- Davis, California, United States
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Research Interests: Geology and Energetics
The effects of Saharan dust aerosols and West African precipitation on the seasonally averaged energetics of African easterly waves (AEWs) are examined using the Weather Research and Forecasting Model coupled to an interactive dust model.... more
The effects of Saharan dust aerosols and West African precipitation on the seasonally averaged energetics of African easterly waves (AEWs) are examined using the Weather Research and Forecasting Model coupled to an interactive dust model. Four experiments are conducted: a control for the period July–September 2008, and three other experiments in which the dust emissions and precipitation are reduced separately and in combination. An analysis of the total energy shows the relative importance of the dust and precipitation to the seasonally averaged AEW strength and AEW tracks, which straddle the African easterly jet (AEJ). Changes in the dust amount have a larger effect on the strength of the AEWs than changes in the precipitation amount. The north AEW track is more strongly affected by changes in dust, while the south AEW track is more strongly affected by changes in precipitation. An analysis of the energy conversions aids in identifying the relative importance of the wave–mean flow interaction pathways that connect the dust and precipitation fields to the AEJ–AEW system. The analysis shows that the variability of the AEWs is primarily coupled to the dust- and precipitation-modified variability of the AEJ through wave–mean flow interaction. These results are discussed in light of tropical cyclone development over the eastern Atlantic Ocean.
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Analytical and numerical analyses are used to examine how structural changes to the African easterly jet (AEJ) mediate the effects of Saharan mineral dust aerosols on the linear dynamics of African easterly waves (AEWs). An analytical... more
Analytical and numerical analyses are used to examine how structural changes to the African easterly jet (AEJ) mediate the effects of Saharan mineral dust aerosols on the linear dynamics of African easterly waves (AEWs). An analytical expression for the generation of eddy available potential energy (APE) is derived that exposes how the AEJ and dust combine to affect the energetics of the AEWs. The expression is also used to interpret the numerical results, which are obtained by radiatively coupling a simplified version of the Weather Research and Forecasting Model to a conservation equation for dust. The WRF-Dust model is used to conduct linear simulations based on five observationally consistent zonal-mean AEJs: a reference AEJ and four other AEJs that are obtained by perturbing the maximum meridional and vertical shear. For a dust distribution consistent with summertime observations over North Africa, the numerical simulations show the following: (i) Irrespective of the AEJ structure or the zonal scale of the AEWs, the dust increases the growth rates of the AEWs. (ii) The growth rates of the AEWs are optimized when the ratio of baroclinic to barotropic energy conversions is largest. (iii) When the energy conversions are sufficiently large, the zonal scale of the fastest-growing AEW shortens. The numerical results confirm the analytical analysis, which shows that the dust effects, which are modulated by the Doppler-shifted frequency, are strongest north of the AEJ axis, a region where the dust augments the preexisting meridional temperature gradient.
Research Interests: Geology and Energetics
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Wave trains and coherent structures are among the most dominant features of the large-scale atmospheric circulation. The role of these wave trains and coherent structures in the low-frequency variability of the Earth's... more
Wave trains and coherent structures are among the most dominant features of the large-scale atmospheric circulation. The role of these wave trains and coherent structures in the low-frequency variability of the Earth's general circulation is well understood observationally, but a dynamical connection between the two has yet to be found. The low-frequency variability in a meridionally sheared, zonally varying background
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ABSTRACT The wave drag associated with the damping and breaking of vertically propagating planetary waves in the stratosphere has far-reaching consequences for the global circulation and climate. The planetary wave drag (PWD) exerts... more
ABSTRACT The wave drag associated with the damping and breaking of vertically propagating planetary waves in the stratosphere has far-reaching consequences for the global circulation and climate. The planetary wave drag (PWD) exerts non-local control over the extratropical stratosphere that manifests as a wave-driven equator- to-pole meridional circulation, termed the Brewer-Dobson circulation (BDC). In the steady state, the BDC can exert "downward control," whereby the body force exerted by the PWD causes a mean meridional circulation and a simultaneous mass adjustment in the surface pressure. Thus any changes in the PWD in the stratosphere will produce a balanced response in the region below. The downward influence exerted by longitudinal variations in stratospheric ozone is examined using a mechanistic chemistry-dynamical model (CDM) of the extratropical atmosphere. The CDM is one-dimensional in height and self-consistently couples dynamics, radiative transfer, and the transport and photochemistry of ozone. The longitudinal variations in ozone induce a zonal-mean body force that affects the residual circulation via the PWD. Under steady-state conditions, for which the "downward control" principle applies, a WKB analysis yields an analytical expression that shows the direct connection between the residual vertical velocity and the transport and photochemistry of ozone. Because the one-dimensional model framework confines the waves to propagate solely in the vertical, a stratospheric reflecting surface is required for the planetary wave-induced ozone heating in the stratosphere to produce non-local changes in that are manifested in the troposphere. These results underscore the importance of longitudinal variations in ozone as a pathway for communicating, via the combined effects of "downward control" and planetary wave reflection, natural and human-caused changes in stratospheric ozone to changes in tropospheric climate.
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Research Interests: Engineering, Physics, Fluid Mechanics, Wave Energy, Modeling, and 15 moreLow Frequency, Instability, Mathematical Sciences, Variability, Topography, Explicit Knowledge, Potential Vorticity, Historic conservation law, Linear Stability, Classical Mechanics, Growth rate, Local stability, Perturbation, Hamiltonian, and Branch point
A theory is developed that describes the effects of topography and potential vorticity (PV) forcing on the dynamics of solitary Rossby waves (SRWs) in zonally varying background flow. The cornerstone of the theory is the background flow,... more
A theory is developed that describes the effects of topography and potential vorticity (PV) forcing on the dynamics of solitary Rossby waves (SRWs) in zonally varying background flow. The cornerstone of the theory is the background flow, which is systematically derived rather than simply being specified as in previous theories. The evolution of the disturbance field is governed by a
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A low‐level barrier jet (LLBJ) formed along the northeast slope of the Tibetan Plateau on March 17, 2010. The LLBJ was accompanied by a major dust event. Numerical simulations conducted with the Weather Research and Forecasting dust... more
A low‐level barrier jet (LLBJ) formed along the northeast slope of the Tibetan Plateau on March 17, 2010. The LLBJ was accompanied by a major dust event. Numerical simulations conducted with the Weather Research and Forecasting dust (WRF‐dust) model show that the formation of the LLBJ was primarily due to mid‐level, southeastward descent of high momentum air, which impinged on the north slope of the Tibetan Plateau, resulting in ageostrophic flow acceleration under geostrophic adjustment. The LLBJ was reinforced by the Bernoulli effect, where the physical barrier associated with the Tibetan Plateau to the southwest and the virtual barrier associated with sloped, packed isentropic surfaces to the northeast combined to constrict the air flow, thus augmenting the acceleration of the air as it entered the Hexi Corridor. The simulations show that the LLBJ, which stayed close to the western entrance of the Hexi Corridor, gradually descended during the daytime until early evening. During t...
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Research Interests: Art and Photography
The relationship between the African easterly jet (AEJ), Saharan mineral dust (SMD) aerosols, and West African precipitation (WAP) is examined using European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) data,... more
The relationship between the African easterly jet (AEJ), Saharan mineral dust (SMD) aerosols, and West African precipitation (WAP) is examined using European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) data, the NASA Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), and the NASA Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA) for July–September 1998–2017. The spatial orientation and structure of AEJs in different SMD–WAP environments are compared. In dustier years, the AEJ is farther east and stronger, rotates clockwise, and has larger zonal and vertical shears. In wetter years, the AEJ is farther north, has a shorter zonal extent, and has larger meridional shear. These changes to the AEJ are a response to the combined effects of the SMD and WAP on the thermal field, which is confirmed through sensitivity tests carried out with the Weather Research and Forecasting Model coupled...
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The direct radiative effects of Saharan mineral dust (SMD) aerosols on the nonlinear evolution of the African easterly jet–African easterly wave (AEJ–AEW) system is examined using the Weather Research and Forecasting Model coupled to an... more
The direct radiative effects of Saharan mineral dust (SMD) aerosols on the nonlinear evolution of the African easterly jet–African easterly wave (AEJ–AEW) system is examined using the Weather Research and Forecasting Model coupled to an online dust model. The SMD-modified AEW life cycles are characterized by four stages: enhanced linear growth, weakened nonlinear stabilization, larger peak amplitude, and smaller long-time amplitude. During the linear growth and nonlinear stabilization stages, the SMD increases the generation of eddy available potential energy (APE); this occurs where the maximum in the mean meridional SMD gradient is coincident with the critical surface. As the AEWs evolve beyond the nonlinear stabilization stage, the discrimination between SMD particle sizes due to sedimentation becomes more pronounced; the finer particles meridionally expand, while the coarser particles settle to the surface. The result is a reduction in the eddy APE at the base and the top of the...
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Necessary conditions for radiative–dynamical instability of quasigeostrophic waves induced by trace shortwave radiative absorbers are derived. The analysis pivots on a pseudomomentum conservation equation that is obtained by combining... more
Necessary conditions for radiative–dynamical instability of quasigeostrophic waves induced by trace shortwave radiative absorbers are derived. The analysis pivots on a pseudomomentum conservation equation that is obtained by combining conservation equations for quasigeostrophic potential vorticity, thermodynamic energy, and trace absorber mixing ratio. Under the assumptions that the absorber-induced diabatic heating rate is small and the zonal-mean basic state is hydrodynamically neutral, a perturbation analysis of the pseudomomentum equation yields the conditions for instability. The conditions, which only require knowledge of the zonally averaged background distributions of wind and absorber, expose the physical processes involved in destabilization—processes not exposed in previous analytical and modeling studies of trace absorber-induced instabilities. The simplicity of instability conditions underscores their utility as a tool that is both interpretive and predictive. The condi...
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In recent years there has been an increasing effort devoted to understanding the physical and dynamical processes that govern the global-scale circulation of the atmosphere. This effort has been motivated, in part, from: (1) a wealth of... more
In recent years there has been an increasing effort devoted to understanding the physical and dynamical processes that govern the global-scale circulation of the atmosphere. This effort has been motivated, in part, from: (1) a wealth of new satellite data; (2) an urgent need to assess the potential impact of chlorofluorocarbons on our climate; (3) an inadequate understanding of the interactions between the troposphere and stratosphere and the role that such interactions play in short and long-term climate variability; and (4) the realization that addressing changes in our global climate requires understanding the interactions among various components of the earth system. The research currently being carried out represents an effort to address some of these issues by carrying out studies that combine radiation, ozone, seasonal thermal forcing and dynamics. Satellite and ground-based data that is already available is being used to construct basic states for our analytical and numerica...
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The scale-dependent transport of Saharan dust aerosols by African easterly waves (AEWs) is examined analytically and numerically. The analytical analysis shows that the meridional and vertical wave transports of dust are modulated by the... more
The scale-dependent transport of Saharan dust aerosols by African easterly waves (AEWs) is examined analytically and numerically. The analytical analysis shows that the meridional and vertical wave transports of dust are modulated by the Doppler-shifted frequency, ωd, and the wave growth rate, ωi, both of which are functions of the zonal wave scale. The analytical analysis predicts that the AEW dust transports, which are driven by the Reynolds stresses acting on the mean dust gradients, are largest for the twin limits: ωd→0, which corresponds to flow near a critical surface, a local effect; and ωi→0, which corresponds to the slowest growing waves, a global effect. The numerical analysis is carried out with the Weather Research and Forecasting (WRF) model, which is radiatively coupled to the dust field. The model simulations are based on an AEW spectrum consistent with observations. The simulations agree with the theoretical predictions: the slowest growing waves have the strongest t...
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A theoretical framework is presented that exposes the radiative–dynamical relationships that govern the subcritical destabilization of African easterly waves (AEWs) by Saharan mineral dust (SMD) aerosols. The framework is built on coupled... more
A theoretical framework is presented that exposes the radiative–dynamical relationships that govern the subcritical destabilization of African easterly waves (AEWs) by Saharan mineral dust (SMD) aerosols. The framework is built on coupled equations for quasigeostrophic potential vorticity (PV), temperature, and SMD mixing ratio. A perturbation analysis yields, for a subcritical, but otherwise arbitrary, zonal-mean background state, analytical expressions for the growth rate and frequency of the AEWs. The expressions are functions of the domain-averaged wave activity, which is generated by the direct radiative effects of the SMD. The wave activity is primarily modulated by the Doppler-shifted phase speed and the background gradients in PV and SMD. Using an idealized version of the Weather Research and Forecasting (WRF) Model coupled to an interactive dust model, a linear analysis shows that, for a subcritical African easterly jet (AEJ) and a background SMD distribution that are consi...
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Forced planetary-scale waves generally extend throughout the troposphere and stratosphere and thus provide an important connection between these two regions of the atmosphere. Because these planetary waves originate from mechanical and... more
Forced planetary-scale waves generally extend throughout the troposphere and stratosphere and thus provide an important connection between these two regions of the atmosphere. Because these planetary waves originate from mechanical and thermal forcing in the troposphere, planetary wave energy propagates upward into the stratosphere where momentum deposition via wave damping drives the zonal-mean stratospheric circulation. Here we present striking evidence showing that the interactions between stratospheric ozone and planetary-scale waves affect the wave damping rate and thus the planetary wave structure. In some cases, the changes in planetary wave structure radiates downward into the troposphere. Using analytical (WKB) and one-dimensional numerical modeling approaches, we show that there is an intimate connection between the zonal-mean background flow, ozone field, and forced planetary wave field in the stratosphere, a connection that in some cases leads to significant changes in t...
Theory and modeling are combined to reveal the physical and dynamical processes that control Saharan dust transport by amplifying African easterly waves (AEWs). Two cases are examined: active transport, in which the dust is radiatively... more
Theory and modeling are combined to reveal the physical and dynamical processes that control Saharan dust transport by amplifying African easterly waves (AEWs). Two cases are examined: active transport, in which the dust is radiatively coupled to the circulation; passive transport, in which the dust is radiatively decoupled from the circulation. The theory is built around a dust conservation equation for dust-coupled AEWs in zonal-mean African easterly jets. The theory predicts that, for both the passive and active cases, the dust transports will be largest where the zonal-mean dust gradients are maximized on an AEW critical surface. Whether the dust transports are largest for the radiatively passive or radiatively active case depends on the growth rate of the AEWs, which is modulated by the dust heating. The theoretical predictions are confirmed via experiments carried out with the Weather Research and Forecasting model, which is coupled to a dust conservation equation. The experim...
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An analytical analysis is combined with numerical modeling simulations in order to expose the physical and dynamical processes that control the zonal-mean transport of Saharan mineral dust aerosols during the incipient growth phase of... more
An analytical analysis is combined with numerical modeling simulations in order to expose the physical and dynamical processes that control the zonal-mean transport of Saharan mineral dust aerosols during the incipient growth phase of African easterly waves. The analytical analysis provides the theoretical basis for understanding and predicting how the waves and background flow combine to affect the zonal-mean eddy transports of dust. The analytically derived transport equations―which are valid for any wave field, irrespective of its spatial or temporal scale―predict that the eddy transports of dust are largest where the maximum in the background dust gradients coincide with a critical surface, i.e., where the Doppler-shifted frequency of the wave field vanishes. Linear simulations of the eddy dust transports are conducted using a mechanistic version of the Weather Research and Forecasting (WRF) model coupled to an interactive dust model. The simulations show that the eddy dust tran...
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The direct radiative effects of Saharan mineral dust aerosols on the linear dynamics of African easterly waves (AEWs) are examined analytically and numerically. The analytical analysis combines the thermody-namic equation with a dust... more
The direct radiative effects of Saharan mineral dust aerosols on the linear dynamics of African easterly waves (AEWs) are examined analytically and numerically. The analytical analysis combines the thermody-namic equation with a dust continuity equation to form an expression for the dust-modified generation of eddy available potential energy GE. The dust-modified GE is a function of the transmissivity and spatial gradients of the dust, which are modulated by the Doppler-shifted frequency. The expression for GE predicts that for a fixed dust distribution, the wave response will be largest in regions where the dust gradients are maximized and the Doppler-shifted frequency vanishes. The numerical analysis uses the Weather Research and Forecasting (WRF) Model coupled to an online dust model to calculate the linear dynamics of AEWs. Zonally averaged basic states for wind, temperature, and dust are chosen consistent with summertime conditions over North Africa. For the fastest-growing AEW, the dust increases the growth rate from ;15% to 90% for aerosol optical depths ranging from t 5 1.0 to t 5 2.5. A local energetics analysis shows that for t 5 1.0, the dust increases the maximum barotropic and baroclinic energy conversions by ;50% and ;100%, respectively. The maxima in the generation and conversions of energy are collocated and occur where the meridional dust gradient is maximized near the critical surface—that is, where the Doppler-shifted frequency is small, in agreement with the prediction from the analytical analysis.
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The weakly nonlinear dynamics of long waves embedded in marginally stable shear flows that vary in the streamwise direction are shown to be governed by a variable-coefficient Boussinesq equation. Depending on the local stability... more
The weakly nonlinear dynamics of long waves embedded in marginally stable shear flows that vary in the streamwise direction are shown to be governed by a variable-coefficient Boussinesq equation. Depending on the local stability characteristics of the flow, new nonmodal or modal instabilities may emerge that serve as natural mechanisms for achieving amplitude thresholds necessary for weakly nonlinear instability and the transition to fully finite-amplitude states.
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Wave trains and coherent structures are among the most dominant features of the large-scale atmospheric circulation. The role of these wave trains and coherent structures in the low-frequency variability of the Earth's general circulation... more
Wave trains and coherent structures are among the most dominant features of the large-scale atmospheric circulation. The role of these wave trains and coherent structures in the low-frequency variability of the Earth's general circulation is well understood observationally, but a dynamical connection between the two has yet to be found. The low-frequency variability in a meridionally sheared, zonally varying background flow is examined using a non-divergent barotropic model on a midlatitude β-plane. In the long, low-frequency limit this model yields a variable-coefficient, Kortweg-deVries (K-dV) equation. The disturbance field governed by this K-dV equation is comprised of both oscillatory Rossby wave packets (ORWPs) and solitary Rossby waves (SRWs). The ORWPs are the atmospheric analogs of low-frequency wave trains and the SRWs are the analogs of coherent structures. The zonally varying background flow has the profound effect of inducing the transformation of wave trains into coherent structures and vice versa. We find that as a wave train propagates through a zonally isolated jet flow that it may organize itself into a coherent structure. The reverse transformation is also possible; the coherent structure may breakdown into a wave train. This organization of wave trains into coherent structures and the breakdown of coherent structures into wave trains is fundamentally due to the effect of the zonally isolated jet flow on the balance between linear dispersion and wave amplitude.
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An ever-increasing body of evidence shows that changes in solar spectral irradiance (SSI) over the 11-year solar cycle (SC) can produce changes in stratospheric ozone. Changes in stratospheric ozone can in turn produce changes in... more
An ever-increasing body of evidence shows that changes in solar spectral irradiance (SSI) over the 11-year solar cycle (SC) can produce changes in stratospheric ozone. Changes in stratospheric ozone can in turn produce changes in planetary wave drag (PWD) via wave-induced ozone heating, which was recently expounded upon in a paper by Nathan and Cordero (2007, JGR-Atmospheres). Because SSI-induced changes in PWD may have potentially far-reaching consequences for the global circulation, ranging from changes in the zonal-mean flow to changes in the Brewer-Dobson circulation, it is important to understand the connection between SSI and PWD. In this study we employ a mechanistic model that couples radiation, ozone and dynamics to derive an analytical expression that shows the explicit connection between SSI and PWD. The sensitivity of the stratospheric circulation, particularly stratospheric sudden warmings, to changes in SSI associated with the SC is explored.
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The effects of dissipation on the weakly nonlinear interactions between a marginally unstable baroclinic wave and a resonant topographic wave are examined using multiple time scales in a quasigeostrophic, two-layer model on a midlatitude... more
The effects of dissipation on the weakly nonlinear interactions between a marginally unstable baroclinic wave and a resonant topographic wave are examined using multiple time scales in a quasigeostrophic, two-layer model on a midlatitude beta plane channel. The lower boundary is characterized by sinusoidal bottom topography. The dissipation is chosen as one or a combination of the following forms: Ekman dissipation at the lower and upper boundaries which may be chosen different in strength, interfacial Ekman dissipation, thickness damping, and potential vorticity damping (PVD). In the absence of topography the baroclinic wave always equilibrates irrespective of the form of the dissipation. If the dissipation is sufficiently weak and due solely to PVD, the baroclinic wave exhibits a damped vacillation symmetric about its steady value. If the form of the dissipation is different from PVD, the baroclinic wave evolves through three distinct stages: initial exponential growth, a damped vacillation in which the overall envelope of the vacillation increases on an intermediate time scale and, finally, an asymptotic approach towards equilibration. In the presence of topography, numerical integrations of the asymptotically derived wave and mean flow evolution equations were carried out for the case where the topographic wave is taken zero initially. It is shown that depending on the form and/or the strength of the dissipation, the asymptotic state of the system is characterized by either a single (stationary) topographic wave state or a mixed wave state. Weak PVD favors the single wave states while, in sharp contrast, other dissipation forms, provided they are sufficiently weak, favor the mixed wave states. Perpetual vacillation was not obtained.
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Finite-amplitude dynamics of a slightly dissipative baroclinic wave in a two-layer, -plane channel model at the point of minimum critical shear are examined. At this point, both the potential vorticity gradient and the Doppler-shifted... more
Finite-amplitude dynamics of a slightly dissipative baroclinic wave in a two-layer, -plane channel model at the point of minimum critical shear are examined. At this point, both the potential vorticity gradient and the Doppler-shifted frequency vanish within the lower layer. Previous studies have shown that for this parameter setting both the magnitude of the dissipation and the harmonics of the fundamental wave play important roles in the nonlinear dynamics of the system. In the present study, the response of the nonlinear dynamical system to zonally varying potential vorticity forcing is examined. When the forcing and dissipation are asymptotically small and of equal magnitude, an analytical analysis indicates that the fundamental wave equilibrates to a steady amplitude regardless of the mode being forced. For sufficiently strong forcing, the system must be solved numerically, in which case it is shown that when a harmonic of the fundamental is forced, the system can exhibit one of two dynamical regimes: steady state or vacillatory. The latter can only exist in the presence of forcing. In sharp contrast, directly forcing the fundamental always results in equilibration of the system. In cases where the fundamental wave equilibrates, it is shown that the total potential vorticity (basic state plus disturbance) may homogenize along streamlines of the fundamental wave, leading to strong vortex formation.
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The research is comprised of the following tasks: use of simple analytical and numerical models of a coupled troposphere-stratosphere system to examine the effects of radiation and ozone on planetary wave dynamics and the tropospheric... more
The research is comprised of the following tasks: use of simple analytical and numerical models of a coupled troposphere-stratosphere system to examine the effects of radiation and ozone on planetary wave dynamics and the tropospheric circulation; use of satellite data obtained from the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument and Solar Backscattered Ultraviolet (SBUV) experiment, in conjunction with National Meteorological Center (NMC) data, to determine the planetary wave vertical structures, dominant wave spectra, ozone spectra, and time variations in diabatic heating rate; and synthesis of the modeling and observational results to provide a better understanding of the effects that stratospheric processes have on tropospheric dynamics.
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ABSTRACT The weakly nonlinear evolution of a free baroclinic wave in the presence of slightly supercritical, vertically sheared zonal flow and a forced stationary wave field that consists of a single zonal scale and an arbitrary number of... more
ABSTRACT The weakly nonlinear evolution of a free baroclinic wave in the presence of slightly supercritical, vertically sheared zonal flow and a forced stationary wave field that consists of a single zonal scale and an arbitrary number of meridional harmonics is examined within the context of the conventional two-layer model. The presence of the (planetary-scale) stationary wave introduces zonal variations in the supercriticality and is shown to alter the growth rate and asymptotic equilibrium of the (synoptic-scale) baroclinic wave via two distinct mechanisms: The first is due to the direct interaction of the stationary wave with the shorter synoptic wave (wave-wave mechanism), and the second is due to the interaction of the synoptic wave with that portion of the mean field that is corrected by the zonally rectified stationary wave fluxes (wave-mean mechanism). These mechanisms can oppose or augment each other depending on the amplitude and spatial structure of the stationary wave field. If the stationary wave field is confined primarily to the upper (lower) layer and consists of only the gravest cross-stream mode, conditions are favorable (unfavorable) for nonzero equilibrium of the free wave. In addition to the time dependent heat flux generated by baroclinic growth of the free wave, its interaction with a stationary wave field consisting of two or more meridional harmonics generates time dependent heat fluxes that vary with period of the free wave. However, if the stationary wave field contains several meridional harmonics of sufficiently large amplitude, the free baroclinic wave is destroyed.
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Interactions between unstable baroclinic and resonant, topographic waves are investigated in a quasi-geostrophic two-layer model on the (beta)-plane with sinusoidal topography and dissipation. The dissipative processes are of two types:... more
Interactions between unstable baroclinic and resonant, topographic waves are investigated in a quasi-geostrophic two-layer model on the (beta)-plane with sinusoidal topography and dissipation. The dissipative processes are of two types: Asymmetric Ekman dissipation, and "internal" dissipation due to interfacial friction and equivalent thermal damping. The weakly nonlinear analysis requires two long time scales to describe the evolution of the baroclinic wave while the topographic wave evolves only on the longest time scale. This is due to the fact that the linear growth rate of the baroclinic wave, which is modified by the topography, is larger than the linear growth rate of the topographic wave. To facilitate the analysis, the method of reconstitution is used to form evolution equations on a combined time scale. It is shown that when dissipation acts only through Ekman layers at the upper and lower boundaries, the baroclinic wave is characterized by growth to a peak value...
The extratropical response to localized, low-frequency tropical forcing is examined using a linearized, non-divergent barotropic model on a sphere. Zonal-mean basic states characterized by solid-body rotation or critical latitudes are... more
The extratropical response to localized, low-frequency tropical forcing is examined using a linearized, non-divergent barotropic model on a sphere. Zonal-mean basic states characterized by solid-body rotation or critical latitudes are considered. An analytical analysis based on WKB and ray tracing methods shows that, in contrast to stationary Rossby waves, westward moving, low-frequency Rossby waves can propagate through the tropical easterlies into the extratropics. It is shown analytically that the difference between the stationary and low-frequency ray paths is proportional to the forcing frequency and inversely proportional to the zonal wavenumber cubed. An expression for the disturbance amplitude is derived that shows the ability of the forced waves to maintain their strength well into middle latitudes depends on their meridional wave scale and northward group velocity, both of which are functions of the slowly varying background flow. A local energetics analysis shows that the...
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Jin and Ghil demonstrate that for topographically resonant flow, low-frequency finite-amplitude oscillations may arise from wave -- wave interactions and topographic form drag. Their model is extended to include a zonally asymmetric... more
Jin and Ghil demonstrate that for topographically resonant flow, low-frequency finite-amplitude oscillations may arise from wave -- wave interactions and topographic form drag. Their model is extended to include a zonally asymmetric vorticity source, which is shown to interact with the perturbation field to produce zonally rectified wave fluxes that dramatically alter the Hopf bifurcation from stationary solutions to low-frequency oscillations. The frequency, intensity, and general character of these oscillations are shown to depend crucially upon the phasing and relative strength of the forcings.
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A linearized barotropic model on a sphere is used to study the stability of a basic state composed of a westward-moving wave and a zonal mean jet. It is found that the inclusion of a very weak jet in the basic state dramatically alters... more
A linearized barotropic model on a sphere is used to study the stability of a basic state composed of a westward-moving wave and a zonal mean jet. It is found that the inclusion of a very weak jet in the basic state dramatically alters the stability of the flow. The alteration of stability characteristics for realistic summer and winter jets is discussed.
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An equatorial beta-plane model of the stratosphere is used to examine the effects of longwave radiational cooling, ozone photochemistry, and ozone advection on the linear spatial modulation of forced equatorial Kelvin waves. The model... more
An equatorial beta-plane model of the stratosphere is used to examine the effects of longwave radiational cooling, ozone photochemistry, and ozone advection on the linear spatial modulation of forced equatorial Kelvin waves. The model atmosphere is described by coupled equations for the zonal and meridional momentum, temperature, mass continuity, and ozone volume mixing ratio. For basic states characterized by a
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Over the past forty years, numerous linear stability studies have been performed in order to explain the origin and structure of observed waves in the atmosphere. Of these studies, only a small fraction have considered the stability of... more
Over the past forty years, numerous linear stability studies have been performed in order to explain the origin and structure of observed waves in the atmosphere. Of these studies, only a small fraction have considered the stability of time-dependent, zonally varying flow or the influence of radiative-photochemical feedbacks on the stability of zonally uniform flow. The stability of such flows is described, and these flows may yield important information concerning the origin, structure, and transient time scales of free waves in the atmosphere. During the period 1990 to 1991, a beta-plane model that couples radiative transfer, ozone advection, and ozone photochemistry with the quasigeostrophic dynamical circulation was developed in order to study the diabatic effects of Newtonian cooling and ozone-dynamics interaction on the linear stability of free planetary waves in the atmosphere. The stability of a basic state consisting of a westward-moving wave and a zonal mean jet was examin...
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The response of the quasi-biennial oscillation (QBO) to zonal-mean ozone perturbations consistent with the 11-year solar cycle is examined using a two-dimensional model of the tropical stratosphere. Driven by prescribed Kelvin and... more
The response of the quasi-biennial oscillation (QBO) to zonal-mean ozone perturbations consistent with the 11-year solar cycle is examined using a two-dimensional model of the tropical stratosphere. Driven by prescribed Kelvin and Rossby-gravity waves at the lower (100 hPa) boundary, the model accounts for wave driven changes in the zonal-mean circulation and thus can simulate the zonal wind, temperature, and ozone QBOs in the tropical stratosphere. We find that 11-year solar cycle-like perturbations to the zonal-mean ozone field alter both the wave-ozone and zonal-mean ozone feedbacks, which combine to affect the structure and period of the QBO. In particular, under conditions representative of solar max, the diabatic heating resulting from ozone feedbacks drives a slightly stronger QBO circulation and produces a shorter QBO period, in agreement with observations of quasi-decadal variability of the QBO. The implications of these results on quasi-decadal variability of the global ci...
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An equatorial beta-plane model of the middle atmosphere is used to analytically examine the effects of radiative cooling and ozone heating on the spatial and temporal evolution of the quasi-biennial oscillation (QBO). Under the assumption... more
An equatorial beta-plane model of the middle atmosphere is used to analytically examine the effects of radiative cooling and ozone heating on the spatial and temporal evolution of the quasi-biennial oscillation (QBO). Under the assumption that the diabatic heating is weak and the background fields of wind, temperature, and ozone are slowly varying, a perturbation analysis yields expressions describing the vertical spatial modulation of Kelvin and Rossby-gravity waves in the presence of ozone. These expressions show that wave-induced changes in the diabatic heating arising from the advection of basic-state ozone reduce the local radiative damping rate by up to 15% below 35 km. In a one-dimensional model of the QBO, eddy ozone heating increases the amplitude of the zonal wind QBO by 1-2 m s21 and increases the oscillation period by about two months. The significance of these results to the observed QBO is discussed.
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Forced planetary waves extend throughout the troposphere and stratosphere and thus provide an important link between these two regions of the atmosphere. Although it is well established that vertically propagating planetary waves... more
Forced planetary waves extend throughout the troposphere and stratosphere and thus provide an important link between these two regions of the atmosphere. Although it is well established that vertically propagating planetary waves generated in the troposphere play a major role in driving the zonal-mean stratospheric circulation, an ever-growing body of evidence shows that the stratosphere, despite its lesser mass, may play a more important role in influencing the tropospheric circulation than previously thought. Here we examine the role of stratospheric ozone heating due to wave-ozone feedbacks in the downward reflection of tropospherically generated planetary waves. Using coupled equations for quasigeostrophic potential vorticity and ozone volume mixing ratio, a WKB analysis yields an analytical expression that shows how coupled wave-ozone interactions in the stratosphere can affect the index of refraction and reflection coefficient of topographically forced planetary waves. The ref...
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A spherical nondivergent barotropic model, linearized about a 300-mb climatological January flow, is used to examine the extratropical response to low-frequency tropical forcing. A two-dimensional WKB analysis shows that the energy... more
A spherical nondivergent barotropic model, linearized about a 300-mb climatological January flow, is used to examine the extratropical response to low-frequency tropical forcing. A two-dimensional WKB analysis shows that the energy propagation depends on the sum of three vectors: the basic state wind vector, a vector that is parallel to the absolute vorticity contours, and the local wave vector. The latter two vectors are functions of the slowly varying background flow and forcing frequency Ï. As Ï decreases, the ray paths approach that of the local wave vector, so that the energy propagates in a direction perpendicular to the wave fronts. The extratropical jet streams have a stronger influence on the long period (>30 day) ray paths than on those of intermediate period (â¼ 10-30 day). Global and local energetics calculations show that the energy conversion from the zonally varying basic flow increases as Ï decreases. The local energetics show that for the long period disturbances...
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Forced planetary waves generally extend throughout the troposphere and stratosphere and thus provide an important link between these two regions of the atmosphere. Because these planetary waves originate from mechanical and thermal... more
Forced planetary waves generally extend throughout the troposphere and stratosphere and thus provide an important link between these two regions of the atmosphere. Because these planetary waves originate from mechanical and thermal forcing in the troposphere, planetary wave energy propagates upward into the stratosphere where momentum deposition via wave damping drives the zonal-mean stratospheric circulation. At the heart of this troposphere-stratosphere paradigm, wherein the troposphere forces the stratosphere, is the momentum deposition associated with the wave damping. Here we present striking evidence showing that the interactions between ozone and the planetary waves not only affects the wave damping rate, but the interactions also produce changes in planetary wave structure and planetary wave fluxes that radiate downward into the troposphere. Using analytical (WKB) and one-dimensional numerical modeling approaches, we show that there is a sensitive and intimate connection amo...
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The effects of wave and zonal mean ozone heating on the evolution of the quasi-biennial oscillation (QBO) are examined using a two-dimensional mechanistic model of the equatorial stratosphere. The model atmosphere is governed by coupled... more
The effects of wave and zonal mean ozone heating on the evolution of the quasi-biennial oscillation (QBO) are examined using a two-dimensional mechanistic model of the equatorial stratosphere. The model atmosphere is governed by coupled equations for the zonal mean and (linear) wave fields of ozone, temperature, and wind, and is driven by specifying the amplitudes of a Kelvin wave and a Rossby-gravity wave at the lower boundary. Wave-mean flow interactions are accounted for in the model, but not wave-wave interactions. A reference simulation (RS) of the QBO, in which ozone feedbacks are neglected, is carried out and the results compared with Upper Atmosphere Research Satelliteobservations. The RS is then compared with three model experiments, which examine separately and in combination the effects of wave ozone and zonal mean ozone feedbacks. Wave-ozone feedbacks alone increase the driving by the Kelvin and Rossby-gravity waves by up to 10%, producing stronger zonal wind shear zones...
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There are several scientific challenges surrounding the effects of the 11-year solar cycle (SC) on climate. Among these challenges are identifying pathways by which a small decadal change in solar irradiance can be amplified beyond what... more
There are several scientific challenges surrounding the effects of the 11-year solar cycle (SC) on climate. Among these challenges are identifying pathways by which a small decadal change in solar irradiance can be amplified beyond what current models imply to produce a significant response in the climate system, and distinguishing the SC signal from other climate signals that arise from human activities and natural causes. Adding to the challenges is the fact that these climate forcing mechanisms are subtle, nonlinearly interacting, and modulated by internal atmospheric variability. Moreover, drawing definitive conclusions from a paucity of SC data - only about four SCs of meteorological data are currently available for statistical analysis poses additional challenges. To meet these challenges, NASA's Living with a Star Targeted Research and Technology (LWS TR&T) Program formed a Sun-Climate Focus Team (FST) in 2005. The main objective of the FST is to provide improved understa...
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The notion that changes in the index of refraction of the planetary waves can affect the large-scale circulation and climate has been circulating in the scientific literature since Charney and Drazin's seminal work more than 40 years... more
The notion that changes in the index of refraction of the planetary waves can affect the large-scale circulation and climate has been circulating in the scientific literature since Charney and Drazin's seminal work more than 40 years ago. In this study we derive a new refractive index for vertically propagating planetary waves that explicitly accounts for stratospheric ozone heating and Newtonian cooling. We use this refractive index as a diagnostic to assess how perturbations in stratospheric ozone, which may arise from human activities, volcanic sources and solar variability, can affect the vertical propagation, attenuation and downward reflection of the planetary waves.
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The wave drag associated with the breaking and dissipation of vertically propagating planetary waves in the stratosphere has far-reaching consequences for the global circulation and climate. The planetary wave drag (PWD) exerts non-local... more
The wave drag associated with the breaking and dissipation of vertically propagating planetary waves in the stratosphere has far-reaching consequences for the global circulation and climate. The planetary wave drag (PWD) exerts non-local control over the extratropical stratosphere that manifests as a wave-driven equator-to- pole meridional circulation. This wave-driven circulation - termed the Brewer-Dobson circulation or residual circulation - is largely responsible for large-scale troposphere-stratosphere mass exchange, departures of the stratosphere away from radiative equilibrium, and the transport of trace constituents from the tropics to the extratropics. In this study we examine the effects of planetary wave induced ozone heating (OH) on the extratropical residual circulation using a mechanistic model that couples dynamics, radiation and the transport and photochemistry of stratospheric ozone. The wave-induced OH, which is effectively confined to the stratosphere, is shown to...
Research Interests: Ozone and Large Scale
The wave drag associated with the damping and breaking of vertically propagating planetary waves in the stratosphere has far-reaching consequences for the global circulation and climate. The planetary wave drag (PWD) exerts non-local... more
The wave drag associated with the damping and breaking of vertically propagating planetary waves in the stratosphere has far-reaching consequences for the global circulation and climate. The planetary wave drag (PWD) exerts non-local control over the extratropical stratosphere that manifests as a wave-driven equator- to-pole meridional circulation, termed the Brewer-Dobson circulation (BDC). In the steady state, the BDC can exert "downward control," whereby the body force exerted by the PWD causes a mean meridional circulation and a simultaneous mass adjustment in the surface pressure. Thus any changes in the PWD in the stratosphere will produce a balanced response in the region below. The downward influence exerted by longitudinal variations in stratospheric ozone is examined using a mechanistic chemistry-dynamical model (CDM) of the extratropical atmosphere. The CDM is one-dimensional in height and self-consistently couples dynamics, radiative transfer, and the transport...
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Wave trains and coherent structures are among the most dominant features of the large-scale atmospheric circulation. The role of these wave trains and coherent structures in the low-frequency variability of the Earth's general... more
Wave trains and coherent structures are among the most dominant features of the large-scale atmospheric circulation. The role of these wave trains and coherent structures in the low-frequency variability of the Earth's general circulation is well understood observationally, but a dynamical connection between the two has yet to be found. The low-frequency variability in a meridionally sheared, zonally varying background
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... Barotropic instability. ; Stability. ; Mots-clés français / French Keywords. Jet. ; Atmosphère. ; Stratosphère. ; Modèle sphérique. ; Modèle linéaire. ; Mode barotrope. ; Instabilité barotrope. ; Stabilité. ; Mots-clés espagnols /... more
... Barotropic instability. ; Stability. ; Mots-clés français / French Keywords. Jet. ; Atmosphère. ; Stratosphère. ; Modèle sphérique. ; Modèle linéaire. ; Mode barotrope. ; Instabilité barotrope. ; Stabilité. ; Mots-clés espagnols / Spanish Keywords. Jet. ; Atmósfera. ; Estratosfera. ; ...
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ABSTRACT The role of ozone in the linear stability of Rossby normal modes is examined in a continuously stratified, extratropical baroclinic atmosphere. The flow is described by coupled equations for the quasi-geostraphic potential... more
ABSTRACT The role of ozone in the linear stability of Rossby normal modes is examined in a continuously stratified, extratropical baroclinic atmosphere. The flow is described by coupled equations for the quasi-geostraphic potential vorticity and ozone volume mixing ratio. A perturbation analysis is carried out under the assumption of weak diabatic heating, which is generated by Newtonian cooling and dynamics-ozone interaction. An expression for the propagation and growth characteristics is obtained analytically in terms of the vertically averaged wave activity, which depends explicitly on the wave spatial structure, photochemistry, and basic state distributions of wind, temperature, and ozone mixing ratio. Calculations show that stationary internal modes, whose amplitudes are largest in the stratosphre, are destabilized by dynamics-ozone interaction and Newtonian cooling, with e-folding times on the order of 20-40 days.
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ABSTRACT The stability of basic states consisting of a jet similar to the stratospheric polar night jet and a traveling wave with a single zonal wavenumber is examined in a linearized nondivergent barotropic model on a sphere. Basic state... more
ABSTRACT The stability of basic states consisting of a jet similar to the stratospheric polar night jet and a traveling wave with a single zonal wavenumber is examined in a linearized nondivergent barotropic model on a sphere. Basic state waves are chosen to resemble observed traveling and stationary features in the winter stratosphere. Results are presented for disturbance growth rates, propagation characteristics, and energy conversion as a function of the basic state wave amplitude. The effects of small amplitude basic state waves on unstable disturbances arising from a zonally symmetric jet are discussed; results are shown where a small amplitude basic state wave dramatically affects the stability characteristics. Evidence is shown that the presence of a traveling wave may favor the appearance of disturbances that include other zonal wavenumbers which move with the basic state wave; this result is discussed in relation to the origin of observed quasi-nondispersive features in the polar winter stratosphere. Results for a stationary wavenumber 1 basic state wave suggest that a distorted polar vortex may be unstable to disturbances that would lead to further distortion. An unstable disturbance for a basic state with an eastward moving wavenumber 2 has components which resemble, in period and location, traveling waves that are observed in the winter stratosphere.
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The diabatic effects of Newtonian cooling and ozone-dynamics interaction on the linear stability of free planetary waves in the atmosphere have been studied using a simple beta-plane model. The model couples radiative transfer, ozone... more
The diabatic effects of Newtonian cooling and ozone-dynamics interaction on the linear stability of free planetary waves in the atmosphere have been studied using a simple beta-plane model. The model couples radiative transfer, ozone advection, and ozone photochemistry with the quasi-geostrophic dynamical circulation. An analytical expression is derived which demonstrates the following: (1) the influence of meridional ozone advection on
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ABSTRACT A mechanistic chemistry-dynamical model is used to evaluate the relative importance of radiative, photochemical, and dynamical feedbacks in communicating changes in lower-stratospheric ozone to the circulation of the stratosphere... more
ABSTRACT A mechanistic chemistry-dynamical model is used to evaluate the relative importance of radiative, photochemical, and dynamical feedbacks in communicating changes in lower-stratospheric ozone to the circulation of the stratosphere and lower mesosphere. Consistent with observations and past modeling studies of Northern Hemisphere late winter and early spring, high-latitude radiative cooling due to lower-stratospheric ozone depletion causes an increase in the modeled meridional temperature gradient, an increase in the strength of the polar vortex, and a decrease in vertical wave propagation in the lower stratosphere. Moreover, it is shown that, as planetary waves pass through the ozone loss region, dynamical feedbacks precondition the wave, causing a large increase in wave amplitude. The wave amplification causes an increase in planetary wave drag, an increase in residual circulation downwelling, and a weaker polar vortex in the upper stratosphere and lower mesosphere. The dynamical feedbacks responsible for the wave amplification are diagnosed using an ozone-modified refractive index; the results explain recent chemistry-coupled climate model simulations that suggest a link between ozone depletion and increased polar downwelling. The effects of future ozone recovery are also examined and the results provide guidance for researchers attempting to diagnose and predict how stratospheric climate will respond specifically to ozone loss and recovery versus other climate forcings including increasing greenhouse gas abundances and changing sea surface temperatures.
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A theory is developed that describes the effects of topography and potential vorticity (PV) forcing on the dynamics of solitary Rossby waves (SRWs) in zonally varying background flow. The cornerstone of the theory is the background flow,... more
A theory is developed that describes the effects of topography and potential vorticity (PV) forcing on the dynamics of solitary Rossby waves (SRWs) in zonally varying background flow. The cornerstone of the theory is the background flow, which is systematically derived rather than simply being specified as in previous theories. The evolution of the disturbance field is governed by a
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The dynamics of solitary Rossby waves (SRWs) embedded in a meridionally sheared, zonally varying background flow are examined using a non-divergent barotropic model centered on a midlatitude f-plane. The zonally varying background flow,... more
The dynamics of solitary Rossby waves (SRWs) embedded in a meridionally sheared, zonally varying background flow are examined using a non-divergent barotropic model centered on a midlatitude f-plane. The zonally varying background flow, which is produced by an external potential vorticity (PV) forcing, yields a modified Korteweg-de Vries (K-dV) equation that governs the spatial-temporal evolution of a disturbance field that
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ABSTRACT The weakly nonlinear evolution of a free baroclinic wave in the presence of slightly supercritical, vertically sheared zonal flow and a forced stationary wave field that consists of a single zonal scale and an arbitrary number of... more
ABSTRACT The weakly nonlinear evolution of a free baroclinic wave in the presence of slightly supercritical, vertically sheared zonal flow and a forced stationary wave field that consists of a single zonal scale and an arbitrary number of meridional harmonics is examined within the context of the conventional two-layer model. The presence of the (planetary-scale) stationary wave introduces zonal variations in the supercriticality and is shown to alter the growth rate and asymptotic equilibrium of the (synoptic-scale) baroclinic wave via two distinct mechanisms: The first is due to the direct interaction of the stationary wave with the shorter synoptic wave (wave-wave mechanism), and the second is due to the interaction of the synoptic wave with that portion of the mean field that is corrected by the zonally rectified stationary wave fluxes (wave-mean mechanism). These mechanisms can oppose or augment each other depending on the amplitude and spatial structure of the stationary wave field. If the stationary wave field is confined primarily to the upper (lower) layer and consists of only the gravest cross-stream mode, conditions are favorable (unfavorable) for nonzero equilibrium of the free wave. In addition to the time dependent heat flux generated by baroclinic growth of the free wave, its interaction with a stationary wave field consisting of two or more meridional harmonics generates time dependent heat fluxes that vary with period of the free wave. However, if the stationary wave field contains several meridional harmonics of sufficiently large amplitude, the free baroclinic wave is destroyed.
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ABSTRACT The linear and weakly nonlinear stability characteristics of spatially growing, long, low frequency baroclinic waves are examined in a continuous atmosphere on a midlatitude β-plane channel in the presence of Ekman friction and... more
ABSTRACT The linear and weakly nonlinear stability characteristics of spatially growing, long, low frequency baroclinic waves are examined in a continuous atmosphere on a midlatitude β-plane channel in the presence of Ekman friction and Newtonian cooling (NC). Under the assumption that the damping mechanisms are sufficiently weak, the linear spatial instability problem is solved analytically and explicit expressions for the zonal wavenumber and spatial growth rate are obtained. The expressions show that Ekman damping is stabilizing whereas NC is destabilizing. The tendency of NC to dominate over Ekman damping increases linearly with frequency and β, and quadratically with reduction in zonal wind at the surface. The zonal wavelength of the disturbance is affected only by the flow supercriticality and NC, which always oppose each other; increasing the NC (supercriticality) increases (decreases) the zonal wavelength.
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ABSTRACT The effects of dissipation on the weakly nonlinear interactions between a marginally unstable baroclinic wave and a resonant topographic wave are examined using multiple time scales in a quasigeostrophic, two-layer model on a... more
ABSTRACT The effects of dissipation on the weakly nonlinear interactions between a marginally unstable baroclinic wave and a resonant topographic wave are examined using multiple time scales in a quasigeostrophic, two-layer model on a midlatitude beta plane channel. The lower boundary is characterized by sinusoidal bottom topography. The dissipation is chosen as one or a combination of the following forms: Ekman dissipation at the lower and upper boundaries which may be chosen different in strength, interfacial Ekman dissipation, thickness damping, and potential vorticity damping (PVD). In the absence of topography the baroclinic wave always equilibrates irrespective of the form of the dissipation. If the dissipation is sufficiently weak and due solely to PVD, the baroclinic wave exhibits a damped vacillation symmetric about its steady value. If the form of the dissipation is different from PVD, the baroclinic wave evolves through three distinct stages: initial exponential growth, a damped vacillation in which the overall envelope of the vacillation increases on an intermediate time scale and, finally, an asymptotic approach towards equilibration. In the presence of topography, numerical integrations of the asymptotically derived wave and mean flow evolution equations were carried out for the case where the topographic wave is taken zero initially. It is shown that depending on the form and/or the strength of the dissipation, the asymptotic state of the system is characterized by either a single (stationary) topographic wave state or a mixed wave state. Weak PVD favors the single wave states while, in sharp contrast, other dissipation forms, provided they are sufficiently weak, favor the mixed wave states. Perpetual vacillation was not obtained.
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ABSTRACT An ever-increasing body of evidence shows that changes in solar spectral irradiance (SSI) over the 11-year solar cycle (SC) can produce changes in stratospheric ozone. Changes in stratospheric ozone can in turn produce changes in... more
ABSTRACT An ever-increasing body of evidence shows that changes in solar spectral irradiance (SSI) over the 11-year solar cycle (SC) can produce changes in stratospheric ozone. Changes in stratospheric ozone can in turn produce changes in planetary wave drag (PWD) via wave-induced ozone heating, which was recently expounded upon in a paper by Nathan and Cordero (2007, JGR-Atmospheres). Because SSI-induced changes in PWD may have potentially far-reaching consequences for the global circulation, ranging from changes in the zonal-mean flow to changes in the Brewer-Dobson circulation, it is important to understand the connection between SSI and PWD. In this study we employ a mechanistic model that couples radiation, ozone and dynamics to derive an analytical expression that shows the explicit connection between SSI and PWD. The sensitivity of the stratospheric circulation, particularly stratospheric sudden warmings, to changes in SSI associated with the SC is explored.