NYTimes article on strikes and ice
Report: Icier Clouds Make More Lightning
By THE ASSOCIATED PRESS
Published: August 11, 2005
Filed at 7:27 p.m. ET
WASHINGTON (AP) -- Poet Robert Frost once pondered whether the world
would end in fire or in ice. Weather researchers say where you find
ice you find fire -- at least in the form of lightning.
Whether the storm was over land, ocean or coastal areas, clouds with
more ice produced more lightning, researchers studying satellite
radar images report in the journal Geophysical Research Letters.
''The new thing is that when you look at different areas of the
planet ... the hypothesis about the importance of ice holds up,''
Walter A. Petersen of the University of Alabama at Huntsville said
He said weather scientists have known there was a relationship
between ice and lightning, but were learning new details by studying
the National Aeronautics and Space Administration satellite images
which can look at both the number of lightning strikes and the volume
of ice in a cloud at the same time.
Crucial is what is called precipitation-sized ice, particles of a
millimeter or so which sometimes can be seen falling as small
hail. ''Where you have more of that, you tend to have more
lightning,'' Petersen said.
These particles crash into smaller ice particles in the swirling
winds inside storm clouds, resulting in a separation of electrical
The charge separated between smaller and larger particles, with the
smaller carrying a positive charge to the top of the thundercloud and
the larger ones with the negative charge sinking to the bottom, he
explained in a telephone interview.
''You effectively make a big battery with positive and negative
ends,'' he said, with the charge building up until it is discharged
The relationship between ice volume and lightning held true over such
varied locations as the Himalaya Mountains, Central Africa,
Madagascar, northern Australia and Florida, the researchers reported.
They found small areas of subtropical South America where lightning
flash density seemed slightly less than would have been expected for
the measured ice amount. Since they could find no physical reason for
this the researchers said it may be a sampling error. They are doing
more research on those areas.
The work was funded by the NASA's Earth Observing System and Earth
Science Enterprise programs.
On the Net:
Geophysical Research Letters: www.agu.org/journals/gl/