Responses of Cloud Distributions to the Large-Scale Dynamical Circulation: Water Budget-Related Dynamical Phase Space and Dynamical Regimes

Abstract:

One primary contributor to the uncertainty in climate sensitivity is the response of cloud distributions to the changing large-scale circulation. An evaluation of cloud responses to changes in large-scale dynamics within climate models during the present climate must be made using available observations before the models can be trusted to predict cloud changes in the future. To establish relationships between cloud and large-scale dynamics, we introduce the water budget-related “dynamical phase space”, which summarizes many commonly-used parameters to represent large-scale dynamical conditions, and are simultaneously tied to the atmospheric water budget. Typical circulation systems such as the ITCZ, the subtropical subsidence regions, the tropical trade winds, and the mid-latitude baroclinic systems can be efficiently identified in regimes of the dynamical phase space. Cloud state histograms defined by cloud top pressure and cloud optical depth retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) are stratified against different regimes in the dynamical phase space to establish the responses of clouds to large-scale dynamical conditions. Furthermore, as an example, these cloud-dynamics relationships are used to evaluate cloud state histograms calculated from the Cloud Feedback Intercomparison Project (CFMIP) Observation Simulation Package (COSP) MODIS simulator incorporated in the Goddard Institute for Space Studies Model E2 (GISS E2). The skills of the model to reproduce cloud responses to the varying large-scale dynamical conditions will be illustrated.