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Abstract While it has been established that pronounced sea-breeze fronts (SBFs) develop under conditions of weak or offshore flow, with the SBF serving as a focus for convection initiation (CI), less is known regarding CI processes during large-scale onshore flow, including the potential existence and influence of embedded SBFs. Challenges that have limited progress in addressing this question include the limited focus on cases under this flow regime and the coarse grid spacing used in prior model-based parameter studies, artificially decreasing the magnitude of convergence or thermodynamic gradients associated with the SBF and potentially leading to substantial errors in the representation of surface fluxes. In Part II of this two-part series, the authors address these prior challenges through execution of a suite of Cloud Model 1 (CM1) large-eddy simulations analyzing the impact of varying the magnitude of the onshore wind component (+2.5 and +5.0 m s⁻¹), and radiative forcing and water surface temperature consistent for summertime in the Great Lakes region. In all simulations, a mesoscale enhancement of onshore flow and return flow was present, with a thermal gradient and convergence collocated with the leading edge of this enhanced flow providing evidence for the presence of a diffuse yet discernible SBF. The SBF progressed inland and separated areas where CI did and did not occur, highlighting the need for increased focus on SBFs and CI in this less-studied flow regime. In conditions of weak onshore flow, surface-based CAPE was larger, CI was more common, and it occurred closer to the coast. 

Abstract The influence of large bodies of water on convection initiation (CI) and the environment in which convection evolves is highly complex due to the wide range of parameters that control relevant processes. A substantial focus of sea-breeze front (SBF) CI research has focused on the role of mesoscale boundary or organized boundary layer circulation interactions with SBFs; however, less research has focused on heterogeneities in convective parameters and how those may affect CI coverage, timing, and location. In this two-part series, the authors present a parameter study of SBF CI through Cloud Model 1 (CM1) large-eddy simulations across a parameter space varying the cross-shore wind component and radiative forcing and water surface temperatures consistent with June, July, and August in the Great Lakes region. In Part I of this series, simulations under conditions of calm, weak, and moderate offshore flow (0, −2.5, and −5.0 m s⁻¹) are presented. CI occurred in all calm simulations, with decreased coverage and frequency of CI in weak offshore flow. CI was least frequent during moderate offshore flow, despite stronger convergence, due to a shear profile that favored undercutting by the SBF under conditions of moderate offshore flow. Surface-based convective available potential energy (SBCAPE) maxima developed on the cool side of the SBF, with convection occurring on the cool side of the SBF in some cases. Analyses are presented with a focus on the nature of the SBF, distribution of convective parameters, and their implications on CI. 

Abstract Insects are declining in abundance and species richness, globally. This has broad implications for the ecology of our planet, many of which we are only beginning to understand. Comprehensive, large-scale efforts are urgently needed to quantify and mitigate insect biodiversity loss. Because there is broad interest in this topic from a range of scientists, policymakers, and the general public, we posit that such endeavors will be most effective with precise and standardized terms. The Entomological Society of America is the world’s largest association of professional entomologists and is ideally positioned to lead the way on this front. We provide here a glossary of definitions for biodiversity loss terminology. This can be used to enhance and clarify communication among entomologists and others with an interest in addressing the multiple overlapping research, policy, and outreach challenges surrounding this urgent issue. 

Abstract Recent idealized modeling studies have highlighted the importance of explicitly simulating realistic convective boundary layer (CBL) structures to assess and represent their influence on mesoscale phenomena. The choice of lateral boundary conditions (LBCs) has a substantial impact on these turbulent structures, including the distribution of kinematic and thermodynamic properties within the CBL. While use of periodic LBCs is ideal, open LBCs are required for nonuniform domains (e.g., multiple air masses or land surface types). However, open LBCs result in an unrealistic, laminar CBL structure near the upstream boundary that undoubtedly impacts the evolution of any simulated phenomena. Therefore, there is a need for a modified open LBC option to mitigate this unrealistic structure, while still permitting users to simulate phenomena in nonuniform domains. The Pennsylvania State University–NCAR Cloud Model 1 (CM1), version 19.8, includes an optional inflow-nudging technique to nudge inflow to the base-state wind profile. For the present study, the authors modified this method to one that nudges toward a continually updated, horizontally averaged profile so that the technique may be used for phenomena under evolving conditions. Simulations using LBC choices, including nudging to either the base state or horizontal average, were evaluated relative to respective dual-periodic LBC control simulations with or without vertical wind shear. The horizontal average nudging technique outperformed the traditional open LBCs and nudging to the base state, as demonstrated using a histogram matching technique applied to grid points within the CBL. Ultimately, this work can be used to assist modelers in assessing which LBCs are appropriate for their intended use. 

Abstract Terrestrial Gamma‐ray Flashes (TGFs) are ten‐to‐hundreds of microsecond bursts of gamma‐rays produced when electrons in strong electric fields in thunderclouds are accelerated to relativistic energies. Space instruments have observed TGFs with source photon brightness down to ∼10¹⁷–10¹⁶. Based on space and aircraft observations, TGFs have been considered rare phenomena produced in association with very few lightning discharges. Space observations associated with lightning ground observations in the radio band have indicated that there exists a population of dimmer TGFs. Here we show observations of TGFs from aircraft altitude that were not detected by a space instrument viewing the same area. The TGFs were found through Monte Carlo modeling to be associated with 10¹⁵–10¹²photons at source, which is several orders of magnitude below what can be seen from space. Our results suggest that there exists a significant population of TGFs that are too weak to be observed from space. 

Despite their structural differences, supercells and quasi-linear convective systems (QLCS) are both capable of producing severe weather, including tornadoes. Previous research has highlighted multiple potential mechanisms by which horizontal vorticity may be reoriented into the vertical at low levels, but it is not clear in which situation what mechanism dominates. In this study, we use the CM1 model to simulate three different storm modes, each of which developed relatively large near-surface vertical vorticity. Using forward-integrated parcel trajectories, we analyze vorticity budgets and demonstrate that there seems to be a common mechanism for maintaining the near-surface vortices across storm structures. The parcels do not acquire vertical vorticity until they reach the base of the vortices. The vertical vorticity results from vigorous upward tilting and simultaneous vertical stretching. While the parcels analyzed in our simulations do have a history of descent, they do not acquire appreciable vertical vorticity during their descent. Rather, during the analysis period relatively large horizontal vorticity develops as a result of horizontal stretching by the horizontal wind, such that it can be effectively tilted into the vertical. 

Abstract. When quantifying temperature changes induced by deforestation (e.g., cooling in high latitudes, warming in low latitudes), satellite data, in situ observations, and climate models differ concerning the height at which the temperature is typically measured/simulated. In this study the effects of deforestation on surface temperature, near-surface air temperature, and lower atmospheric temperature are compared by analyzing the biogeophysical temperature effects of large-scale deforestation in the Max Planck Institute Earth System Model (MPI-ESM) separately for local effects (which are only apparent at the location of deforestation) and nonlocal effects (which are also apparent elsewhere). While the nonlocal effects (cooling in most regions) influence the temperature of the surface and lowest atmospheric layer equally, the local effects (warming in the tropics but a cooling in the higher latitudes) mainly affect the temperature of the surface.In agreement with observation-based studies, the local effects on surface and near-surface air temperature respond differently in the MPI-ESM, both concerning the magnitude of local temperature changes and the latitude at which the local deforestation effects turn from a cooling to a warming (at 45–55∘ N for surface temperature and around 35∘ N for near-surface air temperature). Subsequently, our single-model results are compared to model data from multiple climate models from the Climate Model Intercomparison Project (CMIP5). This inter-model comparison shows that in the northern midlatitudes, both concerning the summer warming and winter cooling, near-surface air temperature is affected by the local effects only about half as strongly as surface temperature. This study shows that the choice of temperature variable has a considerable effect on the observed and simulated temperature change. Studies about the biogeophysical effects of deforestation must carefully choose which temperature to consider.