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Before the storm

Ultrarapid radiation pulses precede gigantic particle jets launched by the Sun

NASADistinct phenomena: ejections of mass are not always accompanied by explosions like thisNASA

In 1989, it was a solar storm that caused the historical blackout that hit Canada and the United States. The interference in the electromagnetic fields generated by the arrival of particles emitted by the Sun disconnected the transmission lines that were operating at the limit. This possibility was just a suspicion, as the Sun shows phases of abnormal production of energy: the best known of them follows an 11-year cycle. The most evident sign of this phenomenon seems inoffensive – the number of spots on the surface of the star increases -, but this is actually the harbinger of an upheaval that is capable of stirring up the space climate regime all over the Solar System. In the course of the ensuing years, explosions occur in these spots that make the regions located in the surface of the Sun shine more brightly, and some of them launch gigantic clouds into space – these are coronal mass ejections, which sometimes extend for more than the diameter of the Sun itself, over 1.4 million kilometers.

Launched at a speed of 1,000 kilometers a second, these bubbles of electrically charged particles fustigate the neighboring heavenly bodies. If the bombardment hits the atmosphere of the Earth two or three days after the explosion, a spectacle of colors arises that tinges the polar nights – the boreal and austral auroras. But there are problems too. Depending on the direction, the speed and the quantity of particles, solar storms can cause temporary breakdowns in satellites, or even destroy them. After the phase in which this activity is at its height – the most recent occurred in 2001 -, the number of spots on the Sun diminishes and the brilliant eruptions become less frequent.

But the star’s calmness is only apparent, as is revealed by studies coordinated by physicist Pierre Kaufmann, from the Radioastronomy and Astrophysics Center of the Mackenzie Presbyterian University (UPM). Using a special telescope constructed in the Argentinean Andes and partly financed by Brazil, Kaufmann’s team detected extremely brief radiation pulses at submillimetric wavelengths, which have helped to characterize an still unidentified activity of the star. They are tenuous flashes – lasting from 100 to 500 thousands of a second – which cannot be captured by the majority of the telescopes on Earth and in space, for being emitted at a very short wavelength, close to the heat waves, but about a thousand times longer than the visible light range. Sometimes classified as far infrared, this radiation has a wavelength shorter than a millimeter and, for this reason, is also known as submillimetric. “The antennas that capture these wavelengths cannot normally be pointed at the Sun without being damaged, norare they prepared for detecting such rapid pulses”, the researchers says.

The São Paulo physicist’s team recently obtained data showing that these pulses of light precede the gigantic solar eruptions, a possible reason for the blackouts that occur on Earth and remain without any know cause. Should a link be demonstrated between the incidents on the planet and solar storms, even outside the peak periods of the activity of the Sun, the study of submillimetric waves takes on importance, for the possibility of explaining even the alterations in the climate. It is known that the cycles of solar activity influence cloud cover in the sky, interfering with the regimes of drought and rainfall all over the planet.

For this reason, the Scientific Committee on Solar-Terrestrial Physics (Scostep), which is part of the United Nations Educational, Scientific and Cultural Organization (Unesco), created an international program with the objective of understanding the influence of the Sun on the climate of the Earth – besides, of course, supplying energy in the form of light and heat. Called Cawses (Climate, Weather and the Sun-Earth System), it will study the solar phenomena that affect the aerospace industry. In 2000, one of the Brasilsat satellites was damaged by solar particles when it was put into orbit. “With a better understanding of the effects of the Sun on the Earth”, says the physicist, “it will be possible to avoid launching satellites in periods when they are more vulnerable and make their operation more reliable.”

The group coordinated by the São Paulo physicist only observed the submillimetric waves emitted by the Sun because the equipment installed in Argentina – the Solar Submillimeter Telescope (SST), in regular operation since last year at El Leoncito Astronomic Complex – captures electromagnetic radiation in two submillimetric bands, corresponding to the frequencies of 212 gigahertz and 405 gigahertz. After monitoring complexes of sunspots with the SST between March 2000 and July 2002, the researchers compared this data with images collected by two pieces of equipment of the Soho (Solar and Heliospheric Observatory) satellite at the exact moment at which ejections of solar masses appear, preceded by six sequences of ultrarapid submillimetric flashes. The objective was to verify what the association is between the ejections of solar mass and the sequences of submillimetric pulses, identified for the first time by Kaufmann three years ago and described in an article published in the Astrophysical Journal of February 2001.

The surprise came when the physicist’s team, made up of Brazilians, Germans, Russians and Argentineans, found that the series of pulses always preceded the gigantic expulsions of mass by the Sun. The ejections of coronal mass release up to 1,000 times more energy than the biggest explosions that occur close to the surface of the star, the chromosphere, seen only a few times in each 11 year cycle of solar activity. They are also much more frequent: every 11 years, there are only two or three gigantic explosions accompanied by brightening in the chromosphere, while there are ejections of coronal mass throughout the whole of this period.

Mysteries of the Sun
In some cases, the comparison between the data revealed something even more curious. The sequence of flashes was followed by the ejection of coronal mass without the typical hallmark of these phenomena: the appearance of brighter areas – chromospheric explosions – over the Sun. On the basis of these observations, the researchers published in July in the Journal of Geophysical Research an article suggesting that these flashes could lie at the origin of the great ejections of solar masses. “The origin of these pulses is still mysterious”, says Kaufmann. “But they indicate a new path for understanding the energy processes that occur close to the surface of the Sun and how they contribute towards launching particles on their way into space.”

Discovered at the beginning of the 70’s, the coronal mass ejections only took on importance after the Soho observatory, which stays in an intermediate orbit between the Earth and the Sun, recorded images of the phenomenon, which interferes in the magnetic field of our planet, and shows that they are more frequent than used to be believed. It is now known that they occur independently of the star’s phase of activity. If the Sun is very active, they are observed dozens of times a week. In the phase of lower activity, they occur dozens of times every month. Now, Kaufmann’s team is looking for statistical data relating the random ejections of solar mass with phenomena on Earth.

The Project
Applications of the Solar Telescope for Submillimetric Waves (nº 99/06126-7); Modality Thematic Project; Coordinator Pierre Kaufmann – Mackenzie Presbyterian University; Investment R$ 137,496.00 and US$ 83,061.06