Studying the Atmospheric Boundary Layer influence on the Surface EnergyBalance Closure combining eddy covariance and Doppler lidar

The eddy covariance technique (EC) is used worldwide to measure surface fluxes of greenhouse
gases and energy balance components. Nevertheless, in the scientific community it is well-known
that EC presents an imbalance of the energy components. In this regard, the atmospheric boundary
layer (ABL) directly influences the mass and energy transfer between surface and atmosphere.
Thus, knowledge and characterization of the ABL might be essential to disentangling the drivers
causing the imbalance of the energy components measured by EC. This work aims to relate ABL
characteristics to the accuracy of the surface energy balance closure (SEBC) obtained by EC.

The study was carried out in an irrigated olive orchard (Olea europaea var. europaea L.) in the
Southeastern Iberian Peninsula (37.9427º N, 3.3002º W and 370 m asl) during the intensive
BLOOM (turBulence and oLea pOllen prOperties experiMent) campaign, from May 19th to June
20th 2022. In order to characterise ABL dynamics, remote sensing techniques are commonly used.
One of them is via Doppler lidar, which provides measurements of wind components and
turbulence-related products at high spatial and temporal resolutions. In particular, a Doppler lidar
Stream Line (HALO photonics) with a temporal resolution of 2 seconds and 10 minutes (for vertical
and scanning measurements, respectively) and 30 m of vertical spatial resolution was used to
retrieve the turbulent kinetic energy dissipation rate (ε) and wind shear (sh) with a common
resolution of 3 minutes as indicators of convective and mechanical sources of turbulence,
respectively. To assess the SEBC, we used (1) a three-axis sonic anemometer (CSAT-3, Campbell
Scientific, Logan, UT, USA) and an enclosed path infrared gas analyser (IRGA, Li-Cor 7200;
Lincoln, NE, USA) on a tower 9 m tall to measure latent heat (λE) and sensible heat (H) fluxes; (2)
an incoming and outgoing short- and long-wave 4-component radiometer (CNR-4, Kipp & Zonen,
Delft, Netherlands) to measure net radiation (Rn); and (3) two each: soil moisture probes (CS616,
CSI), thermocouples (TCAV, CSI) and heat flux plates (HFP01, Hukseflux, Delft, the Netherlands)
at 0.10 m, 0.04 m and 0.08 m depth, respectively to calculate the soil heat flux (G).

Preliminary results show that SEBC enhances under turbulent conditions (slope and R2 from 0.49
and 0.92 to 0.81 and 0.94, respectively). However, when the source of turbulence is mechanical the
SEBC is less accurate (slope and R2 from 0.82 and 0.94 to 0.77 and 0.9, respectively). A more
detailed study based on principal component analysis of the ABL height, skewness of the vertical
wind velocity and vertical profile of horizontal wind, together with ε and sh, among other Dopplerlidar-
derived products is expected to offer reliable information that is highly relevant regarding the
influence of the ABL on the SEBC.

ACKNOWLEDGMENTS: This work was supported by the
Spanish Ministry of Science and Innovation through project PID2020-117825GB-C21
(INTEGRATYON3), the Andalusian regional Development through the projects B-RNM-60-
UGR20 (OLEAGEIs) and P18-RT-3629 (ICAERSA), including European Union ERDF funds.