Satellite Retrievals Show Adiabatic Fraction of Marine Low Clouds Decreasing With Increasing Temperature and Height Above Cloud Base

Cloud adiabatic fraction (f_ad) is an important metric that quantitatively characterizes the impact of atmospheric mixing on cloud thermodynamic properties. Due to the lack of vertical profiling of cloud water, previous studies on the vertical variability of f_ad within clouds have been confined to single cloud scales. Our prior research achieved a breakthrough in the large-scale retrieval of cloud adiabatic fraction, while it only provided two-dimensional information on the adiabatic fraction, leaving the vertical variation of the in-cloud adiabatic fraction unquantified. In this study, utilizing global-scale cloud f_ad data derived from our previous research, we developed a predictive function for global marine low-cloud f_ad based on cloud geometric thickness and cloud base temperature (CBT). This enabled us to successfully estimate the vertical distributions of f_ad within clouds across various temperature conditions on a global scale. The f_ad within clouds exhibits a quadratic reduction from the cloud base to the top, which is more pronounced at higher temperatures. Specifically, as the CBT rises from 2 to 24°C, the f_ad at cloud base diminishes from 0.85 to 0.23. The decreasing trend of f_ad within clouds with increasing temperatures is expected to reduce cloud albedo and coverage potentially constituting a positive radiative cloud feedback mechanism.