Monday, July 1, 2019
Hawaiian tradewinds shifting NE to East, and that means warmer weather for us
It feels
warmer in the Islands, and it is—in part because there are significant changes
in our tradewind flow.
It is not
that the trades have stopped blowing, but that theyʻre blowing from warmer
water, which makes the breeze warmer.
State
Climatologist Pao-Shin Chu said wind
data over the past 40 years show a definite shift in the flow of tradewinds.
Theyʻre blowing more from the warmer waters east of us, and less from the cooler
waters northeast of us.
Chu, a
meteorologist at the University of Hawai`i, compared two sets of decades-long data
for winds at Honolulu Airport. And while the two sets are not precisedly
comparable, they both tell the same story—a shift from northeast trades to easterly
trades.
What does
that mean to the person on the street, or sitting in front of a fan at home, or
selecting restaurants for the efficiency of their air conditioning?
"The
wind from the northeast is cooler than with the easterly component," Chu said.
Chu first
noted the change in a paper published in 2012 in the Journal of Geophysical Research.
He has since reviewed updated numbers and said the trend continues.
That paper,
by Jessica A. Garza, Chu, Chase W. Norton and Thomas A. Schroeder, is entitled "Changes
of the prevailing trade winds over the islands of Hawaii and the North Pacific."
The
researchers looked at wind data from eight stations on land and from ocean
buoys around the Islands. The data runs from 1973 to 2009. Here is a press release on that paper.
"The
northeast trade frequency is found to decrease for all eight stations while the
east trade winds are found to increase in frequency," the authors wrote.
Hawai`i gets
its reputation for having a comfortable climate in part from the remarkable
consistency of the trade wind flow. It is the most consistent wind field on the
planet, the authors said.
When Chu recently
reviewed a newer set of wind numbers, from 1980 to 2014, he found a compable
result: The frequency of northeast trades drops while the frequency of easterly
trades rises.
He said that
at the beginning of the data set, there were 170 days of northeast trades, and
they dropped to 150 by the end of the period.
Meanwhile,
east trades increased from 95 to 120 days.
And there is
other news in trade winds. Chinese researchers report that during the past
century, trade wind speeds have increased in the western Pacific, but decreased
in the eastern Pacific. (Hawai`i is kind of in the middle.)
That study
"Long-term trend of the tropical Pacific trade winds under global warming
and its causes," is by a team lead by Yang Li, an atmospheric scientist at
Chinaʻs Chengdu University.
University of
Hawai`iʻs Chu said he has seen a slight weakening in Hawaiian tradewinds, but
not enough to be statistically significant.
©Jan TenBruggencate 2019
Posted by Jan T at 1:44 PM
Labels: Climate Change, Emergency Management, Marine Issues, Oceanography, Weather
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