Principles

The use of tracer distributions to determine atmospheric transport plays a relatively small role in studies of atmospheric dynamics. This is in considerable contrast to the situation in the oceans, where the classic ocean inverse problem is the inversion of indirect data, generally temperature and salinity, to determine circulation. Of course, in the ocean, temperature and salinity are not passive tracers – through their effect on density, they cause the large-scale circulation. The fact that the foci of inverse problems in oceanography and meteorology are different mainly reflects the atmosphere being better understood than the oceans.

First, there is an extensive atmospheric measurement network, primarily for prediction of weather, with observations at several thousand locations several times a day, which is supplemented by satellite measurements and regular vertical profiles from radiosondes. The closest analogue of the ocean tracer-inversion problem is that of assimilation of meteorological data (see Section 7.3), but the analysis of the atmosphere differs from that of the ocean by virtue of the much greater frequencies both of observations and of analyses. A second difference between the atmosphere and the oceans is that it is easier to model global circulation in the atmosphere than it is for the oceans. The smaller scale of oceanic eddies means that only very recently has it been computationally feasible to model the global ocean with sufficiently fine grids to resolve these eddies.