Cloud adjustments from large-scale smoke–circulation interactions strongly modulate the southeastern Atlantic stratocumulus-to-cumulus transition
<p>Smoke from southern Africa blankets the southeastern Atlantic Ocean from June to October, producing strong and competing aerosol radiative effects. Smoke effects on the transition between overcast stratocumulus and scattered cumulus clouds are investigated along a Lagrangian (air-mass-follo...
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| Format: | Article |
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Copernicus Publications
2022-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/12113/2022/acp-22-12113-2022.pdf |
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| author | M. S. Diamond M. S. Diamond P. E. Saide P. E. Saide P. Zuidema A. S. Ackerman S. J. Doherty S. J. Doherty A. M. Fridlind H. Gordon C. Howes J. Kazil J. Kazil T. Yamaguchi T. Yamaguchi J. Zhang J. Zhang G. Feingold R. Wood |
| author_facet | M. S. Diamond M. S. Diamond P. E. Saide P. E. Saide P. Zuidema A. S. Ackerman S. J. Doherty S. J. Doherty A. M. Fridlind H. Gordon C. Howes J. Kazil J. Kazil T. Yamaguchi T. Yamaguchi J. Zhang J. Zhang G. Feingold R. Wood |
| author_sort | M. S. Diamond |
| collection | DOAJ |
| description | <p>Smoke from southern Africa blankets the southeastern Atlantic Ocean from June to October, producing strong and competing aerosol radiative effects.
Smoke effects on the transition between overcast stratocumulus and scattered
cumulus clouds are investigated along a Lagrangian (air-mass-following)
trajectory in regional climate and large eddy simulation models. Results are
compared with observations from three recent field campaigns that took place
in August 2017: ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES), CLouds and Aerosol Radiative Impacts and
Forcing: Year 2017 (CLARIFY), and Layered Atlantic Smoke Interactions with Clouds (LASIC). The case study is set up around the joint ORACLES–CLARIFY flight that took place near Ascension Island on 18 August 2017. Smoke sampled upstream on an ORACLES flight on 15 August 2017
likely entrained into the marine boundary layer later sampled during the
joint flight.</p>
<p>The case is first simulated with the WRF-CAM5 regional climate model in
three distinct setups: (1) FireOn, in which smoke emissions and any resulting
smoke–cloud–radiation interactions are included; (2) FireOff, in which no smoke emissions are included; (3) RadOff, in which smoke emissions and their microphysical effects are included but aerosol does not interact
directly with radiation. Over the course of the Lagrangian trajectory,
differences in free tropospheric thermodynamic properties between FireOn and
FireOff are nearly identical to those between FireOn and RadOff, showing
that aerosol–radiation interactions are primarily responsible for the free tropospheric effects. These effects are non-intuitive: in addition to the
expected heating within the core of the smoke plume, there is also a
“banding” effect of cooler temperature (<span class="inline-formula">∼1</span>–2 K) and greatly
enhanced moisture (<span class="inline-formula">>2</span> g kg<span class="inline-formula"><sup>−1</sup></span>) at the plume top. This banding effect is caused by a vertical displacement of the former continental boundary layer
in the free troposphere in the FireOn simulation resulting from anomalous
diabatic heating due to smoke absorption of sunlight that manifests
primarily as a few hundred meters per day reduction in large-scale subsidence over the ocean.</p>
<p>A large eddy simulation (LES) is then forced with free tropospheric fields
taken from the outputs for the WRF-CAM5 FireOn and FireOff runs. Cases are
run by selectively perturbing one variable (e.g., aerosol number
concentration, temperature, moisture, vertical velocity) at a time to better
understand the contributions from different indirect (microphysical),
“large-scale” semi-direct (above-cloud thermodynamic and subsidence
changes), and “local” semi-direct (below-cloud smoke absorption) effects.
Despite a more than 5-fold increase in cloud droplet number concentration when including smoke aerosol concentrations, minimal differences in cloud
fraction evolution are simulated by the LES when comparing the base case with a perturbed aerosol case with identical thermodynamic and dynamic forcings.
A factor of 2 decrease in background free tropospheric aerosol concentrations from the FireOff simulation shifts the cloud evolution from a
classical entrainment-driven “deepening–warming” transition to trade cumulus to a precipitation-driven “drizzle-depletion” transition to open cells,
however. The thermodynamic and dynamic changes caused by the WRF-simulated
large-scale adjustments to smoke diabatic heating strongly influence cloud
evolution in terms of both the rate of deepening (especially for changes in
the inversion temperature jump and in subsidence) and in cloud fraction on
the final day of the simulation (especially for the moisture “banding”
effect). Such large-scale semi-direct effects would not have been possible
to simulate using a small-domain LES model alone.</p> |
| first_indexed | 2024-04-11T09:51:24Z |
| format | Article |
| id | doaj.art-006a89bae3864b90818713ca6c0f4666 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-11T09:51:24Z |
| publishDate | 2022-09-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-006a89bae3864b90818713ca6c0f46662022-12-22T04:30:47ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242022-09-0122121131215110.5194/acp-22-12113-2022Cloud adjustments from large-scale smoke–circulation interactions strongly modulate the southeastern Atlantic stratocumulus-to-cumulus transitionM. S. Diamond0M. S. Diamond1P. E. Saide2P. E. Saide3P. Zuidema4A. S. Ackerman5S. J. Doherty6S. J. Doherty7A. M. Fridlind8H. Gordon9C. Howes10J. Kazil11J. Kazil12T. Yamaguchi13T. Yamaguchi14J. Zhang15J. Zhang16G. Feingold17R. Wood18Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USANOAA Chemical Sciences Laboratory (CSL), Boulder, CO, USADepartment of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, USAInstitute of the Environment and Sustainability, University of California, Los Angeles, CA, USARosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USANASA Goddard Institute for Space Studies, New York, NY, USACooperative Institute for Climate, Ocean and Ecosystem Studies, University of Washington, Seattle, WA, USADepartment of Atmospheric Sciences, University of Washington, Seattle, WA, USANASA Goddard Institute for Space Studies, New York, NY, USAEngineering Research Accelerator and Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, USADepartment of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, USACooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USANOAA Chemical Sciences Laboratory (CSL), Boulder, CO, USACooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USANOAA Chemical Sciences Laboratory (CSL), Boulder, CO, USACooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USANOAA Chemical Sciences Laboratory (CSL), Boulder, CO, USANOAA Chemical Sciences Laboratory (CSL), Boulder, CO, USADepartment of Atmospheric Sciences, University of Washington, Seattle, WA, USA<p>Smoke from southern Africa blankets the southeastern Atlantic Ocean from June to October, producing strong and competing aerosol radiative effects. Smoke effects on the transition between overcast stratocumulus and scattered cumulus clouds are investigated along a Lagrangian (air-mass-following) trajectory in regional climate and large eddy simulation models. Results are compared with observations from three recent field campaigns that took place in August 2017: ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES), CLouds and Aerosol Radiative Impacts and Forcing: Year 2017 (CLARIFY), and Layered Atlantic Smoke Interactions with Clouds (LASIC). The case study is set up around the joint ORACLES–CLARIFY flight that took place near Ascension Island on 18 August 2017. Smoke sampled upstream on an ORACLES flight on 15 August 2017 likely entrained into the marine boundary layer later sampled during the joint flight.</p> <p>The case is first simulated with the WRF-CAM5 regional climate model in three distinct setups: (1) FireOn, in which smoke emissions and any resulting smoke–cloud–radiation interactions are included; (2) FireOff, in which no smoke emissions are included; (3) RadOff, in which smoke emissions and their microphysical effects are included but aerosol does not interact directly with radiation. Over the course of the Lagrangian trajectory, differences in free tropospheric thermodynamic properties between FireOn and FireOff are nearly identical to those between FireOn and RadOff, showing that aerosol–radiation interactions are primarily responsible for the free tropospheric effects. These effects are non-intuitive: in addition to the expected heating within the core of the smoke plume, there is also a “banding” effect of cooler temperature (<span class="inline-formula">∼1</span>–2 K) and greatly enhanced moisture (<span class="inline-formula">>2</span> g kg<span class="inline-formula"><sup>−1</sup></span>) at the plume top. This banding effect is caused by a vertical displacement of the former continental boundary layer in the free troposphere in the FireOn simulation resulting from anomalous diabatic heating due to smoke absorption of sunlight that manifests primarily as a few hundred meters per day reduction in large-scale subsidence over the ocean.</p> <p>A large eddy simulation (LES) is then forced with free tropospheric fields taken from the outputs for the WRF-CAM5 FireOn and FireOff runs. Cases are run by selectively perturbing one variable (e.g., aerosol number concentration, temperature, moisture, vertical velocity) at a time to better understand the contributions from different indirect (microphysical), “large-scale” semi-direct (above-cloud thermodynamic and subsidence changes), and “local” semi-direct (below-cloud smoke absorption) effects. Despite a more than 5-fold increase in cloud droplet number concentration when including smoke aerosol concentrations, minimal differences in cloud fraction evolution are simulated by the LES when comparing the base case with a perturbed aerosol case with identical thermodynamic and dynamic forcings. A factor of 2 decrease in background free tropospheric aerosol concentrations from the FireOff simulation shifts the cloud evolution from a classical entrainment-driven “deepening–warming” transition to trade cumulus to a precipitation-driven “drizzle-depletion” transition to open cells, however. The thermodynamic and dynamic changes caused by the WRF-simulated large-scale adjustments to smoke diabatic heating strongly influence cloud evolution in terms of both the rate of deepening (especially for changes in the inversion temperature jump and in subsidence) and in cloud fraction on the final day of the simulation (especially for the moisture “banding” effect). Such large-scale semi-direct effects would not have been possible to simulate using a small-domain LES model alone.</p>https://acp.copernicus.org/articles/22/12113/2022/acp-22-12113-2022.pdf |
| spellingShingle | M. S. Diamond M. S. Diamond P. E. Saide P. E. Saide P. Zuidema A. S. Ackerman S. J. Doherty S. J. Doherty A. M. Fridlind H. Gordon C. Howes J. Kazil J. Kazil T. Yamaguchi T. Yamaguchi J. Zhang J. Zhang G. Feingold R. Wood Cloud adjustments from large-scale smoke–circulation interactions strongly modulate the southeastern Atlantic stratocumulus-to-cumulus transition Atmospheric Chemistry and Physics |
| title | Cloud adjustments from large-scale smoke–circulation interactions strongly modulate the southeastern Atlantic stratocumulus-to-cumulus transition |
| title_full | Cloud adjustments from large-scale smoke–circulation interactions strongly modulate the southeastern Atlantic stratocumulus-to-cumulus transition |
| title_fullStr | Cloud adjustments from large-scale smoke–circulation interactions strongly modulate the southeastern Atlantic stratocumulus-to-cumulus transition |
| title_full_unstemmed | Cloud adjustments from large-scale smoke–circulation interactions strongly modulate the southeastern Atlantic stratocumulus-to-cumulus transition |
| title_short | Cloud adjustments from large-scale smoke–circulation interactions strongly modulate the southeastern Atlantic stratocumulus-to-cumulus transition |
| title_sort | cloud adjustments from large scale smoke circulation interactions strongly modulate the southeastern atlantic stratocumulus to cumulus transition |
| url | https://acp.copernicus.org/articles/22/12113/2022/acp-22-12113-2022.pdf |
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