Search

Eddy activity is particularly prominent in the Southern Ocean due to the instabilities of the Antarctic Circumpolar Current, which plays a critical role in energy transport of the global ocean. In this study, a systematic energetics analysis framework is employed to investigate notable anomalies of an intensified Eddy Kinetic Energy (EKE) event observed in the southwest region of the Kerguelen Plateau in the Indian sector of the Southern Ocean in 2017, utilizing a reanalysis product. The EKE anomalies, presenting across all depths, emerged in April, peaked during the austral winter, and persisted into the subsequent summer. Energetics analysis indicates that the pronounced EKE anomalies are primarily determined by baroclinic instability, with distinct governing mechanisms at the surface and in the internal ocean. The anomalous intrusion of warm Circumpolar Deep Water intensified the baroclinic energy conversion in the subsurface, contributing significantly to the EKE anomalies. Moreover, strong anomalous wind‐induced Ekman pumping served to amplify the lifting of isopycnals, which enhanced the baroclinic instability and subsequently intensified the EKE anomalies. This study sheds new light on underlying mechanisms governing local polar dynamics and provides insights into the intricate interaction between ocean dynamics and energy distribution in the Antarctic region. Plain Language Summary: The Indian sector of the Southern Ocean is known for its dynamic variability, often manifested as jets and eddies. Eddy Kinetic Energy (EKE) is widely used to measure the kinetic energy (KE) as the difference between the total KE and the KE of mean currents. This study found an anomalous event of significant increases in EKE in the southwest region of the Kerguelen Plateau in the Indian sector of the Southern Ocean in 2017. We applied a systematic energetics analysis framework to a reanalysis product to investigate the processes responsible for the observed anomalous event. The results suggest that the main cause was the anomalous intrusion of warm water masses in the upper and deeper ocean layers, which led to the increases in density gradients and then intensified the energy conversion from available potential energy to EKE. Moreover, changes in wind patterns have an impact on the variations of EKE in the upper ocean. This study enhances the understanding of the energy conversions and underlying mechanisms for EKE in polar regimes. Key Points: The subpolar region to the southwest of the Kerguelen Plateau was characterized by anomalous strong Eddy Kinetic Energy (EKE) in 2017The strong regional anomalies in EKE can be primarily attributed to baroclinic instability, with inverse barotropic energy conversionBaroclinic instability is mainly caused by anomalous intrusion of Circumpolar Deep Water, particularly at depths between 500 and 2,000 m [ABSTRACT FROM AUTHOR]

Earth may have been globally ice‐covered at least two times during the Cryogenian Period (720–635 Ma). Previous studies showed that clouds could strongly warm a hard snowball Earth and promote its deglaciation. However, the understanding of clouds was largely based on coarse‐resolution global simulations with parameterized convection and clouds, or high‐resolution cloud‐resolving simulations with explicit convection and clouds but limited to a small domain without the effects of large‐scale circulation. Here we present the first global non‐hydrostatic high‐resolution (30 km) simulation to investigate snowball clouds and their radiative effects. We show that spatial‐temporal cloud distributions exhibit clear meanders (patterns of curved lines rather than straight lines along the west‐east direction) and strong variabilities, which result from the tight interactions among the Inter‐Tropical Convergence Zone, Hadley cells, and baroclinic instability. The net cloud radiative effect is around 20 W m−2 in the tropics, consistent with previous global general circulation model simulations. Plain Language Summary: Earth may have been globally covered by snow and ice during the Cryogenian Period and is known as a hard snowball Earth, which is radically different from modern Earth. Using a global non‐hydrostatic high‐resolution model, within which vertical velocity and clouds are largely explicitly resolved, we find that the clouds on the hard snowball Earth show a more meandering pattern than modern Earth. Meanwhile, our results confirm the warming effect of snowball clouds, implying a lower CO2 concentration to terminate the global glaciation. Key Points: Snowball climate is simulated by a global non‐hydrostatic high‐resolution modelFine structures of clouds, Inter‐Tropical Convergence Zone, Hadley cells, and baroclinic eddies are clearly resolvedOur simulations confirm that clouds have a net warming effect on a hard snowball Earth [ABSTRACT FROM AUTHOR]

Applying a variational analysis, a minimum-enstrophy vortex in three-dimensional (3-D) fluids with continuous stratification is found, under the quasi-geostrophic hypothesis. The buoyancy frequency is held constant. This vortex is an ideal limiting state in a flow with an enstrophy decay while energy and generalized angular momentum remain fixed. The variational method used to obtain two-dimensional (2-D) minimum-enstrophy vortices is applied here to 3-D integral quantities. The solution from the first-order variation is expanded on a basis of orthogonal spherical Bessel functions. By computing second-order variations, the solution is found to be a true minimum in enstrophy. This solution is weakly unstable when inserted in a numerical code of the quasi-geostrophic equations. After a stage of linear instability, nonlinear wave interaction leads to the reorganization of this vortex into a tripolar vortex. Further work will relate our solution with maximal entropy 3-D vortices. [ABSTRACT FROM AUTHOR]

The Meiyu-Baiu front is the main weather system that influences the Yangtze-Huai River area of China in early summer. Convective cells along the Meiyu-Baiu front are very active and often lead to regional flooding disasters. In this study, the multiscale window transform (MWT) and MWT-based multiscale energetics analysis are utilized to investigate the dynamic energy transfers during a typical Meiyu-Baiu rainstorm. It is found that baroclinic instability in the lower stratosphere is possibly a primary trigger for the rainstorm and its diurnal variation. The kinetic energy source for a single rainstorm case varies in its evolution. During shallow convection, the rainstorm itself is a kinetic energy (KE) source. The baroclinic canonical transfer from the rainstorm window brings a lot of available potential energy (APE) to the background flow window, and is further converted into the background flow KE. In contrast, during deep convection, the primary source of KE is the background flow. The barotropic canonical transfer from the background flow contributes to the APE, thus bringing KE into the rainstorm. Implications on Meiyu-Baiu rainstorm forecasting are also discussed. [ABSTRACT FROM AUTHOR]

The main goal of the present work is to compare and contrast the characteristics of distinct monsoon systems like the Indian monsoon system (IMS) and South American monsoon system (SAMS) for the period (1979–2022). In addition, we discuss in some detail the theoretical aspects of the two monsoon systems by examining the energetics and the applicability of "convective quasi-equilibrium, (CQE)." We have also analyzed the precipitation interannual variability of SAMS and IMS considering neutral, El Niño, and La Niña years. Then, a discussion of the applicability of CQE along with the recent changes in surface entropy is presented. In our analysis, we found that interannual variability in the case of SAMS is less than that of IMS, and rainfall of SAMS is not drastically affected by ENSO when compared to IMS. We observed that rainfall characteristics over IMS are more complex than SAMS. The annual cycle of the vertically integrated total kinetic energy (KE) over SAMS is maximum in Austral spring, while the precipitation is higher in Austral summer. This is in sharp contrast to the IMS, where the maximum KE and rainfall coincide, both occurring in July and August. Further analysis showed that the conversion from the mean available potential energy PZ to the eddy available potential energy PE and conversion from PE to KE are important over SAMS. This shows that in South America, baroclinic conversions associated with baroclinic instability are important in austral summer, while over IMS, baroclinic conversions are not important in boreal summer. Our results support CQE for the IMS, but in the case of El Niño, we found that CQE is invalid. For SAMS, the applicability of CQE is climatologically doubtful, but during El Niño, the applicability of CQE is robustly visible. [ABSTRACT FROM AUTHOR]

In geophysical hydrodynamics, baroclinic instability denotes the process in which the perturbations draw the energy from the mean flow potential power. Researchers focus their attention on the baroclinic instability in the Earth's atmosphere and oceans for the meteorological diagnosis and prediction. Under investigation in this paper is a repulsive nonlinear system modeling the marginally unstable baroclinic wave packets in a baroclinic flow. With respect to the amplitude of the baroclinic wave packet and correction to the mean flow resulting from the self-rectification of the baroclinic wave, we present a Lax pair with the changeable parameters and then derive the N-dark-dark soliton solutions, where N is a positive integer. Asymptotic analysis on the N-dark-dark solitons is processed to obtain the algebraic expressions of the N-dark-dark soliton components. We find that the obtained phase shift of each dark-dark soliton component is relevant with the N − 1 spectral parameters. Furthermore, we take N = 3 as an example and graphically illustrate the 3-dark-dark solitons, which are consistent with our asymptotic-analysis results. Our analysis may provide the explanations of the complex and variable natural mechanisms of the baroclinic instability. [ABSTRACT FROM AUTHOR]

Introduction: Statistical methods such as empirical orthogonal functions (EOFs) are often used to model the sound speed profile (SSP). However, their statistical nature often leads to the sample dependence and physical fuzziness. Method: This study proposes a technique for modeling the SSP from the perspective of ocean dynamics. It employs the ocean normal mode, which is the mode of fluid particles motion, to deduce perturbations in the SSP, which is called the ocean mode basis (OMB). Result: The results of SSP reconstruction of in-situ samples showed that a few leading orders of the OMB can provide a compact representation of the SSP. Oscillations of the contours and gradient of the sound speed in thermocline were analyzed by using the first two orders of the projection coefficients of the relationship between the OMB and the baroclinic mode. As a physical model, this technique can also be used to characterize the dynamics of internal solitary waves. Furthermore, the OMB derived from archival date was used for SSP inversion. The results showed that the OMB can reconstruct SSP of a reasonable resolution without requiring in-situ samples. Discussion: Compared with statistical models, the OMB can better explain the ocean dynamics underlying variations in the SSP while requiring fewer samples. [ABSTRACT FROM AUTHOR]

We consider continuous data assimilation applied to a finite element spatial discretization and backward difference temporal discretization of the barotropic vorticity model of geophysical flow. We prove that with sufficient measurement data and properly chosen nudging parameter (guided by our analysis), the proposed algorithm achieves optimal long-time accuracy for any initial condition. While our analysis requires nudging of both the streamfunction and vorticity, our numerical tests indicate that nudging only the streamfunction can be sufficient. [ABSTRACT FROM AUTHOR]

This work investigates the compressible turbulence induced by Richtmyer–Meshkov (RM) instability using high-resolution Navier–Stokes simulations. Special attention is paid to the characteristics of RM turbulence including the mixing width growth, the turbulent kinetic energy (TKE) decay, the mixing degree, inhomogeneity and anisotropy. Three distinct initial perturbation spectra are designed at the interface to reveal the initial condition imprint on the RM turbulence. Results show that cases with initial large-scale perturbations present a stronger imprint on statistical characteristics and also a quicker growth of mixing width, whereas cases with small-scale perturbations present a faster TKE decay, greater mixing level, higher isotropy and homogeneity. A thorough analysis on the inter-scale energy transfer in RM turbulence is also presented with the coarse-graining approach that exposes the two subfilter-scale (SFS) energy fluxes (i.e. deformation work and baropycnal work). A strong correlation between the nonlinear model of baropycnal work (Fluids , 4 (2), 2019) and the simulation results is confirmed for the first time, demonstrating its potential in modelling the RM turbulence. Two primary mechanisms of baropycnal work (the straining and baroclinic generation processes) are explored with this nonlinear model. The evolutions of two SFS energy fluxes exhibit distinct behaviours at various filter scales, in different flow regions and under various flow motions (strain and rotation). It is found that all three cases share the common inter-scale energy transfer dynamics, which is important for modelling the RM turbulence. [ABSTRACT FROM AUTHOR]

This paper addresses the stability of plane Couette flow in the presence of strong density and viscosity stratifications. It demonstrates the existence of a generalised inflection point that satisfies the generalised Fjørtoft criterion of instability when a minimum of kinematic viscosity is present in the base flow. The characteristic scales associated with this minimum are identified as the primary controlling parameters of the associated instability, regardless of the type of stratification. To support this finding, analytical stability models are derived in the long-wave approximation using piecewise linear base flows. Numerical stability calculations are carried out to validate these models and to provide further information on the production of disturbance vorticity. All instabilities are interpreted as arising from the interaction between two vorticity waves. Depending on the type of stratification, these two waves are produced by different physical mechanisms. When both strong density and viscosity stratifications are present, we show that they result from the concurrent action of shear and inertial baroclinic effects. The stability models developed for simple fluid models ultimately shed light on a recently observed unstable mode in supercritical fluids (Ren et al. , J. Fluid Mech. , vol. 871, 2019, pp. 831–864), providing a quantitative prediction of the stability diagram and identifying the dominant mechanisms at play. Furthermore, our study suggests that the minimum of kinematic viscosity reached at the Widom line in these fluids is the leading cause of their instability. The existence of similar instabilities in different fluids and flows (e.g. miscible fluids) is finally discussed. [ABSTRACT FROM AUTHOR]

A unique chain connects the flow over the North Atlantic and the development of cyclones within the Mediterranean basin. One typical mechanism includes several successive processes: upper-level flow perturbations upstream cause Rossby wave breaking (RWB) events along the jet stream, which in turn develop into potential vorticity streamers. These streamers reach the Mediterranean, and through increased baroclinicity they enhance cyclonic activity in the region. Using ERA5 reanalysis data and rain gauge measurements, we provide a systematic analysis connecting wintertime North Atlantic storm track regimes and Eastern Mediterranean cyclones and rainfall. To do so, we use different detection algorithms for each element in the chain (RWBs, streamers and cyclones). A cluster analysis of upper tropospheric eddy kinetic energy reveals a favorable configuration of the storm track where North Atlantic storms are able to propagate farther northeast. This results in upper-level potential vorticity streamers forming more eastward alongside above-average precipitation over the Levant. Meanwhile, other latitudinal positions of the storm track (southward or northward) were found to hinder cyclonic activity in the region and reduce rainfall there. The intense rainy winter of 1991–1992 is brought as a test case to exemplify this mechanism in its extreme. We show that the rain-enhancing storm track regime was prominent throughout most of this season, alongside frequent streamers in the Eastern Mediterranean. [ABSTRACT FROM AUTHOR]

The paper proposes a theory of similarity of quasi-geostrophic vortices against the background of large-scale flows. This information is useful when planning laboratory and numerical experiments to study mesoscale and submesoscale vortex dynamics of vortices interacting with currents. Special attention is paid to studying geometric similarity of phenomena. It is revealed that the complete set of dimensionless similarity numbers of baroclinic vortices includes four dimensionless parameters: the dimensionless intensity of the vortex, the geometric similarity of the background flow (the ratio of the relative vorticity to the deformation coefficient of the background flow), the coefficient of horizontal stretching of the vortex core, and the coefficient of vertical oblateness of the vortex core coinciding with the Burger number. To describe the similarity of barotropic vortices against the background of barotropic flows, the number of necessary dimensionless parameters is reduced by one number: the coefficient of vertical oblateness of the vortex core is eliminated from consideration. When studying axisymmetric vortices or vortex structures close to axisymmetric, another geometric parameter of the vortex is eliminated from consideration—the coefficient of horizontal stretching of the vortex core. As a result, the maximum possible set of similarity parameters includes four dimensionless numbers, and the minimum is two. [ABSTRACT FROM AUTHOR]

Recent studies have highlighted the importance of accurate meteorological conditions for urban transport and dispersion calculations. In this work, we present a novel scheme to compute the meteorological input in the Quick Urban & Industrial Complex (QUIC) diagnostic urban wind solver to improve the characterization of upstream wind veer and shear in the Atmospheric Boundary Layer (ABL). The new formulation is based on a coupled set of Ordinary Differential Equations (ODEs) derived from the Reynolds Averaged Navier–Stokes (RANS) equations, and is fast to compute. Building upon recent progress in modeling the idealized ABL, we include effects from surface roughness, turbulent stress, Coriolis force, buoyancy and baroclinicity. We verify the performance of the new scheme with canonical Large Eddy Simulation (LES) tests with the GPU-accelerated FastEddy solver in neutral, stable, unstable and baroclinic conditions with different surface roughness. Furthermore, we evaluate QUIC calculations with and without the new inflow scheme with real data from the Urban Threat Dispersion (UTD) field experiment, which includes Lidar-based wind measurements as well as concentration observations from multiple outdoor releases of a non-reactive tracer in downtown New York City. Compared to previous inflow capabilities that were limited to a constant wind direction with height, we show that the new scheme can model wind veer in the ABL and enhance the prediction of the surface cross-isobaric angle, improving evaluation statistics of simulated concentrations paired in time and space with UTD measurements. [ABSTRACT FROM AUTHOR]

Extreme precipitation events (EPEs) are among the most pervasive weather hazards in the western Himalayan region (WHR), posing widespread damage to life, infrastructure, and agriculture. This study investigates the synoptic and large‐scale characteristics linked to winter precipitation extremes over the WHR. EPEs are identified as events surpassing the 95th percentile threshold. A composite analysis is employed using two reanalyses—the fifth‐generation European Centre for Medium‐Range Weather Forecasts Reanalysis (ERA5) and the Indian Monsoon Data Assimilation and Analysis (IMDAA)—to elucidate the synoptic conditions conducive to EPEs. Our findings suggest that EPEs in the WHR are linked to an intensified subtropical westerly jet, characteristically shifted to south than normal. Enhanced kinetic energy in the upper troposphere, attributed to increased baroclinic instability, reinforces moisture convergence and strengthens synoptic‐scale circulation, triggering deep convection and supporting EPEs. Notably, the interplay of pronounced Rossby waves sinking over the WHR and regional orography significantly modulates the intensity of western disturbances (WDs). Employing clustering analysis, we observed that the strongest EPEs are linked to anomalous vorticity in the upper to middle troposphere, together with deep convection via strengthened WDs, suggesting the potential role of large‐scale influences. Using Lagrangian method, we identify that the Arabian Sea is the primary moisture source for EPEs in the WHR. We further delved into the role of large‐scale connections and EPEs through quasi‐resonant amplification (QRA) analysis. The findings unveil distinct QRA fingerprints in meridional temperature gradients along with notably magnified, quasi‐stationary midlatitude planetary waves characterized by zonal wave numbers 6/7/8 (baroclinic waves) contributing to EPEs. Overall, our results highlight the underlying physical mechanisms for winter precipitation extremes, emphasizing QRA's role in amplifying planetary waves and promoting EPEs, underscoring the WHR's vulnerability to evolving climatic conditions. [ABSTRACT FROM AUTHOR]

Sea level and its horizontal gradient are an expression of oceanic volume, heat content, and currents. Large‐scale currents have historically been viewed as mostly "baroclinic," and tides as "barotropic," respectively, in the loose sense of being strongly related to the oceanic density distribution or not. In particular, the evolution of the barotropic velocity is influenced by a horizontal pressure‐gradient force that depends on the gradient of a particular depth‐weighting of the density field as well as on the gradient of the sea‐surface elevation ζ; hence, even the tides must be viewed as a product of the coupled interaction of barotropic and baroclinic fields. The purpose of this note is to give dynamical precision to the distinction between barotropic and baroclinic contributions to ζ and the surface pressure‐gradient force −g∇ζ, and, in the particular case of the tides, demonstrate their combined barotropic‐baroclinic interactions with a realistically forced, high‐resolution simulation of the Pacific Ocean circulation. While the different tidal sea‐level contributions manifest a horizontal scale separation (e.g., more barotropic at larger scales; more baroclinic surface pressure‐gradient force at smaller scales), there are cross‐mode corrections in both at the level of tens of percent. The proposed barotropic‐baroclinic decomposition is generally relevant to the sea‐level expression of oceanic currents. Plain Language Summary: Sea‐level variations at tidal frequencies occur because of the "astronomical" gravitational force acting nearly uniformly over the oceanic depth. Thus, they are commonly associated with the depth‐averaged velocity, that is, the barotropic current. However, due to oceanic density stratification and variable bathymetry, the resulting barotropic currents also generate vertically varying (baroclinic) tidal currents that also have an expression in the sea level and surface pressure‐gradient force. A prescription is given for how to decompose sea level and its gradient into its barotropic and baroclinic parts for both tides and currents, and the answers are illustrated using a tide‐resolving simulation of the Pacific Ocean. Key Points: Sea level, measured relative to a geopotential iso‐surface, is the surface dynamic pressure for the oceanic momentum balanceBarotropic and baroclinic dynamics combine in determining the sea levelA decomposition of tidal sea level and pressure‐gradient force in a Pacific Ocean simulation shows barotropic‐baroclinic coupling [ABSTRACT FROM AUTHOR]

Recent observational and modeling studies have demonstrated the substantial influence of the Tibetan Plateau (TP) spring land surface temperature (LST) and subsurface temperature (SUBT) on downstream summer droughts/floods events in East Asia, highlighting the potential application of LST/SUBT on sub-seasonal to seasonal prediction (S2S). In this study, we employ the National Centers for Environment Prediction—Global Forecast System/Simplified Simple Biosphere model version 2 (GFS/SSiB2) to investigate the potential role of the late spring warm LST anomaly over the TP on the extraordinary June 1998 flood in the south of the Yangtze River region. Numerical experiments indicate that the warmer (above normal) May LST over the TP may contribute to the extreme flood of 1998 over the south of the Yangtze River region, with the LST reproducing about 57% and 64% of observed above-normal rainfall anomaly over the south of the Yangtze River region and southeastern China, respectively. Further analyses reveal a possible effect of springtime TP's LST on summer southern and eastern Asian rainfall and identify some hot spots, suggesting that the TP's spring LST effect is not only limited to the Yangtze River region, but to a much larger scale. The imposed warm LST/SUBT over the TP triggers a strong wave activities propagating eastward along the upper-level westerly jet, associated with an increase of the atmospheric baroclinic instability as well as a strengthening and southeastward movement of the South Asian high, leading to intensified moisture convergence and convective instability favorable to the excessive rainfall in the downstream region of East Asia. The results of the 1998 case have also been compared with the results from year of 2003, which had a very cold spring LST anomaly over the TP and a severe downstream June 2003 drought (flood) in southern (northern) of the Yangtze River Basin area. Simulation results provide further evidence of the great importance of the TP spring land surface temperature anomaly in regulating summer extreme hydroclimatic events (e.g. droughts and floods) in South and East Asia. The present study suggests that consideration of LST/SUBT anomalies has a strong potential for more skillful S2S prediction of extreme hydroclimatic events such as floods, droughts and heatwaves over both Southern and Eastern Asia. [ABSTRACT FROM AUTHOR]

The formation of convective flows in a rotating cylindrical layer with an inclined bottom and free surface is studied. Convection is driven by localized cooling at the center of the upper free surface and by rim heating at the bottom near the sidewall. The horizontal temperature difference in a rotating layer leads to the formation of a convective flow with a complex structure. The mean meridional circulation, consisting of three cells, provides a strongly non-uniform differential rotation. As a result of the instability of the main cyclonic zonal flow, the train of baroclinic waves appears in the upper layer. The baroclinic waves provide most of the heat transfer in the middle radii and are responsible for strong temperature and velocity fluctuations. It is shown that the inclination of the bottom is a crucial factor for the structure of the convective cells and the dynamics of the baroclinic waves. The increase in the inclination angle leads to a significant increase in the energy of the waves. The obtained results may be important for heat and mass transfer in various geophysical and industrial systems, including transport of various additives and impurities in rotating crucibles, and crystallization processes. [ABSTRACT FROM AUTHOR]

Barotropic, baroclinic, and Rossby‐Kelvin instabilities exist in the Venus atmosphere, as revealed by previous studies using numerical models. This study aims to deepen our understanding of the instabilities in the Venus atmosphere using the breeding of growing modes (BGM) method for the first time. We conducted a 1‐year model simulation as the control run. First, we conducted identical twin experiments in which random perturbations were added to the control run at the initial time, and they grew freely. Perturbations in the upper layer (UL, 70–100 km altitudes) grow faster at the beginning but saturate earlier at a low value compared to those in the lower layer (LL, 40–70 km altitudes). Next, we implemented the BGM method and conducted multiple breeding cycle experiments with different rescaling amplitudes and intervals, the two parameters of the BGM method. The bred vectors (BVs) from these experiments identified instabilities in various regions. With large rescaling amplitudes, the structure and amplitude of the BVs in the LL closely resembled the deviations in the control run, indicating the growth of BVs due to barotropic, baroclinic, and Rossby‐Kelvin instabilities. Composite mean analysis shows larger BV amplitudes in the morning hemisphere at the 60–70 km altitudes in the mid‐latitudes, indicating enhanced baroclinic instability by the thermal tide. Finally, we estimated the intrinsic predictability related to baroclinic instability for Venus is >1 month, which would be longer than that for the Earth of ∼2 weeks. Plain Language Summary: The Venus atmosphere has been studied by numerical models that take inputs such as temperature and winds and provide evolution. We applied the "breeding of growing mode" method to a numerical model to deepen our understanding of the dynamics of the Venus atmosphere. We use two independent model simulations starting with different inputs. When the differences become larger over time for some areas, it is a sign of instability in those areas. Instabilities can be studied by investigating how the differences change with time in various regions. We found that in the cloud layer at 40–70 km height, the difference grows slowly at the beginning. However, it becomes larger than the difference above the cloud layer at the 70–100 km height in the later stages, indicating that large‐scale instabilities dominate in the cloud layer while small‐scale instabilities dominate above. Additionally, we identified barotropic, baroclinic, and Rossby‐Kelvin instabilities at high, mid, and low latitudes in the cloud layer, respectively. Thermal tide due to solar heating impacts the instability around the cloud top (∼70 km) in the mid‐latitudes. Finally, the predictability of the Venus atmosphere would be longer for the Venus atmosphere (>1 month) than that for the Earth's atmosphere (∼2 weeks). Key Points: Identical twin experiments show that perturbations at 40–70 and 70–100 km altitudes are slow‐growing and fast‐growing modes, respectivelyBreeding cycle experiments generate perturbations associated with barotropic, baroclinic, and Rossby‐Kelvin instabilitiesThe intrinsic predictability related to the baroclinic instability is >1 month, longer than that for the Earth's atmosphere of ∼2 weeks [ABSTRACT FROM AUTHOR]

Using eddy‐resolving Community Earth System Model (CESM) simulations, this study investigates mesoscale eddy energetics and the role of air‐sea interaction for both anticyclonic and cyclonic eddies (AEs and CEs) in the Kuroshio Extension (KE) region. Based on energy budget analysis and eddy tracking algorithm, it is found that eddy energy balance depicts similar characteristics for AEs and CEs. The eddy kinetic energy (EKE) is generated through barotropic instability, vertical buoyancy flux, as well as transported from the upper stream Kuroshio. In addition, the temperature variance, which is directly related to eddy potential energy, is maintained by baroclinic instability. Air‐sea heat flux and wind stress act as eddy killers to move energy from oceanic eddies. For both AEs and CEs, heat exchange between atmosphere and oceanic eddies dominates the dissipation of temperature variance and accounts for more than 60% and 72% of the total dissipation, respectively. In comparison, the role of wind power in damping the EKE is relatively small. Only 14% (5%) of EKE dissipation in AEs (CEs) is attributed to eddy wind power. [ABSTRACT FROM AUTHOR]

Introduction: Assimilating all available observations in numerical models may lead to deterioration of the analysis. Ensemble Forecast Sensitivity to Observations (EFSO) is a method that helps to identify all such observations which benefit the analyses. EFSO has never been tested in an ocean data assimilation system because of a lack of robust formulation of a squared norm against which beneficiality of observations can be estimated. Methods: Here, we explore the efficacy of EFSO in the ocean data assimilation system that comprises the ocean model, Regional Ocean Modeling System (ROMS), coupled to the assimilation system Local Ensemble Transform Kalman Filter (LETKF), collectively called LETKF-ROMS, in the Bay of Bengal by envisaging a novel squared norm. The Bay of Bengal is known for its higher stratification and shallow mixed layer depth. In view of baroclinicity representing the stratification of the ocean, we use the modulus of the baroclinic vector as the squared norm to evaluate forecast errors in EFSO. Results: Using this approach, we identify beneficial observations. Assimilating only the beneficial observations greatly improves the ocean state. We also show that the improvements are more pronounced in the head of the Bay of Bengal where stratification is much higher compared to the rest of the basin. Discussion: Though this approach doesn't degrade the ocean state in other regions of the Indian Ocean, a universal squared norm is needed that can be extended beyond the Bay of Bengal basin. [ABSTRACT FROM AUTHOR]

In this paper, the effects of spring soil moisture (SM) anomalies in the mid‐latitudes on the atmospheric circulation in summer over the Northern Hemisphere (NH) are investigated. The results show that there are two regions of maximum interannual variability of the spring SM in the mid‐latitudes, which are located in central North America (CNA) and Europe and central Asia (ECA). In addition, the interannual variation of spring SM anomalies between CNA and ECA exhibits a seesaw pattern. The CNA–ECA seesaw pattern of the spring SM anomalies leads to the surface heat anomalies having opposite phases in CNA and ECA from spring to summer, which subsequently cause the opposite phase of baroclinicity anomalies in spring. The anomalous meridional temperature advections in spring cause the baroclinicity anomalies to have the same phase around CNA and ECA in summer. Corresponded with the same phase of baroclinicity anomalies, the anomalous centers of the stationary Rossby wave train (RWT) and Rossby wave source (RWS) have the same phase in CNA and ECA in summer. Through analysis of the vorticity budgets, the maintenance mechanism of the RWT in summer is considered as a positive feedback that anomalous meridional winds characterized by a RWT, transport the mean absolute vorticity and subsequently lead to an anomalous RWS, which in turn maintains the stationary RWT. Numerical experiments further demonstrate the effects of CNA–ECA seesaw pattern of spring SM anomalies on stationary RWT and RWS in summer. Plain Language Summary: The interannual variation of soil moisture (SM) anomalies in mid‐latitudes exhibits a seesaw pattern in central North America (CNA) and Europe and central Asia (ECA). When spring SM anomalies are negative in CNA and positive in ECA, positive (negative) sensible heat flux anomalies are observed in CNA (ECA) while negative (positive) latent heat flux anomalies are observed in CNA (ECA) from spring to summer, or vice versa. Influenced by surface heat anomalies, baroclinicity anomalies exhibit a seesaw pattern in CNA and ECA in spring, and have same phase in CNA and ECA in summer due to anomalous meridional temperature advections. The baroclinicity anomalies in CNA and ECA in summer contribute to the same variation of wave‐flow interactions. The Rossby wave train (RWT) induced and maintained by CNA–ECA seesaw pattern of spring SM anomalies in spring can be maintained by its meridional transportation of the mean absolute vorticity in summer. Apparently, spring SM anomalies in the middle latitudes can persistently influence the large‐scale atmospheric circulations over the Northern Hemisphere by maintaining RWT. Key Points: Seesaw pattern of spring soil moisture anomalies in central North America (CNA) and Europe and central Asia (ECA)Baroclinicity anomalies change from opposite to same phase in CNA and ECA during the transition from spring to summerRossby wave train induced by spring CNA–ECA seesaw pattern is maintained by its meridional mean absolute vorticity transportation in summer [ABSTRACT FROM AUTHOR]

Polar lows (PLs) are intense maritime mesoscale weather systems that develop during marine cold air outbreaks at high latitudes. The objective of this review is to describe the advances in polar low research since the last literature review--published 3 years ago--, indicate the knowledge gaps that remain, and suggest promising courses of research. Among the breakthroughs identified here are the first climatology of PLs obtained with a global atmospheric model, and increased evidence showing that baroclinic instability is the main mechanism leading to PL development. Despite these advances, many challenges persist such as the lack of conventional observations of PLs and the need to better understand coupled atmosphere-ocean processes involved in PL development. With the rapid advances in deep learning, this method has the potential to be used for PL forecasting. [ABSTRACT FROM AUTHOR]

Seasonal variation in westward-propagating quasi-10 d waves (Q10DWs) in the mesosphere and lower thermosphere of the Southern Hemisphere (SH) high-latitude regions is investigated using meteor radar (MR) observations for the period of 2012–2016 and using the Specified Dynamics (SD) version of the Whole Atmosphere Community Climate Model (WACCM). The phase difference in meridional winds measured by two MRs located in Antarctica gives observational estimates of the amplitude and phase of the Q10DW with zonal wavenumber 1 (W1). The amplitude of the observed Q10DW-W1 is large around equinoxes. In order to elucidate the variations in the observed Q10DW-W1 and its possible amplification mechanism, we carry out two SD-WACCM experiments nudged towards the MERRA-2 reanalysis from the surface up to ∼ 60 km (EXP60) and ∼ 75 km (EXP75). Results of the EXP75 indicate that the observed Q10DW-W1 can be amplified around regions of barotropic and/or baroclinic instability in the middle mesosphere around 60–70° S. In the EXP60 experiment, it was also found that the Q10DW-W1 is amplified around the regions of instability, but the amplitude is too large compared to MR observations. The large-scale instability in the EXP60 in the SH summer mesosphere is stronger than that in the EXP75 and Microwave Limb Sounder observations. The larger instability in the EXP60 is related to the large meridional and vertical variations in polar mesospheric zonal winds in association with gravity wave parameterization (GWP). Given uncertainties inherent in GWP, these results can suggest that it is possible for models to spuriously generate traveling planetary waves such as the Q10DW, especially in summer, due to excessively strong large-scale instability in the SH high-latitude mesosphere. [ABSTRACT FROM AUTHOR]

Latent heating modifies the jet stream by modifying the vertical geostrophic wind shear, thereby altering the potential for baroclinic development. Hence, correctly representing diabatic effects is important for modelling the mid-latitude atmospheric circulation and variability. Yet, the direct effects of diabatic heating remain poorly understood. For example, there is no consensus on the effect of latent heating on the cross-jet temperature contrast. We show that this disagreement is attributable to the choice of spatio-temporal filtering. Jet representations relying on filtered wind tend to have the strongest latent heating on the cold flank of the jet, thus weakening the cross-jet temperature contrast. In contrast, jet representations reflecting the two-dimensional instantaneous wind field have the strongest latent heating on the warm flank of the jet. Furthermore, we show that latent heating primarily occurs on the warm flank of poleward directed instantaneous jets, which is the case for all storm tracks and seasons. [ABSTRACT FROM AUTHOR]

This study investigates the relationship between the persistence and the zonal scale of atmospheric dipolar modes (DMs). Results from the daily data of ERA5 and the long-term output of an idealized atmospheric model show that the atmospheric DMs with a broader (narrower) zonal scale dipolar structure possess a longer (shorter) persistence. A detailed vorticity budget analysis indicates that the persistence of a hemispheric-scale DM (1/1 DM) and a regional or sectoral DM (1/8 DM) in the model both largely rely on the persistence of the nonlinear eddy forcing. Linear terms can indirectly reduce the persistence of the anomalous nonlinear eddy forcing in a 1/8 DM by modifying the baroclinicity via the arousal of anomalous vertical motions. Therefore, the atmospheric DMs with a broader (narrower) zonal scale possess a longer (shorter) persistence because the effects of the linear terms are less (more) pronounced when the atmospheric DMs have better (worse) zonal symmetry. Further analyses show that the positive eddy feedback effect is weak or even absent in a 1/8 DM and the high-frequency eddy forcing acts more like a concomitant phenomenon rather than a leading driving factor for a 1/8 DM. Thus, the hemispheric-scale DM and the regional or sectoral DMs are different, not only in their persistence but also in their dynamics. [ABSTRACT FROM AUTHOR]

Based on a submesoscale-resolving glider observation from April 25 to May 4, 2018, characteristics and underlying dynamics of submesoscale variability at the edge of an anticyclonic eddy shed from Kuroshio in the Northern South China Sea are explored in this study. Three underwater gliders traveled across the frontal zone and implemented ~ 300 dives, covering a horizontal distance of ~ 160 km and a vertical depth of ~ 500 m in 9 days. The character of k−2 slope for spectral potential energy and the strong lateral buoyancy gradient indicate frontogenesis-induced submesoscale motions on the eddy edge. Further analysis focusing on the potential vorticity and balanced Richardson number reveals the development of symmetric instability (SI), which is associated with the strong lateral gradient of buoyancy at the edge of the anticyclonic eddy in the late spring. [ABSTRACT FROM AUTHOR]

Observations from a tidal estuary show that tidal intrusion fronts occur regularly during flood tides near topographic features including constrictions and bends. A realistic model is used to study the generation of these fronts and their influence on stratification and mixing in the estuary. At the constriction, flow separation occurs on both sides of the jet flow downstream of the narrow opening, leading to sharp lateral salinity gradients and baroclinic secondary circulation. A tidal intrusion front, with a V-shaped convergence zone on the surface, is generated by the interaction between secondary circulation and the jet flow. Stratification is created at the front due to the straining of lateral salinity gradients by secondary circulation. Though stratification is expected to suppress turbulence, strong turbulent mixing is found near the surface front. The intense mixing is attributed to enhanced vertical shear due to both frontal baroclinicity and the twisting of lateral shear by secondary circulation. In the bend, flow separation occurs along the inner bank, resulting in lateral salinity gradients, secondary circulation, frontogenesis, and enhanced mixing near the front. In contrast to the V-shaped front at the constriction, an oblique linear surface convergence front occurs in the bend, which resembles a one-sided tidal intrusion front. Moreover, in addition to baroclinicity, channel curvature also affects secondary circulation, frontogenesis, and mixing in the bend. Overall in the estuary, the near-surface mixing associated with tidal intrusion fronts during flood tides is similar in magnitude to bottom boundary layer mixing that occurs primarily during ebbs. [ABSTRACT FROM AUTHOR]

We examine the ocean energy cycle where the eddies are defined about the ensemble mean of a partially air–sea coupled, eddy-rich ensemble simulation of the North Atlantic. The decomposition about the ensemble mean leads to a parameter-free definition of eddies, which is interpreted as the expression of oceanic chaos. Using the ensemble framework, we define the reservoirs of mean and eddy kinetic energy (MKE and EKE, respectively) and mean total dynamic enthalpy (MTDE). We opt for the usage of dynamic enthalpy (DE) as a proxy for potential energy due to its dynamically consistent relation to hydrostatic pressure in Boussinesq fluids and nonreliance on any reference stratification. The curious result that emerges is that the potential energy reservoir cannot be decomposed into its mean and eddy components, and the eddy flux of DE can be absorbed into the EKE budget as pressure work. We find from the energy cycle that while baroclinic instability, associated with a positive vertical eddy buoyancy flux, tends to peak around February, EKE takes its maximum around September in the wind-driven gyre. Interestingly, the energy input from MKE to EKE, a process sometimes associated with barotropic processes, becomes larger than the vertical eddy buoyancy flux during the summer and autumn. Our results question the common notion that the inverse energy cascade of wintertime EKE energized by baroclinic instability within the mixed layer is solely responsible for the summer-to-autumn peak in EKE and suggest that both the eddy transport of DE and transfer of energy from MKE to EKE contribute to the seasonal EKE maxima. Significance Statement: The Earth system, including the ocean, is chaotic. Namely, the state to be realized is highly sensitive to minute perturbations, a phenomenon commonly known as the "butterfly effect." Here, we run a sweep of ocean simulations that allow us to disentangle the oceanic expression of chaos from the oceanic response to the atmosphere. We investigate the energy pathways between the two in a physically consistent manner in the North Atlantic region. Our approach can be extended to robustly examine the temporal change of oceanic energy and heat distribution under a warming climate. [ABSTRACT FROM AUTHOR]

Weak but persistent synoptic-scale ascent may play a role in the initiation or maintenance of nocturnal convection over the central United States. An analytical model is used to explore the nocturnal low-level jets (NLLJ) and ascent that develop in an idealized diurnally varying frictional (Ekman) boundary layer in a neutrally stratified barotropic environment when the flow aloft is a zonally propagating Rossby wave. Steady-periodic solutions are obtained of the linearized Reynolds-averaged Boussinesq-approximated equations of motion on a beta plane with an eddy viscosity that is specified to increase abruptly at sunrise and decrease abruptly at sunset. Rayleigh damping terms are used to parameterize momentum loss due to radiation of inertia–gravity waves. The model-predicted vertical velocity is (approximately) proportional to the wavenumber and wave amplitude. There are two main modes of ascent in midlatitudes, an afternoon mode and a nocturnal mode. The latter arises as a gentle but persistent surge induced by the decrease of turbulence at sunset, the same mechanism that triggers inertial oscillations in the Blackadar theory of NLLJs. If the Rayleigh damping terms are omitted, the boundary layer depth becomes infinite at three critical latitudes, and the vertical velocity becomes infinite far above the ground at two of those latitudes. With the damping terms retained, the solution is well behaved. Peak daytime ascent in the model occurs progressively later in the afternoon at more southern locations (in the Northern Hemisphere) until the first (most northern) critical latitude is reached; south of that latitude the nocturnal mode is dominant. [ABSTRACT FROM AUTHOR]

A recent study by Liu et al. (2020) suggested that due to the saturation of equatorially trapped planetary waves with different dynamical types, temporal periods, meridional and baroclinic modes, complex layer structures of vertical velocity shear and hence turbulent mixing could frequently occur in the thermocline of the eastern equatorial Pacific. We investigated the occurrence of the interior turbulent mixing as indicated by shear instabilities, above the Equatorial Undercurrent (EUC) core at three equatorial sites along 140°W, 170°W, and 165°E, respectively, based mainly on data from the Tropical Atmosphere and Ocean (TAO) mooring array. We found that turbulent mixing bursts persisted in the thermocline of all three sites. Specifically, the interior turbulent mixing layers (ITMLs) could occur in probability of approximately 68%, 53%, and 48% at the three sites, respectively. The overall occurrence probability shows obvious and similar biannual variations at 140°W and 170°W, which is higher in boreal from late summer to winter and lower in spring. Vertically, the ITMLs are primarily located above the EUC core and prevail in deeper (shallower) layers from late summer to winter (spring). Most ITMLs (70%) lasted for hours to 3 days, and a few of them (15%) for more than 7 days. The thicknesses of ITMLs were concentrated between 15 and 55 m. At 165°E, the vertical distribution of ITML occurrence probability was different from that at 140°W and 170°W, as it did not show a preference for depths; the durations of ITMLs are short (also from hours to several days) and their thicknesses were between 5 and 25 m. These properties, particularly the high occurrence probability, and short durations demonstrated the persistence of thermocline mixing in the western to eastern equatorial Pacific thermocline and confirmed the generation mechanism by persistent equatorial waves as well. [ABSTRACT FROM AUTHOR]

Earth system models suffer from various structural and parametric errors in their representation of nonlinear, multi‐scale processes, leading to uncertainties in their long‐term projections. The effects of many of these errors (particularly those due to fast physics) can be quantified in short‐term simulations, for example, as differences between the predicted and observed states (analysis increments). With the increase in the availability of high‐quality observations and simulations, learning nudging from these increments to correct model errors has become an active research area. However, most studies focus on using neural networks, which while powerful, are hard to interpret, are data‐hungry, and poorly generalize out‐of‐distribution. Here, we show the capabilities of Model Error Discovery with Interpretability and Data Assimilation (MEDIDA), a general, data‐efficient framework that uses sparsity‐promoting equation‐discovery techniques to learn model errors from analysis increments. Using two‐layer quasi‐geostrophic turbulence as the test case, MEDIDA is shown to successfully discover various linear and nonlinear structural/parametric errors when full observations are available. Discovery from spatially sparse observations is found to require highly accurate interpolation schemes. While NNs have shown success as interpolators in recent studies, here, they are found inadequate due to their inability to accurately represent small scales, a phenomenon known as spectral bias. We show that a general remedy, adding a random Fourier feature layer to the NN, resolves this issue enabling MEDIDA to successfully discover model errors from sparse observations. These promising results suggest that with further development, MEDIDA could be scaled up to models of the Earth system and real observations. Plain Language Summary: Numerical models are used to predict the Earth system, for example, from daily weather to the next‐century climate. These models have been developed and validated against observations over decades, however, they still have shortcomings (errors) in their representations of many complex processes, particularly those that are nonlinear and span many scales in time and space. The rapid improvements in the quality and quantity of observational data from the Earth system and advances in machine learning (ML) algorithms provide an opportunity to try to reduce these errors. However, the challenge is that many ML methods require a lot of training data, and it is also often difficult to explain how they are reducing the error. Here, we show the capabilities of a framework called MEDIDA (Model Error Discovery with Interpretability and Data Assimilation), which uses a class of ML methods that provide closed‐form (thus interpretable) equations for what they are learning from the differences between observations and model predictions. We show the success of MEDIDA when applied to a model of atmospheric turbulent circulation. Even when observations are only sparsely (not at every location) available, we show that MEDIDA works accurately once we leverage more recent advances in ML. Key Points: Model error discovery with interpretability and data assimilation is scaled up to geostrophic turbulence and sparse observationsNaive use of neural nets (NNs) as interpolator does not capture small scales due to spectral bias, failing discoveries of closed‐form errorsReducing this bias using random Fourier features enables NNs to represent the full range of scales, leading to successful error discoveries [ABSTRACT FROM AUTHOR]

Mesoscale eddies play an important role in driving the dynamics of the Arctic Ocean. Understanding their behavior is crucial for comprehending the ongoing changes in the region. In this study, by using a novel decade‐long simulation at 1 km resolution with the unstructured‐mesh Finite volumE Sea ice‐Ocean Model, we evaluate the spatial and temporal variability of eddy kinetic energy in the Eurasian Basin. We find that monthly, annual, and interannual variability of EKE near the surface is predominantly influenced by changes in sea ice cover, while the eddy activity at deeper depth, being shielded from the surface by ocean stratification, is more strongly influenced by local baroclinic energy conversion. Moreover, our research demonstrates that eddies in the Eurasian Basin can transport ocean heat from the Atlantic Water layer toward sea ice and cause local basal melting in the order of about 20 cm per month even in wintertime. Our study suggests that eddy activity in the Arctic Ocean will strengthen along with future sea ice decline, and that the impact of ocean heat of the Atlantic Water layer on sea ice retreat may become prominent. Plain Language Summary: Mesoscale eddies are swirling currents that are generally considered the "weather" of the ocean. They can be found everywhere in the ocean and are crucial for understanding many processes such as the transport of heat and salt, the structure of ocean stratification, but also the distribution of nutrients that influence the biological system from algae blooms to micro and macro fauna. Distinct from major eddies in lower latitudes, most eddies in the Arctic Ocean are only about 10 km in diameter. This makes it incredibly hard to simulate them in numerical models because a very high spatial resolution is needed to adequately represent them. In this study we use a simulation with 1 km horizontal resolution to analyze the role of eddies in the Eurasian Basin of the Arctic Ocean and to understand what drives their variability. We found that the dynamics differ greatly between the surface and deeper water layers, with the surface being influenced strongly by sea ice cover, while the deeper layer is shielded from this effect by the stratification. We have also shown that eddies can pump warm water from the Atlantic Water layer up to the mixed layer, thus melting sea ice even in winter. Key Points: Mesoscale eddies in the Eurasian Basin can bring ocean heat from the Atlantic Water layer to sea ice and cause basal melting even in winterVariability of surface eddy kinetic energy is mainly controlled by sea ice coverEddy activity at depth is mainly controlled by baroclinic instability and ocean stratification [ABSTRACT FROM AUTHOR]

Interactions between large-scale waves and the Hadley cell are examined using a linear two-layer model on an f plane. A linear meridional moisture gradient determines the strength of the idealized Hadley cell. The trade winds are in thermal wind balance with a weak temperature gradient (WTG). The mean meridional moisture gradient is unstable to synoptic-scale (horizontal scale of ∼1000 km) moisture modes that are advected westward by the trade winds, reminiscent of oceanic tropical depression–like waves. Meridional moisture advection causes the moisture modes to grow from "moisture-vortex instability" (MVI), resulting in a poleward eddy moisture flux that flattens the zonal-mean meridional moisture gradient, thereby weakening the Hadley cell. The amplification of waves at the expense of the zonal-mean meridional moisture gradient implies a downscale latent energy cascade. The eddy moisture flux is opposed by a regeneration of the meridional moisture gradient by the Hadley cell. These Hadley cell–moisture mode interactions are reminiscent of quasigeostrophic interactions, except that wave activity is due to column moisture variance rather than potential vorticity variance. The interactions can result in predator–prey cycles in moisture mode activity and Hadley cell strength that are akin to ITCZ breakdown. It is proposed that moisture modes are the tropical analog to midlatitude baroclinic waves. MVI is analogous to baroclinic instability, stirring latent energy in the same way that dry baroclinic eddies stir sensible heat. These results indicate that moisture modes stabilize the Hadley cell and may be as important as the latter in global energy transport. Significance Statement: The tropics are characterized by steady circulations such as the Hadley cell as well as a menagerie of tropical weather systems. Despite progress in our understanding of both, little is known about how the mean circulations and the weather systems interact with one another. Here we show that tropical waves can grow by extracting moisture from the Hadley cell, thereby weakening it. They also transport moisture to higher latitudes. Our results challenge the notion that the Hadley cell is the sole transporter of energy out of the tropics and instead favor a view where tropical waves are also essential for the global energy balance. They dry the humid regions and moisten the drier regions via stirring. [ABSTRACT FROM AUTHOR]

Arctic cyclone activity is an important component of the local climate, and the frequent occurrence of extreme summer storms has raised widespread scientific interest. In this paper, we investigated the distinctive structural characteristics of intense summer Arctic cyclones by utilizing ERA‐Interim reanalysis data and employing a deep learning algorithm for cyclone detection. We found that the northern edge of Eurasia (i.e., the marginal ice zone (MIZ)) and the Alpha Ridge of Arctic Ocean (AR, i.e. central Arctic) are the two most active regions for intense Arctic cyclone activities in summer (from June to September). However, the surface conditions and coupling frequency between surface cyclone and tropopause polar vortices (TPVs) are distinct over these two regions. By further analysis of 100 intense cyclone activities in these two areas, respectively, we found that cyclones in MIZ are often smaller in size but higher in intensity at their maximum intensity, and their life cycles are generally shorter. MIZ cyclones are typically accompanied by a large Eady growth rate and frontal structure in the lower troposphere and their intensification primarily attributed to the thermal‐baroclinic process. In contrast, cyclones in AR are more frequently associated with higher potential vorticity (PV) values and pronounced PV downward intrusion from the stratosphere, as well as notable "upper warm‐lower cold" structures. The downward intrusion of TPVs and stratosphere vortices contribute to a decrease in the upper and column air mass deficit, leading to the intensification of surface Arctic cyclones in these regions. Plain Language Summary: In this study, we researched intense summer storms in the Arctic. We found that there are two main areas where these storms occur: the marginal ice zone (MIZ) near Eurasia and the Alpha Ridge (AR) in the central Arctic. However, storms in these two areas have different characteristics. In the MIZ, the storms are smaller but stronger, and they do not last as long. They are mainly driven by instability in the lower troposphere. On the other hand, the storms in AR respond more to the downward intrusion of potential vorticity from the stratosphere. These storms have a unique structure where the upper air is warmer than their surroundings, and the lower air is colder than their surroundings, especially in AR. This structure makes them more intense and longer‐lasting. Exploring these differences helps us understand how Arctic storms work, and how they might be affected by climate change. Key Points: Both the marginal ice zone (MIZ) and Alpha Ridge exhibit active summer Arctic cyclone activities, especially for intense stormsIn the MIZ, baroclinic instability plays a more prominent role in the intensification and maintenance of cyclonesCyclones in Alpha Ridge are more commonly accompanied by potential vorticity downward intrusion, and "upper warm‐lower cold" structures [ABSTRACT FROM AUTHOR]

Introduction: Understanding the underlying dynamics of regional sea-level rise (SLR), which often deviates from global trends, is crucial for mitigating and adapting to the impacts of severe climate change. This study investigated the causes of high regional SLR rates (> 6.0 mm yr-1) around the frontal region near Ulleung Island in the southwestern East/Japan Sea (EJS). Despite exhibiting rates higher than the global average (3.1 mm yr-1) from 1993 to 2020, the reasons for these higher rates in this region have not been clearly elucidated. Methods: We aimed to clarify the quantitative effect of the long-term variations of the Ulleung Warm Eddy (UWE) on the high SLR rates near Ulleung Island based on satellite altimetry and ship-based hydrographic data. Results: During this period, the temperature within the UWE increased, particularly at the temperature-homogeneous layer of approximately 200 m, the lower boundary of the UWE deepened, and the eddy duration per year increased, resulting in high SLR rates within the eddy owing to the steric height rise. The long-term variations in the internal temperature and vertical thickness of the UWE had significantly comparable impacts on SLR rates, with the duration being less influential. The SLR rates by integrating all long-term variations in the UWE (7.6 mm yr-1) quantitatively explained the high long-term SLR rates at Ulleung Island (7.0 mm yr-1). Discussion: The increasing temperature within the UWE was attributed to the rising temperature of water flowing through the southwestern strait (Korean Strait) in late fall, and the deepening lower boundary and the increasing duration of the UWE resulted from the increased horizontal temperature gradients near the front, leading to enhanced baroclinic instability in the subsurface layers. Our findings suggest that long-term variations in mesoscale eddies can significantly influence the regional SLR rates, deviating substantially from the global average in the frontal region. [ABSTRACT FROM AUTHOR]

The Mid-Piacenzian Warm Period (MPWP; 3.0–3.3 Ma), a warm geological period about three million years ago, has been deemed as a good past analog for understanding the current and future climate change. Based on 12 climate model outputs from Pliocene Model Intercomparison Project Phase 2 (PlioMIP2), we investigate tropical atmospheric circulation (TAC) changes under the warm MPWP and associated underlying mechanisms by diagnosing both atmospheric static stability and diabatic processes. Our findings underscore the advantage of analyzing atmospheric diabatic processes in elucidating seasonal variations of TAC compared to static stability assessments. Specifically, by diagnosing alterations in diabatic processes, we achieve a quantitative understanding and explanation the following TAC changes (incl. Strength and edge) during the MPWP: the weakened (annual, DJF, JJA) Northern Hemisphere and (DJF) Southern Hemisphere Hadley circulation (HC), reduced (annual, DJF) Pacific Walker circulation (PWC) and enhanced (annual, JJA) Southern Hemisphere HC and (JJA) PWC, and westward shifted (annual, DJF, JJA) PWC. We further addressed that the increasing bulk subtropical static stability and/or decreasing vertical shear of subtropical zonal wind - two crucial control factors for changes in subtropical baroclinicity - may promote HC widening, and vice versa. Consequently, our study of spatial diabatic heating and cooling, corresponding to upward and downward motions within the TAC, respectively, provides a new perspective for understanding the processes controlling seasonal TAC changes in response to surface warming. [ABSTRACT FROM AUTHOR]

Interactions between the rotating stratified oceanic and atmospheric flows and topography play a fundamental role in Earth's climate. Here we use laboratory experiments in a differentially-heated rotating annulus to explore stratified flow-topography interactions in a dynamical regime of strong background geostrophic turbulence. A localised small-scale topographic ridge is differentially-rotated at a range of angular velocities around the base of the annulus to impose a relative velocity between the stratified fluid and the small ridge. Considering the idealised setup of the laboratory configuration, the experiments exhibit rich dynamics that include, but are not limited to, lee waves, internal bores, baroclinic instabilities, boundary currents, large-scale gyres, blocking, and geostrophic eddies. Despite the complicated nature of the circulations, several bulk properties and features of the system are able to be characterised globally by relatively simple parameters. We find that the most useful parameter for describing the flows is the internal Froude number ( $ Fr_{n} $ F r n ), which is the ratio between the imposed ridge velocity and the internal wave phase speed in the stratified fluid. Standing features that are predominantly barotropic and stationary relative to the ridge are only able to occur when the imposed ridge velocity is less than the internal wave phase speed ( $ |Fr_{n}| | F r n | < 1). This implies that the flow-topography interactions leading to stationary dynamics are primarily internal stratified processes, which steer the flow and shape the background geostrophic turbulence such that it can support standing barotropic features. [ABSTRACT FROM AUTHOR]

Draft tube vortex rope is considered a special cavitation flow phenomenon in tubular turbine units. Cavitation vortex rope is one of the most detrimental factors affecting the safety of hydraulic turbines. In this study, ANSYS CFX software was utilized to numerically simulate the internal cavitation flow of a hydraulic turbine draft tube. The evolution of the cavitation vortex core was characterized by vortex line distribution and vorticity transport equation. The shape and number of blades influenced the revolving direction and distribution characteristics of the vortex close to the runner cone, which formed a counterclockwise-clockwise-counterclockwise distribution pattern. Simultaneously, there were many secondary flows in the draft tube. Mutual cancellation and dissipation between the flows was one of the reasons for reduction in vorticity. When the cross-sectional shape of the draft tube was changed, the vorticity was distributed from the center of the vortex rope to all parts of the cross-sectional draft tube, with extreme values at the center and at the walls. The vortex stretching and dilatation terms played a major role in the change in vorticity, with the baroclinic torque having an effect at the center of the vortex rope, this study is helpful to understand the flow of water in the draft tube and guide the design and optimization of the draft tube in engineering application [ABSTRACT FROM AUTHOR]

Observational analyses reveal that a dominant mode in the South Asian Monsoon region in boreal summer is a westward-propagating synoptic-scale disturbance with a typical wavelength of 4000 km that is coupled with moistening and precipitation processes. The disturbances exhibit an eastward tilt during their development before reaching their maximum activity center. A 2.5-layer model that extends a classic 2-level quasi-geostrophic model by including a prognostic lower-tropospheric moisture tendency equation and an interactive planetary boundary layer was constructed. The eigenvalue analysis of this model shows that the most unstable mode has a preferred zonal wavelength of 4000 km, a westward phase speed of 6 m s−1, an eastward tilt vertical structure, and a westward shift of maximum moisture/precipitation center relative to the lower-tropospheric vorticity center, all of which agree with the observations. Sensitivity experiments show that the moisture–vortex instability determines, to a large extent, the growth rate, while the baroclinic instability helps set up the preferred zonal scale. Ekman-pumping-induced vertical moisture advection prompts an in-phase component of perturbation moisture relative to the low-level cyclonic center, allowing the generation of available potential energy and perturbation growth, regardless of whether or not a low-level mean westerly is presented. In contrast to a previous study, the growth rate is reversely proportional to the convective adjustment time. The current work sheds light on understanding the moisture–vortex and the baroclinic instability in a monsoonal environment with a pronounced easterly vertical shear. [ABSTRACT FROM AUTHOR]

The East Australian Current (EAC) system includes a poleward jet that flows adjacent to the continental shelf, a southward and eastward extension, and a complex eddy field. The EAC jet is often observed to be subsurface intensified. Here, we explain that there are two factors that cause the EAC to develop a subsurface maximum. First, the EAC flows as a narrow current, carrying low-density water from the Coral Sea into the denser waters of the Tasman Sea. This results in horizontal density gradients with a different sign on either side of the jet, negative onshore and positive offshore. According to the thermal wind relation, this produces vertical gradients in southward current that are surface intensified onshore and subsurface intensified offshore. Second, we show that the winds over the shelf are mostly downwelling favorable, drawing the surface EAC waters onshore. This aligns the region of positive horizontal density gradients with the EAC core, producing a subsurface velocity maximum. The presence of a subsurface maximum may produce baroclinic instabilities that play a role in eddy formation and EAC separation from the coast. Significance Statement: Observations of the East Australian Current (EAC) show that the strongest currents are often below the surface at about 100-m depth. Two factors cause this subsurface maximum. First, because the EAC is a narrow jet, carrying warm water southward from the Coral Sea, the density gradient across the jet changes sign, causing surface-intensified currents onshore and subsurface-intensified currents offshore. Second, the wind field over the shelf often pulls the shallow waters shoreward, shifting the waters that cause subsurface intensification to align with the center of the jet, resulting in a subsurface maximum of the EAC. This process may be responsible for the generation of eddies in the Tasman Sea. [ABSTRACT FROM AUTHOR]

This study uses a simple diffusivity formulation to examine flow regime transition and jet–eddy energy partitioning in two-layer quasigeostrophic turbulence. Guided by simulations, the formulation is empirically constructed so that the diffusivity is bounded by a f-plane asymptote (Df) in the limit of vanishing β (termed drag-controlled) while reduced to a drag-independent scaling (Dβ) of Lapeyre and Held toward large β (termed β-controlled). Good agreement is found for diffusivities diagnosed from simulations with both quadratic and linear drag and in 2D turbulence. From the formulation, a regime diagram is readily constructed, with Df/Dβ = 1 separating the drag-controlled and β-controlled regimes. The diagram also sets the parameter range where an eddy velocity scaling is applicable. The quantitative representations of eddy variables then enable a reasonably skillful theory for zonal jet speed to be developed from energy balance. It is shown that, using Df/Dβ ≥ 10, a state where eddy statistics are approximately drag insensitive could be identified and interpreted using wave-damping competitions in slowing an inverse cascade. However, contrary to an existing hypothesis, the energy dissipation in such a state is not dominated by zonal jets. A modest revision for a way to maintain balance while keeping eddies drag insensitive is proposed. In the regime diagram, a subspace of zonostrophic condition, defined as jet dissipation surpassing eddy, is further quantified. It is demonstrated that a rough scaling could help interpret how the relative importance of jet and eddy dissipation varies across the parameter space. [ABSTRACT FROM AUTHOR]

The separation-induced transition on the suction surface of a T106A low pressure turbine blade is a complex phenomenon with implications for aerodynamic performance. In this numerical investigation, we explore an adverse pressure gradient-dominated flow subjected to varying levels of free stream excitation, as the underlying separation-induced transition is a critical factor in assessing blade profile loss. By comprehensively analyzing the effects of free stream turbulence (FST) on the transition process, we delve into the various mechanisms which govern the instabilities underlying bypass transition by studying the instantaneous enstrophy field. This involves solving the two-dimensional (2D) compressible Navier–Stokes equation through a series of numerical simulations, comparing a baseline flow to cases where FST with varying turbulent intensity (T u = 4 % and 7%) is imposed at the inflow. Consistent with previous studies, the introduction of FST is observed to delay flow separation and trigger early transition. We explore the different stages of bypass transition, from the initial growth of disturbances (described by linear stability theory) to the emergence of unsteady separation bubbles that merge into turbulent spots (due to nonlinear interactions), by examining the vorticity dynamics. Utilizing the compressible enstrophy transport equation for the flow in a T106A blade passage, we highlight the various routes of bypass transition resulting from different levels of FST, emphasizing the relative contributions from baroclinicity, compressibility, and viscous terms. [ABSTRACT FROM AUTHOR]

Two- and three-dimensional simulation results obtained using a new high-order incompressible, variable-density vorticity–streamfunction (VS) method and data from previous ninth-order weighted essentially nonoscillatory (WENO) shock-capturing simulations [M. Latini and O. Schilling, "A comparison of two- and three-dimensional single-mode reshocked Richtmyer-Meshkov instability growth," Physica D 401, 132201 (2020)] are used to investigate the nonlinear dynamics of single-mode Richtmyer–Meshkov instability using a model of a Mach 1.3 air(acetone)/SF6 shock tube experiment [J. W. Jacobs and V. V. Krivets, "Experiments on the late-time development of single-mode Richtmyer–Meshkov instability," Phys. Fluids 17, 034105 (2005)]. A comparison of the density fields from both simulations with the experimental images demonstrates very good agreement in the large-scale structure with both methods but differences in the small-scale structure. The WENO method captures the small-scale disordered structure observed in the experiment, while the VS method partially captures such structure and yields a strong rotating core. The perturbation amplitude growth from the simulations generally agrees well with the experiment. The simulation bubble and spike amplitudes agree well at early times. At later times, the WENO bubble amplitude is smaller than the VS amplitude and vice versa for the spike amplitude. The predictions of nonlinear single-mode instability growth models are shown to agree with the simulation amplitudes at early-to-intermediate times but underpredict the amplitudes at later times in the nonlinear regime. Visualizations of the mass fraction and enstrophy isosurfaces, velocity and vorticity fields, and baroclinic vorticity production and vortex stretching terms from the three-dimensional simulations indicate that, with the exception of the small-scale structure within the rollups, the VS and WENO results are in good agreement. [ABSTRACT FROM AUTHOR]

Recent research indicates that the midlatitude oceanic frontal zones are the key regions of ocean–atmosphere interaction. The thermal condition of midlatitude ocean in frontal zones can affect the atmosphere efficiently through both diabatic heating and transient eddy feedback. In this study, the wintertime SST variability in the subarctic frontal zone (SAFZ) of the North Pacific and the associated ocean–atmosphere interaction mechanism are examined based on observational and theoretical analyses. It is found that the SAFZ-related SST anomaly is characterized as a large-scale interannual mode that can persist during the whole winter, and that its evolution is accompanied with local ocean–atmosphere interaction processes. The initial anticyclonic surface wind anomaly associated with the weakened Aleutian Low forces a large-scale warm SST anomaly in midlatitude North Pacific by driving northward Ekman flow and downward heat flux. With the increase of SST anomaly, the air-sea heat flux exchange reverses, indicating that the ocean starts to heat the atmosphere. In addition to increasing the diabatic heating, the warm SST anomaly strengthens the SST gradient in the north part of SAFZ. The low-level atmospheric baroclinicity is adjusted to synchronize with the SAFZ correspondingly due to oceanic thermal influence, causing change of transient eddy activities. Though all the ocean-induced diabatic heating, transient eddy heating and transient eddy vorticity forcing are enhanced over SAFZ, the last physical process plays the most important role in shifting and maintaining the equivalent barotropic atmospheric circulation anomalies. Therefore, the ocean–atmosphere interaction provides a mechanism for the development and maintenance of SAFZ-related anomalies of the North Pacific ocean–atmosphere system throughout the winter. [ABSTRACT FROM AUTHOR]

Observations indicate that symmetric instability is active in the East Greenland Current during strong northerly wind events. Theoretical considerations suggest that mesoscale baroclinic instability may also be enhanced during these events. An ensemble of idealized numerical ocean models forced with northerly winds shows that the short time‐scale response (from 10 days to 3 weeks) to the increased baroclinicity of the flow is the excitation of symmetric instability, which sets the potential vorticity of the flow to zero. The high latitude of the current means that the zero potential vorticity state has low stratification, and symmetric instability destratifies the water column. On longer time scales (greater than 4 weeks), baroclinic instability is excited and the associated slumping of isopycnals restratifies the water column. Eddy‐resolving models that fail to resolve the submesoscale should consider using submesoscale parameterizations to prevent the formation of overly stratified frontal systems following down‐front wind events. The mixed layer in the current deepens at a rate proportional to the square root of the time‐integrated wind stress. Peak water mass transformation rates vary linearly with the time‐integrated wind stress. Mixing rates saturate at high wind stresses during wind events of a fixed duration which means increasing the peak wind stress in an event leads to no extra mixing. Using ERA5 reanalysis data we estimate that between 0.9 Sv and 1.0 Sv of East Greenland Coastal Current Waters are produced by mixing with lighter surface waters during wintertime due to down‐front wind events. Similar amounts of East Greenland‐Irminger Current water are produced. Plain Language Summary: Symmetric instability is a process that leads to the mixing of waters with different densities. Observations show that in winter, when winds blow from the north, along the coast of Greenland, symmetric instability occurs; however, observations are limited which makes it difficult to understand the effect of the instability on the ocean currents in the region. We test the hypothesis that symmetric instability leads to the production of dense waters which are known to form in the region and contribute to the Atlantic Meridional Overturning Circulation (or "ocean conveyor" (Broecker, 1991, https://doi.org/10.5670/oceanog.1991.07)). We find that symmetric instability makes waters at the ocean surface denser, so that subsequent cooling can make them dense enough to sink to the deep ocean. A second type of instability, called baroclinic instability leads to the development of a fresh water "lid" which sits on top of the newly formed water masses, isolating them from the atmosphere. State of the art climate models don't resolve symmetric instability which means they may not get the density structure in the sub‐polar North Atlantic correct, which could lead to errors in ocean heat transports which are important in determining the Earth's climate. Key Points: Gravitational and symmetric instabilities deepen the mixed layer proportional to the square root of time‐integrated down‐front wind stressTime‐mean water mass transformation rates are linearly proportional to the time‐integrated down‐front wind stressDown‐front winds transform 0.9–1.0 Sv of buoyant surface water into East Greenland Coastal Current water between November and April [ABSTRACT FROM AUTHOR]

Watermass transformation in the Irminger Sea, a key region for the Atlantic Meridional Overturning Circulation, is influenced by atmospheric and oceanic variability. Strong wintertime atmospheric forcing in 2015 resulted in enhanced convection and the densification of the Irminger Sea. Deep convection persisted until 2018, even though winters following 2015 were mild. We show that this behavior can be attributed to an initially slow convergence of buoyancy, followed by more rapid convergence of buoyancy. This two‐stage recovery, in turn, is consistent with restratification driven by baroclinic instability of the Irminger Current (IC), that flows around the basin. The initial, slow restratification resulted from the weak horizontal density gradients created by the widespread 2015 atmospheric heat loss. Faster restratification occurred once the IC recovered. This mechanism explains the delayed recovery of the Irminger Sea following a single extreme winter and has implications for the ventilation and overturning that occurs in the basin. Plain Language Summary: The Irminger Sea, between Greenland and Iceland, is known to be an important driver of variability in the global ocean circulation that regulates global climate. During the 2015 winter, the Irminger Sea experienced widespread cooling and buoyancy loss down to 1,000 m, resulting in deeper wintertime mixing than had been observed in the region for many years. This low buoyancy state and deep wintertime mixing persisted from 2015 to 2018, despite a return to average atmospheric wintertime conditions. Here we study how processes that typically provide summertime buoyancy gain to balance wintertime buoyancy loss contribute to the multi‐year recovery of the region. We characterize the recovery of the interior of the Irminger Sea as having two stages: initially slow recovery, followed by more rapid recovery. Our findings are consistent with earlier studies stating that the main source of buoyancy to the interior is eddies shed from the current flowing around the Irminger Sea. This study shows that the deep mixing that is important for global circulation and climate is influenced by changes in the current around the basin. Key Points: Widespread buoyancy loss across the Irminger interior and Irminger Current (IC) delayed the recovery of the interior from strong cooling in 2015Baroclinic instabilities shed from the IC are the dominant source of buoyancy restratifying the sub‐surface Irminger interiorIt is important to consider changes in the IC when considering drivers of variability in convection, ventilation, and the Atlantic Meridional Overturning Circulation [ABSTRACT FROM AUTHOR]

Two anticyclonic intrathermocline eddies (ITEs) were detected by an underwater glider in the northwestern subtropical Pacific Ocean during August-October 2019. They both exhibited a lens-shaped vertical structure within the thermocline with their cores located at ~170 m. The North Pacific Subtropical Mode Water (STMW) was found within the cores of these two ITEs. The lens-shaped structure of ITE1 observed by the glider was very clear since the glider seemed to have moved into its core during the observation. Further analysis reveals that ITE1 displayed no signals at the sea surface and lasted for about 20 days (26 August-14 September 2019). ITE1 was locally formed and the water inside it was a mixture of local water and the water in the northern adjacent area. The low-salinity water at 0-50 m from the northern adjacent area extended southwestward and mixed with the local water. As a result, the local salinity-forced restratification caused a potential vorticity (PV) decrease in the subsurface and finally resulted in the generation of ITE1. The baroclinic instability at 50-170 m may be the main energy source for ITE1 generation. On the other hand, the lens-shaped structure of ITE2 observed by the glider was less prominent since the glider did not move into its core. Further analysis reveals that the lens-shaped structure of ITE2 was also very clear near its core and ITE2 displayed clear signals at the surface as an anticyclonic eddy (AE2). AE2/ITE2 was remotely generated within the main formation region of STMW and then moved southwestward. The low PV STMW was trapped in AE2 and a lens-shaped structure developed in the subsurface. Subduction of the STMW caused the generation of ITE2. [ABSTRACT FROM AUTHOR]

With a particular focus on the Siberian storm track, this study provides new insights into variations in the warm Arctic-cold Eurasia (WACE) temperature anomaly pattern by using reanalysis data. The results show that the Siberian storm track has a significant out-of-phase relationship with both the WACE pattern and Ural blocking on the interannual time scale. The strengthened WACE pattern can weaken the Siberian storm track through a suppression of the low-level atmospheric baroclinicity over midlatitude Eurasia. The weakened Siberian storm track can contribute to the WACE pattern through feedback forcing from synoptic-scale eddies, which can also create favorable conditions for the development of Ural blocking. Composite temporal evolution reveals that the strongest cold Arctic-warm Eurasia pattern is preceded by the peak of the Siberian storm track. The Ural cyclonic circulation reaches its maximum amplitude on the peak day of the Siberian storm track strength and continues to persist for one day with the maximum amplitude due to the feedback forcing resulting from the Siberian storm track. On the intraseasonal time scale, the occurrence of the Siberian storm track activity can serve as an early indication of the diminished Ural blocking andWACE pattern. [ABSTRACT FROM AUTHOR]

Background: Understanding the impact of situational variables on surgical recovery can improve outcomes in total hip arthroplasty (THA). Literature examining hospital outcomes by season remains inconclusive, with limited focus on patient experience. The aim of this study is to investigate if there are differences in hospital and patient-reported outcomes measures (PROMS) after THA depending on the season of the index procedure to improve surgeon preop erative counseling. Methods: A retrospective chart review was performed on patients undergoing primary THA at a single large academic center between January 2013 and August 2020. Demographic, operative, hospital, and PROMs were gathered from the institutional electronic medical record and our institutional joint replacement outcomes database. Results: 6418 patients underwent primary THA and met inclusion criteria. Of this patient population, 1636 underwent surgery in winter, 1543 in spring, 1811 in summer, and 1428 in fall. PROMs were equivalent across seasons at nearly time points. The average age of patients was 65 (+/- 10) years, with an average BMI of 29.3 (+/- 6). Rates of complications including ED visits within 30 days, readmission within 90 days, unplanned readmission, dislocation, fracture, or wound infection were not significantly different by season (P >.05). Conclusion: Our findings indicate no differences in complications and PROMs at 1 year in patients undergoing THA during 4 distinct seasons. Notably, patients had functional differences at the second follow-up visit, suggesting variation in short-term recovery. Patients could be counseled that they have similar rates of complications and postoperative recovery regardless of season. [ABSTRACT FROM AUTHOR]

Nonhydrostatic atmospheric models often use semi‐implicit temporal discretisations in order to negate the time‐step limitation of explicitly resolving the fast acoustic and gravity waves. Solving the resulting system to machine precision using Newton's method is considered prohibitively expensive, and so the nonlinear solver is typically truncated to a fixed number of iterations, often using an approximate Jacobian matrix that is reassembled only once per time step. The present article studies the impact of using various third‐order, four stage Rosenbrock–Wanner schemes, where integration weights are chosen to meet specific stability and order conditions, in comparison to a Crank–Nicolson time discretisation, as is done in the UK Met Office's LFRic model. Rosenbrock–Wanner schemes present a promising alternative on account of their ability to preserve their temporal order with only an approximate Jacobian, and may be constructed to be stiffly‐stable, so as to ensure the decay of fast unresolved modes. These schemes are compared for the 2D rotating shallow‐water equations and the 3D compressible Euler equations at both planetary and nonhydrostatic scales and are shown to exhibit improved results in terms of their energetic profiles and stability. Results in terms of computational performance are mixed, with the Crank–Nicolson method allowing for longer time steps and faster time to solution for the baroclinic instability test case at planetary scales, and the Rosenbrock–Wanner methods allowing for longer time steps and faster time to solution for a rising bubble test case at nonhydrostatic scales. [ABSTRACT FROM AUTHOR]