Radiative impacts on the growth of a population of drops within simulated summertime Arctic stratus

The impact of solar heating and infrared cooling on the growth of a populat ion of drops is studied with two numerical modeling frameworks. An eddy-res olving model (ERM) simulation of Arctic stratus clouds is used to generate a dataset of 500 parcel trajectories that follow the mean dynamic motions o f the simulated cloud. The 500-parcel dataset is used to drive a trajectory ensemble model (TEM) coupled to an explicit microphysical model that inclu des the radiative term in the vapor growth equation. The second framework i s that of the ERM itself. Results from the TEM show that the production of drizzle-sized drops is str ongly dependent upon parcel cloud-top residence time for both radiative- an d nonradiative influenced growth. Drizzle-sized drops can be produced betwe en 20 and 50 min earlier through the inclusion of the radiative term. which corroborates, earlier results. The radiative effect may also cause drops w ith r < 10 mu m to evaporate, producing a bimodal size spectrum. Parcel clo ud-top residence times as short as 12 min can initiate this bimodal spectru m. TEM results show that the radiative effect increases drizzle drop mass p redominately in parcels that Ir tendl to contribute to drizzle even in the absence of the radiative term. Activation of large cloud condensation nucle i appears to have a larger effect un drizzle production than does the radia tive term, ERM simulations show a weak overall influence of the radiative t erm. Drizzle onset occurs earlier when the radiative term is included (abou t 20 min), but there is no strong change in the overall structure or evolut ion of the cloud.