A Practical Approach to Flux Measurements of Long Duration in the Marine Atmospheric Surface Layer

Abstract

The practical limitations imposed by the marine environment on the principal flux-measurement methods for experiments requiring more than a few days? duration are examined. Reservations are presented as to the suitability of the bulk method as a primary determination for fluxes and stability. It is suggested that the profile (or gradient) method is more practical. The influence that marine platforms have upon various flux measurements is discussed. Evidence is presented which suggests that platform-induced distortions, even when the bulk method is used, are probably more severe than is appreciated by many experimenters. Because of the potential for platform-induced distortions, it is argued that marine flux measurements should always be accompanied by an auxiliary flux-determination method. The bulk method is recommended as an adjunct to the profile, method, since the combination can yield two simultaneous determinations with only a modest increase in experimental effort. The appropriate vertical location of meteorological instrumentation is examined in conjunction with its realistically obtainable measurement accuracies. It is concluded that a three-level profile arrangement in which measurement levels are located no lower than 6, 11 and 21 m above the sea surface represents a good combination of utility and flux-measurement accuracy. The practical aspects of employing buoys and marine towers are discussed. Existing offshore oil structures are suggested as possible platforms for measurements over deep to moderately deep water. Onshore towers are suggested as the most practical for measurements close to shore. An extensive bibliography of marine field experiments, methods and instrumentation is presented.