General issues

The previous chapters of this book have described the progress in tracer inversions applied to global-scale problems. In parallel with these developments, there has been increasing interest in problems on smaller scales. Motivations for such work include applications such as monitoring of emissions and also improving our understanding of the observational data used in global inversions.

In this section we consider problems defined with a spatial resolution of order 100 km defined over continental-scale regions. This is a rapidly developing field, with, as yet, relatively little sign of any consolidation of techniques.

Some of the new features that can be expected in going from the global to regional scale are the following.

1. ▪ Data will be needed on synoptic time-scales, rather than monthly means: at Cape Grim, the operational conditions defined as ‘baseline’ apply for less than 50% of the time (see Section 5.2 above). For the remainder of the time, the concentrations of CO2 reflect more local influences. Model studies indicate that, for as much as 70% of the time, air at Cape Grim has been influenced by Tasmania, south-eastern Australia (as illustrated in Figure 9.1), or more westerly parts of the Australian continent). This raises the possibility of using these ‘non-baseline’ data to interpret the local sources and sinks. Similar possibilities arise for other sites on the coasts of continents or on nearby islands.

2. ▪ The nature of the inverse problem is likely to change since the transport characteristics are dominated by advection rather than appearing diffusive.

3. […]