Recent Airborne Doppler Wind Lidar Investigations of OLEs over the Marine Atmospheric Boundary Layer off the Coast of Central California

Since 2000, Simpson Weather Associates (SWA), along with Office of Naval Research (ONR), have flown the Twin Otter Doppler Wind Lidar (TODWL) on board a Naval Post Graduate School/CIRPAS Twin Otter aircraft off the coast of central and southern California to, in part, investigate the wind field and circulations within the Marine Atmospheric Boundary Layer (MABL). During numerous missions and campaigns mainly based out of Monterey, CA, over 250 research flight hours have been flown with a particular emphasis on characterizing and defining winds in the surface layer, coastal jets and Organized Large Eddies (OLEs). Most recently, the TODWL was flown in 2018 off the coast of central California as well as in in 2022 over the Santa Barbara Channel in support of the NSF/NCAR funded Sundowner Wind Experiment (SWEX).

The TODWL is a 2 micron coherent lidar system with a bi-axis scanner operating at 500 MHz and has the ability to take measurements above and below the flight level. The laser beam of TODWL can be adaptively (in flight) directed in a variety of scan patterns including conical scans for vector wind profiles as well as both nadir stares and flight level stares. These last two scanning strategies can provide single shot and line of sight (LOS) winds and SNR (surrogate for aerosol concentrations) as well as turbulence and vertical velocity estimations. Using a sliding range gate technique in the processing of this data, we are able to achieve 25-50 meter resolution along the LOS.

These latter products are key in helping us to describe and characterize organized rolls or OLEs within the MABL which are important for the transport and redistribution of heat and momentum in the lower MABL. Radar and satellite-based SAR are most often used to detect the presence and provide information on the orientation of OLE circulations but the airborne TODWL provides much higher horizontal and vertical resolution measurements of the wind and aerosol fields over extended flight legs. We will present results from the analysis of the two recent campaigns as well as original analysis of TODWL data collected previously in 2003 and 2007. From the analysis of these data, we will show the ubiquitous nature of these OLEs under certain synoptic conditions and detail the alignment, slope, life cycle and dimensions of these MABL OLEs through case study analyses and the generation of composite Probability Density Functions (PDF). Some of these results confirm what has previously been shown in the literature regarding MABL OLEs while, in other cases, they show features and orientations that differ somewhat from what has previously been described.