Monday, 23 January 2017
4E (Washington State Convention Center )
Predictability of the dual-MJO events of November 2011 during the DYNAMO field campaign is examined, with an emphasis on whether or not 30-day NAVGEM and COAMPS simulations initialized 1 November can reproduce a second event which initiates approximately 20 days into the simulation. Results from three 37-km resolution NAVGEM simulations suggest that the ability to reproduce the second MJO is constrained by the ability to correctly depict the ocean, as a simulation using a coupled ocean-atmosphere and another simulation using analyzed SSTs are both successful overall, while a third simulation using fixed SSTs fails to produce the second MJO altogether. In the two successful simulations, an eastward-propagating negative 200-hPa velocity potential anomaly circumnavigates the globe and eventually re-emerges over the western Indian Ocean region, suggesting that the first MJO event plays a role in triggering the second MJO. These NAVGEM simulations are then used as initial and boundary conditions for several 15-km resolution COAMPS simulations, all of which are coupled to NCOM. Somewhat surprisingly, COAMPS is able to reproduce the second MJO even when NAVGEM with fixed SSTs is used, suggesting that processes that occur within the regional COAMPS domain over the Indian Ocean basin can overcome the lack of a globally-circumnavigating eastward signal in the winds. A number of factors that may potentially contribute to increased predictability in the coupled COAMPS simulations are examined, including the development of westward-propagating Rossby waves and a warm-to-cool, back-to-warm “recharge” cycle that occurs in the coupled ocean. Additionally, whether a superior representation by COAMPS versus NAVGEM of two tropical cyclones that develop in the northern Indian Ocean during the simulation period is of relevance to the predictability of larger scales, including the MJO at longer lead times is also examined.
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