The role of gravity waves in producing strong winds in bow echoes

We present two cases (24 and 26 June 2003) from BAMEX in which gravity waves appeared to play an important role in the life cycle of linear mesoscale convective systems (LMCS). The following features are common to each case: a) As the LMCS evolved, intense deep convection located on the upshear side of the existing cold pool moved into the stable cold pool air and produced a gravity wave (or bore) that propagated through the cold pool. b) As the gravity wave (or bore) exited the cold pool region in the direction of propagation of the LMCS, the outflow exhibited a surge in the direction of propagation of the gravity wave, thereby producing a bowing segment of the LMCS. c) Damaging or enhanced surface winds corresponded to the arrival of the gravity wave as it intersected the leading convective line. d) The subsequent demise of the system following this interaction was very rapid.

For the 26 June event, a strong outflow from an adjacent MCS intersected a more recent MCS that developed in the downshear direction. Upon interaction with the cold pool, surface data indicate that the gust front transformed very rapidly to a strong bore with attendant large pressure jumps and a significant increase in wind. This feature propagated through the cold pool, and upon exiting through the leading edge of the existing squall line, produced localized damaging winds. A similar scenario occurred in the 24 June MCS, except that the gravity wave was generated by intense convection that had developed on the upshear side of the same MCS. Data from the Eldora airborne Doppler radar, WSR-88D radars, and surface data are utilized to portray the kinematic structure the leading convection near the region impacted by the gravity