H. Annamalai

During the 2022 Asian summer monsoon, the climatological driest parts of Sindh and Balochistan provinces in southwestern Pakistan and the northern Arabian Sea (regions of climatological heat low, HLOW) experienced unprecedented precipitation (>500% of the normal) whereas precipitation was reduced from the Indo‐Gangetic Plain to the tropical western...

Two Earth system models are analyzed to gain insight into the processes that govern projected changes in the South Asian monsoon. Warmer present‐day base state tropical SSTs contribute to coupled processes that produce greater future tropical Pacific warming in CESM2 with less of an increase in season‐mean monsoon precipitation compared to E3SMv2....

An atmospheric river (AR) is a highly accumulated line of moisture, which often preconditions heavy rainfall events. Considering the short-lived nature of ARs, we aim to understand their characteristics over the western North Pacific (WNP) in boreal summer, focusing on the difference between the post–El Niño (pEN) and non-post–El Niño (npEN) cases...

The effects of differences in climate base state are related to processes associated with the present‐day South Asian monsoon simulations in the Energy Exascale Earth System Model version 2 (E3SMv2) and the Community Earth System Model version 2 (CESM2). Though tropical Pacific and Indian Ocean base state sea surface temperatures (SSTs) are over 1°...

Climate model fidelity in representing ENSO-induced teleconnection is assessed with process-oriented diagnostics that examine a chain of processes, from equatorial Pacific precipitation to the midlatitude circulation pattern over the Pacific–North American regions. Such processes are rarely addressed during model development. Using an upper-troposp...

Sea surface temperatures (SSTs) vary not only due to heat exchange across the air-sea interface but also due to changes in effective heat capacity as primarily determined by mixed layer depth (MLD). Here, we investigate seasonal and regional characteristics of the contribution of MLD anomalies to SST variability using observational datasets. We pro...

Previous studies suggest the nature of the air-sea interaction of the tropical intraseasonal oscillation (ISO) can strongly influence our understanding and simulation of the ISO characteristics. In this study we assess the representation of the surface components in three of the most up-to-date reanalyses, including ERA5, ERA-interim (ERAi), and JR...

Warm sea surface temperature (SST) anomalies have been observed in the subtropical North Pacific around Hawaii in the recent decade, appearing from 2013. We examined the formation mechanisms of the warm SST anomalies in terms of relative contribution of atmospheric surface forcing and oceanic dynamics, using the latest reanalysis products from ECMW...

Earth's changing climate will pose a major threat to terrestrial ecosystems in their present state of equilibrium that support human habitats. Understanding the underlying aspects of climate change that influence ecosystems is crucial to devise adaptation strategies and conservation efforts. To this end, climate classification schemes can be employ...

Motivated by observations of fine scale vertical shear and its contribution to mixing in the tropical ocean, this study explores the impact of vertical resolution in an ocean model on sea surface temperature in the tropical Pacific Ocean. We conduct two model experiments that differ in the vertical discretization only, with the grid spacing in one...

The Indian Ocean Observing System (IndOOS), established in 2006, is a multinational network of sustained oceanic measurements that underpin understanding and forecasting of weather and climate for the Indian Ocean region and beyond. Almost one-third of humanity lives around the Indian Ocean, many in countries dependent on fisheries and rain-fed agr...

Abstract A survey of intraseasonal, seasonal, and interannual precipitation and 850 hPa winds for various monsoon regimes around the world is presented for the Community Earth System Model Version 2 (CESM2) compared to observations and the previous generation CESM1. In CESM2 the south Asian monsoon has a reduction of excessive precipitation in the...

In simulations of the boreal summer Asian monsoon, generations of climate models show a persistent climatological wet bias over the tropical western Indian Ocean and a dry bias over South Asia. Here, focusing on the monsoon developing stages (May–June), process-based diagnostics are first applied to a suite of NCAR models and reanalysis products. T...

The 78th edition of CLIVAR Exchanges focuses on the recent decadal review of the Indian Ocean Observing System (IndOOS) and its outcomes.

Using 5-day averaged precipitation from all initial condition realizations of 33 CMIP5 models for the Historical and RCP8.5 scenarios, we performed an assessment of summer precipitation in terms of amount, onset date, withdrawal date, and length of season using probability distributions of interannual anomalies. Climate change projections were gene...

Full Report of IndOOS-2. The Indian Ocean Observing System (IndOOS) is a network of all the sustained observations in the Indian Ocean. Here we present IndOOS-2, designed for the future, to address changing societal and scientific priorities.

The Indian Ocean Observing System (IndOOS) is an observing network of profiling floats (Argo), a moored tropical array (RAMA), repeat lines of temperature profiles (XBT network), surface drifters (GDP), and tide gauges. Augmenting these networks are satellite remotely-sensed observations, in particular of surface winds, sea level, sea surface tempe...

The Indian Ocean is warming faster than any of the global oceans and its climate is uniquely driven by the presence of a landmass at low latitudes, which causes monsoonal winds and reversing currents. The food, water, and energy security in the Indian Ocean rim countries and islands are intrinsically tied to its climate, with marine environmental g...

Forecasting monsoon rainfall using dynamical climate models has met with little success, partly due to models’ inability to represent the monsoon precipitation annual cycle accurately. Here, we review and examine the nature and dynamical causes of their biases. We discuss the coupled nature of the monsoon annual cycle from observations and then pre...

In the present study, we analyze 30-years output from free run solutions of Climate forecast system version 2 (CFSv2) coupled model to assess the model's representation of extended (>7 days) active and break monsoon episodes over south Asia. Process based diagnostics is applied to the individual and composite events to identify precursor signals in...

This study investigates biases of the climatological mean state of the northern Arabian Sea (NAS) in 31 coupled ocean–atmosphere models. The focus is to understand the cause of the large biases in the depth of the 20°C isotherm [Formula: see text] that occur in many of them. Other prominent biases are the depth [Formula: see text] and temperature [...

Regional climate models (RCMs) are used to downscale the coarse resolution General Circulation Model (GCM) outputs to a finer resolution for hydrological impact studies. However, RCM outputs often deviate from the observed climatological data, and therefore need bias correction before they are used for hydrological simulations. While there are a nu...

Forecasting monsoon rainfall using dynamical climate models has met with little success, partly due to models' inability to represent the monsoon climatological state accurately. In this article the nature and dynamical causes of their biases are investigated. The approach is to analyze errors in multimodel-mean climatological fields determined fro...

This study assesses the ability of a high-resolution downscaling simulation with the regional climate model (RCM) HIRHAM5 in capturing the monsoon basic state and boreal summer intraseasonal variability (BSISV) over South Asia with focus on moist and radiative processes during 1979-2012. A process-based vertically integrated moist static energy (MS...

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...

The term “monsoon-desert mechanism” indicates the relationship between the diabatic heating associated with the South Asian summer monsoon rainfall and the remote response in the western sub-tropics where long Rossby waves anchor strong descent with high subsidence. In CMIP5 twenty-first century climate scenarios, the precipitation over South Asia...

This chapter provides a succinct review of the current understanding of the South Asian summer monsoon and the ability of present-day climate models to represent its variability in a changing climate. Beginning with a processes-based review of the large- and regional-scale aspects of the monsoon precipitation climatology, the systematic model error...

A drought is moving through the Pacific Islands, brought by one of the strongest El Niño events since record keeping began 60 years ago. It started in the southwest Pacific, where it has brought famine to Papua New Guinea and Vanuatu. It is expected to reach the South Pacific, tropical West Pacific, and Hawaiian Islands between December 2015 and Ma...

Dry summers over the eastern Mediterranean are characterized by strong descent anchored by long Rossby waves, which are forced by diabatic heating associated with summer monsoon rainfall over South Asia. The large-scale teleconnection between rising and subsiding air masses is referred to as the “monsoon–desert mechanism.” This study evaluates the...

The study compares the simulated poleward migration characteristics of boreal summer intraseasonal oscillations (BSISO) in a suite of coupled ocean–atmospheric model sensitivity integrations. The sensitivity experiments are designed in such a manner to allow full coupling in specific ocean basins but forced by temporally varying monthly climatologi...

A three-step approach to develop a framework for dynamical seasonal prediction of precipitation over the U.S. Affiliated Pacific Islands (USAPI) is adopted. First, guided by the climatological features of basic variables, a view that climates of the USAPI are connected by large-scale phenomena involving the warm pool, South Pacific convergence zone...

Using pentad rainfall data we demonstrate the benefits of using accumulated rainfall and fractional accumulated rainfall for the evaluation of the annual cycle of rainfall over various monsoon domains. Our approach circumvents issues related to using threshold-based analysis techniques for investigating the life-cycle of monsoon rainfall. In the Co...

The boreal summer Asian monsoon has been evaluated in 25 Coupled Model Intercomparison Project-5 (CMIP5) and 22 CMIP3 GCM simulations of the late twentieth Century. Diagnostics and skill metrics have been calculated to assess the time-mean, climatological annual cycle, interannual variability, and intraseasonal variability. Progress has been made i...

Monsoon rainfall over South Asia has decreased during the last 5 to 6 decades according to several sets of observations. Although sea surface temperature (SST) has risen across the Indo-Pacific warm pool during this period, the expected accompanying increased rainfall has occurred only in the tropical western Pacific. The above changes noted in obs...

The vagaries of South Asian summer monsoon rainfall on short and long timescales impact the lives of more than one billion people. Understanding how the monsoon will change in the face of global warming is a challenge for climate science, not least because our state-of-the-art general circulation models still have difficulty simulating the regional...

Inthepresentresearchtoidentifymoistprocessesthatinitiateandmaintainextendedmonsoonbreaksover South Asia moisture and moist static energy (MSE) budgets are performed on the newly available European Centre for Medium-Range Weather Forecasts Interim reanalysis (ERA-Interim) and ensemble integrations fromacoupledmodel.Thehypothesisthatinteractionbetwee...

The simulation characteristics of theAsian-Australianmonsoon are documented for the Community Climate System Model, version 4 (CCSM4). This is the first part of a two part series examining monsoon regimes in the global tropics in theCCSM4.Comparisons aremade to anAtmosphericModel Intercomparison Project (AMIP) simulation of the atmospheric componen...

The 15-member ensemble hindcasts performed with the National Centers for Environmental Prediction Climate Forecast System (CFS) for the period 1981-2005, as well as real-time forecasts for the period 2006-09, are assessed for seasonal prediction skills over the tropics, from deterministic (anomaly correlation), categorical (Heidke skill score), and...

Diagnostics from observations and multicentury integrations of a coupled model [Geophysical Fluid Dynamics Laboratory (GFDL) coupled model version 2.1 (CM2.1)] indicate that about 65% of the severe monsoons (rainfall > 1.5 standard deviations of its long-term mean) over South Asia are associated with sea surface temperature (SST) anomalies over the...

The present study aims to assess the impacts of climate change on hydrology and rice yield in Bhavani basin of India using SWAT model. The investigation indicates that SWAT can be applied as a decision tool for framing the adaptation strategies under changing climate such as changing the method of cultivation, altering water and fertilizer manageme...

Diagnostics performed with twentieth-century (1861–2000) ensemble integrations of the Geophysical Fluid Dynamics Laboratory Climate Model, version 2.1 (CM2.1) suggest that, during the developing phase, El Niño events that co-occur with the Indian Ocean Dipole Zonal Mode (IODZM; class 1) are stronger than those without (class 2). Also, during class...

During boreal summer, both the monsoon trough and the equatorial Indian Ocean (EIO) receive intense climatological precipitation. At various time scales, EIO sea surface temperature (SST) and/or precipitation variations interact with rainfall along the trough. For instance, during July-August in strong Indian Ocean dipole/zonal mode (IODZM) years,...

This technical brief is a short summary that highlights the need to distinguish between natural climate variations and anthropogenic induced climate change. After briefly providing the basics, we present results from observations that highlights the current climate variations and change over the Cauvery river basin.

This study discloses detailed Madden-Julian oscillation (MJO) characteristics in the two 30-day integrations of the global cloud-system-resolving Nonhydrostatic Icosahedral Atmospheric Model (NICAM) using the all-season real-time multivariate MJO index of Wheeler and Hendon. The model anomaly is derived by excluding the observed climatology because...

This study documents the detailed characteristics of the tropical intraseasonal variability (TISV) in the MRI-20km60L AGCM that uses a variant of the Arakawa-Schubert cumulus parameterization. Mean states, power spectra, propagation features, leading EOF modes, horizontal and vertical structures, and seasonality associated with the TISV are analyze...

Recent diagnostics with the Geophysical Fluid Dynamics Laboratory Climate Model, version 2.1 (GFDL CM2.1), coupled model’s twentieth-century simulations reveal that this particular model demonstrates skill in capturing the mean and variability associated with the South Asian summer monsoon precipitation. Motivated by this, the authors examine the f...

Boreal summer intraseasonal (30–50day) variability (BSISV) over the Asian monsoon region is more complex than its boreal winter counterpart, the Madden–Julian oscillation (MJO), since it also exhibits northward and northwestward propagating convective components near India and over the west Pacific. Here we analyze the BSISV in the CMIP3 and two CM...

Two atmospheric general circulation models (AGCMs), differing in numerics and physical parameterizations, are employed to test the hypothesis that El Niño–induced sea surface temperature (SST) anomalies in the tropical Indian Ocean impact considerably the Northern Hemisphere extratropical circulation anomalies during boreal winter [January–March +1...

In this paper the extensive integrations produced for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) are used to examine the relationship between ENSO and monsoons at interannual and decadal time scales. The study begins with an analysis of the monsoon simulation in the twentieth-century integrations. Six of the...

An atmospheric general circulation model (AGCM) is used to examine the role of Indian Ocean sea surface temperature (SST) anomalies in regional climate variability. In particular, the authors focus on the effect of the basinwide warming that occurs during December through May after the mature phase of El Niño. To elucidate the relative importance o...

Sea surface temperature observations in the eastern equatorial Indian Ocean (EEIO) during the period 1950–2003 indicate that Indian Ocean dipole/zonal mode (IODZM) events are strong in two decades, namely, the 1960s and 1990s. Atmospheric reanalysis products in conjunction with output from an ocean model are examined to investigate the possible rea...

The boreal summer intraseasonal variability (BSISV) associated with the 30–50-day mode is represented by the coexistence of three components: poleward propagation of convection over the Indian and tropical west Pacific longitudes and eastward propagation along the equator. The hypothesis that the three components influence each other has been inves...

Diagnostics from observed precipitation and National Centers for Environmental Prediction–National Center for Atmospheric Research re-analysis products reveal that after the 1976–77 climate shift in the Pacific there was a dramatic change in the response of the Indian summer monsoon (ISM) to El Niño, particularly during the months of July and Augus...

Prior to the 1976-77 climate shift (1950-76), sea surface temperature (SST) anomalies in the tropical Indian Ocean consisted of a basinwide warming during boreal fall of the developing phase of most El Niños, whereas after the shift (1977-99) they had an east-west asymmetry—a consequence of El Niño being associated with the Indian Ocean Dipole/Zona...

The role of the Indian Ocean in regional climate variability has been studied for a long time. Whether the Indian Ocean plays an active role or simply responds passively to the wind and heat flux variability generated elsewhere remains somewhat of an open question. Here we attempt a fairly comprehensive review of the literature relating to the Indi...

Prior to the 1976–77 climate shift (1950–76), sea surface temperature (SST) anomalies in the tropical Indian Ocean consisted of a basinwide warming during boreal fall of the developing phase of most El Niños, whereas after the shift (1977–99) they had an east–west asymmetry—a consequence of El Niño being associated with the Indian Ocean Dipole/Zona...

Atmosphere and ocean model assimilated products, in conjunction with observed precipitation and ocean model estimates of Indonesian Throughflow (ITF) transport and barrier layer thickness, are analyzed to elucidate the role of external (ENSO and ITF) and internal (monsoon) factors in the initiation of the Indian Ocean Zonal Mode (IOZM).The diagnost...

A sufficiently long and consistent atmosphere and ocean model assimilated products, in conjunction with observed precipitation and an ocean model estimates of Indone- sian Throughflow (ITF) and barrier layer thickness (BLT) are diagnosed with a spe- cific goal of elucidating the role of external (ENSO and ITF) and internal (monsoon) factors on the...

 In this study, various diagnostics have been applied to daily observed outgoing longwave radiation (OLR) and ECMWF ReAnalysis (ERA) products to provide a comprehensive description of the active/break cycles associated with the Asian Summer Monsoon and to address the differing behaviour of the two dominant time scales of intraseasonal variability,...

A unique open-ocean upwelling exists in the tropical South Indian Ocean (SIO), a result of the negative wind curl between the southeasterly trades and equatorial westerlies, raising the thermocline in the west. Analysis of in situ measurements and a model-assimilated dataset reveals a strong influence of subsurface thermocline variability on sea su...

The relationship between subseasonal and interannual variability of the Asian summer monsoon has been investigated through analysis of the dominant modes of variability in the 40‐year NCEP/NCAR Re‐analysis, with complementary satellite and surface‐based precipitation data. The hypothesis that the characteristics of monsoon subseasonal variability (...

The year 1997 was characterized by the rapid development of an El Niño whose strength exceeded any previously observed this century. The basic understanding of the influence of El Niño on the Asian summer monsoon suggested that the monsoon should be substantially deficient, yet the all-India rainfall (AIR) was 2% above normal. The reasons for this...

The behavior of the Asian summer monsoon is documented and compared using the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA) and the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) Reanalysis. In terms of seasonal mean climatologies the results suggest that, in several...

The suitability of the European Centre for Medium Range Weather Forecasting (ECMWF) operational wind analysis for the period 1980–1991 for studying interannual variability is examined. The changes in the model and the analysis procedure are shown to give rise to a systematic and significant trend in the large scale circulation features. A new metho...

The latest non-parametric statistical tool Singular Spectrum Analysis (SSA) has been shown to extract deterministic oscillations present in a nonlinear dynamical system. It has been hypothesized that the tropical ocean-atmosphere system consists of both deterministic and stochastic parts in the interannual time scales. In the present study SSA has...

The purpose of this paper is to investigate intraseasonal (30-70 days) and higher frequency (5-30 days) variability and its relationship to interannual variability. Various modelling studies have suggested a link between intraseasonal and interannual variability of the Asian summer monsoon. This relationship has been mainly based upon the similar s...

The goals of this report are: (1) Analyze boreal summer Asian monsoon intraseasonal variability general circulation models--How well do the models represent the eastward and northward propagating components of the convection and how well do the models represent the interactive control that the western tropical Pacific rainfall exerts on the rainfal...