JISAO data
Pacific island rainfall anomaly index, 1892-1996
This index captures ENSO-related rainfall variability in the equatorial Pacific, and is based on stations primarily in the western and central part of the basin. This index is a simpler, slightly redefined, and more up to date version of an earlier index. The old and present indices are highly correlated over the period of common record.

The present index is calculated from two data sets:

  • Eischeid et al. (1991) seasonal data averaged over 4N-4S, 162.5E-87.5W for 1892-1989
  • Hulme (1992) monthly data averaged over 6.25N-6.25S, 159.375E-88.125W for 1905-96
    The Eischeid et al. data are used for 1892-1904 and the Hulme data for 1905-96. References and details of the calculation are given below.
    Pacific island rainfall anomaly index (shaded) and cold tongue SST index (CTI) (line)

    Modern record: 1950-96
    Image showing the rainfall index and CTI. The series seem to follow a 1C to 10 cm/mon relationship for most of the large swings of the indices. The only mismatches are weak wet anomalies during the 1968-69 ENSO, and seemingly too-wet conditions during the 1986-88 ENSO.

    Historical record: 1892-1996
    Image of time series for 1892-1996.

    The rainfall index exhibits fidelity with the CTI over the entire period of record. The correlation coefficient of the two indices is 0.82 for 1950-79 (both time series subjected to a 3-point running mean). In the above figures, the modern (historical) record is smoothed with successive 5- and 3- (9- and 7-) point running means. PostScript files are also available for black and white versions of these figures: 1950-96 and 1892-1996.

    The time series is available as a MATLAB file. ["load eqpacrain18921996.dat" will read the data into the variable "eqpacrain."]

    

The following index values are in mm/mon.
       jan  feb  mar  apr  may  jun  jul  aug  sep  oct  nov  dec
 1892  -17  -17   23   23   23   20   20   20  -57  -57  -57  -10
 1893  -10  -10  -82  -82  -82  -52  -52  -52  -57  -57  -57 -182
 1894 -182 -182 -138 -138 -138  -14  -14  -14  -69  -69  -69  -32
 1895  -32  -32  -78  -78  -78  -78  -78  -78   37   37   37    9
 1896    9    9   -2   -2   -2   60   60   60  120  120  120   76
 1897   76   76  -59  -59  -59  -42  -42  -42   -9   -9   -9  -89
 1898  -89  -89 -122 -122 -122  -69  -69  -69  -81  -81  -81 -192
 1899 -192 -192 -126 -126 -126  110  110  110   49   49   49  144
 1900  144  144  140  140  140   89   89   89   58   58   58   19
 1901   19   19   35   35   35  -74  -74  -74  -71  -71  -71  -96
 1902  -96  -96   47   47   47  138  138  138  171  171  171   39
 1903   39   39  -18  -18  -18  -88  -88  -88  -71  -71  -71 -170
 1904 -170 -170  -46  -46  -46   65   65   65  138  138  138  118
 1905  192  154  205  196  228  157  166  127  207  178  143   91
 1906   37    4  -73  -83  -81  -92  -88  -93  -81   -1    9    2
 1907  -80  -87  -64  -58  -54  -77  -65  -70  -20   40   38   42
 1908    0   63  -73 -104   17   -4   11  -43  -45  -87  -99 -144
 1909 -161 -167 -144 -102  -88  -49  -31  -17  -43  -52 -105 -158
 1910 -177 -162 -127  -68  -42  -16  -48  -50  -61  -57  -67  -85
 1911  -75   60  209  229  145   68   69  109  131  151  149  162
 1912  198  253  224  195   78   22  -20  -21   34   53  115   75
 1913  120   14  -26  -87  -82  -70  -40    7   43   71   67   75
 1914   70   87  128  174  192  268  218  182   20   47   72  109
 1915   75   47   68  184  160   87  -56  -76  -77  -77 -104  -89
 1916 -103  -97 -124 -104  -92  -92  -89  -86  -75  -78 -120 -176
 1917 -194 -176 -127 -104  -72  -71  -65  -55  -52  -53  -94 -151
 1918 -169 -121  -65  -17  -23  104  204  266  199  148  128  140
 1919  190  220  245  172  112   85  134  179  212  178  136   39
 1920   68  100  102   55   35   50   29  -31  -64  -71  -81  -23
 1921    2  -15  -65  -80  -85  -64  -51  -35  -32  -26   23    9
 1922   55    7  -13  -32  -13   12    5  -14  -50  -51  -49  -70
 1923  -82  -66  -31  -18   30   56  106   52   39   32   70  149
 1924  139   93  -12  -49  -70  -76  -70  -68  -47  -41  -60  -95
 1925  -96  -93  -91  -87  -56  -34  -16  -16   30   26   48   55
 1926  111  141  162  139   79   24    8  -19  -23  -48  -65  -91
 1927 -124 -120 -114  -76  -52  -26  -15   -5   -4    5    6   47
 1928   55   32  -15  -43  -45  -28  -18  -16  -34  -34  -48  -39
 1929   -7   10  -18  -54  -37   -7   35   29   24   21   42   62
 1930   81   65   32  -14  -12   17   65  117  105  131  130  151
 1931  124   89   31   14   -4    9   -5  -27  -16  -28  -40  -51
 1932  -35   31   34   41    9  -20  -42  -50  -54  -54  -94  -90
 1933  -88  -56  -56  -30  -10    0  -14  -29  -47  -58  -93 -133
 1934 -129 -101  -71  -57  -34  -27  -23  -45  -48  -37  -45   -4
 1935   -1  -14  -37  -55  -30  -42  -41  -37  -34  -29  -24    5
 1936   33   31   -7  -14  -15    7   -9  -11  -14   29   32   37
 1937   19   -4  -29  -51  -33  -23  -18  -16  -23  -30  -63  -85
 1938 -107 -117 -115  -93  -73  -60  -53  -47  -37  -32  -34  -44
 1939  -17   49   98   85   55   23   26    3   -6   16   47   57
 1940   77   84  125  104  117  113  163  161  170  149  139   93
 1941   69   52   74   70   83  110  117  104   60   51   11   44
 1942   44   50  -17   -8   12   36   44   37   36    5   28   -4
 1943  -12  -33  -37  -36  -10  -13   -6  -30  -35  -36    9   54
 1944   37   25   -8   -6   -4   31   47   51   25   28    1  -37
 1945  -61  -49  -27    4    4   -4  -11  -27  -42  -51  -64  -47
 1946  -60  -34   19   57   94   84   88   45   20    5   23   95
 1947   66   28  -60  -29  -13  -26  -45  -61  -50  -38  -20   29
 1948   83  128  126  116   89   54   14  -23  -41  -33   27  109
 1949  116   86   11   -4  -17   -8  -13  -34  -51  -56  -82 -113
 1950 -126 -133 -118 -104  -81  -69  -63  -61  -55  -61  -68  -81
 1951  -89  -82  -55   25   75  108  112  105   76   21   30   51
 1952   52   14   -5    5   17   -1    1  -19  -16  -18   -4   18
 1953   74   68   87   77   80   51   47   75   91   72   66   34
 1954   -5  -41  -47  -39  -50  -57  -48  -46  -46  -52  -77  -77
 1955  -91  -84  -83  -69  -46  -50  -50  -53  -54  -62  -98 -132
 1956 -139 -114  -59  -24  -15  -21  -28  -32  -38  -48  -64  -96
 1957  -63  -39   15   36   74   93   79   65   84  149  170  161
 1958  126  145  164  172  126   82   41   17  -16   14   46   69
 1959  106   91   90   29    9   -7  -19  -25  -15  -25  -34  -28
 1960  -20  -13  -37  -22  -21  -14  -19  -18  -11  -18  -32  -38
 1961  -18   30   30   33    3    0    1   -9  -11  -32  -63  -86
 1962 -113 -104  -94  -63  -50  -32  -30  -20  -41  -43  -74 -105
 1963 -126 -126  -89  -61  -24   -6   31   40   56   81  116  145
 1964  149  100   17  -64  -88  -84  -64  -60  -56  -66  -53  -54
 1965  -11   -6   29   11   30   59  106  144  158  154  123  158
 1966  153  165   90   59   14   13    2    3  -23  -22  -39  -65
 1967  -75  -82  -62  -52  -37  -39  -36  -31  -30  -26   -3    4
 1968    1  -53  -79  -92  -84  -58  -48  -31  -30   -8  -14    1
 1969   35  108  126  102   62   25   17    1    4    1    9   16
 1970   27   13   19   13    2  -31  -40  -43  -44  -67 -101 -147
 1971 -156 -153 -118  -88  -64  -56  -48  -57  -47  -58  -37  -25
 1972  -26  -60  -71  -13   41   93  101  155  175  192  191  205
 1973  226  172   98   28    2  -40  -55  -76  -64  -71  -85 -123
 1974 -127 -137  -94  -56  -18   34   12    1  -51  -58  -35   -8
 1975   19   39   25    8  -22  -44  -49  -61  -63  -65  -91  -97
 1976  -75  -48  -24    2   54   95  111   95   77   57   71  105
 1977  110  116   91   83   32   10    7   27   22   84   97  131
 1978  115  125   92   41  -19  -51  -52  -52  -43  -50  -21   12
 1979   71   85   50   16   -5   -5  -14  -23   25   34   80   54
 1980   49   57   66   77   31   24   40   30   15    5   -1  -18
 1981   -8   19   84   74   60    7  -14  -29  -28  -30  -18  -53
 1982  -51  -78  -30   -7   21   48  119  142  170  157  194  198
 1983  159  100   42  100  181  213  136   35  -10  -26  -63 -103
 1984 -119 -117  -75  -49  -27  -30  -31  -37  -26  -28  -26  -56
 1985  -84  -87 -102  -86  -77  -51  -31  -43  -39  -31  -39  -40
 1986  -62  -60  -67  -42  -28   21   29   70   88  144  167  259
 1987  307  254  235  214  215  248  250  239  174  109  120  111
 1988  144  114   67   37    1  -29  -57  -68  -60  -74  -99 -121
 1989 -125  -78  -61  -24  -19  -35  -53  -35  -26    0   -2   41
 1990   48  100   82   39    4  -17   15   31   31   48   82   81
 1991  105   68   39   30   42   71   90  144  119  117   90   72
 1992   56    3  112  117   86   12  -22  -14  -12    0   51   35
 1993   40   36   95  143   61   83   87  209   62   22  -12  -21
 1994  -32  -31  -33  -14   15   22   23    2   -4    8   86   81
 1995   -1   -5  -21   43   42  -14    7    2   26   -4   -9  -56
 1996  -47  -21   24   62   65   54  -68  -71  -55 -999 -999 -999
    References:
  • Eischeid, J. K., H. F. Diaz, R. S. Bradley, and P. D. Jones, 1991: A comprehensive precipitation data set for global land areas. Carbon Dioxide Info. Anal. Ctr., Num. Data Prod. TR051.
  • Hulme, M., 1992: A 1951-80 global land precipitation climatology for the evaluation of general circulation models. Climate Dynamics, 7, 57-72.
  • Hulme, M., 1994: Validation of large-scale precipitation fields in general circulation models. Global Precipitation and Climate Change, M. Desbois and F. Desalmand, Eds., NATO ASI Series, Springer-Verlag, 387-406.
  • Eischeid, J. K., C. B. Baker, T. R. Karl, and H. F. Diaz, 1995: The quality control of long-term climatological data using objective data analysis. J. Appl. Meteor., 34, 2787-2795.

    Mike Hulme requests that the following credit be used in publications.
    "gu23wld0096.dat (Version 1.0) constructed and supplied by Dr. Mike Hulme at the Climatic Research Unit, University of East Anglia, Norwich, UK. This work has been supported by the UK Department of the Environment, Transport, and the Regions (Contract EPG 1/1/48)."

    The Climatic Research Unit of the University of East Anglia has several rainfall data sets that are available to researchers.
    Data processing:
    The processing of the two data sets is as follows. The monthly data (Hulme) is smoothed once with 3-point running mean. Anomalies of both data sets are calculated with respect to 1950-79.

    Correlation of seasonal (Eischeid et al.) rainfall and the CTI, 1950-79.
    Image shows six grid boxes in the averaging region with correlations >0.65, and 0.18 for the Galapagos grid box. Other correlations are weak.

    Correlation of monthly (Hulme) rainfall and the CTI, 1950-79.
    Image shows six grid boxes in the averaging region with correlations >0.68, and 0.17 for the Galapagos grid box. Other island correlations are weak.

    The different spatial resolution of the data sets leads to the respective averaging regions being a little different, but the intent is to include the same islands. The rainfall index for each data set is taken as the average of the available gridboxes at each time point. The time series obtained from the two data sets are correlated at 0.922 for the period of common record, 1905-88.

    The number of grid boxes contributing in 1905-96
    Image shows at least 2 grid boxes contributing in 1905-96, and 8 or 9 between the mid-1920s and mid-1980s.
    ASCII file of the number of grid boxes contributing. Only Nauru (0.6S,166.9E) contributes data for 1892-1904. The Galapagos Islands (Eq., 90W) data begins in 1950, which underscores the degree to which this index is more typical of central and western equatorial Pacific rainfall anomalies.

    The seasonal values (Eischeid et al) are ascribed to their constituent calendar months for the years 1892-1904 and the monthly (Hulme) values are used for 1905-96. Seasonal means tend to be smoother than monthly values, and so the values for 1892-1904 are multiplied by the ratio of the standard deviations of the seasonal series for 1950-79. If you don't like this, the original series values calculated from the Eischeid et al. data are provided next.

    The index values from the Eischeid et al. data are available here. The climatology is 1950-79 and no normalization has been performed. The CRU activities superseded those of Eischeid et al., and so the Eischeid et al. data set and the time series linked here will not be updated.

    June 1998
    Todd P. Mitchell (mitchell@atmos.washington.edu)
    JISAO data