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| Titel |
Examination of Arabian Sea SST biases in the HiGEM high resolution coupled climate model and the CMIP3 multi-model dataset |
| VerfasserIn |
Deepthi Marathayil, Len Shaffrey, Andrew Turner, Julia Slingo |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037974
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| Zusammenfassung |
| The Arabian Sea region undergoes a pronounced seasonal cycle relating to upwelling, mixing
and monsoon dynamics. Any variations in high temperatures of the region may
affect the availability of moisture supply to the Indian summer monsoon. Seasonal
analysis has been performed for various ocean and atmosphere data from a present
day control run in the Indian Ocean region of the HiGEM High Resolution Global
Environment Model. When compared with observed and reanalysis datasets such as
HadISST, SODA reanalysis and ARGO floats for SST and ocean potential temperature,
we find a significant cold bias of around 2-C in HiGEM boreal winter SST. This
bias persists through springtime in the northern Arabian Sea, potentially to the
detriment of the subsequent Indian summer monsoon which is deficient in this model.
Meridional cross-sections of ocean potential temperature and salinity along 65-E
also reveal the existence of a deeper mixed layer extending to 300m with highly
saline water in the same area. Near-surface winds in HiGEM reveal very strong
northeasterly wind biases during boreal winter, which may be the result of a strong
north-south air temperature gradient. Compared to estimates from CRU and ERA40, a
large cold bias of more than 8-C is observed in HiGEM surface air temperature
over northern India during the same season. We suspect that the cold SST bias in
the northern Arabian Sea is due to coupling with the strong wind and evaporation
biases in HiGEM. Seasonal analysis of modelled latent heat flux in comparison with
NOCS (National Oceanographic Centre Southampton) data also suggests that the
evaporation rate in HiGEM is too strong over the northern Arabian Sea during
winter.
Similar analysis was also carried out for the 20th century simulations from the CMIP3
multi-model dataset. Most of the models show a similar cold bias in the Arabian Sea SST and
in northern Indian air temperature during boreal winter. However the mixed layer depth
biases show wide variations in each model due to different air-sea interaction processes.
Models with stronger north-to-northeasterly wind biases over the Arabian Sea also show a
large bias in the northern Arabian Sea winter SST. A further related error in the region
consists of excessive winter precipitation over the west equatorial Indian Ocean (WEIO) in
HiGEM and many of the CMIP3 models, related to anomalous low-level convergence
into the region. We explore connections with the Arabian Sea biases further north
with the hypothesis that precipitation biases in the WEIO region, combined with
surface temperature biases over northern India during boreal winter, may act to the
detriment of accurate mean state simulation of the Arabian Sea. Further study is
needed on this topic to determine the impact on the subsequent Indian summer
monsoon. |
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