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Publication Date
12 April 2019

MJO Phases Precede Extreme California Heat Waves

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OLR anomalies and MJO phases in 2 weeks prior to California heat

Using outgoing longwave radiation and velocity potential anomalies the paper shows links between extreme summertime heat waves over California’s Central Valley (CCV) and tropical convection as identified by specific Madden-Julian Oscillation (MJO) phase pairs. Strong MJO pairs 8 and 1 or 2 and 3 occur within two weeks prior to the extreme California heat.


The paper shows for the first time that about half of the extreme summertime heat waves over California are linked to tropical enhanced convection. This provides another analysis tool by which to evaluate climate model simulations.

  • Summertime California heat waves (HWs) are preceded by MJO convection in the Indian Ocean and Southeast Asia and eastern tropical Pacific.
  • In MJO phases 2-3 and 8-1, VP and OLR fields over California are part of a larger response extending into the subtropical eastern Pacific.
  • Cluster 1 HWs heat waves (that form at in California) are more linked to MJO phases than are Cluster 2 ones (from existing HWs heat waves that expand over California).
Point of Contact
Richard Grotjahn
University of California Davis (UC Davis)
Funding Program Area(s)