Challenges in Measurement and Interpretation of the Lidar-retrieved Aerosol Vertical Turbulent Mass Fluxes

NICHOLAS MESKHIDZE, Ajmal Rasheeda Satheesh, Markus Petters, NC State University

     Abstract Number: 333
     Working Group: Instrumentation and Methods

Abstract
Vertical turbulent mass fluxes of particles measured using tall masts and balloon measurements have been used to study the tight coupling between aerosol microphysics and convection. Although such measurements have proven to be valuable for particle concentration and surface-layer meteorological research, mast measurements often raise the issue of representativeness for the broader region of interest (limited spatial extent) while balloons get deployed over shorter periods (limited temporal scope). Active remote sensing can overcome some of the shortcomings of mast and balloon measurements. Active sensors such as lidars and radars can retrieve information on vertical velocity, aerosol extinction and backscatter, linear depolarization ratio, backscatter color ratio, etc. with a spatial and temporal resolution required for the flux measurement. However, interpreting aerosol turbulent fluxes in the atmosphere is challenging as it requires accurate and comprehensive characterization of the boundary layer structure, aerosols, mixing mechanisms, clouds, and vertical profiles of humidity. In this study, using the data collected at the DOE Atmospheric Radiation Measurement Southern Great Plains site in Oklahoma in 2020, we discuss some of the difficulties and offer potential solutions for the interpretation of aerosol vertical turbulent mass fluxes retrieved using Doppler lidar and high spectral resolution lidar. The topics discussed are statistical stationarity, horizontal homogeneity, and ergodicity of the aerosol field (i.e., the fundamental principles of Reynolds decomposition), identification of convective turbulent regions in the boundary layer, eddy covariance and relaxed eddy accumulation techniques of flux measurement, conversion of attenuated backscatter to backscatter and the effect of relative humidity on the aerosol lidar ratio, systematic and random uncertainties (e.g., the integral time scale of turbulence and the instrument level of detection), the frequency response of the instrument and the flux averaging time. We hope our presentation will spark a discussion on potential limitations and best practices of remote sensing applications for aerosol mass flux retrievals.