El Niño–Global Atmospheric Oscillation as the Main Mode of Interannual Climate Variability

The interannual variability of the global mean monthly anomalies of near-surface air temperature, sea-level pressure, wind speed near the surface, amount of precipitation and total cloudiness was investigated. The amplitudes of the anomalies of these hydrometeorological characteristics between opposite phases of the Global Atmospheric Oscillation (GAO) were calculated. The regional element of the GAO in the tropics of the Indian and Pacific Oceans is the Southern Oscillation. The results show that the oscillations of these characteristics are associated with the GAO not only in the tropical belt of the Earth but also in the middle and high latitudes, especially in the Arctic and northern Eurasia. The physical mechanism by which the transition of the GAO from the negative to the positive phase influences the weakening of the Pacific trade winds, and, as a consequence, the onset of El Niño is described.

Interactions of temperature fluctuations of the Pacific, Indian and Atlantic oceans with Global atmospheric oscillation

<p>The predictability of El Niño and La Niña is investigated. In this case, the recently discovered so-called Global Atmospheric Oscillation (GAO) is considered (Serykh et al., 2019). Assuming GAO to be the main mode of short-term climatic variability, this study defines an index that characterizes the dynamics and relationships of the extratropical components of the GAO and El Niño – Southern Oscillation (ENSO). Due to the general propagation of the GAO’s spatial structure from west to east, another index – predictor of ENSO is defined. The cross-wavelet analysis between both of these indices and the Oceanic Niño Index (ONI) is performed. This analysis reveals a range of timescales within which the closest relationship between the GAO and ONI takes place. Using this relationship, it is possible to predict El Niño and La Niña with a lead-time of approximately 12 months (Serykh and Sonechkin, 2020a).</p><p>Using data on the distribution of temperatures in the Pacific, Indian, and Atlantic Oceans, large-scale structures of spatial and temporal variations of these temperatures are investigated (Serykh and Sonechkin, 2020b). A structure is found which is almost identical to the spatial and temporal sea surface temperature (SST) structure that is characteristic of the GAO. Variations in water temperature in a near-equatorial zone of the Pacific Ocean at depths up to about 150 meters behave themselves in the same way as variations in sea surface height and SST. At even greater depths, variations in water temperature reveal a "striped" structure, which is, however, overall similar to that of SST variations. Variations of water temperature at depths in all three oceans spread from east to west along the equator with a period of 14 months. This makes it possible to think that the dynamics of these temperatures are controlled by the so-called Pole tides. The surface North Pacific Pole Tide was found previously responsible for excitation of El Niño (Serykh and Sonechkin, 2019). The deep Pole tides in the Southern Atlantic and Southern Indian Ocean appear to be triggers of the Atlantic El Niño and Indian Ocean Dipole (IOD). Thus, IOD manifests itself at the depth of the thermocline more clearly than on the surface of the Indian Ocean. The out-of-phase behavior of El Niño and IOD is explained by the 180-degree difference in the longitudes of these phenomena.</p><p> </p><p><strong>References</strong></p><p>Serykh I.V., Sonechkin D.M. Nonchaotic and globally synchronized short-term climatic variations and their origin // Theoretical and Applied Climatology. 2019. Vol. 137. No. 3-4. pp 2639–2656. https://doi.org/10.1007/s00704-018-02761-0</p><p>Serykh I.V., Sonechkin D.M., Byshev V.I., Neiman V.G., Romanov Yu.A. Global Atmospheric Oscillation: An Integrity of ENSO and Extratropical Teleconnections // Pure and Applied Geophysics. 2019. Vol. 176. pp 3737–3755. https://doi.org/10.1007/s00024-019-02182-8</p><p>Serykh I.V., Sonechkin D.M. El Niño forecasting based on the global atmospheric oscillation // International Journal of Climatology. 2020a. https://doi.org/10.1002/joc.6488</p><p>Serykh I.V., Sonechkin D.M. Interrelations between temperature variations in oceanic depths and the Global atmospheric oscillation // Pure and Applied Geophysics. 2020b. Vol. 177. pp 5951–5967. https://doi.org/10.1007/s00024-020-02615-9</p>