A Study of the Impact of PECAN Field Campaign Observations on the Numerical Prediction of Nocturnal Convection Initiation using a GSI-Based Ensemble Data Assimilation System

While convection initiation (CI) in well-mixed, daytime boundary layers is moderately well-understood, the initiation of new convection at night is relatively unexplored. Since both the thermodynamic environments and the dynamic forcing mechanisms responsible for producing convection are fundamentally different after sunset, the impacts of storm-scale data assimilation cannot be assumed to be the same between night and day. The Plains Elevated Convection at Night (PECAN) field project provided a unique observation set related to nocturnal convection, including high-frequency thermodynamic and kinematic profilers, mobile surface observations, and aircraft observations. The assimilation of this dataset can aid in analyses of key nocturnal features that are not easily observed by conventional observations.

This study applies a GSI-based EnKF data assimilation system to multiple nocturnal CI events to determine the impact of assimilating PECAN observations. A successful forecast of CI timing, location, and orientation for a 26 June 2015 event was only achieved by assimilating all available PECAN observations. Improvements in elevated moisture layers by both the Atmospheric Emitted Radiance Interferometer (AERI) and mobile surface observations enhanced parcel buoyancy, while Doppler LIDAR and radio wind profilers strengthened convergence near the terminus of the nocturnal low-level jet (LLJ). These results indicate that even a small network of profilers can improve forecasts of severe convective events. Findings that will be presented at the conference include data denial experiments for each PECAN observation type, as well as an analysis of the physical mechanisms responsible for CI.