27 research outputs found
2,000-year-long temperature and hydrology reconstructions from the Indo-Pacific warm pool
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 460 (2009): 1113-1116, doi:10.1038/nature08233.Northern Hemisphere surface temperature reconstructions suggest that the late
twentieth century was warmer than any other time during the past 500 years and
possibly any time during the past 1,300 years. These temperature
reconstructions are based largely on terrestrial records from extra-tropical or highelevation
sites; however, global average surface temperature changes closely follow
those of the global tropics, which are 75% ocean. In particular, the tropical Indo-
Pacific warm pool (IPWP) represents a major heat reservoir that both influences
global atmospheric circulation and responds to remote northern latitude forcings.
Here we present a decadally resolved continuous sea surface temperature (SST)
reconstruction from the IPWP that spans the past two millennia and overlaps the
instrumental record, enabling both a direct comparison of proxy data to the
instrumental record and an evaluation of past changes in the context of twentieth
century trends. Our record from the Makassar Strait, Indonesia, exhibits trends that
are similar to a recent Northern Hemisphere temperature reconstruction.
Reconstructed SST was, however, within error of modern values during the Medieval
Warm Period from about AD 1000 to AD 1250, towards the end of the Medieval Warm
Period. SSTs during the Little Ice Age (approximately ad 1550–1850) were variable,
and 0.5 to 1°C colder than modern values during the coldest intervals. A companion
reconstruction of δ18O of sea water—a sea surface salinity and hydrology indicator—
indicates a tight coupling with the East Asian monsoon system and remote control of
IPWP hydrology on centennial–millennial timescales, rather than a dominant
influence from local SST variation.This work
was financially supported by the US NSF and the Ocean Climate Change Institute of
WHOI
Coupled atmosphere–mixed layer ocean response to ocean heat flux convergence along the Kuroshio Current Extension
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Climate Dynamics 36 (2011): 2295-2312, doi:10.1007/s00382-010-0764-8.The winter response of the coupled atmosphere-ocean mixed layer system to
anomalous geostrophic ocean heat flux convergence in the Kuroshio Extension is
investigated by means of experiments with an atmospheric general circulation model
coupled to an entraining ocean mixed layer model in the extra-tropics. The direct
response consists of positive SST anomalies along the Kuroshio Extension and a
baroclinic (low-level trough and upper-level ridge) circulation anomaly over the North
Pacific. The low-level component of this atmospheric circulation response is weaker in
the case without coupling to an extratropical ocean mixed layer, especially in late winter.
The inclusion of an interactive mixed layer in the tropics modifies the direct coupled
atmospheric response due to a northward displacement of the Pacific Inter-Tropical
Convergence Zone which drives an equivalent barotropic anomalous ridge over the North
Pacific. Although the tropically-driven component of the North Pacific atmospheric
circulation response is comparable to the direct response in terms of sea level pressure
amplitude, it is less important in terms of wind stress curl amplitude due to the mitigating
effect of the relatively broad spatial scale of the tropically-forced atmospheric
teleconnection.We gratefully acknowledge
financial support from NOAA’s Office of Global Programs (grant to C. Deser and Y.-O.
Kwon). Y.-O. Kwon is also supported through the Claudia Heyman Fellowship of the
WHOI Ocean Climate Change Institute
Sensitivity of Asian Summer Monsoon precipitation to tropical sea surface temperature anomalies
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Attribution of 2012 extreme climate events: does air-sea interaction matter?
In 2012, extreme anomalous climate conditions occurred around the globe. Large areas of North America experienced an anomalously hot summer, with large precipitation deficits inducing severe drought. Over Europe, the summer of 2012 was marked by strong precipitation anomalies with the UK experiencing its wettest summer since 1912 while Spain suffered severe drought. What caused these extreme climate conditions in various regions in 2012? This study compares attribution conclusions for 2012 climate anomalies relative to a baseline period (1964–1981) based on two sets of parallel experiments with different model configurations (with coupling to an ocean mixed layer model or with prescribed sea surface temperatures) to assess whether attribution conclusions concerning the climate anomalies in 2012 are sensitive to the representation of air-sea interaction. Modelling results indicate that attribution conclusions for large scale surface air temperature (SAT) changes in both boreal winter and summer are generally robust and not very sensitive to air-sea interaction. This is especially true over southern Europe, Eurasia, North America, South America, and North Africa. Some other responses also appear to be insensitive to air-sea interaction: for example, forced increases in precipitation over northern Europe and Sahel, and reduced precipitation over North America and the Amazon in boreal summer. However, the attribution of circulation and precipitation changes for some other regions exhibits a sensitivity to air-sea interaction. Results from the experiments including coupling to an ocean mixed layer model show a positive NAO-like circulation response in the Atlantic sector in boreal winter and weak changes in the East Asian summer monsoon and precipitation over East Asia. With prescribed sea surface temperatures, some different responses arise over these two regions. Comparison with observed changes indicates that the coupled simulations generally agree better with observations, demonstrating that attribution methods based on atmospheric general circulation models have limitations and may lead to erroneous attribution conclusions for regional anomalies in circulation, precipitation and surface air temperature