Comparison Of Different Stages (ENSO Developing And Decaying) Of Mega-ENSO And Conventional ENSO Climatic Impacts

The El Nino Southern Oscillation (ENSO, hereafter conventional ENSO), as the most important atmosphere-ocean coupling phenomenon, has already been proved to be a source of predictability, and has profound impacts on global weather and climate. Mega-ENSO was first introduced by Wang et al. as a leading mode of global sea surface temperature (SST) variability with a multi-timescale from interannual to interdecadal. The mega-ENSO is defined in an area including both the tropical Pacific and its subtropical extensions. With such a boarder spatial-temporal scale that differs from the conventional ENSO, mega-ENSO index may contain richer or more complicated climate information than a conventional ENSO index does, although it belongs to the same ENSO system. For example, it is a main driving force of Northern Hemisphere summer monsoon rainfall including the Indian summer monsoon rainfall and East Asian Summer Monsoon Rainfall, while such contribution cannot be detected in the conventional ENSO.Monsoon is important for agricultural production, water availability, and food security is well-documented. Interannual monsoon variability strongly affects agricultural production. Disruptions in the monsoon Rainfall can lead to substantial losses in crop production that, in turn, may affect the food security of the large and growing population. Thus, it is crucial and necessary to capture new predictability sources and improve the prediction skill of the monsoon.Furthermore, ENSO and the monsoon are two primary interacting components in the climate system. Previous studies have mainly focused on the influence of ENSO on the monsoon. Due to the phase-locking nature of ENSO, the monsoon occurs in either the developing or decaying phase of an ENSO event. However, most previous studies primarily focus on conventional ENSO, and few of them have been conducted on its developing phase. The main purpose of using the mega-ENSO index is to obtain more complete information of the ENSO system. The main purpose of using the mega-ENSO index is to obtain a more complete description of the ENSO system and its climatic impact. Given that the mega-ENSO is defined to reflect a broader range of variability than the conventional ENSO, it would be interesting and important to investigate whether the responses of the ISR and the associated atmospheric circulation to the mega-ENSO signal significantly differs from the responses to the conventional ENSO signal. This motivates the current studyThe impacts of typical ENSO and atypical ENSO events on the ISR remain unclear during their developing summer. This study examines the different linkages of typical ENSO-ISR and atypical ENSO-ISR. During the developing summer of typical El Nino, negative rainfall anomalies are seen over the northeastern Indian subcontinent, while the anomalous rainfall pattern is almost the opposite for typical La Nina; as for the atypical ENSO, the approximate "linear opposite" phenomenon vanishes. Furthermore, an anomalous global zonal wave train is found at mid-latitude zones, with a local tri-pole circulation pattern over the central-eastern Eurasia during the typical ENSO developing summer, which might be an explanation of corresponding rainfall response over the Indian Peninsula. By contrast, such features are not obvious during the atypical ENSO developing summer. Among 106-year historical runs (1900-2005) of 9 state-of-the-art models from the Coupled Model Inter-comparison Project Phase 5 (CMIP5), HadGEM2-ES exhibits a promising skill in simulating the anomalous circulation pattern over mid-latitude and central-eastern Eurasia. Probably, it is the models’ability of capturing the typical ENSO-ISR linkage and the characteristic of typical ENSO that make the difference.The impacts of typical ENSO and atypical ENSO events on the EASR remain unclear during their decaying summer. This study examines the different linkages of typical ENSO-EASR and atypical ENSO-EASR. During the decaying summer of typical El Nino, tripole rainfall anomalies are seen over the eastern Asian, while the anomalous rainfall pattern is almost the opposite for typical La Nina; as for the atypical ENSO, the phenomenon vanishes. Furthermore, an anomalous global zonal wave train is found at mid-latitude zones during the typical ENSO developing summer, which might be an explanation of corresponding rainfall response over the East Asia. By contrast, such features are not obvious during the atypical ENSO decaying summer. Among 106-year historical runs (1900-2005) of 9 state-of-the-art models from the CMIP5, HadCM3 exhibits a promising skill in simulating the anomalous circulation pattern over mid-latitude and central-eastern Eurasia. Probably, it is the models’ability of capturing the typical ENSO-ISR、ENSO-EASR linkage and the characteristic of typical ENSO that make the difference.