Abstract
The equatorial westerly wind bursts (WWBs) play an important role in modulating and predicting the El Niño-Southern Oscillation (ENSO). In this study, the ability of the Community Atmospheric Model version 4 (CAM4) and the Community Climate System Model version 4 (CCSM4) in simulating WWBs is systematically evaluated. Many characteristics of WWBs, including their longitude distributions, durations, zonal extensions, variabilities at seasonal, intraseasonal, and interannual timescales, as well as their relations with the Madden–Julian Oscillation (MJO) and ENSO, are discussed. Generally speaking, these characteristics of WWBs can be successfully reproduced by CAM4, owning to the improvement of the deep convection in the model. In CCSM4, significant bias such as the lack of the equatorial Pacific WWBs in boreal spring season and the weak modulation by a strong MJO are found. Our findings confirm the fact that the WWBs are greatly modulated by the surface temperature. It’s also suggested that improving the air-sea coupling in CCSM4 may improve model performance in simulating WWBs, and may further improve the predictability of ENSO in the coupled model.
Highlights
Wind bursts (WWBs), the sudden but strong westerly zonal wind anomalies, are a distinct synoptic to intraseasonal atmospheric feature in the tropics from the Indian Ocean to the central Pacific Ocean (Hartten 1996; Harrison and Vecchi 1997; Seiki and Takayabu 2007)
Our results indicate that Community Atmospheric Model version 4 (CAM4) has a good performance in simulating the monthly distribution of Westerly wind bursts (WWBs), but there is a significant bias in simulating the seasonality of the temporal peak of WWBs in the western Pacific (WP) and central Pacific (CP) regions
The WWBs simulations in CAM4 and Community Climate System Model version 4 (CCSM4) are evaluated in this study
Summary
Wind bursts (WWBs), the sudden but strong westerly zonal wind anomalies, are a distinct synoptic to intraseasonal atmospheric feature in the tropics from the Indian Ocean to the central Pacific Ocean (Hartten 1996; Harrison and Vecchi 1997; Seiki and Takayabu 2007). Using 18 climate models in the Coupled Model Intercomparison Project phase 3 (CMIP3), Seiki et al (2011) assessed the simulation of WWBs and its relation with ENSO. It’s not clear whether the modeled WWBs exhibit a stronger phase locking characteristic in boreal winter when more WWBs occur (Harrison and Vecchi 1997) It has not be examined yet whether the WWBs in late boreal spring and summer seasons over the central equatorial Pacific, which is important for triggering and maintaining the strong El Niño (McPhaden 1999; Menkes et al 2014; Chen et al 2015; Xue and Kumar 2016; Hu and Fedorov 2016; Lian et al 2017), can be correctly simulated in the coupled model.
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