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Key Points A method to concoct non‐stationary data series is proposed Eddy covariance and wavelet analysis methods underestimate turbulent momentum flux under non‐stationary condition by about 50% Mexican hat wavelet method has the potential to accurately calculate flux of non‐stationary turbulence after correction 

The surface wind structure and vertical turbulent transport processes in the eyewall of hurricane Isabel (2003) are investigated using six large-eddy simulations (LESs) with different horizontal grid spacing and three-dimensional (3D) sub-grid scale (SGS) turbulent mixing models and a convection permitting simulation that uses a coarser grid spacing and one-dimensional vertical turbulent mixing scheme. The mean radius-height distribution of storm tangential wind and radial flow, vertical velocity structure, and turbulent kinetic energy and momentum fluxes in the boundary layer generated by LESs are consistent with those derived from historical dropsonde composites, Doppler radar, and aircraft measurements. Unlike the convection permitting simulation that produces storm wind fields lacking small-scale disturbances, all LESs are able to produce sub-kilometer and kilometer scale eddy circulations in the eyewall. The inter-LES differences generally reduce with the decrease of model grid spacing. At 100-m horizontal grid spacing, the vertical momentum fluxes induced by the model-resolved eddies and the associated eddy exchange coefficients in the eyewall simulated by the LESs with different 3D SGS mixing schemes are fairly consistent. Although with uncertainties, the decomposition in terms of eddy scales suggests that sub-kilometer eddies are mainly responsible for the vertical turbulent transport within the boundary layer (~1 km depth following the conventional definition) whereas eddies greater than 1 km become the dominant contributors to the vertical momentum transport above the boundary layer in the eyewall. The strong dependence of vertical turbulent transport on eddy scales suggests that the vertical turbulent mixing parameterization in mesoscale simulations of tropical cyclones is ultimately a scale-sensitive problem. 

Horizontal boundary layer roll vortices are a series of large-scale turbulent eddies that prevail in a hurricane’s boundary layer. In this paper, a one-way nested sub-kilometer-scale large-eddy simulation (LES) based on the Weather Research and Forecasting (WRF) Model was used to examine the impact of roll vortices on the evolution of Hurricane Harvey around its landfall from 0000 UTC 25 August to 1800 UTC 27 August 2017. The simulation results imply that the turbulence in the LES can be attributed mainly to roll vortices. With the representation of roll vortices, the LES provided a better simulation of hurricane wind vertical structure and precipitation. In contrast, the mesoscale simulation with the YSU PBL scheme overestimated the precipitation for the hurricane over the ocean. Further analysis indicates that the roll vortices introduced a positive vertical flux and thinner inflow layer, whereas a negative flux maintained the maximum tangential wind at around 400 m above ground. During hurricane landfall, the weak negative flux maintained the higher wind in the LES. The overestimated low-level vertical flux in the mesoscale simulation with the YSU scheme led to overestimated hurricane intensity over the ocean and accelerated the decay of the hurricane during landfall. Rainfall analysis reveals that the roll vortices led to a weak updraft and insufficient water vapor supply in the LES. For the simulation with the YSU scheme, the strong updraft combined with surplus water vapor eventually led to unrealistic heavy rainfall for the hurricane over the ocean.

 

Soil thermal properties play important roles in dynamic heat and mass transfer processes, and they vary with soil water content (θ) and bulk density (ρ_b). Bothθandρ_bchange with time, particularly in recently tilled soil. However, few studies have addressed the full extent of soil thermal property changes withθandρ_b. The objective of this study is to examine how changes inρ_bwith time after tillage impact soil thermal properties (volumetric heat capacity,C_v, thermal diffusivity,k, and thermal conductivity,λ). The study provides thermal property values as functions ofθandρ_band of air content (n_air) on undisturbed soil cores obtained at selected times following tillage. Heat pulse probe measurements of thermal properties were obtained on each soil core at saturated, partially saturated (θat pressure head of −50 kPa) and oven‐dry conditions. Generally,kandλincreased with increasingρ_bat the three water conditions. TheC_vincreased asρ_bincreased in the oven‐dry and unsaturated conditions and decreased asρ_bincreased in the saturated condition. For a givenθ, a largerρ_bwas associated with larger thermal property values, especially forλ. The figures ofC_v,kandλversusθandρ_b, as well asC_v,kandλversusn_air, represented the range of soil conditions following tillage. Trends in the relationships of thermal property values withθandρ_bwere described by 3‐D surfaces, whereas each thermal property had a linear relationship withn_air. Clearly, recently tilled soil thermal property values were quite dynamic temporally due to varyingθandρ_b. The dynamic soil thermal property values should be considered in soil heat and mass transfer models either as 3‐D functions ofθandρ_bor as linear functions ofn_air.

Thermal property values for a range ofθandρ_bwere measured on undisturbed soil cores.

Freshly tilled soil thermal property values were quite dynamic temporally.

The thermal property values of a tilled soil were described as 3‐D surfaces withθandρ_b.

The thermal property values of a tilled soil varied linearly withn_air.