VITAMIN E
For those unfortunates who do not benefit from the University environment, that's pronounced "El Weenie-o", and reflects the climatic influence that an occasional fluctuation in the tropical Pacific Ocean exerts on Virginia. Or, quoting University of Delaware's Laurence Kalkstein, "It's the vitamin E of climate: according to some people it explains everything, but it really does precious little around here". Dr. Kalkstein has advised us that he's more "uncertain" about Delaware than Virginia.
Multiple Choice. We're referring, of course, to the 1997 edition of "El Niño", which is
a) weakening as of this writing
b) overblown
c) credited with the worst storm in history in the eastern North Pacific ocean
d) supposed to get worse with global warming
e) stamps out malaria that is supposed to get worse with global warming
f) all of the above
Of course the answer is "f"! Otherwise we wouldn't use such a childish rhetorical device as an ersatz-exam. But maybe that's enough of an affront to our loyal readers' sensibilities as to encourage further reading of our study of El Niño and Virginia weather.
"El Niño" is a bit more complicated than our poor attempt at humor. In fact, there's a lot of confusion about what it is, and no one has (in our humble opinion) a very good explanation as to why it happens.
El Niño is the Spanish reverential for the Christ Child, and El Niños--a sensible change in the weather along the coast of Peru that often occurs around Christmas--have been noted at least for centuries by the locals.
The "normal" way of the weather down there is pretty boring, but also fairly profitable for those who make a living from the sea. Much of the time, the strong and persistent east-to-west trade winds that blow across the Pacific ocean continually drag water away from the Peruvian coast and send it towards the Philippines. It's a fact that sea level in those islands is usually about two feet higher than it is in Peru as a result of all this transfer.
The effect of the persistent removal of surface water along the South American coast is that some of the lower, cooler water is dragged towards the surface, or "upwells", and along with it come a ton of nutrients that would normally be sinking out of sight. Nutrients bring fish, mainly anchovies, and as long as this process continues there's plenty to catch.
The result of all this is that warm water keeps piling up in the western Pacfic. It's called the "warm pool", and is the warmest spot in the world's large oceans. (Some small shallow ones like the Red Sea are warmer.) And colder water continues to upwell off of Peru so that the eastern tropical Pacific is usually quite a bit cooler than the western portion.
As the worlds climates and currents travel southward towards the end of the year, the east-to-west trade winds are displaced to the south for a brief period, usually around Christmas. This changes the weather dramatically along the coast of South America, by shifting the winds from east to west, which stops the upwelling, stopping fishing and generally enforcing a long holiday rest, festivals and socializing.
This temporary interruption in the normal way of things used to be called "El Niño". But there is a longer and more important change that takes place when, instead of being a phenomenon of a few weeks length, the current reversal establishes itself for a year or so. That's what "El Niño" means now. To attempt an explanation of all this requires a few brief digressions...
Hot air over the western Pacific is buoyant with respect to its surroundings, and as a result there are a lot of thunderstorms and a persistent area of lowered atmospheric pressure at the surface. The opposite occurs in the east, where there's downward motion because of the colder, denser air. This suppresses precipitation, making the west coast of South America one of the driest places on the planet.
These areas of upwards and downwards motion form a complete circulation where air normally moves westward with the low-level trade winds, rises over the Pacific hot spot, and then returns eastward at high altitude to the South American coast, descending and maintaining the loop as it falls back into the trade winds.
The phenomenon was first noted in the scientific literature by G.T. Walker in 1924, and the circulation bears his name. It didn't get his name until several decades later. In the interim he was derided as a crank for finding something so stupid, irrelevant, and probably erroneous. The weather paladins of the time simply didn't think such a thing could exist, and so it didn't. [If this type of behavior sounds familiar in today's climate of hysteria, you're just a cynic!]
ILLUSTRATION: Schematic of the Walker Circulation (from Henderson-Sellers and Robinson, maybe?)
The relative upward motion over the hot spot means that air is leaving, so barometric pressure tends to be low in the western Pacific, while the opposite is true in the east.
This is considered the "normal" way of things. However, for reasons that are hardly well understood, the circulation occasionally reverses, resulting in high pressure in the western Pacific and low pressure in the east.
This pattern of linked changes in pressure between the western and eastern Pacific is called the "Southern Oscillation", and is expressed as the difference in surface pressure between Darwin, Australia and Tahiti. When the difference (Tahiti minus Darwin) is negative, pressures are higher at at Darwin and, if the difference exceeds a standard statistical threshold, El Niño is born.
The difference in pressure is known as the Southern Oscillation Index (SOI) and is one of the standard measurements of El Niñoness.
What El Niño really does, then, is to stop the upwelling of cold water along the South American coast. Obviously when El Ni&ntlide;o goes away, there's more cold water than before, trapped beneath the surface. So when the upwelling begins again, sea surface temperatures off Peru drop with a vengeance. This "reverse phase" of El Niño is known as La Niña.
This means that El Niño has an influence on global temperature. When the trade winds reverse, the reduction in cold upwelling creates a temporary spike in global temperature. But when the cold water comes roaring back (La Niña), temperatures drop below the secular average. One's also left to conclude that the stronger the El Niño, the greater the amount of cold upwelling that is suppressed, and therefore the succeeding La Niña becomes stronger, too. So everything gets stronger and stronger and stronger until climate ends? Obviously not--there are some unknown stabilizing factors in the climate that are as obvious as the fact that the planet, a mere 15°C above freezing in average surface temperature, has never froze over.
Judging from the nightly El Niño Updates, this must be causing an awful lot of death and destruction in the United States. Alas, a look at what El Niño really does around here makes the news seem a bit sensationalistic. With regard to news stories about our atmospheric environment, we're sure that's just a temporary aberration, no?
There is a statistical linkage between the existence of El Niños and a strengthening of westerly winds over the subtropical atlantic. Some of the enhanced upward motion in the Eastern Pacific gets displaced to the east, often in the form of a very strong band of winds that crosses Mexico and emerges into the Gulf and Atlantic. This band, called the subtropical jet stream, is very apparent in satellite images during El Niño fall and winter.
Hurricanes--especially strong hurricanes--are generally "disturbances in the easterlies", or strong circulations that form within the east-to-west trade winds that blow across the Atlantic subtropics, in search of the earth's thermal equator (where the upward motion of the warmest zone sucks in the trades). As easterly disturbances, hurricanes are especially disrupted by winds from the opposite direction. Suffice it to say that westerly winds destroy the delicate balance of the hurricane that is required to mow down subdivisions.
That same subtropical jet stream adds energy (speed) to the more common westerly jet (the one that appears on the evening weather program), which itself is the mother to almost all low pressure systems. When big enough, these cyclones produce the migratory cold rains and snows of winter that make people wish for global warming.
Statistical studies over the United States show that the region where cyclonic activity tends to be most altered by El Niño is in the Pacific Southwest, especially in California south of Point Concepcion (that's the thing that juts out between Santa Barbara and San Francisco). This means Los Angeles, which means Hollywood and Malibu Canyon where people who care more than the average american, i.e. actors, live. It's a fact that a good El Niño is likely to wash a few of these homes--or at least a significant portion of some--into the Pacific. And others, higher up the canyon, often become mobile homes on the peculiar mix of slippery goo that covers the mountains of the Los Angeles basin. The predilection of El Niño for homes of the rich and possibly famous in Malibu may explain our current fascination with the phenomenon.
Somewhere back in the beginning of this hype, USA Today carried an above-the-fold screamer about upcoming El Niño death and destruction, noting that the last big one, in 1982-83, caused a billion dollars of damage from winter storms. These storms occurred over a four month period, mainly in Southern California.
It's pretty much accepted that the westerly winds that El Niño promotes in the subtropical Atlantic suppress hurricane activity, creating fewer storms and fewer strong ones. As a result of El Niño's appearance this summer, crack hurricane prognosticator Bill Grey of Colorado State University ratcheted down his forecast. And, in general, he's been right. There were a spate of weaklings in July, before El Niño kicked in, and since then, we have experienced one of the quietest hurricane seasons on record.
In 1992, Hurricane Andrew 14-20 billion dollars of damage, much of it occurring in a four hour period. Contrast that to 1982-83 El Niño damage, which comes out as pretty small beer, Andrew was a Category 4 (out of 5) hurricane. During this century, there have been 13 Category 4 and 2 Category five strikes on the U.S. Gulf and Atlantic Coasts. That's about one every seven years or so. Because almost the entire coast from Brownsville, Texas to Eastport, Maine now sports vacation palaces, condos, or Sea Oatels (as in Nags Head, North Carolina), every 4 or 5 that hits is going to be at least in Andrew's price range.
So El Niño causes a billion in damage, and the average category 4 or 5 hurricane damage, on a per-year basis, costs about 3 billion. If El Niño suppresses even half (two-thirds may be a more likely figure) of the frequency of these big bombs, it looks like a moneymaker for the good ole USA.
Jim Brenner of the Florida Division of Forestry has noted that El Niños are strongly associated with the suppression of wildfires in Florida. Under non El Niño conditions, seasonal dryness in the winter and early spring (January-May) promotes burning.
*(Footnote). Apologies to the late Norman Maclean. Most folks know him for A River Runs Through It. Pretty good. But his final book, Young Men and Fire, is a must read for any natural phenomenon addict.
Substantial amounts of real estate--about 200,000 acres a year--goes up in smoke. 12% of those fires are caused by lightning, and they are relatively big, burning about 23% of the total fired acreage.There's a pretty strong negative correlation between El Niño and fire in Florida, as shown in our figure.
But that's about as far as it goes. Some of our state employee colleagues got fired up about this and asked us to run an analysis of Virginia forest fires and El Niño. The next figure shows the simple lack of correlation. No matter how much we torture El Niño data, he seems not to confess to arson.
We know everyone is blaming every weather event on El Niño, but we can't find much at all in Virginia. We looked at all six climatological divisions (Tidewater, Eastern Piedmont, Western Piedmont, Northern, Central Mountain, and Southwestern) and found only one significant correlation with the SOI (remember, that's "Southern Oscillation Index", or the pressure difference between Darwin, Australia and Tahiti). The correlation is a suppression of rainfall in Tidewater during September and October hurricane season. This is consistent with the general observation that El Niño years tend to have few - and wimpy - hurricanes in the Atlantic basin. I suppose folks could get all exercised about this, inasmuch as 40% of the average September rainfall on the Virginia Eastern Shore comes from hurricanes, but there just don't seem to be a lot of tears out there, with people missing their evacuation orders from Virginia and Buckroe Beaches.
Lack of hurricanes can associate with moisture deficits in eastern Virginia--if there isn't a lot of other rainfall and the hurricane deficit extends throughout the July-October main season. But El Niño doesn't seem to have enough influence to penetrate beyond September and October. So don't blame "the kid" the next time corn yields are down.
Our table shows the matrix of "explained variance" between the climatological division precipitation and the SOI. These figures reflect the percent of year-to-year variation in precipitation that can be statistically related to the SOI.
Because there are so many years of record (the SOI goes back to 1895) even a relatively small amount of variation - a bit more than 4% - is statistically significant. In other words, the relationship between the SOI and rainfall is better than the relationship between random numbers and rainfall when the explained variance is a tad above 4%.
The profound number of zeroes in the first two decimal places in the explained variance table bears testimony to the abjectly minor relationship between Virginia monthly precipitation and El Niño. And the only time and place where the numbers are better than random (September and October in Tidewater) the explained variance values are a whopping 5.4% and 4.3%, respectively. Somehow that's not the kind of thing we really want to bet the farm on.
The 1993 "Storm of the Century" occurred during the last, relatively mild El Niño. It was embedded in a fairly warm winter. The last decent El Niño, in 1986-87, also saw a relatively mild winter, with the exception of two major snowstorms that fell within 84 hours, and buried much of the state with depths of between 20 and 24 inches.
Then, of course, there was the big "blizzard" (it wasn't) of January 1996, but it fell during a La Niña. Maybe - as is the current vogue - both phases of ENSO, El Niño and La Niña, are becoming more extreme and that's what's driving these snowstorms.
NOT. Our illustration below shows the (lack of) relationship between Virginia snowfall and El Niño/La Niña. Oh, we suppose, one could torture the data enough and say that when the ENSO index is near zero (i.e. "normal") that there is some weak peak in snowfall‹but what does that say? That occasional big snowstorms are normal here? Dog my cats! Fido my Raoul, Virginia's own weather cat!!
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The hype came faster and more furious than a tornado late last summer. We were about to see the biggest El Niño in history! Make that the last 100 years; or at least as big as the big one in 1983; oh maybe not quite as big; uh, it's just another El Niño; oh no! It's disappearing!!
There are several ways to size El Niño. For years, climatologists have used the Southern Oscillation Index (SOI) which is simply the adjusted pressure difference between Darwin, Australia and Tahiti. When the difference is more than one unit (standard deviation) negative, we arbitrarily say there's an El Niño on.
The time history of the SOI doesn't make this El Niño look like anything special, after all. As of this writing, it looks like it has hit bottom, somewhere in the vicinity of the 1994 and 1987 versions, which were nothing special. It doesn't look to be anywhere close to the 1982-83 show.
The newer, improved method is called the "multivariate ENSO index", and it measures more variables at more places. This one goes El Niño when it is +1.0 (rather than the SOI's 1.0). As can be seen from our illustration, while this one rocketed up pretty smartly, it has now dropped off. The "comparison" strong El Niños all go into decline once such a dropoff occurs. So, unless this one is completely different - and there is no physical reason to expect such a thing - the party's over. Big deal.
Professor Al Strong of the Naval Academy is one of the nation's El Niño experts, having studied it by satellite for nearly two decades. Strong has recently noted that the 1972-73 El Niño (see chart) was so big that much of the sea surface temperature data was either discounted or thrown away, because folks at that time didn't think such huge temperature reversals were possible. That's why the 72-73 one might have actually been the biggest. Unless you "fill in the blanks" like we have, it just doesn't look physically like any of the others.
It's too bad that the cheap mail that we have to use is so slow, and that holiday schedules for printers, binders, and mailers will make this document - being written in November - arrive probably after the first of the year. Online users, of course, will see this thing by early December. (Hint: get connected or depend on "the old fashioned way")
By the time the mail snail delivers, El Niño is liable to be moribund. That's because the new "multivariate ENSO index" ("MENSOI") took such a huge drubbing in late October and early November.
Death appears most likely to occur early in 1998, not much after the turn of the year. That's no doubt going to have some impact on global temperature records, which appear on an annual (calendar year) basis. Because El Niño suppresses cold water upwelling, and because it was concentrated specifically in calendar year 1997, look for news stories in January that last year was the hottest year in the global temperature record. That's what you would expect if El Niño dominated a single year during an already warm time.
Of course, this also means that the following La Niña, when the cold water comes back like gangbusters, is likely to be concentrated in 1998. Maybe there will be a big drop in the global record between 1997 and 1998 - prompting reports that the climate is becoming more variable. At least that's what MENSOI should say.