Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Impact of synoptic scale processes on boundary layer depth variability over an arid region using Radiosonde and Lidar observations

Auteur : Anand, Michael Andrew

Université de soutenance : Texas Tech University

Grade : Master of Science (MS) 2022

Résumé partiel
Understanding of the atmospheric boundary layer (ABL) thermodynamics and ABL depths (zi) is critical for a wide range of applications including weather forecasting, wind energy, aviation, and air quality and transport models and associated studies on turbulence mixing of tracers and greenhouse gases. ABL dynamics under advection over arid regions remained underexplored though critical for rapidly warming climate of 21st century. Additionally, obtaining some comprehensive details on the impact of horizontal advection on ABL is also important as the ABL undergoes substantial dynamic changes during advective processes (e.g., frontal passages). Most NWP models strictly rely on ABL parameterization schemes under steady-state assumptions while the empirical studies also consider horizontally homogeneous atmospheric conditions for estimating ABL depth (zi) growth rates. Under advective processes numerical models of ABL thermodynamic state suffer from two limitations : (1) the modelled vertical profiles of thermodynamic parameters are influenced by advection and (2) the parameterization schemes that diagnose zi are not fully accurate due to the fact that schemes are based on steady-state assumptions. Within this work, we explored how synoptic events impact daytime zi variability in different seasons over an arid region (here, three sites in West Texas : Lubbock, Amarillo, and Midland) by using radiosonde-derived thermodynamic profiles during more than 20 synoptic events and ground-based Doppler lidar measurements within two case studies (a cold front passage and a dryline passage over Lubbock). Additionally, all the cases for radiosonde based analyses were further classified into four categories, cases with only : (1) elevated mixed layer, (2) dryline (3) elevated mixed layer and dryline and (4) no elevated mixed layer and dryline. Results suggest that zi decreases substantially during frontal passages yielding shallower zi in the cold sector than the warm sector. We also found that zi in the post-frontal airmass remained more uniform throughout the year compared to the zi in the prefrontal airmass indicating a clearer zi seasonal cycle pattern in the warm sector and the impact of airmass advection on zi variability

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