APCC BSISO (Boreal Summer Intraseasonal Oscillation) Index

The Boreal Summer Intraseasonal Oscillation (BSISO), one of the dominant phenomena over the Asian summer monsoon region, is characterized by northward/northeastward propagation over the Indian summer monsoon region and northward/northwestward propagation over the Western North Pacific-East Asian region, including equatorial eastward propagation.

The BSISO forecast activity has been initiated in 2013 with the goal of improving our ability to understand and forecast the BSISO based on numerical models in cooperation with the CAS/WCRP Working Group on Numerical Experimentation (WGNE) Madden Julian Oscillation (MJO) Task Force, and hosted at the APEC Climate Center (APCC).

The method to define the BSISO indices uses multivariate empirical orthogonal functions (MV-EOF) analysis of daily mean outgoing longwave radiation (OLR) and 850-hPa zonal wind (U850) anomalies over the Asian summer monsoon region (10S-40N, 40-160E) from 1 May to 31 October (Lee et al. 2013). The OLR and U850 anomalies are obtained by removing the slow annual cycle (mean and first three harmonics of climatological annual variation) as well as the effect of interannual variability by subtracting the running mean of the last 120 days as in Wheeler and Hendon (2004). The two anomaly fields are each normalized by their area averaged temporal standard deviation over the Asian summer monsoon region. After applying the MV-EOF on the normalized OLR and U850 anomalies, the first four MV-EOF modes are identified as important for representing the BSISO over the Asian summer monsoon region.

BSISO participating models

Table 1. Organization
Abbreviation for model Center/Institution Country System name
BOM Bureau of Meteorology Australia ACCESS-S1
CWB Central Weather Bureau Chinese Taipei TCWB1T1.1
ECM European Centre for Medium-Range Weather Forecasts ECMWF council ECMWF Ensemble Forecast
CFS National Oceanic and Atmospheric Administration United States of America CFSv2
CFS National Oceanic and Atmospheric Administration United States of America GFS

BSISO Temporal Coverage

Daily or sub-daily data up to 20 days (16 days for GFS) lead time from May to October
*Lead time means the length of time between the issuance of a forecast and the occurrence of the phenomena that were predicted

Data Format



APCC(APEC Climate Center, Busan, Korea)

More information on each model and BSISO index is available at: Model Description, Forecast


  1. Lee, J.-Y., B. Wang, M. C. Wheeler, X. Fu, D. E. Waliser, and I.-S. Kang, 2013: Real-time multivariate indies for the boreal summer intraseasonal oscillation over the Asian summer monsoon region. Climate Dynamics, 40, 493-509.
  2. Wheeler, M. C. and H. H. Hendon, 2004: An all-season real-time multivariate MJO index: Development of an index for monitoring and prediction. Monthly Weather Review, 132, 1917-1932.



When you use the APCC BSISO Index data in any documents or publications, please acknowledge us by including the following text, “The authors acknowledge the participant operation centers for making their forecast data available for analysis and the APEC Climate Center for collecting and archiving them and for organizing APCC BSISO forecast.”

BSISO data is updated daily and may change depending on operational situation.


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