A numerical study of tropical cross-tropopause transport by convective overshoots during the TROCCINOX golden day

International audienceObservations obtained during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) golden day have revealed the presence of ice particles up to 410 K (18.2 km) 2 km above the local tropopause. The case is investigated using a three-dimensional quadruply nested non-hydrostatic simulation and Meteosat Second Generation (MSG) observations. The simulation fairly well reproduces the measurements along the flight track. A reasonable agreement with MSG observations is also achieved: the 10.8-µm brightness temperature (BT) minimum of 187 K is reproduced (a value 6 K colder than the environmental cold-point temperature) as well as the positive BT difference between the 6.2- and 10.8-µm bands, an overshoot signature. The simulation produces several overshooting plumes up to 410 K yielding an upward transport of water vapour of a few tons per second across the tropical tropopause. The estimated mass flux agree with those derived from over tracer budgets indicating that convection transport mass across the tropopause

The influence of biogenic emissions from Africa on tropical tropospheric ozone during 2006: a global modeling study

We have performed simulations using a 3-D global chemistry-transport model to investigate the influence that biogenic emissions from the African continent exert on the composition of the troposphere in the tropical region. For this purpose we have applied two recently developed biogenic emission inventories provided for use in large-scale global models (Granier et al., 2005; LathiSre et al., 2006) whose seasonality and temporal distribution for biogenic emissions of isoprene, other volatile organic compounds and NO is markedly different. The use of the 12 year average values for biogenic emissions provided by LathiSre et al. (2006) results in an increase in the amount of nitrogen sequestrated into longer lived reservoir compounds which contributes to the reduction in the tropospheric ozone burden in the tropics. The associated re-partitioning of nitrogen between PAN, HNO3 and organic nitrates also results in a similar to 5% increase in the loss of nitrogen by wet deposition. At a global scale there is a reduction in the oxidizing capacity of the model atmosphere which increases the atmospheric lifetimes of CH4 and CO by similar to 1.5% and similar to 4%, respectively. Comparisons against a range of different measurements indicate that applying the 12 year average of LathiSre et al. (2006) improves the performance of TM4_AMMA for 2006 in the tropics. By the use of sensitivity studies we show that the release of NO from soils in Africa accounts for between similar to 2-45% of tropospheric ozone in the African troposphere, similar to 10% in the upper troposphere and between similar to 5-20% of the tropical tropospheric ozone column over the tropical Atlantic Ocean. The subsequent reduction in OH over the source regions allows enhanced transport of CO out of the region. For biogenic volatile organic C1 to C3 species released from Africa, the effects on tropical tropospheric ozone are rather limited, although this source contributes to the global burden of VOC by between similar to 2-4% and has a large influence on the organic composition of the troposphere over the tropical Atlantic Ocean

Air pollution during the 2003 European heat wave as seen by MOZAIC airliners

This study presents an analysis of both MOZAIC profiles above Frankfurt and Lagrangian dispersion model simulations for the 2003 European heat wave. The comparison of MOZAIC measurements in summer 2003 with the 11-year MOZAIC climatology reflects strong temperature anomalies (exceeding 4°C) throughout the lower troposphere. Higher positive anomalies of temperature and negative anomalies of both wind speed and relative humidity are found for the period defined here as the heat wave (2–14 August 2003), compared to the periods before (16–31 July 2003) and after (16–31 August 2003) the heat wave. In addition, Lagrangian model simulations in backward mode indicate the suppressed long-range transport in the mid- to lower troposphere and the enhanced southern origin of air masses for all tropospheric levels during the heat wave. Ozone and carbon monoxide also present strong anomalies (both ~+40 ppbv) during the heat wave, with a maximum vertical extension reaching 6 km altitude around 11 August 2003. Pollution in the planetary boundary layer (PBL) is enhanced during the day, with ozone mixing ratios two times higher than climatological values. This is due to a combination of factors, such as high temperature and radiation, stagnation of air masses and weak dry deposition, which favour the accumulation of ozone precursors and the build-up of ozone. A negligible role of a stratospheric-origin ozone tracer has been found for the lower troposphere in this study. From 29 July to 15 August 2003 forest fires burnt around 0.3×10<sup>6</sup> ha in Portugal and added to atmospheric pollution in Europe. Layers with enhanced CO and NO<sub>y</sub> mixing ratios, advected from Portugal, were crossed by the MOZAIC aircraft in the free troposphere over Frankfurt. A series of forward and backward Lagrangian model simulations have been performed to investigate the origin of anomalies during the whole heat wave. European anthropogenic emissions present the strongest contribution to the measured CO levels in the lower troposphere (near 30%). This source is followed by Portuguese forest fires which affect the lower troposphere after 6 August 2003 and even the PBL around 10 August 2003. The averaged biomass burning contribution reaches 35% during the affected period. Anthropogenic CO of North American origin only marginally influences CO levels over Europe during that period

Regional lightning NOx sources during the TROCCINOX experiment

A lightning NOx (LiNOx) source has been implemented in the deep convection scheme of the Meso-NH mesoscale model following a mass-flux formalism coherent with the transport and scavenging of gases inside the convective scheme. In this approach the vertical transport of NO inside clouds is calculated by the parameterization of deep convective transport, thus eliminating the need for apriori LiNOx profiles. Once produced inside the convective column, NO molecules are redistributed by updrafts and downdrafts and detrained in the environment when the conditions are favorable. The model was applied to three particular flights during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) campaign over the tropical area around Bauru on 3-4 March 2004. The convective activity during the three flights was investigated using brightness temperature at 10.7μm observed from GOES-12 satellite. The use of a model-to-satellite approach reveals that the simulation appears rather realistic compared to the observations. The diurnal cycle of the simulated brightness temperature, CAPE, number of IC flashes, NO entrainment flux are in phase, with a succession of three marked peaks at 18:00 UTC (15:00 LT). These simulated peaks precede the observed afternoon one by about three hours. Comparison of the simulated NOx with observations along the flight tracks show that the model reproduces well the observed NOx levels when the LiNOx source is applied. The budget of entrainment, detrainment and LiNOx convective fluxes shows that the majority of the NO detrained back to the environment comes from lightning source inside the convective columns. Entrainment of NO from the environment and vertical transport from the boundary layer were not significant during the episode. The troposphere is impacted by detrainment fluxes of LiNOx from 4 km altitude to 16 km with maximum values around 14 km altitude. Detrainment fluxes vary between 75 kg(N)/s during nighttime to 400 kg(N)/s at the times of maximun convective activity. Extrapolation of the regional LiNOx source would yield a global LiNOx production around 5.7 Tg(N)/year which is within the current estimates but should not hide the overestimation of the number of flash rates by the model

the Creative Commons Attribution 3.0 License. Atmospheric Chemistry and Physics

The influence of biogenic emissions from Africa on tropical tropospheric ozone during 2006: a global modeling stud

Global model simulations of air pollution during the 2003 European heat wave

Three global Chemistry Transport Models – MOZART, MOCAGE, and TM5 – as well as MOZART coupled to the IFS meteorological model including assimilation of ozone (O<sub>3</sub>) and carbon monoxide (CO) satellite column retrievals, have been compared to surface measurements and MOZAIC vertical profiles in the troposphere over Western/Central Europe for summer 2003. The models reproduce the meteorological features and enhancement of pollution during the period 2–14 August, but not fully the ozone and CO mixing ratios measured during that episode. Modified normalised mean biases are around −25% (except ~5% for MOCAGE) in the case of ozone and from −80% to −30% for CO in the boundary layer above Frankfurt. The coupling and assimilation of CO columns from MOPITT overcomes some of the deficiencies in the treatment of transport, chemistry and emissions in MOZART, reducing the negative biases to around 20%. The high reactivity and small dry deposition velocities in MOCAGE seem to be responsible for the overestimation of O<sub>3</sub> in this model. Results from sensitivity simulations indicate that an increase of the horizontal resolution to around 1°×1° and potential uncertainties in European anthropogenic emissions or in long-range transport of pollution cannot completely account for the underestimation of CO and O<sub>3</sub> found for most models. A process-oriented TM5 sensitivity simulation where soil wetness was reduced results in a decrease in dry deposition fluxes and a subsequent ozone increase larger than the ozone changes due to the previous sensitivity runs. However this latest simulation still underestimates ozone during the heat wave and overestimates it outside that period. Most probably, a combination of the mentioned factors together with underrepresented biogenic emissions in the models, uncertainties in the modelling of vertical/horizontal transport processes in the proximity of the boundary layer as well as limitations of the chemistry schemes are responsible for the underestimation of ozone (overestimation in the case of MOCAGE) and CO found in the models during this extreme pollution event

Global model simulations of air pollution during the 2003 European heat wave

Three global Chemistry Transport Models - MOZART, MOCAGE, and TM5 - as well as MOZART coupled to the IFS meteorological model including assimilation of ozone (O-3) and carbon monoxide (CO) satellite column retrievals, have been compared to surface measurements and MOZAIC vertical profiles in the troposphere over Western/Central Europe for summer 2003. The models reproduce the meteorological features and enhancement of pollution during the period 2-14 August, but not fully the ozone and CO mixing ratios measured during that episode. Modified normalised mean biases are around -25% (except similar to 5% for MOCAGE) in the case of ozone and from -80% to -30% for CO in the boundary layer above Frankfurt. The coupling and assimilation of CO columns from MOPITT overcomes some of the deficiencies in the treatment of transport, chemistry and emissions in MOZART, reducing the negative biases to around 20%. The high reactivity and small dry deposition velocities in MOCAGE seem to be responsible for the overestimation of O-3 in this model. Results from sensitivity simulations indicate that an increase of the horizontal resolution to around 1 degrees x1 degrees and potential uncertainties in European anthropogenic emissions or in long-range transport of pollution cannot completely account for the underestimation of CO and O-3 found for most models. A process-oriented TM5 sensitivity simulation where soil wetness was reduced results in a decrease in dry deposition fluxes and a subsequent ozone increase larger than the ozone changes due to the previous sensitivity runs. However this latest simulation still underestimates ozone during the heat wave and overestimates it outside that period. Most probably, a combination of the mentioned factors together with underrepresented biogenic emissions in the models, uncertainties in the modelling of vertical/horizontal transport processes in the proximity of the boundary layer as well as limitations of the chemistry schemes are responsible for the underestimation of ozone (overestimation in the case of MOCAGE) and CO found in the models during this extreme pollution event