1. MEAN CIRCULATION The strongest blocking in the Northern Hemisphere

• Main Authors: A. James Wagner, Yi Io
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1969
• Subjects: Arctic; Greenland; Taymyr; Midwinter; Aleutian Ridge; Spitzbergen; Taymyr Peninsula
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.395.2317; http://docs.lib.noaa.gov/rescue/mwr/097/mwr-097-04-0351.pdf

was over Greenland where 700-mb heights averaged 170m Blocking, which had become strong in the Western above normal for the month (fig. 2). Slightly weaker Hemisphere during December (Green, 1969), increased blocking was located between Spitzbergen and Novaya further during January 1969. The Aleutian ridge con- Zemlya. The magnitude of this extensive high-latitude tinued to build and developed a small High center (see blocking shows in the zonal profile of sea-level pressure the monthly mean 700-mb map (fig. 1)) with heights as for January 1969 compared with the January normal much as 150 m above normal (fig. 2). Anomalous flow (fig. 3). Sea-level pressure averaged more than 8 mb from an unusually cold Canadian Arctic source led to above normal north of 60 " N. in the western portion of frequent intense cyclogenesis just off the Paciiic Northwest the hemisphere. coast, reflected in a sharp trough with heights 110 m Cyclonic activity was stronger than normal in low and below normal. Flow from a separate center of cyclonic middle latitudes from the eastern Atlantic through the activity north of Hawaii contributed to strong confluence Mediterranean, and over eastern Asia where surface Lows in the California area. This helped produce record- cross the cold landmass infrequently during midwinter. breaking heavy rains and disastrous floods in some areas The principal 700-mb monthly mean Low center which of the State. had been near the Taymyr Peninsula during December