Some good links:

https://www.climate.gov/news-features/blogs/enso/what-mjo-and-why-do-we-care

http://www.esrl.noaa.gov/psd/map/clim/olr_modes/mapanim2.html

https://www.youtube.com/watch?v=bA230B4w9t8

http://envam1.env.uea.ac.uk/mjo.html