The large-scale meteorology of the western North Pacific region during the Global Tropospheric Experiment (GTE) Pacific Exploratory Mission-West Phase B (PEM-West B) study period, February 7 to March 15, 1994, is described. Mean streamline/isotach charts and both zonal and meridional cross sections are presented which contrast the wind conditions encountered during PEM-West B and the earlier Pacific Exploratory Mission-West Phase A (PEM-West A) expedition (September 17 to October 21, 1991). Further, vertical profiles of wind and thermodynamic variables are presented to show the differing air mass structures during the two periods, using operational rawinsonde data from stations at Guam, Hong Kong, Tateno (Japan), and Yan An (China). Finally, five case studies indicating the variety of chemical source signatures and transport patterns studied in the campaign are displayed and discussed. ¿ 1997 American Geophysical Union