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Subject: [SEAC+ANNOUNCE] GL: Do Humans Affect Hurricane and Rainfall Patterns?
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URL: http://www.eurekalert.org/releases/asu-wehurr.html
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STUDY SUGGESTS WEEKLY HURRICANE AND RAINFALL PATTERNS ARE LINKED
TO EAST COAST POLLUTION
5 August 1998
Contact: James Hathaway
Hathaway@asu.edu
602-965-6375
Arizona State University College of Liberal Arts & Sciences
Who hasn't felt like going back to work on Monday has affected the
weather? It turns out the weather itself may indeed be controlled
by the weekly calendar, and that even mighty Atlantic hurricanes
may feel the punch of the workweek, according to a study by two
Arizona State University researchers appearing in the journal
Nature.
Examining some basic data sets in a way that has never been tried
before, ASU climatologists Randall Cerveny and Robert Balling, Jr.
have found proof for what many a weekend boater has secretly
suspected: rain is most likely to occur along the Atlantic coast
on the weekend and the weather is most likely to be better on a
Monday, Tuesday or Wednesday. The most obvious culprit is the
"natural" cloud-seeding effect created by the massive drift of East
Coast pollution, which also follows a well defined weekly cycle.
The gray, smelly cloud of pollution has a strange silver lining,
however. While pollution makes for more rainy weekends, it also
apparently reduces the intensity of hurricanes that hit over the
weekend, such that weekend hurricanes tend to be much weaker than,
say, Tuesday storms.
"Hurricanes are the biggest storms that we have on this planet, in
terms of energy and precipitation," noted Cerveny. "And what we've
found is that we're having an impact on them. It's a little
daunting, when you start to think about it."
Cerveny and Balling examined and compared three different data sets
-- daily carbon monoxide and ozone measurements from a Canadian
monitoring station on Sable Island off the coast of Nova Scotia,
daily satellite-derived rainfall data for the Atlantic Ocean, and
databases of coastal Atlantic hurricane measurements. In each
case, when the two ASU scientists examined the data by day of the
week, they found significant differences between days, and similar
patterns of variation, with pronounced differences between
beginnings and the ends of weeks. All three sets of climate data
revealed a seven-day cycle.
"The human week is not a natural time period," said Balling.
"Human effect on weather is the only explanation."
"If you're going to go out boating in the Atlantic, you're going
to get wet if it's a weekend," Cerveny said. "And what we suggest
is that this is probably linked to the pollution cycle."
In examining precipitation in the Atlantic, they found no daily
variation when looking at the ocean as a whole, but a pronounced
sine-wave pattern of variation for just the coastal areas, with
average daily precipitation rising on Thursday and into the weekend
and then dipping from Sunday through the middle of the week.
Balling notes that when the team analyzed satellite data grid cells
for an area a little further away from the coast, they found the
same pattern, time-shifted in accordance with the rate of pollution
drift.
Though the study does not directly address causation, a comparable
fluctuation in the levels of East Coast air pollution points to an
obvious connection. The fact that coastal hurricane intensity data
taken from 1945 to 1996 follow a similar pattern (rather than being
statistically uniform for each day of the week, as one would
expect), supports this hypothesis.
"The fact that pollution can affect rainfall is actually well
understood," said Balling. "We just had to look for the evidence
in the right place. The hurricane data, though, surprised the heck
out of me."
"We knew that cities have an effect on local weather with urban
heat islands and so forth, and people are pretty sure that we're
having a general global effect with carbon dioxide," said Cerveny.
"But nobody had ever looked at the in-between area of large-scale
regional weather. We appear to be affecting global weather on a
scale that is comparable to El Nino."
The hypothesis is particularly important when applied to
hurricanes, because of the destructive potential of the storms.
Cerveny and Balling looked at 50 years worth of hurricane records,
which include observations taken every 6 hours and found surprising
statistical differences with important implications.
"Storms are substantially weaker during the first part of the week
and stronger in the last part of the week," said Cerveny.
"Pollution's thermal changes on the storm are apparently helping
hurricanes blow themselves out. The difference is as high as 10
miles-per-hour wind speed, downgrading the storm almost as much as
a Saffir-Simpson Scale category, meaning that if a hurricane were
to hit on Tuesday or Thursday, it might be a Category 3, but if it
were to hit on a Saturday or Sunday, it might be only be a Category
2."
Cerveny notes that the effect is similar to a weather-control
method once attempted in a military experiment: "Back in the 1960s,
the military had a project called Project Storm Fury that was
developed to cloud-seed hurricanes. What we're suggesting here is
that they were on the right track, but they just didn't do it on
a large enough scale. We're looking at the combined pollution from
the entire eastern seaboard -- that's what it takes to influence
a hurricane."
Though the study has interesting implications, what most surprised
the ASU scientists was the fact that no other researcher had ever
attempted to analyze these major data sets in such a basic way.
"Interestingly, no one had ever looked at this pollution data from
a daily standpoint before and, curiously, nobody has bothered to
look at seven-day cycles in the weather data," said Cerveny.
"Oftentimes the most fundamental research is that way you say to
yourself 'why didn't anybody look at this' When we were putting
this together, we went through every journal we could find, saying
'somebody has got to have done this before!' Luckily for us, no one
had."
Cerveny and Balling's study can by found in the August 6 issue of
Nature. A simplified version can also be found on the World Wide
Web at http://www.asu.edu/clas/geography/nature/. *
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