A DIAGNOSIS OF 2 BLOCKING EVENTS THAT OCCURRED SIMULTANEOUSLY IN THE MIDLATITUDE NORTHERN-HEMISPHERE

Using the Goddard Laboratory for Atmospheres Goddard Earth Observing S ystem-1 analyses, the horizontal distribution of atmospheric forcing p rocesses involved in the growth, maintenance, and decay of two Norther n Hemisphere midlatitude blocking anticyclones that occurred simultane ously were examined, with the goal of determining whether there was a dynamic connection between the two cases. The complete form of the Zwa ck-Okossi equation, which is a generalization of the Petterssen-Sutcli ffe development equation, was used as the primary diagnostic tool. The basic analyses were partitioned into their planetary-scale and synopt ic-scale components (noninteraction) 500-hPa height tendencies, as wel l as scale interaction 500-hPa height tendencies. Based on the results of this diagnosis, there was no dynamic connection between these bloc king anticyclones. This result agrees with findings of other studies b ased on a statistical analysis of simultaneous blocking. These results also imply that blocking may be a local phenomenon. The diagnostic re sults from these blocking events were, in many respects, similar to th ose of previous studies. However, some key differences were found. For example, it was found here that for both mode 2 blocking events, temp erature advection was an important mechanism in block formation. Earli er results showed vorticity advection as the primary atmospheric forci ng process in block formation for a mode 1 block. Also, the scale-part itioned results show that upstream cyclones contributed to block forma tion and intensification in these events directly through the synoptic -scale component, often with the support of the interaction component, of the total forcing. Earlier scale-partitioned results showed that t he interaction component of the total forcing was most important in th e formation of a mode 1 block.