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Publication Date
12 April 2019

Evidence of Specific MJO Phase Occurrence with Summertime California Central Valley Extreme Hot Weather



This study examines associations between California Central Valley (CCV) heat waves and the Madden Julian Oscillation (MJO). These heat waves have major economic impacts. Our prior work showed that CCV heat waves are frequently preceded by convection over the tropical Indian and eastern Pacific oceans, in patterns identifiable with MJO phases. The main analysis method examines lagged composites (formed after each MJO phase pair) of CCV synoptic station temperature, outgoing longwave radiation (OLR), and velocity potential (VP). Over the CCV, positive temperature anomalies are observed only after the Indian Ocean (phases 2-3) or the eastern Pacific Ocean (phases 8-1) convection (implied by OLR and VP fields). The largest fractions of the CCV hot days occur during those two phase pairs. OLR and VP composites have significant subsidence and convergence above divergence over the CCV during heat waves, and these structures are part of a larger pattern extending into the subtropical eastern Pacific during MJO phase pairs 2-3 and 8-1. Prior studies showed that CCV heat waves can be roughly grouped into two clusters: Cluster 2 is preceded by a heat wave over northwestern North America, while Cluster 1 is not. OLR and VP composite analyses are applied separately to these two clusters. However, for Cluster 2, the subsidence and VP over the CCV are not significant, and the large-scale VP pattern has a low correlation with the MJO lagged composite field. Therefore, the association between the MJO convection and subsequent CCV heat wave is more evident in Cluster 1 than Cluster 2.

“Evidence Of Specific Mjo Phase Occurrence With Summertime California Central Valley Extreme Hot Weather”. 2019. Advances In Atmospheric Sciences 36: 589-602. doi:10.1007/s00376-019-8167-1.
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