Satyaban B RatnaIndia Meteorological Department | IMD · Climate Research and Services
Satyaban B Ratna
M.Sc., M.Tech., Ph.D. (PostDoc in UK Japan Italy)
About
37
Publications
25,785
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693
Citations
Citations since 2017
Introduction
My work aims to advance our knowledge of large-scale ocean-atmosphere interactions and their influence on climate. In particular, I am interested in the problems of the role of the ocean on climate variability ranging from interannual to multidecadal time scales and diagnosing physical mechanisms. Recently, in my current capacity at IMD, I started involving myself more with operational climate predictions and services.
Additional affiliations
April 2017 - March 2020
November 2014 - February 2017
May 2013 - September 2014
Education
August 2005 - October 2009
Publications
Publications (37)
This study attempts to understand the asymmetry in the Indian Summer Monsoon Rainfall (ISMR) response to two types of La Niña whether they evolved from El Niño or La Niña in the previous boreal winter season. It was seen that nine La Niña years during the monsoon season were preceded by El Niño (hereafter ELLA) whereas eight were preceded by La Niñ...
The El Niño-Southern Oscillation (ENSO) is one of the major drivers of prominent ocean-atmosphere coupled phenomenon over the equatorial Pacific Ocean that strongly modulates the interannual variability of Indian summer monsoon rainfall (ISMR). However, the relationship between ENSO-ISMR has gone through secular variation during different decades....
This poster highlights how the relationship between El Niño Southern Oscillation (ENSO) and Indian Summer Monsoon Rainfall (ISMR) is changing in the recent decades. The various responses from the atmosphere which are responsible for this changing ENSO-ISMR relationship are also shown.
The ambition to develop sustainable and healthy cities requires city-specific policy and practice founded on a multidisciplinary evidence base, including projections of human-induced climate change. A cascade of climate models of increasing complexity and resolution is reviewed, which provides the basis for constructing climate projections-from glo...
The Indian Ocean Dipole (IOD) is one of the dominant modes of variability of the tropical Indian Ocean and it has been suggested to have a crucial role in the teleconnection between the Indian summer monsoon and El Niño Southern Oscillation (ENSO). The main ideas at the base of the influence of the IOD on the ENSO-monsoon teleconnection include the...
The positive Indian Ocean Dipole (IOD) event in 2019 was among the strongest on record, while the Indian Summer monsoon (ISM) was anomalously dry in June then very wet by September. We investigated the relationships between the IOD, Pacific sea surface temperature (SST) and ISM rainfall during 2019 with an atmospheric general circulation model forc...
We simulate the response of Asian summer climate to Atlantic multidecadal oscillation (AMO)-like sea surface temperature (SST) anomalies using an intermediate-complexity general circulation model (IGCM4). Experiments are performed with seven individual AMO SST anomalies obtained from CMIP5/PMIP3 global climate models as well as their multimodel mea...
This study investigates mechanisms and nonlinearities in the response of the Asian Summer Monsoons (ASM) to high-latitude thermal forcings of different amplitudes. Using a suite of runs carried out with an intermediate-complexity atmospheric general circulation model, we find that the imposed forcings produce a strong precipitation response over th...
We examine the relationships in models and
reconstructions between the multidecadal variability of surface temperature
in East Asia and two extratropical modes of variability: the Atlantic
Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO). We
analyse the spatial, temporal and spectral characteristics of the climate
modes in t...
Oceanic reanalyses are powerful products to reconstruct the historical 3D-state of the ocean and related circulation. At present a challenge is to have oceanic reanalyses covering the whole 20th century. This study describes the exercise of comparing available datasets to force Mediterranean Sea and global oceanic reanalyses from 1901 to present. I...
We examine the relationships in models and reconstructions between the multidecadal variability of surface temperature in East Asia and two extratropical modes of variability: the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal oscillation (PDO). We analyze the spatial, temporal and spectral characteristics of the climate modes in L...
The warming of the Indian Ocean (IO) of the last decades has evinced interest among the research community due to its important role in driving the global climate variability. The enhanced warming of the tropical IO due to climate change has caused a significant shift in the heat budget of the climate system. Here we investigate the differences in...
A set of 17 experiments, using various combinations of physical parameterization schemes in the Weather Research and Forecasting (WRF) model, were carried out to choose a combination suitable for simulating the Indian summer monsoon. The model experiments, forced with the ERA-Interim reanalysis data, were at 30 km horizontal resolution. The WRF mod...
The recent Indian Ocean (IO) warming and its relation with the El Niño Southern Oscillation (ENSO) is investigated using available ocean and atmospheric reanalyses. By comparing the events before and after 1976 (identified as a threshold separating earlier and recent decades with respect to global warming trends), our results indicate that the IO h...
An attempt is made in this study to verify the performance of the regional climate model Weather Research and Forecasting (WRF) in downscaling extreme seasonal climate over Southeast Asia. First, the model performance is tested by using the European Centre for medium-range weather forecasting (ECMWF) reanalysis (ERA) interim reanalysis data as the...
This study investigates the capability of a regional climate model in simulating the climate variability over Southeast Asia (SE Asia). The present-day climate, covering the period 1991 to 2015, was dynamically downscaled using the Weather Research and Forecasting (WRF) model with a horizontal resolution of 27 km. The initial and boundary condition...
Southern Europe (Italy and the surrounding countries) experienced an unusual wet summer in 2014. The monthly rainfall in July 2014 was 84% above (more than three standard deviation) normal with respect to the 1982–2013 July climatology. The heavy rainfall damaged agriculture, and affected tourism and overall economy of the region. In this study, we...
During boreal winters, cold waves over India are primarily due to transport of cold air from higher
latitudes. However, the processes associated with these cold waves are not yet clearly understood.
Here by diagnosing a suite of datasets, we explore the mechanisms leading to the development and
maintenance of these cold waves. Two types of cold wav...
India suffers from major heatwaves during March-June. The rising trend of number of intense heatwaves in recent decades has been vaguely attributed to global warming. Since the heat waves have a serious effect on human mortality, root causes of these heatwaves need to be clarified. Based on the observed patterns and statistical analyses of the maxi...
In an attempt to improve the forecast skill of the austral summer precipitation over South Africa, an ensemble of 1-month-lead seasonal hindcasts generated by the Scale Interaction Experiment-Frontier Research Center for Global Change (SINTEX-F2v) coupled global circulation model is downscaled using the Weather Research and Forecasting (WRF) Model....
Southern Africa receives most of its rainfall during the austral summer season. Due to its predominantly agro-based economy, reliable prediction of seasonal rainfall is regarded as a high priority. As a result, a number of studies have previously been carried out in the region to verify the skill of regional-scale atmospheric models, in generating...
The Indo-Pacific Ocean (i.e. region between 30E and 150E) has been experiencing a warming since the 1950s. At the same time, the large-scale summer monsoon rainfall over India and the moisture over the East Africa/Arabian Sea are both decreasing. In this study, we intend to investigate how the decrease of moisture over the East Africa/Arabian Sea i...
The Indo-Pacific Ocean (i.e. region between 30°E and 150°E) has been experiencing a warming since the 1950s. At the same time, the large-scale summer monsoon rainfall over India and the moisture over the East Africa/Arabian Sea are both decreasing. In this study, we intend to investigate how the decrease of moisture over the East Africa/Arabian Sea...
The prediction skill of dynamical downscaling is evaluated for climate forecasts over southern Africa using the Advanced Research Weather Research and Forecasting (WRF) model. As a case study, forecasts for the December-February (DJF) season of 2011/12 are evaluated. Initial and boundary conditions for the WRF model were taken from the seasonal for...
Austral summer rainfall over the period 1991/1992 to 2010/2011 was
dynamically downscaled by the weather research and forecasting (WRF)
model at 9 km resolution for South Africa. Lateral boundary conditions
for WRF were provided from the European Centre for medium-range weather
(ECMWF) reanalysis (ERA) interim data. The model biases for the rainfal...
Strong cases of the tropical temperate troughs (TTT) that are responsible for the most of the summer rainfall over subtropical southern Africa are analyzed. An index for identifying the TTT is introduced for the first time using anomalies of outgoing longwave radiation (OLR) and the wind. The TTT is associated with a ridge-trough-ridge wave-like st...
The performance of cumulus parameterization schemes in the short range prediction of rainfall
during onset phase of the Indian Southwest Monsoon (ISM) was evaluated using Fifth-Generation
Pennsylvania State University / National Center for Atmospheric Research Mesoscale Model
(MM5). MM5 model was used to predict rainfall at 30 km resolution up to 7...
This paper presents the results of an analysis of the daily rainfall of 329 rain gauge stations data over Maharashtra, a state in India, during the summer monsoon season, June to September, for the 11 year period from 1998 to 2008. Mesoscale analysis of the daily rainfall data is performed by converting the station rainfall data into gridded format...
Land-surface processes are one of the important drivers for weather and climate systems over the tropics. Realistic representation of land surface processes in mesoscale models over the region will help accurate simulation of numerical forecasts. The present study examines the influence of Land Use/ Land Cover Change (LULC) on the forecasting of cy...
This paper discusses the simulations of Indian summer monsoon (ISM) using a high-resolution National Center for Environmental Prediction (NCEP) T170/L42 model for a 20-year period (1985–2004) with observed Sea Surface Temperature (SSTs) as boundary conditions and using five initial conditions in the first week of May. Good agreement is found betwee...
The paper is devoted to examine the ability of a high-resolution National Center for Environmental Prediction (NCEP) T170/L42 Atmospheric General Circulation Model (AGCM), for exploring its utility for long-range dynamical prediction of seasonal Indian summer monsoon rainfall (ISMR) based on 5-members ensemble for the hindcast mode 20-year (1985-20...
Numerical prediction experiments using a high resolution mesoscale model NCAR MM5 were performed to simulate an unusual extreme precipitation event that occurred over west coast region of India on 26 July 2005. During this event, unprecedented precipitation of 90–100 cm was recorded over northeast parts of Mumbai City, India causing enormous losses...
A nonhydrostatic atmospheric model with a resolution of 30 km is used to make predictions of the rainfall during the onset phase of the southwest monsoon (SWM) of 2003. Model predictions of the pentad rainfall time series indicate good predictions up to lead time of 5 days. The correlation coefficients (CCs) between the model-predicted and observed...
Questions
Question (1)
The pre-industrial and last millennium (past 1000) simulations in the CMIP5 extends over a period of about 1000 years. What is the best way to generate anomalies for the time series of surface temperature and SST produced by CMIP5 models. I mean, how the base period for anomalies are considered. Also, what are the best practices used to remove the trend from such long term time series data.
Projects
Project (1)
In order to predict the evolution of inter-regional linkages this century, it is crucial to understand how they have evolved in the past. This is particularly important because extremes such as drought are modulated by decadal variability. Our study is motivated by recent identification of multidecadal links between 2000-year reconstructions of Tibetan Plateau precipitation and Northern Hemisphere temperature. We will go far beyond this initial finding by combining insights gained from coupled climate models and observations (instrumental, tree-ring and documentary records) to identify large-scale modes that link the variability of tropical monsoons and northern extratropical climates on multiple timescales. We will (i) better understand the teleconnections between monsoon and extratropical regions (with particular emphasis on the Arctic), (ii) evaluate the ability of climate models to reproduce observed behaviour including regional extremes, (iii) explore mechanisms that drive the observed behaviour and understand how the linkages may evolve under future climate change using simulations with a hierarchy of models. Paleoclimate records, including temperature- sensitive tree-ring records from the Eurasian Arctic and precipitation-sensitive series from the Asian monsoon regions provide a unique opportunity to identify associations on annual to multidecadal timescales. CMIP5 and CMIP6 "control" and "last millennium" runs will be used to assess simulated unforced variability and response to forcings such as volcanoes and to consider SST and atmospheric circulation patterns associated with periods of extremes in the monsoon, extratropical and Arctic regions. New simulations with imposed anomalies (e.g. sea or land surface temperatures in particular regions) in conjunction with external forcing will be designed to explore the roles of basin-wide changes or land-surface interactions in generating and synchronising decadal variability. Implications for future climate change will be considered using model simulations and our improved understanding of mechanisms.
