The Radiative Effects of Weather States Identified by ISCCP

The International Satellite Cloud Climatology Project (ISCCP) D1 gridded cloud product contains the joint distribution of cloud top pressure and cloud optical depth at each 280 km grid cell observed daily every 3-hours. The patterns of these joint distributions can be used to identify, via cluster analysis, distinct states of the atmosphere at the mesoscale, which ISCCP terms "weather states". The spatiotemporal distribution of distinct weather states is now available as a separate ISCCP D1 product for four geographical regions, tropics, extended low latitudes, northern midlatitudes and southern midlatitudes. This presentation will focus on the radiative effects of the weather states for these regions as revealed by their association with matching radiative fluxes (RFs) and cloud radiative effects (CREs) provided by the ISCCP FD dataset for the period 1984-2003. Specifically, we will present the salient features of the contribution of the different weather states to surface and top of the atmosphere RFs and CREs. Particular areas of focus will be: a) The seasonal cycle of the mean radiative contributions of the various weather states and the relationship between their relative strength and their frequency of occurence; b) the identification of the most dominant weather states in terms of their relative radiative contributions; c) the range of possible RFs and CREs for individual weather states and the degree to which they overlap with those of other weather states within the same region; d) the spatial patterns for select weather states and regions of the RF and CRE contributions and their correlation with the spatial patterns of the frequency of occurence of the weather states themselves. The above analysis will be useful for large scale models wishing to implement higher-order tests to verify the realism of their cloud-radiation simulations: besides the verisimilitude of their cloud types, the fidelity of their corresponding radiative contributions can also be examined.