Potential Temperature Gradient Research Articles

Processes Associated with Convection Initiation in the North American Mesoscale Forecast System, Version 3 (NAMv3)

Abstract In support of the Next Generation Global Prediction System (NGGPS) project, processes leading to convection initiation in the North American Mesoscale Forecast System, version 3 (NAMv3) are explored. Two severe weather outbreaks—occurring over the southeastern United States on 28 April 2014 and the central Great Plains on 6 May 2015—are forecast retrospectively using the NAMv3 CONUS (4 km) and Fire Weather (1.33 km) nests, each with 5-min output. Points of convection initiation are identified, and patterns leading to convection initiation in the model forecasts are determined. Results indicate that in the 30 min preceding convection initiation at a grid point, upward motion at low levels of the atmosphere enables a parcel to rise to its level of free convection, above which it is accelerated by the buoyancy force. A moist absolutely unstable layer (MAUL) typically is produced at the top of the updraft. However, when strong updrafts are collocated with large vertical gradients of potential temperature and moisture, noisy vertical profiles of temperature, moisture, and hydrometeor concentration develop beneath the rising MAUL. The noisy profiles found in this study are qualitatively similar to those that resulted in NAMv3 failures during simulations of Hurricane Joaquin in 2015. The CM1 cloud model is used to reproduce these noisy profiles, and results indicate that the noise can be mitigated by including explicit vertical diffusion in the model. Left unchecked, the noisy profiles are shown to impact convective storm features such as cold pools, precipitation, updraft helicity intensity and tracks, and the initiation of spurious convection.

Synoptic-scale atmospheric circulation anomalies associated with summertime daily precipitation extremes in the middle–lower reaches of the Yangtze River Basin

The mechanisms of short-lived precipitation extremes in boreal summer over the middle–lower reaches of the Yangtze River Basin (MLYRB) during 1961–2014 are explored using gridded observational and reanalysis datasets. Daily precipitation extremes are defined by the 75th and 95th percentiles and identified for selected regions in the MLYRB. Moisture budget analysis is utilized to quantify the major factors responsible for the variability of extreme precipitation events. Then the atmospheric variables are composited according to these extreme events, to illustrate the temporal evolution of the corresponding synoptic-scale structures. The results show that moisture flux convergence plays a dominant role in the variations of extreme rainfall for both percentile events, and the contribution of evaporation is not evident. Moreover, the dynamic component associated with changes in atmospheric circulation makes a larger contribution than the nonlinear component, followed by the thermodynamic component, owing to changes in specific humidity. The moisture transport pathways increase with increasing magnitude of extreme rainfall intensity. Circulation field anomalies move into the MLYRB during the onset of precipitation extremes for both percentile cases, with stronger anomalies occurring for the 95th percentile cases. Furthermore, the water vapor fluxes transported from the Northwest Pacific are pronounced during the 95th percentile events. A cross-section of specific humidity and vertical gradient of equivalent potential temperature further indicates that dynamic properties play a crucial role in the development of extreme precipitation events linked with quasi-stationary frontal activities across the MLYRB during the past few decades. Composites of Eady growth rate and outgoing longwave radiation anomalies reveal that extratropical cyclones passing through the MLYRB produce a large amount of extreme rainfall by synoptic disturbance.

Effect of the Eyewall Cold Pool on the Inner Rainband of a Tropical Cyclone

AbstractThe low‐level cold pool just under a tropical cyclone eyewall and its effect on the formation of inner rainbands are studied, through idealized convection‐permitting simulations. Analysis of the potential temperature budget indicates that the formation of the eyewall cold pool (ECP) results from the evaporation of eyewall rainfall. The ECP is a barrier to boundary layer inflow, which results in clear convergence and vertical updraft at its outer edge. A budget analysis of the vertical motion tendency also indicates that the sum of the buoyancy and vertical pressure gradient terms makes a large contribution to the vertical updraft at the outer edge of the ECP. This then promotes the formation of convection cells and an inner rainband. Two sensitivity experiments further verify that the intensity of the ECP‐triggered inner rainbands is positively correlated with the magnitude of the radial gradient of potential temperature at the outer edge of the ECP.

A New Perspective toward Cataloging Northern Hemisphere Rossby Wave Breaking on the Dynamic Tropopause

Abstract Rossby wave breaking (RWB) events are a common feature on the dynamic tropopause and act to modulate synoptic-scale jet dynamics. These events are characterized on the dynamic tropopause by an irreversible overturning of isentropes and are coupled to troposphere-deep vertical motions and geopotential height anomalies. Prior climatologies have focused on the poleward streamer, the equatorward streamer, or the reversal in potential temperature gradient between the streamers, resulting in differences in the frequencies of RWB. Here, a new approach toward cataloging these events that captures both streamers is applied to the National Centers for Environmental Prediction Reanalysis-2 dataset for 1979–2011. Anticyclonic RWB (AWB) events are found to be nearly twice as frequent as cyclonic RWB (CWB) events. Seasonal decompositions of the annual mean find AWB to be most common in summer (40% occurrence), which is likely due to the Asian monsoon, while CWB is most frequent in winter (22.5%) and is likely due to the equatorward shift in mean baroclinicity. Trends in RWB from 1980 to 2010 illustrate a westward shift in North Pacific AWB during winter and summer (up to 0.4% yr−1), while CWB in the North Pacific increases in winter and spring (up to 0.2% yr−1). These changes are hypothesized to be associated with localized changes in the two-way interaction between the jet and RWB. The interannual variability of AWB and CWB is also explored, and a notable modality to the frequency of RWB is found that may be attributable to known low-frequency modes of variability including the Arctic Oscillation, the North Atlantic Oscillation, and the Pacific–North American pattern.

Analytical solution to a thermodynamic model for the sensitivity of afternoon deep convective initiation to the surface Bowen ratio

The tendency of convective rainfall to initiate over a wetter or drier land surface is a critical feedback process in the climate system, influencing the hydrological cycle on a variety of spatial scales, especially in parts of the world where water is limited. A simple algebraic solution is derived from fundamental physical equations, to predict the sign of this convective rainfall feedback with the surface. The tendency for convection to occur is evaluated by the rate at which the convective boundary‐layer top approaches the level of free convection. Well‐known integral models predict the rate of ascent of the boundary‐layer top, which tends to be faster over a dry surface. The associated changes in equivalent potential temperature in the boundary layer determine the rate at which the level of free convection descends, typically faster over a wet surface, as a function of the ambient profile, the thermodynamic forcing and the surface Bowen ratio. The resulting system is controlled by three parameters. Two nondimensional parameters determine whether there is wet or dry “advantage”; the Bowen ratio at the boundary‐layer top and a “convective instability parameter,” defined as the ratio of the vertical gradient of saturated equivalent potential temperature at the level of free convection to the profile stability just above the boundary layer. A dimensional function, dependent on the surface fluxes, the boundary‐layer depth, and the profile stability, provides the magnitude of the response. In comparison with previous work, the solution is both rigorously derived from physical principles and encapsulated in a simple algebraic form. A first evaluation of the theoretical framework has been made using data from a convection‐permitting numerical model simulation over India, and this indicates that the equations successfully determine the conditions under which convection is triggered over dry surfaces.

Subseasonal Change in the Seesaw Pattern of Precipitation between the Yangtze River Basin and the Tropical Western North Pacific during Summer

There is a well-known seesaw pattern of precipitation between the tropical western North Pacific (WNP) and the Yangtze River basin (YRB) during summer. This study identified that this out-of-phase relationship experiences a subseasonal change; that is, the relationship is strong during early summer but much weaker during mid-summer. We investigated the large-scale circulation anomalies responsible for the YRB rainfall anomalies on the subseasonal timescale. It was found that the YRB rainfall is mainly affected by the tropical circulation anomalies during early summer, i.e., the anticyclonic or cyclonic anomaly over the subtropical WNP associated with the precipitation anomalies over the tropical WNP. During mid-summer, the YRB rainfall is mainly affected by the extratropical circulation anomalies in both the lower and upper troposphere. In the lower troposphere, the northeasterly anomaly north of the YRB favors heavier rainfall over the YRB by intensifying the meridional gradient of the equivalent potential temperature over the YRB. In the upper troposphere, the meridional displacement of the Asian westerly jet and the zonally oriented teleconnection pattern along the jet also affect the YRB rainfall. The subseasonal change in the WNP–YRB precipitation relationship illustrated by this study has important implications for the subseasonalto- seasonal forecasting of the YRB rainfall.

Characterizing the influence of the marine stratocumulus cloud on the land fog at the Atacama Desert

Fog in the Atacama Desert is a virtually untapped source of fresh water in the driest place on Earth. Focusing on understanding the role played by marine stratocumulus (Sc) in the development of land-fog, we analyse surface observations made along a steep transect at different heights. These observations are combined with numerical experiments performed using the Weather Research and Forecasting Model (WRF). We find two main diurnal regimes based on atmospheric thermal stability, both of which determine the formation and dissipation of fog. These are (a) a well-mixed regime characterized by low gradients of potential temperature and specific humidity, low diurnal variability, and presence of Sc cloud-fog. (b) A stratified regime characterized by high gradients of potential temperature and specific humidity, high diurnal variability, but no Sc clouds nor presence of fog. By using the parcel method, initialised with surface observations, we characterize the Sc cloud of nine typical fog events, estimating a mean cloud depth of 566 m between 740 m (±150 m) and 1307 m (±30 m). Fog observations at ground level agree with these cloud-base and cloud-top estimates, showing a liquid water mixing ratio of Sc cloud-fog in the range 0.3–0.7 g kg−1. The study reveals that the advection of marine Sc cloud and the stability of the boundary layer are key processes in the formation and dissipation of fog. Sc cloud advection over land is modulated by upwind and driven by topography and local circulation. We conclude that a realistic characterization of Sc cloud-fog is possible by combining limited surface observations and numerical experiments.

Coastally trapped disturbances caused by the tramontane wind on the northwestern Mediterranean: numerical study and sensitivity to short‐wave radiation

The Tramontane‐Cierzo wind system is a recurrent feature of the northwestern Mediterranean basin in front of the Catalan coast (northeast Spain). Associated with this feature, northeast wind surges occasionally affect the coast and become a weather hazard for low‐level aircraft operations, affecting for example the Barcelona international airport. This article first reports these surges characterizing them as Coastal‐Trapped Disturbances (CTDs). Climatological features are described, showing that CTDs occur frequently during the warm season and between the afternoon and the evening. We classified CTDs into two synoptic patterns related to the location of a mid‐level tropospheric geopotential trough and the Iberian Peninsula: pattern A, with the trough crossing eastwards along the north of Spain; and pattern B, with the trough over the Mediterranean, after crossing the Iberian Peninsula. To study the CTDs in detail, numerical simulations were conducted using the non‐hydrostatic and convection‐permitting numerical weather prediction model HARMONIE‐AROME. Two cases, one for each synoptic pattern, were studied showing that CTDs generate in the discontinuity between cool outflows and warmer air progressing southward as a density current, trapped by the mountain ranges parallel to the coastline. Cool outflows may have two different sources: in Pattern A the origin of the cold air is the tramontane itself, while in Pattern B convective outflows associated with storm downdraughts play this role. Both cases show similarities with CTDs studied on the California coast, showing an antitriptic and ageostrophic flow behind the CTD. An additional numerical sensitivity experiment was conducted by varying the short‐wave radiation to explore the effects of diabatic warming on CTDs. It is demonstrated that a large warming influences CTDs by enhancing the potential temperature gradient between the density current and the environment, modulating their intensity and speed.

Reexamining the Gradient and Countergradient Representation of the Local and Nonlocal Heat Fluxes in the Convective Boundary Layer

Abstract Turbulent mixing in the daytime convective boundary layer (CBL) is carried out by organized nonlocal updrafts and smaller local eddies. In the upper mixed layer of the CBL, heat fluxes associated with nonlocal updrafts are directed up the local potential temperature gradient. To reproduce such countergradient behavior in parameterizations, a class of planetary boundary layer schemes adopts a countergradient correction term in addition to the classic downgradient eddy-diffusion term. Such schemes are popular because of their simple formulation and effective performance. This study reexamines those schemes to investigate the physical representations of the gradient and countergradient (GCG) terms, and to rebut the often-implied association of the GCG terms with heat fluxes due to local and nonlocal (LNL) eddies. To do so, large-eddy simulations (LESs) of six idealized CBL cases are performed. The GCG fluxes are computed a priori with horizontally averaged LES data, while the LNL fluxes are diagnosed through conditional sampling and Fourier decomposition of the LES flow field. It is found that in the upper mixed layer, the gradient term predicts downward fluxes in the presence of positive mean potential temperature gradient but is compensated by the upward countergradient correction flux, which is larger than the total heat flux. However, neither downward local fluxes nor larger-than-total nonlocal fluxes are diagnosed from LES. The difference reflects reduced turbulence efficiency for GCG fluxes and, in terms of physics, conceptual deficiencies in the GCG representation of CBL heat fluxes.

The Thermodynamic Structure of Arctic Coastal Fog Occurring During the Melt Season over East Greenland

An automated method to classify Arctic fog into distinct thermodynamic profiles using historic in-situ surface and upper-air observations is presented. This classification is applied to low-resolution Integrated Global Radiosonde Archive (IGRA) soundings and high-resolution Arctic Summer Cloud Ocean Study (ASCOS) soundings in low- and high-Arctic coastal and pack-ice environments. Results allow investigation of fog macrophysical properties and processes in coastal East Greenland during melt seasons 1980–2012. Integrated with fog observations from three synoptic weather stations, 422 IGRA soundings are classified into six fog thermodynamic types based on surface saturation ratio, type of temperature inversion, fog-top height relative to inversion-base height and stability using the virtual potential temperature gradient. Between 65–80% of fog observations occur with a low-level inversion, and statically neutral or unstable surface layers occur frequently. Thermodynamic classification is sensitive to the assigned dew-point depression threshold, but categorization is robust. Despite differences in the vertical resolution of radiosonde observations, IGRA and ASCOS soundings yield the same six fog classes, with fog-class distribution varying with latitude and environmental conditions. High-Arctic fog frequently resides within an elevated inversion layer, whereas low-Arctic fog is more often restricted to the mixed layer. Using supplementary time-lapse images, ASCOS microwave radiometer retrievals and airmass back-trajectories, we hypothesize that the thermodynamic classes represent different stages of advection fog formation, development, and dissipation, including stratus-base lowering and fog lifting. This automated extraction of thermodynamic boundary-layer and inversion structure can be applied to radiosonde observations worldwide to better evaluate fog conditions that affect transportation and lead to improvements in numerical models.

Perspective of Micro Process Engineering for Thermal Food Treatment.

Micro process engineering as a process synthesis and intensification tool enables an ultra-short thermal treatment of foods within milliseconds (ms) using very high surface-area-to-volume ratios. The innovative application of ultra-short pasteurization and sterilization at high temperatures, but with holding times within the range of ms would allow the preservation of liquid foods with higher qualities, thereby avoiding many unwanted reactions with different temperature–time characteristics. Process challenges, such as fouling, clogging, and potential temperature gradients during such conditions need to be assessed on a case by case basis and optimized accordingly. Owing to the modularity, flexibility, and continuous operation of micro process engineering, thermal processes from the lab to the pilot and industrial scales can be more effectively upscaled. A case study on thermal inactivation demonstrated the feasibility of transferring lab results to the pilot scale. It was shown that micro process engineering applications in thermal food treatment may be relevant to both research and industrial operations. Scaling of micro structured devices is made possible through the use of numbering-up approaches; however, reduced investment costs and a hygienic design must be assured.

Vertical structure of atmospheric boundary layer over Ranchi during the summer monsoon season

Thermodynamic structure and variability in the atmospheric boundary layer have been investigated with the help of balloon-borne GPS radiosonde over a monsoon trough station Ranchi (Lat. 23°45′N, Long. 85°43′E, India) during the summer monsoon season (June–September) for a period of 2011–2013. Virtual potential temperature gradient method is used for the determination of mixed layer height (MLH). The MLH has been found to vary in the range of 1000–1300 m during the onset, 600–900 m during the active and 1400–1750 m during the break phase of monsoon over this region. Inter-annual variations noticed in MLH could be associated with inter-annual variability in convection and rainfall prevailing over the region. Along with the MLH, the cloud layer heights are also derived from the thermodynamic profiles for the onset, active and break phases of monsoon. Cloud layer height varied a lot during different phases of the monsoon. For the determination of boundary-layer convection, thermodynamic parameter difference (δθ = θes− θe) between saturated equivalent potential temperature (θes) and equivalent potential temperature (θe) is used. It is a good indicator of convection and indicates the intense and suppressed convection during different phases of monsoon.

Orientation effect of asymmetric diatomic molecules in transport diffusion

Non-equilibrium transport is an important research area in statistical physics. The influences of the structures of polyatomic molecules on their transport have attracted the attention of researchers. Up to now, most of researchers deemed that temperature gradient is the main factor for molecular orientation and neglected the effect of the chemical potential gradient on the molecular orientation. To make up the deficiency in the study of chemical potential gradients, we build a non-equilibrium system with both chemical potential gradient and temperature gradient, and study the transport diffusion behavior of asymmetric diatomic molecules by using molecular dynamics and Monte Carlo methods. It is found that the diatomic molecules implement the orientation effect during non-equilibrium transport. Under the chemical potential gradient, the molecular orientation effect leads to the fact that the large atom tends to be in the direction of low concentration particle bath, while the small atom tends to be in the direction of high concentration particle bath. The molecular orientation is opposite to the direction of the flow. Under the temperature gradient, the molecular orientation effect leads to the fact that the large atom tends to be in the direction of high temperature particle bath, while the small atom tends to be in the direction of low temperature particle bath. The molecular orientation is the same as the direction of the flow. The orientation direction caused by concentration gradients is opposite to that caused by temperature gradients and it appears as a competitive relationship. At the same time, the influence of the asymmetry of the molecule itself on the molecular orientation is also studied. The larger the asymmetry of the molecule itself (σB/σA), the more obvious the molecular orientation effect is. When σB/σA>1.6, the influence of the asymmetry of the molecule itself on the orientation effect is gradually saturated. When σB/σA=1, which is also for a symmetric molecule, even if neither the temperature gradient nor the chemical potential gradient is zero, no molecular orientation occurs. We explain the physical mechanism of orientation through the principle of minimum entropy production. This work is of theoretical significance for in depth understanding the relationship between mass transport and molecular structure under non-equilibrium conditions.

Multi-scale temporospatial variability of the East Asian Meiyu-Baiu fronts: characterization with a suite of new objective indices

The Meiyu-Baiu front (MBF) is the primary weather system modulating the monsoonal rainfall in East Asia, and it exhibits pronounced variability across multiple temporal and spatial scales. A suite of new objective indices based upon daily reanalysis data are developed to characterize such variability, which include an “intensity” index effectively measuring the meridional gradient of equivalent potential temperature across the frontal zone, a “location” index documenting the central latitude and longitude of the front, and a “stationarity” index corresponding to the standard deviation of the daily central latitude. All these indices are characterized by strong interannual to interdecadal variations. Specifically, the MBF has shown a tendency of southwestward shift since the mid-1990s and become more stationary over southern China with reduced intraseasonal meandering. The western North Pacific subtropical high (WNPSH) is the main circulation feature affecting the location of the MBF on interannual timescales. The MBF moves northward (southward) when the WNPSH is anomalously strong (weak) and the surface high over the region of 35°–50°N/100°–120°E is anomalously weak (strong). When the WNPSH is strong, the MBF is often situated northwest to its climatological position and becomes more stationary. On interdecadal timescales, enhanced activity of high latitude blocking over East Asia is often accompanied with a stronger but less stationary MBF while a negative phase of the Arctic Oscillation favors a southward-shifted and more stationary MBF.

Marginal sea surface temperature variation as a pre-cursor of heat waves over the Korean Peninsula

This study examines the role of the marginal sea surface temperature (SST) on heat waves over Korea. It is found that sea surface warming in the south sea of Korea/Japan (122-138°E, 24- 33°N) causes heat waves after about a week. Due to the frictional force, the positive geopotential height anomalies associated with the south sea warming induce divergent flows over the boundary layer. This divergent flow induces the southerly in Korea, which leads to a positive temperature advection. On the other hand, over the freeatmosphere, the geostrophic wind around high-pressure anomalies flows in a westerly direction over Korea during the south sea warming, which is not effective in temperature advection. Therefore, the positive temperature advection in Korea due to the south sea warming decreases with height. This reduces the vertical potential temperature gradient, which indicates a negative potential vorticity (PV) tendency over Korea. Therefore, the high-pressure anomaly over the south sea of Korea is propagated northward, which results in heat waves due to more incoming solar radiation.

Characterization of the structure and cross‐shore transport properties of a coastal upwelling filament using three‐dimensional finite‐size Lyapunov exponents

AbstractThe three‐dimensional structure, dynamics, and dispersion characteristics of a simulated upwelling filament in the Iberian upwelling system are analyzed using Lagrangian tools. We used a realistic regional simulation of the western Iberian shelf which is concomitant with an in situ oceanographic campaign that surveyed the area. We compute 3‐D fields of finite‐size Lyapunov exponents (FSLE) from 3‐D velocity fields and extract the field's ridges to study the spatial distribution and temporal evolution of the Lagrangian Coherent Structures (LCSs) evolving around the filament. We find that the most intense curtain‐like LCSs delimit the boundaries of the whole filamentary structure whose general properties match well the observations. The filament interior is characterized by small dispersion of fluid elements. Furthermore, we identify a weak LCS separating the filament into a warmer vein and a colder filament associated with the interaction of a mesoscale eddy with the upwelling front. The cold upwelled water parcels move along the filament conserving their density. The filament itself is characterized by small dispersion of fluid elements in its interior. The comparison of LCSs with potential temperature and salinity gradient fields shows that the outer limits of the filament coincide with regions of large hydrographic gradients, similar to those observed, explaining the isolation of the interior of the filament with the surrounding waters. We conclude that the Lagrangian analysis used in this work is useful in explaining the dynamics of cross‐shore exchanges of materials between coastal regions and the open ocean due to mesoscale processes.

Factors controlling Hadley circulation changes from the Last Glacial Maximum to the end of the 21st century

AbstractThe Hadley circulation (HC) extent and strength are analyzed in a wide range of simulated climates from the Last Glacial Maximum to global warming scenarios. Motivated by HC theories, we analyze how the HC is influenced by the subtropical stability, the near‐surface meridional potential temperature gradient, and the tropical tropopause level. The subtropical static stability accounts for the bulk of the HC changes across the simulations. However, since it correlates strongly with global mean surface temperature, most HC changes can be attributed to global mean surface temperature changes. The HC widens as the climate warms, and it also weakens, but only robustly so in the Northern Hemisphere. On the other hand, the Southern Hemisphere strength response is uncertain, in part because subtropical static stability changes counteract meridional potential temperature gradient changes to various degrees in different models, with no consensus on the response of the latter to global warming.

Recirculation over complex terrain

AbstractThis study generated eddy covariance data to investigate atmospheric dynamics leeward of a small, forested hillside in upstate New York. The causes and effects of recirculation eddies were examined to support the larger goal of improving measurement of the exchange of energy, moisture, and trace gases between the terrestrial biosphere and the atmosphere over complex terrain. Sensors operated at five different altitudes on two separate towers—one at the top of the hill and one down the slope to the east—for approximately 8 weeks in the spring of 2013. During the experiment, the vertical potential temperature gradient was found to be the primary factor for determining whether winds interacting with the terrain features caused a recirculating eddy leeward of the hill. The study found evidence that the recirculation influenced carbon dioxide flux and caused the air column to be vertically well mixed.

Effects of Boundary Layer Vertical Mixing on the Evolution of Hurricanes over Land

Abstract After a hurricane makes landfall, its evolution is strongly influenced by its interaction with the planetary boundary layer (PBL) over land. In this study, a series of numerical experiments are performed to examine the effects of boundary layer vertical mixing on hurricane simulations over land using a research version of the NCEP Hurricane Weather Research and Forecasting (HWRF) Model with three landfalling hurricane cases. It is found that vertical mixing in the PBL has a strong influence on the simulated hurricane evolution. Specifically, strong vertical mixing has a positive impact on numerical simulations of hurricanes over land, with better track, intensity, synoptic flow, and precipitation simulations. In contrast, weak vertical mixing leads to the strong hurricanes over land. Diagnoses of the thermodynamic and dynamic structures of hurricane vortices further suggest that the strong vertical mixing in the PBL could cause a decrease in the vertical wind shear and an increase in the vertical gradient of virtual potential temperature. As a consequence, these changes destroy the turbulence kinetic energy in the hurricane boundary layer and thus stabilize the hurricane boundary layer and limit its maintenance over land.

Turbulent Mechanical Energy Budget in Stably Stratified Baroclinic Flows over Sloping Terrain

Analysis of second-moment budget equations in a slope-oriented coordinate frame exhibits the pathways of exchange between the potential energy of mean flow and the total turbulent mechanical energy. It is shown that this process is controlled by the inclination of the potential temperature gradient. Hence, this parameter should be considered in studies of turbulence in slope flows as well as the slope inclination. The concept of turbulent potential energy is generalized to include baroclinicity, and is used to explain the role of along-slope turbulent heat flux in energy conversions. A generalization of static stability criteria for baroclinic conditions is also proposed. In addition, the presence of feedback between the turbulent heat flux and the temperature variance in stably-stratified flows is identified, which implies the existence of oscillatory modes characterized by the Brunt–Väisäla frequency.