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

How do Asian Highlands Affect Phase-Preferred Rossby Waves and Related Heat Extremes?

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

Large-scale topography is thought to cause the phase preference of quasi-stationary Rossby waves (QSWs), which are closely linked with mid-latitude weather extremes. However, this causality remains inconclusive. Therefore, this study examines how the Asian highlands, particularly the Tibetan–Iranian Plateau (TIP), affect QSWs and related summer heat extremes through climate model simulations and recently proposed complex network analysis. The simulation results indicate that removing TIP or its thermal forcing slightly alters the strength of QSWs' phase preference but does not eliminate it. Additionally, the preferred phase of low wavenumber waves (3, 4, and 5) shifts significantly when TIP or its thermal forcing is removed, while the preferred phase of higher 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 related to wave–5 are zonally displaced when TIP or its thermal forcing is removed, while those linked to wave–6 remain unaffected. Furthermore, a complex network of concurrent daily heat extremes across four mid-latitude regions affected by wave–6 (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 TIP's mechanical effect (comparing the removing-TIP-thermal experiment with the removing-TIP experiment). These responses of concurrent heat extremes are effectively understood from the perspective of wave packets.