Relationships Between Surface Fluxes and Boundary Layer Dynamics: Statistics at the Land-Atmosphere Feedback Observatory (LAFO)

We studied the convective boundary layer (CBL) processes and surface fluxes long-term statistics by using a combination of two Doppler lidars (DLs) and an eddy-covariance station (EC) at the Land-Atmosphere Feedback Observatory (LAFO), Stuttgart, Germany (Abbas et al., 2024). At LAFO (Späth et al, 2023), one DL is continuously operated in vertical pointing mode, while the second is in six-beam scanning mode, both providing high-resolution data with resolutions of 1 s and 30 m. From this combination of DLs, we derived the profiles of vertical wind variance (Lenschow et al, 2000; Wulfmeyer et al, 2024), horizontal wind variance and turbulent kinetic energy (TKE) as well as CBL depth 𝑧_𝑖 (Bonin et al., 2017; Bonin et al., 2018). The surface turbulent fluxes are acquired from an EC station in the agricultural fields of our university ~500 m away from the DLs. Daytime statistics are derived from 20 convective days from May to July 2021 with cloud cover < 40%. In this data set, we found a maximum of the CBL height averaged over all these days ⟨𝑧_𝑖⟩ of (1.53 ±0.07) km at 13:30 UTC, which is about 2 hours after local noon. We found counter-clockwise hysteresis patterns between the CBL height and the surface fluxes. In the development phase, these relationships were approximately linear. In the early afternoon, the relationships reached a peak phase with both large fluxes and high values of ⟨𝑧_𝑖⟩. At 12:00 UTC, just after local noon, the maximum values of vertical, horizontal, and total TKE were 0.55 m²s^-2, 1.26 m²s^-2 and 1.71 m²s^-2 at heights of (0.30±0.06)⟨𝑧_𝑖⟩ , (0.56±0.06)⟨𝑧_𝑖⟩, and (0.40±0.06)⟨𝑧_𝑖⟩, respectively. In the decay phase in the later afternoon, the relationships show non-linear patterns with larger values of ⟨𝑧_𝑖⟩ for the same surface fluxes than in the morning. Furthermore, we analyzed relationships between the vertical and horizontal wind components and total TKE. Also, here, we found non-linear patterns in the three CBL phases.

Abbas, S. S., et al., 2024, https://doi.org/10.5194/egusphere-2024-3878
Späth et al., 2023, https://doi.org/10.5194/gi-12-25-2023
Lenschow et. al., 2000, https://doi.org/10.1175/1520-0426(2000)017<1330:MSTFOM>2.0.CO;2
Wulfmeyer et al., 2024, https://doi.org/10.5194/amt-17-1175-2024
Bonin et. al., 2017, https://doi.org/10.5194/amt-10-3021-2017
Bonin et. al., 2018, https://doi.org/10.1175/JTECH-D-17-0159.1