GNSS Zenith Wet Delay as a Boundary Layer Diagnostic: Regime‐Dependent Turbulence Signatures From Large Eddy Simulation and Observations

Abstract

Global Navigation Satellite Systems (GNSS) provide continuous measurements of zenith wet delay (ZWD), reflecting column‐integrated atmospheric water vapor. While the slowly varying ZWD is routinely assimilated in numerical weather prediction, the rapid fluctuations on timescales of seconds to minutes that arise from boundary‐layer turbulence remain underexploited. We test the hypothesis that the variance and the cutoff frequency of the von Kármán model fitted to the ZWD power spectrum carry diagnostic information about boundary‐layer state. We develop a diurnal coherence framework based on Dynamic Time Warping, extrema lags and phase‐resolved slope ratios. The framework is calibrated on large‐eddy simulations (LES) of an idealized convective boundary layer. In the simulation, tracks turbulent kinetic energy (TKE) synchronously, leads TKE by half an hour and trails the integrated humidity and temperature variances by 1–1.5 hr, and the boundary‐layer‐averaged horizontal wind speed is out of phase with both spectral parameters during convection. The framework is then applied without modification to 3 years of co‐located GNSS and Doppler LiDAR observations at Payerne, Switzerland (249 clear‐sky days, stratified by season). The summer subset reproduces the simulated patterns, with tracking TKE and – remaining out of phase. Lags are longer in the observations than in the LES, consistent with sources of variability absent from the idealized simulation. Bootstrap uncertainties on remain below 5% throughout the diurnal cycle. These results support the use of ZWD spectral parameters as a diagnostic of convective boundary‐layer state, complementary to dedicated remote‐sensing instruments.