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It is shown that a quantitative relation exists between the stratospheric polar cap potential vorticity and the 100-hPa eddy heat flux. A difference in potential vorticity between years is found to be linearly related to the flux difference integrated over time, taking into account a decrease in relaxation time scale with height in the atmosphere. This relation (the PV--flux relation) is then applied to the 100-hPa flux difference between 2008/09 and the climatology (1989-2008) to obtain a prediction of the polar cap potential vorticity difference between the 2008/09 winter and the climatology. A prediction of the 2008/09 polar cap potential vorticity is obtained by adding this potential vorticity difference to the climatological potential vorticity. The observed polar cap potential vorticity for 2008/09 shows a large and abrupt change in the potential vorticity in midwinter, related to the occurrence of a major sudden stratospheric warming in January 2009; this is also captured by the potential vorticity predicted from the 100-hPa flux and the PV--flux relation. The results of the mean PV--flux relation show that, on average, about 50% of the interannual variability in the state of the Northern Hemisphere stratosphere is determined by the variations in the 100-hPa heat flux. This explained variance can be as large as 80% for more severe events, as demonstrated for the 2009 major warming. DOI: 10.1175/2010JAS3569.1

Byline: A. F. Tuck (1), D. J. Donaldson (2), M. H. Hitchman (3), E. C. Richard (4), H. Tervahattu (5), V. Vaida (6), J. C. Wilson (7) Abstract: This paper is in response to the Editorial Essay by Crutzen and the Editorial Comment by Cicerone in the August 2006 issue of Climatic Change. We reprise the evidence from atmospheric nuclear weapon testing in the 1950s and 1960s which is salient to the mooted maintenance of an artificial sulphate aerosol layer in the lower stratosphere, including a hitherto and now posthumous unpublished analysis of the 185.sup.W Hardtack data. We also review recent investigations by ourselves, which have considerable bearing on some relevant questions concerning meteorological dynamics, aerosol chemistry and physics and the photodissociation of stratospheric sulphuric acid. Author Affiliation: (1) Chemical Sciences Division 6, NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO, 80305-3337, USA (2) Department of Chemistry, University of Toronto, Toronto, Ontario, Canada (3) Atmospheric and Oceanic Sciences, University of Wisconsin, Madison, WI, USA (4) Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA (5) Nordic Envicon Oy, Helsinki, Finland (6) Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA (7) Department of Engineering, University of Denver, Denver, CO, USA Article History: Registration Date: 11/03/2008 Received Date: 21/02/2007 Accepted Date: 19/02/2008 Online Date: 12/04/2008

Using a hierarchy of models, and observations, the effect of vertical shear in the lower stratosphere on baroclinic instability in the tropospheric midlatitude jet is examined. It is found that increasing stratospheric shear increases the phase speed of growing baroclinic waves, increases the growth rate of modes with low synoptic wavenumbers, and decreases the growth rate of modes with higher wavenumbers. The meridional structure of the linear modes, and their acceleration of the zonal mean jet, changes with increasing stratospheric shear, but in a way that apparently contradicts the observed stratosphere-troposphere northern annular mode (NAM) connection. This contradiction is resolved at finite amplitude. In nonlinear life cycle experiments it is found that increasing stratospheric shear, without changing the jet structure in the troposphere, produces a transition from anticyclonic (LC1) to cyclonic (LC2) behavior at wavenumber 7. All life cycles with wavenumbers lower than 7 are LC1, and all with wavenumber greater than 7 are LC2. For the LC1 life cycles, the effect of increasing stratospheric shear is to increase the poleward displacement of the zonal mean jet by the eddies, which is consistent with the observed stratosphere-troposphere NAM connection. Finally, it is found that the connection between high stratospheric shear and high-tropospheric NAM is present by NCEP-NCAR reanalysis data.

The isotopic composition of long-lived trace molecules provides a window into atmospheric transport and chemistry. Carbon dioxide is a particularly powerful tracer, because its abundance remains >100 parts per million by volume (ppmv) in the mesosphere. Here, we successfully reproduce the isotopic composition of C[O.sub.2] in the middle atmosphere, which has not been previously reported. The mass-independent fractionation of oxygen in C[O.sub.2] can be satisfactorily explained by the exchange reaction with O([sup.1]D). in the stratosphere, the major source of O([sup.1]D) is [O.sub.3] photolysis. Higher in the mesosphere, we discover that the photolysis of [sup.16][O.sup.17]O and [sup.16][O.sup.18]O by solar Lyman-[alpha] radiation yields O([sup.1]D) 10-100 times more enriched in [sup.17]O and [sup.18]O than that from ozone photodissociation at lower altitudes. This latter source of heavy O([sup.1]D) has not been considered in atmospheric simulations, yet it may potentially affect the 'anomalous' oxygen signature in tropospheric C[O.sub.2] that should reflect the gross carbon fluxes between the atmosphere and terrestrial biosphere. Additional laboratory and atmospheric measurements are therefore proposed to test our model and validate the use of C[O.sub.2] isotopic fractionation as a tracer of atmospheric chemical and dynamical processes. biogeochemical cycles | C[O.sub.2] | mesosphere | stratosphere

Air density is a key sensing object for its high variability especially in the mesosphere, and ozone plays an important role in the physical, chemical, and radiant processes in the atmosphere system. Therefore it is essential to obtain their global vertical distributions jointly with high precision and vertical resolution. There is little work on joint retrieval of air density and ozone distributions using the ultraviolet limb-scan technique, although much work has been done on ozone measurement. Numerical simulations of joint air density and ozone retrieval in the middle atmosphere (20-90 km) are carried out using limb-scattered radiances at four bands (255, 300, 320, and 340 nm). Results show that joint retrieval of dual parameters using the limb-scan technique is feasible with high precision in nearly the whole region concerned, where air density and ozone have a precision of 1%-2% and 3%-5%, respectively, provided that high measurement precision and accurate correction of multiple-scattered radiance at long ultra-violet bands are ensured. OCIS codes: 010.4950, 280.0280.

Lower-stratospheric and upper-tropospheric disturbances over Thailand during 12-21 January 2000 werestudied using the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment-Tropics (GAME-T) intensive rawinsonde observations with fine temporal sampling intervals of 3 h. Analysis was focused on the wind disturbances with a period shorter than about 10 days. Frequency spectra showed three distinct peaks: a 1-day period above a height of 20 kin, a near-inertial period around 19 and 27 km, and periods of 2.5-9 days (or longer) in the height range of 12-17 km. The wave with a 1-day period was interpreted as a diurnal tide. A comparison with the migrating tide in the global-scale wave model showed that the observational results had larger amplitude and shorter vertical wavelength than the model. The difference between the observation and the model may be caused by the superposition of the nonmigrating tide. The wave with the near-inertial period was interpreted as an internal inertial gravity wave. A hodograph analysis was performed in order to investigate the wave properties. It was found that the wave, which appeared at a height around 19 km (just above the tropopause level), propagated southwestward with a ground-based group velocity of about 1.4 m [s.sup.-1]. The longer period disturbances, which appeared at heights of 12-17 km, had layered structures with the vertical scales of 2-4 km. They were considered to be due to inertial instability, based on the fact that the potential vorticity of the background atmosphere was nearly zero and that their phase structures were consistent with theory. It was shown by a backward trajectory analysis that the air parcel with negative potential vorticity had its origin in equatorial Indonesia. It was also shown by a forward trajectory analysis that the air parcel was transported to the Pacific south of Japan. This is consistent with the existence of similar layered disturbances that are shown using rawinsonde data at a station there.

This paper examines the nature and robustness of internal stratospheric variability, namely the variability resulting from the internal dynamics of the stratosphere itself, as opposed to that forced by external sources such as the natural variability of the free troposphere. Internal stratospheric variability arises from the competing actions of radiative forcing, which under perpetual winter conditions strengthens the polar vortex, and planetary wave breaking, which weakens it. The results from a stratosphere-only model demonstrate that strong internal stratospheric variability, consisting of repeated sudden warming-type events, exists over a wide range of realistic radiative and wave forcing conditions, and is largely independent of other physical and numerical parameters. In particular, the coherent form of the variability persists as the number of degrees of freedom is increased, and is therefore not an artifact of severe model truncation. Various diagnostics, including three-dimensional representations of the potential vorticity, illustrate that the variability is determined by the vertical structure of the vortex and the extent to which upward wave propagation is favored or inhibited. In this paper, the variability arising from purely internal stratosphere dynamics is isolated by specifying thermal and wave forcings that are completely time independent, in a second paper, the authors investigate the relative importance of internal and external variability by considering time-dependent wave forcing as a simple representation of tropospheric variability.

The possibility that the tropopause could be lower during an ice-age cooling leads to an examination of the general sensitivity, of global circulations to the tropopause height by altering a constant stratospheric temperature [T.sub.s] in calculations with a dry, global, multilevel, spectral, primitive equation model subject to a simple Newtonian heating function. In general, lowering the tropopause by increasing the stratospheric temperature causes the jet stream to move to lower latitudes and the eddies to become smaller. Near the standard state with [T.sub.s], = 200 K, the jets relocate themselves equatorward by 2[degrees] in latitude for every 5 K increase in the stratospheric temperature. A double-jet system, with centers at 30 and 60[degrees] latitude, occurs when the equatorial tropopause drops to 500 mb (for [T.sub.s] = 250 K), with the high-latitude component extending throughout the stratosphere. The eddy momentum flux mainly traverses poleward across the standard jet at 40[degrees], in keeping with the predominantly equatorward propagation of the planetary waves. But when the jet lies at 30[degrees] (for [T.sub.s], = 225 K) the flux converges on the jet in keeping with planetary waves that propagate both equatorward and poleward. Two sets of such wave propagation occur in the double-jet system. As the troposphere becomes even shallower, the flux reverts to being primarily poleward across the jet (for [T.sub.s] 260 K) but then becomes uniquely primarily equatorward across the jet (for [T.sub.s] 275 K) before the circulation approaches extinction. Thus the existence of a predominantly poleward flux in the standard state appears to be parametrically fortuitous.

Characterizing the interaction of hydrogen chloride (HCI) with polar stratospheric cloud ice particles is essential for understanding the processes responsible for ozone depletion. We studied the interaction of gas-phase HCI with ice between 243 and 186 K by using (i) ellipsometry to monitor the ice surface and (ii) coated-wall flow tube experiments, both with chemical ionization mass spectrometry detection of the gas phase. We show that trace amounts of HCI induce formation of a disordered region, or quasi-liquid layer, at the ice surface at stratospheric temperatures. We also show that surface disordering enhances the chlorine activation reaction of HCI with chlorine nitrate (CION[O.sub.2]) and also enhances acetic acid (C[H.sub.3]COOH) adsorption. These results impact our understanding of the chemistry and physics of ice particles in the atmosphere. chlorine activation | ice chemistry | ozone depletion | stratosphere

The objective of the Microwave Limb Sounder THz module on the Aura satellite is to measure stratospheric and mesospheric OIL This paper describes the optical design, alignment, calibration, and performance of the THz module. The calibration uncertainty for one limb scan is substantially less than the precision due to radiometric noise. For averages of many scans, the dominant calibration uncertainty of 2 % is due to uncertainty in beam efficiency. Index Terms--Mesosphere, OH, stratosphere, THz.

The concept of downward control proposes a mechanism for the impact of the stratospheric circulation on the troposphere. Momentum forcing at upper-stratospheric levels induces a meridional circulation that eventually reaches the surface. So far, a lack of sufficiently accurate data hindered an observational test of this downward propagation. The concept is extended in this paper by looking at the effect of angular momentum forcing in prescribed regions in the lower stratosphere on the tropospheric circulation. In that case, the European Centre for Medium-Range Weather Forecasts Reanalysis Project (ERA) data can be used to investigate the atmospheric response to forcing in a prescribed domain. It is found that these forcing events are quite short lived and that angular momentum flux convergence in the prescribed domain is highly correlated with convergence outside this forcing area. Typically, these fields of convergence and also divergence extend to the surface in a quasibarotropic manner outside the Tropics. This structure of the forcing is not compatible with the assumptions of the downward control concept. The observed related meridional circulation therefore differs widely from that predicted. In particular, there is no obvious descent of the circulation to the ground. Even so, such forcing events are accompanied by an intensive exchange of angular momentum between stratosphere and troposphere. The confinement of the forcing to the selected forcing domain is reasonably strict in the Tropics. A relatively narrow tongue of angular momentum is growing at the equator underneath the forcing area. Frictional torques play a role in this development. Altogether, the forcing events as selected involve a strong angular momentum exchange between stratosphere and troposphere but are not suited for a test of the downward control concept. Alternatives are discussed.

The excitation of Rossby waves on the edge of the stratospheric polar vortex, due to time-dependent topographic forcing, is studied analytically and numerically in a simple quasigeostrophic f-plane model. When the atmosphere is compressible, the linear response of the vortex is found to have two distinct components. The first is a spectrum of upward-propagating waves that are excited by forcing with temporal frequencies within a fixed 'Charney-Drazin' range that depends on the angular velocity at the vortex edge and the vortex Burger number. The second component of the response is a barotropic mode, which is excited by forcing with a fixed temporal frequency outside the Charney-Drazin range. The relative magnitude of the two responses, in terms of total angular pseudomomentum, depends on the ratio of the horizontal scale of the forcing to the Rossby radius. Under typical stratospheric conditions the barotropic response is found to dominate. Nonlinear simulations confirm that the linear results remain relevant to understanding the response in cases when strongly nonlinear Rossby wave breaking ensues. It is shown that a sudden warming, or rapid increase in vortex angular pseudomomentum, can be generated at much lower forcing amplitudes when the barotropic mode is resonantly excited compared to when the upward-propagating waves are excited. A numerical simulation of a 'barotropic sudden warming' due to excitation of the barotropic mode by a relatively weak topographic forcing is described.

A new two-moment bulk microphysics scheme is implemented into the polar version of the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) to simulate arctic mixed-phase boundary layer stratiform clouds observed during Surface Heat Budget of the Arctic (SHEBA) First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) Arctic Cloud Experiment (ACE). The microphysics scheme predicts the number concentrations and mixing ratios of four hydrometeor species (cloud droplets, small ice, rain, snow) and includes detailed treatments of droplet activation and ice nucleation from a prescribed distribution of aerosol obtained from observations. The model is able to reproduce many features of the observed mixed-phase cloud, including a near-adiabatic liquid water content profile located near the top of a well-mixed boundary layer, droplet number concentrations of about 200-250 [cm.sup.-3] that were distributed fairly uniformly through the depth of the cloud, and continuous light snow falling from the cloud base to the surface. The impacts of droplet and ice nucleation, radiative transfer, turbulence, large-scale dynamics, and vertical resolution on the simulated mixed-phase stratiform cloud are examined. The cloud layer is largely self-maintained through strong cloud-top radiative cooling that exceeds 40 K [day.sup.-l]. It persists through extended periods of downward large-scale motion that tend to thin the layer and reduce water contents. Droplet activation rates are highest near cloud base, associated with subgrid vertical motion that is diagnosed from the predicted turbulence kinetic energy. A sensitivity test neglecting subgrid vertical velocity produces only weak activation and small droplet number concentrations (

A simple atmospheric general circulation model (GCM) is used to investigate the transient response of the stratosphere-troposphere system to externally imposed pulses of lower-tropospheric planetary wave activity. The atmospheric GCM is a dry, hydrostatic, global primitive-equations model, whose circulation includes an active polar vortex and a tropospheric jet maintained by baroclinic eddies. Planetary wave activity pulses are generated by a perturbation of the solid lower boundary that grow and decay over a period of 10 days. The planetary wave pulses propagate upward and break in the stratosphere. Subsequently, a zonal-mean circulation anomaly propagates downward, often into the troposphere, at lags of 30-100 days. The evolution of the response is found to be dependent on the state of the stratosphere-troposphere system at the time the pulse is generated. In particular, on the basis of a large ensemble of these simulations, it is found that the length of time the signal takes to propagate downward from the stratosphere is controlled by initial anomalies in the zonal-mean circulation and in the zonal-mean wave drag. Criteria based on these anomaly patterns can be used, therefore, to predict the long-term surface response of the stratosphere troposphere system to a planetary wave pulse up to 90 days after the pulse is generated. In an independent test, it is verified that the initial states that most strongly satisfy these criteria respond in the expected way to the lower-tropospheric wave activity pulse.

This paper considers the propagation of waves on the edge of a stratospheric polar vortex, represented by a three-dimensional patch of uniform potential vorticity in a compressible quasigeostrophic system. Waves are initialized by perturbing the vortex from axisymmetry in the center of tire vortex, and their subsequent upward and downward propagation is measured in terms of a nonlinear, pseudomomentum-based wave activity. Under conditions typical of the winter stratosphere, the dominant direction of wave propagation is downward, and wave activity accumulates in the lower vortex levels. The reason for the preferred downward propagation arises from a recent result of Scott and Dritschel, which showed that the three-dimensional Green's function in the compressible system contains an anisotropy that causes a general differential rotation in a finite volume vortex. The sense of the differential rotation is to stabilize the upper vortex and destabilize the lower vortex. This mechanism is particularly interesting in view of recent interest in the downward influence of the stratosphere on the troposphere and also provides a possible conservative, balanced explanation of the formation of the robust dome plus annulus potential vorticity structure observed in the upper stratosphere.

Fast measurements of three scalars, ozone, dimethyl sulfide (DMS), and total water, are used to investigate the entrainment process in the stratocumulus-topped boundary layer (STBL) observed over the eastern subtropical Pacific during the second Dynamics and Chemistry of Marine Stratocumulus Experiment (DYCOMS-II). Direct measurement of the flux profiles by eddy covariance is used to estimate the entrainment velocity, the average rate at which the boundary layer grows diabatically via incorporation of overlying free tropospheric air. The entrainment velocities observed over the course of the mission, which took place during July 2001, ranged from 0.12 to 0.72 cm [s.sup.-1] and appear to outpace the estimated large-scale subsidence as the boundary layer advects over warmer sea surface temperatures. Observed entrainment velocities display only a weak correlation with the buoyancy Richardson number defined at the inversion, which suggests that processes other than inversion strength, such as wind shear, might play a larger role in driving entrainment in the STBL than previously recognized. This study is the first to use DMS as an entrainment tracer because the high-rate mass spectrometric technique has only recently been developed. The biogenic sulfur compound shows great promise for such investigations in marine environments because the free tropospheric concentrations are virtually nonexistent, and it therefore serves as an unambiguous marker of boundary layer air. As such, individual mixing events can be analyzed to determine the mixing fraction of boundary layer and free tropospheric air, and in several such cases buoyancy reversal was observed despite the absence of large-scale dissipation of the cloud field as postulated by cloud-top entrainment instability. Moreover, the redundancy attained in using three separate scalars allows for an investigation of the average height scales above the inversion from where air is blended into the STBL, and this tends to be less than 80 m above the mean inversion height, implying that the entrainment process occurs on very small scales.

Accurate and reliable predictions and an understanding of future changes in the stratosphere are major aspects of the subject of climate change. Simulating the interaction between chemistry and climate is of particular importance, because continued increases in greenhouse gases and a slow decrease in halogen loading are expected. These both influence the abundance of stratospheric ozone. In recent years a number of coupled chemistry-climate models (CCMs) with different levels of complexity have been developed. They produce a wide range of results concerning the timing and extent of ozone-layer recovery. Interest in reducing this range has created a need to address how the main dynamical, chemical, and physical processes that determine the long-term behavior of ozone are represented in the models and to validate these model processes through comparisons with observations and other models. A set of core validation processes structured around four major topics (transport, dynamics, radiation, and stratospheric chemistry and microphysics) has been developed. Each process is associated with one or more model diagnostics and with relevant datasets that can be used for validation. This approach provides a coherent framework for validating CCMs and can be used as a basis for future assessments. Similar efforts may benefit other modeling communities with a focus on earth science research as their models increase in complexity.

We describe an inversion method for determining the composition, density, and size of stratospheric clouds and aerosols by satellite remote sensing. The method, which combines linear least-squares minimization and Monte Carlo techniques, is tested with pure synthetic IR spectra. The synthetic spectral data are constructed to mimic mid-IR spectra recorded by the Improved Limb Atmospheric Spectrometer (ILAS-I and ILAS-II) instruments, which operate in the solar occultation mode and record numerous polar stratospheric cloud events. The advantages and limitations of the proposed technique are discussed. In brief we find that stratospheric aerosol in the size range from 0.5 to 4.0 [micro]m can be retrieved to an accuracy of 30%. We also show that the chemical composition of common stratospheric aerosols can be determined, whereas identification of their phases from mid-IR satellite remote-sensing data alone appears to be questionable. OCIS codes: 280.1100, 290.1090.

The inversion method for simultaneous gas ([O.sub.3], N[O.sub.2], HN[O.sub.2], [N.sub.2]O, C[H.sub.4], [H.sub.2]O, CFC-11, CFC-12, [N.sub.2][O.sub.5], and ClON[O.sub.2]) and aerosol retrievals from broadband continuous IR spectra of occultation measurements is described. Both gas and aerosol physical modeling with consideration of the multicomponent character of aerosol and polar stratospheric clouds (PSCs) are used to minimize the difference between measured and modeled transmittance spectra under smoothness constraints imposed on particle-size distributions for each PSC component and positive constraints on all gas and aerosol parameters. The method is tested by numerical simulations in which synthetic occultation measurements inherent to the improved limb atmospheric spectrometer are used. The study reveals that the method has significant advantages over other approaches based on offset or gas--window--channel aerosol correction for accurate gas retrievals and provides additional information on the particle-size composition, volume density, and chemical component character of PSCs. OCIS codes: 280.0280, 280.1100, 010.1280.

Analysis of the 250-560 [cm.sup.-1] spectral continuum of Titan's north polar hood just after spring equinox reveals, in addition to the ubiquitous aerosol, a tenuous but relatively uniform cloud of small particles permeating the lower stratosphere at altitudes between 58 and 90 km. Voyager 1 IRIS data suggest the particles are highly scattering, almost certainly condensed organics, with radii between 1 and 5 [micro]m. Mole fractions for the condensed material range between 4 x [10.sup.-8] and 4 x [10.sup.-6], depending upon particle size. Vapor pressure arguments imply condensed nitriles near 90 km, the most likely being HCN, with condensed hydrocarbons such as [C.sub.2][H.sub.6] restricted to regions considerably nearer the tropopause. No direct chemical identification is possible. Negligible methane supersaturation in the troposphere at 67.4[degrees] N latitude, when compared with degrees of supersaturation at other latitudes, hints at precipitation fluxes of north polar stratospheric condensates during the previous northern winter that were perhaps three orders of magnitude greater than those at low latitudes during that time. A scale height of 1.5 times the density scale height above 160 km is reaffirmed for the photochemical aerosol of the north polar hood. There appears to be a depletion of aerosol somewhere below 160 km. An aerosol mole fraction ~8 x [10.sup.-8] at 160 km is inferred, about 33% greater than the value derived in a previous study. The Cassini CIRS instrument, with its expanded spectral range and higher spectral resolution, should be able to provide highly complementary information for the time period coveting most of the northern winter season. Keywords: Titan; Condensates; Stratosphere; Clouds

The aerosol extinction measurements in the ultraviolet and visible wavelengths by the balloonborne spectrometer Spectroscopie d'Absorption Lunaire pour l'Observation des Minoritaires Ozone et [NO.sub.x] (SALOMON) show that aerosols are present in the middle stratosphere, above 25-km altitude. These observations are confirmed by the extinction measurements performed by a solar occultation radiometer. The balloonborne Laboratoire de Meteorologie Dynamique (LMD) counter instrument also confirms the presence of aerosol around 30-km altitude, with an unrealistic excess of micronic particles assuming that only liquid sulfate aerosols are present. An unexpected spectral structure around 640-nm observed by SALOMON is also detectable in extinction measurements by the satellite instrument Stratospheric Aerosols and Gas Experiment III. This set of measurements could indicate that solid aerosols were detected at these altitude ranges. The amount of soot detected up to now in the lower stratosphere is too low to explain these measurements. Thus, the presence of interplanetary dust grains and micrometeorites may need to be invoked. Moreover, it seems that these grains fill the stratosphere in stratified layers. OCIS codes: 010.1110, 280.1100.

The Airborne Millimeter- and Submillimeter Observing System (AMSOS) is a total-power radiometer for observations of the 183.3-GHz water vapor rotational line, operated onboard a Learjet aircraft of the Swiss Air Force. The radiometer is also used to observe the 175.45-GHz ozone line in the other sideband. The neatly designed quasi optics provide a regular and narrow output beam with a half-power beam-width angle of 1.2[degrees] and efficient sideband switching. A [lambda]/4-quasi-optical isolator is used for baseline reduction securing attenuation of internal reflections by more than 30 dB. A low noise temperature of the ambient-temperature-operating system (1900 K) and excellent target pointing (better than 0.1[degrees]) provide a good duty cycle and reliable calibration. A reliable control over the radiometer's operational parameters, like system stability and system temperatures, and higher automatization were required to come up with high demands of an onboard operation. The measured spectra look typical for the region and time where they were observed. Index Terms--Microwave remote sensing, quasi optics, stratosphere, water vapor.

This paper investigates the vertical filtering of parameterized gravity wave pseudomomentum flux in the troposphere-stratosphere version of the Met Office Unified Model. Gravity wave forcing is parameterized using the Warner and McIntyre spectral gravity wave parameterization. The same amount of isotropic pseudomomentum flux per unit mass is launched from the planetary boundary layer at each grid point. The parameterization models the azimuthally dependent Doppler shifting and breaking of the gravity wave spectrum as it is filtered by the background atmosphere. The result is an anisotropic distribution of pseudomomentum flux among azimuthal sectors that varies greatly with altitude and location. This gives an idealized global climatology of nonorographic gravity waves. The filtering effect of the atmosphere in this climatology is diagnosed using the 'zonal anisotropy.' Results show areas where observational measurements could be targeted to find the most prominent features in the gravity wave field. Such areas include, for example, the summer stratosphere where zonal anisotropy is very large and where there is a significant localization in latitude and longitude of patches of high zonal anisotropy. Comparisons are also made with recent observational estimates of gravity wave fluxes and test whether wind filtering of a homogeneous, azimuthally isotropic source is enough to reproduce observed features of the gravity wave field.

Stratospheric [O.sub.3] and ClO were simultaneously observed off the northeastern coast of Japan by the Balloon-Borne Superconducting Submillimeter-Wave Limb-Emission Sounder (BSMILES) developed at National Institute of Information and Communications Technology. BSMILES is a highly sensitive submillimeter radiometer that exploits the superconductor-insulator-superconductor (SIS) technology for atmospheric research. This paper presents the first BSMILES spectra, and describes the details of the calibration process. The vertical profiles of [O.sub.3] and ClO have been also retrieved. In spite of some calibration uncertainties the obtained profiles are in relatively good agreement with previous and other available measurements. Index Terms--Balloon-borne observation, limb sounder, microwave spectroscopy, retrieval of atmospheric profile, stratospheric chemistry, submillimeter wave, superconducting receiver.

Normal modes of a linear vertical shear (Eady shear) are studied within the linearized primitive equations for a rotating stratified fluid above a rigid lower boundary. The authors' interest is in modes having an inertial critical layer present at some height within the flow. Below this layer, the solutions can be closely approximated by balanced edge waves obtained through an asymptotic expansion in Rossby number. Above, the solutions behave as gravity waves. Hence these modes are an example of a spatial coupling of balanced motions to gravity waves. The amplitude of the gravity waves relative to the balanced part of the solutions is obtained analytically and numerically as a function of parameters. It is shown that the waves are exponentially small in Rossby number. Moreover, their amplitude depends in a nontrivial way on the meridional wavenumber. For modes having a radiating upper boundary condition, the meridional wavenumber for which the gravity wave amplitude is maximal occurs when the tilts of the balanced edge wave and gravity waves agree.

The new microwave Radiometer for Atmospheric Measurements at Summit (RAMAS) has started operation at Summit station, Greenland (72[degrees]N, 38[degrees]W, 3200 m), and is now being prepared for continuous measurements. RAMAS operates in the frequency band from 265-280 GHz with an instantaneous bandwidth of currently 1 GHz. It observes the emission of thermally induced rotational transitions of a variety of stratospheric trace gases, including [O.sub.3], CIO, [N.sub.2]0, HN[O.sub.3], and HCN. Tropospheric water vapor content, a major constraint on ground-based microwave radiometry, is exceptionally low at Summit station. Initial measurements and retrieved profiles are presented, demonstrating the excellent measurement conditions. Index Terms--Ground based, microwave radiometry, new instrument, ozone, stratosphere.

A transport equation based on mass-weighted isentropic zonal means applies to the diagnosis for the meridional ozone transport in the troposphere and stratosphere. The mean and eddy ozone fluxes are estimated from the global distributions of the temperature, wind, and ozone. In comparison with the conventional Eulerian mean and transformed Eulerian mean (TEM), the present diagnosis has advantages for the expression of eddy transport terms. The adiabatic eddy flux is separated from the diabatic eddy flux, which is parallel to the isentropic surface. The analysis shows that the eddy flux is almost adiabatic except that it is significantly affected by diabatic effects near the lower troposphere. Another advantage lies in the mean meridional transport. Although it is almost similar to the TEM, significant differences can be found near the Antarctic polar vortex due to nongeostrophic effects. Furthermore, the isentropic diagnosis expresses a strong equatorward flux near the lower boundary, while the TEM hardly does this because of inadequate treatment of the lower-boundary conditions. The life cycle of ozone can be understood through the exact estimation of the transport terms. Although the stratospheric meridional transport is mainly performed by the Brewer-Dobson circulation, the strong poleward eddy ozone flux is caused by planetary wave breaking, especially in the winter hemisphere. In the extratropics, the ozone subsides from the stratosphere to the troposphere by mean downward motions, mainly diffused to the lower latitudes probably due to strong baroclinic waves and effectively lost through chemical processes in the lower troposphere.

An exceptionally strong stratospheric sudden warming (SSW) that spontaneously occurs in a very simple stratosphere--troposphere AGCM is discussed. The model is a dry, hydrostatic, primitive equation model without planetary stationary waves. Transient baroclinic wave-wave interaction in the troposphere thus provides the only source of upward-propagating wave activity into the stratosphere. The model's SSW is grossly similar to the Southern Hemisphere major SSW of 2002: it occurs after weaker warmings 'precondition' the polar vortex for breaking, it involves a split of the polar vortex, and it has a downward-propagating signature. These similarities suggest that the Southern Hemisphere SSW of 2002 might itself have been caused by transient baroclinic wave-wave interaction. The simple model used for this study also provides some insight into how often such extreme events might occur. The frequency distribution of SSWs in the model has exponential, as opposed to Gaussian, tails. This suggests that very large amplitude SSWs, though rare, might occur with higher frequency than might be naively expected.

Satellite-based solar occultation measurements during the 2002 austral winter have been used to reconstruct global, three-dimensional ozone distributions. The reconstruction method uses correlations between potential vorticity and ozone to derive 'proxy' distributions from the geographically limited occultation observations. Ozone profiles from the Halogen Occultation Experiment (HALOE), the Polar Ozone and Aerosol Measurement III (POAM III), and the Stratospheric Aerosol and Gas Experiment II and III (SAGE II and III) are incorporated into the analysis. Because this is one of the first uses of SAGE III data in a scientific analysis, preliminary validation results are shown. The reconstruction method is described, with particular emphasis on uncertainties caused by noisy and/or multivalued correlations. The evolution of the solar occultation data and proxy ozone fields throughout the winter is described, and differences with respect to previous winters are characterized. The results support the idea that dynamical forcing early in the 2002 winter influenced the morphology of the stratosphere in a significant and unusual manner, possibly setting the stage for the unprecedented major stratospheric warming in late September. The proxy is compared with ozone from mechanistic, primitive equation model simulations of passive ozone tracer fields during the time of the warming. In regions where chemistry is negligible compared to transport, the model and proxy ozone fields agree well. The agreement between, and changes in, the large-scale ozone fields in the model and proxy indicate that transport processes, particularly enhanced poleward transport and mixing, are the primary cause of ozone changes through most of the stratosphere during this unprecedented event. The analysis culminates with the calculation of globally distributed column ozone during the major warming, showing quantitatively how transport of low-latitude air to the polar region in the middle stratosphere led to the diminished ozone hole in 2002.

Breakup of the polar stratospheric vortex in the Northern Hemisphere is an event that is known to be predictable for up to a week or so ahead. This is illustrated using data from the 45-yr ECMWF Re-Analysis (ERA-40) for the sudden warmings of January 1958 and February 1979 and operational ECMWF data for February 2003. It is then shown that a similar level of skill was achieved in operational forecasts for the split of the southern stratospheric vortex in late September 2002. The highly unusual flow conditions nevertheless exposed a computational instability of the forecast model. Analyses and forecasts from reruns using improved versions of the forecasting system are presented. Isentropic maps of potential vorticity and specific humidity provide striking pictures of the advective processes at work. Forecasts as well as analyses are shown to be in good agreement with radiosonde measurements of the temperature changes associated with vortex movement, distortion, and breakup during August and September. Forecasts from 17 September onward capture the remarkable temperature rise of about 60[degrees]C recorded at 20 hPa by the Halley radiosonde station as the vortex split. Objective forecast verification and data denial experiments are used to characterize the performance of the observing and data assimilation systems and to infer overall forecast, analysis, and observation accuracy. The observations and analyses from 1957 onward in the ERA-40 archive confirm the extreme nature of the 2002 event. Secondary vortex development by barotropic instability is also discussed; in analyses for early October 2002, the process is active in the breakup of the weaker of the two vortices formed by the late-September split.

This study examines the temporal evolution of the tropospheric circulation following large-amplitude variations in the strength of the Southern Hemisphere (SH) stratospheric polar vortex in data from 1979 to 2001 and following the SH sudden stratospheric warming of 2002. In both cases, anomalies in the strength of the SH stratospheric polar vortex precede similarly signed anomalies in the tropospheric circulation that persist for more than 2 months. The SH tropospheric circulation anomalies reflect a bias in the polarity of the SH annular mode (SAM), a large-scale pattern of climate variability characterized by fluctuations in the strength of the SH circumpolar flow. Consistent with the climate impacts of the SAM, variations in the stratospheric polar vortex are also followed by coherent changes in surface temperatures throughout much of Antarctica. The results add to a growing body of evidence that suggests that stratospheric variability plays an important role in driving climate variability at Earth's surface on a range of time scales.

The conditions that lead to the major warming over Antarctica in late September 2002 are examined. In many respects, the warming resembled wave-2 warmings seen in the Northern Hemisphere; the winter cyclonic circulation was split into two smaller cyclones by a large amplitude planetary wave disturbance that appeared to propagate upward from the troposphere. However, in addition to this classic warming mechanism, distinctive stratospheric vacillations occurred throughout the preceding winter months. These vacillations in wave amplitude, Eliassen-Palm fluxes, and zonal-mean zonal winds are examined. By comparison with a numerical model experiment, it is shown that the vacillation is accompanied by a systematic weakening of the westerly winds over the season. This preconditions the Antarctic circulation, and it is argued that it allows anomalously strong vertical propagation of planetary waves from the troposphere into the stratosphere. By contrast, a survey of previous winters shows that stratospheric westerlies usually vary much more gradually, with vacillations only occurring for short periods of time, if at all, in a given winter. Similar vacillations in a numerical model of the stratosphere only occur if the forcing amplitude is above a certain value. However, the level of winter-mean wave activity entering the stratosphere during 2002 is not unprecedented, and there is still some uncertainty over the cause of the onset and persistence of the vacillation and, ultimately, the major warming.

The Southern Hemisphere (SH) stratospheric winter of 2002 was the most unusual winter yet observed in the SH climate record. Temperatures near the edge of the Antarctic polar vortex were considerably warmer than normal over the entire course of the winter. The polar night jet was considerably weaker than normal and was displaced more poleward than has been observed in previous winters. These record high temperatures and weak jet resulted from a series of wave events that took place over the course of the winter. The propagation of these wave events from the troposphere is diagnosed from time series of Eliassen-Palm flux vectors and autoregression time series. Strong levels of planetary waves were observed in the midlatitude lower troposphere. The combinations of strong tropospheric waves with a low index of refraction at the tropopause resulted in the large stratospheric wave forcing. The wave events tended to occur irregularly over the course of the winter, and the cumulative effect of these waves was to precondition the polar night jet for the extremely large wave event of 22 September. This large wave event resulted in the first ever observed major stratospheric warming in the SH and split the Antarctic ozone hole. The combined effect of all of the 2002 winter wave events resulted in the smallest ozone hole observed since 1988. The sequence of stratospheric wave events was also found to be strongly associated with unusually strong levels of wave 1 in the SH tropospheric subtropics.

The vertical mixing of tracers in the stratosphere is mainly due to patches of three-dimensional turbulence. which are highly intermittent in time and space. A simple heuristic model of this form of mixing is developed and employed to examine the effect of small-scale mixing on passive stratospheric tracers. The model is based on random-walk ideas, and it leads to an analog of the usual advection-diffusion equation in which the diffusion operator is replaced by a convolution operator taking the intermittency of the mixing into account. In its simplest form, this operator is defined by two parameters: these are estimated from midlatitude lower-stratospheric balloon data using a stochastic model of turbulent patches. The behavior of tracer distributions in some idealized flows shows how intermittency makes mixing less effective in damping the small-scale tracer fluctuations that arise through differential advection. This has consequences for stratospheric tracer distributions, which are demonstrated using numerical simulations based on observed stratospheric winds. Specifically, the new model of mixing leads to a horizontal tracer spectrum that is shallower, and closer to a k e power law, than the spectrum obtained with a diffusive parameterization of mixing. The horizontal scale below which intermittent mixing differs significantly from diffusion is estimated to be 15 km or so: remarkably, this coincides with the dissipative scale below which dissipation by small-scale mixing is crucial for tracer evolution.

The combined effects of advection and diffusion on the equilibrium spatial structure of a tracer whose spatial variation is maintained by a large-scale forcing are considered. Motivated by the lower stratosphere, the flow is taken to be large-scale, time-dependent, and purely horizontal but varying in the vertical, with the vertical shear much larger than horizontal velocity gradients. As a result, the ratio [alpha] between horizontal and vertical tracer scales is large. (For the lower stratospheric surf zone [alpha] has been shown to be about 250.) The diffusion parameterizes the mixing effects of small-scale processes. The three space dimensions and the large range between the forcing scale and the diffusive scale mean that direct numerical simulation would be prohibitively expensive for this problem. Instead, an ensemble approach is used that takes advantage of the separation between the large scale of the flow and the small scale of the tracer distribution. This approach, which has previously been used in theoretical investigations of two-dimensional flows, provides an efficient technique to derive statistical properties of the tracer distributions such as horizontal-wavenumber spectrum. First, the authors consider random-strain models in which the velocity gradient experienced by a fluid parcel is modeled by a random process. The results show the expected [k.sup.-1] Batchelor spectrum at large scales, with a deviation from this form at a scale that is larger by a factor [alpha] than the diffusive scale found in the absence of vertical shear. This effect may be crudely captured by replacing the diffusivity [kappa] by an 'equivalent diffusivity' [[alpha].sup.2][kappa], but the diffusive dissipation is then substantially overestimated, and the spectrum at large k is too steep. This may be attributed to the failure of the equivalent diffusivity to capture the variability of the vertical shear. The technique is then applied to lower-stratospheric velocity fields. For realistic values of the diffusivity [kappa], the spectrum is found to be affected by diffusion at surprisingly large scales. For the value [kappa] ~ [10.sup.-2] [m.sup.2] [s.sup.-1] suggested in several recent papers, the diffusion is sufficiently strong that there is no clear [k.sup.-1] regime, consistent with observations. The spectrum is then relatively well approximated by the observed [k.sup.2] power law in the range 20-200 km, but significantly steeper at smaller scales. For the molecular value [kappa] = [10.sup.-4] [m.sup.2] [s.sup.-1], in contrast, an unrealistic [k.sup.-1] regime appears.

Column ozone and satellite-derived temperature records with lengths >20 yr are consistent with the existence of a long-term, quasi-decadal oscillation (QDO) of the tropical lower stratosphere. Using a one-dimensional model for the quasi-biennial oscillation (QBO) of ozone and temperature, it is found that decadal variability of the QBO can account for, at most, only a minor fraction of the tropical lower-stratospheric QDO. One additional source of long-term variability in the Tropics is extratropical wave forcing, which is an important driver of the Brewer-Dobson circulation. To investigate possible long-term variability of extratropical wave forcing, daily and monthly mean meridional eddy heat fluxes are calculated at a series of lower-stratospheric pressure levels over a 23-yr period using National Centers for Environmental Prediction (NCEP) reanalysis data. A decadal variation of the low-pass-filtered extratropical eddy heat flux is present in the Northern Hemisphere with an amplitude that increases with increasing altitude. In the extratropical Southern Hemisphere, a decadal variation is also present but is less regular, possibly owing to reduced radiosonde data coverage. A simplified model of the contribution of extratropical wave forcing to long-term variations in tropical lower-stratospheric ozone and temperature is then formulated based on the ozone chemical continuity and thermodynamic energy equations. Using this model together with empirically derived regression relationships between short-term changes in extratropical eddy heat flux and tendencies in both tropical column ozone and lower-stratospheric temperature, it is found that decadal variations of extratropical wave forcing in both hemispheres may be sufficient to explain much of the amplitude and the phase of the observed QDO of the tropical lower stratosphere.

Ertel's potential vorticity P is in widespread use as a diagnostic of dynamical processes in the stratosphere. For a variety of applications, however, the exponential increase of P with altitude is problematic. For this reason, Lait proposed a modified potential vorticity [[PI].sub.L], where a physically meaningful scaling is introduced that removes much of the altitude dependence of P. Here a generalized form of [[PI].sub.L] is proposed by introducing an additional degree of freedom in the scaling. This generalized modified potential vorticity [[PI].sub.g] possesses the same conservation properties as [[PI].sub.L] itself and as the classic potential vorticity P but can be adjusted more closely to the specific situation under investigation. Comparison, over a large altitude range in the stratosphere, of fields of [[PI].sub.g] with dynamical measures of the polar vortex edge and with observations of the long-lived trace gas [N.sub.2]O shows that [[PI].sub.g] constitutes a more intuitively interpretable quantity than [[PI].sub.L].

In the stratosphere, chemical tracers are drawn systematically from the equator to the pole. This observed Brewer-Dobson circulation is driven by wave drag, which in the stratosphere arises mainly from the breaking and dissipation of planetary-scale Rossby waves. While the overall sense of the circulation follows from fundamental physical principles, a quantitative theoretical understanding of the connection between wave drag and Lagrangian transport is limited to linear, small-amplitude waves. However, planetary waves in the stratosphere generally grow to a large amplitude and break in a strongly nonlinear fashion. This paper addresses the connection between stratospheric wave drag and Lagrangian transport in the presence of strong nonlinearity, using a mechanistic three-dimensional primitive equations model together with offline particle advection. Attention is deliberately focused on a weak forcing regime, such that sudden warmings do not occur and a quasi-steady state is reached, in order to examine this question in the cleanest possible context. Wave drag is directly linked to the transformed Eulerian mean (TEM) circulation, which is often used as a surrogate for mean Lagrangian motion. The results show that the correspondence between the TEM and mean Lagrangian velocities is quantitatively excellent in regions of linear, nonbreaking waves (i.e., outside the surf zone), where streamlines are not closed. Within the surf zone, where streamlines are closed and meridional particle displacements are large, the agreement between the vertical components of the two velocity fields is still remarkably good, especially wherever particle paths are coherent so that diabatic dispersion is minimized. However, in this region the meridional mean Lagrangian velocity bears little relation to the meridional TEM velocity, and reflects more the kinematics of mixing within and across the edges of the surf zone. The results from the mechanistic model are compared with those from the Canadian Middle Atmosphere Model to test the robustness of the conclusions.

Gravity waves generated by convective heating are widely believed to have vertical wavelengths approximately twice the depth of the heating. The frequency, horizontal, and vertical wavelengths of gravity waves are, however, mutually related through the gravity wave dispersion relationship. For forcing of a given frequency, waves of vertical wavelength of twice the depth of the heating will be efficiently excited only if the horizontal forcing projects significantly onto horizontal scales compatible with the vertical-to-horizontal wavenumber ratio given by the dispersion relationship. The preferred vertical wavelength depends on a nondimensional parameter relating the frequency, horizontal, and vertical scales of the forcing. For the high-frequency waves that dominate the momentum flux in the upper stratosphere and mesosphere, the maximum vertical flux of horizontal momentum generally occurs for waves with vertical wavelengths much greater than twice the depth of the heating.

The impact of a parameterized spectrum of gravity waves on the simulation of the stratosphere in the Met Office Unified Model (UM) is investigated. In the extratropical mesosphere, the gravity wave forcing acts against the mean zonal wind and it dominates over the resolved wave forcing. In the extratropical stratosphere, the gravity wave forcing gives a small acceleration in the direction of the mean zonal wind. Both summer and winter stratospheric jets have improved maximum strength and tilt with height when the parameterized gravity wave forcing is included, although the southern winter jet is still more vertically aligned than in observational analyses. The timing of the seasonal breakdown of the southern winter vortex is also improved by the addition of gravity wave forcing. In the Tropics, the most obvious impact is that the model reproduces the quasi-biennial oscillation (QBO) with a realistic mean and range of periods. It also reproduces most of the observed asymmetries between the easterly and westerly phases of the oscillation. The sensitivity of this modeled QBO to horizontal diffusion parameters is investigated and it is shown that diffusion set to damp out grid-length disturbances can also attenuate the QBO due to its long period, particularly in the narrower westerly phase. (Manuscript received 20 June 2001, in final form 24 September 2001)

A fine calibration of the depolarization ratio is required for a detailed interpretation of lidar-observed polar stratospheric clouds. We propose a procedure for analyzing data by using atmospheric depolarization lidar. The method is based on a plot of [[delta].sub.T] versus (1 - [R.sub.T.sup.-1]), where [[delta].sub.T] is the total depolarization ratio and [R.sub.T] is the total backscattering ratio. Assuming that there are only spherical particles in some altitude ranges of the lidar data, the characteristics of the plot of [[delta].sub.T] versus (1 - [R.sub.T.sup.-1]) lead to a simple but effective calibration method for [[delta].sub.T]. Additionally, the depolarization of air molecules [[delta].sub.m] can be determined in the process of [[delta].sub.T] calibration. We compared determined values with theoretically calculated values for the depolarization of air to test the proposed method. The [[delta].sub.m] value was calculated from the lidar data acquired at Ny-[Angstrom]lesund (79 [degrees] N, 12 [degrees] E), Svalbard in winter 1994--1995. When only sulfate aerosols were present on 4 December 1994, [[delta].sub.m] was 0.46 [+ or -] 0.35%. When the particles consisted of sulfate aerosols and spherical particles of polar stratospheric clouds on 4 January 1995, [[delta].sub.m] was 0.45 [+ or -] 0.07%. Both [[delta].sub.m] values were in good agreement with the theoretically calculated value, 0.50 [+ or -] 0.03%. OCIS codes: 010.1100, 010.1310, 010.3640.

The situ observations were used to evaluate the primary mechanisms that control NOx-HNO3 exchange and to understand their control over the partitioning between NO2 and HNO3 in regions of continuous sunlight. The steady-state description of NOx-HNO3 exchange reveals the significant influence of the tight correlation between the photolysis rate of HNO3 and [OH] established in situ measurements throughout the lower stratosphere.

The cause of the largely natural total ozone decline in the stratosphere from its spring maximum to fall minimum in the northern hemisphere is addressed and shown that this is mainly due to NO(sub x)-catalyzed ozone destruction. An interesting result of the analysis is that, rather irrespective of the starting values of total ozone in early spring, chemical ozone loss yields about the same minimum total ozone amounts in early fall.

The extensive measurement campaigns by the NASA ER-2 research aircraft have obtained a nearly pole-to-pole database of the species that control HOx (OH + HO2) chemistry. The measurements in the lower stratosphere shows a remarkably tight correlation of OH concentration with the solar zenith angle (SZA).

The gas-phase reactions between HOx and NOx are used in determining the chemical composition of both the troposphere and stratosphere. In the case of OH + NO2, there are almost certainly two intermediates, HOONO and HONO2, but no evidence for the stable HOONO formation is seen at 230 K.

An investigation into the infrared absorptions of the (HC1)*(H2SO4) complex was carried out by placing a gaseous mixture of AR/HC1/H2SO4 on a cold tip.