A Simple Two-dimensional Parameterisation for Flux Footprint Predictions

Abstract:

Linking data of surface-atmosphere exchange processes over various temporal and spatial scales still poses a major challenge. Footprint models are often used to bridge these scales, for interpretation of flux-tower measurements, to derive location and size of the source area, to estimate the contribution of passive scalar sources to these measured fluxes, and to combine measured fluxes with remotely sensed data. With increasing numbers of flux towers within large monitoring networks (e.g., AMERIFLUX, ICOS, NEON), span of observations from these towers, and availability of airborne flux measurements, there has been an increasing demand for reliable footprint models that can be applied for long time series and outside the surface layer.

In this contribution, we present a two-dimensional footprint parameterisation and example applications. The footprint parameterisation is based on a novel scaling approach for the lateral distribution of the flux footprint and on an updated version of the footprint parameterisation of Kljun et al. (2004). The footprint parameterisation has been developed and evaluated using simulations of the Lagrangian stochastic particle dispersion model LPDM-B (Kljun et al., 2002), covering a broad range of boundary layer conditions and measurement heights. The new footprint parameterisation requires inputs that can be determined from flux-tower measurements. It can be easily applied to data of long-term monitoring programmes as well as for quick footprint estimates in the field.