A Brief Climatology of Doppler Lidar Derived Mixed Layer Heights over Indianapolis

Quantification of the mixing layer is crucial for understanding the dispersion of pollutants and trace gases throughout the atmosphere.  However, it is difficult to obtain continuous and reliable estimates of the mixing height during all times of day from a single instrument. Vertically oriented backscatter lidars are not able to measure shallow mixing depths due to minimum range issues.  Additionally, these lidars may not be able to distinguish a residual layer from a mixed layer.  Radiosondes often provide reliable estimates of the mixing height during convective conditions, but they only provide a snapshot of the environment at the time of launch.  Scanning Doppler lidars show promise in being able to provide continuous automated estimates of the mixing depth, but there are challenges to making an accurate measurement.  From these observations, long-term statistics of the evolution of the mixing depth during different seasons can be made.

Herein, we present statistics of the mixing height as observed in the Indianapolis area during the Indianapolis Flux Experiment (INFLUX).  At this site, a scanning Doppler lidar has been operational for the majority of 3+ years, since spring 2013.  The mixing height is automatically identified every 20 minutes using a fuzzy logic technique, which will be briefly described.  For verification, Doppler lidar derived mixing heights will be compared with in situ observations from aircraft and other instrumentation. Additionally, the relationship between the diurnal mixing height and the large-scale weather conditions and mean wind speed will be discussed. Statistics of the mixing depth during different seasons will also be presented, which are useful for understanding air quality and interpreting surface based trace gas measurements in the larger context of the INFLUX project.