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

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.&#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&#8217;s leg from 3rd to 25th 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.

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Lightning-produced NOx over Brazil during TROCCINOX: airborne measurements in tropical and subtropical thunderstorms and the importance of mesoscale convective systems

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-2987-2007 ◽

2007 ◽

Vol 7 (11) ◽

pp. 2987-3013 ◽

Cited By ~ 60

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.

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Ozone, hydroperoxides, oxides of nitrogen, and hydrocarbon budgets in the marine boundary layer over the South Atlantic

Journal of Geophysical Research Atmospheres ◽

10.1029/95jd03631 ◽

1996 ◽

Vol 101 (D19) ◽

pp. 24221-24234 ◽

Cited By ~ 88

Author(s):

Brian Heikes ◽

Meehye Lee ◽

Daniel Jacob ◽

Robert Talbot ◽

John Bradshaw ◽

...

Keyword(s):

Boundary Layer ◽

Marine Boundary Layer ◽

South Atlantic ◽

Oxides Of Nitrogen ◽

The South

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Lightning-produced NOx over Brazil during TROCCINOX: Airborne measurements in tropical and subtropical thunderstorms and the importance of mesoscale convective systems

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-2561-2007 ◽

2007 ◽

Vol 7 (1) ◽

pp. 2561-2621 ◽

Cited By ~ 1

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.

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The surface thermal signature and air–sea coupling over the Agulhas rings propagating in the South Atlantic Ocean interior

Ocean Science Discussions ◽

10.5194/osd-10-2327-2013 ◽

2013 ◽

Vol 10 (6) ◽

pp. 2327-2361

Author(s):

J. M. A. C. Souza ◽

B. Chapron ◽

E. Autret

Keyword(s):

Boundary Layer ◽

Atlantic Ocean ◽

Atmospheric Boundary Layer ◽

Surface Wind ◽

South Atlantic ◽

South Atlantic Ocean ◽

Ekman Pumping ◽

Marine Atmospheric Boundary Layer ◽

The South ◽

Sst Anomalies

Abstract. The surface signature of the Agulhas rings propagating across the South Atlantic Ocean is observed based on 3 independent datasets: TMI/AMSR-E satellite sea surface temperature, Argo profiling floats and a merged winds product derived from scatterometer observations and reanalysis results. A persistent pattern of cold (negative) SST anomalies in the eddy core, with warm (positive) anomalies at the boundary is revealed. This pattern contrasts with the classical idea of a warm core anti-cyclone. Taking advantage of a moving reference frame corresponding to the altimetry-detected Agulhas rings, modifications of the surface winds by the ocean induced currents and SST gradients are evaluated using satellite SST and wind observations. As obtained, the averaged stationary thermal expression and mean eddy-induced circulation are coupled to the marine atmospheric boundary layer, leading to surface wind anomalies. Consequently, an average Ekman pumping associated with these mean surface wind variations is consistently emerging. This average Ekman pumping is found to very well explain the SST anomaly signatures of the detected Agulhas rings. Particularly, this mechanism seems to be the key factor determining that these anti-cyclonic eddies exhibit stationary imprints of cold SST anomalies near their core centers. A residual phase with the maximum SSH anomaly and wind speed anomaly is found to the right of the mean wind direction, apparently maintaining a coherent stationary thermal expression coupled to the marine atmospheric boundary layer.

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Atmospheric Response to Mesoscale Sea Surface Temperature Anomalies: Assessment of Mechanisms and Coupling Strength in a High-Resolution Coupled Model over the South Atlantic*

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0195.1 ◽

2015 ◽

Vol 72 (5) ◽

pp. 1872-1890 ◽

Cited By ~ 33

Author(s):

David Byrne ◽

Lukas Papritz ◽

Ivy Frenger ◽

Matthias Münnich ◽

Nicolas Gruber

Keyword(s):

Boundary Layer ◽

Atmospheric Boundary Layer ◽

Surface Wind ◽

Rapid Change ◽

South Atlantic ◽

Secondary Flows ◽

Small Scale ◽

Atmospheric Response ◽

The South ◽

Oceanic Eddies

Abstract Many aspects of the coupling between the ocean and atmosphere at the mesoscale (on the order of 20–100 km) remain unknown. While recent observations from the Southern Ocean revealed that circular fronts associated with oceanic mesoscale eddies leave a distinct imprint on the overlying wind, cloud coverage, and rain, the mechanisms responsible for explaining these atmospheric changes are not well established. Here the atmospheric response above mesoscale ocean eddies is investigated utilizing a newly developed coupled atmosphere–ocean regional model [Consortium for Small-Scale Modeling–Regional Ocean Modelling System (COSMO-ROMS)] configured at a horizontal resolution of ~10 km for the South Atlantic and run for a 3-month period during austral winter of 2004. The model-simulated changes in surface wind, cloud fraction, and rain above the oceanic eddies are very consistent with the relationships inferred from satellite observations for the same region and time. From diagnosing the model’s momentum balance, it is shown that the atmospheric imprint of the oceanic eddies are driven by the modification of vertical mixing in the atmospheric boundary layer, rather than secondary flows driven by horizontal pressure gradients. This is largely due to the very limited ability of the atmosphere to adjust its temperature over the time scale it takes for an air parcel to pass over these mesoscale oceanic features. This results in locally enhanced vertical gradients between the ocean surface and the overlying air and thus a rapid change in turbulent mixing in the atmospheric boundary layer and an associated change in the vertical momentum flux.

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Hydrogen peroxide in the marine boundary layer over the South Atlantic during the OOMPH cruise in March 2007

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-6971-2015 ◽

2015 ◽

Vol 15 (12) ◽

pp. 6971-6980 ◽

Cited By ~ 7

Author(s):

H. Fischer ◽

A. Pozzer ◽

T. Schmitt ◽

P. Jöckel ◽

T. Klippel ◽

...

Keyword(s):

Boundary Layer ◽

Hydrogen Peroxide ◽

Atmospheric Chemistry ◽

Marine Boundary Layer ◽

Austral Summer ◽

Circulation Model ◽

South Atlantic ◽

Strong Increase ◽

Global Circulation Model ◽

The South

Abstract. In the OOMPH (Ocean Organics Modifying Particles in both Hemispheres) project a ship measurement cruise took place in the late austral summer from 01 to 23 March 2007. The French research vessel Marion Dufresne sailed from Punta Arenas, Chile (70.85° W, 53.12° S), to Réunion island (55.36° E, 21.06° S) across the South Atlantic Ocean. In situ measurements of hydrogen peroxide, methylhydroperoxide and ozone were performed and are compared to simulations with the atmospheric chemistry global circulation model EMAC (ECHAM/MESSy Atmospheric Chemistry). The model generally reproduces the measured trace gas levels, but it underestimates hydrogen peroxide mixing ratios at high wind speeds, indicating too-strong dry deposition to the ocean surface. An interesting feature during the cruise is a strong increase of hydrogen peroxide, methylhydroperoxide and ozone shortly after midnight off the west coast of Africa due to an increase in the boundary layer height, leading to downward transport from the free troposphere, which is qualitatively reproduced by the model.

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