[A-AS10] Stratosphere-troposphere (Atmospheric) Processes And their Role in Climate

[AAS10-P12] Tropical cyclone response over Mozambique Strait with respect to QBO phases

*Nawo Eguchi¹, Kunihiko Kodera² (1.Research Institute for Applied Mechanics, Kyushu University, 2.Meteorological Research Institute)

Keywords:Stratosphere-Troposphere Interaction, Quasi-Biennial Oscillation, Tropical Cyclones, Mozambique Strait

During the Quasi-Biennial Oscillation (QBO) is in the easterly phase, the stratosphere in the equatorial region becomes an upward anomaly, and the temperature also becomes a low anomaly (Fig. 1a, b). Therefore, it is known that tropical convective activity (including intraseasonal variations such as the MJO) becomes active during the QBO easterly phase. We also noted that easterly wind/low temperature anomalies also occur in the lower stratosphere in the subtropics at the same time as shown in Figure 1a, and investigated the relationship between tropical cyclones (TCs) and QBO, paying particular attention to the Mozambique Strait in the southern Indian Ocean during the Northern Hemisphere winter (from December to February).
Based on IBTrAC's tropical cyclone data, 65 tropical cyclones occurred in the Mozambique Strait area (40E-50E, 25S-15S) from December to February in the boreal winter from 1988 to 2021. Of these, 30 TCs occurred during the easterly phase of QBO (Fig. 2). Although the frequency of occurrence of TCs during the east-west phase is almost the same, there is a difference in the maximum wind speed, suggesting that TCs develop more strongly during the easterly phase. Additionally, in the boreal winter of 2011-2012, there was a stratospheric sudden warming (SSW), which is the minor warming, indicating that the intensity of TCs has increased. At the same time, TCs have also formed off the coast of northern Australia, except the Mozambique Strait.