Interactions of middle latitude troughs and tropical disturbances on 4-6 week time scales

We are examining the following sequence of events: midlatitude upper tropospheric troughs move equatorward into the subtropics in the form of "equatorward Rossby wave breaking" described by Thorncroft et al (1993); they leave behind extended quasi-stationary frontal zones and intense quasi-stationary convective zones; these regions excite equatorial Rossby waves (following the reasoning of Sobel and Horinouchi 2000) that propagate westward; under favorable conditions of background convergence, like that existing in the western north Pacific, these waves grow in amplitude and spawn tropical cyclones; the tropical cyclones move northwestward and eventually recurve into middle latitudes; the extratropical transition of these systems excites downstream energy propagation in the middle latitudes; and amplifying downstream troughs enter the subtropics and re-ignite the process. One full cycle lasts about 6 weeks. The Madden-Julian Oscillation sometimes plays an important role in facilitating such events, sometimes not. Examples of such midlatitude-tropical interactions will be provided. These represent a time scale beyond the synoptic scale and provide a bridge between synoptic and seasonal variations.