PLEASE POST

 

MMM      SEMINAR      NCAR

 

Organized Convection and Mesoscale Vortices: Observations from BAMEX (2003)

 

Christopher Davis

National Center for Atmospheric Research, Boulder, Colorado, USA

 

     The Bow Echo and MCV Experiment (BAMEX) took place during the late spring of 2003 over central North America. One of the two primary objectives was to observe the formation and mature structure of mesoscale convective vortices (MCVs) and their relation to deep, moist convection. MCVs form within nocturnal mesoscale convective systems, and often survive as quasi-balanced remnants of convection. In many cases, they persist into the heating cycle of the next day and can focus new convection, sometimes culminating in a multi-day sequence of causally linked convective systems with attendant heavy rainfall. Observations of developing MCVs from airborne Doppler radars will be presented, as will observations of mature MCVs using dropsonde and wind profiler data.

     Analysis of forming MCVs show that these circulations initially develop as part of a line of deep, moist convection, preferentially on the “poleward” end of the line. Vortices on different scales are present. The largest of these outlives the convection and has a horizontal scale of 50-100 km, and is confined to the lowest 5 km of the troposphere. The cyclonic circulation around the mesoscale vortices appears to reinforce the descending rear-inflow jet and accentuate the bowing of the leading-line of convection.

     Five mature MCVs, having persisted beyond their parent convection were also observed. We present analysis of the kinematic and thermodynamic structure of each MCV, including a demonstration of dynamical balance solely based on observations. Vertical motion within the circulation of each vortex is computed and used to interpret spatial variations of thermodynamic conditions that focus the development of new convection. In two of the cases, the mesoscale kinematic and thermodynamic modification due to the MCV promotes severe weather in an otherwise benign environment. Horizontal advection of temperature induced by the MCV is significant in some cases, leading to the structures resembling extratropical cyclones, but with length scales of only a few hundred kilometers.

 

Monday, 27 February 2006, 3:30 PM

Refreshments 3:15 PM

NCAR-Foothills Laboratory

3450 Mitchell Lane

Bldg 2 Auditorium (Rm1022)