scholarly journals Lightning-produced NO<sub>x</sub> over Brazil during TROCCINOX: airborne measurements in tropical and subtropical thunderstorms and the importance of mesoscale convective systems

2007 ◽  
Vol 7 (11) ◽  
pp. 2987-3013 ◽  
Author(s):  
H. Huntrieser ◽  
H. Schlager ◽  
A. Roiger ◽  
M. Lichtenstern ◽  
U. Schumann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
South Atlantic ◽  
Convective System ◽  
The South ◽  
Air Masses ◽  
Upper Troposphere ◽  
Airborne Measurements ◽  
Mixing Ratios ◽  
Mesoscale Convective ◽  
Upward Transport

Abstract. During the TROCCINOX field experiments in February–March 2004 and February 2005, airborne in situ measurements of NO, NOy, CO, and O3 mixing ratios and the J(NO2) photolysis rate were carried out in the anvil outflow of thunderstorms over southern Brazil. Both tropical and subtropical thunderstorms were investigated, depending on the location of the South Atlantic convergence zone. Tropical air masses were discriminated from subtropical ones according to the higher equivalent potential temperature (Θe) in the lower and mid troposphere, the higher CO mixing ratio in the mid troposphere, and the lower wind velocity in the upper troposphere within the Bolivian High (north of the subtropical jet stream). During thunderstorm anvil penetrations, typically at 20–40 km horizontal scales, NOx mixing ratios were distinctly enhanced and the absolute mixing ratios varied between 0.2–1.6 nmol mol−1 on average. This enhancement was mainly attributed to NOx production by lightning and partly due to upward transport from the NOx-richer boundary layer. In addition, CO mixing ratios were occasionally enhanced, indicating upward transport from the boundary layer. For the first time, the composition of the anvil outflow from a large, long-lived mesoscale convective system (MCS) advected from northern Argentina and Uruguay was investigated in more detail. Over a horizontal scale of about 400 km, NOx, CO and O3 absolute mixing ratios were significantly enhanced in these air masses in the range of 0.6–1.1, 110–140 and 60–70 nmol mol−1, respectively. Analyses from trace gas correlations and a Lagrangian particle dispersion model indicate that polluted air masses, probably from the Buenos Aires urban area and from biomass burning regions, were uplifted by the MCS. Ozone was distinctly enhanced in the aged MCS outflow, due to photochemical production and entrainment of O3-rich air masses from the upper troposphere – lower stratosphere region. The aged MCS outflow was transported to the north, ascended and circulated, driven by the Bolivian High over the Amazon basin. In the observed case, the O3-rich MCS outflow remained over the continent and did not contribute to the South Atlantic ozone maximum.

scholarly journals Lightning-produced NO<sub>x</sub> over Brazil during TROCCINOX: Airborne measurements in tropical and subtropical thunderstorms and the importance of mesoscale convective systems

2007 ◽  
Vol 7 (1) ◽  
pp. 2561-2621 ◽  
Author(s):  
H. Huntrieser ◽  
H. Schlager ◽  
A. Roiger ◽  
M. Lichtenstern ◽  
U. Schumann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
South Atlantic ◽  
Convective System ◽  
The South ◽  
Air Masses ◽  
Upper Troposphere ◽  
Airborne Measurements ◽  
Mixing Ratios ◽  
Mesoscale Convective ◽  
Upward Transport

Abstract. During the TROCCINOX field experiments in February–March 2004 and February 2005, airborne in situ measurements of NO, NOy, CO, and O3 mixing ratios and the J(NO2) photolysis rate were carried out in the anvil outflow of thunderstorms over southern Brazil. Both tropical and subtropical thunderstorms were investigated, depending on the location of the South Atlantic convergence zone. Tropical air masses were discriminated from subtropical ones according to the higher equivalent potential temperature (Θe) in the lower and mid troposphere, the higher CO mixing ratio in the mid troposphere, and the lower wind velocity and proper wind direction in the upper troposphere. During thunderstorm anvil penetrations, typically at 20–40 km horizontal scales, NOx mixing ratios were on average enhanced by 0.2–1.6 nmol mol−1. This enhancement was mainly attributed to NOx production by lightning and partly due to upward transport from the NOx-richer boundary layer. In addition, CO mixing ratios were occasionally enhanced, indicating upward transport from the boundary layer. For the first time, the composition of the anvil outflow from a large, long-lived mesoscale convective system (MCS) advected from northern Argentina and Uruguay was investigated in more detail. Over a horizontal scale of about 400 km, NOx, CO and O3 mixing ratios were significantly enhanced in these air masses in the range of 0.6–1.1, 110–140 and 60–70 nmol mol−1, respectively. Analyses from trace gas correlations and a Lagrangian particle dispersion model indicate that polluted air masses, probably from the Buenos Aires urban area and from biomass burning regions, were uplifted by the MCS. Ozone was distinctly enhanced in the aged MCS outflow, due to photochemical production and entrainment of O3-rich air masses from the upper troposphere – lower stratosphere region. The aged MCS outflow was transported to the north, ascended and circulated, driven by the Bolivian High over the Amazon basin. In the observed case, the O3-rich MCS outflow remained over the continent and did not contribute to the South Atlantic ozone maximum.

scholarly journals Biomass burning pollution in the South Atlantic upper troposphere: GLORIA trace gas observations and evaluation of the CAMS model

2021 ◽  
Author(s):  
Sören Johansson ◽  
Gerald Wetzel ◽  
Felix Friedl-Vallon ◽  
Norbert Glatthor ◽  
Michael Höpfner ◽  
...  
Keyword(s):  
Cross Sections ◽  
Central Africa ◽  
South Atlantic ◽  
Trace Gas ◽  
The South ◽  
Transport Pathways ◽  
Filamentary Structure ◽  
Upper Troposphere ◽  
Airborne Measurements ◽  
Mixing Ratios

Abstract. In this study, we present simultaneous airborne measurements of peroxyacetyl nitrate (PAN), ethane (C2H6), formic acid (HCOOH), methanol (CH3OH), and ethylene (C2H4) above the South Atlantic in September and October 2019. Observations were obtained from the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA), as two-dimensional altitude cross-sections along the flight path. The flights were part of the SouthTRAC (Transport and Composition in the Southern Hemisphere Upper Troposphere/Lower Stratosphere) campaign with the German High Altitude and Long range research Aircraft (HALO). On two flights (8 September 2019 and 7 October 2019), large enhancements of all these substances were found between 7 and 14 km altitude with maximum volume mixing ratios (VMRs) of 1000 pptv of PAN, 1400 pptv for C2H6, 800 pptv for HCOOH, 4500 pptv for CH3OH, and 200 pptv for C2H4. One flight shows a common filamentary structure in the trace gas distributions, while the second flight is characterized by one large plume. Using backward trajectories, we show that measured pollutants are likely originating from South America and central Africa, where elevated PAN VMRs are visible at the surface layer of the Copernicus Atmosphere Monitoring Service (CAMS) model during the weeks before both measurements. In comparison to simulation results of the CAMS reanalysis interpolated onto the GLORIA measurement geolocations, we show that the model is able to reproduce the overall structure of the measured pollution trace gas distributions. For PAN, the absolute VMRs are in agreement with the GLORIA measurements, too. However, C2H6 and HCOOH are generally underestimated by the model, while CH3OH and C2H4, the species with the shortest atmospheric lifetimes of the discussed pollution trace gases, are overestimated by CAMS. The good agreement between model and observations for PAN suggests that the general transport pathways and emissions locations are well captured by the model. The poorer agreement for other species is therefore most likely linked to model deficiencies in the representation of loss processes and emission strength.

Dynamics of the Stratiform Sector of a Tropical Cyclone Rainband

2013 ◽  
Vol 70 (7) ◽  
pp. 1891-1911 ◽  
Author(s):  
Anthony C. Didlake ◽  
Robert A. Houze
Keyword(s):  
Boundary Layer ◽  
Doppler Radar ◽  
Mesoscale Convective System ◽  
Convective System ◽  
Stratiform Region ◽  
Mesoscale Convective ◽  
Upward Transport ◽  
Radial Outflow ◽  
Convective Cells ◽  
Low Entropy

Abstract Airborne Doppler radar documented the stratiform sector of a rainband within the stationary rainband complex of Hurricane Rita. The stratiform rainband sector is a mesoscale feature consisting of nearly uniform precipitation and weak vertical velocities from collapsing convective cells. Upward transport and associated latent heating occur within the stratiform cloud layer in the form of rising radial outflow. Beneath, downward transport is organized into descending radial inflow in response to two regions of latent cooling. In the outer, upper regions of the rainband, sublimational cooling introduces horizontal buoyancy gradients, which produce horizontal vorticity and descending inflow similar to that of the trailing-stratiform region of a mesoscale convective system. Within the zone of heavier stratiform precipitation, melting cooling along the outer rainband edge creates a midlevel horizontal buoyancy gradient across the rainband that drives air farther inward beneath the brightband. The organization of this transport initially is robust but fades downwind as the convection dissipates. The stratiform-induced secondary circulation results in convergence of angular momentum above the boundary layer and broadening of the storm's rotational wind field. At the radial location where inflow suddenly converges, a midlevel tangential jet develops and extends into the downwind end of the rainband complex. This circulation may contribute to ventilation of the eyewall as inflow of low-entropy air continues past the rainband in both the boundary layer and midlevels. Given the expanse of the stratiform rainband region, its thermodynamic and kinematic impacts likely help to modify the structure and intensity of the total vortex.

scholarly journals Reducing the Biases in Simulated Radar Reflectivities from a Bulk Microphysics Scheme: Tropical Convective Systems

2011 ◽  
Vol 68 (10) ◽  
pp. 2306-2320 ◽  
Author(s):  
Stephen E. Lang ◽  
Wei-Kuo Tao ◽  
Xiping Zeng ◽  
Yaping Li
Keyword(s):  
Mesoscale Convective System ◽  
Convective System ◽  
Microphysics Scheme ◽  
Upper Troposphere ◽  
Convective Systems ◽  
Mixing Ratios ◽  
Ice Nuclei ◽  
Mesoscale Convective ◽  
Immersion Freezing ◽  
Cloud Ice

Abstract A well-known bias common to many bulk microphysics schemes currently being used in cloud-resolving models is the tendency to produce excessively large reflectivity values (e.g., 40 dBZ) in the middle and upper troposphere in simulated convective systems. The Rutledge and Hobbs–based bulk microphysics scheme in the Goddard Cumulus Ensemble model is modified to reduce this bias and improve realistic aspects. Modifications include lowering the efficiencies for snow/graupel riming and snow accreting cloud ice; converting less rimed snow to graupel; allowing snow/graupel sublimation; adding rime splintering, immersion freezing, and contact nucleation; replacing the Fletcher formulation for activated ice nuclei with that of Meyers et al.; allowing for ice supersaturation in the saturation adjustment; accounting for ambient RH in the growth of cloud ice to snow; and adding/accounting for cloud ice fall speeds. In addition, size-mapping schemes for snow/graupel were added as functions of temperature and mixing ratio, lowering particle sizes at colder temperatures but allowing larger particles near the melting level and at higher mixing ratios. The modifications were applied to a weakly organized continental case and an oceanic mesoscale convective system (MCS). Strong echoes in the middle and upper troposphere were reduced in both cases. Peak reflectivities agreed well with radar for the weaker land case but, despite improvement, remained too high for the MCS. Reflectivity distributions versus height were much improved versus radar for the less organized land case but not for the MCS despite fewer excessively strong echoes aloft due to a bias toward weaker echoes at storm top.

scholarly journals Cloud-scale modelling of the impact of deep convection on the fate of oceanic bromoform in the troposphere: a case study over the west coast of Borneo

2020 ◽  
Author(s):  
Paul D. Hamer ◽  
Virginie Marécal ◽  
Ryan Hossaini ◽  
Michel Pirre ◽  
Gisèle Krysztofiak ◽  
...  
Keyword(s):  
Boundary Layer ◽  
West Coast ◽  
Deep Convection ◽  
Convective System ◽  
The West ◽  
Upper Troposphere ◽  
Convective Systems ◽  
Mixing Ratios ◽  
The Impact

Abstract. Coastal oceans emit bromoform (CHBr3) that can be transported rapidly to the upper troposphere by deep convection. In the troposphere, the spatial and vertical distribution of CHBr3 and its product gases (PGs) depend on emissions, chemical processing, transport by large scale flow, convection, and associated washout. This paper presents a modelling study on the fate of CHBr3 and its PGs in the troposphere. A case study at cloud scale was conducted along the west coast of Borneo, when several deep convective systems triggered in the afternoon and early evening of November 19th 2011. These systems were sampled by the Falcon aircraft during the field campaign of the SHIVA project. We analyse these systems using a simulation with the cloud-resolving meteorological model C-CATT-BRAMS at 2 × 2 km resolution that describes transport, photochemistry, and washout of CHBr3. We find that simulated CHBr3 mixing ratios and the observed values in the boundary layer and the outflow of the convective systems agree. However, the model underestimates the background CHBr3 mixing ratios in the upper troposphere, which suggests a missing source. An analysis of the simulated chemical speciation of bromine within and around each simulated convective system during the mature convective stage reveals that > 85 % of the bromine derived from CHBr3 and its PGs is transported vertically to the point of convective detrainment in the form of CHBr3 and that the remaining small fraction is in the form of organic PGs, principally insoluble brominated carbonyls produced from the photo-oxidation of CHBr3. The model simulates that within the boundary layer and free troposphere, the inorganic PGs are only present in soluble forms, i.e., HBr, HOBr, and BrONO2, and consequently, within the convective clouds, the inorganic PGs are almost entirely removed by wet scavenging. For the conditions of the simulated case study Br2 plays no significant role in the vertical transport of bromine. This likely results from the small simulated quantities of inorganic bromine involved, the presence of HBr in large excess compared to HOBr and the less soluble BrO, and the relatively quick removal of soluble compounds within the convective column. This prevalence of HBr is a result of the wider simulated regional atmospheric composition whereby background tropospheric ozone levels are exceptionally low.

scholarly journals Origins and characterization of CO and O<sub>3</sub> in the African upper troposphere

2021 ◽  
Author(s):  
Victor Lannuque ◽  
Bastien Sauvage ◽  
Brice Barret ◽  
Hannah Clark ◽  
Gilles Athier ◽  
...  
Keyword(s):  
Wind Shear ◽  
Asian Monsoon ◽  
Shear Zones ◽  
Hadley Cell ◽  
Trade Winds ◽  
Air Masses ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Hadley Cells

Abstract. Between December 2005 and 2013, the In-service Aircraft for a Global Observing System (IAGOS) program produced almost daily in situ measurements of CO and O3 between Europe and southern Africa. IAGOS data combined with measurements from the IASI instrument onboard the Metop-A satellite (2008–2013) are used to characterize meridional distributions and seasonality of CO and O3 in the African upper troposphere (UT). The FLEXPART particle dispersion model and the SOFT-IO model which combines the FLEXPART model with CO emission inventories are used to explore the sources and origins of the observed transects of CO and O3. We focus our analysis on two main seasons: December to March (DJFM) and June to October (JJASO). These seasons have been defined according to the position of Intertropical Convergence Zone (ITCZ), determined using in situ measurements from IAGOS. During both seasons, the UT CO meridional transects are characterized by maximum mixing ratios located 10° from the position of the ITCZ above the dry regions inside the hemisphere of the strongest Hadley cell (132 to 165 ppb at 0–5° N in DJFM and 128 to 149 ppb at 3–7° S in JJASO), and decreasing values south- and north-ward. The O3 meridional transects are characterized by mixing ratio minima of ~ 42–54 ppb at the ITCZ (10–16° S in DJFM and 5–8° N in JJASO) framed by local maxima (~ 53–71 ppb) coincident with the wind shear zones North and South of the ITCZ. O3 gradients are strongest in the hemisphere of the strongest Hadley cell. IASI UT O3 distributions in DJFM have revealed that the maxima are a part of a crescent-shaped O3 plume above the Atlantic Ocean around the Gulf of Guinea. CO emitted at the surface is transported towards the ITCZ by the trade winds and then convectively uplifted. Once in the upper troposphere, CO enriched air masses are transported away from the ITCZ by the upper branches of the Hadley cells and accumulate within the zonal wind shear zones where the maximum CO mixing ratios are found. Anthropogenic and fires both contribute, by the same order of magnitude, to the CO budget of the African upper troposphere. Local fires have the highest contribution, drive the location of the observed UT CO maxima, and are related to the following transport pathway: CO emitted at the surface is transported towards the ITCZ by the trade winds and further convectively uplifted. Then UT CO enriched air masses are transported away from the ITCZ by the upper branches of the Hadley cells and accumulate within the zonal wind shear zones where the maxima are located. Anthropogenic CO contribution is mostly from Africa during the entire year, with a low seasonal variability, and is related to similar transport circulation than fire air masses. There is also a large contribution from Asia in JJASO related to the fast convective uplift of polluted air masses in the Asian monsoon region which are further westward transported by the tropical easterly jet (TEJ) and the Asian monsoon anticyclone (AMA). O3 minima correspond to air masses that were recently uplifted from the surface where mixing ratios are low at the ITCZ. The O3 maxima correspond to old high altitude air masses uplifted from either local or long distance area of high O3 precursor emissions (Africa and South America during all the year, South Asia mainly in JJASO), and must be created during transport by photochemistry. This analysis of meridional transects contribute to a better understanding of distributions of CO and O3 in the intertropical African upper troposphere and the processes which drive these distributions. Therefore, it provides a solid basis for comparison and improvement of models and satellite products in order to get the good O3 for the good reasons.

Variability of the atmospheric electric field in the South Atlantic marine boundary layer from the SAIL campaign

2021 ◽  
Author(s):  
Susana Barbosa ◽  
Mauricio Camilo ◽  
Carlos Almeida ◽  
Guilherme Amaral ◽  
Nuno Dias ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Electric Field ◽  
Buenos Aires ◽  
Marine Boundary Layer ◽  
South Atlantic ◽  
Atmospheric Electric Field ◽  
Surface Ionization ◽  
Diurnal Pattern ◽  
The South ◽  
Near Surface

&lt;p&gt;The marine boundary layer offers a unique opportunity to investigate the electrical properties of the atmosphere, as the effect of natural radioactivity in driving near surface ionization is significantly reduced over the ocean, and the concentration of aerosols is also typically lower than over land. This work addresses the temporal variability of the atmospheric electric field in the South Atlantic marine boundary layer based on measurements from the SAIL (Space-Atmosphere-Ocean Interactions in the marine boundary Layer) project. The SAIL monitoring campaign took place on board the Portuguese navy tall ship NRP Sagres during its circumnavigation expedition in 2020.&amp;#160; Two identical field mills (CS110, Campbell Scientific) were installed on the same mast but at different heights (about 5 and 22 meters), recording the atmospheric electric field every 1-second. Hourly averages of the atmospheric electric field are analyzed for the ship&amp;#8217;s leg from 3&lt;sup&gt;rd&lt;/sup&gt; to 25&lt;sup&gt;th&lt;/sup&gt; March, between Buenos Aires (South America) and Cape Town (South Africa). The median daily curve of the electric field has a shape compatible with the Carnegie curve, but significant variability is found in the daily pattern of individual days, with only about 30% of the days exhibiting a diurnal pattern consistent with the Carnegie curve.&lt;/p&gt;

Fluxes at the Benthic Boundary Layer - A Global View from the South Atlantic

2003 ◽  
pp. 401-430 ◽  
Author(s):  
C. Hensen ◽  
K. Pfeifer ◽  
F. Wenzhöfer ◽  
A. Volbers ◽  
S. Schulz ◽  
...  
Keyword(s):  
Boundary Layer ◽  
South Atlantic ◽  
Benthic Boundary Layer ◽  
The South ◽  
Global View

scholarly journals Properties of a Mesoscale Convective System in the Context of an Isentropic Analysis

2015 ◽  
Vol 72 (5) ◽  
pp. 1945-1962 ◽  
Author(s):  
Agnieszka A. Mrowiec ◽  
O. M. Pauluis ◽  
A. M. Fridlind ◽  
A. S. Ackerman
Keyword(s):  
Mass Transport ◽  
Mass Flux ◽  
Potential Temperature ◽  
Substantial Reduction ◽  
Flux Ratio ◽  
Mesoscale Convective System ◽  
Convective System ◽  
High Entropy ◽  
Mixing Ratios ◽  
Mesoscale Convective

Abstract Application of an isentropic analysis of convective motions to a simulated mesoscale convective system is presented. The approach discriminates the vertical mass transport in terms of equivalent potential temperature. The scheme separates rising air at high entropy from subsiding air at low entropy. This also filters out oscillatory motions associated with gravity waves and isolates the overturning motions associated with convection and mesoscale circulation. The mesoscale convective system is additionally partitioned into stratiform and convective regions based on the radar reflectivity field. For each of the subregions, the mass transport derived in terms of height and an isentropic invariant of the flow is analyzed. The difference between the Eulerian mass flux and the isentropic counterpart is a significant and symmetric contribution of the buoyant oscillations to the upward and downward mass fluxes. Filtering out these oscillations results in substantial reduction of the diagnosed downward-to-upward convective mass flux ratio. The analysis is also applied to graupel and snow mixing ratios and number concentrations, illustrating the relationship of the particle formation process to the updrafts.

scholarly journals Continental outflow from the US to the upper troposphere over the North Atlantic during the NASA INTEX-NA Airborne Campaign

2008 ◽  
Vol 8 (7) ◽  
pp. 1989-2005 ◽  
Author(s):  
S. Y. Kim ◽  
R. Talbot ◽  
H. Mao ◽  
D. Blake ◽  
S. Vay ◽  
...  
Keyword(s):  
Boundary Layer ◽  
North Atlantic ◽  
The United States ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
The North ◽  
Southeastern Us ◽  
The Us ◽  
The North Atlantic ◽  
Continental Outflow

Abstract. A case of continental outflow from the United States (US) was examined using airborne measurements from NASA DC-8 flight 13 during the Intercontinental Chemical Transport Experiment – North America (INTEX-NA). Mixing ratios of methane (CH4) and carbon monoxide (CO) at 8–11 km altitude over the North Atlantic were elevated to 1843 ppbv and 134 ppbv respectively, while those of carbon dioxide (CO2) and carbonyl sulfide (COS) were reduced to 372.4 ppmv and 411 pptv respectively. In this region, urban and industrial influences were evidenced by elevated mixing ratios and good linear relationships between urban and industrial tracers compared to North Atlantic background air. Moreover, low mixing ratios and a good correlation between COS and CO2 showed a fingerprint of terrestrial uptake and minimal dilution during rapid transport over a 1–2 day time period. Analysis of synoptic conditions, backward trajectories, and photochemical aging estimates based on C3H8/C2H6 strongly suggested that elevated anthropogenic tracers in the upper troposphere of the flight region were the result of transport via convection and warm conveyor belt (WCB) uplifting of boundary layer air over the southeastern US. This mechanism is supported by the similar slope values of linear correlations between long-lived (months) anthropogenic tracers (e.g., C2Cl4 and CHCl3) from the flight region and the planetary boundary layer in the southeastern US. In addition, the aircraft measurements suggest that outflow from the US augmented the entire tropospheric column at mid-latitudes over the North Atlantic. Overall, the flight 13 data demonstrate a pervasive impact of US anthropogenic emissions on the troposphere over the North Atlantic.

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