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1. Analysis of Fire-Induced Circulations during the FireFlux2 Experiment

   https://doi.org/10.3390/fire6090332  

   Benik, Jeremy T.; Farguell, Angel; Mirocha, Jeffrey D.; Clements, Craig B.; Kochanski, Adam K. (September 2023, Fire)

   Despite recent advances in both coupled fire modeling and measurement techniques to sample the fire environment, the fire–atmosphere coupling mechanisms that lead to fast propagating wildfires remain poorly understood. This knowledge gap adversely affects fire management when wildland fires propagate unexpectedly rapidly and shift direction due to the fire impacts on local wind conditions. In this work, we utilized observational data from the FireFlux2 prescribed burn and numerical simulations performed with a coupled fire–atmosphere model WRF-SFIRE to assess the small-scale impacts of fire on local micrometeorology under moderate wind conditions (10–12 m/s). The FireFlux2 prescribed burn provided a comprehensive observational dataset with in situ meteorological observations as well as IR measurements of fire progression. To directly quantify the effects of fire–atmosphere interactions, two WRF-SFIRE simulations were executed. One simulation was run in a two-way coupled mode in which the heat and moisture fluxes emitted from the fire were injected into the atmosphere, and the other simulation was performed in a one-way coupled mode for which the atmosphere was not affected by the fire. The difference between these two simulations was used to analyze and quantify the fire impacts on the atmospheric circulation at different sections of the fire front. The fire-released heat fluxes resulted in vertical velocities as high as 10.8 m/s at the highest measurement level (20 m above ground level) gradually diminishing with height and dropping to 7.9 m/s at 5.77 m. The fire-induced horizontal winds indicated the strongest fire-induced flow at the lowest measurement levels (as high as 3.3 m/s) gradually decreasing to less than 1 m/s at 20 m above ground level. The analysis of the simulated flow indicates significant differences between the fire-induced circulation at the fire head and on the flanks. The fire-induced circulation was much stronger near the fire head than at the flanks, where the fire did not produce particularly strong cross-fire flow and did not significantly change the lateral fire progression. However, at the head of the fire the fire-induced winds blowing across the front were the strongest and significantly accelerated fire progression. The two-way coupled simulation including the fire-induced winds produced 36.2% faster fire propagation than the one-way coupled run, and more realistically represented the fire progression. 

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2. Convective Circulations and the Coriolis Force: A Mechanism for Upscale Momentum Fluxes in the Tropics

   https://doi.org/10.1175/JAS-D-24-0160.1  

   Goldsmith, Edward J; Biello, Joseph A; Igel, Matthew R (May 2025, Journal of the Atmospheric Sciences)

   Abstract In the study of subgrid-scale tropical convection, the importance of retaining the frequently omitted “nontraditional” component of the Coriolis force is increasingly being recognized. A number of recent papers have developed linear theories examining the behavior of a diabatic heat-source-driven convective circulation in the presence of the full Coriolis force, and it was shown that the nontraditional Coriolis terms drive vertical shears on the large scales through upscale fluxes of momentum. In the present work, we generalize these results to the nonlinear regime, using a formal asymptotic theory based upon the fact that rotation is a second-order effect compared with advection by the vertical component of velocity at subgrid scales. Ultimately, we demonstrate that the same basic flow structures persist, with a particular emphasis on the counterrotating vortex pair induced by the nontraditional Coriolis terms which drive a westward tilt in convection. We compute the form of the upscale momentum flux convergence in the nonlinear regime, greatly extending the regimes of validity provided by the simple analytical expressions previously given in the linear case. This study constitutes an important step toward being able to accurately and consistently parameterize the large-scale vertical shear driven by nonlinear, subgrid convective processes under the influence of the nontraditional Coriolis force terms. 

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3. North American Winter Dipole: Observed and Simulated Changes in Circulations

   https://doi.org/10.3390/atmos10120793  

   Chien, Yu-Tang; Wang, S.-Y. Simon; Chikamoto, Yoshimitsu; Voelker, Steve L.; Meyer, Jonathan D.; Yoon, Jin-Ho (December 2019, Atmosphere)

   In recent years, a pair of large-scale circulation patterns consisting of an anomalous ridge over northwestern North America and trough over northeastern North America was found to accompany extreme winter weather events such as the 2013–2015 California drought and eastern U.S. cold outbreaks. Referred to as the North American winter dipole (NAWD), previous studies have found both a marked natural variability and a warming-induced amplification trend in the NAWD. In this study, we utilized multiple global reanalysis datasets and existing climate model simulations to examine the variability of the winter planetary wave patterns over North America and to better understand how it is likely to change in the future. We compared between pre- and post-1980 periods to identify changes to the circulation variations based on empirical analysis. It was found that the leading pattern of the winter planetary waves has changed, from the Pacific–North America (PNA) mode to a spatially shifted mode such as NAWD. Further, the potential influence of global warming on NAWD was examined using multiple climate model simulations. 

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4. Influence of Walker circulations on East African rainfall

   https://doi.org/10.1007/s00382-020-05579-7  

   Zhao, Siyu; Cook, Kerry H. (April 2021, Climate Dynamics)

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5. The Role of Surface Potential Vorticity in the Vertical Structure of Mesoscale Eddies in Wind-Driven Ocean Circulations

   https://doi.org/10.1175/JPO-D-23-0203.1  

   Zhang, Wenda; Griffies, Stephen_M; Hallberg, Robert_W; Kuo, Yi-Hung; Wolfe, Christopher_L_P (June 2024, Journal of Physical Oceanography)

   Abstract The vertical structure of ocean eddies is generally surface-intensified, commonly attributed to the dominant baroclinic modes arising from the boundary conditions (BCs). Conventional BC considerations mostly focus on either flat- or rough-bottom conditions. The impact of surface buoyancy anomalies—often represented by surface potential vorticity (PV) anomalies—has not been fully explored. Here, we study the role of the surface PV in setting the vertical distribution of eddy kinetic energy (EKE) in an idealized adiabatic ocean model driven by wind stress. The simulated EKE profile in the extratropical ocean tends to peak at the surface and have ane-folding depth typically smaller than half of the ocean depth. This vertical structure can be reasonably represented by a single surface quasigeostrophic (SQG) mode at the energy-containing scale resulting from the large-scale PV structure. Due to isopycnal outcropping and interior PV homogenization, the surface meridional PV gradient is substantially stronger than the interior PV gradient, yielding surface-trapped baroclinically unstable modes with horizontal scales comparable to or smaller than the deformation radius. These surface-trapped eddies then grow in size both horizontally and vertically through an inverse energy cascade up to the energy-containing scale, which dominates the vertical distribution of EKE. As for smaller horizontal scales, the EKE distribution decays faster with depth. Guided by this interpretation, an SQG-based scale-aware parameterization of the EKE profile is proposed. Preliminary offline diagnosis of a high-resolution simulation shows the proposed scheme successfully reproducing the dependence of the vertical structure of EKE on the horizontal grid resolution. 

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