A Case Study of Lid Evolution Using Analyses of Observational Data and a Numerical Model Simulation

Abstract

A case of lid formation and evolution over the southern Great Plains during early spring is analyzed using conventional data analysis and a 120-h simulation from the Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model, Version 4 (MM4). The authors begin with a brief discussion of the evolution of the synoptic-scale circulation during the different phases of the lid development cycle in this case and follow with a description of MM4 as it was configured for this study. The model results are then used to supplement the data analyses in an examination of how the synoptic-scale circulation evolves and how it influences the physical and dynamical processes acting on the elevated mixed layer (EML) and low-level moist-layer source regions of the North American plateau and the Gulf of Mexico, respectively. The importance of choosing an appropriately large model domain and long simulation period in order to document properly the sequence of events, focusing primarily on the precursors to, and genesis of, the lid environment is stressed. The 120-h simulation allows one to focus on the ways in which synoptic and mesoscale processes interact to produce the observed mesoscale lid features such as inversions, moist layers, and EMLs over Texas, Oklahoma, and the adjacent coastal region.