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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Mar 2019

Research article | 13 Mar 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Observations and hypotheses related to low to middle free tropospheric aerosol, water vapor and altocumulus cloud layers within convective weather regimes: A SEAC4RS case study

Jeffrey S. Reid1, Derek J. Posselt2, Kathleen Kaku3, Robert A. Holz4, Gao Chen5, Edwin W. Eloranta4, Ralph E. Kuehn4, Sarah Woods6, Jianglong Zhang7, Bruce Anderson5, T. Paul Bui8, Glenn S. Diskin5, Patrick Minnis5, Michael J. Newchurch9, Simone Tanelli2, Charles R. Trepte5, K. Lee Thonrhill5, and Luke D. Ziemba5 Jeffrey S. Reid et al.
  • 1US Naval Research Laboratory, Marine Meteorology Division Monterey CA
  • 2Jet Propulsion Laboratory, Pasadena CA
  • 3General Dynamics, Naval Research Laboratory, Monterey CA
  • 4Space Sciences Engineering Center, University of Wisconsin, Madison WI
  • 5NASA Langley Research Center, Science Directorate, Hampton VA
  • 6SPEC Inc. Boulder CO
  • 7University of North Dakota, Grand Forks, ND
  • 8NASA Ames Research Center, Mountain View, CA
  • 9Atmospheric Science Department, University of Alabama in Huntsville, Huntsville, AL

Abstract. The NASA Studies of Emissions & Atmospheric Composition, Clouds & Climate Coupling by Regional Surveys (SEAC4RS) project included goals related to aerosol particle lifecycle in convective regimes. Using the University of Wisconsin High Spectral Resolution Lidar system at Huntsville, Alabama USA and the NASA DC-8 research aircraft, we investigate the altitude dependence of aerosol, water vapor and Altocumulus (Ac) properties in the free troposphere from a canonical August 12, 2013 convective storm case as a segue to a presentation of a mission wide analysis. It stands to reason that any moisture detrainment from convection must have an associated aerosol layer. Modes of covariability between aerosol, water vapor and Ac are examined relative to the boundary layer entrainment zone, 0 °C level, and anvil, a region known to contain Ac clouds and a complex aerosol layering structure (Reid et al., 2017). Multiple aerosol layers in regions warmer than 0 °C were observed within the PBL entrainment zone. At 0 °C there is a proclivity for aerosol and water vapor detrainment from storms, in association with melting level Ac shelves. Finally, at temperatures colder than 0 °C, weak aerosol layers were identified above Cumulus congestus tops (~0 °C and ~ 20 °C). Stronger aerosol signals return in association with anvil outflow. In situ data suggest that detraining particles undergo aqueous phase or heterogeneous chemical or microphysical transformations, while at the same time larger particles are being scavenged at higher altitudes leading to enhanced nucleation. We conclude by discussing hypotheses regarding links to aerosol emissions and potential indirect effects on Ac clouds.

Jeffrey S. Reid et al.
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Jeffrey S. Reid et al.
Jeffrey S. Reid et al.
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Publications Copernicus
Short summary
New highly sensitive lidar systems demonstrate complex but faint aerosol features associated with altocumulus clouds in the middle free troposphere. Such aerosol layers formed in convective outflow are explored. Using the NASA SEAC4RS mission airborne dataset, free tropospheric layers are shown to have strong relationships to mid-level tropospheric clouds, an important but difficult-to-model or monitor cloud regime for climate studies.
New highly sensitive lidar systems demonstrate complex but faint aerosol features associated...