Global Weather States from the ISCCP D1 Cloud Dataset

Introduction

The International Satellite Cloud Climatology Project (ISCCP) D1 gridded cloud product contains the distribution of cloud top pressure and cloud optical depth at each grid cell observed every 3-hours daily from 1983-2009. The distribution of cloud top pressure (PC) and optical depth (tau) fractions is referred to as a PC-tau histogram. A histogram displaying cloud top pressure and optical depth over some region reveals information regarding the type of clouds present (Rossow and Schiffer, 1999). Each PC-tau histogram contains 42 boxes, 6 optical thickness bins and 7 cloud top pressure bins (the bin sizes are not linear). One D1 PC-tau histogram contains the relative percentage of pixels that fall into each of these 42 boxes in the corresponding grid box (2.5°x2.5°).



Global Weather State Data and Softwares

We extend to the whole globe the analysis approach of Jakob and Tselioudis (2003, henceforth JT03) that uses the patterns of cloud propertyeach representing a distinct structure characterized by the horizontal distribution of ISCCP D1 cloud optical depth and cloud top pressure. To access the dataset, download the ISCCP Global 3-hrly WS dataset then untar file isccp_d1-gws1983-2009.tar Use the Fortran read program read_02_ISCCP_GWS.f to access the dataset. Detailed instructions can be found within the read code. Please note that the data was created in Big Endian Format.


Numerical Mean Centroids for Global WS

The mean-centroid ASCII dataset contains a total of 12 clusters (11 cloudy and 1 clear-sky scenes). Each of the 11 cloudy clusters consists of 42 element vector of cloud fraction (in %) in the same order as ISCCP D1's parameters #30d to #71d (six cloud optical thickness ranges over seven cloud top pressure ranges from TOA to surface) with the last,12th cluster for clear sky (all = 0.) Sample code read_GL11_centroids.f is available to read the mean-centroid ASCII dataset for the GWS data product. The PC-TAU histograms (centeroid patterns) for eleven GWS are presented in the Figure 1, where the Relative Frequency of Occurance (RFO) of each WS is shown at the top of each histograms. Figure 2 presents global maps of the average RFO of the GWS in the same order as Figure 1.


Weather StatesFigure 1
Weather StatesFigure 2

References

  • 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.
  • Rossow, W.B., and R.A. Schiffer (1999), ISCCP cloud data products, Bull. Amer. Meteor. Soc., 72, 2-20.
  • Tselioudis, G.,W.B. Rossow., Y. Zhang, D. Konsta (2012) Global Weather States and their Properties from Passive and Active Satellite Cloud RetrievalsJ. Climate (Submitted)