B. N. Goswami

Cotton University · Department of Physics

The predictability of the Indian summer monsoon rainfall (ISMR) at any given time period depends on the strength of its relationship with predictable drivers like the El Nino and Southern Oscillation (ENSO) that are known to undergo significant epochal variations. While a similar relationship between the Eurasian snow cover fraction (SCF) and ISMR...

While the El Niño-Southern Oscillation and Indian Summer Monsoon Rainfall (ISMR) relationship is weak in recent years, a strong correlation between May Southern Annular Mode Index (SAMI) and June–July (JJ) ISMR is a southern hemispheric source of ISMR predictability. Here, using observed and reanalysis data, we find that the SAMI–ISMR relationship...

In the backdrop of a significant improvement in weather prediction with Numerical Weather Prediction models, quantitative prediction of the intensity of heavy rainfall events and associated disasters has remained a challenge. Encouraged by the recent emergence of compelling observational evidence for a significant electrical influence on cloud/rain...

Many studies of cloud electrification have suggested that the presence of precipitation in the mixed phase region of the cloud is essential for charge separation and lightning initiation in clouds. However, observations of the rain gush phenomenon, a transient amplification in near-surface intensity after an overhead lightning also suggest that the...

With the recognition that the circulation is strongly coupled with the Indian summer monsoon rainfall (ISMR), a number of large‐scale circulation indices have been proposed to represent the Indian summer monsoon to aid diagnosis of teleconnections with ISMR and evaluation of simulations by climate models. The circulation indices, however, correlate...

With the increasing population in the region, quantification of global warming impact on the mean and daily extremes of NEI rainfall (NEIR) is crucial for food security and preservation of the region’s biodiversity hotspot. Here, using a long (~ 200 years) record of seasonal mean NEIR, we separate oscillatory modes of variability from the secular t...

Reliable projections of Indian Summer Monsoon Rainfall (ISMR) to the next century by climate models is critical for policy toward sustainable development goals but depends on sensitivity of the models simulating ISMR as global mean temperature changes. Here, using observed ISMR and historical global temperature (1850–2005), we find that the mean IS...

A robust estimate of the ENSO-Indian summer monsoon rainfall (ISMR) relationship in a changing climate is critically important for projection of the ISMR predictability. In this study, we show that the increasing nonlinear trend of ISMR and global sea surface temperatures (SST) associated with the trend of the global warming mode leads to a ‘long-t...

Swenson et al. (2020) (hereafter SN20) raise some technical issues on observed correlations between the synoptic variances and the seasonal mean of area averaged (all India or central India) Indian summer monsoon rainfall (ISMR) reported in Saha et al. (2019) (hereafter SA19). SN20 did not comment on the other major finding of SA19 on model based p...

In the backdrop of a revolution in weather prediction by Numerical Weather Prediction (NWP) models, quantitative prediction of intensity of heavy rainfall events and associated disasters has remained a challenge. Encouraged by compelling evidence of electrical influences on cloud/rain microphysical processes, here we propose a hypothesis that modif...

A major sub-seasonal variability of the tropics and sub-tropics, the quasi-biweekly mode (QBM), is known to have significant influence on the seasonal mean of the south Asian monsoon rainfall. A coupled Atmosphere–Ocean General Circulation Model (AOGCM) being essential for seasonal prediction, the ability of the AOGCMs in simulating the space–time...

The El Nino and Southern Oscillation (ENSO) ‘diversity’ has been considered as a major factor limiting its predictability, a critical need for disaster mitigation associated with the trademark climatic swings of the ENSO. Improving climate models for ENSO forecasts relies on deeper understanding of the ENSO diversity but currently at a nascent stag...

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...

The high propensity of deficient monsoon rainfall over the Indian sub-continent in the recent 3 decades (seven deficient monsoons against 3 excess monsoon years) compared to the prior 3 decades has serious implications on the food and water resources in the country. Motivated by the need to understand the high occurrence of deficient monsoon during...

Large socio‐economic impact of the Indian Summer Monsoon (ISM) extremes motivated numerous attempts at its long range prediction over the past century. However, a rather low potential predictability (PP) of the seasonal ISM, contributed significantly by ‘internal’ interannual variability was considered insurmountable. Here we show that the ‘interna...

Eurasian snow is one of the slowly varying boundary forcings, that is known to have significant influences on the mean and variability of the Indian summer monsoon rainfall (ISMR). A multilayer complex snow scheme, incorporated into the state‐of‐the‐art coupled Climate Forecast System version 2 (CFSv2) showed significant improvements in the simulat...

To study the atmospheric moisture transport processes from the source to a receiver region, isotopic analysis of rainwater from Port Blair (as source region), the Andaman Islands, Bay of Bengal has been carried out. In addition to the island site, rainwater collected at three sites on the Indian mainland (as receiver region) namely Nagpur, Kolkata,...

Large socio-economic impact of the Indian Summer Monsoon (ISM) extremes motivated numerous attempts at its long range prediction over the past century. However, a rather estimated low potential predictability limit (PPL) of seasonal prediction of the ISM, contributed significantly by 'internal' interannual variability was considered insurmountable....

In the backdrop of extensive laboratory and theoretical evidence of broadening of the drop size distribution (DSD) of raindrops in the presence of electric field, quantification of the same in observed tropical clouds is lacking. Here this is quantified using the DSD measured by a microrain radar at 2,400-, 1,200-, and 600-m heights from the surfac...

The skill of the statistical as well as physics-based coupled climate models in predicting the El Ni\~no-Southern Oscillation (ENSO) is limited by their inability to represent the observed ENSO nonlinearity. A promising alternative, namely a deterministic nonlinear dynamical model derived from an observed ENSO timeseries, however, has remained elus...

Simulation of the spatial and temporal structure of the monsoon intraseasonal oscillations (MISOs), which have effects on the seasonal mean and annual cycle of Indian summer monsoon (ISM) rainfall, remains a grand challenge for the state-of-the-art global coupled models. Biases in simulation of the amplitude and northward propagation of MISOs and r...

An outstanding problem of climate models is the persistent dry bias in simulating precipitation over the south Asian summer monsoon region. Guided by observations, it is hypothesized that the dry-bias in simulating precipitation by the models is related to underestimation of high pass variance by most models. An analysis of the simulated mean and v...

The duration and extreme fluctuations of prolonged wet or dry spells associated with intraseasonal variability during extreme monsoon have devastating impacts on agrarian-based economy over Indian subcontinent. This study examines the potential predictability limit of intraseasonal transitions between rainy to non-rainy phases (i.e., active to brea...

Modification of the vertical structure of non-adiabatic heating by significant abundance of the stratiform rain in the tropics has been known to influence the large-scale circulation. However, the role of the stratiform rain on the space–time evolution of the observed Boreal summer monsoon intraseasonal oscillations (MISO) has so far been ignored....

Acknowledging the challenge of simulating the mean and intraseasonal variability of Indian Summer monsoon by a coupled climate model CFSv2 (originally adopted from NCEP, USA), a holistic and thorough approach through modifying physical processes namely the cloud and convection is being presented in this report. Considering the CFSv2 systematic bi...

Rising propensity of precipitation extremes and concomitant decline of summer-monsoon rains are amongst the most distinctive hydroclimatic signals that have emerged over South Asia since 1950s. A clear understanding of the underlying causes driving these monsoon hydroclimatic signals has remained elusive. Using a state-of-the-art global climate mod...

Skillful prediction of the “active” and “break” spells of monsoon intraseasonal oscillations during the South Asian monsoon season is crucial for the socio-economic fate of one-sixth of the world’s population, yet it remains a grand challenge problem. The limited skill of our coupled weather and climate models is largely due to our inability to rep...

Highlights: This paper demonstrates that the observed decrease in moderate rainfall events and their intensity, decrease in seasonal rainfall and increase in temperature extremes over India during 1951 through 2005 have been partly caused by anthropogenic land-use/land-cover change (LULCC). High-resolution regional climate model (RegCM4) simulati...

An attempt is made here to evaluate the skill of forecast during boreal summer monsoon regime over the Indian region using the Observation Simulation System Experiment (OSSE) with Doppler Wind LIDAR (DWL) onboard International Space Station (ISS), assimilated in the initial condition. Through various techniques such as pattern correlation, root mea...

Some enticing evidence of multi-decadal variability of the Indian Summer Monsoon Rainfall (ISMR) during 1871-2000 has been linked to the Atlantic Multi-decadal Oscillation (AMO, Goswami et al., 2006). However, neither the periodicity and its stationarity nor its origin could be established unambiguously from the relatively short record. Using three...

Using long daily rainfall (113 years) data, clear evidence of modulation of the statistics of sub-seasonal active and break spells of the Indian summer monsoon rainfall (ISMR) by the El Niño and Southern Oscillation (ENSO) is unraveled. We show that during the El Niño (La Nina) years, the frequency of longer break (active) spells and shorter active...

An analysis of a 5-yr (from 1 January 2009 to 31 December 2013) free run of the superparameterized (SP) Climate Forecast System (CFS) version 2 (CFSv2) (SP-CFS), implemented for the first time at a spectral triangular truncation at wavenumber 62 (T62) atmospheric horizontal resolution, is presented. The SP-CFS simulations are evaluated against obse...

Daily moderate rainfall events, that constitute a major portion of seasonal summer monsoon rainfall over central India, have decreased significantly during the period 1951 till 2005. Mean and extreme near surface daily temperature during the monsoon season have also increased by a maximum of 1–1.5 °C. Using simulations made with a high-resolution r...

There are large uncertainties looming over the status and fate of the South Asian summer monsoon, with several studies debating whether the monsoon is weakening or strengthening in a changing climate. Our analysis using multiple observed datasets demonstrates a significant weakening trend in summer rainfall during 1901–2012 over the central-east an...

Interactions between midlatitude disturbances and the monsoonal circulation are significant for the Indian Summer Monsoon (ISM) rainfall. This paper presents examples of monsoon–midlatitude linkage through anticyclonic Rossby Wave Breaking (RWB) over West Asia during June, July and August of the years 1998–2010. RWB events over West Asia are identi...

Role of the cloud parameterization scheme and critical relative humidity (RHcrit) for large-scale precipitation is examined for simulating Indian summer monsoon (ISM) by theNational Centers for Environmental Prediction (NCEP) climate forecast system version 2 (CFSv2). The major biases of the model simulations namely dry bias over the major continen...

We present here the analysis of the 664-day (from 21 May 2008 to 15 March 2010) free run of the first time implemented superparameterized (SP-) Climate Forecast System (CFS) version 2 (CFSv2) (SP-CFS) at T62 resolution. The SP-CFS simulations are evaluated against observations and traditional convection parameterized CFSv2 simulations at T62 resolu...

Based on extensive analysis of observations and a series of climate model experiments, here we establish that slow variations of northern hemispheric extra-tropical sea surface temperature (SST) anomalies can augment seasonal predictability of the south Asian monsoon. The SST conditions and performance of the south Asian monsoon during 2013 boreal...

Role of the cloud parameterization scheme and critical relative humidity (RHcrit) for large-scale precipitation is examined for simulating Indian summer monsoon (ISM) by theNational Centers for Environmental Prediction (NCEP) climate forecast system version 2 (CFSv2). The major biases of the model simulations namely dry bias over the major continen...

We have evaluated the simulation of Indian summer monsoon and its intraseasonal oscillations in the National Centers for Environmental Prediction (NCEP) climate forecast system model (CFS) version 2 (CFSv2). The dry bias over the Indian landmass in the mean monsoon rainfall is one of the major concerns. Our analysis shows a possible bias in the co-...

With the goal of building an Earth System Model (ESM) appropriate for detection, attribution and projection of changes in the South Asian monsoon, a state-of-the-art seasonal prediction model, namely the Climate Forecast System version 2 (CFSv2) has been adapted to a climate model suitable for extended climate simulations at the Indian Institute of...

Future projections of the Indian summer monsoon rainfall (ISMR) and its large-scale thermodynamic driver are studied by using CMIP5 model outputs. While all models project an increasing precipitation in the future warming scenario, most of them project a weakening large-scale thermodynamic driver arising from a weakening of the upper tropospheric t...

Simulation of Indian summer monsoon in superparameterized CFSv2

The role of moist processes in short range forecasts of Indian Ocean tropical cyclones (TCs) track and intensity and upscale error cascade from cloud-scale processes affecting the intrinsic predictability of TCs were investigated using the Weather Research and Forecasting (WRF) model with parameterized and explicitly resolved convection. Comparing...

The performance of ECHAM5 atmospheric general circulation model (AGCM) is evaluated to simulate the seasonal mean and intraseasonal variability of Indian summer monsoon (ISM). The model is simulated at two different vertical resolutions, with 19 and 31 levels (L19 and L31, respectively), using observed monthly mean sea surface temperature and compa...

A diagnostic study of the space–time characteristics of the summer monsoon intraseasonal oscillations (MISO) during strong monsoon (SM) and weak monsoon (WM) years is carried out to gain insight on the role of the seasonal mean states on the MISOs using long observational and reanalysis datasets. Prominent asymmetry is noted in the duration and mag...

In an attempt to unravel the interactions between cloud microphysics and dynamics that make shallow clouds precipitate heavily in this region, some unique observations of rain and cloud microphysical parameters are presented here from two stations, Pune and Mahabaleshwar, one each on the lee and windward sides respectively of the Western Ghat (WG)...

An ensemble prediction system (EPS) is devised for the extended range prediction (ERP) of monsoon intraseasonal oscillations (MISO) of Indian summer monsoon (ISM) using National Centers for Environmental Prediction Climate Forecast System model version 2 at T126 horizontal resolution. The EPS is formulated by generating 11 member ensembles through...

An ensemble prediction system (EPS) is devised for the extended range prediction (ERP) of mon-soon intraseasonal oscillations (MISO) of Indian summer monsoon (ISM) using National Centers for Environmental Prediction Climate Forecast System model version 2 at T126 horizontal resolution. The EPS is formulated by generating 11 member ensembles through...

Impact of bias correction of sea surface temperature (SST) forecast on extended range (ER, ∼3–4 weeks) prediction skill is studied using the bias-corrected forecasted SST from Climate Forecast System version 2 (CFSv2) as the boundary condition for running the Global Forecast System version 2 (GFSv2) model. Potential predictability limit is comparab...

The ability of the stratospheric Quasi-Biennial Oscillation (QBO) to modulate tropospheric circulation allows it to modulate tracks of tropical cyclones (TCs). This possibility is examined using data on the cyclone tracks over the Bay of Bengal (BOB) during the period 1948–2010. TC tracks (excluding the El Niño-Southern Oscillation years) when stra...

Changes in the amplitude and phase of the diurnal cycle of rainfall due to changes in the background circulation and thermodynamics associated with the intraseasonal variability of Indian summer monsoon have important implications for weather prediction over the region. Hourly rainfall data available at 91 Indian stations for 30 years of observatio...

We have evaluated the simulation of Indian summer monsoon and its intraseasonal oscillations in the National Centers for Environmental Prediction climate forecast system model version 2 (CFSv2). The dry bias over the Indian landmass in the mean monsoon rainfall is one of the major concerns. In spite of this dry bias, CFSv2 shows a reasonable northw...