upper troposphere

Saturn inhabits a dynamical regime of rapidly rotating, internally heated atmospheres similar to Jupiter. Zonal winds have remained fairly steady since the time of Voyager except in the equatorial zone and slightly stronger winds occur at deeper levels. Eddies supply energy to the jets at a rate somewhat less than on Jupiter and mix potential vorticity near westward jets. Convective clouds exist preferentially in cyclonic shear regions as on Jupiter but also near jets, including major outbreaks near 35°S associated with Saturn electrostatic discharges, and in sporadic giant equatorial storms perhaps generated from frequent events at depth. The implied meridional circulation at and below the visible cloud tops consists of upwelling (downwelling) at cyclonic (anti-cyclonic) shear latitudes. Thermal winds decay upward above the clouds, implying a reversal of the circulation there. Warm-core vortices with associated cyclonic circulations exist at both poles, including surrounding thick high clouds at the south pole. Disequilibrium gas concentrations in the tropical upper troposphere imply rising motion there. The radiativeconvective boundary and tropopause occur at higher pressure in the southern (summer) hemisphere due to greater penetration of solar heating there. A temperature "knee" of warm air below the tropopause, perhaps due to haze heating, is stronger south of the equator as well. Saturn's south polar stratosphere is warmer than predicted by radiative models and enhanced in ethane, suggesting subsidence-driven adiabatic warming there. Recent modeling advances suggest that shallow weather layer theories of jet pumping may be viable if water condensation is the source of energy input driving the flow, and that deep convective cylinder models with a sufficiently large tangent cylinder radius can reproduce observed flow features as well.

The methodology and validation of upper tropospheric humidity (UTH) measurements by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) are described. The MLS instrument was not specifically designed to measure UTH, but its measurement is achieved by modeling the radiance signal from a window channel as the instrument field of view is scanned through the troposphere. UTH is retrieved as a piecewise-linear function in relative humidity with respect to ice (% RHi) with breakpoints at 147,215, 316, and 464 hPa. MLS version 4.9 is believed to be the most accurate version to date; its estimated global-averaged accuracy(precision) is 23(21), 22(10), 22(8), and 50(19) %RHi at 147, 215, 316, and 464, hPa respectively. The validation of UTH is established by its consistency with (1) climatological fields, (2) coincident comparisons with in situ Vaisala RS80 balloon sondes, frostpoint hygrometers and Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft measurements, (3) cirrus observations, and (4) meteorological dynamics and assimilation fields. MLS climatological UTH is morphologically consistent with Stratospheric Aerosol and Gas Experiment II and Vaisala zonal climatologies. Comparisons with coincident in situ data show a wide range of agreement. Relative to the other in situ instruments, V4.9 MLS humidities agree on average within 11% at 147 hPa, 3-36% dry at 215 hPa, and 14-39% dry at 316 and 464 hPa. The standard deviation of the individual comparisons about the mean between MLS UTH and the other techniques is approximately 25 %RHi at all heights. Humidity measurements in cirrus are compared with UARS Cryogenic Limb Array Etalon Spectrometer (CLAES) extinction measurements and an MLS cirrus detection algorithm. CLAES extinction measurements from 316 to 147 hPa which indicate the presence of cirrus correspond well with MLS UTH measurements greater than •100 %RHi. Global MLS UTH distributions appear consistent with those expected from upper tropospheric dynamics and with the Goddard Data Assimilation Office humidity fields.

A model for the accelerated calculation of clear sky fluxes based on the line-by-line radiance model FASCODE has been developed and applied to the calculation of cooling rates for atmospheric water vapor. The model achieves computational accuracies for the longwave upwelling ...

Heavy rainfall events in austral summer are responsible for almost all the natural disasters in Southeast Brazil. They are mostly associated with two types of atmospheric perturbations: Cold Front (53%) and the South Atlantic Convergence Zone (47%). The important question of what synoptic characteristics distinguish a heavy rainfall event (HRE) from a normal rainfall event (NRE) is addressed in this study. Here, the evolutions of such characteristics are identified through the anomalies with respect to climatology of the composite fields of atmospheric variables. The anomalies associated with HRE are significantly more intense than those associated with NRE in all fundamental atmospheric variables such as outgoing long-wave radiation, sea-level pressure, 500-hPa geopotential, lower and upper tropospheric winds. The moisture flux convergence over Southeast Brazil in the HRE composites is 60% larger than in the NRE composites. The energetics calculations for the HRE that occurred in the beginning of February 1988 strongly suggest that the barotropic instability played an important role in the intensification of the perturbation. These results, especially the intensities of the wind, pressure anomalies, and the moisture convergence are useful for the meteorologists of the Southeast Brazil for forecasting heavy precipitation.

A case study of new particle formation in the region downwind of a mesoscale convective system stretching across much of the central United States is presented. Airborne measurements were made of condensation nuclei (CN), cloud particle surface area, water vapor, and other gases. CN concentrations were greatly enhanced above and downwind of the cirrus anvil, with maximum concentrations of 45,000 per standard cm 3. Volatility and electron microscope measurements indicated that most of the particles were likely to be small sulfate particles. The enhancement extended over at least a 600-km region. Multivariate statistical analysis revealed that high CN concentrations were associated with surface tracers, as well as convective elements. Convection apparently brings gas-phase particle precursors from the surface to the storm outflow region, where particle nucleation is favored by the extremely low temperatures. Simple calculations showed that deep convective systems may contribute to a substantial portion of the background aerosol in the upper troposphere at midlatitudes.

Processes occurring in the tropical upper troposphere (UT), the Tropical Transition Layer (TTL), and the lower stratosphere (LS) are of importance for the global climate, for stratospheric dynamics and air chemistry, and for their influence on the global distribution of water vapour, trace gases and aerosols. In this contribution we present aerosol and trace gas (in-situ) measurements from the tropical UT/LS over Southern Brazil, Northern Australia, and West Africa. The instruments were operated on board of the Russian high altitude research aircraft M-55 "Geophysica" and the DLR Falcon-20 during the campaigns TROCCI

Version 3 of the Atmospheric Trace Molecule Spectroscopy ͑ATMOS͒ experiment data set for some 30 trace and minor gas profiles is available. From the IR solar-absorption spectra measured during four Space Shuttle missions ͑in 1985, 1992, 1993, and 1994͒, profiles from more than 350 occultations were retrieved from the upper troposphere to the lower mesosphere. Previous results were unreliable for tropospheric retrievals, but with a new global-fitting algorithm profiles are reliably returned down to altitudes as low as 6.5 km ͑clouds permitting͒ and include notably improved retrievals of H 2 O, CO, and other species. Results for stratospheric water are more consistent across the ATMOS spectral filters and do not indicate a net consumption of H 2 in the upper stratosphere. A new sulfuric-acid aerosol product is described. An overview of ATMOS Version 3 processing is presented with a discussion of estimated uncertainties. Differences between these Version 3 and previously reported Version 2 ATMOS results are discussed. Retrievals are available at http:͞͞atmos.jpl.nasa.gov͞atmos.

Thumbnail link to Figure 1 Figure 1. Map showing Europe and the area of the airborne measurements (within the circle). The solid square indicates the location of the DLR operation center (Oberpfaffenhofen near Munich). G, Germany; F, France; A, Austria; I, ...

Gas phase HCl was measured from the marine boundary layer (MBL) to the lower stratosphere from the NASA DC-8 during five science flights (41 h) of the Intercontinental Chemical Transport Experiment-Phase B (INTEX-B) field campaign. In the upper troposphere/lower stratosphere (UT/LS, 8-12 km) HCl was observed to range from a few tens to 100 pptv due to stratospheric influence with a background tropospheric level of less than 2 pptv. In the 8-12 km altitude range, a simple analysis of the O 3 /HCl correlation shows that pure stratospheric and mixed tropospheric/stratospheric air masses were encountered 30% and 15% of the time, respectively. In the mid troposphere (4-8 km) HCl levels were usually below 2 pptv except for a few cases of stratospheric influence and were much lower than reported in previous work. These data indicate that background levels of HCl in the mid and upper troposphere are very low and confirm its use in these regions as a tracer of stratospheric ozone. However, a case study suggests that HCl may be produced in the mid troposphere by the dechlorination of dust aerosols. In the remote marine boundary layer HCl levels were consistently above 20 pptv (up to 140 pptv) and strongly correlated with HNO 3. Cl atom levels were estimated from the background level of HCl in the MBL. This analysis suggests a Cl concentration of ∼3×10 3 atoms cm −3 , which corresponds to the lower range of previous studies. Finally, the observed HCl levels are compared to predictions by the Real-time Air Quality Modeling System (RAQMS) to assess its ability to characterize the impact of stratospheric transport on the upper troposphere.

One stratospheric carbonyl sulfide (COS) vertical profile in the Arctic polar vortex has been retrieved from air samples collected by the MPAE balloon-borne cryogenic sampler on January 18, 1992, at Kiruna, Sweden. The measurements were made in the altitude range 7.5-28.5 km. The upper tropospheric volume mixing ratios of COS were 355 4-60 pptv. The stratospheric profile shows that COS is subject to considerable subsidence this time of the year. The lowest VMRs were encountered at around 20 km altitude, while above that height a COS increase was observed. A possible explanation could be reversible .uptake of COS by frozen sulfuric acid aerosols. KOURTIDIS ET AL.' CARBONYL SULFIDE IN THE POLAR VORTEX KOURTIDIS ET AL' CARBONYL SULFIDE IN THE POLAR VORTEX Chin, M., and D. D. Davis, Global sources and sinks of OCS and CS2 and their distributions, Global Biogeochernical Cycles, 7, 321-337, 1993. Crutzen, P. J., The possible importance of CSO for the sulfate layer of the stratosphere, Geophys. Res. Left., 3, 73-76, 1976. Fabian, P., Atmospheric sampling, Adv. Space Res., 1, 17-27, 1981.

We evaluate black carbon (BC) model predictions from the AeroCom model intercomparison project by considering the diversity among year 2000 model simulations and comparing model predictions with available measurements. These model-measurement intercomparisons include BC surface and aircraft concentrations, aerosol absorption optical depth (AAOD) retrievals from AERONET and Ozone Monitoring Instrument (OMI) and BC column estimations based on AERONET. In regions other than Asia, most models are biased high compared to surface concentration measurements. However compared with (column) AAOD or BC burden retreivals, the models are generally biased low. The average ratio of model to retrieved AAOD is less than 0.7 in South American and 0.6 in African biomass burning regions; both of these regions lack surface concentration measurements. In Asia the average model to observed ratio is 0.7 for AAOD and 0.5 for BC surface concentrations. Compared with aircraft measurements over the Americas at latitudes between 0 and 50N, the average model is a factor of 8 larger than observed, and most models exceed the measured BC standard deviation in the mid to upper troposphere. At higher latitudes the average model to aircraft BC ratio is 0.4 and models underestimate the observed BC loading in the lower and middle troposphere associated with springtime Arctic haze. Low model bias for AAOD but overestimation of surface and upper atmospheric BC concentrations at lower latitudes suggests that most models are underestimating BC absorption and should improve estimates for refractive index, particle size, and optical effects of BC coating. Retrieval uncertainties and/or differences with model diagnostic treatment may also contribute to the model-measurement disparity. Largest AeroCom model diversity occurred in northern Eurasia and the remote Arctic, regions influenced by anthropogenic sources. Changing emissions, aging, removal, or optical properties within a single model generated a smaller change in model predictions than the range represented by the full set of AeroCom models. Upper tropospheric concentrations of BC mass from the aircraft measurements are suggested to provide a unique new benchmark to test scavenging and vertical dispersion of BC in global models.

The meteorological and photochemical nature of the South Atlantic Ocean tropospheric column ozone maximum is examined by analyzing the Geophysical Fluid Dynamics Laboratory (GFDL) Global Chemical Transport Model (GCTM) simulation during the Southern Hemisphere late winter. An ozone maximum of greater than 40 Dobson units is produced by the GCTM over the South Atlantic Ocean. The model is evaluated against available meteorological and ozone data and found to be in good qualitative agreement with observed wind fields, satellite measurements of tropospheric column ozone, tropospheric column ozone produced from ozonesonde data, and vertical profiles from ozonesondes. A quantitative analysis is performed over an area of the South Atlantic Ocean essentially devoid of local NO x sources and for a time, September, when the regional tropospheric ozone mass is at a maximum. The tropospheric mass of reactive nitrogen transported into the region is a result of source contributions from lightning (49%), biomass burning (36%), and 15% from the remaining NO x sources (fossil fuel plus biogenic plus stratosphere plus aircraft). Even with the removal of biomass burning NO x from the ozone photochemical system, the GCTM still produces an oceanic tropospheric column ozone maximum, suggesting the ozone phenomenon existed before agricultural burning by humans. The structure of clean air CO/CH 4 net chemistry consists of ozone production in the upper troposphere (+2.2 Tg/month), weak destruction in the middle troposphere (-1.8 Tg/month), and strong destruction in the lower troposphere (-4.2 Tg/month). Through photochemistry, the two largest NO x sources help control the vertical profile of ozone with lightning dominating in the upper troposphere, while the relative importance of biomass burning is virtually constant throughout the troposphere. A mass budget analysis of ozone over the tropospheric South Atlantic Ocean reveals that net mass transport of ozone into the domain is nearly balanced by net chemical destruction and deposition and that the mass transport into and out of the region are comparable to the chemical production and destruction terms. The three-dimensional circulation governing the ozone vertical structure is one of horizontal mass convergence and net chemical production supplying ozone to the upper troposphere which is fluxed downward by subsidence and removed in the boundary layer by net chemical destruction, deposition, and horizontal mass divergence. 17,393 17,394 MOXIM AND LEVY: SOUTH ATLANTIC OCEAN TROPOSPHERIC OZONE MAXIMUM ucts was indicated by the work of Andreae [1983] in which aerosols of the type dominated by burning of biomass were detected off the coast of Brazil. Additionally, Logan and Kirchhoff [1986], speculated that the high concentrations of ozone in the upper troposphere over Natal are the result of the mixing of ozone-rich boundary layer air over Brazil to the free troposphere where subsequent westerlies above 400 mbar provide transport to Natal. The real surprise as to the extent of the influence of biomass burning on the SAO region was revealed by the pioneering work on the distribution of tropospheric column ozone from satellite data (referred to as the tropospheric ozone residual (TOR)) [Fishman et al., 1990, 1991]. This technique allowed for the first time an examination of horizontal tropospheric gradients over much of the globe. In particular, Fishman's analysis detected a large ozone maximum over the SAO during the austral spring with a closed contour of greater than 40 Dobson units (DUs) over the ocean isolated from the continental biomass burning regions of both Africa and South America. The analysis clearly indicated that an interaction of atmospheric transport of ozone and its precursors along with in situ photochemistry was somehow focused in this remote region. This finding concentrated interest in the region and eventually led to an intensive field mission, the Southern Tropical Atlantic Region Experiment (STARE), consisting of two campaigns; Transport and Atmospheric Chemistry Near the Equator-Atlantic (TRACE-A) and Southern African Fire-Atmosphere Research Initiative (SAFARI). It was conducted in September-October 1992 and provided an extensive data set from which the meteorology and atmospheric chemistry of the tropical SAO could be explored [Andreae et al., 1996]. During the early 1990s the first attempts to examine the SAO ozone maximum utilizing numerical models were performed. To investigate the role of ozone transport, Krishnamurti et al. [1993] used the Florida State University global spectral model to simulate the evolution of tropospheric ozone during October. Starting from a height-dependent, zonally symmetric ozone distribution and neglecting photochemistry, they found that the model dynamics produced tropospheric column ozone patterns somewhat similar to the observed, suggesting that general synoptic transport tends to accumulate ozone off the west coast of southern Africa. In a later study, Krishnamurti et al. [ 1996] further emphasized the role transport plays in accumulating ozone and its precursors in the SAO by demonstrating that a "dynamics alone" 1-week model integration produced a correlation coefficient of roughly 0.8 with observational total atmospheric ozone from the Total Ozone Mapping Spectrometer (TOMS). Richardson [ 1994] and Olson [ 1996] also examined ozone transport to the SAO using the Geophysical Fluid Dynamics Laboratory (GFDL) global transport model. By constraining the inert tracer (no chemistry) to reproduce observed seasonal ozone increases over continental burning regions, integrating the model over an entire year, and comparing with available satellite residuals, it was demonstrated that while the model could reasonably reproduce the shape of the seasonal cycle, it was able to account for no more than 25% of the seasonal increase over the SAO. Also, utilizing nearby ozonesonde data as a surrogate for the vertical distribution of the tropospheric column ozone and comparing with the simulated ozone profile, it was found that the largest model deficits occurred in the upper troposphere. Assuming that the underestimate resulted from the lack of net photochemical production of ozone, the results showed that a net source of-5 ppbv per day in the upper troposphere over the SAO was needed to make up the deficit, which was not unreasonable when compared to current estimates from observations and models [e.g.,

We have developed a global three-dimensional chemical transport model called Model of Ozone and Related Chemical Tracers (MOZART), version 2. This model, which will be made available to the community, is built on the framework of the National Center for Atmospheric Research (NCAR) Model of Atmospheric Transport and Chemistry (MATCH) and can easily be driven with various meteorological inputs and model resolutions. In this work, we describe the standard configuration of the model, in which the model is driven by meteorological inputs every 3 hours from the middle atmosphere version of the NCAR Community Climate Model (MACCM3) and uses a 20-min time step and a horizontal resolution of 2.8°latitude  2.8°longitude with 34 vertical levels extending up to approximately 40 km. The model includes a detailed chemistry scheme for tropospheric ozone, nitrogen oxides, and hydrocarbon chemistry, with 63 chemical species. Tracer advection is performed using a flux-form semi-Lagrangian scheme with a pressure fixer. Subgrid-scale convective and boundary layer parameterizations are included in the model. Surface emissions include sources from fossil fuel combustion, biofuel and biomass burning, biogenic and soil emissions, and oceanic emissions. Parameterizations of dry and wet deposition are included. Stratospheric concentrations of several long-lived species (including ozone) are constrained by relaxation toward climatological values. The distribution of tropospheric ozone is well simulated in the model, including seasonality and horizontal and vertical gradients. However, the model tends to overestimate ozone near the tropopause at high northern latitudes. Concentrations of nitrogen oxides (NO x) and nitric acid (HNO 3) agree well with observed values, but peroxyacetylnitrate (PAN) is overestimated by the model in the upper troposphere at several locations. Carbon monoxide (CO) is simulated well at most locations, but the seasonal cycle is underestimated at some sites in the Northern Hemisphere. We find that in situ photochemical production and loss dominate the tropospheric ozone budget, over input from the stratosphere and dry deposition. Approximately 75% of the tropospheric production and loss of ozone occurs within the tropics, with large net production in the tropical upper troposphere. Tropospheric production and loss of ozone are three to four times greater in the northern extratropics than the southern extratropics. The global sources of CO consist of photochemical production (55%) and direct emissions (45%). The tropics dominate the chemistry of CO, accounting for about 75% of the tropospheric production and loss. The global budgets of tropospheric ozone and CO are generally consistent with the range found in recent studies. The lifetime of methane (9.5 years) and methylchloroform (5.7 years) versus oxidation by tropospheric hydroxyl radical (OH), two useful measures of the global abundance of OH, agree well with recent estimates. Concentrations of nonmethane hydrocarbons and oxygenated intermediates (carbonyls and peroxides) generally agree

Quantitative models of deep convection play a central role to improve understanding of weather, trace gas distributions, and radiative regime of the upper troposphere. Cloud-resolving models of deep convection are useful tools to simulate relevant processes. Observations of tracers such as CO 2 can provide critical constraints on mass transport within these models. However, such measurements do not span the entire four-dimensional domain in space and time. We introduce a new method to improve tracer constraints on such models, combining a Receptor-Oriented Atmospheric Modeling (ROAM) framework with airborne and ground-based CO 2 data. We illustrate the application of ROAM in generating initial and boundary conditions of CO 2 for cloud-resolving model simulations, for a case study in the CRYSTAL-FACE campaign. Observations and model results were compared for CO 2 profiles from the surface up to 16 km, inside and outside of a deep convective cloud. ROAM generated concentration fields that agreed within 0.5 ppm (1s) of observations outside the cloud. When ROAM-derived initial and boundary CO 2 concentrations were fed to a state-of-the-art cloud-resolving model (DHARMA), the combined modeling system successfully reproduced observed concentration differences, 0.2-0.8 ppm, between in-cloud and out-of-cloud air at 9 $ 14 km. Results suggest that $25% of air at 14 km was lifted through the convective system from the PBL. This study demonstrates the potential of the receptor-oriented framework to constrain redistribution of air within convective systems using CO 2 , and it points to the need for better coordinated tracer measurements in future field missions.

The radiative effects of upper tropospheric (UT) clouds observed by CloudSat and Aura MLS during June-July-August 2008 are examined and contrasted. We find that the UT cloud occurrence frequency observed by MLS is more than CloudSat by 4-10% in the tropical average and by 40$60% near the tropopause in the deep convective regions. The clouds detected by MLS but missed by CloudSat (denoted as TCC) typically have visible optical thickness less than 0.2. TCC produce a tropical-mean net warming of 3.5 W/m 2 at the top-of-atmosphere and net cooling of 1.2 W/m 2 at the surface. They induce a net radiative heating in the UT. Their heating rate at 200 hPa is $0.35 K/day in the tropical-mean and $0.8 K/day over South Asia, which is about 3-4 times the clear-sky radiative heating rate. Hence, they are potentially important in affecting the mass transport rates from the troposphere to the stratosphere.

Three semi-permanent cloud bands exist in the Southern Hemisphere extending southeastward from the equator, through the tropics, and into the subtropics. The most prominent of these features occurs in the South Pacific and is referred to as the South Pacific Convergence Zone (SPCZ). Similar bands, with less intensity, exist in the South Indian and Atlantic oceans. We attempt to explain the physical mechanisms that promote the diagonal orientation of the SPCZ and the processes that determine the timescales of its variability. It is argued that the slowly varying sea surface temperature patterns produce upper tropospheric wind fields that vary substantially in longitude. Regions where 200 hPa zonal winds decrease with longitude (i.e., negative zonal stretching deformation, or oU ox\0) reduce the group speed of the eastward propagating synoptic (3-6 day period) Rossby waves and locally increase the wave energy density. Such a region of wave accumulation occurs in the vicinity of the SPCZ, thus providing a physical basis for the diagonal orientation and earlier observations that the zone acts as a ''graveyard'' of propagating synoptic disturbances. In essence, oU ox ¼ 0 demarks the boundary of the graveyard while regions where oU ox\0 denote the graveyard itself. Composites of the life cycles of synoptic waves confirm this hypothesis. From the graveyard hypothesis comes a more general theory accounting for the SPCZ's spatial orientation and its longer term variability influenced by the El Niño-Southern Oscillation (ENSO), or alternatively, the changing background SST associated with different phases of ENSO.

The Earth Observing System (EOS) Microwave Limb Sounder (MLS) aboard the Aura satellite has provided essentially daily global measurements of ozone (O 3) profiles from the upper troposphere to the upper mesosphere since August of 2004. This paper focuses on validation of the MLS stratospheric standard ozone product and its uncertainties, as obtained from the 240 GHz radiometer measurements, with a few results concerning mesospheric ozone. We compare average differences and scatter from matched MLS version 2.2 profiles and coincident ozone profiles from other satellite instruments, as well as from aircraft lidar measurements taken during Aura Validation Experiment (AVE) campaigns. Ozone comparisons are also made between MLS and balloon-borne remote and in situ sensors. We provide a detailed characterization of random and systematic uncertainties for MLS ozone. We typically find better agreement in the comparisons using MLS version 2.2 ozone than the version 1.5 data. The agreement and the MLS uncertainty estimates in the stratosphere are often of the order of 5%, with values closer to 10% (and occasionally 20%) at the lowest stratospheric altitudes, where small positive MLS biases can be found. There is very good agreement in the latitudinal distributions obtained from MLS and from coincident profiles from other satellite instruments, as well as from aircraft lidar data along the MLS track.

The properties of midlatitude cirrus clouds are examined using one year of continuous vertically pointing millimeter-wave cloud radar data collected at the Atmospheric Radiation Measurement Program Southern Great Plains site in Oklahoma. The goal of this analysis is to present the cloud characteristics in a manner that will aid in the evaluation and improvement of cirrus parameterizations in large-scale models. Using a temperature-and radar reflectivity-based definition of cirrus, the occurrence frequency of cirrus, the vertical location and thickness of cirrus layers, and other fundamental statistics are examined. Also the bulk microphysical properties of optically thin cirrus layers that occur in isolation from other cloud layers are examined. During 1997, it is found that cirrus were present 22% of the time, had a mean layer thickness of 2.0 km, and were most likely to occur in the 8.5-10-km height range. On average, the cirrus clouds tended to be found in layers in which the synoptic-scale vertical velocity was weakly ascending. The mean synoptic-scale vertical motion in the upper troposphere as derived from Rapid Update Cycle model output was ϩ0.2 cm s Ϫ1. However, a significant fraction of the layers (33%) were found where the upper-tropospheric large-scale vertical velocity was clearly descending (w Ͻ Ϫ1.5 cm s Ϫ1). Microphysical properties were computed for that subset of cirrus events that were optically thin (infrared emissivity Ͻ 0.85) and occurred with no lower cloud layers. This subset of cirrus had mean values of ice water path, effective radius, and ice crystal concentration of 8 g m Ϫ2 , 35 m, and 100 L Ϫ1 , respectively. Although all the cloud properties demonstrated a high degree of variability during the period considered, the statistics of these properties were fairly steady throughout the annual cycle. Consistent with previous studies, it is found that the cloud microphysical properties appear to be strongly correlated to the cloud layer thickness and mean temperature. Use of these results for parameterization of cirrus properties in large-scale models is discussed.

Seasonal variations of wind in the troposphere are analyzed based on operational rawinsondes at 11 stations over Indonesia for 1992-1999 and the results are compared with NCEP reanalysis. For meridional wind, an annual oscillation caused by north-south shift of a meridional (Hadley-type) circulation is clearly found. Winter-poleward flow of the upper-tropospheric meridional circulation is stronger than summer-poleward flow. The winter (southern) hemispheric cell in northern summer has a larger invasion across the equator (as suggested in the zonal-mean Hadley cell), and weaker meridional flows than the winter (northern) hemispheric cell in northern winter. Along the boundary of twin meridional circulation cells, a zonal (Walker-type) circulation seems to exist, and has easterly (westerly) wind in the

The studies in China on the formation of the summertime subtropical anticyclone on the climate timescale are reviewed. New insights in resent studies are introduced. It is stressed that either in the free atmosphere or in the planetary boundary, the descending arm of the Hadley cell cannot be considered as a mechanism for the formation of the subtropical anticyclone. Then the theories of thermal adaptation of the atmosphere to external thermal forcing and the potential vorticity forcing are developed to understand the formation of the subtropical anticyclone in the three-dimensional domain. Numerical experiments are designed to verify these theories. Results show that in the boreal summer, the formation of the strong South Asian High in the upper troposphere and the subtropical anticyclone over the western Pacific in the middle and lower troposphere is, to a great extent, due to the convective latent heating associated with the Asian monsoon, but affected by orography and the surface sensible heating over the continents. On the other hand, the formation of the subtropical anticyclone at the surface over the northern Pacific and in the upper troposphere over North America is mainly due to the strong surface sensible heating over North America, but affected by radiation cooling over the eastern North Pacific. Moreover, in the real atmosphere such individual thermal forcing is well organized. By considering the different diabatic heating in synthesis, a quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer. A distinct circulation pattern accompanies this heating pattern. The global summer subtropical heating and circulation may be viewed as "mosaics" of such quadruplet heating and circulation patterns respectively. At last, some important issues for further research in understanding and predicting the variations of the subtropical anticyclone are raised.

We have developed a parametrization of Jovian moist convection based on a heat engine model of moist convection. In comparison to other moist convection schemes, this framework allows the computation of the total available convective energy TCAPE and the corresponding mass flux M as dynamic variables from the mean atmospheric state. The effects of this parametrization have been investigated both analytically and numerically. In agreement with previous numerical experiments and observations, the inclusion of moist convection leads to heat and water vapor transport from the water condensation level into higher altitudes. The time development of the modeled convective events was found to be strongly influenced by a rapid reduction of kinetic energy and a subsequent lowering of the cumulus tower's top in response to convective heating. We have tested the sensitivity of the scheme to different variations in the fractional cloud coverage and under the inclusion of external radiative forcing towards a stable/ unstable temperature profile. While the time development of convective events differs in response to these variations, the general moist convective heating and moistening of the upper troposphere was a robust feature observed in all experiments.

The mechanism of troposphere-stratosphere exchange in the tropics was investigated from space-borne observations of the horizontal distributions of troposphericorigin long-lived species, nitrous oxide (N 2 O), methane (CH 4) and carbon monoxide (CO), from 150 to 70 hPa in March-April-May by the ODIN/Sub-Millimeter Radiometer (SMR), the Upper Atmosphere Research Satellite (UARS)/Halogen Occultation Experiment (HALOE) and the TERRA/Measurements Of Pollution In The Troposphere (MOPITT) instruments in 2002-2004, completed by recent observations of the AURA/Microwave Limb Sounder (MLS) instrument during the same season in 2005. The vertical resolution of the satellite measurements ranges from 2 to 4 km. The analysis has been performed on isentropic surfaces: 400 K (lower stratosphere) for all the species and 360 K (upper troposphere) only for CO. At 400 K (and 360 K for CO), all gases show significant longitudinal variations with peak-to-trough values of ∼5-11 ppbv for N 2 O, 0.07-0.13 ppmv for CH 4 , and ∼10 ppbv for CO (∼40 ppbv at 360 K). The maximum amounts are primarily located over Africa and, depending on the species, secondary more or less pronounced maxima are reported above northern South America and SouthEast Asia. The lower stratosphere over the Western Pacific deep convective region where the outgoing longwave radiation is the lowest, the tropopause the highest and the coldest, appears as a region of minimum concentration of tropospheric trace species. The possible impact on trace gas concentration at the tropopause of the inhomogeneous distribution and intensity of the sources, mostly continental, of the horizontal and vertical transports in the troposphere, and of cross-tropopause transport was explored with the MOCAGE Chemistry Transport Model. In the

Convective clouds and thunderstorms redistribute air pollutants vertically, and by altering the chemistry and radiative balance of the upper troposphere, these local actions can have global consequences. To study these effects, measurements of trace gases ozone, Os, carbon monoxide, CO, and odd nitrogen were made aboard the NCAR Sabreliner on 18 flights over the southern Great Plains during June 1985. To demonstrate chemical changes induced by vertical motions in the atmosphere and to facilitate comparison with computer model calculations, these data were categorized according to synoptic flow patterns. Part 1 of this two-part paper details the alternating pulses of polar and maritime air masses that dominate the vertical mixing in this region. In this paper, trace gas measurements are presented as altitude profiles (0-12 km) with statistical distributions of mixing ratios for each species in each flow pattern. The polar flow regime is characterized by northwesterly winds, subsiding air, and convective stability. Concentrations of CO and total odd nitrogen (NOy) are relatively high in the shallow planetary boundary layer (PBL) but decrease rapidly with altitude. Ozone, on the other hand, is uniformly distributed, suggesting limited photochemical production; in fact, nitric oxide, NO, mixing ratios fell below 10 ppt (parts per 10 •2 by volume) in the midtroposphere. The maritime regime is characterized by southerly surface winds, convective instability, and a deep PBL; uniformly high concentrations of trace gases were found up to 4 km on one flight. Severe storms occur in maritime flow, especially when capped by a dry layer, and they transport large amounts of CO, Os, and NOy into the upper troposphere. Median NO levels at high altitude exceeded 300 ppt. Lightning produces spikes of NO (but not CO) with mixing ratios sometimes exceeding 1000 ppt. This flow pattern tends to leave the midtroposphere relatively clean with concentrations of trace gases similar to those observed in the polar category. During frontal passage both stratiform and convective clouds mix pollutants more uniformly into the middle and upper levels; high mixing ratios of CO are found at all altitudes, and Os levels are highest of any category, implicating photochemical production. These results illustrate the importance of convection in tropospheric chemistry. Use of average trace gas profiles or eddy diffusion parameterized vertical mixing can lead to errors of 30 to 50% in 03 and CO concentrations and an order of magnitude for odd nitrogen.

During 9 March-9 April 2004, the North Slope of Alaska Arctic Winter Radiometric Experiment was conducted at the Atmospheric Radiation Measurement Program's (ARM) "Great White" field site near Barrow, Alaska. The major goals of the experiment were to compare microwave and millimeter wavelength radiometers and to develop forward models in radiative transfer, all with a focus on cold (temperature from

This paper presents extensive validation analyses of ozone observations from the Atmospheric Chemistry Experiment (ACE) satellite instruments: the ACE Fourier Transform Spectrometer (ACE-FTS) and the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) instrument. The ACE satellite instruments operate in the mid-infrared and ultraviolet-visible-nearinfrared spectral regions using the solar occultation technique. In order to continue the long-standing record of solar occultation measurements from space, a detailed quality assessment is required to evaluate the ACE data and validate their use for scientific purposes. Here we compare the latest ozone data products from ACE-FTS and ACE-MAESTRO with coincident observations from satellite-borne, airborne, balloon-borne and ground-based instruments, by analysing volume mixing ratio profiles and partial column densities. The ACE-FTS version 2.2 Ozone Update product reports more ozone than most correlative measurements from the upper troposphere to the lower mesosphere. At altitude levels from 16 to 44 km, the mean differences range generally between 0 and +10% with a slight but systematic positive bias (typically +5%). At higher altitudes (45-60 km), the ACE-FTS ozone amounts are significantly larger than those of the comparison instruments by up to ∼40% (typically +20%). For the ACE-MAESTRO version 1.2 ozone data product, agreement within ±10% (generally better than ±5%) is found between 18 and 40 km for the sunrise and sunset measurements. At higher altitudes (45-55 km), systematic biases of opposite sign are found between the ACE-MAESTRO sunrise and sunset observations. While ozone amounts derived from the ACE-MAESTRO sunrise occultation data are often smaller than the coincident observations (by as much as −10%), the sunset occultation profiles for ACE-MAESTRO show results that are qualitatively similar to ACE-FTS and indicate a large positive bias (+10 to +30%) in this altitude range. In contrast, there is no significant difference in bias found for the ACE-FTS sunrise and sunset measurements. These systematic effects in the ozone profiles retrieved from the measurements of ACE-FTS

Atmos. Chem. Phys., 6, 1567–1584, 2006 www.atmos-chem-phys.net/6/1567/2006/ © Author(s) 2006. This work is licensed under a Creative Commons License. ... Modelling study of the impact of deep convection on the utls air ... V. Marécal1, ED Rivi`ere1,*, G. Held2, ...

We use aircraft observations obtained during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission to examine the distributions and source attributions of O 3 and NO y in the Arctic and sub-Arctic region. Using a number of marker tracers, we distinguish various air masses from the background troposphere and examine their contributions to NO x , O 3 , and O 3 production in the Arctic troposphere. The background Arctic troposphere has a mean O 3 of ∼60 ppbv and NO x of ∼25 pptv throughout spring and summer with CO decreasing from ∼145 ppbv in spring to ∼100 ppbv in summer. These observed mixing ratios are not notably different from the values measured during the 1988 ABLE-3A and the 2002 TOPSE field campaigns despite the significant changes in emissions and stratospheric ozone layer in the past two decades that influence Arctic tropospheric composition. Air masses associated with stratosphere-troposphere exchange are present throughout the mid and upper troposphere during spring and summer. These air masses, with mean O 3 concentrations of 140-160 ppbv, are significant direct sources of O 3 in the Arctic troposphere. In addition, air of stratospheric

Two Holocene ice core records from East Antarctica (Vostok and EPICA-Dome C) were analysed for dust concentration and size distribution at a temporal resolution of 1 sample per $50 years. A series of volcanic markers randomly distributed over the common part of the ice cores (from 9.8 to 3.5 kyear BP) ensures accurate relative dating (±33 years). Dust-size records from the two sites display oscillations structured in cycles with sub-millennial and secular scale frequencies that are apparently asynchronous. The power spectra of the composite sum (S) of the two dust-size records display spectral energy mostly for 150-to 500year periodicities. On the other hand, the 200-year band is common to both records and the 200 year components of the two sites are out-of-phase (100-year lead or lag) over $5.5 kyear, a phenomenon also reflected by a significant (>99% conf. lev.) band in the power spectra of the composite difference (D) of the two size records. During long-range transport, mineral dust originating from the Southern Hemisphere continents is graded to a variable extent depending on the altitude and duration of atmospheric transport. Relatively coarse dust is associated with air mass penetration from the middlelower troposphere and conversely relatively fine dust with upper troposphere air masses or the influence of subsidence over the Antarctic plateau, a hypothesis already proposed for the changes that occurred during the Last Glacial Maximum to Holocene transition (Delmonte et al. 2004b). Moreover, we assume that the overall fluctuation of air mass advection over Antarctica depends on the meridional pressure gradient with respect to low latitudes, i.e. the Antarctic Oscillation (AAO). We therefore suggest a regional variability in atmospheric circulation over East Antarctica. The 150-500 year power spectrum of the composite (S) parameter represents the long term variability of the AAO, imprinted by secular internal oscillations probably related to the southern ocean-climatic system. On the other hand, the D dust composite parameter suggests a persistent atmospheric dipole over East Antarctica delivering coarser (finer) dust particles alternatively to Vostok and Dome C regions with a bi-centennial periodicity. Indeed, a seesaw phenomenon in dust size distribution was already observed at three East Antarctic sites during the last deglaciation (Delmonte et al. 2004b) and was interpreted as a progressive reduction of the eccentricity of the polar vortex with respect to the geographic south pole. Interestingly, the D parameter shows a pronounced 200-year oscillation mode, throwing new light on the unresolved question of a possible relationship between climate and solar activity.

The ability of 15 atmospheric general circula-326 Slingo et al.: Intraseasonal oscillation in 15 atmospheric general circulation models sonal oscillations appear to have precipitation distributions which are better correlated with warm sea surface temperatures. These models predominantly employ convective parameterizations which are closed on buoyancy rather than moisture convergence.

We investigate the extent to which the azimuthally-averaged fields from a three-dimensional, nonhydrostatic, tropical cyclone model can be captured by axisymmetric balance theory. The secondary (overturning) circulation and balanced tendency for the primary circulation are obtained by solving a general form of the Sawyer-Eliassen equation with the diabatic heating, eddy heat fluxes and tangential momentum sources (eddy momentum fluxes, boundary-layer friction and subgrid-scale diffusion) diagnosed from the model. The occurrence of regions of weak symmetric instability at low levels and in the upper-tropospheric outflow layer requires a regularization procedure so that the Sawyer-Eliassen equation remains elliptic. The balanced calculations presented capture a major fraction of the azimuthally-averaged secondary circulation of the three-dimensional simulation except in the boundary layer, where the balanced assumption breaks down and where there is an inward agradient force. In particular, the balance theory is shown to significantly underestimate the low-level radial inflow and therefore the maximum azimuthal-mean tangential wind tendency. In the balance theory, the diabatic forcing associated with the eyewall convection accounts for a large fraction of the secondary circulation. The findings herein underscore both the utility of axisymmetric balance theory and also its limitations in describing the axisymmetric intensification physics of a tropical cyclone vortex.

We use ozone (O 3) and carbon monoxide (CO) satellite measurements from the Tropospheric Emission Spectrometer (TES), simulations from the Real-time Air Quality Modeling System (RAQMS) and aircraft data from the NASA DC8 aircraft to characterize the chemical and dynamical evolution of Asian wildfire plumes during the spring ARCTAS campaign 2008. On the 19 April, NASA DC8 O 3 and aerosol Differential Absorption Lidar (DIAL) observed two biomass burning plumes originating from NorthWestern Asia (Kazakhstan) and SouthEastern Asia (Thailand) that advected eastward over the Pacific reaching North America in 10 to 12 days. Using both TES observations and RAQMS chemical analyses, we track the wildfire plumes from their source to the ARCTAS DC8 platform. Comparison between satellite O 3 and CO measurements and model results show consistency when the TES averaging kernel and constraint vector are applied to the model. However, RAQMS CO simulations suggest that TES observations do not capture the full range of CO variability in the plume due to low sensitivity. In both plumes, exchanges between the stratosphere and the troposphere tend to be a major factor influencing O 3 concentrations. However, fire emissions of ozone precursors increase photochemical ozone production, particularly in the Thailand wildfire plume. Analysis shows that the Kazakhstan plume is responsible for increases of O 3 and CO mixing ratios up to 6.4 ppbv and 38 ppbv in the lower troposphere, and the Thailand plume is responsible for increases of O 3 and CO mixing ratios up to 11 ppbv and 71 ppbv in the upper troposphere. 1 Introduction Wildfire emissions affect atmospheric composition on global scales (Andreae, 1983; Reichle et al., 1986; Fishman et al., 1990; Soja et al., 2007) with levels of carbon monoxide (CO), carbon dioxide (CO 2) and nitrogen oxides (NO x) comparable to fos

The GPS/MET (Global Positioning System/Meteorology) experiment was carried out between April 1995 and February 1997. Height profiles of the atmospheric refractive index were obatined at 1-60km from the active limb sounding of occulted radio signals from the GPS satellites. By assuming the hydrostatic relation for a dry atmosphere, a new global data set of high resolution temperature profiles has become available. This paper deals with the determination of the thermal structure near the tropopause in the equatorial region using the GPS/MET data. First, we have compared the GPS/MET profiles with troposphere when effects of humidity are small, and about 2K in the lower stratosphere. The GPS/MET profiles are found to be very unique in revealing detailed temperature structure, including sharp inversions and step-wise increase of temperature gradient near the tropical tropopause, which has not been achieved by a conventional satellite measurement. The monthly mean value of the minimum temperature (Tmin) near the tropopause agreed well between radiosonde profiles at Bandung and the GPS/MET results, showing an annual variation with warm enhancements in August-September, and broader cold periods from January to April. The altitude corresponding to Tmin became lower/higher for warmer/colder Tmin. Taking advantage of the global coverage of the GPS/MET data, we have investigated the longitude distribution of Tmin and Hmin , which generally agreed well with earlier studies.

An atmospheric general circulation model of intermediate complexity is used to investigate the origin and structure of the climate change in the second half of the twentieth century. The variability of the atmospheric flow is considered as a superposition of an internal part, due to intrinsic dynamical variability, and an external part, due to the variations of the sea surface temperature (SST) forcing. The two components are identified by performing a 50-member ensemble of atmospheric simulations with prescribed, observed SSTs in the period 1949-2002. The large number of realizations allows the estimation of statistics of the atmospheric variability with a high confidence level. The analysis performed focuses on interdecadal and interannual variability of 500 hPa geopotential height in the Northern Hemisphere (NH) during winter. The model reproduces well the structure of the observed trend (defined as the difference in the two 25-year intervals 1977-2001 and 1952-1976), particularly in the Pacific region, and about half of the amplitude of the signal. The trend in 500 hPa height projects mainly onto the second empirical orthogonal function (EOF), both in the observations and in the model ensemble. However, differences between the modelled and the observed variability are found in the pattern of the second EOF in the Atlantic sector. SST changes associated with the El Nin˜o southern oscillation (ENSO) are responsible for about 50% of the signal of the 500 hPa height trend in the Pacific. A second 50-member ensemble is used to evaluate the sensitivity of interdecadal variability to an increase in CO 2 optical depth compatible with observed concentration changes. In this second experiment, the simulated trend includes a statistically significant contribution from the positive phase of the Arctic oscillation (AO). Such a contribution is also found in observations. Furthermore, the additional CO 2 forcing accounts for part of the NH trend in near-surface temperature, and brings the zonal-mean temperature changes in the stratosphere and uppertroposphere closer to observations.

Recent studies using NO, NOy, OH and HO 2 (HOx) partitioning of NOy and HOx concentrations in the UT at observations have postulated acetone and convection of midlatitudes. The importance of these quantities in relation toO3 peroxides as significant sources of HOx in the upper troposphere production over the Pacific has been reviewed elsewhere [Folkins (UT). This work focuses on the effect these additional HOx et al., 1998]. sources have on the modeled NOy partitioning and comparisons of the modeled NOx/NOy ratio to observations. The measured NOx/NOy ratio is usually much higher than predicted regardless Observations of the presence of acetone in the model. The exception occurs The observations reported here were obtained with instruments for air parcels having low NOy and 0 3 values. For these air on board the NASA ER-2 high-altitude aircraft during the parcels the measured NOx/NOy ratio is much lower than the October-November 1995 (fall) January-February 1996 (winter), calculated ratio unless acetone is included in the model. In all ' and July-August 1996 (summer) phases of the Stratospheric cases acetone increases •he fraction of NOy that is peroxy acetyl Tracers of Atmospheric Transport (STRAT) campaign. The nitrate (PAN) from typical values of much less than 0.1 to values flights originated from Moffett Field, California (38 ø N, 122øW), as high as 0.35. Including acetone also reduces the scatter in a and Barbers Point Naval Air Station, Hawaii (21 ø N, 158øW). comparison between modeled and observed NOx/NOy ratios. The data used here are descent data obtained from both locations the partitioning of the reactive nitrogen reservoir (NO y) is critical for understanding the photochemistry of this region and predicting the effects of anthropogenic perturbations such as aircraft emissions [Ehhalt and Rohrer, 1994; WMO, 1994]. The reactive nitrogen and hydrogen families are coupled by the reactions of OH with NO2 and nitric acid (HNO3), and HNO3 photolysis. These reactions are also the principal gas-phase reaction pathways between NOx and the less reactive NOy species. in this work we use a box model constrained by observed NO and long-lived tracer species to examine the

An idealized vertical-meridional zonally symmetrical version of the Méso-NH model is used to study the response of tropospheric ozone to the dynamics of the West African monsoon, as well as surface emissions and NO x-production by lightning (LNOx). An O 3-NO x-VOC chemical scheme has been added to the dynamical model, including surface emissions and a parameterization of the LNOx production. The model shows that the ozone precursors emitted at the surface are uplifted by deep convection and then advected in the upper branches of the Hadley cells on both sides of the Inter Tropical Convergence Zone (ITCZ). The NO x produced by lightning promotes chemical ozone production in the middle and upper troposphere from the oxidation of CO and VOCs. The analysis of the convective and chemical tendencies shows that the ozone minimum at the ITCZ is induced by venting of ozone-poor air masses into the upper troposphere. The bi-dimensional model suffers from limitations due to the absence of exchange with the higher latitudes and ventilation in the zonal direction. Despite of these restrictions, sensitivity simulations show that the LNOx source and biogenic VOCs are necessary to create the meridional gradient of ozone observed by the Measurements of OZone and water vapor by in-service AIrbus airCraft (MOZAIC) aircrafts in the southern Hadley cell. The LNOx source is also required to maintain the meridional ozone gradient up to 24°N in the northern Hadley cell. The modeled meridional gradient of O 3 in the upper troposphere ranges from 0.22 to 0.52 ppbv/deg without the LNOx source and from 0.60 to 1.08 ppbv/deg with the LNOx source, in the southern and the northern cells respectively.

As part of the Intercomparison of Radiation Codes in Climate Models (ICRCCM) project, careful comparisons of the performance of a large number of radiation codes were carried out, and the results compared with those of benchmark calculations. In this paper, we document the performance of a number of parameterized models which have been heavily used in climate and numerical prediction research at three institutions: Geophysical Fluid Dynamics Laboratory (GFDL), National Center for Atmospheric Research (NCAR), and Goddard Institute for Space Studies (GISS). 1.

Aircraft measurements of ozone (O 3) and its precursors, including NO, CO, H 2 O, and nonmethane hydrocarbons (NMHCs), were made over the western Pacific in the 20°-45°N latitude range in January and April-May 2002 during the Pacific Exploration of Asian Continental Emission (PEACE)-A and B campaigns. These measurements have provided data sets that, in combination with Transport and Chemical Evolution over the Pacific (TRACE-P) data taken in March 2001, enable studies of O 3 photochemistry from winter to late spring. A photochemical box model is used to calculate ozone formation (F(O 3)) and destruction (D(O 3)) rates constrained by the observed species concentrations. The values of F(O 3) and D(O 3) are controlled directly by NO, J(O 1 D) (O 3 photolysis frequency), H 2 O, OH, and HO 2. Changes in HO 2 concentration cause corresponding changes in both F(O 3) and D(O 3), leading to their coupling. Concentrations of these species, which are strongly influenced by photochemistry and transport from the Asian continent, underwent large seasonal variations. In the boundary layer (0-3 km), NO was much higher in January than in April-May, because of stronger winds, lower convective activities, and lower oxidation rates by OH in winter. The net O 3 formation rate, given by P(O 3) = F(O 3) À D(O 3), was largely positive in the boundary layer at 30°-45°N (1.5 À 4 ppbv d À1) in January, mainly because of high NO and low H 2 O values. Net O 3 formation continued from January to the end of March, demonstrating that the western Pacific is an important O 3 source region during this season. Net O 3 formation nearly ceased by late April/May because of the decrease in NO and the increase in H 2 O. In the latitude range of 20°-30°N, P(O 3) in the boundary layer was positive in January and turned negative by March. The earlier transition was mainly due to lower NO and higher H 2 O concentrations, combined with weaker transport and higher temperatures than those at 30°-45°N. The upper troposphere (6-12 km) has been shown to be a region of net O 3 formation throughout most of the year because of high NO and low H 2 O. The present study illustrates that a decrease in the net O 3 formation rate at 20°-45°N latitude from winter to late spring is explained systematically by the increases in J(O 1 D), H 2 O, OH, and HO 2 (primarily due to increases in temperature and solar radiation) and the decrease in NO (primarily due to decrease in transport from the Asian continent). Differences in the seasonal variation of O 3 photochemistry observed over the North American continent are interpreted in terms of the differences in factors controlling O 3 formation and destruction.

This paper presents extensive bias determination analyses of ozone observations from the Atmospheric Chemistry Experiment (ACE) satellite instruments: the ACE Fourier Transform Spectrometer (ACE-FTS) and the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) instrument. Here we compare the latest ozone data products from ACE-FTS and ACE-MAESTRO with coincident observations from nearly 20 satellite-borne, airborne, balloonborne and ground-based instruments, by analysing volume mixing ratio profiles and partial column densities. The ACE-FTS version 2.2 Ozone Update product reports more ozone than most correlative measurements from the upper troposphere to the lower mesosphere. At altitude levels from 16 to 44 km, the average values of the mean relative differences are nearly all within +1 to +8%. At higher altitudes (45-60 km), the ACE-FTS ozone amounts are significantly larger than those of the comparison instruments, with mean relative differences of up to +40% (about +20% on average). For the ACE-MAESTRO version 1.2 ozone data product, mean relative differences are within ±10% (average values within ±6%) between 18 and 40 km for both the sunrise and sunset measurements. At higher altitudes (∼35-55 km), systematic biases of opposite sign are found between the ACE-MAESTRO sunrise and sunset observations. While ozone amounts derived from the ACE-MAESTRO sunrise occultation data are often smaller than the coincident observations (with mean relative differences down to −10%), the sunset occultation profiles for ACE-MAESTRO show results that are qualitatively similar to ACE-FTS, indicating a large positive bias (mean relative differences within +10 to +30%) in the 45-55 km altitude range. In contrast, there is no significant systematic difference in bias found for the ACE-FTS sunrise and sunset measurements.

Global high resolution observations of upper tropospheric composition are needed to under-stand the small scale processes in this region most critical to climate change. Sensitivity of surface climate to UTLS variability and dynamical couplings, impact of convection and pyro-convection on the UTLS, and trace gas exchange between stratosphere and troposphere are largely unresolved science questions. Existing data of the mid and upper troposphere also lack the necessary detail to serve as useful upper boundary for models of the lower troposphere. These issues are due to limitations in vertical and horizontal resolution of contemporary space data, and their poor coverage for reasons of cloud and aerosol interference. PREMIER, one of three candidate ESA Earth Explorer mission concepts currently undergoing feasibility study, is the first space mission concept dedicated to the study of the mid / upper troposphere and lower stratosphere. It will carry limb-sounding spectrometers in the inf...

Carbon monoxide (CO) volume mixing ratio (VMR) profiles have been retrieved from ship-borne solar absorption spectra recorded in the Atlantic between 80°N and 70°S. CO profiles can be retrieved up to 30 km with a maximum altitude resolution of 4 km for a few layers. CO enhancements due to biomass burning have been detected. Recurring enhancements of CO were detected in the upper troposphere (10-15 km) in the equatorial regions and in the southern Atlantic (20°S-30°S). These enhancements could be traced back to African biomass burning sources as well as sources as far as South America. Similar results are observed in CO measurements from space by the Measurements of Pollution in the Troposphere (MOPITT) instrument. However, some enhancements in the upper troposphere especially above the source regions are difficult to distinguish from the MOPITT data. Results from the Model of Atmospheric Transport and Chemistry from the Max Planck Institute for Chemistry (MATCH-MPIC) show good agreement with the FTIR results. An analysis of the model data allows the quantification of the contributions of different sources such as biomass burning, fossil fuel combustion, and oxidation of methane (CH 4) and nonmethane hydrocarbons (NMHC).

We present the first ground-based solar absorption Fourier Transform Infrared (FTIR) spectrometric measurements in the inner tropics over several years. The FTIR observations agree well with satellite data from the MOPITT instrument. MATCH-MPIC model simulations reproduce the mean vertical structure of the FTIR observations. The model is generally not able to reproduce the extreme enhancements seen during the specific biomass burning events by both observation instruments. Nevertheless, the model indicates that beyond the background source of CO from methane oxidation, the main contributions to the CO mixing ratios are the episodic convective injection of NMHCs and CO from South American biomass burning into the upper troposphere, along with long range transport of African biomass burning CO, particularly during spring. In future studies with more extensive observed time series, observations such as these will be valuable for evaluating ongoing improvements in global chemistry transport models.