TY - JOUR
T1 - Atmospheric energy budget response to idealized aerosol perturbation in tropical cloud systems
AU - Dagan, Guy
AU - Stier, Philip
AU - Christensen, Matthew
AU - Cioni, Guido
AU - Klocke, Daniel
AU - Seifert, Axel
N1 - Publisher Copyright:
© Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.
PY - 2020/4/17
Y1 - 2020/4/17
N2 - The atmospheric energy budget is analysed in numerical simulations of tropical cloud systems to better understand the physical processes behind aerosol effects on the atmospheric energy budget. The simulations include both shallow convective clouds and deep convective tropical clouds over the Atlantic Ocean. Two different sets of simulations, at different dates (10-12 and 16-18 August 2016), are simulated with different dominant cloud modes (shallow or deep). For each case, the cloud droplet number concentration (CDNC) is varied as a proxy for changes in aerosol concentrations without considering the temporal evolution of the aerosol concentration (for example due to wet scavenging, which may be more important under deep convective conditions). It is shown that the total column atmospheric radiative cooling is substantially reduced with CDNC in the deepcloud-dominated case (by &tild; 10:0Wm-2), while a much smaller reduction (&tild; 1:6Wm-2) is shown in the shallowcloud-dominated case. This trend is caused by an increase in the ice and water vapour content at the upper troposphere that leads to a reduced outgoing longwave radiation, an effect which is stronger under deep-cloud-dominated conditions. A decrease in sensible heat flux (driven by an increase in the near-surface air temperature) reduces the warming by &tild; 1:4Wm-2 in both cases. It is also shown that the cloud fraction response behaves in opposite ways to an increase in CDNC, showing an increase in the deep-cloud-dominated case and a decrease in the shallow-cloud-dominated case. This demonstrates that under different environmental conditions the response to aerosol perturbation could be different.
AB - The atmospheric energy budget is analysed in numerical simulations of tropical cloud systems to better understand the physical processes behind aerosol effects on the atmospheric energy budget. The simulations include both shallow convective clouds and deep convective tropical clouds over the Atlantic Ocean. Two different sets of simulations, at different dates (10-12 and 16-18 August 2016), are simulated with different dominant cloud modes (shallow or deep). For each case, the cloud droplet number concentration (CDNC) is varied as a proxy for changes in aerosol concentrations without considering the temporal evolution of the aerosol concentration (for example due to wet scavenging, which may be more important under deep convective conditions). It is shown that the total column atmospheric radiative cooling is substantially reduced with CDNC in the deepcloud-dominated case (by &tild; 10:0Wm-2), while a much smaller reduction (&tild; 1:6Wm-2) is shown in the shallowcloud-dominated case. This trend is caused by an increase in the ice and water vapour content at the upper troposphere that leads to a reduced outgoing longwave radiation, an effect which is stronger under deep-cloud-dominated conditions. A decrease in sensible heat flux (driven by an increase in the near-surface air temperature) reduces the warming by &tild; 1:4Wm-2 in both cases. It is also shown that the cloud fraction response behaves in opposite ways to an increase in CDNC, showing an increase in the deep-cloud-dominated case and a decrease in the shallow-cloud-dominated case. This demonstrates that under different environmental conditions the response to aerosol perturbation could be different.
UR - http://www.scopus.com/inward/record.url?scp=85083781568&partnerID=8YFLogxK
U2 - 10.5194/acp-20-4523-2020
DO - 10.5194/acp-20-4523-2020
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AN - SCOPUS:85083781568
SN - 1680-7316
VL - 20
SP - 4523
EP - 4544
JO - Atmospheric Chemistry and Physics
JF - Atmospheric Chemistry and Physics
IS - 7
M1 - 20
ER -