地球惑星科学専攻 地球科学輻合部特別講演会

講演題名：
Reconstruction of Near-Global Precipitation Variations Based on Gauges
and Correlations with SST and SLP

講演者：
Dr. Thomas M. Smith
NOAA/NESDIS/STAR/SCSB, University of Maryland, College Park, Maryland,
USA

日時・場所:
2010年5月31日(月) 16：30〜17：30
京都大学理学部1号館5階563号室

講演要旨:
Over the last 15 years a number of methods were developed for
reconstructing near-global temperature and surface pressure variations
using historical data and reconstruction statistics.  Reconstruction
statistics are based on the more dense modern data, and satellite data
are especially valuable because of their more nearly complete sampling.
 Those reconstructions help to more clearly show climate variations over
more than a hundred years.  Reconstructions are especially valuable over
the oceans where data are limited, and both sea-surface temperature
(SST) and sea-level pressure (SLP) variations have been reconstructed
using mostly for historical ship observations.  Oceanic precipitation is
another important climate variable, and a reconstruction of that would
also be of value.  However, historical oceanic precipitation data are
limited because historical ship reports are typically only qualitative
if they exist at all.  In addition, individual precipitation events have
smaller time and space scales than SST or SLP, making the available
ocean-area records less representative of large-scale monthly or
longer-term variations.

Using satellite-based precipitation estimates for reconstruction
statistics, several groups have attempted to reconstruct monthly-average
historical precipitation over oceans from land and island gauge
variations.  Those studies use the largest land-sea spatial modes to
estimate ocean-area variations associated with the modes.  A weighted
sum of the modes is formed using the land and island historical gauge
data to determine the best weights for the modes.  This method works
best for precipitation associated with large-scale modes accounting for
large parts of the variance, such as ENSO or NAO.  In our experiments we
first tested this gauge-based method, making improvements where
possible.  We found that this method can resolve much of the oceanic
interannual precipitation variation.  For multi-decadal variations we
found this method to be less reliable.  Those variations account for
less overall variance than interannual modes like ENSO, and may need
more sampling to be reliably reconstructed.  Therefore we developed a
second reconstruction method that indirectly estimates precipitation
from SST and SLP.  This indirect method does not use the gauge data, but
it is able to reconstruct large-scale land variations where gauges are
available.  Over the oceans the indirect method shows increasing
interannual variations, consistent with theoretical estimates for a
warming world.  These two reconstructions, one direct from land and
island gauges and the other indirect for correlations with SST and SLP,
are combined to form a monthly reconstruction of historical
precipitation beginning 1900.

問い合わせ先:
重 尚一