560 / 2024-09-18 13:07:00

Impact of the Tibetan-Iranian Plateau on Phase-Preferred Rossby Waves and Related Heat Extremes

Rossby waves,Tibetan-Iranian Plateau,Weather extremes,Numerical experiment

Session 4 - Extreme Weather and Climate Events: Observations and Modeling

The large-scale topography, such as the Tibetan-Iranian Plateau (TIP), has been suggested to cause the phase preference of high-amplitude quasi-stationary Rossby waves (QSWs), which are strongly linked with mid-latitude weather extremes. However, this causal relationship remains inconclusive. Therefore, this study employs a more realistic climate model to explore how removing TIP or its thermal forcing affects QSWs and associated heat extremes in summer. The results indicate that removing TIP or its thermal forcing slightly alters the extent of QSWs’ phase preference but does not eliminate it. Additionally, the phase preferred by small wavenumber waves (3, 4, and 5) shifts significantly when removing TIP or its thermal forcing, while the phase preferred by larger wavenumber waves (6, 7, and 8) remains nearly unchanged. During weeks dominated by phase-preferred and high-amplitude wave–5 or wave–6—the two strongest components of mid-latitude QSWs—significant surface air temperature maxima are observed in association with upper-level anticyclones. Temperature maxima are zonally displaced in accordance with the changed phase of wave–5 when TIP or its thermal forcing is removed, but maxima related to wave–6 are unaffected by TIP. Furthermore, a complex network analysis of concurrent daily heat extremes in four midlatitude regions affected by wave–6 anticyclones (Europe, central Eurasia, eastern Asia, and North America) reveals that, heat extremes concurrence intensifies with TIP’s thermal effect (comparing the control run with the removing-TIP-thermal experiment) but diminishes with its mechanical effect (comparing the removing-TIP-thermal experiment with the removing-TIP experiment).