Identifying the Deep‐Inflow Mixing Features in Orographically‐Locked Diurnal Convection

• Published in: Geophysical research letters Vol. 50; no. 10
• Main Authors: Chang, Yu‐Hung, Chen, Wei‐Ting, Wu, Chien‐Ming, Kuo, Yi‐Hung, Neelin, J. David
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.05.2023; Wiley
• Subjects: Air mass transport; Air masses; Atmospheric circulation; Circulation; Columns (structural); Convection; Convective development; deep inflow; Diurnal; diurnal convection; Energy; Energy transfer; Energy transport; Height; Hot spots; Inflow; Large eddy simulation; Locking features; Lower atmosphere; Mass flux; Mass transport; Moist static energy; moist static energy transport; orographic locking; Orographic precipitation; Precipitation; Radiosondes; Simulation; Storm tracks; Storms; Summer circulation; TaiwanVVM; Updraft; Upstream; Taiwan
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL103107

Orographically‐locked diurnal convection involves interactions between local circulation and the thermodynamic environment of convection. Here, the relationships of convective updraft structures over orographic precipitation hotspots and their upstream environment in the TaiwanVVM large‐eddy simulations are analyzed for the occurrence of the orographic locking features. Strong convective updraft columns within heavily precipitating, organized systems exhibit a mass flux profile gradually increasing with height through a deep lower‐tropospheric inflow layer. Enhanced convective development is associated with higher upstream moist static energy (MSE) transport through this deep‐inflow layer via local circulation, augmenting the rain rate by 36% in precipitation hotspots. The simulations provide practical guidance for targeted observations within the most common deep‐inflow path. Preliminary field measurements support the presence of high MSE transport within the deep‐inflow layer when organized convection occurs at the hotspot. Orographically‐locked convection facilitate both modeling and field campaign design to examine the general properties of active deep convection. Plain Language Summary Under the weather regime that favors the development of local circulation in summer, diurnal convection occurs over specific areas of Taiwan. To investigate this orographic locking feature of diurnal convection, we performed a set of simulations with realistic complex Taiwan topography by TaiwanVVM and initiated with radiosonde observations to represent the variability of the background environment. In the simulations, strong updrafts are identified for orographically‐locked diurnal convection over precipitation hotspots. The vertical air mass transport of heavily‐precipitating updrafts increases with height throughout the lower atmosphere, implying a lateral inflow. The analysis of local circulation confirms the presence of the inflow layer, enhancing the development of orographically‐locked diurnal convection via rich energy transport from upstream. A field campaign, guided by the simulations, released the Storm Tracker mini‐radiosondes to quantify the upstream environment of the most common deep‐inflow path on 26 August 2022. The initial analysis supports the existence of high energy transport within the inflow layer when diurnal convection occurs over the precipitation hotspot. The results highlight the importance of non‐local inflow, transporting energy through the local circulation to supply the growth of orographically‐locked diurnal convection. Key Points In TaiwanVVM simulations, the convective updraft structure of orographically‐locked diurnal convection exhibits a deep layer of inflow The terrain‐constrained path of coherent inflow layer by local circulation augments convection development over the precipitation hotspots Initial field observations guided by TaiwanVVM detect high moist static energy transport upstream of the precipitation hotspots