Dust forecast for the 2009 Atlantic hurricane season
There will be less African dust than usual over the tropical Atlantic during this year's hurricane season, according to a new experimental dust forecast issued by Dr. Amato Evan of the University of Wisconsin. Dr. Evan used a statistical model that correlated levels of dust activity in past years with rainfall over the Sahel region of Africa and a natural regional wind pattern known as the North Atlantic Oscillation (NAO). He forecasts that dust levels over the Main Development Region (MDR, 8 - 20°N & 15 - 65°W) for Atlantic hurricanes during this year's hurricane season will be similar to last year's below-average levels, thanks in large part to plentiful rains over the Sahel region of Africa during the 2008 rainy season (Figure 1). However, the dust levels expected this year do not approach the record lows seen in 1994 and 2005. Dust forecasts made in May or June are skillful going out five months, with a skill 11 - 16% better than a "no-skill" forecast using climatology.
Figure 1. Rainfall over the Sahel region of Africa was generally 50 - 100 mm (2 - 4 inches) above average during the 2008 rainy season (about 20 - 80% above average). The heavy rains promoted vigorous vegetation growth in 2009, resulting in less bare ground capable of generating dust. Image credit: NOAA/Climate Prediction Center.
The Sahara and the Sahel: significant sources of dust
The summertime dust that affects Atlantic tropical storms originates over the southwestern Sahara (18° - 22° N) and the northwestern Sahel (15° - 18° N) (Figure 2). The dust that originates in the Southwest Sahara stays relatively constant from year to year. However, the dust from the northwestern Sahel varies significantly from year to year, and understanding this variation may be a key factor in improving our forecasts of seasonal hurricane activity in the Atlantic. The amount of dust that gets transported over the Atlantic depends on a mix of three main factors: the large scale and local scale weather patterns (windy weather transports more dust), how wet the current rainy season is (wet weather will wash out dust before it gets transported over the Atlantic), and how dry and drought-damaged the soil is. The level of drought experienced in the northwestern Sahel during the previous year's rainy season (June - October) is the key factor of the three in determining how much dust gets transported over the Atlantic during hurricane season, according to a January 2004 study published in Geophysical Research Letters published by C. Moulin and I. Chiapello. A dry rainy season the previous year will make an expanded area of loose soil which can create dust. It is also possible that the corresponding changes in vegetation can alter the regional weather patterns, causing more dust production.
Figure 2. Map of the mean summer dust optical thickness derived from satellite measurements between 1979 and 2000. Maximum dust amounts originate in the northern Sahel (15° to 18° N) and the Sahara (18° to 22° N). The Bodele depression in Chad is also an active dust source. Image credit: Evidence of the control of summer atmospheric transport of African dust over the Atlantic by Sahel sources from TOMS satellites (1979-2000) by C. Moulin and I. Chiapello, published in January 2004 in Geophysical Research Letters.
How dust suppresses hurricanes
Dust acts as a shield which keeps sunlight from reaching the surface. Thus, large amounts of dust can keep the sea surface temperatures up to 1°C cooler than average in the hurricane Main Development Region (MDR) off the coast of Africa, providing hurricanes with less energy to form and grow. Dust also affects the Saharan Air Layer (SAL), an layer of dry, dusty Saharan air that rides up over the low-level moist air over the tropical Atlantic. At the boundary between the SAL and low-level moist air where the trade winds blow is the trade wind inversion--a region of the atmosphere where the temperature increases with height. Since atmospheric temperature normally decreases with height, this "inversion" acts to but the brakes on any thunderstorms that try to punch through it. This happens because the air in a thunderstorm's updraft suddenly encounters a region where the updraft air is cooler and less buoyant than the surrounding air, and thus will not be able to keep moving upward. The dust in the SAL absorbs solar radiation, which heats the air in the trade wind inversion. This makes the inversion stronger, which inhibits the thunderstorms that power a hurricane. The dust may also act to interfere with the formation of cloud drops and rain drops that these thunderstorms need to grow, but little is known about such effects. It is possible that dust may act to help hurricanes by serving as "condensation nuclei"--centers around which raindrops can form and grow.
For additional reading
Dr. Evan published a study in Science magazine this March showing that 69% of the increase in Atlantic sea surface temperatures over the past 26 years could be attributed to decreases in the amount of dust in the atmosphere.
Jeff Masters
Reader Comments
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Barbados is great. I notice it is a highly developed island, have alot of churches, almost all their parishes have church origins, I think. But the Cricket Kensington Oval and downtowm Bridgetown was best sites of all.
Probably one of the biggest difference is topography. Barbados is relatively flat causing it to be dry and hot. While here in SK we are mountainous and thus more likely to receive relief rainfall and sometimes a cooler rainshadow.
Becuz of this they have much more landuse available. The center of our island is unpopulated just a few farmers on the hillsides.
-20 windchill with 6 ft of snow on the ground ever seen snow up close before 456
AOI #1
AOI #2
Now what did he ever do to deserve that kind of invitation... be nice :)
The coldest nights I porbably could of remembered was the winter 2007-2008 and 19C is cold for us.
Finally someone that hates cold weather lol
Most people here enjoy it more than warm weather.
OK, after that last remark... you deserve Toronto in January. 19C cold... sheesh.
I don't like snow... Victoria is a Weather Anomaly, due to its unique location. We seldom get snow, and when we do it normally gone in a day or two.... last couple years due to ummm GW.. we have been getting some wicked winters??
Normally we can golf year round.
"This happens because the air in a thunderstorm's updraft suddenly encounters a region where the updraft air is cooler and less buoyant than the surrounding air, and thus will not be able to keep moving upward."
I thought that an inversion was where you have some warmer air aloft?
sam
well probably during the winter of 2007-2008, many palces across the global receive chillin conditions, porbably snow in Iraq is the most striking. Some scientist said La Nina had cooled the global that winter.
Afghanistan's coldest winter kills over 900
And one my favorite blog posts, lol
January Highlights Feb 1 08
Happy February to all!
Lets get down to the nitty gritty. You say Global Warming, I say Global Cooling. January saw much cold winter weather, not just in the United States, but also around the Northern Hemisphere. Parts of the Middle East saw their first snow in history. I witness my first cold front in living memory, and I live in the Caribbean. A cold front was analyzed near 11N in the Tropical Atlantic. Snow flurries were detected on radar just offshore Southeast Florida, just as 08 began. Again, some say Global warming, I say Global cooling.
Under certain conditions, the normal vertical temperature gradient is inverted such that the air is colder near the surface of the Earth. This can occur when, for example, a warmer, less dense air mass moves over a cooler, denser air mass. This type of inversion occurs in the vicinity of warm fronts, and also in areas of oceanic upwelling such as along the California coast. With sufficient humidity in the cooler layer, fog is typically present below the inversion cap. An inversion is also produced whenever radiation from the surface of the earth exceeds the amount of radiation received from the sun, which commonly occurs at night, or during the winter when the angle of the sun is very low in the sky. This effect is virtually confined to land regions as the ocean retains heat far longer. In the polar regions during winter, inversions are nearly always present over land.
A warmer air mass moving over a cooler one can "shut off" any convection which may be present in the cooler air mass. This is known as a capping inversion. However, if this cap is broken, either by extreme convection overcoming the cap, or by the lifting effect of a front or a mountain range, the sudden release of bottled-up convective energy — like the bursting of a balloon — can result in severe thunderstorms. Such capping inversions typically precede the development of tornadoes in the midwestern United States. In this instance, the "cooler" layer is actually quite warm, but is still denser and usually cooler than the lower part of the inversion layer capping it.
lol, I actually don't take sides, but at that time, I was commenting on article I was reading.
Seems to be a wall between the Epac and the GOM/BOC
lol
You appear to be doing a H*ll of a job :)
They are pretty high (near Bahamas/Eastern GOM) but I don't know if they will cool or continue to warm. SSts are dynamic and they can get cooler in 2 weeks time, but with rather cloud free skies, only wind stress could cool those waters.
Also notice the SSTs in the Central Caribbean are relatively cooler (not related to the 2005 map) and that was due to the week-2 weeks long period of convection earlier back.
The MDR is still cooler in 2009 though but troubling in that that is not where we are expecting much development this year. Rather closer to home.
The Bahamas, Gulfstream, and Eastern GOM are definitely warmer than 2005.
Well I guess the GOMEX is the place to look this season.
OK, you can stop now. Days of 92-95 degree heat gets old real quickly!
The southeastern Atlantic seaboard needs to be careful as well. The Gulfstream has been significantly cooler than normal the past few years, but now it looks like it is warming back up to normal levels. A hot, deep Gulfstream can make a system bomb like nothing else, as storms like Andrew or Hugo can show.
only place I see thats significantly warmer than 05'is the GS and part of the west atlantic ,the waters in the bahamas and the eastern GOM looks a bit cooler than 05',IMO
Conditions at SBPT2 as of
(9:06 pm CDT on 06/20/2009)
0206 GMT on 06/21/2009:
Air Temperature (ATMP): 82.9 °F
Water Temperature (WTMP): 87.8 °F
Good warm evening everyone.
Interesting seeing the diving dry air heading south over the eastern side of NA into the Atl.
I read that birds will get caught in the eye of a storm and ride for hundreds of miles. They become so exhausted they just fall out of the sky where the eye passes. Some storm chasers driving down a deserted I-10 during Rita told how they were just falling everywhere. It is strange. :( poor birdies.
The weirdest thing we found from a hurricane was a broken fishing pole amd someones bait bucket. Lol. Dont know where they came from but Ike left em in the front yard.
218
How do you lose ice, and get colder at the same time? Salt on the ice - just like when making ice cream. (salt or something else that depresses the freezing point) Maybe something on the dust?
200mb Vorticity - North Atlantic - Latest Available - Large Scale
NATIONAL WEATHER SERVICE TALLAHASSEE FL
935 PM EDT SAT JUN 20 2009
...A HEAT ADVISORY REMAINS IN EFFECT FOR SOUTHEAST ALABAMA...
SOUTHWEST AND SOUTH CENTRAL GEORGIA AS WELL AS THE EASTERN FLORIDA
PANHANDLE AND FLORIDA BIG BEND FROM 1 PM EDT (NOON CDT) SUNDAY
AFTERNOON UNTIL 8 PM EDT (7 PM CDT) SUNDAY EVENING...
.UPDATE...OUTSIDE OF A FEW MINOR TWEAKS IN THE GRIDS...NO MAJOR
UPDATES ARE NEEDED THIS EVENING. TEMPERATURES MANAGED TO REACH
THE CENTURY MARK FOR THE FIFTH CONSECUTIVE DAY HERE IN TALLAHASSEE
AND RANGED FROM 96 NEAR THE COAST TO 103 AT TALLAHASSEE. DOTHAN
WAS THE SECOND HIGHEST ACROSS THE LOCAL AREA AT 102 DEGREES.
APALACHICOLA DID TIE THE OLD RECORD THAT WAS SET IN 1998 AT 98
DEGREES TODAY. OUTSIDE OF THE HEAT AND A FEW STORMS SOUTH OF DIXIE
COUNTY EARLIER...THINGS REMAINED VERY QUIET ACROSS MUCH OF THE
REGION THIS AFTERNOON AND EVENING. EXPECT THESE CONDITIONS TO
CONTINUE INTO THE OVERNIGHT HOURS TONIGHT WITH LOWS ONLY DROPPING
TO THE MID 70S INLAND AND ONLY DOWN TO AROUND 80 AT THE COAST.
SUNDAY WILL BE VERY SIMILAR TO THE PAST FEW DAYS WITH TEMPERATURES
EXPECTED TO REACH 100 TO 102. THEREFORE...THE HEAT ADVISORY WILL
CONTINUE FOR SUNDAY AFTERNOON.
Should we get some Trough syrup? :)
What is your take Drak,the heat is pumping up and something has to give ?
The Earth needs to vent, right?
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