Closer look at Earth
Van Allen Belts: This data-based visualization shows the Van Allen Belts pulsing from solar particles over ten days. The gap that appears toward the end shows a cleared-out safe zone for satellites. The red ring represents the orbit of the IMAGE satellite, which dips into the safe zone every few days.
(Credit: NASA/Tom Bridgman)
Space Scientists Uncover Causes Of Gap In Van Allen Belts
A team of British and US scientists have discovered that the gap in the Van Allen radiation belts is formed by natural wave turbulence in space, not by lightning. The discovery settles years of controversy among space scientists about the mechanisms responsible for causing the gap and has important implications for space weather forecasting
High above the Earth's atmosphere, energetic charged particles are trapped in the Earth's magnetic field where they form the Van Allen radiation belts. Energetic electrons, travelling close to the speed of light, occupy two doughnut shaped zones, usually separated by a gap known as the slot region.
The underlying mechanism that clears the slot region of electrons has been the subject of intense scientific debate. Now, based on analysis of wave data collected over 13 months by the CRRES satellite, Dr Nigel Meredith of British Antarctic Survey and colleagues from BAS, the University of California, Los Angeles and the University of Iowa, believe that the gap is most likely formed by natural wave turbulence in space, rather than by lightning as the alternative theory suggests. Their results are published in the Journal of Geophysical Research this week.
According to lead author, Dr Nigel Meredith:
"Last year NASA scientists suggested that lightning-generated radio waves leaking out into space are responsible for the gap between the two belts by dumping particles into the atmosphere. Since lightning occurs far more often over land than water, waves in space should also occur more over land. However, after analysing satellite data we found that there is no land-ocean variation at frequencies less than 1 kiloHertz where the waves are most intense. Instead, wave activity increases during geomagnetic disturbances driven by the Sun, suggesting that natural wave turbulence is responsible for the gap."
"The results are important, because a better understanding of the radiation belts will help modellers forecast space weather more accurately, helping to protect both astronauts and satellites from radiation hazards."
Van Allen radiation belts
The Van Allen radiation belts were the foremost discovery of the space age after being detected by the first US satellite Explorer I, which was launched during the International Geophysical Year of 1957-58. They are composed of energetic charged particles trapped inside the Earth's magnetic field, which surrounds the Earth like a ring doughnut. Energetic electrons in the Earth's Van Allen radiation belts occupy two distinct regions. The inner zone, which typically extends from altitudes of 200 km to 7000 km in the equatorial plane, is relatively stable. In contrast, the outer zone, which typically lies between 13,000 km and 40,000 km in the equatorial plane, is highly dynamic. The gap between the two zones, known as the slot region, is usually devoid of energetic electrons. However, the slot can fill during strong magnetic storms, such as witnessed during the so-called Halloween storm in 2003. Particles in the slot are subsequently lost, following interactions with the radio waves, on a time-scale of days.
Combined Release and Radiation Effects Satellite
The Combined Release and Radiation Effects Satellite (CRRES) was a joint NASA and U.S. Department of Defense mission to study the near Earth space environment and the effects of the Earth's radiation environment on microelectronic components. The satellite was launched on 25 July 1990 and operated in a highly elliptical geosynchronous transfer orbit with a perigee of 305 km, an apogee of 35,768 km and an inclination of 18o. The orbital period was approximately 10 hours. The satellite swept through the Van Allen radiation belts on average approximately 5 times per day, providing good coverage of this important region for 13 months.
Radio waves in space, known as plasmaspheric hiss, are responsible for the formation of the slot region between the inner and outer radiation belt. While the details of the loss process are well known, the source of these waves has been a matter of intense debate for several decades.
There are two competing theories. One theory maintains that the radio waves are generated locally via natural turbulence in space, arising from particles injected during enhanced magnetic activity driven by the Sun. The other theory suggests that the radio waves, generated by lightning activity on Earth, leak into space and evolve into hiss after multiple reflections in space.
Enhanced fluxes of energetic particles damage spacecraft and are a risk to humans in space. Improved understanding of the weather in space will help protect the satellites and astronauts operating in these regions.
Jupiter, Saturn, Uranus and Neptune all have strong magnetic fields and radiation belts. Improved understanding of the significant processes affecting the Earth's radiation belts will help astronomers to understand the radiation belts of other planets.
British Antarctic Survey is a world leader in research into global issues in an Antarctic context. It is the UK's national operator and is a component of the Natural Environment Research Council. It has an annual budget of around £40 million, runs eight research programmes and operates five research stations, two Royal Research Ships and five aircraft in and around Antarctica.
For more information please visit: British Antartic Survey
Original text Science Daily 27th September 2006
New scientific Challenges And Goals
For European Living Planet Program
The Changing Earth:
ESA's Living Planet
by Staff Writers Paris, France (ESA)
Space Daily Sep 28, 2006
ESA announces a new science strategy for the future direction of its Living Planet Programme, addressing the continuing need to further our understanding of the Earth System and the impact that human activity is having.
The Changing Earth: New Scientific Challenges for ESA's Living Planet Programme focuses on the most fundamental challenge facing humanity at the beginning of the 21st century - that being global change. As we begin to understand more about the Earth as a system, it is very apparent that human activity is having a profound and negative impact on our environment.
For example, our understanding of carbon dioxide as a greenhouse gas, and the strong link between atmospheric carbon dioxide concentrations and temperature both point to human activity leading to a warmer world, unlike anything seen over the last million years. A better knowledge of the Earth System and the impact that increasing human activity is having is of crucial importance in providing the basis for the management of our environment and our ability to derive sustainable benefit.
Since observing the Earth from space first became possible more than forty years ago, satellite missions have become central to monitoring and learning about how the Earth works. Looking to the future, the new strategy for ESA's Living Planet Programme aims to assess the most important Earth-science questions to be addressed in the years to come. It outlines the observational challenges that these raise, and the contribution that the Agency can make through the programme.
Volker Liebig, ESA Director of Earth Observation stated, "These challenges will guide ESA's efforts in providing essential Earth-observation information to all relevant user communities, in close cooperation with our international partners."
Underpinning the new strategy is a set of ambitious objectives, which include:
Launch a steady flow of missions addressing key issues in Earth science. Provide an infrastructure to allow satellite data to be quickly and efficiently exploited in areas of research and applications. Provide a unique contribution to global Earth Observation capabilities, complementing satellites operated by other agencies and in-situ observing systems. Provide an efficient and cost-effective process whereby science priorities can be rapidly translated into space missions, adequately resourced with associated ground support. Support the development of innovative approaches to instrumentation.
ESA has been dedicated to observing the Earth from space ever since the launch of its first meteorological mission, Meteosat, back in 1977. Following the success of this first mission, the subsequent series of Meteosat satellites developed by ESA and operated by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), together with ERS-1, ERS-2 and Envisat have been providing us with a wealth of invaluable data about the Earth, its climate and changing environment.
Since its conception in the 1990s, ESA's Living Planet Programme has grown to include the family of Earth Explorers, the well-established meteorological missions and the development of the space component for GMES (Global Monitoring for Environment and Security), which is a joint initiative between the European Commission and ESA.
When the Living Planet Programme was first established a new approach to satellite observations for Earth science was formed by focusing on the missions being defined, developed and operated in close cooperation with the science community. By involving the science community right from the beginning in the definition of new missions and introducing a peer-reviewed selection process, it is ensures that a resulting mission is developed efficiently and provides the exact data required by the user.
So far, this approach has resulted in the selection six Earth Explorer missions with another six currently under assessment study. Two Earth Explorer satellites are scheduled for launch next year - GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) and SMOS (Soil Moisture and Ocean Salinity).
While the Earth Explorer series forms the science and research element of the Living Planet Programme the so-called Earth Watch element is designed to facilitate the delivery of Earth-observation data for use in operational services.
Earth Watch includes the well-established meteorological missions with EUMETSAT and new missions focusing on the environment and civil security under GMES. Within this element of the programme, the MetOp mission, which was jointly established by ESA and EUMETSAT, will be Europe's first polar-orbiting weather satellite when it is launched in October.
Although the Earth Watch element of the programme is designed to provide data that underpins operational services, it will also contribute significantly to Earth science, in particular through the collection of longer time series of observations than those provided by research missions. In turn, the Earth Explorers will provide new understanding that paves the way for new operational services. This synergy is also highlighted in the Living Planet Programme's strategy for the coming years.
With the Living Planet Programme's new strategy in place, ESA will build on past success by continuing to play a central role in developing the global capacity to understand planet Earth, predict environmental changes and help mitigate the negative effects of global change on the population.
Cosmic Rays in Atlas by Plato 27th Sept 2006
Gravitational Radiation by Plato 27th Sept 2006
Solar B and Van Allen Belts by Plato 28th Sept 2006
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