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Impact of daily fluctuations on long‐term predictability of the Atlantic meridional overturning circulation
Author(s) -
von Storch J.S.,
Haak H.
Publication year - 2008
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2007gl032385
Subject(s) - predictability , climatology , term (time) , forcing (mathematics) , environmental science , thermohaline circulation , flux (metallurgy) , atmospheric sciences , physics , mathematics , geology , statistics , materials science , metallurgy , quantum mechanics
The first continuous assessment of the Atlantic meridional overturning circulation (MOC) indicates strong MOC variability on time scales of about a few weeks. A large part of this variability results from, or is related to, wind stress forcing, which is not predictable beyond a few weeks. The presence of short‐term MOC fluctuations could significantly limit long‐term MOC predictability which owes its potential to the slow components in ocean dynamics. To quantify this limitation, two null hypotheses that address not only the existence but also the strength of slow dynamics are tested. Daily and yearly MOC time series generated by the ECHAM5/MPI‐OM model are used for this purpose. The tests compare the variance generated by slow dynamics with that of short‐terms fluctuations that extend into low frequencies. The comparison is done for total variances as well as for variances within different low‐frequency ranges. It is found that the model's slow dynamics become noticeable only on time scales longer than three years. The variance generated by the slow dynamics dominate that related to the low‐frequency extension of unpredictable noise only on time scales longer than 10 years. In order to utilize the potential predictability originating from slow processes, a prediction should correctly capture slow processes in the initial state by assimilating observations over a period of at least three years.