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vertical wavelength perturbations are also damped by the vertical dissipation, reducing their growth rate. Therefore, intense oceanic vortices may be closer to the marginal stability limit than expected and the generalized Rayleigh criterion can greatly overestimate the unstable region in the parameter space. One of the main results of Lazar et al. (2013a) was to provide a stronger instability criterion for the inertial instability by taking into account both the stratification and the dissipation
vertical wavelength perturbations are also damped by the vertical dissipation, reducing their growth rate. Therefore, intense oceanic vortices may be closer to the marginal stability limit than expected and the generalized Rayleigh criterion can greatly overestimate the unstable region in the parameter space. One of the main results of Lazar et al. (2013a) was to provide a stronger instability criterion for the inertial instability by taking into account both the stratification and the dissipation
1. Introduction A large body of experimental field data exists in the literature describing turbulence statistics for atmospheric surface layer (ASL) flow over uniform surfaces with variable atmospheric stabilities (e.g., Businger et al. 1971 ; Kaimal et al. 1976 ; Nieuwstadt 1984 ; Poulos et al. 2002 ). Far fewer comprehensive datasets exist for ASLs that interact with urban roughness elements. This is especially the case for real cities and is largely a result of the difficulties
1. Introduction A large body of experimental field data exists in the literature describing turbulence statistics for atmospheric surface layer (ASL) flow over uniform surfaces with variable atmospheric stabilities (e.g., Businger et al. 1971 ; Kaimal et al. 1976 ; Nieuwstadt 1984 ; Poulos et al. 2002 ). Far fewer comprehensive datasets exist for ASLs that interact with urban roughness elements. This is especially the case for real cities and is largely a result of the difficulties
1. Introduction When examining the zonally averaged climate of the atmosphere, one of the first quantities one notices is the change of temperature with height, or equivalently the static stability. Temperature decreases with height throughout the troposphere, but (∂ T /∂ z ) varies as a function of latitude and of height, as well as with season and climatic regime. The lapse rate/static stability is also of fundamental importance to the general circulation: it determines the buoyancy frequency
1. Introduction When examining the zonally averaged climate of the atmosphere, one of the first quantities one notices is the change of temperature with height, or equivalently the static stability. Temperature decreases with height throughout the troposphere, but (∂ T /∂ z ) varies as a function of latitude and of height, as well as with season and climatic regime. The lapse rate/static stability is also of fundamental importance to the general circulation: it determines the buoyancy frequency
directions depending on the sense of their own spin ( Fiorino and Elsberry 1989 ). Oceanic vortices can generate regions of anomalous mixing ( Provenzale 1999 ) and contribute to large-scale transport ( Dong et al. 2014 ). The stability and transport properties of baroclinic vortical flows on the β plane are the main topics to be addressed in this study. Laboratory experiments ( Griffiths and Linden 1981 ; Thivolle-Cazat et al. 2005 ) and numerical simulations ( Ikeda 1981 ; Flierl 1988 ; Helfrich
directions depending on the sense of their own spin ( Fiorino and Elsberry 1989 ). Oceanic vortices can generate regions of anomalous mixing ( Provenzale 1999 ) and contribute to large-scale transport ( Dong et al. 2014 ). The stability and transport properties of baroclinic vortical flows on the β plane are the main topics to be addressed in this study. Laboratory experiments ( Griffiths and Linden 1981 ; Thivolle-Cazat et al. 2005 ) and numerical simulations ( Ikeda 1981 ; Flierl 1988 ; Helfrich
1. Introduction The interaction between the freshwater cycle and the Atlantic meridional overturning circulation (AMOC) has been discussed for many years (e.g., Stommel 1961 ; Bryan 1986 ; Rahmstorf et al. 2005 ; Manabe and Stouffer 1988 ). Recent work has suggested that the key determination of the stability of the AMOC to changes in the freshwater flux depends on whether the AMOC salinifies or freshens the Atlantic ( Rahmstorf 1996 ). A diagnostic indicator, initially the AMOC freshwater
1. Introduction The interaction between the freshwater cycle and the Atlantic meridional overturning circulation (AMOC) has been discussed for many years (e.g., Stommel 1961 ; Bryan 1986 ; Rahmstorf et al. 2005 ; Manabe and Stouffer 1988 ). Recent work has suggested that the key determination of the stability of the AMOC to changes in the freshwater flux depends on whether the AMOC salinifies or freshens the Atlantic ( Rahmstorf 1996 ). A diagnostic indicator, initially the AMOC freshwater
1. Introduction There is a vast amount of literature devoted to understanding the stability of steady shear flows and a much more limited body of work exploring the stability of time-periodic shear flows. In contrast, nature has few if any flows that are truly steady or periodic because variations are ubiquitous in physical systems. The fact that almost all geophysical fluids are aperiodic motivates the need to better understand the dynamics of aperiodic flows in general and shear flows in
1. Introduction There is a vast amount of literature devoted to understanding the stability of steady shear flows and a much more limited body of work exploring the stability of time-periodic shear flows. In contrast, nature has few if any flows that are truly steady or periodic because variations are ubiquitous in physical systems. The fact that almost all geophysical fluids are aperiodic motivates the need to better understand the dynamics of aperiodic flows in general and shear flows in
stability to urban environments: atmospheric stability (as defined by the Richardson number) is determined by both mechanical stresses and buoyant forcing. For an urban setting, building-induced mechanical stresses are thought to dominate the production of turbulence, overriding any stability effects and creating nearly neutral atmospheric conditions at least in the most densely built-up urban areas and immediately downwind of these areas. Results from our recent simulations of two releases of sulfur
stability to urban environments: atmospheric stability (as defined by the Richardson number) is determined by both mechanical stresses and buoyant forcing. For an urban setting, building-induced mechanical stresses are thought to dominate the production of turbulence, overriding any stability effects and creating nearly neutral atmospheric conditions at least in the most densely built-up urban areas and immediately downwind of these areas. Results from our recent simulations of two releases of sulfur
latent heat release by modifying the static stability, since the vertical velocity is both associated with latent heat release and multiplies the dry static stability in the thermodynamic equation ( Kiladis et al. 2009 ). Bjerknes (1938) showed that the relevant static stability for moist convection is larger than a parcel argument would suggest if both the updraft and the subsiding environment are taken into account. In the case of tropical dynamics, effective static stabilities that account for
latent heat release by modifying the static stability, since the vertical velocity is both associated with latent heat release and multiplies the dry static stability in the thermodynamic equation ( Kiladis et al. 2009 ). Bjerknes (1938) showed that the relevant static stability for moist convection is larger than a parcel argument would suggest if both the updraft and the subsiding environment are taken into account. In the case of tropical dynamics, effective static stabilities that account for
1. Introduction Observations show that on daily to interannual time scales, stratiform low cloud fraction (CF) is strongly correlated with the lower-tropospheric stability (LTS), defined as the difference between the potential temperature θ of the free troposphere (700 hPa) and the surface, LTS = θ 700 − θ 0 ( Slingo 1987 ; Klein and Hartmann 1993 ; Klein 1997 ; Wood and Hartmann 2006 ). Relationships between LTS and CF from observations in the Tropics ( Slingo 1980 ) and subtropics
1. Introduction Observations show that on daily to interannual time scales, stratiform low cloud fraction (CF) is strongly correlated with the lower-tropospheric stability (LTS), defined as the difference between the potential temperature θ of the free troposphere (700 hPa) and the surface, LTS = θ 700 − θ 0 ( Slingo 1987 ; Klein and Hartmann 1993 ; Klein 1997 ; Wood and Hartmann 2006 ). Relationships between LTS and CF from observations in the Tropics ( Slingo 1980 ) and subtropics
strength of the modeled temperature inversion. Klein and Hartmann (1993 , hereafter KH93) showed that the lower-tropospheric stability (LTS), which they defined as the potential temperature difference between surface and 700 hPa, provides a remarkable indicator of low-cloud fraction on seasonal time scales. Their result is reproduced in Fig. 1 and shows their linear regression between seasonal area-mean LTS and LCF for the six subtropical stratocumulus regions identified in Fig. 2 . Also shown is
strength of the modeled temperature inversion. Klein and Hartmann (1993 , hereafter KH93) showed that the lower-tropospheric stability (LTS), which they defined as the potential temperature difference between surface and 700 hPa, provides a remarkable indicator of low-cloud fraction on seasonal time scales. Their result is reproduced in Fig. 1 and shows their linear regression between seasonal area-mean LTS and LCF for the six subtropical stratocumulus regions identified in Fig. 2 . Also shown is
