The role of synoptic/planetary-scale interactions during the development of a blocking anticyclone

The period 19-21 January 1979 marked the development of a blocking anticyclone over the North Atlantic Ocean preceded by explosive cyclogenesis about 500 km south of Nova Scotia. Using fields derived from GLA analyses of the FGGE SOP-I data set, the general behavior of this block is diagnosed using the extended height tendency equation. Results indicate that vorticity advection was the primary forcing mechanism during the block development. Interestingly, despite pronounced northward warm air advection, the direct forcing of the block by thermal advection was relatively small. Rather, the thermal forcing was strongest in the upstream cyclone, which in view of the subsequent role of scale interactions in the block development suggests an indirect role for thermal advection -from Authors