Preprints
https://doi.org/10.5194/egusphere-2024-392
https://doi.org/10.5194/egusphere-2024-392
20 Feb 2024
 | 20 Feb 2024

Differences in aerosol and cloud properties along the central California coast when winds change from northerly to southerly

Kira Zeider, Grace Betito, Anthony Bucholtz, Peng Xian, Annette Walker, and Armin Sorooshian

Abstract. Wind reversals resulting in southerly flow along the California coast are not well understood in terms of how aerosol and cloud characteristics change. This gap is addressed using airborne field measurements enhanced with data from space-borne remote sensing (Moderate Resolution Imaging Spectroradiometer), surface stations (Interagency Monitoring of Protected Visual Environments), and models (Navy Aerosol Analysis and Prediction System and Coupled Ocean/Atmosphere Mesoscale Prediction System), with a focus on sub- and supermicron aerosol, and cloud microphysical variables: cloud droplet number concentration (Nd), cloud optical thickness (COT), and cloud droplet effective radius (re). Southerly flow coincided with higher values of submicron aerosol concentration (Na) and mass concentrations of species representative of fine aerosol pollution (NO3- and nss-SO42-) and shipping/continental emissions (V, oxalate, NH4+, Ni, OC, and EC). Supermicron Na did not change, however, heightened levels of acidic species in southerly flow coincided with reduced Cl-:Na+ suggestive of Cl- depletion in salt particles. Clouds responded correspondingly in southerly flow, with more acidic cloud water, higher levels of similar species as in the aerosol phase (e.g., NO3-, nss-SO42-, NH4+, V), along with elevated values of Nd and COT and reduced re during campaigns with similar cloud liquid water paths. Case study flights help to visualize offshore pollution gradients and highlight the sensitivity of the results to the presence of widespread smoke coverage including how associated plumes have enhanced supermicron Na. These results have implications for aerosol-cloud interactions during wind reversals, and have relevance for weather, public welfare, and aviation.

Kira Zeider, Grace Betito, Anthony Bucholtz, Peng Xian, Annette Walker, and Armin Sorooshian

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-392', Mikael Witte, 29 Mar 2024
  • RC2: 'Comment on egusphere-2024-392', Zachary Lebo, 01 Apr 2024
Kira Zeider, Grace Betito, Anthony Bucholtz, Peng Xian, Annette Walker, and Armin Sorooshian
Kira Zeider, Grace Betito, Anthony Bucholtz, Peng Xian, Annette Walker, and Armin Sorooshian

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Short summary
The predominant wind direction along the California coast (northerly) reverses several times during the summer (to southerly). The effects of these wind reversals on aerosol and cloud characteristics are not well understood. Using data from multiple datasets we found that southerly flow periods had enhanced signatures of anthropogenic emissions due to shipping/continental sources, and clouds had more but smaller droplets.