Airborne Measurements of Scale-Dependent Latent Heat Flux Impacted by Water Vapor and Vertical Velocity Over Heterogeneous Land Surfaces During the CHEESEHEAD19 Campaign

The water vapor transport associated with latent heat flux (LE) in the planetary boundary layer (PBL) is critical for the atmospheric hydrological cycle, radiation balance, and cloud formation. The spatiotemporal variability of LE and water vapor mixing ratio (rv) are poorly understood due to the scale-dependent and nonlinear atmospheric transport responses to land surface heterogeneity. Here, airborne in situ measurements with the wavelet technique are utilized to investigate scale-dependent relationships among LE, vertical velocity (w) variance (sigma w2 ${\sigma }_{w}<^>{2}$), and rv variance (sigma H2O2 ${\sigma }_{\mathrm{H}2\mathrm{O}}<^>{2}$) over a heterogeneous surface during the Chequamegon Heterogeneous Ecosystem Energy-balance Study Enabled by a High-density Extensive Array of Detectors 2019 (CHEESEHEAD19) field campaign. Our findings reveal distinct scale distributions of LE, sigma w2 ${\sigma }_{w}<^>{2}$, and sigma H2O2 ${\sigma }_{\mathrm{H}2\mathrm{O}}<^>{2}$ at 100 m height, with a majority scale range of 120 m-4 km in LE, 32 m-2 km in sigma w2 ${\sigma }_{w}<^>{2}$, and 200 m-8 km in sigma H2O2 ${\sigma }_{\mathrm{H}2\mathrm{O}}<^>{2}$. The scales are classified into three scale ranges, the turbulent scale (8-200 m), large-eddy scale (200 m-2 km), and mesoscale (2-8 km) to evaluate scale-resolved LE contributed by sigma w2 ${\sigma }_{w}<^>{2}$ and sigma H2O2 ${\sigma }_{\mathrm{H}2\mathrm{O}}<^>{2}$. The large-eddy scale in PBL contributes over 70% of the monthly mean total LE with equal parts (50%) of contributions from sigma w2 ${\sigma }_{w}<^>{2}$ and sigma H2O2 ${\sigma }_{\mathrm{H}2\mathrm{O}}<^>{2}$. The monthly temporal variations mainly come from the first two major contributing classified scales in LE, sigma w2 ${\sigma }_{w}<^>{2}$, and sigma H2O2 ${\sigma }_{\mathrm{H}2\mathrm{O}}<^>{2}$. These results confirm the dominant role of the large-eddy scale in the PBL in the vertical moisture transport from the surface to the PBL, while the mesoscale is shown to contribute an additional similar to 20%. This analysis complements published scale-dependent LE variations, which lack detailed scale-dependent vertical velocity and moisture information. The vertical water vapor transport in the planetary boundary layer (PBL), and the associated latent heat flux (LE), are critical for the atmospheric hydrological cycle, radiation balance, and cloud formation. However, the vertical moisture transport varies nonlinearly at multiple scales due to the land surface heterogeneity across multiple properties. This study investigates the scale-resolved impact of water vapor and vertical velocity on LE, using data collected aboard an atmospheric research aircraft flying low above the surface in summer over northern Wisconsin during the CHEESEHEAD19 campaign. This study finds that LE and water vapor variance is largest at the large-eddy scale in PBL and at the mesoscale. In contrast, vertical velocity variance is primarily present in turbulent and large-eddy scales in PBL. This study confirms the significant role of the large-eddy scale in PBL in contributing to the majority of the vertical moisture transport from the surface to the PBL top. These findings provide better insight into the factors influencing LE at different scales. The scale-dependent distribution of latent heat flux, vertical velocity variance, and water vapor variance at 100 m over a heterogeneous surface is described In the large-eddy scale, 70% of total latent heat flux is contributed by 50% of total vertical velocity variance and 50% of total water vapor variance The large-eddy scale contributes most of the vertical moisture transport from the surface to the Planetary Boundary Layer