Meridional movement of geopotential height anomalies in the subtropics and the relationship to the base‐state flow

Abstract

Qualities of the meridional movements of geopotential height anomalies in the upper troposphere of the subtropics are analysed via wavelet analysis using a meridional–temporal partial Morlet wavelet. Results show that power, which represents increased presence or amplitude of waves with direct meridional movement, is increased in regions where the corresponding equatorial winds in the upper troposphere are westerly or weakly easterly. Furthermore, equatorward power is enhanced near subtropical jet exit regions whereas poleward power is enhanced in jet entrance regions. Regressions of upper‐tropospheric winds, geopotential height, and outgoing long‐wave radiation (OLR) against the wavelet transforms demonstrate that the wavelets are identifying signals with tropical–extratropical interactions that are connected to organized convection in the tropics. The relationship of power with background‐state flow characteristics, including the horizontal winds and shear, are evaluated. Instead of the zonal wind and meridional shear of the zonal wind (du/dy), both the meridional wind and the zonal shear of the meridional wind (dv/dx) appear to have a clearer relationship with the power. Power is favoured for waves whose movement is aligned in the same direction as the meridional wind, and reduced in the opposite direction. Additionally, power increases with increasing zonal shear of the meridional wind in the Northern Hemisphere and with decreasing zonal shear of the meridional wind in the Southern Hemisphere. Power in the equatorward direction is stronger than in the poleward direction and more heavily influenced by background flow characteristics. Furthermore, power for wavelets with smaller meridional and temporal scales tends to have a higher sensitivity to the background horizontal flow as compared to larger meridional and temporal scales.

Quasi‐biennial oscillation impacts on Madden–Julianoscillation‐associatedtropical–extratropical interactions and Kelvin waves

“…Since Rossby waves moving toward the Equator also impact MJO‐associated circulations in the Western Hemisphere and proximate to Africa (e.g. Roundy, 2014; Sakaeda and Roundy, 2015; Gahtan and Roundy, 2020; 2021), the QBO may also impact the evolution of the Rossby wave component of the MJO's response pattern that propagates back into the tropics. This extratropical Rossby wave radiation back into the tropics may be relevant for the translation of the MJO signal around the world to initiate secondary events (e.g.…”