Initial Trends in Cloud Amount from the AVHRR Pathfinder Atmospheres Extended (PATMOS-x) Data Set Andrew K Heidinger, Michael J Pavolonis**, Aleksandar Jelenak*, Mitch Goldberg and Dan Tarpley NOAA/NESDIS Office of Research and Applications; *I. M. Systems Group, Inc.; ** UW/CIMSS P 6.9 Introduction Total Cloud Amount Comparisons for July High Cloud Amount Comparisons for July Time Series of Cloud Amount for July Are the PATMOS-x Trends Physically Consistent? Conclusions PATMOS-x Description This paper presents initial and preliminary comparison of the trends in total and high cloud amount from a new data-set (PATMOS-x) and two existing satellite cloud climatologies; ISCCP and the HIRS cloud climatology from the University of Wisconsin (UWHIRS). Our goal is to demonstrate that the PATMOS-x data-set provides new information for studying climate variability during the satellite era. This work uses only data from NOAA’s Advanced Very High Resolution Radiometer (AVHRR) GAC (4 km spatial resolution) from July though all data from all AVHRR’s will be processed through PATMOS-x. The AVHRR Pathfinder Atmospheres Extended (PATMOS-x) data set is a new reprocessing of the entire AVHRR GAC data-set conduced by the NOAA/NESDIS Office of Research and Applications. PATMOS-x offers more products and new algorithms compared to its predecessor (PATMOS). It also includes data from the morning-orbit and the NOAA-klm sensors. Lastly, PATMOS-x includes improved calibration and navigation procedures. The spatial resolution of the PATMOS-x data is nominally 0.5 degree though 0.25 degree data may be produced. Daily and Monthly fields are standard products. PATMOS-x includes over 120 parameters including radiance, cloud and surface products in a HDF format. Comparison with PATMOS One problem that was identified with PATMOS, was the large discontinuities in total cloud amount time series during the transition from one satellite to the next (denoted as vertical lines in the figure). PATMOS-x applies an improved cloud mask (CLAVR-x) that appears to have removed these inter-satellite artifacts in the cloud amount time series (see right). This analysis compares the spatial distribution of the trends in the daily-averaged total cloud amount from ISCCP(left), PATMOS-x (center) and UW/HIRS (right). The top panel shows the July mean fields of total cloud amount and the lower row shows the spatial distribution of the linear trend (%/year) determined for all Julys in each grid-cell. ISCCP and PATMOS-x show areas of positive trends off the California Coast, the Philippines Sea, and over Western Europe. ISCCP and PATMOS-x show negative trends in the Tropical Pacific and the Gulf of Mexico. UW/HIRS shows some similar features but with less distinct patterns. ISCCP also shows generally negative trends over many regions. The results for the daily-averaged July High Cloud Amount comparisons are shown below for ISCCP (right), PATMOS-x (center) and UW/HIRS(right). The top row shows the mean fields and the bottom row shows the linear trends (%/year) for the roughly 20 year series for each grid-cell. ISCCP and PATMOS-x show some similar patterns, notably positive trends in the Philippine Sea and Equatorial Indian Ocean and negative trends in the North-Eastern Pacific. UW/HIRS shows the positive trends in the Arabian Sea and the Philippine Sea but also shows positive trends in many regions. This analysis compares zonally averaged time series. The most significant discrepancy in trends occurs in the total cloud amount time series from 60N to 60S. PATMOS-x and UW/HIRS indicate no significant trend while ISCCP** shows a consistent downward trend. In the High Cloud Amount from 20N to 20S time series, ISCCP and PATMOS-x show little trend, while UW/HIRS shows a significant positive trend. However, when expressed as the ratio of High Cloud Amount to the Total Cloud Amount, PATMOS-x and UW/HIRS show similar positive trends. Separating the algorithmic versus the actual geophysical meaning of these trends is an area of continuing research. * Note, the relative differences in cloud amount are large but are likely due to differences in spatial resolution and in the methodologies used to estimate cloud amounts; ** ISCCP daytime only high cloud amount values were more similar to PATMOS-x Assuming clouds are generally colder than the surface, increases in cloud amount should be correlated with decreases in the observed 11  m radiance. For the PATMOS-x data, this appears to be the case for both the total and high cloud amounts. Therefore the PATMOS-x trends are physically consistent with the observed 11 micron radiances. Other correlations with other geophysical parameters will be analyzed. The PATMOS-x project from the NOAA/NESDIS Office of Research and Applications offers a new data-set to climate researchers. PATMOS-x provides new cloud products beyond that offered by PATMOS and includes improved calibration and navigation. The initial analyses of the PATMOS-x cloud amount time series indicates that the large inter-satellite jumps observed in PATMOS are much reduced. The zonal and spatial distribution of the total and high cloud amount trend offers some similarities with ISCCP and UW/HIRS but there is little consensus between the three. PATMOS-x should offer new information because it uses more spectral information than used in ISCCP and at a much finer spatial resolution than used in UWHIRS. We are exploring the use of new sensors (i.e. CALIPSO & CLOUDSAT) to help place “error bars” on these cloud climatologies. www: