Title: Impacts of ENSO events on cloud radiative effects in preindustrial conditions: Changes in cloud fraction and their dependence on interactive aerosol emissions and concentrations

Abstract

The impacts of the El Niño–Southern Oscillation (ENSO) events on shortwave and longwave cloud radiative effects (CRE_SW and CRE_LW) and the underlying changes in cloud fraction as well as aerosol emissions, wet scavenging and transport are quantified using three 150-year simulations in preindustrial conditions by the CESM model. Compared to recent observations from Clouds and the Earth’s Radiant Energy System (CERES), the model simulation successfully reproduced larger variations of CRE_SW over the tropical western and central Pacific, Indonesian regions, and the eastern Pacific Ocean, as well as large variations of CRE_LW located mainly within the tropics. The ENSO cycle is found to dominate interannual variations of cloud radiative effects, especially over the tropics. Relative to those during La Niña events, simulated cooling (warming) effects from CRE_SW (CRE_LW) during El Niño events are stronger over the tropical western and central Pacific Ocean, with the largest difference exceeding 40 Wm^–2 (30 Wm^–2), with weaker effects of 10–30 Wm^–2 over Indonesian regions and the subtropical Pacific Ocean. Here, sensitivity tests show that variations of cloud radiative effects are mainly driven by ENSO-related changes in cloud fraction. The variations in medium and high cloud fractions each account for about 20–50% of the interannual variationsmore » of CRE_SW over the tropics and almost all of the variations of CRE_LW between 60°S and 60°N. The variation of low cloud fraction contributes most interannual variations of CRESW over the mid-latitude oceans. Variations in natural aerosol concentrations considering emissions, wet scavenging and transport explained 10–30% of the interannual variations of both CRE_SW and CRE_LW over the tropical Pacific, Indonesian regions and the tropical Indian Ocean. Changes in wet scavenging of natural aerosol modulate the variations of cloud radiative effects. Because of increased (decreased) precipitation over the tropical western Pacific Ocean in El Niño (La Niña) events, increased (decreased) wet scavenging of natural aerosols dampens more than 4–6% of variations of cloud radiative effects averaged over the tropics. In contrast, increased surface winds cause feedbacks that increase sea spray emissions that enhance the variations by 3–4% averaged over the tropics.« less

Authors:

Yang, Yang ^[1]; Russell, Lynn M. ^[2]; Xu, Li ^[2]; Lou, Sijia ^[2]; Lamjiri, Maryam A. ^[2]; Somerville, Richard C. J. ^[2]; Miller, Arthur J. ^[2]; Cayan, Daniel R. ^[2]; DeFlorio, Michael J. ^[2]; Ghan, Steven J.  ^[3];

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Liu, Ying ^[3]; Singh, Balwinder ^[3]; Wang, Hailong ^[3]; Yoon, Jin-Ho ^[4]; Rasch, Philip J. ^[3]

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+ Show Author Affiliations

1. Univ. of California, San Diego, La Jolla, CA (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Univ. of California, San Diego, La Jolla, CA (United States)
3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
4. Gwangju Inst. of Science and Technology, Gwangju (South Korea)

Publication Date:

Thu May 19 00:00:00 EDT 2016

Research Org.:

Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE; National Science Foundation (NSF)

OSTI Identifier:

1326147

Report Number(s):

PNNL-SA-113420
Journal ID: ISSN 2169-897X; KP1703010

Grant/Contract Number:  

AC05-76RL01830; AGS1048995; SC0006679

Resource Type:

Journal Article: Accepted Manuscript

Journal Name:

Journal of Geophysical Research: Atmospheres

Additional Journal Information:

Journal Volume: 121; Journal Issue: 11; Journal ID: ISSN 2169-897X

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; ENSO; cloud radiative effects; aerosol