- Southern Oscillation Index (SOI) from University of East Anglia
- 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
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.
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.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.
This data set will be updated as new data is made available.
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
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.
Name and Directory Information
- 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
- Filename
- so_osc_indx
- Directory Path
- /data/inter_disc/surf_temp_press/soi/giss
Not Applicable
Theoretical Basis of DataThe 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.
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).
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.
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
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.
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.
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.
| 
| 
|
|
| NASA | Goddard | GDAAC | CIDC |
Last update:Mon Oct 27 14:53:05 EDT 1997