Impact of deep convection in the tropical tropopause layer in West Africa: in-situ observations and mesoscale modelling

Fierli, F.; Orlandi, E.; Law, Kathy S.; Cagnazzo, Chiara; Cairo, F.; Schiller, C.; Borrmann, Stephan; Donfrancesco, G. Di; Ravegnani, F.; Volk, C. M.

doi:10.5194/acp-11-201-2011

Cited by 19 publications

(23 citation statements)

References 47 publications

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“…For the SCOUT-AMMA study in the lower panel the SO 2 source contributions were located in East Africa and East India/South-East Asia. The latter is in qualitative agreement with the calculations by , who showed that ∼40 % of the air masses in the mid-TTL over West Africa during SCOUT-AMMA were influenced by injection of lower tropospheric air from Asia and India, while Fierli et al (2011) concluded that over Africa regional deep convection played a role as well. In Fig.…”

Section: Transport Model Calculations and Estimation Of So 2 Loadingssupporting

confidence: 80%

“…Finally, a new approach to the region above the same MCS was performed before the Geophysica turned back to the mission base. The level of main outflow of this MCS was located at the 353 K level according to Fierli et al (2011). These authors investigate the convective uplift of air masses due to this particular MCS and find highly variable convective ages from a few up to 48 h.…”

Section: Case Studies Of Three Npf Events Over South America and Overmentioning

confidence: 99%

“…Fierli et al (2011) provides indications for local convection, formed in the Sahelian region extending from Sudan to West Africa. This local convection may have been superimposed on a mainly zonal air mass transport that prevailed throughout the SCOUT-AMMA mission with direct impact on the composition of the tropical UT.…”

Section: Campaign Locations and Research Aircraftmentioning

confidence: 99%

“…One local flight over West Africa (10-13 • N and 1.5-8 • W) on 7 August 2006 (Case 2 and 3) was focused on measurements at the cloud top and in the outflow region of a dissolving intense MCS over southern Mali (Cairo et al, 2010a;Fierli et al, 2011). The flight track of the Geophysica followed a direct approach towards the region above the MCS top and the subsequent flight section allowed for measurements with increasing distance from the MCS.…”

Section: Case Studies Of Three Npf Events Over South America and Overmentioning

confidence: 99%

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In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism

Weigel

Borrmann²,

Kazil³

et al. 2011

Atmos. Chem. Phys.

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118

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Abstract. New particle formation (NPF), which generates nucleation mode aerosol, was observed in the tropical Upper Troposphere (UT) and Tropical Tropopause Layer (TTL) by in situ airborne measurements over South America (JanuaryMarch 2005), Australia (November-December 2005), West Africa (August 2006) and Central America (2004. Particularly intense NPF was found at the bottom of the TTL. Measurements with a set of condensation particle counters (CPCs) with different d p50 (50 % lower size detection efficiency diameter or "cut-off diameter") were conducted on board the M-55 Geophysica in the altitude range of 12.0-20.5 km and on board the DLR Falcon-20 at up to 11.5 km altitude. On board the NASA WB-57F size distributions were measured over Central America in the 4 to 1000 nm diameter range with a system of nucleation mode aerosol specCorrespondence to: R. Weigel (weigelr@uni-mainz.de) trometers. Nucleation mode particle concentrations (N NM ) were derived from these measurements which allow for identifying many NPF events with N NM in the range of thousands of particles per cm 3 . Over Australia and West Africa, we identified NPF in the outflow of tropical convection, in particular of a Mesoscale Convective System (MCS). Newly formed particles with N NM > 1000 cm −3 were found to coexist with ice cloud particles (d p > 2 µm) as long as cloud particle concentrations remained below 2 cm −3 . The occurrence of NPF within the upper troposphere and the TTL was generally confined within 340 K to 380 K potential temperature, but NPF was of particular strength between 350 K and 370 K (i.e. ∼1-4 km below the cold point tropopause). Analyses of the aerosol volatility (at 250 • C) show that in the TTL on average 75-90 % of the particles were volatile, compared to typically only 50 % in the extra-tropical UT, indicative for the particles to mainly consist of H 2 SO 4 -H 2 O and possibly organic compounds. Along two flight segments over Central and South America (24 February 2005 and 7 August Published by Copernicus Publications on behalf of the European Geosciences Union. 2006, at 12.5 km altitude) in cloud free air, above thin cirrus, particularly high N NM were observed. Recent lifting had influenced the probed air masses, and N NM reached up to 16 000 particles cm −3 (ambient concentration). A sensitivity study using an aerosol model, which includes neutral and ion induced nucleation processes, simulates N NM in reasonable agreement with the in situ observations of clear-air NPF. Based on new, stringent multi-CPC criteria, our measurements corroborate the hypothesis that the tropical UT and the TTL are regions supplying freshly nucleated particles. Our findings narrow the altitude of the main source region to the bottom TTL, i.e. to the level of main tropical convection outflow, and, by means of measurements of carbon monoxide, they indicate the importance of anthropogenic emissions in NPF. After growth and/or coalescence the nucleation mode particles may act as cloud condensation nuclei in the tropical UT, or, upon ...

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Section: Transport Model Calculations and Estimation Of So 2 Loadingssupporting

confidence: 80%

Section: Case Studies Of Three Npf Events Over South America and Overmentioning

confidence: 99%

Section: Campaign Locations and Research Aircraftmentioning

confidence: 99%

Section: Case Studies Of Three Npf Events Over South America and Overmentioning

confidence: 99%

See 2 more Smart Citations

In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism

Weigel

Borrmann²,

Kazil³

et al. 2011

Atmos. Chem. Phys.

Self Cite

118

View full text Add to dashboard Cite

show abstract

“…This corresponds well with observations carried out during the AMMA (African Monsoon Multidisciplinary Analyses) campaign during July and August 2006. Aircraft based measurements of several gas species were used to show the main convective outflow to be around 200 hPa in this region, and on certain days up to 100 hPa Fierli et al, 2011). Satellite based measurements of CO during the same time period show a convective influence up to around 220 hPa, with CO distributions above 150 hPa being controlled by large-scale transport (Barret et al, 2008).…”

Section: Location Of Convectionmentioning

confidence: 99%

Representation of tropical deep convection in atmospheric models – Part 2: Tracer transport

et al. 2011

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Abstract. The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP), chemical transport, and chemistry-climate models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short-lived tracers (with a lifetime of 6 h) within the tropical troposphere. Peak convective outflow altitudes rangeCorrespondence to: C. R. Hoyle (christopher.hoyle@env.ethz.ch) from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to be different between the models, even among those which source their forcing data from the same NWP model (ECMWF). The differences are less pronounced for longer lived tracers, however they could have implications for modelling the halogen burden of the lowermost stratosphere through transport of species such as bromoform, or short-lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are strongly influenced by the convective transport parameterisations, and different boundary layer mixing parameterisations also have a large impact on the modelled tracer profiles. Preferential locations for rapid transport from the surface into the upper troposphere are similar in all models, and are mostly concentrated over the western Pacific, the Maritime Continent and the Indian Published by Copernicus Publications on behalf of the European Geosciences Union. Ocean. In contrast, models do not indicate that upward transport is highest over western Africa.

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Assessing the performance of WRF model in predicting high-impact weather conditions over Central and Western Africa: an ensemble-based approach

et al. 2018

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Impact of deep convection in the tropical tropopause layer in West Africa: in-situ observations and mesoscale modelling

Cited by 19 publications

References 47 publications

In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism

In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism

Representation of tropical deep convection in atmospheric models – Part 2: Tracer transport

Assessing the performance of WRF model in predicting high-impact weather conditions over Central and Western Africa: an ensemble-based approach

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