A035-0001
Airborne High Spectral Resolution Lidar-2 Measurements of Enhanced Depolarization in Marine Aerosols

Tuesday, 8 December 2020
Poster
Richard Anthony Ferrare1, Johnathan W Hair1, Chris A Hostetler1, David B Harper1, Shane T Seaman1, Taylor J Shingler1, Marta A Fenn2, Amy Jo Scarino3, Sharon P Burton1, Anthony L Cook1, Mark Vaughan1, Hongyu Liu4, Bo Zhang4, Glenn S Diskin5, Paquita Zuidema6, Seethala Chellappan6, Richard Moore1, Ewan Crosbie7, Luke D Ziemba1, Kenneth Lee Thornhill II1, Claire E Robinson7, Michael Shook1, Joseph Schlosser8 and Armin Sorooshian9, (1)NASA Langley Research Center, Hampton, VA, United States, (2)SSAI, Hampton, VA, United States, (3)Science Systems and Applications Inc., Hampton, VA, United States, (4)National Institute of Aerospace, Hampton, VA, United States, (5)NASA Langley Research Ctr, Hampton, VA, United States, (6)University of Miami, Miami, FL, United States, (7)Science Systems and Applications, Inc., Hampton, VA, United States, (8)University of Arizona, Chemical and Environmental Engineering, Tucson, AZ, United States, (9)University of Arizona, Department of Chemical and Environmental Engineering, Tucson, AZ, United States
Abstract:
Airborne NASA Langley Research Center (LaRC) High Spectral Resolution Lidar‑2 (HSRL‑2) measurements acquired during the recent NASA EVS-3 Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE) revealed enhanced particulate linear depolarization associated with aerosols within the marine boundary layer. These HSRL‑2 observations were acquired off the east coast of the United States in February and March 2020 when this lidar was deployed on the NASA LaRC UC-12 aircraft. HSRL-2 measured profiles of aerosol backscattering, extinction, and depolarization at 355 and 532 nm and aerosol backscattering and depolarization at 1064 nm.

Typically HSRL-2 measures low (<5%) linear particulate depolarization associated with marine sea salt aerosols. However, during several ACTIVATE flights, particularly those that occurred with outbreaks of cold, dry air, linear particulate depolarization exceeded 15-20% (532 nm) for aerosols within a few hundred meters above the surface. These high values indicated that these particles were nonspherical. Elevated depolarization values were also observed at 355 and 1064 nm. HSRL-2 measured aerosol extinction/backscatter ratio (“lidar ratio”) values around 20-25 sr (355 and 532 nm) that are typically associated with sea salt particles. Coincident measurements of relative humidity from dropsondes released from the UC-12 and in situ Diode Laser Hygrometer (DLH) measurements flown on the NASA HU-25 aircraft showed that highest depolarization values of these nonspherical particles were found when the relative humidity (RH) was below 50-60%. These lidar observations of elevated depolarization associated with sea salt aerosol are consistent with previous lidar measurements of sea salt aerosols in dry conditions. We discuss these HSRL-2 measurements also in the context of coincident airborne in situ measurements of particle size and composition acquired on the HU-25 aircraft.

We also found that CALIOP satellite measurements observed elevated depolarization during some similar cold air outbreaks. In such cases, the operational CALIOP algorithms attributed the elevated depolarization to nonspherical dust particles rather than the more likely scenario of nonspherical sea salt particles associated with low RH.

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