Spatial and Temporal Variability of GPCP Precipitation Estimates By C. F. Ropelewski Summarized from the generous input Provided by G. Huffman, R. Adler, S. Curtis, P. Arkin, X. Yin J.Janowiak, P. Xie R. Ferraro P. Bauer C.Beck, J.Grieser, B.Rudolf M. Bell, B. Blumenthal, B. Lyon F. R. Robertson T. Smith Presented at the 30 th Climate Diagnostics and Prediction WS, Oct 2005 State College, PA Go LIONS

Characteristics of the GPCP Data Set Global Complete Monthly Precipitation Analysis January 1979 to Present 2.5 o latitude by 2.5 o longitude Input data Satellite Infrared (geostationary0 Microwave (from mid-1987) Gauge data (Global Precipitation Climatology Center (GPCC) operated by the DWD Output Data Satellite only Merged gauge and satellite Monthly, pentad, daily

“Real-time” monthly gauge data from the GTS

P estimated a 2.61 mm/day Yearly Standard Deviation 0.03mm/day Estimated mean global rainfall rates Major GPCP contributions Estimates of the global Precipitation patterns

Figure 1a. Zonal mean precipitation, land versus ocean, , after Adler et al, (2003) Courtesy of Scott Curtis

Figure 1b. Zonal mean precipitation, land versus ocean, versus After Adler et al, (2003) Courtesy of Scott Curtis

Fig 2. Mean GPCP precipitation (mm/day) Courtesy John Janowiak

Mean Annual Cycle

Standard deviations of Annual mean GPCP Precipitation Courtesy Michael Bell

Fig 5b. Mean annual cycle (mm/day) Global (white), Northern Hemisphere (green), Southern Hemisphere (yellow).

Fig 5c. Mean annual cycle of precipitation. Oceans (green), Global (white), Land (yellow). Courtesy P. Arkin

Fig. 6a Annual cycle of zonal mean GPCP Precipitation (mm/day) and b) the difference between total period zonal mean 1979 – 2002 and /87. Courtesy J. Janowiak

Fig 3 (top) Mean GPCP Precipitation P (left) P (middle) P (right) Courtesy P. Arkin Fig 4 Mean Differences P1 minus P2 left-middle P2minus P3 rt-middle P1 minus P3 bottom Courtesy P. Arkin

Fig. 3a, Mean precipitation for P1 ( ) – Includes a Major ENSO Warm episode but no microwave estimates. (Courtesy P. Arkin)

Fig. 3b, Mean precipitation for P2 ( ) – no major ENSO warm Episodes, includes microwave estimates. (Courtesy P. Arkin)

Fig 4a P1 minus P2 8 year mean GPCP precipitation. (Courtesy P. Arkin)

Fig. 3c, Mean precipitation for P3 ( ) – Major ENSO warm Episode, includes microwave estimates. (Courtesy P. Arkin)

Fig. 4b P2 minus P3 eight year periods. Highlights ENSO-No ENSO

Fig 4c P1 minus P3. Shows the differences in strengths between the 1982/83 and 1997/98 ENSOs and due to the addition of microwave estimates. (Courtesy P. Arkin)

Fig.7 Seasonal mean precipitation (mm/day) for a) DJF, b) MAM, c) JJA and d) SON. Courtesy P. Arkin

Fig. 8 Standard deviations

P estimated at 2.61 mm/day Yearly Standard Deviation 0.03mm/day Time series of GPCP annual mean global precipitation See Allen, M.R. and W. J. Ingram, 2002: Constraints on future changes in climate and the Hydrologic cycle. Nature, 419,

Figure 9. (a) Global averages of monthly precipitation (mm day -1 ) for ocean, total, and land. From Adler et al

Fig. 9b) Tropical (30 o N-30 o S) averages of monthly precipitation anomalies (mm day -1 ) for (top) total, (middle) ocean, and (bottom) land. Vertical dashed lines indicate the months of significant volcanic eruptions. The thin black curves indicate the Niño-3.4 SST index ( o C). After Adler et al 2003.

Fig. 11. Time series of zonal mean precipitation anomaly. Vertical arrow shows the approximate introduction of microwave data Courtesy P. Arkin

Fig 10 Alternate. Zonal means for tropics only.

a b c d e f g h Fig 10. Time series of zonally averaged GPCP estimates over land (left hand panels) and over the ocean (right hand panels). Zonal averages are for 50N to 90N (a,e); 25N to 50N (b,f); 25S to 25N (c,g) and 50S to 25S (d,h). The introduction of microwave data in 1987 is evident for the data over land.

4. LINEAR TREND FIT ZONAL AVERAGE Zonal averages of 25- year linear trend show quite different trends in different lat. bands – again, note regional coherence. 25°S-25°N ~.08 / 3.1 = ~ 2.5% 25°-50°N ~ -.12 / 2.4 = ~ -5.4% Land and Ocean are not uniformly related. Fig 10a Linear trends in the zonally averaged GPCP estimated precipitation. Huffman et al.

Figure 12. Map of linear changes in GPCP precipitation anomalies from January 1979 to December The thin black contour outlines the local 1% significance level. Courtesy Huffman, Curtis and Adler

Fig 12 Spatial correlations between global trend maps computed for the 1979 to 2004 period and trends computed from successively fewer years. E.g., the spatial correlation at “lag” 1 is for the 1980 to 2004 period and so on. (from Smith et al., 2005).

Fourth Rotated EOF of the GPCP Annual data for the period This REOF accounts for 6% of the total variance. (From Smith et al. 2005)

Summary: The GPCP Data provide (relatively) consistent and complete global precipitation estimates from (1979) 1988 to the present. These data identify (illuminate) features of the large-scale precipitation fields not (well) known before. E.g, oceanic precipitation patterns, storm tracks, individual ENSO patterns. Global precipitation shows no significant trends over the period of record…however regional “trends” are evident in the tropics. These aren’t easily untangled from instrumental differences and differences in ENSO in the 17 (25) yr record. These are research data. For real-time monitoring go to CAMS-OPI or other “operational” estimates (eventually go to CMORPH).