Dynamical and Chemical Behavior of the Lower Stratosphere and Interactions with the Troposphere

Equivalent-barotropic calculations, in tandem with Lagrangian analyses, reveal how changes of total ozone follow from vertical and horizontal transport by planetary waves. Those calculations also throw light on how diabatic motions comprising the Brewer-Dobson circulation develop from quasi-horizontal advection by planetary waves. Potential temperature along a material surface indicates organized subsidence inside the polar-night vortex, resembling tracer observations from UARS. Lagrangian histories illustrate that this sinking motion follows in large part from parcels being driven out of thermodynamic equilibrium by planetary waves, especially at high latitudes. Irreversible heat transfer then produces a net drift of air across isentropic surfaces as parcels orbit about the displaced vortex. By driving mean-meridional overturning in the stratosphere, this downward drift is ultimately responsible for transferring ozone from the tropics to the extratropical lower stratosphere. It also introduces horizontal structure into the distribution of total ozone, which surfaces clearly in ozone trends. High-resolution global cloud imagery constructed from 6 satellites simultaneously observing the Earth was used to investigate the spectrum of equatorial waves generated by tropical convection and propagating vertically into the stratosphere. The results indicate that temperature variability is dominated by planetary-scale equatorial waves like the Kelvin mode, which agrees with satellite observations of the tropical stratosphere. However, the Kelvin mode accounts for only about 30 - 50% of the eastward momentum flux radiating into the stratosphere, the remainder coming from gravity waves. An algorithm was developed to determine 3-dimensional atmospheric motion from satellite tracer measurements. Based on Lagrangian constraints, the algorithm circumvents limitations of the traditional scheme for inferring motion from temperature measurements and determines the circulation in the tropics as reliably as elsewhere. A study of deep convection revealed that the highest towers (those penetrating into stratospheric air and controlling tropopause height and composition through convective mixing) occur in close association with the diurnal cycle of convection. Clouds colder than 220 K develop almost entirely in association with the diurnal cycle of convection over tropical landmasses and substantially in association with it even over maritime regions

Planetary circulations in the presence of transient and self-induced heating

The research program focuses on large-scale circulations and their interaction with the global convective pattern. An 11-year record of global cloud imagery and contemporaneous fields of motion and temperature have been used to investigate organized convection and coherent variability of the tropical circulation operating on intraseasonal time scales. This study provides a detailed portrait of tropical variability associated with the so-called Madden-Julian Oscillation (MJO). It reveals the nature, geographical distribution, and seasonality of discrete convective signal, which is a measure of feedback between the circulation and the convective pattern. That discrete spectral behavior has been evaluated in light of natural variability of the ITCZ associated with climatological convection. A composite signature of the MJO, based on cross-covariance statistics of cloud cover, motion, and temperature, has been constructed to characterize the lifecycle of the disturbance in terms of these properties. The composite behavior has also been used to investigate the influence the MJO exerts on the zonal-mean circulation and the involvement of the MJO in transfers of momentum between the atmosphere and the solid Earth. The aforementioned observational studies have led to the production of two animations. One reveals the convective signal in band-pass filtered OLR and compares it to climatological convection. The other is a 3-dimensional visualization of the composite lifecycle of the MJO. With a clear picture of the MJO in hand, feedback between the circulation and the convective pattern can be diagnosed meaningfully in numerical simulations. This process is being explored in calculations with the linearized primitive equations on the sphere in the presence of realistic stability and shear. The numerical framework represents climatological convection as a space-time stochastic process and wave-induced convection in terms of the vertically-integrated moisture flux convergence. In these calculations, frictional convergence near the equator emerges as a key to feedback between the circulation and the convective pattern. At low latitudes, nearly geostrophic balance in the boundary layer gives way to frictional balance. This shifts the wave-induced convection into phase with the temperature anomaly and allows the attending heating to feed back positively onto the circulation. The calculations successfully reproduce the salient features of the MJO. They are being used to understand the growth and decay phases of the composite lifecycle and the conditions that favor amplification of the MJO

Physics of the atmosphere and climate

Murry Salby's new book provides an integrated treatment of the processes controlling the Earth-atmosphere system, developed from first principles through a balance of theory and applications. This book builds on Salby's previous book, Fundamentals of Atmospheric Physics. The scope has been expanded into climate, with the presentation streamlined for undergraduates in science, mathematics and engineering. Advanced material, suitable for graduate students and as a resource for researchers, has been retained but distinguished from the basic development. The book provides a conceptual yet quantitative understanding of the controlling influences, integrated through theory and major applications. It leads readers through a methodical development of the diverse physical processes that shape weather, global energetics and climate. End-of-chapter problems of varying difficulty develop student knowledge and its quantitative application, supported by answers and detailed solutions online for instructors.Machine generated contents note: 1. The Earth-atmosphere system; 2. Thermodynamics of gases; 3. The second law and its implications; 4. Heterogeneous systems; 5. Transformations of moist air; 6. Hydrostatic equilibrium; 7. Static stability; 8. Radiative transfer; 9. Aerosol and cloud; 10. Atmospheric motion; 11. Atmospheric equations of motion; 12. Large-scale motion; 13. The planetary boundary layer; 14. Atmospheric waves; 15. The general circulation; 16. Dynamic stability; 17. Influence of the ocean; 18. Interaction with the stratosphere.Revised ed. of: Fundamentals of atmospheric physics. 1996.666 page(s)2nd ed

Dynamical and Chemical Behavior of the Lower Stratosphere and Interactions with the Troposphere

This research program investigated changes of dynamical and chemical structure of the lower stratosphere and how they are related to elements of the tropospheric general circulation. These considerations were explored in total ozone data from TOMS on board the Nimbus-7 satellite. It was shown that most of the daily variance of total ozone was accounted for by quasi-horizontal transport of ozone along isentropic surfaces in the lower stratosphere. Air descending along theta surfaces experiences compression that increases the local ozone number density and column abundance. Just the reverse is experienced by air ascending along isentropics surfaces. Together, these mechanisms provide an explanation for ozone "mini-hole" phenomenon, which punctuates the circulation of the Southern Hemisphere

Influence of planetary wave activity on the stratospheric final warming and spring ozone

A three-dimensional model of dynamics and photochemistry is used to investigate the influence of planetary wave activity on the seasonal evolution of the wintertime stratosphere, which dictates springtime conditions. The final warming and springtime ozone are each found to depend strongly upon planetary wave activity during the disturbed season. The integrations reproduce their observed dependence, which enters through anomalous upward Eliassen-Palm (EP) flux from the troposphere and equatorial wind associated with the Quasi-Biennial Oscillation (QBO). Of those major influences, changes of upward EP flux are predominant. Changes representative of those in the observed record alter the timing of the final warming by as much as 1–2 months. Much the same lag distinguishes warm and cold winters in the observed record. Accompanying the shift in the final warming is a change of ozone at spring equinox. Magnified over the Arctic, anomalous springtime ozone develops largely through anomalous isentropic mixing by planetary waves. Such mixing, which precedes the final warming, incorporates ozone-rich air from lower latitude, leading to enriched polar ozone during spring. Relative to disturbed conditions, springtime polar ozone under undisturbed conditions appears depleted by some 60 DU. Derived through anomalous transport, the same difference characterizes observed changes between warm and cold winters. Much of the apparent depletion is eventually eliminated with the onset of isentropic mixing, as it is in the observed record. Together with anomalous dynamical structure, such behavior has implications important to the interpretation of interannual changes

On the wintertime increase of Arctic ozone : relationship to changes of the polar-night vortex

Interannual changes of springtime ozone over the Arctic follow from anomalous transport and chemical depletion, two mechanisms that control the wintertime increase of ozone. Attempts to disentangle these contributions to anomalous ozone rest upon the isolation of air over the Arctic. To elucidate changes of Arctic ozone between warm and cold winters, their latitude-height structure is investigated in the solar backscatterd ultraviolet record and then related to contemporaneous changes of dynamical structure in the National Centers for Environmental Prediction record. Structural differences between warm and cold winters imply a major contribution to anomalous Arctic ozone from horizontal transport. Anomalous isentropic mixing by planetary waves appears conspicuously in the structure of March ozone, which has been driven into coincidence with θ surfaces following warm winters but remains deflected across them following cold winters. In concert with anomalous downwelling of ozone-rich air, this mechanism accounts for at least two thirds of the observed deficit of springtime ozone over the Arctic following cold winters. About half of the observed deficit during March is erased during April, when weakening of the vortex following cold winters eventually opens the Arctic to isentropic mixing by planetary waves. Delayed relative to warm winters, isentropic mixing during cold winters ultimately leads to much the same ozone structure. This significantly reduces the anomaly between warm and cold winters from that found a month earlier. The observed reduction is consistent with the estimated contribution to anomalous Arctic ozone from isentropic mixing.11 page(s

Changes of the Antarctic ozone hole : controlling mechanisms, seasonal predictability, and evolution

The ozone hole changes considerably from one year to the next. It varies between conditions in which springtime ozone is strongly depleted to others in which ozone is only weakly depleted. Those changes are shown to closely track anomalous planetary wave forcing of the residual circulation. The strong coherence with planetary wave forcing is consistent with similar coherence of springtime temperature, which modulates Polar Stratospheric Cloud (PSC). By controlling the lifetime of PSC, anomalous wave forcing determines the net activation of chlorine and bromine and, hence, springtime depletion of ozone during individual years. The strong coherence with planetary wave forcing affords long-range predictability. It supports a seasonal forecast of springtime depletion, which, through the ozone mass deficit, perturbs ozone across much of the Southern Hemisphere during subsequent months of summer. Conditioned upon wintertime wave structure, a hindcast of springtime depletion faithfully predicts the anomalous ozone observed. A reliable forecast of tropospheric planetary waves would thus enable springtime depletion to be predicted. The current evolution of Antarctic ozone is dominated by dynamically-induced changes. Representing its climate variability, those large changes obscure the more gradual evolution of springtime depletion, like that associated with the decline of chlorine. The strong dependence on planetary wave forcing, however, enables dynamically-induced changes of ozone to be identified accurately. Removing them unmasks the secular variation of Antarctic ozone, the part coherent over a decade and longer. Independent of dynamically-induced changes, that component discriminates to changes associated with stratospheric composition. It reveals a gradual but systematic rebound over the last decade. The upward trend is shown to be robust, significant at the 99.5% level. Uncertainty in this trend is thus small enough to make the probability of it arising through chance alignment of error less than 0.5%. The discriminated component mirrors the decline of effective stratospheric chlorine, representing a gradual return of springtime ozone toward its level in 1980 of 10-15%. It enables Antarctic ozone to be tracked relative to changes of chlorine, CO₂, and other features of climate more reliably than is otherwise possible.11 page(s

Global Kelvin waves in the upper atmosphere excited by tropospheric forcing at midlatitudes

Nonlinear integrations with a 3-D primitive equation model of the middle and upper atmosphere reveal global-scale Kelvin waves. Owing to their meridional extent, these eastward propagating disturbances can be excited by tropospheric fluctuations over much of the globe. Stochastic forcing in the midlatitude troposphere produces an eastward response that involves the Kelvin normal mode, with barotropic vertical structure, as well as a continuum of vertically propagating Kelvin waves. Having periods of order a day and shorter, those disturbances are all global. Transient fluctuations representative of midlatitude weather systems reproduce observed Kelvin structure and amplitude near the tropopause. Vertical amplification then leads to wind fluctuations at mesospheric and thermospheric altitudes of 5–15 m/s. Approaching tidal amplitudes, global Kelvin waves should therefore represent a measurable if not prominent feature at those altitudes.11 page(s