Leveraging the Madden-Julian Oscillation and Equatorial Rossby Waves to Improve Probabilistic Temperature Forecasts

Past research has demonstrated the associations between large-scale, organized tropical convection and the extratropical circulation. These studies focused on the excitation of Rossby wave trains in the extratropical circulation by organized convection on intraseasonal and subseasonal time scales. As these waves evolve over the North Pacific and North America, they are often steered by the background westerly flow into the tropics of the eastern Pacific Ocean and, to a lesser extent, eastern Atlantic Ocean. Observational studies have demonstrated that circulations resembling equatorial Rossby (ER) waves often develop in association with the intrusion of extratropical upper-tropospheric troughs into the deep tropics, and intersect lower frequency convection over the West Pacific. The intersection of this convection and the westward moving ER waves further enhances the lower-frequency convection, often associated with the Madden-Julian oscillation (MJO), which helps to excite new wave trains in the extratropics. This framework for studying tropical-extratropical interactions has been used to show that knowing the location of ER waves during an active MJO event yields more information about the extratropical circulation than knowing only about the MJO or ER waves separately. Associations between the MJO and ER waves have been utilized to index historical probabilities for extreme heat and cold events for regions of interest in the Northern Hemisphere extratropics. These events are indexed by the Real-time Multivariate MJO (RMM) index and OLR filtered in the ER wave band (periods of 10-100 days, and wavenumbers 1-14 westward). Historical event probabilities are then tabulated for the regions of interest, and are used in real time to issue probabilistic forecasts for extreme heat and cold events for these regions.