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Modulation of tropical convection by breaking Rossby waves

This work discusses observations of both the convective‐inhibiting and convective‐promoting properties associated with Rossby waves that break in the extratropics and extend into the tropics. Two tropical drought periods—times of reduced tropical cloudiness and rainfall—were observed during mid to late November 2005 over a wide area of north‐west Australia, with an observed eruption of a nearby synoptic tropical cloud band in between times. Both convective inhibition and promotion appear to be linked to the descent of dry upper tropospheric air within a series of tropopause folds; convective inhibition was observed within the dry pool itself, whilst convective promotion was observed on the high moisture gradient at the leading edge of an advancing dry slot. A range of satellite images, surface rain gauges, radiosonde and ozonesonde data are used in conjunction with back trajectories and European Centre for Medium‐Range Weather Forecasts (ECMWF) analysis fields to investigate the origins and dynamics associated with these convective events, showing each to be ultimately linked to breaking Rossby wave activity on the southern subtropical jet. Together, these observations support a growing number of studies linking midlatitude tropopause‐level dynamics with the modulation of tropical deep convection, an influence that is poorly characterized when considering the climatology of tropical cloudiness and rainfall. Copyright © 2008 Royal Meteorological Society