Jökull - 01.12.1969, Side 52

It turned out that the correlation coefficient
between the ice incidence estimated from this
formula and the actual ice incidence was 0.93,
taking into account 45 years of observations.
This is a highly significant correlation and
should justify an annual ice forecast issued at
the end of November.
Having obtained this prognostic formula one
may ask liow accurately the forecast can be
stated. In the first place it is very difficult to
determine the actual annual ice incidence witli
greater accuracy than to the next whole month,
even if we have in the computations used one
decimal figure in these values. The forecast is
by nature more uncertain. According to tlie
scatter diagram in Fig. 4 this additional un-
certainty may be estimated to correspond to
± 0.3° C in the determination of the JM-
temperature. Accorclingly it seems reasonable
to state the annual ice forecasts as listed be-
low:
TABLE 1
JM-temperature Forecast,
0 C months
2.1 or higher 0
1.5-2.0 0-1
1.4 1
1.0—1.3 1-2
O GO 1 o o 1-3
p 1 O 2-4
0.4 2-5
0.3 3-5
0.2 3-6
0.0, 0.1 4-7
-0.1 4-8
In the following table we give the estimated
and actual ice incidence for every ice year
when the JM-temperature has been available:
Of these 46 pairs of estimated and actual
values 41 cases give the actual ice incidence
within the estimated interval. Particularly in
the last decade with alternating light and
heavy ice years, the “forecasts” are very satis-
factory.
In Fig. 5 the estimated and actual ice incid-
ence may be studied graphically.
TABLE2
Ice incidence
Ice year Estimated Actual
1921/1922 1 0
1922/1923 0-1 0
1923/1924 0-1 0
1924/1925 0 0
1925/1926 0 0
1926/1927 0-1 0
1927/1928 0-1 0
1928/1929 0 1
1929/1930 0-1 0
1930/1931 0 0
1931/1932 0 2
1932/1933 0-1 0
1933/1934 0 0
1934/1935 0 0
1935/1936 0 0
1936/1937 0 0
1937/1938 0 1
1938/1939 0 0
1939/1940 0 0
1941/1942 0 0
1943/1944 1-2 2
1944/1945 0-1 0
1945/1946 0 1
1946/1947 0 0
1947/1948 0 0
1948/1949 1-2 1
1949/1950 0 0
1950/1951 0 0
1951/1952 0-1 0
1952/1953 0 0
1953/1954 0 0
1954/1955 0 0
1955/1956 0-1 0
1956/1957 0-1 0
1957/1958 0 0
1958/1959 0 0
1959/1960 0 0
1960/1961 0 0
1961/1962 0 0
1962/1963 1-2 1
1963/1964 0 0
1964/1965 3-5 4
1965/1966 0-1 0
1966/1967 1-2 2
1967/1968 4-7 5
1968/1969 3-6 5
48 JÖKULL 19. ÁR
J