On the relationship of polar mesospheric cloud ice water content, particle radius and mesospheric temperature and its use in multi-dimensional models

摘要

The distribution of ice layers in the polar summer mesosphere (called polarmesospheric clouds or PMCs) is sensitive to background atmosphericconditions and therefore affected by global-scale dynamics. To investigatethis coupling it is necessary to simulate the global distribution of PMCswithin a 3-dimensional (3-D) model that couples large-scale dynamics withcloud microphysics. However, modeling PMC microphysics within 3-D globalchemistry climate models (GCCM) is a challenge due to the high computationalcost associated with particle following (Lagrangian) or sectionalmicrophysical calculations. By characterizing the relationship between thePMC effective radius, ice water content (iwc), and local temperature (T) from anensemble of simulations from the sectional microphysical model, theCommunity Aerosol and Radiation Model for Atmospheres (CARMA), we determinedthat these variables can be described by a robust empirical formula. Thecharacterized relationship allows an estimate of an altitude distribution ofPMC effective radius in terms of local temperature and iwc. For our purposes weuse this formula to predict an effective radius as part of a bulkparameterization of PMC microphysics in a 3-D GCCM to simulate growth,sublimation and sedimentation of ice particles without keeping track of thetime history of each ice particle size or particle size bin. This allowscost effective decadal scale PMC simulations in a 3-D GCCM to be performed.This approach produces realistic PMC simulations including estimates of theoptical properties of PMCs. We validate the relationship with PMC data fromthe Solar Occultation for Ice Experiment (SOFIE).