THE INFLUENCE OF THE LOCALIZATION OF POSITIVE SURFACE TEMPERATURE ANOMALIES IN THE EQUATORIAL PACIFIC OCEAN ON THE PROPAGATION OF WAVE ACTIVITY FROM THE TROPOSPHERE TO THE STRATOSPHERE IN MODEL EXPERIMENTS

During an El Niño event an area of intense convection is formed above the area of positive sea surface temperature (SST) anomalies in the equatorial Pacific Ocean. This leads to the formation of a Rossby wave, which propagates from low to high latitudes and can lead to changes in largescale atmospheric circulation in mid-latitudes and, as a consequence, to a change in the vertical wave activity flow from the troposphere to the stratosphere. In recent decades, a new type of El Niño – El Niño Modoki – has been increasingly observed. During El Niño Modoki positive SST anomalies are observed in the central part of the equatorial Pacific Ocean, in contrast to the anomalies of the canonical El Niño, which are observed in the east part. The paper shows differences in the nature of the propagation of wave activity in model experiments with SST anomalies located in areas corresponding to the events of the canonical El Niño (Nino 3 region) and El Niño Modoki (Nino 4 region). It was found that, with comparable amplitudes of SST anomalies, the stratospheric polar vortex is more weakened when the localization of the anomalies corresponds to the El Niño Modoki phenomenon. Statistically significant differences in the weakening of the intensity of the stratospheric polar vortex between experiments are observed at the beginning of the extended winter period (November–December) and in spring (March– April). When the anomalies are located in the central part of the equatorial Pacific Ocean, a doubling of the frequency of final sudden stratospheric warmings (SSWs) is observed compared to the experiment where the anomalies correspond to the localization of the canonical El Niño. The more frequent occurrence of SSWs, both final and intraseasonal, in the El Niño Modoki experiment compared to the canonical El Niño is explained by an increase in the meridional component of the three-dimensional flux of wave activity in case of more westerly position of the SST anomaly. This increase is recorded both immediately before the SSW and throughout the winter period (December–February).