We found a match
Your institution may have rights to this item. Sign in to continue.
- Title
Unveiling aerosol-cloud interactions Part 2: Minimizing the effects of aerosol swelling and wet scavenging in ECHAM6-HAM2 for comparison to satellite data.
- Authors
Neubauer, David; Christensen, Matthew W.; Poulsen, Caroline; Lohmann, Ulrike
- Abstract
Aerosol-cloud interactions (ACI) are uncertain and the estimates of the ACI effective radiative forcing (ERFaci) magnitude show a large variability. Within the Aerosol_cci project the susceptibility of cloud properties to changes in aerosol properties are derived from the high resolution AATSR dataset using the Cloud-Aerosol Pairing Algorithm (CAPA) (as described in our companion paper) and compared to susceptibilities from the global aerosol climate model ECHAM6-HAM2 and MODIS-CERES data. For ECHAM6-HAM2 the dry aerosol is analysed to mimic the effect of CAPA. Furthermore the analysis is done for different environmental regimes. The aerosol-liquid water path relationship in ECHAM6-HAM2 is systematically stronger than in AATSR-CAPA data and cannot be explained by an overestimation of autoconversion when using diagnostic precipitation but rather by aerosol swelling in regions where humidity is high and clouds are present. When aerosol water is removed from the analysis in ECHAM6-HAM2 the strength of the susceptibilities of liquid water path, cloud droplet number concentration and cloud albedo as well as ERFaci agree much better with the ones of AATSR-CAPA or MODIS-CERES. For comparing satellite derived to model derived susceptibilities this study finds it more appropriate to use dry aerosol in the computation of model susceptibilities. We further find that while the observed relationships of different satellite sensors (AATSR-CAPA vs. MODIS-CERES) are not always consistent for tested environmental conditions the relationships in ECHAM6-HAM2 are missing a strong dependence on environmental conditions which is an indication that feedback processes like cloud top entrainment are missing or not well represented in the model. Next to aerosol swelling, also wet scavenging and aerosol processing have an impact on liquid water path, cloud albedo and cloud droplet number susceptibilities. Aerosol processing leads to negative liquid water path susceptibilities to changes in aerosol index (AI) in ECHAM6-HAM2, likely due to aerosol size changes by aerosol processing. This is an indication that AI is not necessarily a better proxy for cloud condensation nuclei than the less size dependent aerosol optical depth. Our results indicate that for statistical analysis of aerosol-cloud interactions the unwanted effects of aerosol swelling, wet scavenging and aerosol processing need to be minimized when computing susceptibilities of cloud variables to changes in aerosol.
- Subjects
ATMOSPHERIC aerosols; ATMOSPHERIC models; RADIATIVE forcing; ATMOSPHERIC radiation; HUMIDITY; PRECIPITATION scavenging
- Publication
Atmospheric Chemistry & Physics Discussions, 2017, p1
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acp-2017-449