M. Rajeevan

• M.Sc, Ph.D
• MOES Distiniguished Scientist and Former Secretary Ministry of Earth Sciences at Ministry of Earth Sciences

Gridded precipitation products are inherently uncertain and predominantly deterministic, which limits their applicability in data assimilation systems and hydrologic modeling. This limitation is significant in developing countries such as India, where the observation network is sparse and non-uniform, topography is complex, and hydrometeorological...

In this review article, we discuss how monsoon monitoring and forecasting has evolved over the last 150 years. Since there are several other articles in this issue on short-range and operational forecasts of the IMD, we focus only on the details of monsoon monitoring, extended range forecasts (10-30 days) and seasonal forecasts (up to one season)....

The increase in the frequency of extreme precipitation in different parts of the world is well documented and a cause for concern in terms of global climate change. Although clouds are the only source of precipitation, there is a lack of knowledge about the type of clouds involved in extreme precipitation events. Satellite- and ground-based observa...

Air pollution poses a significant environmental risk to large cities worldwide, including New Delhi, India's capital. Occurrence of frequent episodes of elevated levels of air pollution during October to March in Delhi and National Capital Tertiary (Delhi-NCT) chokes its ∼32 million residents every year. Current air quality models lack the ability...

Accurate fog prediction in densely urbanized cities poses a challenge due to the complex influence of urban morphology on meteorological conditions in the urban roughness sublayer. This study implemented a coupled WRF‐Urban Asymmetric Convective Model (WRF‐UACM) for Delhi, India, integrating explicit urban physics with Sentinel‐updated USGS land‐us...

Drought, a prolonged natural event, profoundly impacts water resources and societies, particularly in agriculturally dependent nations like India. This study focuses on subseasonal droughts during the Indian summer monsoon season using standardized precipitation index (SPI). Analyzing hindcasts from the National Centre for Medium Range Weather Fore...

With the changing climate, the study of fog formation is essential due to the impact of the complexity of natural and anthropogenic aerosols. The evolution of the droplet size distribution in the presence of different aerosol species remains poorly understood. To make progress towards reducing the uncertainty of fog forecasts, the Eulerian–Lagrangi...

To investigate the mechanisms responsible for severe convection linked with a variety of mesoscale, synoptic systems over the Indian region, a preliminary analysis is conducted. Using IMD RSRW/Reanalysis (ERA5)/Lightning (TRMM LIS) products both local‐scale thermodynamics and large‐scale background conditions responsible for the major lightning hot...

Accurate fog prediction in densely urbanized cities poses a challenge due to the complex influence of urban morphology on meteorological conditions in the urban roughness sublayer. This study implemented a coupled WRF-Urban Asymmetric Convective Model (WRF-UACM) for Delhi, India, integrating explicit urban physics with Sentinel-updated USGS land-us...

Skills in NINO3.4 sea surface temperature (SST) prediction provide a benchmark for evaluation of the current generation of machine learning models. Several empirical data-driven models rely on capturing low-frequency variability of the SST anomalies over the east and west Pacific as a dominant predictor. The physical processes contributing to the S...

The demand for effective methods to augment precipitation over arid regions of India has been increasing over the past several decades as the changing climate brings warmer average temperatures. In the fourth phase of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX-IV), a scientific investigation was conducted over a...

This chapter provides summaries of the 2022 temperature and precipitation conditions across seven broad regions: North America, Central America and the Caribbean, South America, Africa, Europe and the Middle East, Asia, and Oceania. In most cases, summaries of notable weather events are also included. Local scientists provided the annual summary fo...

Tropical cyclones do not form easily near the equator but can intensify rapidly, leaving little time for preparation. We investigate the number of near-equatorial (originating between 5°N and 11°N) tropical cyclones over the north Indian Ocean during post-monsoon season (October to December) over the past 60 years. The study reveals a marked 43% de...

Northeast Monsoon of South Asia

The presence of persistent heavy fog in northern India during winter creates hazardous situations for transportation systems and disrupts the lives of about 400 million people. The meteorological factors responsible for its genesis and predictability are not yet completely understood in this region. Given its high potential for socio-economic impac...

Abstract Heat wave has become a great concern for India in the recent years due to its disastrous impact on various sectors including health. Thus, accurate forecasts of heat wave events well in advance are required for preparing adequate mitigation strategies. The present study assesses the prediction skill of numerical weather prediction models i...

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...

Dominant modes of SST in the west and east Pacific show strong but regionally different gradients caused by waves, internal dynamics, and anthropogenic warming, which drives air-sea interaction in the Pacific. The study discusses the relative contribution of SST gradients over the western and eastern Pacific to the prediction skill of SST in the ce...

The present study evaluates the skill of seasonal forecasts of temperatures over India during April to June using the Monsoon Mission Coupled Forecasting System (MMCFS) model hindcasts, which are initialized with February initial conditions. Model hindcast data of 1981–2017 period have been used for the analysis. The India Meteorological Department...

The campaign mode observational program 'Winter Fog Experiment' (WiFEX) was set up at the Indira Gandhi International Airport (IGIA), New Delhi, during the winter months of 2016–17 and 2017–18. Using the WiFEX data, in this study, we examine the microphysical structure of fog formed in a polluted environment and attempt to predict visibility (Vis)...

The previous studies on temperature trends are based on temperatures observed at a fixed hour (maximum and minimum temperatures). In this study, trends in sub-daily (hourly) temperatures are examined using quality temperature data from 66 Indian stations spread over the country. The season April–May–June and the data period of 1975–2012 have been c...

The present study highlights the role of high-resolution land data assimilation in improving the prediction of the radiation fog and near-surface meteorological variables. The performance of the Weather Research and Forecasting (WRF) model coupled with the High-Resolution Land Data Assimilation System (HRLDAS) is evaluated for a dense fog event tha...

The evaluation and usefulness of lightning prediction for the Indian subcontinent are demonstrated. Implementation of the lightning parameterizations based on storm parameters, in the Weather Research and Forecasting (WRF) Model, with different microphysics schemes are carried out. With the availability of observed lightning measurements over Mahar...

This study focuses on assessing different quantile mapping (QM) bias correction approaches based on empirical and parametric methods to bias-correct the Indian Monsoon Data Assimilation and Analysis (IMDAA) precipitation data subsequently calibrate the National Centre for Medium Range Weather Forecasting (NCMRWF) Unified Model operational forecasts...

Dense fog events and their micrometeorological characteristics and structural evolution at Indira Gandhi International Airport (IGIA), New Delhi, during the Winter Fog Experiment (WiFEX) are illustrated in this study. Four dense fog events that occurred in January 2016 for which visibility dropped below 200 m have been selected. Depending on the vi...

The new normal dates of onset/progress and withdrawal of southwest monsoon over the country are computed based on the operationally declared dates of these events by India Meteorological Department (IMD) during recent years. The normal onset/progress dates were calculated based on 1961-2019 data and that of withdrawal were calculated based on 1971-...

The ensemble predictions were more skillful than the deterministic forecasts , as they were able to predict rainfall anomalies.

IMDAA: A Regional Reanalysis for the Indian Monsoon high-resolution satellite-era regional reanalysis produced by the Indian Monsoon Data Assimilation and Analysis (IMDAA) project has recently been made available to researchers (https://rds. ncmrwf.gov.in). This 40-year reanalysis (1979-2018) at 12-km resolution covers a large geographical domain (...

This novel study explains a plausible physical mechanism for rainfall initiation over the southeast peninsular India (SEPI, referred to be a ‘rain shadow’ region) during the southwest monsoon season. Further, the contrasting rainfall patterns between the rain shadow region and central India (CI) are also elucidated through the response of the marit...

Tropical cyclones do not form easily near the equator but can intensify rapidly, leaving little time for preparation. We investigated the number of near-equatorial (originating between 5°N and 11°N) tropical cyclones over the north Indian Ocean during post-monsoon seasons (October to December) over the past 60 years. A marked 43% decline in the num...

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...

A high resolution regional reanalysis of the Indian Monsoon Data Assimilation and Analysis (IMDAA) project is made available to researchers for deeper understanding of the Indian monsoon and its variability. This 12 km resolution reanalysis covering the satellite-era from 1979 to 2018 using 4D-Var data assimilation method and the UK Met Unified Mod...

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....

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...

During 2015, the southwest monsoon (SWM) rainfall over the country remained deficient with seasonal rainfall of about 86% of the long period average (Table 1.1). Last year, the seasonal rainfall deficiency over the country as a whole was 12% (www.imd.gov.in). Thus, this is a fourth episode of two consecutive years, with deficient monsoon, similar t...

To enhance the knowledge of various physical mechanisms related to the evolution of Tropical Mesoscale Convective Systems (MCSs), detailed analysis has been performed using suite of observations (weather radar, electric field mill, surface weather station, flux tower, microwave radiometer and wind profilers) available at Gadanki (13.5°N/79.2°E), lo...

The initiation of the Indian summer monsoon circulation during late May / early June arises through large-scale land-sea thermal contrast and setting up of negative pressure gradient between the Monsoon Trough over the Indo-Gangetic plains and the Mascarene High over the subtropical Indian Ocean. The meridional pressure gradient together with the E...

This novel study explains a physical mechanism for the rainfall initiation over the southeast peninsular India (SEPI, referred to be a ‘rain shadow’ region) during the southwest monsoon season. Further, the contrasting rainfall patterns between the rain shadow region and central India (CI,) are also elucidated through the response of the maritime c...

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...

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...

Availbale online at https://www.tropmet.res.in/~lip/Publication/Technical-Reports/TR-6.pdf

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...

Sea surface temperature (SST) and upper ocean heat content (OHC, upper 700 m) in the tropical Indian Ocean underwent rapid warming during 1950–2015, with the SSTs showing an average warming of about 1 °C. The SST and OHC trends are very likely to continue in the future, under different emission scenarios. Climate models project a rise in tropical I...

This chapter discusses observed and projected changes in global climate to set the context, after which it discusses the scientific issues around the complexity of regional climate over the Indian subcontinent, with a focus on the Indian Monsoon. It introduces the Earth System Model from India (IITM-ESM), and synthesises the major findings of the r...

Precipitation is an important component of the global water cycle, and the impacts of anthropogenic climate change on precipitation have significant implications on agricultural activities (Porter et al. 2014).

The overall decrease of seasonal summer monsoon rainfall during the last 6–7 decades has led to an increased propensity for droughts over India. Both the frequency and spatial extent of droughts have increased significantly during 1951–2016. In particular, areas over central India, Climate model projections indicate a high likelihood of increase in...

Rain gauge data are routinely recorded and used around the world. However, their sparsity and inhomogeneity make them inadequate for climate model calibration and many other climate change studies. Various algorithms and interpolation techniques have been developed over the years to obtain adequately distributed datasets. Objective interpolation me...

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...

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...

A global forecast system model at a horizontal resolution of T1534 (\({\sim }12.5\, \hbox {km}\)) has been evaluated for the monsoon seasons of 2016 and 2017 over the Indian region. It is for the first time that such a high-resolution global model is being run operationally for monsoon weather forecast. A detailed validation of the model therefore...

Past studies using observational data suggested an increase in day time temperatures and frequency and duration of heat waves over India during the pre-monsoon season (April–June). In this study, the characteristics (frequency and duration) of heat waves over India in future warming scenario has been examined using nine CMIP5 models. The RCP4.5 sce...

In the present research we explored the variability of convective available potential energy (CAPE) during wet and dry spells over southeast India. Comparison between India Meteorological Department (IMD) observations and reanalysis products (NCEP, ERA-interim, and MERRA) reconfirms that gridded data sets can be utilized to fill the void of observa...

We report the first ambient measurements of thirteen VOCs for investigations of emissions and air quality during fog and non-fog wintertime conditions at a tower site (28.57° N, 77.11° E, 220 m amsl) in the megacity of Delhi. Measurements of acetonitrile (biomass burning (BB) tracer), isoprene (biogenic emission tracer in daytime), toluene (a traff...

The present study evaluates the performance of four planetary boundary layer (PBL) parameterization schemes combined with five cloud microphysics schemes in Weather Research Forecasting (WRF) model, specifically for an advection fog event occurred during 4–6 December 2014 at Barkachha, rural site in the Indo-Gangetic plain (IGP). For this purpose,...

Data on mass concentration of PM2.5 and its carbonaceous and water soluble inorganic chemical ions were compiled through sampling of PM2.5 at Indira Gandhi International Airport, Delhi during Dec. 16, 2015-Feb. 15, 2016 under Winter Fog Experiment (WIFEX) program of the Ministry of Earth Sciences (MoES) and analysing the samples. The data so genera...

Winter-to-early spring non-monsoonal precipitation over the Western Himalayas (WH) primarily comes from eastward propagating synoptic-scale weather systems known as western disturbances (WDs). Earlier studies have noted that an increasing trend of synoptic-scale WD activity in the past few decades has contributed to enhanced propensity of daily pre...

In this study, the sensitivity of Weather Research and Forecasting (WRF) model to predict life-cycle of a dense fog occurred on the 23-24 January 2016 is evaluated using different model configurations. For the first time the Intensive Observational Periods (IOPs) were made during the unique WInter Fog EXperiment (WIFEX) took place over Delhi, India...

High-resolution soil moisture/temperature (SM/ST) are critical components of the growing demand for fine-scale products over the Indian monsoon region (IMR) which has diverse land-surface characteristics. This demand is fueled by findings that improved representation of land-state help improve rainfall/flood prediction. Here we report on the develo...

Indian summer monsoon of 2015 was deficient with prominence of short-lived (long-lived) active (break) spells. The real-time extended range forecasts disseminated by Indian Institute of Tropical Meteorology using an indigenous ensemble prediction system (EPS) based on National Center for Environmental Predictions’s climate forecast system could bro...

The fog Experiment was carried out in Delhi to characterize the chemical and microphysical properties of dense fogs occur in the winter season over the northern part of India. This study provides results on aerosol and fog water chemistry, and micro-physical properties during dense fog (around 25 events) occurred during 2015 – 2018 winter seasons....

This study examines the benefit of using Ocean Mean Temperature (OMT) to aid in the prediction of the sign of Indian Summer Monsoon Rainfall (ISMR) anomalies. This is a statistical examination, rather than a process study. The thermal energy needed for maintaining and intensifying hurricanes and monsoons comes from the upper ocean, not just from th...

Beach erosion is a chronic problem along many shores of the Indian coast. As coastal population continues to grow and community infrastructures are threatened by erosion, there is increased demand for accurate information regarding past and present trends and rates of shoreline movement. There is also a need for a comprehensive analysis of shorelin...

We studied the impact of the odd-even traffic rule (implemented in Delhi during 1-15 January 2016) on primary traffic emissions using measurements of 13 volatile organic compounds, carbon monoxide, carbon dioxide and methane at a strategic arterial road in Delhi (28.57N, 77.11E, 220 m amsl). Whole air samples (n = 27) were collected during the od...

High resolution hybrid atmospheric water budget over the South Asian monsoon region is examined. The regional characteristics, variability, regional controlling factors and the interrelations of the atmospheric water budget components are investigated. The surface evapotranspiration was created using the High Resolution Land Data Assimilation Syste...

The Indian Monsoon Region (IMR) has undergone notable land cover and land use change (LCLUC) in response to a dramatic increase in population and economic growth. While the changes in characteristics of LCLUC have been documented in various studies, the realistic representation of these changes within a dynamic hydroclimatic framework remains a cha...

We studied the impact of the odd-even traffic rule (implemented in Delhi during 1-15 January 2016) on primary traffic emissions using measurements of 13 volatile organic compounds, carbon monoxide, carbon dioxide and methane at a strategic arterial road in Delhi (28.57N, 77.11E, 220 m amsl). Whole air samples (n = 27) were collected during the od...

Main objective of the present paper is to examine the role of various parameterization schemes in simulating the evolution of mesoscale convective system (MCS) occurred over south-east India. Using the Weather Research and Forecasting (WRF) model, numerical experiments are conducted by considering various planetary boundary layer, microphysics, and...

The Arctic Region is warming at an alarming rate due to snow/ice-temperature feedback as a result of increase in greenhouse gases and other anthropogenic activities. Due to the Arctic amplification of warming, the Arctic sea ice here is melting at a faster rate of about 0.67 million km² per decade. Past observational data suggest that the Indian Mo...

The primary goal of present study is to investigate the impact of assimilation of conventional and satellite radiance observations in simulating the mesoscale convective system (MCS) formed over south east India. An assimilation methodology based on Weather Research and Forecasting model three dimensional variational data assimilation is considered...

The frequency and intensity of fog episodes during the winter season has been increasing during the past decade over the megacity of Delhi due to the high pollution load. The role of atmospheric aerosols is very important in the life cycle of fog in the urban areas. This paper presents the results on the variation in aerosol optical properties (sca...

The variability of meteorological droughts over India for the period 1901–2010 is examined using district-wise and all-India drought indices, viz Standardized Precipitation Index (SPI) and Standardized Precipitation-Evapotranspiration Index (SPEI). All-India droughts were observed during 18 % of the years considered. Even though frequency of modera...

The amount of solar radiation reaching the Earth’s surface is a major component of the surface energy balance and drives a large number of diverse surface as well as atmospheric processes. Over India, aerosols and clouds are the two major controlling factors that affect the shortwave and long-wave radiative fluxes. The present chapter reviews all t...

In this chapter, variability and long-term trends of heavy rainfall events and rainstorms over India during the monsoon season (June to September) are documented. For analyzing extreme rainfall events, rain gauge station and gridded data for the period 1901–2010 have been used. For studying rainstorms, another gridded rainfall data set of 1951–2010...

In this chapter, long-term trends in annual and seasonal surface air temperatures over India for the period 1901–2010 have been examined. During the period 1901–2010, annual mean, maximum, and minimum temperatures averaged over the country as a whole exhibited a significant increasing trend of 0.60, 1.0, and 0.18 °C per hundred years, respectively....

Main objective of the present paper is to examine the role of various parameterization schemes in simulating the evolution of mesoscale convective system (MCS) occurred over south-east India. Using the Weather Research and Forecasting (WRF) model, numerical experiments are conducted by considering various planetary boundary layer, microphysics, and...

The primary goal of present study is to investigate the impact of assimilation of conventional and satellite radiance observations in simulating the mesoscale convective system (MCS) formed over south east India. An assimilation methodology based on Weather Research and Forecasting model three dimensional variational data assimilation is considered...