H. Kelder

An ozone climatology based on ozonesonde and satellite measurements

An ozone climatology is presented, based entirely on ozone observations over the target period 1980–1991. The climatology gives zonal mean ozone values, as well as the corresponding interannual standard deviation, for 17 zonal bands (80°S–S0°N) at 19 pressure levels (1000–0.3 hPa), for each month of the year. It is intended mainly for climate simulations with general circulation models (GCMs). For the troposphere and lower stratosphere (1000–10 hPa) the climatology is compiled from ozonesonde observations of 30 ozonesonde stations located around the world. To account for tropospheric longitudinal variability within a zonal band, a data set giving tropospheric total ozone values between 50°S and 50°N is used. For stations within this latitude range the tropospheric profile is scaled with a factor derived from this data set to make it more representative of the zonal mean. Consequently, the corrected profiles of the individual stations are combined within each zonal band, using weighted averaging. These zonal profiles are then attached to zonal monthly mean SBUV-SBUV/2 (solar backscattered ultraviolet) observations in the stratosphere (30–0.3 hPa). Three overlap layers, at 30, 20, and 10 hPa, give an indication of how well these two data sets match. Where possible, the integral of the combined ozone profiles is made consistent with total ozone mapping (TOMS) profiles, by applying a correction factor to the ozonesonde part of the profile, derived from TOMS minus the integrated SBUV-SBUV/2 profile. The resulting climatology is compared with three other ozone climatologies: the predecessor of this one, a climatology compiled by the State University of New York, and a climatology used in the GCM at the Max Planck Institute in Hamburg, Germany. Apparent improvements are better consistent with TOMS (compared with the first climatology) and more realistic ozone values in the tropics and polar regions (compared with the first and second climatologies). There is an overall strong improvement compared with the third climatology, which was generated from an analytical formula and old ozone observations in the 1970s. A unique further advantage of the current climatology is the accompanying standard deviation climatology, giving an indication of the natural variability and reliability of the mean ozone values.

Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology 2. Tropospheric variability and the zonal wave-one

(1) The first view of stratospheric and tropospheric ozone variability in the Southern Hemisphere tropics is provided by a 3-year record of ozone soundings from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network (http://croc.gsfc.nasa.gov/ shadoz). Observations covering 1998-2000 were made over Ascension Island, Nairobi (Kenya), Irene (South Africa), Reunion Island, Watukosek (Java), Fiji, Tahiti, American Samoa, San Cristobal (Galapagos), and Natal (Brazil). Total, stratospheric, and tropospheric column ozone amounts usually peak between August and November. Other features are a persistent zonal wave-one pattern in total column ozone and signatures of the quasi-biennial oscillation (QBO) in stratospheric ozone. The wave-one is due to a greater concentration of free tropospheric ozone over the tropical Atlantic than the Pacific and appears to be associated with tropical general circulation and seasonal pollution from biomass burning. Tropospheric ozone over the Indian and Pacific Oceans displays influences of the waning 1997-1998 El Nino, seasonal convection, and pollution transport from Africa. The most distinctive feature of SHADOZ tropospheric ozone is variability in the data, e.g., a factor of 3 in column amount at 8 of 10 stations. Seasonal and monthly means may not be robust quantities because statistics are frequently not Gaussian even at sites that are always in tropical air. Models and satellite retrievals should be evaluated on their capability for reproducing tropospheric variability and fine structure. A 1999- 2000 ozone record from Paramaribo, Surinam (6� N, 55� W) (also in SHADOZ) shows a marked contrast to southern tropical ozone because Surinam is often north of the Intertropical Convergence Zone (ITCZ). A more representative tropospheric ozone climatology for models and satellite retrievals requires additional Northern Hemisphere tropical data. INDEXTERMS: 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 1640 Global Change: Remote sensing; 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 9305 Information Related to Geographic Region: Africa; 9325 Information Related to Geographic Region: Atlantic Ocean; KEYWORDS: Free-words-ozone, tropospheric ozone, ozonesondes, satellite ozone, tropical climatology, wave-one, biomass burning, El Nino, satellite retrievals

Validation of Aura Microwave Limb Sounder Ozone by ozonesonde and lidar measurements

We present validation studies of MLS version 2.2 upper tropospheric and stratospheric ozone profiles using ozonesonde and lidar data as well as climatological data. Ozone measurements from over 60 ozonesonde stations worldwide and three lidar stations are compared with coincident MLS data. The MLS ozone stratospheric data between 150 and 3 hPa agree well with ozonesonde measurements, within 8% for the global average. MLS values at 215 hPa are biased high compared to ozonesondes by A`20% at middle to high latitude, although there is a lot of variability in this altitude region. Comparisons between MLS and ground-based lidar measurements from Mauna Loa, Hawaii, from the Table Mountain Facility, California, and from the Observatoire de Haute-Provence, France, give very good agreement, within A`5%, for the stratospheric values. The comparisons between MLS and the Table Mountain Facility tropospheric ozone lidar show that MLS data are biased high by A`30% at 215 hPa, consistent with that indicated by the ozonesonde data. We obtain better global average agreement between MLS and ozonesonde partial column values down to 215 hPa, although the average MLS values at low to middle latitudes are higher than the ozonesonde values by up to a few percent. MLS v2.2 ozone data agree better than the MLS v1.5 data with ozonesonde and lidar measurements. MLS tropical data show the wave one longitudinal pattern in the upper troposphere, with similarities to the average distribution from ozonesondes. High upper tropospheric ozone values are also observed by MLS in the tropical Pacific from June to November.

A Simulation of the Separate Climate Effects of Middle-Atmospheric and Tropospheric CO2 Doubling

Abstract The separate climate effects of middle-atmospheric and tropospheric CO2 doubling have been simulated and analyzed with the ECHAM middle-atmosphere climate model. To this end, the CO2 concentration has been separately doubled in the middle-atmosphere, the troposphere, and the entire atmosphere, and the results have been compared to a control run. During NH winter, the simulated uniformly doubled CO2 climate shows an increase of the stratospheric residual circulation, a small warming in the Arctic lower stratosphere, a weakening of the zonal winds in the Arctic middle-atmosphere, an increase of the NH midlatitude tropospheric westerlies, and a poleward shift of the SH tropospheric westerlies. The uniformly doubled CO2 response in most regions is approximately equal to the sum of the separate responses to tropospheric and middle-atmospheric CO2 doubling. The increase of the stratospheric residual circulation can be attributed for about two-thirds to the tropospheric CO2 doubling and one-third to the...

A trajectory-based estimate of the tropospheric ozone column using the residual method

We estimate the tropospheric column ozone using a forward trajectory model to increase the horizontal resolution of the Aura Microwave Limb Sounder (MLS) derived stratospheric column ozone. Subtracting the MLS stratospheric column from Ozone Monitoring Instrument total column measurements gives the trajectory enhanced tropospheric ozone residual (TTOR). Because of different tropopause definitions, we validate the basic residual technique by computing the 200-hPa-to-surface column and comparing it to the same product from ozonesondes and Tropospheric Emission Spectrometer measurements. Comparisons show good agreement in the tropics and reasonable agreement at middle latitudes, but there is a persistent low bias in the TTOR that may be due to a slight high bias in MLS stratospheric column. With the improved stratospheric column resolution, we note a strong correlation of extratropical tropospheric ozone column anomalies with probable troposphere-stratosphere exchange events or folds. The folds can be identified by their colocation with strong horizontal tropopause gradients. TTOR anomalies due to folds may be mistaken for pollution events since folds often occur in the Atlantic and Pacific pollution corridors. We also compare the 200-hPa-to-surface column with Global Modeling Initiative chemical model estimates of the same quantity. While the tropical comparisons are good, we note that chemical model variations in 200-hPa-to-surface column at middle latitudes are much smaller than seen in the TTOR.

Stratosphere‐troposphere exchange: A model and method intercomparison

This paper presents one of the first extensive intercomparisons of models and methods used for estimating stratosphere-troposphere exchange (STE). The study is part of the European Union project Influence of Stratosphere Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity (STACCATO). Nine different models and methods, including three trajectory methods, one Eulerian method, two Lagrangian and one Eulerian transport model, and two general circulation models applied the same initialization. Stratospheric and tropospheric tracers have been simulated, and the tracer mass fluxes have been calculated through the tropopause and the 700 hPa surface. For a 12-day case study over Europe and the northeast Atlantic the simulated tracer mass fluxes have been intercompared. For this case the STE simulations show the same temporal evolution and the same geographical pattern of STE for most models and methods, but with generally different amplitudes (up to a factor of 4). On the other hand, for some simulations also the amplitudes are very similar.

On the relation between ozone and potential vorticity

As ozone mixing ratio correlates well with potential vorticity, column integrated ozone (“total ozone”) should correlate with column integrated potential vorticity. Daily maps of these fields are analyzed, and it is shown that this correlation holds well, notably during the winter and spring. During a few short periods however, the correlation breaks down.

Improvement and Evaluation of the Parameterisation of Nitrogen Oxide Production by Lightning

Abstract In order to describe the production of nitrogen oxides (NO x ) by lightning in chemistry-transport models the spatial and temporal distribution of this NO x source needs to be specified. Various meteorological model parameters can be used as a proxy for specifying this distribution. In order to determine the most suitable parameter as a proxy for lightning, we have correlated different meteorological quantities from the ECMWF model, such as convective precipitation and cloud top height, with ground-based lightning observations made during the EULINOX project. Convective precipitation gave the best correlation for summer conditions over Europe. Using the established relationship between convective precipitation and lightning intensity, we have tested different vertical distributions of the NO x lightning source in the global chemistry-transport model TM3. The model simulated NO fields have been compared with the NO observations made during the 1998 EULINOX and the 1997 POLINAT/SONEX campaigns. We found that a prescribed lightning NO x profile gave the best agreement with the observations. The observations covered various conditions: typical background situations, inside thunderstorms, and the outflow of thunderstorms of various ages. The model underestimated the NO concentrations in cases of fresh lightning NO x , likely due to its insufficient spatial and temporal resolution, but under most other circumstances the new parameterisation performed reasonably well, and is a clear improvement over the previously used parameterisation based on cloud top heights.

Some observations of gravity-wave-induced structure in ozone and water vapour during EASOE

During the EASOE campaign, measurements were made of temperature and different minor constituents, with the help of instrumented balloons. The vertical profiles nearly always show small scale structures. Here we show that on two different days a large part of these small scale structure can be explained by the transport induced by waves. The role of waves is supported by a good correlation found between the small scale structure of the minor constituents profiles and the temperature profile. Furthermore on 11 December 1991 lidar measurements show the trace of a wave on a polar stratospheric cloud (Godin et al. 1993).Comparison of some of its characteristics with what was found in water vapour and ozone measurement profiles carried out the same day, confirm the role of the wave in the minor constituent fluctuations.

A 3D chemistry transport model study of changes in atmospheric ozone due to aircraft NOX emissions

Abstract The effect of present day aircraft emissions of nitrogen oxides (NOx = NO + NO2) on atmospheric NOx and ozone concentrations is investigated with the global three-dimensional chemistry transport model CTMK. This model uses 12-hourly meteorological data from the ECMWF analysis and includes parameterizations for subgrid scale processes such as convection. CTMK includes an ozone chemistry module containing the methane and carbon monoxide oxidation chain for the troposphere and lower stratosphere. It is found by using the ANCAT aircraft NOx emission invertory that aviation contributes to 20–100 pptv of the NOx at cruise altitudes in northern mid-latitudes, which corresponds to 30–80 and 20–50% of the background mixing ratios for January and July, respectively. This perturbation in NOx occurs mainly in the North Atlantic Flight Corridor and is transported eastwards. The resulting increase in upper tropospheric ozone is 2–3 ppbv (2%) in January and 5–10 ppbv (3%) in July. The ozone perturbation is almost zonally symmetric and attains maximum values at northern mid-latitudes in January and in the polar region in July. The calculated effect of aircraft emissions is found to be small (i.e. less than 5 pptv for NOx and less than 1 ppbv for 03) in the southern hemisphere. The perturbation of NOx by the aircraft emissions at cruise altitudes in northern mid-latitudes is large compared to the standard deviation. Therefore, it is expected that the effect of aviation on NOx is distinguishable from the contribution from other NOx sources. As the modelled natural variability of ozone is already about 30%, it will not be easy to detect the ozone perturbation due to aircraft NOx emissions.