scholarly journals The seasonal vertical distribution of the Saharan Air Layer and its modulation by the wind

2013 ◽  
Vol 13 (22) ◽  
pp. 11235-11257 ◽  
Author(s):  
C. Tsamalis ◽  
A. Chédin ◽  
J. Pelon ◽  
V. Capelle
Keyword(s):  
South America ◽  
Vertical Distribution ◽  
North Atlantic ◽  
Deposition Velocity ◽  
Dust Particles ◽  
Dust Aerosols ◽  
Saharan Air Layer ◽  
Western Africa ◽  
The North ◽  
The North Atlantic

Abstract. The Saharan Air Layer (SAL) influences large-scale environment from western Africa to eastern tropical Americas, by carrying large amounts of dust aerosols. However, the vertical distribution of the SAL is not well established due to a lack of systematic measurements away from the continents. This can be overcome by using the observations of the spaceborne lidar CALIOP onboard the satellite CALIPSO. By taking advantage of CALIOP's capability to distinguish dust aerosols from other types of aerosols through depolarization, the seasonal vertical distribution of the SAL is analyzed at 1° horizontal resolution over a period of 5 yr (June 2006–May 2011). This study shows that SAL can be identified all year round displaying a clear seasonal cycle. It occurs higher in altitude and more northern in latitude during summer than during winter, but with similar latitudinal extent near Africa for the four seasons. The south border of the SAL is determined by the Intertropical Convergence Zone (ITCZ), which either prohibits dust layers from penetrating it or reduces significantly the number of dust layers seen within or south of it, as over the eastern tropical Atlantic. Spatially, near Africa, it is found between 5° S and 15° N in winter and 5–30° N in summer. Towards the Americas (50° W), SAL is observed between 5° S and 10° N in winter and 10–25° N in summer. During spring and fall, SAL is found between the position of winter and summer not only spatially but also vertically. In winter, SAL occurs in the altitude range 0–3 km off western Africa, decreasing to 0–2 km close to South America. During summer, SAL is found to be thicker and higher near Africa at 1–5 km, reducing to 0–2 km in the Gulf of Mexico, farther west than during the other seasons. SAL is confined to one layer, of which the mean altitude decreases with westward transport by 13 m deg−1 during winter and 28 m deg−1, after 30° W, during summer. Its mean geometrical thickness decreases by 25 m deg−1 in winter and 9 m deg−1 in summer. Spring and fall present similar characteristics for both mean altitude and geometrical thickness. Wind plays a major role not only for the transport of dust within the SAL but also by sculpting it. During winter, the trade winds transport SAL towards South America, while in spring and summer they bring dust-free maritime air masses mainly from the North Atlantic up to about 50° W below the SAL. The North Atlantic westerlies, with their southern border occurring between 15 and 30° N (depending on the season, the longitude and the altitude), prevent the SAL from developing further northward. In addition, their southward shift with altitude gives SAL its characteristic oval shape in the northern part. The effective dry deposition velocity of dust particles is estimated to be 0.07 cm s−1 in winter, 0.14 cm s−1 in spring, 0.2 cm s−1 in summer and 0.11 cm s−1 in fall. Finally, the African Easterly Jet (AEJ) is observed to collocate with the maximum dust load of the SAL, and this might promote the differential advection for SAL parts, especially during summer.

scholarly journals The seasonal vertical distribution of the Saharan Air Layer and its modulation by the wind

2013 ◽  
Vol 13 (2) ◽  
pp. 4727-4784 ◽  
Author(s):  
C. Tsamalis ◽  
A. Chédin ◽  
J. Pelon ◽  
V. Capelle
Keyword(s):  
South America ◽  
West Africa ◽  
Vertical Distribution ◽  
North Atlantic ◽  
Large Scale ◽  
Deposition Velocity ◽  
Horizontal Resolution ◽  
Dust Particles ◽  
Dust Aerosols ◽  
Saharan Air Layer

Abstract. The Saharan Air Layer (SAL) influences large scale environment from West Africa to eastern tropical America, by carrying large amounts of dust aerosols. However, the vertical distribution of the SAL is not well established due to a lack of systematic measurements away from the continents. This can be overcome by using the observations of the space lidar CALIOP on board CALIPSO. By taking advantage of CALIOP capability to distinguish dust aerosols from other types of aerosols through depolarization, the seasonal vertical distribution of the SAL is analysed at 1 degree horizontal resolution over a period of 5 yr (June 2006–May 2011). This study shows that SAL can be identified all year round displaying a clear seasonal cycle. It occurs higher in altitude and more northern in latitude during summer than during winter, but with similar latitude extent near Africa for the four seasons. The south border of the SAL is determined by the Intertropical Convergence Zone (ITCZ), which either prohibits dust layers to penetrate it or reduces significantly the number of dust layers seen in or south of it, as over the eastern tropical Atlantic. Spatially, near Africa, it is found between 5° S–15° N in winter going at 5–30° N in summer. Towards America (50° W), SAL is observed between 5° S–10° N in winter and 10–25° N in summer. During spring and fall, SAL is found between the position of winter and summer not only spatially, but also vertically. In winter, SAL occurs in the altitude range 0–3 km off West Africa, decreasing to 0–2 km close to South America. During summer, SAL is found to be thicker and higher near Africa at 1–5 km, reducing to 0–2 km in the Gulf of Mexico, farther west than during the other seasons. SAL is confined to one layer, of which the mean altitude is decreasing with westward transport by 13 m deg−1 during winter and 28 m deg−1, after 30&deg W, during summer. Its mean geometrical thickness is decreasing by 25 m deg−1 in winter and 9 m deg−1 in summer. Spring and fall present similar characteristics for both mean altitude and geometrical thickness. Wind plays a major role not only for the transport of dust within the SAL, but also by sculpting it. During winter, the trade winds transport SAL towards South America, while in spring and summer they scavenge dust aerosols below it by bringing maritime air masses from North Atlantic up to about 50° W. The North Atlantic westerlies, with their southern border occurring between 15° N and 30° N (depending on the season, the longitude and the altitude), prevent the SAL to develop further northward. In addition, their southward shift with altitude gives SAL its characteristic oval shape in the northern part. The effective dry deposition velocity of dust particles is estimated to be 0.07–0.08 cm s−1 in winter, 0.13–0.15 cm s−1 in spring and fall, and 0.2 cm s−1 in summer. Finally, the African Easterly Jet (AEJ) is observed to collocate with the maximum dust load of the SAL and this might promote the differential advection for SAL parts, especially during summer.

scholarly journals Precipitation and Water Vapor Transport in the Southern Hemisphere with Emphasis on the South American Region

2009 ◽  
Vol 48 (9) ◽  
pp. 1902-1912 ◽  
Author(s):  
Josefina Moraes Arraut ◽  
Prakki Satyamurty
Keyword(s):  
Water Vapor ◽  
South America ◽  
North Atlantic ◽  
Vapor Transport ◽  
Water Vapor Transport ◽  
The South ◽  
Meridional Transport ◽  
Moisture Flow ◽  
The North ◽  
The North Atlantic

Abstract December–March climatologies of precipitation and vertically integrated water vapor transport were analyzed and compared to find the main paths by which moisture is fed to high-rainfall regions in the Southern Hemisphere in this season. The southern tropics (20°S–0°) exhibit high rainfall and receive ample moisture from the northern trades, except in the eastern Pacific and the Atlantic Oceans. This interhemispheric flow is particularly important for Amazonian rainfall, establishing the North Atlantic as the main source of moisture for the forest during its main rainy season. In the subtropics the rainfall distribution is very heterogeneous. The meridional average of precipitation between 35° and 25°S is well modulated by the meridional water vapor transport through the 25°S latitude circle, being greater where this transport is from the north and smaller where it is from the south. In South America, to the east of the Andes, the moisture that fuels precipitation between 20° and 30°S comes from both the tropical South and North Atlantic Oceans whereas between 30° and 40°S it comes mostly from the North Atlantic after passing over the Amazonian rain forest. The meridional transport (across 25°S) curve exhibits a double peak over South America and the adjacent Atlantic, which is closely reproduced in the mean rainfall curve. This corresponds to two local maxima in the two-dimensional field of meridional transport: the moisture corridor from Amazonia into the continental subtropics and the moisture flow coming from the southern tropical Atlantic into the subtropical portion of the South Atlantic convergence zone. These two narrow pathways of intense moisture flow could be suitably called “aerial rivers.” Their longitudinal positions are well defined. The yearly deviations from climatology for moisture flow and rainfall correlate well (0.75) for the continental peak but not for the oceanic peak (0.23). The structure of two maxima is produced by the effect of transients in the time scale of days.

Growing multicentennial-scale precipitation variability in Eastern Brazil during the late Holocene

2020 ◽  
Author(s):  
André Bahr ◽  
Stefanie Kaboth-Bahr ◽  
Andrea Jaeschke ◽  
Christiano Chiessi ◽  
Francisco Cruz ◽  
...  
Keyword(s):  
South America ◽  
North Atlantic ◽  
Precipitation Amount ◽  
Moisture Distribution ◽  
The South ◽  
The Past ◽  
The North ◽  
Eastern Brazil ◽  
Future Global Warming ◽  
The North Atlantic

<p>Eastern Brazil belongs to the ecologically most vulnerable regions on Earth due to its extreme intra- and inter-annual variability in precipitation amount. In order to constrain the driving forces behind this strong natural fluctuations we investigated a high-resolution sediment core taken off the Jequitinhonha river mouth in central E Brazil to reconstruct Holocene river run-off and moisture availability in the river’s catchment. Modern day climate in the hinterland of the Jequitinhonha is influenced by the South American Summer Monsoon (SASM), in particular by the manifestation of the South Atlantic Convergence Zone (SACZ) during austral summer. Variations in the position and strength of the SACZ will have immediate impact on the moisture balance over the continent and hence influence sediment and water delivery. Our multi-proxy records, comprising XRF core-scanning, grain size, mineralogical (XRD), as well as organic biomarker analyses indicate abrupt centennial scale variations between dry and wet conditions throughout the past ~5 kyrs. Our results document a gradual weakening of the SASM over the past ~2,7 kyrs driven by changes in the intertropical heat distribution. This long-term trend is superposed by centennial to millennial-scale spatial shifts in moisture distribution that result from migrations of the SACZ. The combination of both processes caused increasingly pronounced aridity spells in eastern South America over the past 2 kyrs. As the spatial fluctuations were triggered by freshwater anomalies in the North Atlantic, we surmise that enhanced meltwater input into the North Atlantic due to future global warming might severely increase the risk for mega-droughts in tropical South America.</p>

Vertical distribution of cephalopods at 11°N, 20°W in the North Atlantic

1975 ◽  
Vol 55 (2) ◽  
pp. 369-389 ◽  
Author(s):  
C. C. Lu ◽  
M. R. Clarke
Keyword(s):  
Vertical Distribution ◽  
North Atlantic ◽  
The North ◽  
North Eastern ◽  
The North Atlantic

This is one of a series of four papers dealing with vertical distribution of cephalopods in the North Eastern Atlantic at six stations near 20° W and at about 10° intervals from 60°N to 11° N (Clarke & Lu, 1974, 1975 a; Lu & Clarke, 1975). The present study is based upon a series of hauls made at discrete horizons between o and 2000 m with opening-closing nets during both daylight and darkness. The collections were made for the ecological programme of the National Institute of Oceanography, Wormley, Surrey, England (now part of the Institute of Oceanographic Sciences).

Vertical distribution of cephalopods at 40°N, 53°N and 60°N at 20°W in the North Atlantic

1975 ◽  
Vol 55 (1) ◽  
pp. 143-163 ◽  
Author(s):  
C. C. Lu ◽  
M. R. Clarke
Keyword(s):  
Vertical Distribution ◽  
North Atlantic ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The 1960S ◽  
The Vertical Distribution

Little work on vertical distribution of cephalopods was possible before the development, in the 1960s, of sophisticated opening-closing devices usable on midwater trawls such as the 10 ft Isaacs Kidd trawl (IKMT; Foxton, 1963; Aron et al. 1964) and the series of rectangular midwater trawls developed by the Institute of Oceanographic Sciences (previously the National Institute of Oceanography) (Clarke, 1969 a; Baker et al. 1973). These developments have resulted in three papers on vertical distribution of cephalopods in the North Atlantic (Clarke, 1969 ft; Gibbs & Roper, 1970; Clarke & Lu, 1974) and one for the Mediterranean (Roper, 1972). The present paper describes the vertical distribution of cephalopods caught at 40° N 20° W, 53° N 20° W and 60° N 20° W in the North Atlantic based upon day and night series of horizontal hauls between the surface and 2000 m using the RMT combination net (Baker et al. 1973).

Vertical distribution, seasonality and troposphericity of ice-supersaturated air masses in the northern mid-latitudes from regular in-situ observations by passenger aircraft

2020 ◽  
Author(s):  
Andreas Petzold ◽  
Susanne Rohs ◽  
Mihal Rütimann ◽  
Patrick Neis ◽  
Berkes Florian ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Vertical Distribution ◽  
North Atlantic ◽  
Observation Data ◽  
European Research ◽  
Air Masses ◽  
The North ◽  
The North Atlantic ◽  
Passenger Aircraft ◽  
The Vertical Distribution

<p>The vertical distribution and seasonal variation of water vapour volume mixing ratio (H<sub>2</sub>O VMR), relative humidity with respect to ice (RH<sub>ice</sub>) and particularly of regions with ice-supersaturated air masses (ISSR) in the extratropical upper troposphere and lowermost stratosphere are investigated at northern mid-latitudes over the regions Eastern North America, the North Atlantic and Europe for the period 1995 to 2010.</p><p>Observation data originate from regular and continuous long-term measurements of H<sub>2</sub>O VMR, temperature and RH<sub>ice</sub> by instrumented passenger aircraft in the framework of the European research program MOZAIC which is continued as European research infrastructure IAGOS (from 2011; see www.iagos.org). The observation data are analysed with respect to the thermal and dynamical tropopauses, as provided by ERA-Interim. Additionally, collocated O<sub>3</sub> observations from MOZAIC are used as tracer for stratospheric air masses.</p><p>Our key results provide in-depth insight into seasonal and regional variability and tropospheric nature of ice-supersaturated air masses at various distances from the tropopause layer. For the vertical distribution and seasonal variation of ISSR occurrence we show a comparison of our results to radio soundings and to satellite observations of cirrus cloud occurrence from AIRS and TOVs Path B instruments. Finally, for all three regions, we investigate the trends and the dependencies of ISSR occurrence on the North Atlantic Oscillation (NAO) index.</p>

Observations on the Vertical Distribution of the Genus Acanthephyra (Crustacea: Decapoda) in the eastern North Atlantic, with particular reference to Species of the ‘purpurea’ Group.

1972 ◽  
Vol 73 ◽  
pp. 301-313 ◽  
Author(s):  
P. Foxton
Keyword(s):  
Vertical Distribution ◽  
North Atlantic ◽  
South Atlantic ◽  
The North ◽  
Mesopelagic Zone ◽  
Vertical Distributions ◽  
The North Atlantic ◽  
Eastern North Atlantic ◽  
The Vertical Distribution ◽  
Mesopelagic Species

SynopsisThe vertical distribution of pelagic decapods has been investigated at six positions, each located approximately at 10° interval of latitude between 11°N and 60°N in the eastern North Atlantic. An account of the day and night depth distribution of four mesopelagic species, Acanthephyra purpurea, A. pelagica, A. sexspinosa and A. acanthitelsonis, and four bathypelagic species, A. prionota, A. curtirostris, A. acutifrons and A. stylorostratis, is presented. The four mesopelagic species have vertical distributions which vary latitudinally in association with geographical gradients in temperature, the mesopelagic zone from about the latitude of 28°N cooling both polewards and equatorwards. It is concluded that environmental temperature is a major factor in controlling the vertical ranges of these species although other physical variables, principally light, must also be involved.A faunal boundary exists in the region of 18°N, where the North Atlantic species A. purpurea and A.pelagica are replaced by the Central and South Atlantic species A. sexspinosa and A. acanthitelsonis. The nature of the physical boundary is not clear, but it is tentatively proposed that it represents a relatively broad area where the North Atlantic Central Water and South Atlantic Central Water meet.

Vertical distribution of cephalopods at 18°N 25°W in the North Atlantic

1975 ◽  
Vol 55 (1) ◽  
pp. 165-182 ◽  
Author(s):  
M. R. Clarke ◽  
C. C. Lu
Keyword(s):  
Vertical Distribution ◽  
North Atlantic ◽  
The North ◽  
The North Atlantic

The present work is part of an analysis of catches made with rectangular midwater trawls (RMTs) in the North Atlantic at about 20°W and at 60°N, 53°N, 40°N (all in Lu & Clarke, 1975), 30°N (Clarke & Lu, 1974), 18°N and 11°N (Lu & Clarke, 1975). The collections were made for the ecological programme of the National Institute of Oceanography, Wormley, England (now part of the Institute of Oceanographic Sciences).

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