June 1 marks the traditional start of the Atlantic hurricane season.  The past several years have seen an increase in hurricanes from the previous number of years.  All sorts of reasons go into why this is the case, and I don’t want to go into all of them.  A great many of these effects are natural cyclic effects, and we seem to have hit a period when many of them are tending to be peaking at about the same time.  I rather think that last year’s record breaking hurricane season was just a statistical fluke.  Hey, you always get statistical outliers, right?  In years past, all we could do was sit and wait to see how and when the storms developed.  When ships docked, you got information about where storms had been at sea, but you didn’t really know where they were until they hit land.  You also didn’t have any good feel for how bad they’d be until they hit land, either.  However, satellites changed things.  Now, we can see storms developing at sea.  We know where they are and where they appear to be heading.  Now, we can measure all sort of meteorological parameters from satellites.  Combining these measurements with data collected at the surface and from aircraft, we are getting pretty good at predicting where storms will go and how strong they will be when they get there (at least for a few days into the future).  We still have trouble with predicting storms before they form, as in what the hurricane season will be like, but we are getting better at that, too.

So, what does this season look to bring?  I have a personal interest in this as I have some very close friends and family living near the coast.  They were affected last year by the storms (Hey, with so many, it would have been hard for the storms to miss all of them!).  There are several interesting developments.

First, the last few decades seem to have been a period of unusually few storms.  So, even returning to normal will look like a lot more storms, and will in fact represent an increase in the number of storms over what people are used to.  Sadly, it was during this period of unusually few storms that people built along the coast, expecting that climate pattern to continue.  But, an average is just that --- an average.  Seasons with unusually few storms are balanced by seasons with more than average storms.  A couple decades of quiet is balanced by a couple of active hurricane decades.  So, even discounting any human related factors, if any, we can expect more hurricanes the next few years.

Earlier this year, there were reports of a La Nina developing in the Pacific.  This cooling of water does not have as big of an effect on Atlantic hurricanes as an El Nino warming, but it can have some effect, it seems.  Recent data, though, shows that the cooler water is now warming up quite nicely, so La Nina is no longer a factor.

The Sun has about an 11 year sunspot cycle, and it is currently working its way up from solar minimum.  For some reason, this seems to mean more storms, but that is one of the cyclic variables that I mentioned earlier.

A new variable, though, is Saharan dust.  This is new in that we have only just begun to study it, not new in the sense that it wasn’t there before.  The hot, dry, dusty air of the Sahara spills out over the eastern Atlantic Ocean.  This Saharan Air Layer (SAL) had the effect of suppressing hurricane development and intensification.  It also suppresses rainfall.  The SAL is monitored from aircraft, but it can also be seen from space.  The SAL carries dust, and this dust is visible from satellites.  The Sahara, one of the driest places on Earth, accounts for much of the dust in the Earth’s atmosphere.  This dust seems to be increasing.  One reason may be that poor water management in African nations is resulting in the expansion of the Sahara.  However, as the Sahara expands, it impacts weather and climate in the region, causing more drought, resulting in more dust and a larger SAL.  In other words, the system has a positive feedback loop.  Now, this is bad for northern Africa.  However, it has an effect in that it can suppress hurricane development.  What is not clear, though, is if it really suppresses hurricane development, or simply moves it farther to the west.  Some Saharan dust clouds are so large that they can even cross the Atlantic.  Florida occasionally experiences the effects of Saharan dust, primarily in the form of hazy skies and colorful sunrises and sunsets.

GOES satellites and NOAA aircraft have been monitoring the signs of the SAL.  However, on STS-107, the last flight of the Columbia, there was a special purpose instrument designed specifically to study the Saharan dust clouds.  This was the Mediterranean Israeli Dust Experiment (MEIDEX) package.  MEIDEX was the reason that Columbia carried and Israeli astronaut, Ilian Ramon.  MEIDEX did not look just at the Mediterranean.  Yes, that was one of its target study areas.  But, it also looked at the eastern Atlantic Ocean, primarily studying the motion of Saharan dust clouds.  Though the MEIDEX package was destroyed when Columbia burned up and broke apart upon reentry over Texas, most of the data survived.  In years past, instruments such as this would collect and store data to be studied when the instrument returned to Earth.  Modern telemetry capabilities, though, permit almost all data to be transmitted to Earth during the mission itself.  So, we can take comfort in knowing that the astronauts did not die in vain.  The work they did in space survives them, but at a very high price.

So, what can we say from all of this?  Well, it isn’t really clear.  Studies of these Saharan dust clouds are just starting.  However, it looks like there may be a little more dust this year than last.  That favors fewer hurricanes.

Now, before anyone goes around rejoicing, think about what I am saying:  there will be fewer hurricanes than a record breaking active year.  That still doesn’t mean that there won’t be more than average, just not as many as last year.

-Astroprof