The simulation of the boreal summer intraseasonal oscillation (BSISO) has been analyzed in the historical run of the 32 models, which participated in the Coupled Model Intercomparison Project phase5 (CMIP5), and it is shown that the current state‐of‐the‐art general circulation models (GCMs) still have difficulties to properly simulate the BSISO. Compared to CMIP3 models, more CMIP5 models simulated the northward propagation of BSISO. The majority of the models could not simulate the spatial pattern of BSISO variance over the Asian summer monsoon (ASM) region and many of them failed to capture all the three peak centers of BSISO variance over the Indian summer monsoon region. Many of the models underestimated the BSISO variance over the equatorial Indian Ocean, and it is associated with the seasonal mean dry biases over this region. A reasonable representation of the intraseasonal sea surface temperature and its coupling to the convection over the equatorial Indian Ocean and an equatorial eastward propagation of convective anomalies beyond 100^°E assure realistic simulation of BSISO over the ASM domain. We found that the models MIROC5, IPSL‐CM5A‐LR, GFDL‐CM3, CMCC‐CM, and MPI‐ESM‐LR are able to represent reasonable BSISO characteristics and can be used to unravel the modulation of BSISO characteristics due to various projected climate changes.

This study compares the simulation and prediction skill of the Indian summer monsoon at two different horizontal resolutions viz., T126 (~100 km) and T382 (~38 km) using 28 years of hindcast runs of the National Centers for Environmental Prediction Climate Forecast System version 2 (CFSv2) model. It is found that the simulation of the mean state of the South Asian summer monsoon, its variance, and prediction skill of the all India summer monsoon rainfall (AISMR) are better represented in the high‐resolution configuration (T382) of the CFSv2 compared to the low‐resolution (T126) configuration. In the high‐resolution run, the systematic bias in the teleconnection between the AISMR and Indian Ocean Dipole (IOD) has considerably reduced and the teleconnections between the AISMR and El Niño–Southern Oscillation (ENSO) remained same. We hypothesize that the better simulation of mean climate and IOD‐AISMR teleconnection in high‐resolution configuration (T382) of CFSv2 are responsible for the improved prediction skill of AISMR in T382 configuration. Although the T382 configuration of CFSv2 has shown a significant improvement in the simulation and prediction of Indian summer monsoon as compared to the T126 configuration, several parallel efforts are still essential to understand the processes controlling some of the systematic biases of CFSv2 and those efforts are underway as part of the Monsoon Mission project.

Simulation of Indian summer monsoon features by latest coupled model of National Centers for Environmental Prediction (NCEPs) Climate Forecast System version 2 (CFSv2) is attempted in its long run. Improvements in the simulation of Indian summer monsoon as compared with previous version (CFSv1) is accessed and areas which still require considerable refinements are introduced. It is found that, spatial pattern of seasonal mean rainfall and wind circulations are more realistic in CFSv2 as compared with CFSv1. Variance and northward propagation of intraseasonal oscillation (ISO), which also contribute to the seasonal mean rainfall are remarkably improved. However, the central Indian dry bias still persists and amplified. Pervasive cold bias in surface (2 m air temperature) as well as in the whole troposphere is further increased in CFSv2. These cold biases may be partly attributed to the lack of model's ability to realistically simulate the ratio of convective and stratiform rainfall. Sea‐surface temperature (SST) over the Indian Ocean is underestimated in CFSv2. However, CFSv1 shows east–west dipole structure in the bias. The teleconnection of El Nino Southern Oscillation (ENSO) and Indian summer monsoon rainfall (ISMR) in terms of Niño3 SST and monsoon rainfall correlation is more realistic in the latest version of the model. Overall, there are substantial improvements in CFSv2 as compared with CFSv1, but it has to evolve further to realistically simulate the mean and variability of ISMR.

Atlantic Zonal Mode (AZM) and Indian summer monsoon rainfall (ISMR) are known to have an inverse relationship, which means that the cold (warm) phases of AZM result in strong (weak) ISMR. Here, we report that the inverse relationship between AZM and ISMR has significantly strengthened in recent decades. The cause of this strengthening relationship has been investigated. We find a robust increase in interannual variability of Sea Surface Temperature (SST) over the eastern tropical Atlantic Ocean in recent decades, which implies an increase in the number of strong AZM events towards the end of the 20^th century. The increase in strong AZM events alters the large‐scale monsoon circulation over the Indian subcontinent by enhancing the Kelvin wave response into the Indian Ocean, leading to an enhanced AZM‐ISMR teleconnection. This demands a better representation of the AZM‐ISMR teleconnection in climate models for improving seasonal monsoon prediction in a warming world.