Space - scale resolved surface fluxes across a heterogeneous,
mid-latitude forested landscape
Abstract
The Earth’s surface is heterogeneous at multiple scales owing to spatial
variability in various properties. The atmospheric responses to these
heterogeneities through fluxes of energy, water, carbon and other
scalars are scale-dependent and non-linear. Although these exchanges can
be measured using the eddy covariance technique, widely used tower-based
measurement approaches suffer from spectral losses in lower frequencies
when using typical averaging times. However, spatially resolved
measurements such as airborne eddy covariance measurements can detect
such larger scale (meso-{$\beta$},
$\gamma$) transport. To evaluate the prevalence and
magnitude of these flux contributions we applied wavelet analysis to
airborne flux measurements over a heterogeneous mid-latitude forested
landscape, interspersed with open water bodies and wetlands. The
measurements were made during the Chequamegon Heterogeneous Ecosystem
Energy-balance Study Enabled by a High-density Extensive Array of
Detectors (CHEESEHEAD19) intensive field campaign. We ask, how do
spatial scales of surface-atmosphere fluxes vary over heterogeneous
surfaces across the day and across seasons? Measured fluxes were
separated into smaller-scale turbulent and larger-scale mesoscale
contributions. We found significant mesoscale contributions to H and LE
fluxes through summer to autumn which wouldn’t be resolved in single
point tower measurements through traditional time-domain half-hourly
Reynolds decomposition. We report scale-resolved flux transitions
associated with seasonal and diurnal changes of the heterogeneous study
domain. This study adds to our understanding of surface atmospheric
interactions over unstructured heterogeneities and can help inform
multi-scale model-data integration of weather and climate models at a
sub-grid scale.