The newest observations from the Ulysses spacecraft suggest the heliospheric chaos of solar maximum occupies a unique and rather short-lived portion of the solar cycle; the majority of the cycle is dominated by large polar coronal holes and a relatively simple solar wind structure, according to Southwest Research Institute (SwRI) space scientists.
As the spacecraft completes its second pass around the sun in its unique high-latitude orbit over the sun's poles, scientists are learning more about the variable behavior of the solar wind over the 11-year solar cycle. During its solar odyssey already 10 years in duration, Ulysses measures, among other things, the solar wind, the plasma of hot ionized gas that flows out from the sun.
"The solar wind behaves quite differently during the most active part of the solar cycle," reported Dr. David J. McComas at the Ulysses/Voyager/ACE Heliospheric Workshop on October 15.
McComas, who is the principal investigator of a Ulysses experiment called the Solar Wind Observations Over the Poles of the Sun (SWOOPS) and executive director of Space Science and Engineering at SwRI, collaborated with researchers from Los Alamos National Laboratory, NASA's Jet Propulsion Laboratory, and Imperial College, London.
"The solar maximum data expose a remarkably different and more complicated three-dimensional solar wind structure than the simple structure observed throughout most of the solar cycle," continued McComas. During most of the solar cycle, the solar wind at high latitudes is almost uniformly fast, while lower latitudes emit a wind of varying speeds. The polar solar wind at maximum is slower and gustier than at other times.
"Another interesting discovery from the most recent data collected since July is that the heliospheric chaos of solar maximum is apparently very short-lived; soon after solar maximum, within a year, we already see a return to a predominantly fast solar wind at high latitudes."
While the Earth's magnetic field reverses only once every 200,000 years or so, the sun's internal magnet flips every 11 years. As it flips, the magnetic field becomes disordered, and the surface of the sun becomes more active.
This period of change is called solar maximum because the sun's entire surface sprouts small, short-lived coronal holes and streamers. In addition, bubbles of gas and energy called coronal mass ejections, which shoot away from the sun in every direction, are far more common around solar maximum.
>From 1992 through 1997, Ulysses saw strong and unipolar magnetic fields at both poles of the sun. Large, dark, persistent X-ray coronal holes formed in the solar atmosphere over the polar caps. The solar wind structure is simple at solar minimum, with fast, hot flows from polar coronal holes, which remain open over long periods of time.
The reversal of the magnetic field has a particularly dramatic effect on the poles. The sun's polar coronal holes shrink and ultimately disappear around solar maximum because the magnetic field is unevenly spread around the surface of the sun.
"The solar wind we observe at all latitudes around solar maximum looks a lot like previous observations near the solar equator, or the ecliptic plane, throughout the solar cycle," said McComas.
"Recent observations of faster solar winds indicate that the sun's dipole has indeed reversed," said McComas. The most recent fast winds are quantitatively as well as qualitatively different from winds observed earlier in this pass.
The new data, when statistically compared with data from the first orbit, are virtually indistinguishable from the polar winds observed at solar minimum. The winds are almost uniformly hot and fast and have relatively constant composition and density, indicating that polar coronal holes are beginning to reform within a year of solar maximum.
"Because solar activity remains high, it is not clear whether the northern polar coronal hole forming will grow and stabilize to become the sort of multi-year polar coronal hole observed throughout much of the previous solar cycle," continued McComas.
"However, it is clear that the sun can, and in this case, does start to form large polar holes very soon after solar maximum."
Ulysses, launched in 1990 with a gravity assist from Jupiter to create its unique solar polar orbit, is a joint venture of NASA and the European Space Agency.
Southwest Research Institute
Subscribe To SpaceDaily Express
Ulysses Reaches The Sun's North Pole
Paris (ESA) Oct 11, 2001
For the second time in its 11-year lifetime, ESA's Ulysses spacecraft is about to fly over the Sun's north pole. On Saturday, 13 October, it will reach its highest north solar latitude (80 degrees north). At about the same time, solar and heliospheric scientists will meet in Oxnard, California, to discuss the latest findings about the heliosphere, the vast region of space blown out by the solar wind and over which our Sun holds sway.
|The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.|