TY - CPAPER AU - R.N. Bannister AU - Mike Cullen BT - ECMWF Workshop on Flow-dependent aspecyts of data assimilation, 11-13 June 2007 CY - Shinfield Park, Reading DA - 2007 LA - eng PB - ECMWF PP - Shinfield Park, Reading PY - 2007 SP - 101 EP - 112 T2 - ECMWF Workshop on Flow-dependent aspecyts of data assimilation, 11-13 June 2007 TI - A regime-dependent balanced control variable based on potential vorticity ER -