In 1971, meteorologists Roland Madden and Paul Julian studied weather data from near equatorial Pacific islands. To their surprise, tropospheric winds, pressure and rainfall oscillated with a period of about 40 to 50 days.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/resolving-atmospheric-enigma
[2] http://admin.indiaenvironmentportal.org.in/category/author/dennis-l-hartmann
[3] http://admin.indiaenvironmentportal.org.in/category/author/harry-h-hendon
[4] http://admin.indiaenvironmentportal.org.in/category/journal/science
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/oceans-and-seas
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/indian-ocean
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/atmosphere-and-ozone-layer
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/atmosphere-science
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/el-nino
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/monsoons
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-change
[12] http://admin.indiaenvironmentportal.org.in/category/thesaurus/rainfall-pattern