GTE: Pacific Exploratory Missions

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In the vast regions of the Pacific ocean, the chemistry that controls the composition of the atmosphere may very well represent the last vestiges of the natural processes that were prevalent prior to significant human influences on the global atmosphere. Yet, along the north western rim of the Pacific are the most populated countries of the world. The potential for these countries to emerge as major industrial centers, with the concurrent pollution is just beginning to be recognized. Recent evidence from satellite observations also suggest that the southern Pacific Ocean region, while more removed from industrial countries in the northern hemisphere, may be subject to pollution from long range transport of biomass burning from Africa and South America.

Early in the formative stages of the GTE program (See GTE Implementation), ad hoc committees convened to review the NASA Tropospheric Chemistry program recommended as one of the major studies for the GTE Pacific Exploratory Missions (PEM) in the Pacific region. The PEM campaigns have to date consisted of two field missions in the north western Pacific region, PEM-West A & B, and one mission in the south central Pacific ocean, PEM-Tropics. (See Map of PEM-Campaigns)

Other international components within the International Global Atmospheric Chemistry (IGAC) Program have also recognized the importance of the Pacific ocean region. A major study to provide early detection and understanding of the impact of industrial and natural emissions from the Asian continent on the north western Pacific region was initiated in the early 1990's. This study, the East Asia/North Pacific Regional Study (APARE), was a project within the IGAC Program. Collaborating programs including initiatives in Taiwan, Japan, The Peoples Republic of China, Hong Kong, and programs sponsored by the National Atmospheric and Aeronautics Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the National Center for Atmospheric Research (NCAR).

A major component of APARE was the NASA Pacific Exploratory Mission-West (PEM-West). The broad objective of the PEM-West/APARE initiative is to study chemical processes and long range transport over the northwest Pacific ocean, and to estimate the magnitude of the human impact on the oceanic atmosphere over this region, particularly for tropospheric and sulfur species. The joint PEM-West/APARE initiative consisted of two major field studies conducted during two different seasons of the year. The first phase, PEM-West (A), was conducted in September - October, 1991, a season of the year characterized by minimum outflow from the Asian continent. The second phase, PEM-West(B), was conducted during February-March , 1994 a season of the year characterized by significant outflow from the Asian continent. Both phases of PEM-West included intensive airborne measurements of trace gases from the NASA DC-8 aircraft coordinated with measurements at surface sites, and during PEM-West A with airborne measurements from a collaborating Japanese program. The following sections of the PEM-West web page briefly describes the experimental design for the PEM-West A and PEM-West B phases with a brief summary of the results from each mission.

The second field campaign in the Pacific Exploratory Missions, PEM-Tropics, has been focussed on the south tropical Pacific region. The field deployment phase of the PEM-Tropics mission was completed in early October, 1996. PEM-Tropics involved the NASA DC-8 and P-3B aircraft operating jointly from bases in Tahiti, and Easter Island, and the P-3B operating from Christmas Island, and Guayaquil, Ecuador, and the DC-8 from Christchurch, NZ, and Nadi, Fiji. The mission design for PEM-Tropics is briefly described in the following web pages.

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