Extreme precipitation characteristics driven by atmosphere-oceanic modes in the Uruguay river basin based on convective-permitting model simulations

Chun, Kwok; Danaila, Luminita; Fossa, Manuel; Massei, Nicolas; Yetemen, Omer; Ezber, Yasemin; Çağlar, Ferat; Toker, Emir; Lutfi Sen, Omer

Abstract

Subtropical areas are sensitive climate transition regions that are affected by atmospheric oscillations linked to tropical heat sources and the stratosphere. In South America, we hypothesise that the quasi-biennial oscillation (QBO) is related to large-scale climate variability linked to hotter and wetter subtropical areas. From the US National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis, the QBO is quantified using the westerly phase based on the 30mb averaged zonal wind at the equator. Results show that the westerly phase of QBO would slow down the jet stream in the subtropical regions of the Southern Hemisphere. Higher pressure in subtropical areas of South America is linked to higher local temperatures in the region. These patterns could be related to the dipole of sea level pressure anomalies at the southernmost reaches of the South American continent. However, there are more subtle spatial variations related to the QBO over subtropical regions, when the convective-permitting model (CPM) simulation between 2001 and 2017 from the NCAR South American Affinity Group (SAAG) is investigated.

For the Convective-Permitting Model simulations, the deep convection parameterisation is switched off at a 4km scale. Although the Buenos Aires side of the Paraná River outlet has a positive 3-month leading relationship between the westerly phase of QBO and the local temperature, the deseasonalised temperature time series inside the Uruguay basin has a significant negative relationship with the QBO. Based on scaling relationships from a spectrum analysis, the effects of the Southern Annular Mode (SAM) and El Niño–Southern Oscillation (ENSO) on temperature time series of Convective-Permitting Model simulations are further explored.

Overall, the QBO effects would have critical implications for changing atmospheric temperature and moisture conditions in the South American tropical areas. It is worthwhile to further investigate how the expanding Hadley cell related to a warning atmosphere would affect specific humidity and temperature in the regions because of the circulation of the stratosphere. A framework is proposed to study how changing atmospheric temperature and moisture due to the QBO effect would shift regional potential vegetation stress.

• Presentation Conference Type: Presentation / Talk
• Conference Name: Advancing Subtropical Climate Dynamics: Diagonal Convergence Zones, Droughts, and Floods in Past, Present and Future Climates
• Start Date: Aug 1, 2022
• End Date: Aug 5, 2022
• Deposit Date: Aug 19, 2022
• Publicly Available Date: Aug 22, 2022
• Keywords: Extremes; Climatology; Turbulence; Quasi-Biennial Oscillation (QBO); air-sea interaction; heatwaves
• Public URL: https://uwe-repository.worktribe.com/output/9890146
• Publisher URL: https://indico.ictp.it/event/9771/speakers