Eastern Pacific Emitted Aerosol Cloud Experiment

Abstract

Aerosol–cloud–radiation interactions are widely held to be the largest single source of uncertainty in climate model projections of future radiative forcing due to increasing anthropogenic emissions. The underlying causes of this uncertainty among modeled predictions of climate are the gaps in our fundamental understanding of cloud processes. There has been significant progress with both observations and models in addressing these important questions but quantifying them correctly is nontrivial, thus limiting our ability to represent them in global climate models. The Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE) 2011 was a targeted aircraft campaign with embedded modeling studies, using the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft and the research vessel Point Sur in July and August 2011 off the central coast of California, with a full payload of instruments to measure particle and cloud number, mass, composition, and water uptake distributions. EPEACE used three emitted particle sources to separate particle-induced feedbacks from dynamical variability, namely 1) shipboard smoke-generated particles with 0.05–1-μm diameters (which produced tracks measured by satellite and had drop composition characteristic of organic smoke), 2) combustion particles from container ships with 0.05–0.2-μm diameters (which were measured in a variety of conditions with droplets containing both organic and sulfate components), and 3) aircraft-based milled salt particles with 3–5-μm diameters (which showed enhanced drizzle rates in some clouds). The aircraft observations were consistent with past large-eddy simulations of deeper clouds in ship tracks and aerosol– cloud parcel modeling of cloud drop number and composition, providing quantitative constraints on aerosol effects on warm-cloud microphysics.

Precipitation susceptibility in marine stratocumulus and shallow cumulus from airborne measurements

“…E-PEACE included sampling controlled releases of (i) smoke from the deck of the research vessel Point Sur, and (ii) salt aerosol from the TO research aircraft, along with sampling (iii) exhaust from container ships transiting across the study area (see Fig. 2 from Russell et al, 2013). During 9 out of 30 E-PEACE flights, salt powder (diameter of 1-10 µm) was directly introduced into the cloud decks to examine the effects of giant cloud condensation nuclei (GCCN) on the initiation of warm precipitation (Jung et al, 2015).…”

Sources of nitrate in stratocumulus cloud water: Airborne measurements during the 2011 E-PEACE and 2013 NiCE studies

“…A general overview of the E-PEACE campaign is provided by Russell et al (2013). The present study is primarily based on measurements made during NiCE; however, data from E-PEACE are included to provide additional statistics and thus more confidence for a subset of the results.…”

Precipitation effects of giant cloud condensation nuclei artificially introduced into stratocumulus clouds

“…The data used in this study were obtained from the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIR-PAS) Twin Otter (TO) aircraft that was flown in support of the Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE, 2011), which took place off the central coast of California during July and August 2011 (Russell et al, 2013). The CIRPAS TO research aircraft was instrumented with (1) three in situ probes that characterize aerosol, clouds, and precipitation size distributions, (2) standard meteorological instruments that measure the atmospheric thermodynamic and wind structures, and (3) an upward-facing frequency modulated continuous wave (FMCW) cloud radar.…”

“…were acquired at both 1 and 10 Hz resolutions. For detailed information on the probes and the cloud radar used in this study, see Russell et al (2013), and Table 1 and Fig. 1 of Jung and Albrecht (2014).…”