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Despite many observational studies on the atmospheric boundary layer (ABL) depth zi variability across various time scales (e.g., diurnal, seasonal, annual, and decadal), zi variability before, during, and after frontal passages over land, or simply zi variability as a function of weather patterns, has remained relatively unexplored. In this study, we provide an empirical framework using 5 years (2014–18) of daytime rawinsonde observations and surface analyses over 18 central and southeastern U.S. sites to report zi variability across frontal boundaries. By providing systematic observations of front-relative contrasts in zi (i.e., zi differences between warm and cold sectors, ) and boundary layer moisture (i.e., ABL-q) regimes in summer and winter, we propose a new paradigm to study zi changes across cold-frontal boundaries. For most cases, we found deeper zi over the warm sector than the cold sector in both summer and winter, although with significant site-to-site variability in Δzi. Additionally, our results show a positive ΔqABL (i.e., frontal contrasts in ABL-q) in summer and winter, supporting what is typically observed in midlatitude cyclones. We found that a front-relative ΔqABL of 1 g kg−1 often yielded at least a 100-m Δzi across the frontal boundary in both summer and winter. This work provides a synoptic-scale basis for zi variability and establishes a foundation for model verification to examine the impact of airmass exchange associated with advection on zi. This work will advance our understanding of ABL processes in synoptic environments and help unravel sources of front-relative zi variability. Significance Statement The atmospheric boundary layer (ABL) is the lowermost part of the atmosphere adjacent to Earth’s surface. The irregular motion of air inside the ABL plays an essential role in relocating air near the surface to the free troposphere. Meteorologists use ABL depth in weather forecast models to determine the atmosphere’s ability to dilute or enrich tracers within the ABL. However, knowledge about the changes in ABL depth during stormy conditions remains incomplete. Here, we investigate how the ABL depth varies before and after cold-frontal passages. We found that ABL depths were much deeper before the cold-frontal passages than after. This knowledge will help us develop new approaches to consider how storms modify the ABL in weather forecast models.

Variability of dairy process wastewater (PWW) nitrogen (PWW-N) content makes precise fertilizing of forage challenging. Our objective was to improve measurement accuracy of PWW-N. We characterized PWW-N and quantified its variability using over 1,000 PWW samples from 91 lagoons on commercial California dairies. We used statistical modeling and stochastic simulations to compare the accuracy of various protocols for measuring PWW-N applied to forage crops. Electrical conductivity (EC) was positively correlated with N concentration within a lagoon (conditional R

The thermodynamic properties of the atmospheric boundary layer (ABL) play an important role in several atmospheric processes such as convection initiation, turbulence mixing, the exchange of heat and momentum, and cloud-microphysics. Since the ABL depth (henceforth, BLD) defines the volume of the ABL, many studies consider BLD to be a key scaling parameter to understand and quantify ABL mixing processes. However, most of these studies attributed both BLD temporal and horizontal variability on various scales solely to the impact of underlying surface forcing via locally generated buoyancy fluxes and static stability. We argue that the impact of horizontal advection is often neglected yet important for a more thorough understanding of ABL thermodynamics and kinematics. Here we identified four potentially advection-dominated ABL regimes across (1) the urban-rural interface, (2) complex terrain and adjacent plains, (3) the land-sea interface where horizontal transport of marine boundary layer airmasses influences the regional ABL over coastal areas, and (4) frontal environments where mid-latitude cyclones affect ABL processes via passages of cold and warm frontal boundaries. We then introduced a conceptual framework based on observations so that ABL processes are explained not only by surface forcing but also by horizontal advection of mass, momentum, and energy. This work will help advance our understanding of ABL processes and single out potential sources that trigger drastic changes in ABL thermodynamic features including the BLDs under diverse horizontal advection environments.