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Lightning illuminates a towering anvil cloud. Image Credit: Nicholas T

Jun 03, 2008
Electric Clouds

Cloud formations often exhibit structure that could be the result of something other than blowing winds. Does ionized plasma actually shape the clouds?

"Thunderstorms are not electricity generators, they are passive elements in an interplanetary circuit, like a self-repairing leaky condenser. The energy stored in the cloud ‘condenser’ is released as lightning when it short-circuits. The short-circuits can occur either within the cloud or across the external resistive paths to Earth or the ionosphere. The charge across the cloud ‘condenser’ gives rise to violent vertical electrical winds within the cloud, not vice versa." --- Wal Thornhill, 2004

In a recent press release, scientists from the Weizmann Institute and the Goddard Space Flight Center announced that a mysterious zone of previously undiscovered particles fills the airspace around clouds.

Ilan Koren of the Weizmann Institute wrote: “The effects of this zone are not included in most computer models that estimate the impact of aerosols on climate. This could be one of the reasons why current measurements of this effect don’t match our model estimates.”

In 1999 and then in 2002 NASA launched the Aqua and Terra satellites as part of an ongoing project to study aerosol distribution around the world. The Moderate Resolution Imaging Spectroradiometer (MODIS) packages onboard each of the satellites are designed to operate like “eyes in the sky”, analyzing the various frequencies of visible light reflected by objects below.

Because different targets like lakes, mountains or clouds return different spectral signatures, those reflections can be categorized and the source of the signal identified. In particular, MODIS looks for the spectra of particulates and gasses that are thought to influence the climate changes known as “global warming”.

What appears to be clear blue sky around clouds, such as in the image above, is actually a region of particles that do not correspond to water vapor or the pollution-induced gasses that investigators expected to see. Since clouds have a high albedo and scatter polarized light from their outer margins, it is challenging for the MODIS research team to detect anything near them. So that glare from specular distortion does not obscure their results they avoid scanning an area about one kilometer distant from cloud boundaries.

Scientists know of the hazy halo of particles that is sometimes visible around individual clouds, but the discovery of elevated aerosol levels encompassing the entire expanse was unexpected. Whole sections of sky are filled with particles. However, after analyzing data from thousands of observations the researchers found that the concentration of aerosols systematically increased closer to the clouds. In order to determine if their measurements were accurate the investigators sought the assistance of another NASA-sponsored research group to confirm their observations.

The Aerosol Robotic Network is a collection of automated platforms installed around the world. The devices reduce glare effects as they measure the volume and size of aerosols between the instruments and the sun. When a cloud blocks the sun, the instruments take no scheduled readings, which provides an indirect measure of the cloud’s presence.

Ilan Koren noted:

"We found that the region affected by this cloud field 'twilight zone' extends to tens of kilometers beyond the identified cloud edge. This suggests that 30 to 60 percent of the atmosphere previously labeled as 'cloud-free' is actually affected by cloud-aerosol processes that reflect solar energy back into space."

Ions attract water in the atmosphere instead of through the commonly described process of neutral dust motes building up raindrops through a process of condensation. They may also charge the dust hanging in the air making it more attractive to water vapor.

The Earth is an electrically charged body within the stream of ions permeating space and holds an electric field at its surface of 50 – 200 volts per meter. The electricity from space is carried by the barrage of ionic particles emitted by the sun as the “solar wind” and speeds along massive Birkeland currents through the circuit. Because water molecules are electric dipoles and are attracted to an opposite polar charge, such as that on another water molecule, they will clump together and align themselves within the Earth’s “fair weather field”. No “seeds” are necessary for water vapor to form clouds.

The electromagnetic field beneath a thunderstorm increases (up to 10,000 volts per meter) because it acts like a capacitor, storing energy from the surrounding environment. Observations have shown that a "wind" of charged particles blows toward the developing storm, which could be interpreted as a current flowing into the base of the clouds. The surrounding air is pulled along with the current flow and creates the powerful updrafts that sometimes rise into the stratosphere.

It might be the flood of ions into and out of clouds that is forming the “twilight zone” of unidentified particles that so mystifies the scientific community.

By Stephen Smith
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