Extension of the bimodal intraseasonal oscillation index using JRA-55 reanalysis
Advanced Search
Select up to three search categories and corresponding keywords using the fields to the right. Refer to the Help section for more detailed instructions.

Search our Collections & Repository

For very narrow results

When looking for a specific result

Best used for discovery & interchangable words

Recommended to be used in conjunction with other fields



Document Data
Clear All
Clear All

For additional assistance using the Custom Query please check out our Help Page


Extension of the bimodal intraseasonal oscillation index using JRA-55 reanalysis

Filetype[PDF-2.40 MB]


  • Journal Title:
    Climate Dynamics
  • Personal Author:
  • NOAA Program & Office:
  • Description:
    This study aims to extend the bimodal intraseasonal oscillation (ISO) index, developed by Kikuchi et al. (Clim Dyn 38:1989–2000, 2012), using JRA-55 reanalysis back in time to 1958. The bimodal ISO index is composed of two distinct ISO indices: the Madden–Julian oscillation (MJO) index and the boreal summer ISO (BSISO) index, each aiming to capture the ISO behavior during boreal winter and summer, respectively. These indices are derived by means of extended empirical orthogonal function (EEOF) analysis applied to outgoing longwave radiation (OLR) during boreal winter and summer, respectively. By combining the MJO and BSISO indices, the state of the ISO can be reasonably represented over the course of the year. First, the original index is updated using observed OLR until recently (–Jan. 2017) with a modification of the use of extended winter and summer months (Dec.–Apr./Jun.–Oct.) instead of normal winter and summer months (Dec.–Feb./Jun.–Aug.) in EEOF analysis. The updated version is quite consistent with the original counterpart, whereas it is arguably able to represent the ISO more faithfully throughout the year. In the same manner, a JRA-55-based index is constructed. Although JRA-55 OLR has systematic biases, the resulting JRA-55-based bimodal ISO index is in excellent agreement with the observation-based index. A comparison between JRA-55 and its subset, JRA-55C (satellite observations are not assimilated at all) suggests that the JRA-55-based index is reliable even in the pre-satellite era. Interannual variability and long-term trend of the ISO activity are also discussed. The newly developed, long-term JRA-55-based index will be useful for a number of applications.
  • Keywords:
  • Source:
    Climate Dynamics, 54(1), 919-933
  • DOI:
  • Document Type:
  • Funding:
  • Rights Information:
    Accepted Manuscript
  • Compliance:
  • Main Document Checksum:
  • Download URL:
  • File Type:

Supporting Files

  • No Additional Files
More +

You May Also Like

Checkout today's featured content at repository.library.noaa.gov

Version 3.26.1