PDO-20 annual means
  1854.     -0.8067
  1855.     -0.7508
  1856.     -0.4517
  1857.     -0.1642
  1858.      0.0300
  1859.     -1.0333
  1860.     -0.0075
  1861.     -0.8775
  1862.     -0.0692
  1863.      0.0233
  1864.     -0.2275
  1865.     -0.4025
  1866.     -0.4433
  1867.     -0.3075
  1868.     -0.2100
  1869.      0.7750
  1870.     -0.6142
  1871.     -0.3758
  1872.     -0.8258
  1873.     -0.9775
  1874.     -0.1000
  1875.     -1.0083
  1876.     -1.1508
  1877.     -0.8308
  1878.      0.6442
  1879.     -0.6708
  1880.     -1.8108
  1881.     -0.5092
  1882.     -1.7500
  1883.     -1.2917
  1884.      0.5375
  1885.      0.0858
  1886.     -0.7875
  1887.     -1.1858
  1888.      0.5367
  1889.      0.1583
  1890.     -0.7558
  1891.     -0.4083
  1892.     -1.0975
  1893.     -1.7767
  1894.     -2.9075
  1895.     -0.6683
  1896.     -0.3500
  1897.      0.4542
  1898.      0.3300
  1899.     -0.3650
  1900.      0.5208
  1901.     -0.0833
  1902.      1.0933
  1903.      0.1283
  1904.      0.7317
  1905.      1.1600
  1906.      0.5083
  1907.      0.5175
  1908.      0.4317
  1909.     -0.9033
  1910.     -0.7525
  1911.     -0.5867
  1912.      0.0500
  1913.      0.1308
  1914.     -0.4292
  1915.     -0.0950
  1916.     -1.7625
  1917.     -1.2383
  1918.      0.0617
  1919.     -0.8475
  1920.     -1.4242
  1921.     -1.2758
  1922.     -0.9350
  1923.     -0.4000
  1924.     -1.1117
  1925.     -0.3125
  1926.      1.5875
  1927.     -0.0058
  1928.      0.0042
  1929.      0.4750
  1930.      0.1367
  1931.      0.6325
  1932.     -0.5542
  1933.     -1.6375
  1934.      0.7817
  1935.      0.4717
  1936.      1.4808
  1937.     -0.0758
  1938.     -0.1367
  1939.     -0.3542
  1940.      1.8300
  1941.      2.3700
  1942.      0.2217
  1943.     -0.1708
  1944.     -0.9142
  1945.     -0.6508
  1946.     -0.1692
  1947.      0.4167
  1948.     -0.9067
  1949.     -1.5592
  1950.     -2.1558
  1951.     -1.1592
  1952.     -1.3458
  1953.     -0.6350
  1954.     -0.2608
  1955.     -2.2225
  1956.     -1.7483
  1957.      0.5175
  1958.      0.9367
  1959.      0.2450
  1960.      0.0933
  1961.     -0.6983
  1962.     -1.0458
  1963.     -0.2433
  1964.     -0.9700
  1965.     -0.1475
  1966.     -0.4608
  1967.     -0.8242
  1968.     -0.1950
  1969.     -0.2458
  1970.     -0.6117
  1971.     -1.4092
  1972.     -1.0100
  1973.     -1.2425
  1974.     -0.3533
  1975.     -1.4975
  1976.      0.0208
  1977.     -0.0350
  1978.     -0.0667
  1979.      0.1100
  1980.      0.3450
  1981.      0.7000
  1982.     -0.2275
  1983.      1.2733
  1984.      0.5500
  1985.      0.0108
  1986.      0.9942
  1987.      1.0217
  1988.     -0.2058
  1989.     -0.4792
  1990.     -0.9675
  1991.     -0.7850
  1992.      0.6708
  1993.      1.0683
  1994.     -0.6783
  1995.      0.4708
  1996.      0.5667
  1997.      1.2817
  1998.     -0.5975
  1999.     -1.9067
  2000.     -0.9000
  2001.     -1.2108
  2002.     -0.3325
  2003.      0.1533
  2004.     -0.3300
  2005.     -0.2233
  2006.     -0.5617
  2007.     -0.8483
  2008.     -1.7667
  2009.     -0.9383
  2010.     -1.2975
  2011.     -1.9133
  2012.     -1.5900
  2013.     -1.1850
  2014.      0.6808
  2015.      0.8692
  2016.      0.4992
  2017.     -0.0842
  2018.     -0.4958
  2019.     -0.2375