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  • Author or Editor: Peter van Velthoven x
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Joëlle Ovarlez
and
Peter van Velthoven

Abstract

During the POLINAT (Pollution from Aircraft Emissions in the North Atlantic Flight Corridor) experiment, water vapor content was measured with a frost-point hygrometer on board the DLR (Deutsche Forschungsanstalt für Luft-und-Raumfahrt) Falcon research aircraft. Model estimates of the water vapor mixing ratio along the flight track of the aircraft have been interpolated from 6-h ECMWF analyses. Comparisons are made between the in situ measurements and the model data for 16 POLINAT flights. In the high troposphere, the mixing ratio from the model is generally larger than the measured one, with differences amounting to a few percent up to 100%. But at mixing ratios below 20 ppmv and in the stratosphere, the mixing ratios from the model are generally smaller than the measured ones. The observed differences in the high troposphere can be explained by the low accuracy of radiosonde data at low temperatures and/or at small relative humidities. In the stratosphere, due to the technical limitations of radiosonde hygrometers, the water vapor concentration is set to a constant value at each ECMWF analysis step. Despite these discrepancies, many of the small-scale features are, at least in a qualitative sense, reproduced by the model.

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Peter Siegmund
,
Henk Eskes
, and
Peter van Velthoven

Abstract

The ozone budget in the Antarctic region during the stratospheric warming in 2002 is studied, using ozone analyses from the Royal Netherlands Meteorological Institute (KNMI) ozone-transport and assimilation model called TM3DAM. The results show a strong poleward ozone mass flux during this event south of 45°S between about 20 and 40 hPa, which is about 5 times as large as the ozone flux in 2001 and 2000, and is dominated by eddy transport. Above 10 hPa, there exists a partially compensating equatorward ozone flux, which is dominated by the mean meridional circulation. During this event, not only the ozone column but also the ozone depletion rate in the Antarctic region, computed as a residual from the total ozone tendency and the ozone mass flux into this region, is large. The September–October integrated ozone depletion in 2002 is similar to that in 2000 and larger than that in 2001. Simulations for September 2002 with and without ozone assimilation and parameterized ozone chemistry indicate that the parameterized ozone chemistry alone is able to produce the evolution of the ozone layer in the Antarctic region in agreement with observations. A comparison of the ozone loss directly computed from the model’s chemistry parameterization with the residual ozone loss in a simulation with parameterized chemistry but without ozone assimilation shows that the numerical error in the residual ozone loss is small.

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Henk Eskes
,
Arjo Segers
, and
Peter van Velthoven

Abstract

The Southern Hemisphere major warming event in September 2002 has led to a breakup of the vortex in the middle and higher stratosphere and to a corresponding splitting of the ozone hole. Daily 3D ozone forecasts, produced at the Royal Netherlands Meteorological Institute (KNMI) with a tracer transport and assimilation model based on the ECMWF dynamical forecasts, provided an accurate prediction of this event a week prior to the actual breakup of the vortex. The ozone forecast model contains parameterizations for gas phase and heterogeneous chemistry. Initial states for the forecast are obtained from the assimilation of near-real-time ozone data from the Global Ozone Monitoring Experiment (GOME) on European Space Agency (ESA) Remote Sensing Satellite-2 (ERS-2). In this paper, the ozone forecasts and analyses are discussed as produced before, during, and after the event. These fields are compared with ground-based Dobson, ozonesonde, and Total Ozone Mapping Spectrometer (TOMS) observations. The total ozone comparisons show that the location of the vortex edge is generally well described by the 5–7-day forecasts in September and October. The GOME assimilation compared with TOMS shows a good correspondence concerning vortex location and ozone features but also reflects clear differences in the average ozone amount between the two retrieval schemes. The assimilation system produces realistic ozone profiles, apart from a systematic underestimation of ozone around 150 hPa inside the vortex in August–October.

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Jason Edward Williams
,
Rinus Scheele
,
Peter van Velthoven
,
Idir Bouarar
,
Kathy Law
,
Béatrice Josse
,
Vincent-Henri Peuch
,
Xin Yang
,
John Pyle
,
Valérie Thouret
,
Brice Barret
,
Cathy Liousse
,
Frédéric Hourdin
,
Sophie Szopa
, and
Anne Cozic

The authors present results obtained during the chemistry-transport modeling (CTM) component of the African Monsoon Multidisciplinary Analysis Multimodel Intercomparison Project (AMMAMIP) using the recently developed L3JRCv2 emission dataset for Africa, where emphasis is placed on the summer of 2006. With the use of passive tracers, the authors show that the application of different parameterizations to describe advection, vertical diffusion, and convective mixing in a suite of state-of-the-art global CTMs results in significantly different transport mechanisms westward of the African continent. Moreover, the authors identify that the atmospheric composition over the southern Atlantic is governed by air masses originating from southern Africa for this period, resulting in maximal concentrations around 5°S. Comparisons with ozonesonde measurements at Cotonou (6.2°N, 2.2°E) indicate that the models generally overpredict surface ozone and underpredict ozone in the upper troposphere. Moreover, using recent aircraft measurements, the authors show that the high ozone concentrations that occur around 700 hPa around 5°N are not captured by any of the models, indicating shortcomings in the description of transport, the magnitude and/or location of emissions, or the in situ chemical ozone production by the various chemical mechanisms employed.

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