ISCCP Cloud Regime and Weather State Products

Here, we extend to the whole subtropics (±35° latitude) the analysis approach of Jakob and Tselioudis (2003, henceforth JT03) that uses the patterns of cloud property joint distributions at mesoscale (cloud type mixtures) to identify distinct states of the tropical atmosphere. As for Tropical Weather State analysis, the histogram patterns that describe cloud variability are identified using the K-Means clustering algorithm (Anderberg, 1973) applied to 3-hourly PC-&tau histograms for each 2.5° region, including completely clear regions.

To download the analysis software, click HERE.

The optimum cluster centroids are identified for K=8 as shown above and reported below on the left. Next, each PC-TAU histogram for each 3-hr time step in each 2.5° map grid cell over the whole subtropics is assigned to one of these clusters. We refer to these as "weather states" (WS) because JT03 showed that these cloud property patterns are associated with distinct states of the tropical atmosphere (Fu et al. 1990, 1994, Lau and Crane 1995, Del Genio and Kovari 2002). Variations of WS can then be represented by the frequency of occurrence maps for daily or longer time accumulations shown below.

Note: Weather state values range from 1-8. In the cluster datasets, the value 0 indicates Clear; value 98 indicates darkness; and value 99 indicates missing data.

To download the dataset (D1.WS.ET.dat), click HERE.

To download the cluster centroid (D1_ST_all.cent8.3.dat), click HERE.

To download the routine converting those datasets in binary files, click HERE.

More information are available on the ISCCP website ... just follow this LINK !

• Anderberg, M.R. (1973), Cluster analysis for applications, 359 pp., Academic Press, New York, NY, USA.
• Del Genio, A.D., and W.K. Kovari (2002), Climatic properties of tropical precipitating convection under varying environmental conditions, J. Climate, 15, 2597-2615.
• Fu, R., A.D. Del Genio and W.B. Rossow (1990), Behavior of deep convective clouds in the tropical Pacific deduced from ISCCP radiance data, J. Climate, 3, 1129-1152.
• Fu, R., A.D. Del Genio and W.B. Rossow (1994), Influence of ocean surface conditions on atmospheric vertical thermodynamic structure and deep convection, J. Climate, 7, 1092-1108.
• Jakob, C., and G. Tselioudis (2003), Objective identification of cloud regimes in the Tropical Western Pacific, Geophys. Res. Lett., 30, 1-4, DOI 10.1029/2003GL018367.
• Lau, N-C., and M.W. Crane (1995), A satellite view of the synoptic-scale organization of cloud properties in midlatitude and tropical circulation systems, Mon. Wea. Rev., 107, 1984-2006.