In this paper we analyze distinct layers seen in the tropospheric ozone and water vapor profiles taken during NASA's Global Tropospheric Experiment (GTE) Pacific Exploratory Mission in the Tropical Pacific (PEM-Tropics) Phase B campaign. In summary, fewer layers were observed in this campaign than during the PEM-Tropics A campaign. However, of those layers found, there were relatively more ozone-rich-water-vapor-poor layers (68% versus 52%). The percentage of the sampled troposphere occupied by layers during PEM-Tropics B was less than half of that found during PEM-Tropics A (8% versus 20%). The differences between these two campaigns suggest a seasonal variation in the occurrence of layers. This is confirmed using measurements made by the Southern Hemisphere Additional Ozonesondes (SHADOZ) network. ¿ 2001 American Geophysical Union