APS@home
At the moment, we're calculating the footprint of flux measurements. When we directly measure how fast gases / particles / energy are being emitted from an ecosystem, we measure at a single point above the surface. The question is which areas of the surface are influencing what we see?
If we have a fairly heterogeneous surface, it's important to know exactly which parts of the surface are producing the gases that we measure. For example if we're looking at ammonia, is all this ammonia coming from the fertilised field over there, or is it the cow shed over on the left? If it's the field, are we only measuring emissions from the field, or are we also seeing an influence from the wheat field further upwind?
All these things influence our interpretation of the measurements we make. Another example. If I make a measurement, and estimate that Oak Savannah ecosystems absorb x micrograms of CO2 per hectare per hour during the day, I need to be sure that I'm actually measuring an Oak Savannah, rather than the grass pasture that's a bit further away from the measurement site. It's a quality control thing, and it's important because it's estimates from measurements like these that are used as input for global climate models.
The way we do this is to simulate the turbulence near the measurement location, and follow notional "particles" as they're transported by the turbulence upwards to our measurement height. This gives us an estimate of where on the surface gases are coming from.
In the past, people have always used analytical models to give rough estimates. However, we've found that in places like tall crop fields and forests, this doesn't work well.
There are plans to extend the model to include ozone, organic carbon and nitrogen chemistry, but I'm waiting for a colleague to supply a reaction scheme. Don't know how long it's going to take him.
Who is involved?
APS@home is based at the Centre for Atmospheric Science at the University of Manchester.