scholarly journals Chemistry, transport and dry deposition of trace gases in the boundary layer over the tropical Atlantic Ocean and the Guyanas during the GABRIEL field campaign

2007 ◽  
Vol 7 (2) ◽  
pp. 4781-4855 ◽  
Author(s):  
A. Stickler ◽  
H. Fischer ◽  
H. Bozem ◽  
C. Gurk ◽  
C. Schiller ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Atlantic Ocean ◽  
Dry Deposition ◽  
Trace Gases ◽  
Deposition Velocity ◽  
Organic Peroxides ◽  
Tropical Atlantic ◽  
Tropical Atlantic Ocean ◽  
Positive Tendency

Abstract. We present a comparison of different Lagrangian and steady state box model runs with measurement data obtained during the GABRIEL campaign over the tropical Atlantic Ocean and the rainforest in the Guyanas, October 2005. Lagrangian modelling of boundary layer (BL) CO constrained by measurements of reactive trace gases and radiation is used to derive a horizontal gradient (≈5.6 pmol/mol km−1) of this compound from the ocean to the rainforest (east to west). This is significantly smaller than that derived from the measurements (16–48 pmol/mol km−1), indicating that photochemical production from organic precursors alone cannot explain the observed strong gradient. It appears that HCHO is overestimated by the Lagrangian and "steady state" models, which include dry deposition but not exchange with the free troposphere (FT). The relatively short lifetime of HCHO (50–100 min) implies substantial BL-FT exchange. The mixing-in of FT air affected by African and South American biomass burning at an estimated rate of 0.12 h−1 increases the CO and lowers the HCHO mixing ratios, leading to a better agreement with measurements. A 24 h mean deposition velocity of 1.35 cm/s for H2O2 over the ocean as well as over the rainforest is deduced assuming BL-FT exchange adequate to the results for CO. The measured increase of the organic peroxides from the ocean to the rainforest (≈0.66 nmol/mol d−1) is significantly overestimated by the Lagrangian model, even when using high values for the deposition velocity and the entrainment rate. Our results point at either heterogeneous loss of organic peroxides and/or their radical precursors or a missing reaction path of peroxy radicals not forming peroxides in isoprene chemistry. We calculate a mean integrated daytime net ozone production (NOP) in the BL of (0.2±5.9) nmol/mol (ocean) and (2.4±2.1) nmol/mol (rainforest). The NOP strongly correlates with NO and shows a positive tendency in the boundary layer over the rainforest.

scholarly journals Chemistry, transport and dry deposition of trace gases in the boundary layer over the tropical Atlantic Ocean and the Guyanas during the GABRIEL field campaign

2007 ◽  
Vol 7 (14) ◽  
pp. 3933-3956 ◽  
Author(s):  
A. Stickler ◽  
H. Fischer ◽  
H. Bozem ◽  
C. Gurk ◽  
C. Schiller ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atlantic Ocean ◽  
Dry Deposition ◽  
Deposition Velocity ◽  
Ozone Production ◽  
Organic Peroxides ◽  
Tropical Atlantic ◽  
Model Calculations ◽  
Tropical Atlantic Ocean ◽  
Positive Tendency

Abstract. We present a comparison of different Lagrangian and chemical box model calculations with measurement data obtained during the GABRIEL campaign over the tropical Atlantic Ocean and the Amazon rainforest in the Guyanas, October 2005. Lagrangian modelling of boundary layer (BL) air constrained by measurements is used to derive a horizontal gradient (≈5.6 pmol/mol km−1) of CO from the ocean to the rainforest (east to west). This is significantly smaller than that derived from the measurements (16–48 pmol/mol km−1), indicating that photochemical production from organic precursors alone cannot explain the observed strong gradient. It appears that HCHO is overestimated by the Lagrangian and chemical box models, which include dry deposition but not exchange with the free troposphere (FT). The relatively short lifetime of HCHO implies substantial BL-FT exchange. The mixing-in of FT air affected by African and South American biomass burning at an estimated rate of 0.12 h−1 increases the CO and decreases the HCHO mixing ratios, improving agreement with measurements. A mean deposition velocity of 1.35 cm/s for H2O2 over the ocean as well as over the rainforest is deduced assuming BL-FT exchange adequate to the results for CO. The measured increase of the organic peroxides from the ocean to the rainforest (≈0.66 nmol/mol d−1) is significantly overestimated by the Lagrangian model, even when using high values for the deposition velocity and the entrainment rate. Our results point at either heterogeneous loss of organic peroxides and/or their radical precursors, underestimated photodissociation or missing reaction paths of peroxy radicals not forming peroxides in isoprene chemistry. We calculate a mean integrated daytime net ozone production (NOP) in the BL of (0.2±5.9) nmol/mol (ocean) and (2.4±2.1) nmol/mol (rainforest). The NOP strongly correlates with NO and has a positive tendency in the boundary layer over the rainforest.

scholarly journals Mechanisms Controlling the Annual Cycle of Precipitation in the Tropical Atlantic Sector in an Atmospheric GCM*

2004 ◽  
Vol 17 (24) ◽  
pp. 4708-4723 ◽  
Author(s):  
M. Biasutti ◽  
D. S. Battisti ◽  
E. S. Sarachik
Keyword(s):  
Boundary Layer ◽  
Atlantic Ocean ◽  
Annual Cycle ◽  
Convective Available Potential Energy ◽  
Net Energy ◽  
Tropical Atlantic ◽  
Atlantic Sector ◽  
Tropical Atlantic Ocean ◽  
Low Level ◽  
The Impact

Abstract A set of AGCM experiments is used to study the annual cycle of precipitation in the region surrounding the tropical Atlantic Ocean. The experiments are designed to reveal the relative importance of insolation over land and the (uncoupled) SST on the annual cycle of precipitation over the tropical Atlantic Ocean, Africa, and the tropical Americas. SST variations impact the position of the maritime ITCZ by forcing the hydrostatic adjustment of the atmospheric boundary layer and changes in surface pressure and low-level convergence. The condensation heating released in the ITCZ contributes substantially to the surface circulation and the maintenance of the SST-induced ITCZ anomalies. The remote influence of SST is felt in equatorial coastal areas and the Sahel. The circulation driven by condensation heating in the maritime ITCZ extends to the coastal regions, thus communicating the SST signal onshore. Conversely, the Sahel responds to variations in SST through boundary layer processes that do not involve the maritime ITCZ. The atmospheric response to changes in subtropical SST is advected inland and forces changes in sea level pressure and low-level convergence across a large part of tropical Africa. The impact of local insolation on continental precipitation can be explained by balancing net energy input at the top of the atmospheric column with the export of energy by the divergent circulation that accompanies convection. Increased insolation reduces the stability of the atmosphere in the main continental convection centers, but not in monsoon regions. Insolation over land impacts the intensity of the maritime ITCZ via its influence on precipitation in Africa and South America. Reduced land precipitation induces the cooling of the Atlantic upper troposphere and the enhancement of convective available potential energy in the maritime ITCZ.

scholarly journals Correction to: Weakened SST variability in the tropical Atlantic Ocean since 2000

2021 ◽  
Author(s):  
Arthur Prigent ◽  
Joke F. Lübbecke ◽  
Tobias Bayr ◽  
Mojib Latif ◽  
Christian Wengel
Keyword(s):  
Atlantic Ocean ◽  
Tropical Atlantic ◽  
Tropical Atlantic Ocean ◽  
Sst Variability

scholarly journals Simulated Dust Aerosol Impacts on Western Sahelian Rainfall: Importance of Ocean Coupling

2018 ◽  
Vol 31 (22) ◽  
pp. 9107-9124 ◽  
Author(s):  
Asha K. Jordan ◽  
Anand Gnanadesikan ◽  
Benjamin Zaitchik
Keyword(s):  
Atlantic Ocean ◽  
North Africa ◽  
Negative Impact ◽  
Positive Impact ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Tropical Atlantic ◽  
Tropical Atlantic Ocean ◽  
Ocean Atmosphere ◽  
Sahel Region ◽  
Dust Precipitation

North Africa is the world’s largest source of mineral dust, and this dust has potentially significant impacts on precipitation. Yet there is no consensus in published studies regarding the sign or magnitude of dust impacts on rainfall in either the highly climate-sensitive Sahel region of North Africa or the neighboring tropical Atlantic Ocean. Here the Geophysical Fluid Dynamics Laboratory (GFDL) Climate Model 2 (GFDL CM2.0) with Modular Ocean Model, version 4.1 (MOM4.1), run at coarse resolution (CM2Mc) is applied to investigate one poorly characterized aspect of dust–precipitation dynamics: the importance of sea surface temperature (SST) changes in mediating the atmospheric response to dust. Two model experiments were performed: one comparing Dust-On to Dust-Off simulations in the absence of ocean–atmosphere coupling, and the second comparing Dust-On to Dust-Off with the ocean fully coupled. Results indicate that SST changes in the coupled experiment reduce the magnitude of dust impacts on Sahel rainfall and flip the sign of the precipitation response over the nearby ocean. Over the Sahel, CM2Mc simulates a net positive impact of dust on monsoon season rainfall, but ocean–atmosphere coupling in the presence of dust decreases the inflow of water vapor, reducing the amount by which dust enhances rainfall. Over the tropical Atlantic Ocean, dust leads to SST cooling in the coupled experiment, resulting in increased static stability that overrides the warming-induced increase in convection observed in the uncoupled experiment and yields a net negative impact of dust on precipitation. These model results highlight the potential importance of SST changes in dust–precipitation dynamics in North Africa and neighboring regions.

scholarly journals Impact of intraseasonal wind bursts on sea surface temperature variability in the far eastern tropical Atlantic Ocean during boreal spring 2005 and 2006: focus on the mid-May 2005 event

Ocean Science ◽  
2018 ◽  
Vol 14 (4) ◽  
pp. 849-869 ◽  
Author(s):  
Gaëlle Herbert ◽  
Bernard Bourlès
Keyword(s):  
Atlantic Ocean ◽  
Surface Temperature ◽  
Kelvin Waves ◽  
Sea Surface ◽  
Tropical Atlantic ◽  
Gulf Of Guinea ◽  
Atmospheric Conditions ◽  
Tropical Atlantic Ocean ◽  
Boreal Spring ◽  
Wind Bursts

Abstract. The impact of boreal spring intraseasonal wind bursts on sea surface temperature variability in the eastern tropical Atlantic Ocean in 2005 and 2006 is investigated using numerical simulation and observations. We especially focus on the coastal region east of 5° E and between the Equator and 7° S that has not been studied in detail so far. For both years, the southerly wind anomalies induced cooling episodes through (i) upwelling processes, (ii) vertical mixing due to the vertical shear of the current, and for some particular events (iii) a decrease in incoming surface shortwave radiation. The strength of the cooling episodes was modulated by subsurface conditions affected by the arrival of Kelvin waves from the west influencing the depth of the thermocline. Once impinging the eastern boundary, the Kelvin waves excited westward-propagating Rossby waves, which combined with the effect of enhanced westward surface currents contributed to the westward extension of the cold water. A particularly strong wind event occurred in mid-May 2005 and caused an anomalous strong cooling off Cape Lopez and in the whole eastern tropical Atlantic Ocean. From the analysis of oceanic and atmospheric conditions during this particular event, it appears that anomalously strong boreal spring wind strengthening associated with anomalously strong Hadley cell activity prematurely triggered the onset of coastal rainfall in the northern Gulf of Guinea, making it the earliest over the 1998–2008 period. No similar atmospheric conditions were observed in May over the 1998–2008 period. It is also found that the anomalous oceanic and atmospheric conditions associated with the event exerted a strong influence on rainfall off northeast Brazil. This study highlights the different processes through which the wind power from the South Atlantic is brought to the ocean in the Gulf of Guinea and emphasizes the need to further document and monitor the South Atlantic region.

The barrier layer in the western tropical Atlantic Ocean

1999 ◽  
Vol 26 (14) ◽  
pp. 2069-2072 ◽  
Author(s):  
K. Pailler ◽  
B. Bourlès ◽  
Y. Gouriou
Keyword(s):  
Atlantic Ocean ◽  
Barrier Layer ◽  
Tropical Atlantic ◽  
Tropical Atlantic Ocean
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