[A-AS04] Evolution of Global Environmental Research based on Atmospheric Vertical Motions

[AAS04-03] The Opportunity to Investigate the Atmospheric Vertical Motion From Diurnal Convection over Complex Topography of Tropical Mountainous Islands

*Wei-Ting Chen¹ (1.National Taiwan University)

Keywords:diurnal convection, complex topography, local circulation, orographically-locked convection

Diurnal convection is the dominant mode of precipitation variability over tropical islands. In a convectively suppressed large-scale environment, the active development of land-sea and mountain-valley breezes and boundary layer dynamics over complex topography significantly modulate the initiation and organization of convective systems, resulting in distinct occurrence hotspots. In this presentation, we will demonstrate how these orographically locked diurnal convective systems provide a valuable opportunity to study the key processes modulating atmospheric vertical motion. Using large eddy simulations (LES) with the Vector Vorticity Equation cloud-resolving Model (VVM) over an idealized ocean-plain-mountain terrain configuration, we identified multiple precipitation peaks within the diurnal cycle of mountain-locked convection, a feature supported by long-term ground observations in the southwestern mountains of Taiwan. While the first precipitation peak is sensitive to the initial environmental CAPE, the second peak, involving more organized convection and a higher probability of extreme rainfall, is significantly modulated by the MSE transport of local circulation. Differences in the mechanisms and convection-environment interactions lead to opposite responses to initial mid-level ambient moisture between the two peaks—the second peak strengthens in an initially drier environment. Furthermore, pseudo-global warming experiments using the semi-realistic TaiwanVVM LES with Taiwan's realistic topography revealed the expansion and intensification of orographically locked convection in the southwestern foothills of Taiwan, with cold pool-related processes playing a key role in this response. High-resolution simulations and high-frequency in situ observations over the Taipei Basin also indicate that cold pool-sea breeze interactions and cold pool-cold pool collisions can significantly influence the location of convection initiation and propagation, resulting in high sensitivity of afternoon convection in the Taipei Basin to low-level background wind direction. Based on these findings, we propose a strategy that combines LES, high-resolution ground observations, and satellite observations, particularly from EarthCARE, to study the vertical motion associated with orographically locked diurnal convection.