scholarly journals Tropical–Extratropical Interactions Associated with an Atlantic Tropical Plume and Subtropical Jet Streak

2005 ◽  
Vol 133 (9) ◽  
pp. 2759-2776 ◽  
Author(s):  
Peter Knippertz
Keyword(s):  
North America ◽  
South America ◽  
Atlantic Ocean ◽  
North Atlantic Ocean ◽  
Cloud Formation ◽  
Cloud Band ◽  
The North ◽  
Northwest Africa ◽  
Subtropical Jet ◽  
Upper Level

Abstract Tropical plumes (TPs) are elongated bands of upper- and midlevel clouds stretching from the Tropics poleward and eastward into the subtropics, typically accompanied by a subtropical jet (STJ) streak and a trough on their poleward side. This study uses ECMWF analyses and high-resolution University of Wisconsin–Nonhydrostatic Modeling System trajectories to analyze the multiscale complex tropical–extratropical interactions involved in the genesis of a pronounced TP and STJ over the NH Atlantic Ocean in late March 2002 that was associated with extreme precipitation in arid northwest Africa. Previous concepts for TP genesis from the literature are discussed in the light of this case study. Analysis of the upper-level flow prior to the TP formation shows a northeastward propagation and a continuous acceleration of the STJ over the Atlantic Ocean equatorward of a positively tilted upper-level trough to the west of northwest Africa. Both dynamic and advective processes contribute to the generation of the accompanying cloud band. The northern portion of the TP consists of parcels that exit a strong STJ streak over North America, enter the deep Tropics over South America, and then accelerate into the Atlantic STJ, accompanied by strong cross-jet ageostrophic motions, rising, and cloud formation. The southern portion is formed by parcels originating in the divergent outflow from strong near-equatorial convection accompanying the TP genesis. A local increase in the Hadley overturning is found over the tropical Atlantic and east Pacific/South America and appears to be related to low inertial stability at the outflow level and to low-level trade surges associated with the cold advection, sinking, and lower-level divergence underneath two strong upper-level convergence centers in the eastern portions of both a subtropical ridge over North America and an extratropical ridge over the North Atlantic Ocean. Evidence is presented that the convective response lags the trade surge by several days.

scholarly journals A meandering polar jet caused the development of a Saharan cyclone and the transport of dust toward Greenland

2019 ◽  
Vol 16 ◽  
pp. 49-56 ◽  
Author(s):  
Diana Francis ◽  
Clare Eayrs ◽  
Jean-Pierre Chaboureau ◽  
Thomas Mote ◽  
David M. Holland
Keyword(s):  
North Atlantic Ocean ◽  
Dust Emission ◽  
Saharan Dust ◽  
The Arctic ◽  
Main Stream ◽  
Dust Deposition ◽  
Ice Melt ◽  
The North ◽  
Northwest Africa ◽  
Upper Level

Abstract. In this study, we identify a new mechanism by which dust aerosols travel over long distances across the eastern side of the North Atlantic Ocean toward the Arctic. The meandering polar jet was at the origin of both dust emission through cyclogenesis over Northwest Africa and poleward transport of the uplifted dust towards the Arctic, through cut-off circulation. The dust emission was associated with an intense Saharan cyclone that formed over Northwest Africa in early April 2011. The formation of the cyclone was caused by the intrusion into subtropics, of a high-latitude-upper-level trough, linked to the meandering polar jet. The trough initiated cyclogenesis over Northwest Africa after orographic blocking by the Anti-Atlas Mountains. The still meandering polar jet led to the formation of a cut-off low further south with which the Saharan dust-cyclone merged 2 d later and moved northward with the main stream. Beside satellite observations, a simulation at high resolution was performed using the prognostic-dust permitting model MesoNH. The total dust load carried during this event to areas located north of 40∘ N was estimated by the model to be 38 Tg and dust deposition was estimated to be 1.3 Tg. The Saharan dust reaching Greenland was accompanied by warm and moist air masses that caused a rise in surface temperature of about 10 ∘C for more than 3 consecutive days over the southeastern Greenland. Ice melt over this area of Greenland was detected in the brightness temperature observations.

scholarly journals Climate and vegetation changes around the Atlantic Ocean resulting from changes in the meridional overturning circulation during deglaciation

2012 ◽  
Vol 8 (4) ◽  
pp. 2819-2852
Author(s):  
D. Handiani ◽  
A. Paul ◽  
L. Dupont
Keyword(s):  
North America ◽  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Meridional Overturning Circulation ◽  
Tropical Africa ◽  
Climate Conditions ◽  
The North ◽  
Meridional Overturning ◽  
The North Atlantic

Abstract. The Bølling-Allerød (BA, starting ~ 14.5 ka BP) is one of the most pronounced abrupt warming periods recorded in ice and pollen proxies. The leading explanation of the cause of this warming is a sudden increase in the rate of deepwater formation in the North Atlantic Ocean and the resulting effect on the heat transport by the Atlantic Meridional Overturning Circulation (AMOC). In this study, we used the University of Victoria (UVic) Earth System-Climate Model (ESCM) to run simulations, in which a freshwater perturbation initiated a BA-like warming period. We found that under present climate conditions, the AMOC intensified when freshwater was added to the Southern Ocean. However, under Heinrich event 1 (HE1, ~ 16 ka BP) climate conditions, the AMOC only intensified when freshwater was extracted from the North Atlantic Ocean, possibly corresponding to an increase in evaporation or a decrease in precipitation in this region. The intensified AMOC led to a warming in the North Atlantic Ocean and a cooling in the South Atlantic Ocean, resembling the bipolar seesaw pattern typical of the last glacial period. In addition to the physical response, we also studied the simulated vegetation response around the Atlantic Ocean region. Corresponding with the bipolar seesaw hypothesis, the rainbelt associated with the Intertropical Convergence Zone (ITCZ) shifted northward and affected the vegetation pattern in the tropics. The most sensitive vegetation area was found in tropical Africa, where grass cover increased and tree cover decreased under dry climate conditions. An equal but opposite response to the collapse and recovery of the AMOC implied that the change in vegetation cover was transient and robust to an abrupt climate change such as during the BA period, which is also supported by paleovegetation data. The results are in agreement with paleovegetation records from Western tropical Africa, which also show a reduction in forest cover during this time period. Further agreement between data and model results was found for the uplands of North America and Southern Europe, where grassland along with warm and dry climates were simulated. However, our model simulated vegetation changes in South and North America that were much smaller than reconstructed. Along the west and east coast of North America we simulated drier vegetation than the pollen records suggest.

BIOGEOGRAPHY AND ORIGINS OF THE NORTH AMERICAN STONEFLIES (PLECOPTERA)

1988 ◽  
Vol 120 (S144) ◽  
pp. 31-37 ◽  
Author(s):  
H.B.N. Hynes
Keyword(s):  
North America ◽  
South America ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Far East ◽  
Bering Strait ◽  
The West ◽  
East Europe ◽  
The North ◽  
The Far East

AbstractThe present distributions of stonefly genera in North America, their occurrence as endemics, or as shared with the Far East, Europe and South America, are considered in conjunction with geological history. It is concluded that the Plecoptera of North America have four sources of origin.There was an ancient eastern fauna shared with Europe before the formation of the North Atlantic Ocean. A second group moved in from the west during the formation of the western mountains. After formation of the isthmus one genus moved northward from South America. After the Pleistocene period several species migrated from the Bering Strait region, possibly from an Alaskan refugium. Some of these have clearly moved eastward, but a few may have moved westward.

scholarly journals The origin of deep ocean microseisms in the North Atlantic Ocean

2008 ◽  
Vol 464 (2091) ◽  
pp. 777-793 ◽  
Author(s):  
Sharon Kedar ◽  
Michael Longuet-Higgins ◽  
Frank Webb ◽  
Nicholas Graham ◽  
Robert Clayton ◽  
...  
Keyword(s):  
North America ◽  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Deep Ocean ◽  
Ocean Waves ◽  
Ocean Wave ◽  
Pressure Oscillations ◽  
The North ◽  
The North Atlantic

Oceanic microseisms are small oscillations of the ground, in the frequency range of 0.05–0.3 Hz, associated with the occurrence of energetic ocean waves of half the corresponding frequency. In 1950, Longuet-Higgins suggested in a landmark theoretical paper that (i) microseisms originate from surface pressure oscillations caused by the interaction between oppositely travelling components with the same frequency in the ocean wave spectrum, (ii) these pressure oscillations generate seismic Stoneley waves on the ocean bottom, and (iii) when the ocean depth is comparable with the acoustic wavelength in water, compressibility must be considered. The efficiency of microseism generation thus depends on both the wave frequency and the depth of water. While the theory provided an estimate of the magnitude of the corresponding microseisms in a compressible ocean, its predictions of microseism amplitude heretofore have never been tested quantitatively. In this paper, we show a strong agreement between observed microseism and calculated amplitudes obtained by applying Longuet-Higgins' theory to hindcast ocean wave spectra from the North Atlantic Ocean. The calculated vertical displacements are compared with seismic data collected at stations in North America, Greenland, Iceland and Europe. This modelling identifies a particularly energetic source area stretching from the Labrador Sea to south of Iceland, where wind patterns are especially conducive to generating oppositely travelling waves of same period, and the ocean depth is favourable for efficient microseism generation through the ‘organ pipe’ resonance of the compression waves, as predicted by the theory. This correspondence between observations and the model predictions demonstrates that deep ocean nonlinear wave–wave interactions are sufficiently energetic to account for much of the observed seismic amplitudes in North America, Greenland and Iceland.

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