Contribution of the sea surface temperature over the Mediterranean-Black Sea to the decadal shift of the summer North Atlantic Oscillation |
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| Authors: | Jianqi Sun Wei Yuan |
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| Institution: | Nansen-Zhu International Research Centre (NZC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029; Climate Change Research Center (CCRC), Chinese Academy of Sciences, Beijing 100029,China Meteorological Administration Training Centre, Beijing 100081 |
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| Abstract: | Recent observational study has shown that the southern center of the summer North Atlantic
Oscillation (SNAO) was located farther eastward after the late 1970s compared to before. In this study,
the cause for this phenomenon is explored. The result shows that the eastward shift of the SNAO southern
center after the late 1970s is related to the variability of the Mediterranean-Black Sea (MBS) SST. A
warm MBS SST can heat and moisten its overlying atmosphere, consequently producing a negative sea level
pressure (SLP) departure over the MBS region. Because the MBS SST is negatively correlated with the SNAO,
the negative SLP departure can enhance the eastern part of the negative-phase of the SNAO southern center,
consequently producing an eastward SNAO southern center shift. Similarly, a cold MBS SST produces an eastward
positive-phase SNAO southern center shift.
The reason for why the MBS SST has an impact on the SNAO after the late 1970s but why it is not the case
beforehand is also discussed. It is found that this instable relationship is likely to be attributed to
the change of the variability of the MBS SST on the decadal time-scale. In 1951--1975, the variability of
the MBS SST is quite weak, but in 1978--2002, it becomes more active. The active SST can enhance the
interaction between the sea and its overlying atmosphere, thus strengthening the connection between the
MBS SST and the SNAO after the late 1970s. The above observational analysis results are further confirmed
by sensitivity experiments. |
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| Keywords: | summer North Atlantic Oscillation Mediterranean-Black Sea sea surface temperature decadal variability |
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