Stability-Dependent Structural Changes in Surface-Layer Wind Profiles over the Horqin Grassland

The stable boundary layer (SBL) over land exhibits pronounced vertical decoupling and structural heterogeneity that remain challenging to diagnose using routine operational monitoring. Here, we utilize a three-year continuous multi-level tower dataset (N=40,630 quality-controlled 15-min records at 2, 10, 20, and 50 m) over the Horqin Grassland to characterize stability-dependent modifications of surface-layer wind structure and near-surface kinetic energy. Using the bulk Richardson number (Rib) and raw thermal gradients (ΔTv/Δz), we identify a stability-driven reduction in vertical wind coupling, with a statistical change-point cluster centered near Rib≈0.30 (95% CI: 0.09–0.52). Cross-level correlation analysis empirically localizes a structural transition zone to the 10–20 m interval, separating a faster, shear-driven upper layer from a dynamically suppressed near-surface flow under strong stability. Concurrently, near-surface horizontal kinetic energy (HKE02) undergoes a 47% (nighttime) to 55% (full-record) median reduction, while horizontal wind-direction variability (σθ_02) broadens due to low-wind meandering, and sub-hourly vertical velocity variance (σw,LF2) is suppressed by 57–72% across all heights. Multidimensional scaling (MDS) reveals a statistically significant phase-space compaction under high stability (d˜high=2.13 vs. d˜low=2.67, p<0.001), with adjusted odds ratios highlighting thermal gradient (OR=5.80), wind shear (OR=1.52), and directional variability (OR=1.34) as dominant positive predictors. These empirical patterns remain robust under temporal-holdout validation (Year-1 calibration vs. Years 2–3 validation; consensus breakpoint Rib=0.161 vs. 0.156) and seasonal/wind-speed stratifications. The results demonstrate that routine 15-min multi-level tower networks provide valuable observational constraints on surface-layer structural transitions, informing boundary-layer parameterizations in numerical weather prediction models and near-surface dispersion assessments.