TY - JOUR
T1 - Decomposing aerosol cloud radiative effects into cloud cover, liquid water path and Twomey components in marine stratocumulus
AU - Goren, Tom
AU - Rosenfeld, Daniel
PY - 2014/3/1
Y1 - 2014/3/1
N2 - A method for separating the three components of the marine stratocumulus (MSC) aerosol cloud interactions radiative effects, i.e., the cloud cover, liquid water path (LWP) and cloud drop radius (Twomey), was developed and tested. It is based on the assumption that changes in MSC cloud regimes that occur at short distance in homogeneous meteorological conditions are related to respective changes in the concentration of cloud condensation nuclei (CCN). The method was applied to 50 cases of well defined transitions from closed to open cells. It was found that the negative cloud radiative effect (CRE) over the closed cells is on average higher by 109±18Wm-2 than that over the adjacent open cells. This large negative CRE is composed of the cloud cover (42±8%), LWP (32±8%) and Twomey (26±6%) effects. This shows that the Twomey effect, which is caused by change in droplet concentration for a given LWP, contributes only a quarter of the difference in CRE, whereas the rest is contributed by added cloud water to the open cells both in the horizontal (cloud cover effect) and in the vertical (LWP effect) dimensions. The results suggest the possibility that anthropogenic aerosols that affect MSC-regime-changes might incur large negative radiative forcing on the global scale, mainly due to the cloud cover effect.
AB - A method for separating the three components of the marine stratocumulus (MSC) aerosol cloud interactions radiative effects, i.e., the cloud cover, liquid water path (LWP) and cloud drop radius (Twomey), was developed and tested. It is based on the assumption that changes in MSC cloud regimes that occur at short distance in homogeneous meteorological conditions are related to respective changes in the concentration of cloud condensation nuclei (CCN). The method was applied to 50 cases of well defined transitions from closed to open cells. It was found that the negative cloud radiative effect (CRE) over the closed cells is on average higher by 109±18Wm-2 than that over the adjacent open cells. This large negative CRE is composed of the cloud cover (42±8%), LWP (32±8%) and Twomey (26±6%) effects. This shows that the Twomey effect, which is caused by change in droplet concentration for a given LWP, contributes only a quarter of the difference in CRE, whereas the rest is contributed by added cloud water to the open cells both in the horizontal (cloud cover effect) and in the vertical (LWP effect) dimensions. The results suggest the possibility that anthropogenic aerosols that affect MSC-regime-changes might incur large negative radiative forcing on the global scale, mainly due to the cloud cover effect.
KW - Aerosols indirect radiative effects
KW - Cloud radiative forcing
KW - Cloud-aerosols interactions
KW - Marine stratocumulus
UR - http://www.scopus.com/inward/record.url?scp=84891794013&partnerID=8YFLogxK
U2 - 10.1016/j.atmosres.2013.12.008
DO - 10.1016/j.atmosres.2013.12.008
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AN - SCOPUS:84891794013
SN - 0169-8095
VL - 138
SP - 378
EP - 393
JO - Atmospheric Research
JF - Atmospheric Research
ER -