23 July 2009
Breakthrough in Hurricane Predictions?? Maybe!
Posted by Dan Satterfield
There was an intriguing paper in Science this month about tropical cyclone predictions.
Every spring, there is considerable media attention to the forecasts from Colorado State and NOAA, on how many hurricanes we can expect. Every spring, I remind my viewers that these forecasts have little skill. Nonetheless, you cannot learn to forecast something unless you try and trying brings new knowledge and insight. So have at it, but tell the public that there is low confidence in the forecast.
The connection between El Nino, and La Nina, and Atlantic hurricanes has long been known, and the current ENSO phase is an important ingredient in these seasonal forecasts of tropical cyclone activity. Specifically, an El Nino tends to increase wind shear over the Atlantic and reduce the number of hurricanes, while La Nina does pretty much the opposite. An El Nino seems to be brewing right now and may hold down the number of storms this year.
El Nino, La Nina and Cen. Pac. Warming- image From Kim et al. in Science 3 July 2009- complete cite in text.
Some El Nino years have turned out to rather active though, and three scientists at Georgia Tech. (H.-M. Kim, P. J. Webster, J. A. Curry, Science 325, 77 (2009) may have discovered one reason!
The answer?
CENTRAL PACIFIC WARMING (CPW)
El Nino is a warming of waters in the Eastern Pacific. Eastern Pacific Warming (EPW). La Nina is a cooling of waters in the Eastern Pacific (EPC). There also seems to be a cycle of warming in the sea surface temps. of water in the Central Pacific. This (CPW) warming has a strong connection to hurricanes too. Not only that, but it has a strong connection to storms that affect the Gulf and East coast of the U.S, Mexico and Canada! Apparently even stronger a connection than El Nino.
Greg Holland from NCAR wrote a perspectives piece on the paper by Webster-Kim and Curry and speculates that perhaps some El Nino events in the past have been misidentified even.
From Hye Mi Kim and colleagues. Red is >normal T. Cyc. activity. Blue is below normal.
Wait, there’s more!
Forecasting the development of an El Nino, or La Nina ahead of time is very difficult. Especially if we are between cycles. There is a forecast wall, in the early spring, that makes it nearly impossible. So, insurance companies and residents cannot know whether an El Nino or La Nina is coming for hurricane season. These CPW events are, according to Kim et.al. MUCH more forecastable!
So they may have found a new method of forecasting tropical cyclone numbers, that is more accurate, and easier to forecast than in the past!
You do that, and you get published in what is perhaps the most distinguished peer reviewed journal, of them all!
SCIENCE.
Later,
Dan
ps: If you want to really understand how El Nino’s begin and end, then Taichiro Sakagami has made it easy. His videos are highly recommended.
Dan Satterfield has worked as an on air meteorologist for 32 years in Oklahoma, Florida and Alabama. Forecasting weather is Dan's job, but all of Earth Science is his passion. This journal is where Dan writes about things he has too little time for on air. Dan blogs about peer-reviewed Earth science for Junior High level audiences and up.
Hey Dan,
Your article motivate me to learn more for these meteorological issues and I just found also this link that NASA has also a very interesting Animation compares the effects of La Nina and El Nino on the formation of Atlantic Hurricanes that supports your points as well concerning forecasting procedures.
http://svs.gsfc.nasa.gov/vis/a010000/a010000/a010047/
Best wishes friend,
Gabriel
So how much is the Saharan dust a factor? I have been keeping up with NHC reports this year and it seems like the dust is tearing those Eastern Atlantic tropical waves apart. If this is so, will dust become more of a factor in the future? Does climate change has something to do with excessive dust?
The answer is possibly to both! Knowledge is scant, but it’s getting more and more interest. As for Climate, the world is a dustier place during glacier periods, very strong evidence for that. As for predictions of future “dustiness” as he planet warms…not sure. Will ask around. My first guess is less dust, and feel pretty confident on that. (Planet as a whole- with some areas like U.S. SW and Plains getting dustier as rainfall drops).
Do you have anything in Peer reviewed Science to back up your claim of sunspots and tropical cyclone frequency? I do not publish unsubstantiated theories or opinions unless they are backed up with some real science.
The NHC says pretty much the same thing your saying Dan. It is incomplete research. Was just thinking you might have another angle on it. I submitted this question to them:
What happens when a large plume of soot (like the Asian brown cloud) encounters a cyclone? Can it make it stronger? Weaker? Both? Or no effect?
This was the reply:
That’s a good question and one that we don’t have a great handle on yet. Here are a few thoughts on this issue:
1) There have been some studies that have shown that pollution aerosols can act as cloud condensation nuclei (CCN), promoting rain in a cloud. In other words, the tiny pollution particles act as a magnet for water vapor to condense onto. Get enough water vapor condensing onto a CCN and a raindrop eventually forms. If this is indeed true, then you can imagine an atmosphere where there is a certain amount of water vapor in the air. If we add more pollution to the atmosphere and therefore increase the number of CCN, then we end up with more particles that have to share the available water vapor that’s in the air. So that water vapor gets spread “thinner” and fewer particles can actually attract enough water vapor to form a raindrop. The end result would be a reduction in rainfall, which could conceivably even affect a cyclone. Again though, this is still an ongoing area of research and not always predictable.
2) We’ve also been looking at natural sources of dust that comes from desert regions. NOAA has been looking at how Saharan dust storms can affect hurricanes. What we’ve found is that these dust storms have very dry air and strong winds that can suppress storm development. Some scientists are even looking at how the dust itself can affect cloud formation in a seedling tropical disturbance. These dust storms are big (the size of the lower 48 US states) and can travel as far west as the Caribbean, Central America, and South Florida. For more info on these dust storms, see this link:
http://www.aoml.noaa.gov/hrd/tcfaq/A17.html
3) Some studies are also finding that Saharan dust storms (and possibly even pollution plumes and other desert dust sources around the world) can actually cool the oceans in the tropics. If there’s enough dust over time, the amount of solar energy that reaches and warms the ocean surface might actually get filtered out a bit. Of course, hurricanes usually need warm ocean water to form (usually above 80 deg F or so). So, in this case, aerosols might have an additional (though indirect) negative impact on storms.
Hope this helps.
Regards,
Jason
What happens when a large plume of soot (like the Asian brown cloud) encounters a cyclone? Can it make it stronger? Weaker? Both? Or no effect?
**************
Jason Dunion
NOAA/AOML/Hurricane Research Division Phone: 860-295-0555
4301 Rickenbacker Causeway Fax: 305-361-4402
Miami, FL 33149
Very interesting stuff!