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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Lun Iun 03, 2013 3:42 pm 
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Incep aici o mica serie de postari pentru a arata rolul sau efectele desertului asupra Ciclonilor tropicaliUnderstanding the Atlantic Hurricane Season: The Saharan Air Layer
Imagine
SAL conceptual model illustrating the following properties: geographic location of the African continent, ICTZ, and dust plume, surface flow (solid yellow arrows), particle trajectories (dashed yellow arrows), mid-level easterly jet (thick red arrow), 700 hPa wave axis (thin red arrow), regions of convection, and the rise of the SAL base to the west (Karyampudi et al. 1999).

Intense heating over Africa during the Northern Hemisphere Summer creates surface low pressure (a heat low) which enhances inflow and convergence. The convergent air rises in turbulent convective currents to the 500 mb level leading to a dry, well mixed layer.

The temperature/moisture/pressure gradient between the arid Saharan Desert and the moister Guinea coast causes a general low level flow from the Gulf Guinea north into the desert. The resulting thermal wind flows at 700 mb from the desert to the Gulf but is reflected to the right of motion due to the force of Coriolis. This thermal wind becomes an easterly jet known as the African Easterly Jet (AEJ or MLEJ). Instability south of the jet causes African Easterly Waves (Tropical Waves).

During the passage of these waves, the pressure gradient fluctuates and the resulting wind shift allows dry well-mixed layer of dust to leave the African coast and travel westward in what we call the Saharan Air Layer or SAL.

What is the Saharan Air Layer?

A dry, well mixed layer of dry air that formed over Northern Africa during the summer and propagate westward across the tropical Atlantic, sometimes reaching as far as the Caribbean and United States.

How Does the Saharan Air Layer formed?

Due to intense heating over Africa which causes air to rise in turbulent convection which help suspend dust particles in the lower troposphere.

At what level is the SAL normally found?

About the surface to 500 mb.

How does the SAL layer propagate from Africa across the tropical Atlantic?

Through the pressure and wind fluxes brought out by passing tropical waves.

What are the impacts on tropical disturbances?

The entrainment of mid-level dry air suppresses convection by cooling the mid-levels and resulting in downdrafts rather than updrafts. Though there have been cases where the associated AEJ help to increase positive voricity along initial disturbances, like Tropical Storm Ernesto in 2000.

How Do I Track the SAL?

The Saharan Air Layer can be tracked by various tools. My favorites include total precipitable water (PW) loops and SAL products by the CIMSS; and visible satellite imagery. In the former, SAL is indicated by low PW values while in the latter; SAL is indicated by a hazy, milky appearance. Be sure not to confuse this milky appearance with circus clouds. Other tools include aerosol mapping, RGB imagery and MODIS imagery from NASA.

Saharan Air Layer Variability

The main variability of African dust includes November-May Rainfall over Sahel and the strength and position of the Subtropical Ridge. Drier Sahel rainfall increases the chances of dust concentration over the continent but is rather more complicated than that. Drier conditions also contribute to less intense African Tropical Waves and as we saw, these waves help propagate the dust into the Atlantic, so fewer waves could mean less dust events.

The other factor is not well understood but, the strength and position of the subtropical ridge can determine how the dust propagates westward.

Interesting Facts

The SAL sometimes contributes to spectacular sunsets due to the refraction caused by the dust particles.

The SAL reduces air quality, especially in the Lesser Antilles and evidence of the SAL is sometimes evident by the milky and hazy appearance when looking at the sky, along with the aforementioned spectacular sunsets.

The SAL is an intraseasonal modulator of not only tropical cyclone activity but the rainy season over the Caribbean.

The aerosol particles in the SAL can act as condensation nuclei for the formation clouds.

Some of this information was made possibly by Phoebe Anne Woodworth; Division of Meteorology and Physical Oceanography, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida
Imagine
Photo of the Saharan Air Layer taken from the NOAA P-3 Orion after SALEX mission 20060918h during the ferry back to Barbados. Saharan dust gives the sky an orange glow during this late afternoon sunset in the eastern Caribbean. Small cumulus clouds can be seen poking through the tops of the dust layer.
Totul e luat de aici, dar posibil sa vi se incarce mai greu.
http://www.wunderground.com/blog/Weather456/comment.html?entrynum=203&tstamp=


Ultima oară modificat de Roberta 93 pe Lun Iun 03, 2013 4:18 pm, modificat 1 dată în total.

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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Lun Iun 03, 2013 3:46 pm 
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Imagine


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Lun Iun 03, 2013 4:15 pm 
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Membru din: Mar Mar 26, 2013 8:42 pm
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Imagine
Figure 1. Depiction of favorable and unfavorable conditions for tropical cyclone development.

Imagine
Figure 2. Conceptual model of the African Easterly Jet through 5W west. Correction: where it says 850 mb geopotential it should say 500 mb geopotential height.

Imagine
Figure 3. A montage showing the main causes of vertical wind shear with TUTT axis and troughs in the upper level westerlies (purple), African Easterly Jet (yellow) and the El Nino Southern Oscillation/Subtropical Jet (red).

Voi reveni cu detalii despre TUTT (Tropical Upper Tropospheric Trough)


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Lun Iun 03, 2013 5:55 pm 
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Despre TUTT;
http://www.google.ro/imgres?imgurl=http://www.aoml.noaa.gov/hrd/tcfaq/graphics/small_TUTT2.jpg&imgrefurl=http://www.aoml.noaa.gov/hrd/tcfaq/A10.html&usg=__44CA_nG9pwdW-kJ4QvtlYP5bi70=&h=215&w=312&sz=24&hl=ro&start=1&zoom=1&tbnid=GKGDw7EjEGs7KM:&tbnh=81&tbnw=117&ei=u5-sUZqzEoLaPJ6FgagP&prev=/images%3Fq%3Dtropical%2Bupper%2Btropospheric%2Btrough%26sa%3DX%26hl%3Dro%26gbv%3D2%26tbm%3Disch&itbs=1&sa=X&ved=0CCoQrQMwAA


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Lun Iun 03, 2013 7:03 pm 
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Hmmm...unde naiba ajung?
Rolul ciclonilor topicali in formarea TUTT deci acest TUTT are un dublu rol. Cel putin dublu...
http://journals.ametsoc.org/doi/pdf/10.1175/1520-0469(1999)056%3C2891%3ATROTCI%3E2.0.CO%3B2


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Lun Iun 03, 2013 7:09 pm 
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Aici sunt cateva animatii dragute si cateva explicatii sumare despre TUTT, pentru cei grabiti.
Scurt si la obiect!
http://www.meted.ucar.edu/lobjects/hurrican/tutt/


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Lun Iun 03, 2013 7:21 pm 
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Este o finalizare a unui cut-off, dar la randul lui, un ciclon tropical determina un TUTT...
Interesant, un cerc vicios! Pana la urma energia decide. Efectele mecanice nu pot avea loc fara "acordul" termodinamicii. Termodinamica va guverna, mecanic ar fi un fel de efect de feed-back.
Da, poate singurul efect de feed-back MECANIC evidentiat acum in carnetelul meu.


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Lun Iun 03, 2013 8:04 pm 
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Diapozitive dragute, despre TUTT.
Merg din scroll.
http://www.mccrones.com/tropical/METR498/chp7-n-8.ppt#1


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Mar Iun 04, 2013 3:55 pm 
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Imagine

Ciclonii tropicali iau nastere din furtunile tropicale, care la randul lor sunt furtuni obisnuite initial.


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Mar Iun 04, 2013 4:08 pm 
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Praful Saharian ucide norii. Are efect de racire asupra Atlanticului.
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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Mie Iun 05, 2013 4:59 pm 
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Cum ii pazeste ca un gardian...Saharian air layer.
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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Sâm Aug 17, 2013 1:40 am 
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http://journals.ametsoc.org/doi/full/10.1175/1525-7541(2003)004%3C1119%3AANNATR%3E2.0.CO%3B2

http://www.cpc.ncep.noaa.gov/products/fews/AFR_CLIM/AMS_ARC2a.pdf



ARHIVA incepand cu 1 noiembrie 2007

http://hydrology.princeton.edu/~justin/research/project_global_monitor/index_africa.html

Nu e vorba de Sahara, insa e foarte important.
http://oas.gsfc.nasa.gov/MenaWisp/Publications/2008/2008_NHD_SERVIR_Africa_Nzoia_Flood_Modeling.pdf


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Sâm Aug 17, 2013 3:29 pm 
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De aici se poate monitoriza temperatura dar si anomalia SST a Atlanticului Tropical.

http://wattsupwiththat.com/2013/08/15/mid-august-hurricane-development-region-sea-surface-temperature-anomaly-update/


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Sâm Aug 24, 2013 2:40 pm 
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http://www.goes-r.gov/products/opt2-green-vegetation-fraction.html


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 Subiectul mesajului: Re: Sahara,actuala si cea umeda.
MesajScris: Mie Aug 28, 2013 11:59 pm 
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http://www.climb-fp7.eu/media/documents/CLIMB%20-%20Chiba.pdf
Water and irrigated farming systems (EAU4Food)
Water harvesting (WAHARA)
Natural resources management (AFROMAISON)
Drought monitoring, forecasting and adaptation (DEWFORA)
Waste water treatment by means of biotechnology (WATERBIOTECH)
Water-related vector-borne diseases (HEALTHY FUTURES)
http://africanclimate.net/en
http://www.dewfora.net/
http://www.wahara.eu/
http://www.afromaison.net/
http://www.healthyfutures.eu/
http://www.waterbiotech.eu/
http://www.eau4food.info/
http://www.africa-cluster.eu/home/index


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