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[CIDC FTP Data]
[ Southern Oscillation Index CIDC Data on FTP]
Data Access
Southern Oscillation Index (SOI) from University of East Anglia
[rule]
Readme Contents
Data Set Overview
Sponsor
Original Archive
Future Updates
The Data
Characteristics
Source
The Files
Format
Name and Directory Information
Companion Software
The Science
Theoretical Basis of Data
Processing Sequence and Algorithms
Scientific Potential of Data
Validation of Data
Contacts
Points of Contact
References
[rule]
Data Set Overview
Concerns have grown over recent years about the low-frequency
fluctuations in the El Nino-Southern Oscillation (ENSO) and its
possible modulation by the greenhouse effect. In order to gain a
greater understanding of the longer term variability and influence
of this near global, ocean-atmosphere phenomenon, attempts have
been made to distinguish between wider ranging ENSO phases based
on related eastern hemisphere events and more localized El Nino
events, which influence only the immediate South American region.
The Southern Oscillation Index (SOI) based on the Tahiti-Darwin
mean sea level pressure difference is an important indicator in
the study of these events.
The method of calculation for the SOI is given in Ropelewski and
Jones (1987). There are various ways of differencing the Tahiti
and Darwin data. All missing Darwin data are infilled from
Djakarta. Missing Tahiti data are infilled from Apia, Samoa Suva,
Fiji and Santiago, Chile. Because of the missing data, some of the
years before about 1920 are somewhat less reliable than the later
values.
Sponsor
The production and distribution of this data set are funded by
NASA's Earth Science enterprise. The data are not copyrighted;
however, we request that when you publish data or results using
these data please acknowledge as follows:
The authors wish to thank Phil D. Jones, C.F.
Ropelewski, R.J. Allan and the Climatic Research Unit,
School of Environmental Sciences, University of East
Anglia, Norwich, U.K., for the production of this data
set, and the Distributed Active Archive Center (Code
902.2) at the Goddard Space Flight Center, Greenbelt,
MD, 20771, for putting these data in their present
format and distributing them. These distribution
activities were sponsored by NASA's Earth Science
enterprise.
Original Archive
This data set was constructed by the Climatic Research Unit (CRU)
at East Anglia University. This is also the location of the
primary archive and the source for detailed information concerning
this data set. The data in its original format can be obtained
from CRU points of contact.
Future Updates
This data set will be updated as new data is made available.
The Data
Characteristics
* Parameters: Normalized pressure difference Tahiti minus
Darwin
* Units: Dimensionless
* Typical Range:
* Temporal Coverage: January, 1866 - May, 1997
* Temporal Resolution: Monthly means
* Spatial Coverage: The region of the South Pacific between
Darwin, Australia (131 deg E., 12 deg S.) and Papeete, Tahiti
(149 deg W, 17 deg S).
* Spatial Resolution: Point data
Source
This dataset was compiled from a variety of sources. Data for
Tahiti covering the period 1875 to 1933 were taken at the hospital
in Papeete and obtained from manuscript records held by the French
Meteorological Service. Additional data for Tahiti covering the
period between 1932 to 1934 were obtained from Reseau Mondial.
Data for Darwin for the period after 1908 were obtained from the
Commonwealth Bureau of Meteorology in Australia. Data for Darwin
for the period 1876 to 1907 were obtained from reports by the
Adelaide Observatory in South Australia, with overlapping data
from the Smithsonian Institution and the Australian Bureau of
Meteorology. Recently, additional data obtained from publications
of the Adelaide Observatory held in the Northern Territory Branch
of the Australian Archives were found that extends the coverage to
the period 1865 to 1881. Data from Tahiti and Darwin were obtained
from World Weather Records publications for the period after 1935.
The Files
Format
* File Size: 1 file, ~13000 bytes
* Data Format: ascii, tabular, one row per year
Left column: year
Next 12 columns: monthly mean values
right column: annual average
* Headers, trailers and delimiters: NA
* Fill value: none
Name and Directory Information
Filename
so_osc_indx
Directory Path
/data/inter_disc/surf_temp_press/soi/giss
Companion Software
Not Applicable
The Science
Theoretical Basis of Data
The Southern Oscillation (SO) is a planetary scale phenomenon
involving a negative correlation between pressure over Indonesia
and pressure over the southeastern Pacific. It is related to
fluctuations in the intensity and position of the Walker
circulation, an east-west cell with its upward branch near
Indonesia and downward branch over the tropical eastern Pacific.
When the Southern Oscillation is coupled with warming of the ocean
off Peru and Ecuador (El Nino) the resulting El Nino/Southern
Oscillation (ENSO) event can effect weather and precipitation over
much of the Tropics and Subtropics. The Southern Oscillation Index
(SOI)is based on the mean sea level pressure difference between
Tahiti, French Polynesia and Darwin, Australia (Tahiti - Darwin).
For more detailed information, see Ropelewski and Jones (1987) and
Allan et al. (1991).
Processing Sequence and Algorithms
Bias corrections were made to the surface pressures as follows:
The earlier pressure records are not considered to be as
consistent as the later measurements and therefore certain bias
adjustments were made (Ropelewski and Jones, 1987).
Years Location Bias correction in millibars
1896 Tahiti + 1.0
1909-16 Tahiti + 0.5
1917-25 Tahiti + 2.0
1927-34 Tahiti - 1.6
1882-July 1898 Darwin + 1.0
It is believed that the + 1.0 bias correction made to the Darwin
pressure data prior to August 1898 could be due in part to changes
made to the type of barometer used and in part to changes in the
barometer cistern height. In fact documentation exist that suggest
this possibility, (Todd, 1910 and Griffiths, 1910).
To form the SOI, the annual cycle of pressure at each station was
removed by forming anomalies, or differences, from the long-term
monthly averages. These monthly anomalies were then normalized by
the appropriate monthly standard deviations, and then the
difference Tahiti minus Darwin was taken. The 1951-1980 period was
used as the base period for computations of the means and standard
deviations.
Scientific Potential of Data
The Southern Oscillation Index (SOI) is useful in several types of
studies such as:
* Studies of Australian weather and rainfall patterns (McBride
and Nicholls, 1983).
* The relationship between sea surface warmings off the coast
of Peru (EL Ninos) and the Southern Oscillation (Deser and
Wallace, 1987)
* Examination and identification of El Nino/Southern
Oscillation events (Rasmusson, 1985).
Validation of Data
The bias-corrected pressure data for Papeete, Tahiti, as the base
station, were compared to Santiago, Apia, Suva, and Darwin through
the computation of monthly correlation coefficients for the
1890-1934 and the 1935-85 time period. Differences were found
between the two time periods but were no greater than differences
found when comparisons were made between other station pairs. It
is therefore believed that there are no unique inconsistencies in
the early Tahiti pressure data. However, because of some questions
concerning the earlier data, the SOI for the years 1935 onward are
considered to be of somewhat higher quality than those for the
earlier years.
Comparisons have been made with various other methods of SOI
computation. The early CRU Tahiti/Darwin SOI is in broad agreement
with a Seasonal Southern Oscillation index (Wright, 1989). There
are similarities in temporal structure but a slightly weaker index
magnitude. The CRU-SOI was in almost complete agreement with the
index computed by Troup (1965). Comparison of the CRU-SOI with
another form of the Southern Oscillation Index by Trenberth (1976)
shows that the Trenberth form of the index had considerably more
amplitude but did reflect the same positive and negative trends in
most cases. Elliott and Angell (1988) examine the relationship
between a number of different Southern Oscillation indices.
Contacts
Points of Contact
For information about or assistance in using any DAAC data,
contact
EOS Distributed Active Archive Center (DAAC)
Code 902.2
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
Internet: daacuso@daac.gsfc.nasa.gov
301-614-5224 (voice)
301-614-5268 (fax)
To inquire about or order the original CRU Southern Oscillations
Index data set, contact
Dr. P.D. Jones
Climatic Research Unit
School of Environmental Sciences
University of East Anglia
Norwich NR4 7TJ
UNITED KINGDOM
Internet: P.Jones@uea.ac.uk
Telephone: (0603) 592090
Dr. Robert J. Allan
CSIRO, Division of Atmospheric Research
Station Street, Aspendale
Vic Postal Address:
Private Bag No. 1, Mordialloc, Vic 3195
Melbourne, Australia
References
Allan, R. J., N. Nicholls, P. D. Jones, and I. J. Butterworth,
1991: A further extension of the Tahiti-Darwin SOI, Early ENSO
events and Darwin pressure, J. Climate, 4, 743-749.
Deser, C., and J.M. Wallace, 1987: El Nino events and their
relation to the Southern Oscillation: 1925-1986, J. Geophys. Res.,
92, 14189-14196.
Elliott, W. P., and J. K. Angell, 1988: Evidence for changes in
Southern Oscillation Relationships during the last 100 years, J.
Climate,, 1, 729-737.
Griffiths, R.F., 1910: Meteorological Observations Made at the
Adelaide Observatory During the Year 1907, Government Printer,
Adalaide, South Australia, 250 pp.
McBride, J.L., and N. Nicholls, 1983: Seasonal Relationships
between Australian rainfall and the Southern Oscillation, Mon.
Wea. Rev., 111, 1998-2004.
Rasmussen, E.M., 1985: El Nino and variations in climate, American
Scientist,73, 168-177.
Ropelewski, C. F., and P. D. Jones, 1987: An extension of the
Tahiti-Darwin Southern Oscillation Index, Mon. Wea. Rev., 115,
2161-2165.
Todd, C., 1879-1910: Meteorological Observations made at the
Adelaide Observatory for the Years 1879 to 1906, Government
Printer, Adelaide, South Australia.
Todd, C., 1881: Meteorological Observations made at the Adelaide
Observatory for the Years 1879, Government Printer, Adelaide,
South Australia, 250 pp.
Trenberth, K. E., 1976: "Spatial and Temporal Variations of the
Southern Oscillation, Quart. J. Roy. Meteor. Soc., 102, 639-653.
Troup, A.J., 1965: The Southern Oscillation, Quart. J. Roy.
Meteor. Soc., 91, 490-506.
Wright, P.B., 1989: Homogenized Long-Period Southern Oscillation
Indices, Int. J. Climatol., 9, 33-54.
------------------------------------------------------------------------
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