The impact of seasonalities on direct radiative effects and radiative heating rates of absorbing aerosols above clouds

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.