Evaluation of a New Approach for Entrainment and Detrainment Rate Estimation

Entrainment and detrainment rates (epsilon and delta) constitute the most critical free parameters in mass flux schemes commonly employed for cumulus parameterizations. Recently, Zhu et al. (2021) introduced a new approach that utilizes aircraft observations to simultaneously estimate epsilon and delta for cumulus clouds, overcoming the limitation of other observation-based approaches that solely yield epsilon without offering insights into delta. This study aims to comprehensively evaluate the reliability of this new approach. First, evaluation using an Explicit Mixing Parcel Model demonstrates the capability of the new approach to back-calculate predetermined epsilon and delta based on the physical properties before and after the entrainment mixing. Second, evaluation using large-eddy simulations illustrates that the new approach yields consistent epsilon and delta profiles compared to the traditional approach. Sensitivity tests indicate a weak sensitivity of the estimated delta with the new approach to the entrained air source. A decrease in the proportion of cloudy air in the assumed detrained air leads to a reduction in the estimated delta, while epsilon remains unaffected. Finally, the most appropriate assumptions for entrained and detrained air are discussed. Estimating epsilon for cumulus parameterizations involves acquiring ambient air more than 500 m away from the cloud edge as entrained air. Due to implicit mean field approximations in the traditional approach, determining the optimal assumption for detrained air properties proves challenging. This study confirms the reliability of the new approach in estimating epsilon and delta, providing confidence in its application to extensive observational data and advancement in parameterization. Cumulus clouds play a crucial role in weather and climate models and accurately estimating parameters like entrainment and detrainment rates is essential for their representation. Recent research by Zhu et al. (2021) offers a new approach to simultaneously estimate both entrainment and detrainment rates using aircraft observations. This study thoroughly evaluates the reliability of this approach. Based on two advanced high-resolution models, the new approach proves effective in calculating entrainment and detrainment rates. Sensitivity tests on the source of entrained air and the assumption for detrained air are conducted. To accurately estimate entrainment rates used for cumulus parameterizations, it is advisable to obtain entrained air more than 500 m from the cloud edge. This study faces challenges in determining optimal detrained air properties as the traditional approach of deriving the properties of detrained air-that it is equal to its mean value within the cloud-is flawed. Overall, this study affirms the reliability of the new approach in estimating entrainment and detrainment rates, boosting confidence in its application to extensive observational data and the improvement of cumulus parameterizations. A new approach for simultaneously estimating entrainment and detrainment rates in observations is comprehensively evaluated Results from two high-resolution models affirm the reliability of the new approach The optimal source of entrained air for estimating entrainment rates required in cumulus parameterizations is identified