Heat waves and MJO: prospects for subseasonal excessive heat outlooks

Heat waves affect human health and several sectors of the economy from agriculture and fisheries to energy production. For example, the heat wave that affected Chicago in 1995 led to approximately 750 heat-related deaths over a period of five days. The principal cause and origin of this heat wave was a slow-moving, hot, and humid air mass which was produced by a very strong upper-level ridge of high pressure. This ridge originated as an amplification of the climatologically normal weak ridge which exists in the western United States in July. Its growth was a downstream adjustment of the westerly winds to a major weather disturbance affecting the subtropical ridge in the western Pacific Ocean several days before. At the same time a MJO event was established in the Indian Ocean and propagated northeastward. In this work we are classifying heat events that occurred around the globe based on their intensity and duration. For this classification we use temperature and humidity at 2 meters from the NOAA/NCAR Reanalysis-1. We then use the Real-time Multivariate MJO index (RMM) for classifying the phase and intensity of MJO events in the period of 1-4 weeks before the occurrence of a heat event. Finally, we use these results to discuss the potential for subseasonal excessive heat outlooks.