Abstract
Abstract. The NASA Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) project included goals related to aerosol particle life cycle 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 12 August 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 planetary boundary layer 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 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.
Highlights
IntroductionMuch of the focus of aerosol–cloud radiation studies (i.e., the first indirect effect) has been on either planetary boundary layer (PBL) Stratocumulus (Sc) or Cumulus clouds (Cu, e.g., Twomey et al, 1977 and many subsequent citations) or the injection of aerosol particles and their precursors into the upper troposphere and lower stratosphere by deep precipitating convection from Cumulonimbus (Cb, e.g., Pueschel et al, 1997; Kulmala et al, 2004; Waddicor et al, 2012; Saleeby et al, 2016), pyro-convection (e.g., Fromm et al, 2008, 2010; Lindsay and Fromm, 2008) and volcanic activity (e.g., Jensen and Toon, 1992; DeMott et al, 1997; Amman et al, 2003)
Water vapor and wind levels included from the 12 August, 18:40 UTC, SEACIONS radiosonde release are further provided in Fig. 3a, b and c respectively and High Spectral Resolution Lidar (HSRL)
Alto stratus (As) the storms later passed over Huntsville, observations collected by the DC-8 provided context for the UW HSRL lidar observations described in Sect
Summary
Much of the focus of aerosol–cloud radiation studies (i.e., the first indirect effect) has been on either planetary boundary layer (PBL) Stratocumulus (Sc) or Cumulus clouds (Cu, e.g., Twomey et al, 1977 and many subsequent citations) or the injection of aerosol particles and their precursors into the upper troposphere and lower stratosphere by deep precipitating convection from Cumulonimbus (Cb, e.g., Pueschel et al, 1997; Kulmala et al, 2004; Waddicor et al, 2012; Saleeby et al, 2016), pyro-convection (e.g., Fromm et al, 2008, 2010; Lindsay and Fromm, 2008) and volcanic activity (e.g., Jensen and Toon, 1992; DeMott et al, 1997; Amman et al, 2003). The above authors and others (e.g., Gedzelman, 1988) note these cloud types receive comparatively little attention in the scientific community relative to their importance. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and CloudSat retrievals attribute to Ac as much as 30 % area coverage in Southeast Asia and the summertime eastern continental United States (e.g., Zhang et al, 2010, 2014; Sassen and Wang, 2012). This is in agreement with observer-based cloud climatologies (e.g., Warren et al, 1986, 1988)
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