Assessment of the Ability of CMIP6 GCMS to Simulate the Boreal Summer Intraseasonal Oscillation Over Southeast Asia

Abstract

The boreal summer intraseasonal oscillation (BSISO) plays an important role in the intraseasonal variability of a wide range of weather and climate phenomena across the region modulated by the Asian summer monsoon system. This study evaluates the strengths and weaknesses of 19 Coupled Model Intercomparison Project Phase 6 (CMIP6) models to reproduce the basic characteristics of BSISO. The models' rainfall and largescale climates are evaluated against GPCP and ERA5 reanalysis datasets. All models exhibit intraseasonal variance of 30–60-day bandpass-filtered rainfall and convection anomalies but with diverse magnitude when compared with observations. The CMIP6 models capture the structure of the eastward/northward propagating BSISO at wavenumbers 1 and 2 but struggle with the intensity and location of the convection signal. Nevertheless, the models show a good ability to simulate the power spectrum and coherence squared of the principal components of the combined empirical orthogonal function (CEOF) and can capture the distinction between the CEOF modes and red noise. Also, the result shows that some CMIP6 models can capture the coherent intraseasonal propagating features of the BSISO as indicated by the Hovmöller diagram. The contribution of latent static energy to the relationship between the moist static energy and intraseasonal rainfall over Southeast Asia is also simulated by the selected models, albeit the signals are weak. Taking together, some of the CMIP6 models can represent the summertime climate and intraseasonal variability over the study region, and can also simulate the propagating features of BSISO, but biases still exist.

Sub-seasonal to seasonal drivers of dry extreme rainfall events over Northeast Thailand

“…The dataset has been developed by the Research Institute for Humanity and Nature (RIHM) and the Meteorological Research Institute of Japan Meteorological Agency (MRI/JMA) and is available for all land areas in Asia from 1951 to 2015 at a spatial resolution of 0.25 • . The credibility of these datasets to represent rainfall characteristics over Asia has been documented in previous studies (e.g., He et al, 2019;Kim I. et al, 2019;Kim K. et al, 2019;Abatan et al, 2021;Khadka et al, 2022).…”

“…ENSO is an atmospheric-oceanic mode of variability on interannual time scales that is known to play a dominant role in controlling the climate variability of tropical and subtropical areas, with significant weather impacts (Todd et al, 2018;Roy et al, 2019;Pillai et al, 2021). The BSISO, which is characterized by 10-20-day and 30-60-day time scales, is known to play an important role in determining the intraseasonal variability of the Asian summer monsoon system (Li et al, 2015;Hsu et al, 2016;Lee et al, 2017;Yang et al, 2020;Abatan et al, 2021).…”

Contrasting controls on convection at latitude zones near and away from the equator for the Indian summer monsoon

“…Several generations of Coupled Model Intercomparison Project (CMIP) models, including the latest CMIP6, are unable to reproduce this variability [60][61][62]. A recent study has reported an unduly weak relationship between MSE and precipitation in these models [63]. It is also likely that these models do not capture the mechanisms influencing the build-up of MSE in the BL away from the equator, including over Indian landmass, and hence fail to promote off-equatorial precipitating convection.…”

Expansion of winter ENSO‐associated rainfall affected area in Southeast Asia under warmer climate

“…Studies also have been performed to understand the changes in monsoon rainfall under CMIP6 simulations in the past (Gusain et al, 2020) and future (Ha et al, 2020; Wang et al, 2020). Abatan et al (2021) used CMIP6 models to look at the characteristics of boreal summer intraseasonal oscillation (BSISO) in SEA, while Zhu et al (2020) assessed the performance of CMIP6 models in simulating climate extremes.…”

“…Studies also have been performed to understand the changes in monsoon rainfall under CMIP6 simulations in the past (Gusain et al, 2020) and future (Ha et al, 2020;Wang et al, 2020). Abatan et al (2021) used CMIP6 models to look at the characteristics of boreal summer intraseasonal oscillation (BSISO) in SEA, while Zhu et al (2020) assessed the performance of CMIP6 models in simulating climate extremes. Cai et al (2015) suggested that many climate models tend to reproduce stronger warming along the equator under warmer climate, which is related with the weaker evaporative warming damping in the equatorial region compared to the evaporative warming damping over the off-equator region.…”