Influence of El Niño‐Southern Oscillation on baroclinic instability and storm tracks in the Southern Hemisphere

• Published in: International journal of climatology Vol. 41; no. S1; pp. E93 - E109
• Main Authors: Machado, Jeferson Prietsch, Justino, Flávio, Souza, Caio Demétrio
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.01.2021; Wiley Subscription Services, Inc
• Subjects: baroclinic activity; Baroclinic instability; Climate; climatology; Cyclogenesis; Cyclones; El Nino; El Nino phenomena; El Nino-Southern Oscillation event; ENSO; Extratropical cyclones; Growth rate; Heat transport; Kinetic energy; La Nina; Mathematical analysis; Meridional heat transport; Seasonal variability; Seasonal variation; Seasonal variations; Southern Hemisphere; Southern Oscillation; Storm tracks; Storms; Teleconnection patterns; Weather; Wind shear; Southern Hemisphere
• ISSN: 0899-8418; 1097-0088
• DOI: 10.1002/joc.6651

Earth's weather and climate are strongly influenced by synoptic scale systems such as extratropical cyclones. From this point of view, investigating the mechanisms associated with cyclogenesis, such as baroclinic instability (BI), which are defined by the thermal gradient and wind shear, are extremely important. However, atmospheric teleconnection patterns such as the El Niño‐Southern Oscillation (ENSO) phenomenon may affect BI in the preferred region of extratropical cyclones, known as the storm track (ST) region. Therefore, the present study shows the impact of ENSO on BI and STs in the Southern Hemisphere. BI is determined by means of the Eady growth rate method, while the STs are calculated from the kinetic energy and by means of the meridional heat transport. In general, the results show that STs calculated from the BI and the kinetic energy show seasonal variability during ENSO events. This results in Southern Hemisphere extratropical cyclones being more intense with trajectories towards lower (higher) latitudes during El Niño (La Niña) summers. In contrast, little difference is seen in El Niño and La Niña winters. For the calculation of the meridional heat transport at 500 hPa, the Climate Forecast System Reanalysis produced weaker transport relative to ERA‐Interim and previous studies. Extratropical cyclones are responsible for transporting heat and moisture towards the poles, representing an important mechanism in the energy and water vapour balance in the atmosphere. The preferred regions of formation of extratropical cyclones, known as the storm tracks (STs), contribute directly to weather and climate conditions, causing changes in air temperature, winds and large volumes of precipitation. The STs also play a key role in the general circulation of the atmosphere.