diurnal land surface heating is shown to have an effect on CAPE and precipi...
Book
This book focuses on the development of physical parameterization over the last 2 to 3 decades and provides a roadmap for its future development. It covers important physical processes: convection, clouds, radiation, land-surface, and the orographic effect. The improvement of numerical models for predicting weather and climate at a variety of place...
Article
South India has seen significant changes in climate. Previous studies have shown that the southern part of India is more susceptible to effects of climate change than the rest of the country. We performed a rigorous climate model-based detection and attribution analysis to determine the root cause of the recent changes in climate over South India u...
Presentation
Many observations and studies have shown that the water availability in most the major river basins of Asia are perilled by climate change. Hence, an insight into the hydroclimatological change and variability at a river basin scale is crucial and is important for efficient water resource management and planning strategies. An increase in global av...
Conference Paper
Many observations and studies have shown that the water availability in most the major river basins of Asia are perilled by climate change. Hence, an insight into the hydroclimatological change and variability at a river basin scale is crucial and is important for efficient water resource management and planning strategies. An increase in global av...
Article
Equatorward propagating precipitation episodes over the Bay of Bengal have been documented in many previous observational studies. Proposed propagation mechanisms include mean surface to midtropospheric wind shear driving the convection orthogonal to the lower tropospheric winds and the gravity currents generated by outflow from convection initiate...
Article
Full-text available
The aim of this paper is to identify relative roles of different land-atmospheric conditions, apart from sea surface temperature (SST), in determining early vs. late summer monsoon intensity over India in a high resolution general circulation model (GCM). We find that in its early phase (June–July; JJ), pre-monsoon land-atmospheric processes play m...
Article
Full-text available
Amazon discharges a large volume of freshwater into the ocean, yet its impact on climate is largely unknown. Climate projections show that a warmer northern tropical Atlantic Ocean together with a warmer equatorial Pacific lead to extreme droughts in the Amazonia, considerably reducing the Amazon runoff. Here we present results from coupled model s...
Article
Full-text available
The frequent occurrence of flood and drought worldwide has drawn attention to assessing whether the hydroclimatology of major river basins has changed. The Mahanadi river basin (MRB) is the major source of fresh water for both Chattisgarh and Odisha states (71 million people approximately) in India. The MRB (141 600 km² area) is one of the most vul...
Article
In boreal summer (June–September), most of the Indian land and its surroundings experience rainrates exceeding 6 mm day\(^{-1}\) with considerable spatial variability. Over southern Bay of Bengal (BoB) along the east coast of the Indian peninsula (henceforth referred to as the Bay of Bengal cold pool or BoB-CP), the rain intensity is significantly...
Article
Full-text available
Deep and shallow convection calculations occupy significant times in atmosphere models. These calculations also present significant load imbalances due to varying cloud covers over different regions of the grid. In this work, we accelerate these calculations on Intel{\textregistered} Xeon Phi{\texttrademark} Coprocessor Systems. By employing dynami...
Article
Frequent occurrence of flood and drought worldwide has drawn attention to assess whether the hydroclimatology of major river basins has changed. Mahanadi river basin (MRB) is the major source of fresh water for both Chattisgarh and Odisha states (71 million population approximately) of India. The MRB (141,600 km2 area) is one of the most vulnerable...
Conference Paper
Climate change and climate variability are sensitive to hydroclimatological processes, and is essential to understand and interpret properly. In the present study, spatio-temporal seasonal changes in precipitation, maximum and minimum temperatures (Tmax and Tmin) over Sri Lanka and Tamil Nadu during period 1950-2012 are investigated employing modif...
Article
Full-text available
On account of its strong absorption of solar and terrestrial radiation, black carbon (BC) aerosol is known to impact large-scale systems, such as the Asian monsoon and the Himalayan glaciers, in addition to affecting the thermal structure of the lower atmosphere. While most studies focus on the near-surface abundance and impacts of BC, our study ex...
Article
Full-text available
The Indian summer monsoon (ISM) shows quasi-rhythmic intraseasonal oscillations (ISO) manifested as alternate ‘active’ phases of copious rainfall and quiescent phases of ‘break’. Within these periodic phases, the daily rainfall shows large variability and exhibits spatiotemporally sporadic extreme rainfall events. The recent decades have witness...
Article
Full-text available
Indian monsoon varies in its nature over the geographical regions. Predicting the rainfall not just at the national level, but at the regional level is an important task. In this article, we used a deep neural network, namely, the stacked autoencoder to automatically identify climatic factors that are capable of predicting the rainfall over the hom...
Article
Full-text available
Climate change impact assessment has become one of the most important subjects of the research community because of the recent increase in frequency of extreme events and changes in the spatio-temporal patterns of climate. This paper analyses the ability of 46 coupled climate models from CMIP5 and CMIP3 (Coupled Model Inter-comparison Project phase...
Article
Full-text available
On account of its strong absorption of solar and terrestrial radiations, Black Carbon (BC) aerosol is known to impact large scale systems such as the Asian monsoon, Himalayan glaciers etc, besides affecting the thermal structure of lower atmosphere. While most studies focus on the near-surface abundance and impacts of BC, our study, using online re...
Poster
High Resolution Simulation of Indian Monsoon Precipitation and Implications on Cumulus Parameterizations
Poster
Full-text available
One of the most widely-studied topics regarding the Indian summer monsoon is its intraseasonal variability (ISV), often marked by active and break spells of rainfall. In a recent study, using observational data, we have shown that the relative strength of the northward propagating low-frequency ISV mode has a significant decreasing trend during the...