| Abstrakt: |
The impact of seasonalities on direct radiative effects ( DREs) and radiative heating rates ( RHRs) of absorbing aerosols above clouds in the southeast Atlantic is examined using radiative transfer calculations. For an aerosol optical thickness of 0.6 located between 0 and 4 km, a cloud optical thickness of 9.0 and a cloud effective radius of 12.8 µm at 0.55 µm located between 1 and 2 km, the diurnally averaged RHR at noon in the aerosol layer increases from ∼6.6 K day−1 in June to ∼8.9 K day−1 in October. In June (October), the RHR in the cloud layer at noon is 1.3 (1.7) K day−1 higher than the case of pristine clouds. However, an elevated aerosol layer (2-4 km) reduces the RHR by ∼0.2 K day−1 in the cloud layer relative to a pristine cloudy case. The DRE at top-of-atmosphere ( TOA) reaches its peak when the solar zenith angle ( SZA) is 54°. The DRE increases (decreases) with SZA for SZA less (greater) than 54°. The primary peak DRE is ∼29.5 W m−2 at 5.0°S 5.0°E, occurring at 0800 UTC. At noon, the DRE at TOA is ∼18.9, ∼20.5 and ∼23.1 W m−2 at 5.0°S, 15.0°S and 25.0°S along 5.0°E, respectively. This study provides data and theoretical understanding to help positioning science flights that target measurements of above-cloud aerosol radiative effects. [ABSTRACT FROM AUTHOR] |
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