RE: [escepticos] aerohielitos

[Luis Alfonso Gámez <vader@...>]

El artículo de los aerohielito de Geotimes al que nos hemos referido varios
periódicos.

Saludos,

Luis Alfonso

 Atmospheric Sciences
Hailstones fall from clear Spanish skies
On Jan. 8, news spread through the media in Spain that a chunk of ice fell
from clear skies and hit a car in Tocina, a village close to Seville. The
piece broke into two pieces, one weighing 1.2 kilograms and the other 1.7.
Between Jan. 8 and Jan. 31, at least 50 such falls were reported.
  Documented references of blocks of ice falling from clear skies go back to
the first half of the 19th century (e.g. 1829 in Córdoba, Spain: 2 kg; 1851
in New Hampshire: 1 kg). Recent cases include a 9-kilogra, fall in Batley,
West Yorkshire in 1991. Probably the best-documented fall of an ice chunk
was April 2, 1973, in Manchester, England. The block weighed 2 kilograms and
consisted of 51 layers of ice. Its origin was not determined.
Though some of the recent falls in Spain have been confirmed as practical
jokes perpetrated after initial reports of the phenomenon ? people froze
large quantities of tap water and left the blocks of ice close to a public
area or road ? we have verified the authenticity of nine falls (more than 10
kilograms of ice) that occurred from Jan. 8 to Jan. 17.

Chemical and isotopic analyses were performed in five of the specimens. Our
results offer evidence of chemical and isotopic heterogeneity (even within
each block), with large densities of ions ? up to five times larger than
normal meteoric waters ? and corresponding to solutions of halite, calcite,
anhydrite and quartz or feldspar aerosols.

The distribution of the samples on Craig?s meteoric water line suggests
either a variation in condensation temperature or isotopic exchanges during
the formation of each ice chunk. These data, together with the high
frequency of the events, indicate that the chunks aren?t minicomets and didn
?t come from aircraft. They may result from an atmospheric phenomenon.

A hailstone is a product of the updrafts and downdrafts that develop inside
the cumulonimbus clouds of a thunderstorm, where supercooled water droplets
exist. The change of droplets to ice necessitates not only a temperature
below 0 degrees Celsius, but also a catalyst in the form of tiny particles
of solid matter that become freezing nuclei. Continued deposits of
super-cooled water cause the ice crystals to grow into hailstones.
Hailstones have been found as large as grapefruits and weighing up to 7.5
pounds.

The possible explanation for how the recent ice chunks form may hinge on the
classical nucleation and growth processes. We assume that at the high region
of the atmosphere (i.e., 6 kilometers) the vapor water saturation may be
near equilibrium. It is well known that both the energy of nucleation and
the critical nuclei that can eventually grow tend to infinity if saturation
is close to one. Therefore the ice could not be formed under these
conditions. However, if conditions for extra cooling exist ? large
concentrations of ions, aerosols, etc ? then the nucleation energy reduces
(heterogeneous nucleation) and the nuclei that can grow are formed. Another
possibility could be that a crystallite from the lowermost stratosphere
enters a region of humidity, where it begins growing.

Ozone distribution maps from NASA show that, on Jan. 5, a thin jet of ozone
depression passed through all the areas in Spain where the ice falls took
place. It is commonly posited that global warming and ozone depression are
linked. Despite the fact that the greenhouse effect leads to an increase in
the global mean surface temperature, it leads to cooling in the
stratosphere. Perhaps the aforementioned nucleating crystallites enter the
upper troposphere. There, where humidity is more abundant, they start
growing, evidencing that the greenhouse effect is beginning to show. We
suggest paying more attention to the fall of these unusual chunks of ice,
which could be indicating that changes are taking place in the atmosphere.

Submitted by:
Jesús Martínez-Frías, Departamento de Geología, Museo Nacional de Ciencias
Naturales, Madrid, Spain; Fernando López-Vera, Departamento de Geología,
Geoquímica y Química Agrícola, Madrid, Spain; Nicolás García, Laboratorio de
Fisica de Sistemas Pequeños, Madrid, Spain; Antonio Delgado, Departamento de
C.C. de la Tierra y Química Ambiental, Granada, Spain; Roberto García,
Laboratorio de XRD y Electroforesis, MNCN, Madrid, Spain; Pilar Montero,
Instituto del Frío, Madrid, Spain

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