Evaluating the Influence of Gravity Waves on Synoptic Cirrus in the ModelE3 Climate Model

Cirrus clouds are an important factor in the Earth’s energy budget but the controls on their occurrence and radiative properties are challenging to represent and evaluate in climate models. Atmospheric gravity waves that are not generally resolved in climate models strongly influence the macrophysical and microphysical properties of synoptic cirrus globally. In particular, locally enhanced updrafts increase the supersaturation available to drive cirrus formation and may alter the relative roles of heterogeneous and homogeneous nucleation. Robustly evaluating the influence of gravity waves on cirrus formation and evolution is therefore necessary for better quantifying the radiative impacts of cirrus in current and future climates. Here, we study the influence of gravity waves on cirrus in a 1D model with bin microphysics (DHARMA) and in a global climate model (ModelE3). Because substantial uncertainties still exist in microphysical processes that control ice nucleation, growth and aggregation, we first simulate a well-studied case from the SPARTICUS campaign over Oklahoma using a quasi-Lagrangian column approach and an ensemble of gravity wave scenarios derived from collocated Doppler cloud radar retrievals of vertical wind speed. We find that the inclusion of gravity waves produces more realistic cirrus properties relative to in situ observations than can be achieved by only varying uncertain microphysical parameters (ice crystal properties, mass accommodation coefficient, nucleation mode and scheme, aggregation efficiency). Baseline 1D simulations without gravity waves are also compared with ModelE3 run in single-column mode. We next evaluate the gravity wave parameterization in ModelE3 using all available Doppler cloud radar retrievals over Oklahoma and results from a high-resolution GEOS5 simulation globally. We evaluate baseline and ModelE3 sensitivity tests in which vertical wind speed perturbations derived from the gravity wave parameterization are included in the calculation of ice nucleation and growth.