African Dust???

[marcane_1973]

10-20 years ago there was never much talk and discussion about this african dust. I have been tracking Atlantic Hurricanes for close to 19 years in the days of legendary John Hope (RIP) and one of my other favorites Neil Frank. In that time I never remembered hearing about this African dust. Did it even exist or an issue at that time? Why in recent years has African dust been showing up more and more in the Atlantic? Hope someone can help answer these questions for me Hope everyone on S2k has a great weekend. Enjoy these quiet times in the Tropics while you can PEACE!!!

[feederband]

Yeah I know...I heard of "SAL" about 4 years ago...Before that I had never heard of it...Now I here about it all the time...That wont form to much SAL out there...

[wxman57]

I'm quite sure that the dust was out there in the past, just as it is now. But until recently, we didn't have the high-resolution satellite imagery to detect it.

[Aquawind]

The hurricane issue isn't the dust itself but the subsidence and dry air associated with it...then again it may be enhancing activity.. Here is a pretty good read about it..

http://orca.rsmas.miami.edu/~phoebe/myweb3/SALpaper.pdf

[HURRICANELONNY]

I never knew that a wave passing could cause an increase in SAL. Nice read. Alot to learn about SAL and it's influence on tropical systems. I don't know for sure but I think July is usually when the SAL is at its worst.

[jrod]

I know it was strong in '94, in Florida we had a few hazy days that summer and the ocean water had a color to because of SAL

[HUC]

OK.What i can say,for me looking the Atlantic since 1956(51 years now!!!) the sal was always existant,BUT,it is sure that in the years of 1971 to 1973,the occurence and intensity of Sal had increased significantly. Since these years there are many more occurenceof SAL
Apparently that is in relation withhthe extension of the sahel belt,and the decreased in west African rains since yhe begining of the 70th.
A study was made by the Met office of Martinica,by a weather man wich name is Lefel.
I will try to obtain a copy .

[clfenwi]

A couple of years ago, I did some searching through the AMS journal archives in response to a similar question.

I apparently browsed through this article (don't seem to have it on my computer anymore, however):

Carlson, Toby N., Prospero, Joseph M.
The Large-Scale Movement of Saharan Air Outbreaks over the Northern Equatorial Atlantic
Journal of Applied Meteorology 1972 11: 283-297

and concluded that the term Saharan Air Layer dates back to at least 1968.

As wxman57 suggests, however, it wasn't until more recently that it's been on observable in a usable fashion on satellites (mid to late 1980's).

Just because it was observable, of course, didn't mean that people realized the significance of it.

This article:

Dunion, Jason P., Velden, Christopher S.
The Impact of the Saharan Air Layer on Atlantic Tropical Cyclone Activity
Bulletin of the American Meteorological Society 2004 85: 353-365

is what I credited for making SAL a household word.

[O Town]

I was just thinking of asking the same question about SAL a few days ago.
Great read Aquawind, thanks.

[benny]

A couple of years ago, I did some searching through the AMS journal archives in response to a similar question.

I apparently browsed through this article (don't seem to have it on my computer anymore, however):

Carlson, Toby N., Prospero, Joseph M.
The Large-Scale Movement of Saharan Air Outbreaks over the Northern Equatorial Atlantic
Journal of Applied Meteorology 1972 11: 283-297

and concluded that the term Saharan Air Layer dates back to at least 1968.

As wxman57 suggests, however, it wasn't until more recently that it's been on observable in a usable fashion on satellites (mid to late 1980's).

Just because it was observable, of course, didn't mean that people realized the significance of it.

This article:

Dunion, Jason P., Velden, Christopher S.
The Impact of the Saharan Air Layer on Atlantic Tropical Cyclone Activity
Bulletin of the American Meteorological Society 2004 85: 353-365

is what I credited for making SAL a household word.

I'm pretty sure that dust has been coming off of Africa for thousands of years. Didn't they find all this African dust offshore of N. America that had been around for centuries (at the bottom of the sea?)

On a related topic... too much is made of the dust. The dust during the peak of the hurricane season in 2005 and 2006 was almost the same east of the Lesser Antilles. I wouldn't pay too much attention to it.

[MiamiensisWx]

I'm pretty sure that dust has been coming off of Africa for thousands of years. Didn't they find all this African dust offshore of N. America that had been around for centuries (at the bottom of the sea?)

On a related topic... too much is made of the dust. The dust during the peak of the hurricane season in 2005 and 2006 was almost the same east of the Lesser Antilles. I wouldn't pay too much attention to it.

If I recall correctly, most of the inhibitive factors against Cape Verde development were induced by the stable mid-level air mass. This environment was quite hostile for convective initiation (i.e. 2006). The SAL isn't dust; that's an oversimplification of the complex thermodynamics. It is a layer of dry Sahelian air which is dispersed from the African continent. In addition, it is a symptom of the upper-level pattern. A strong Azores ridge (500 mbar) can spread a hostile air mass over the MDR. It can disperse SAL and strong low-level easterly shear. I think the MDR environment is influenced by the monsoonal trough over equatorial Africa... so that may signal some clues with respect to the SAL and mid-level thermodynamics. It would affect the tropical Atlantic (east of 60W).

[benny]

I'm pretty sure that dust has been coming off of Africa for thousands of years. Didn't they find all this African dust offshore of N. America that had been around for centuries (at the bottom of the sea?)

On a related topic... too much is made of the dust. The dust during the peak of the hurricane season in 2005 and 2006 was almost the same east of the Lesser Antilles. I wouldn't pay too much attention to it.

If I recall correctly, most of the inhibitive factors against Cape Verde development were induced by the stable mid-level air mass. This environment was quite hostile for convective initiation (i.e. 2006). The SAL isn't dust; that's an oversimplification of the complex thermodynamics. It is a layer of dry Sahelian air which is dispersed from the African continent. In addition, it is a symptom of the upper-level pattern. A strong Azores ridge (500 mbar) can spread a hostile air mass over the MDR. It can disperse SAL and strong low-level easterly shear. I think the MDR environment is influenced by the monsoonal trough over equatorial Africa... so that may signal some clues with respect to the SAL and mid-level thermodynamics. It would affect the tropical Atlantic (east of 60W).

Most of the really stable air was west of 60w in the Atlantic basin in 2006. Otherwise we wouldn't have had so many storms form from waves near and east of the islands. Most people think the SAL is just the dust-- of course that's not right. At this point, to me, dust is interesting but not very relevant to an intensity forecast. If people could figure when the dry air/dust was affecting the hurricane ,then maybe it would be useful. Otherwise... it is just a plot that looks good until the eye pops out with dust all around the hurricane (see Hurricane Helene of last year)

[clfenwi]

I'm pretty sure that dust has been coming off of Africa for thousands of years. Didn't they find all this African dust offshore of N. America that had been around for centuries (at the bottom of the sea?)

On a related topic... too much is made of the dust. The dust during the peak of the hurricane season in 2005 and 2006 was almost the same east of the Lesser Antilles. I wouldn't pay too much attention to it.

Just to clarify something, the citations were to indicate when researchers began to investigate the phenomenon; not to imply that the phenomenon began at that point. Claiming that it's something that hasn't been going one for a long period of time is probably about as sane as claiming that eyewall replacement cycles didn't start occurring until the 1970's.

[marcane_1973]

Thanks for all your comments guys and especially for that link on that interesting read that you gave me Aquawind. It was very interesting...