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  • Solar Flare

     

    X-rays and UV radiation emitted by solar flares can affect Earth’s ionosphere and disrupt long-range radio communications. Direct radio emission at decimetric wavelengths may disturb operation of radars and other devices operating at these frequencies.

    Solar flares were first observed on the Sun by Richard Christopher Carrington and independently by Richard Hodgson in 1859 as localized visible brightenings of small areas within a sunspot group. Stellar flares have also been observed on a variety of other stars.

    The frequency of occurrence of solar flares varies, from several per day when the Sun is particularly “active” to less than one each week when the Sun is “quiet”. Large flares are less frequent than smaller ones. Solar activity varies with an 11-year cycle (the solar cycle). At the peak of the cycle there are typically more sunspots on the Sun, and hence more solar flares.

    Solar flares are classified as A, B, C, M or X according to the peak flux (in watts per square meter, W/m2) of 100 to 800 picometer X-rays near Earth, as measured on the GOES spacecraft. Each class has a peak flux ten times greater than the preceding one, with X class flares having a peak flux of order 10−4 W/m2. Within a class there is a linear scale from 1 to 9, so an X2 flare is twice as powerful as an X1 flare, and is four times more powerful than an M5 flare. The more powerful M and X class flares are often associated with a variety of effects on the near-Earth space environment. Although the GOES classification is commonly used to indicate the size of a flare, it is only one measure. This extended logarithmic classification is necessary because the total energies of flares range over many orders of magnitude, following a uniform distribution with flare frequency roughly proportional to the inverse of the total energy. Stellar flares and earthquakes show similar power-law distributions.[2]

    [edit] Hazards

    Solar flares strongly influence the local space weather of the Earth. They produce streams of highly energetic particles in the solar wind and the Earth’s magnetosphere that can present radiation hazards to spacecraft and astronauts. The soft X-ray flux of X class flares increases the ionisation of the upper atmosphere, which can interfere with short-wave radio communication and can increase the drag on low orbiting satellites, leading to orbital decay. Energetic particles in the magnetosphere contribute to the aurora borealis and aurora australis.

    Solar flares release a cascade of high energy particles known as a proton storm. Protons can pass through the human body, doing biochemical damage.[3] The proton storms are produced in the solar wind, and hence present a hazard to astronauts during interplanetary travel. Most proton storms take two or more hours from the time of visual detection to reach Earth’s orbit. A solar flare on January 20, 2005 released the highest concentration of protons ever directly measured,[4] taking only 15 minutes after observation to reach Earth, indicating a velocity of approximately one-half light speed.

    The radiation risks posted by prominences and coronal mass ejections (CMEs) are among the major concerns in discussions of manned missions to Mars, the moon, or any other planets. Some kind of physical or magnetic shielding would be required to protect the astronauts. Originally it was thought that astronauts would have two hours time to get into shelter, but based on the January 20, 2005 event, they may have as little as 15 minutes to do so. Energy in the form of hard x-rays are considered dangerous to spacecraft and are generally the result of large plasma ejection in the upper chromosphere.

    [edit] Observations

    The following missions have flares as their main observation target.

    • Yohkoh – The Yohkoh (originally Solar A) spacecraft observed the Sun with a variety of instruments from its launch in 1991 until its failure in 2001. The observations spanned a period from one solar maximum to the next. Two instruments of particular use for flare observations were the Soft X-ray Telescope (SXT), a glancing incidence low energy X-ray telescope for photon energies of order 1 keV, and the Hard X-ray Telescope (HXT), a collimation counting instrument which produced images in higher energy X-rays (15-92 keV) by image synthesis.
    • GOES – The GOES spacecraft are satellites in geostationary orbits around the Earth that have measured the soft X-ray flux from the Sun since the mid 1970s, following the use of similar instruments on the SOLRAD satellites. GOES X-ray observations are commonly used to classify flares, with A, B, C, M, and X representing different powers of ten — an X-class flare has a peak 2-8 Å flux above 0.0001 W/m2.
    • RHESSI – RHESSI is designed to image solar flares in energetic photons from soft X rays (~3 keV) to gamma rays (up to ~20 MeV) and to provide high resolution spectroscopy up to gamma-ray energies of ~20 MeV. Furthermore, it has the capability to perform spatially resolved spectroscopy with high spectral resolution.
    • Hinode – A new spacecraft, originally called Solar B, was launched by the Japan Aerospace Exploration Agency in September 2006 to observe solar flares in more precise detail. Its instrumentation, supplied by an international collaboration including Norway, the U.K., and the U.S., and Africa focuses on the powerful magnetic fields thought to be the source of solar flares. Such studies shed light on the causes of this activity, possibly helping to forecast future flares and thus minimize their dangerous effects on satellites and astronauts.[5].

    The most powerful flare of the last 500 years was the first flare to be observed, and occurred in September 1859: it was reported by British astronomer Richard Carrington and left a trace in Greenland ice in the form of nitrates and beryllium-10, which allow its strength to be measured today (New Scientist, 2005).

    [edit] Prediction

    Current methods of flare prediction are problematic, and there is no certain indication that an active region on the Sun will produce a flare. However, many properties of sunspots and active regions correlate with flaring. For example, magnetically complex regions (based on line-of-sight magnetic field) called delta spots produce most large flares. A simple scheme of sunspot classification due to McIntosh is commonly used as a starting point for flare prediction. Predictions are usually stated in terms of probabilities for occurrence of flares above M or X GOES class with 24 or 48 hours. The U.S. National Oceanic and Atmospheric Administration (NOAA) issues forecasts of this kind.

  • Options for Railway Locomotives

    Latest update {Draft XI:05) of “Post-Carbon Australian Options for Railway Locomotives”  has been released on the net for public comment from my website at http://www.auzgnosis.com/pgs/auzloco.htm  (while the draft will still have the same file-name I will keep updating the actual file there to the latest version as any future improvement are made).                       

    I’d be real happy for readers to circulate this email to anybody they think may find this interesting. Any & all feedback most appreciated.  I am very aware that the whole envisaged project is a monster.  The aim of writing the paper was to get the broad community to muse about the long-term futures of land-transport across Australia’s vast dry landmass.

    Appreciate any pointers for getting some university facilities playing around with, testing these broad ideas.

     

    Would be interested in any feedback, Many Thanks
      W.Shawn Gray

  • Solar panels are not fashion accessories

     

    Of course, just a fraction of that area of buildings would suffice because we would want to mix and match renewable technologies – large and small, onshore and offshore – so matching loads and compensating for the fact that solar generates by day and not by night.

    Second, Monbiot says the government’s scheme targets money where economies of scale are “impossible” – an incorrect assumption because solar electricity costs will inevitably fall to the point, within just a few years, where they are cheaper than any form of fossil fuel and nuclear electricity. Systemic economies of scale in solar manufacturing and installation techniques are causing rapid reductions in solar PV costs globally, just as Ofgem and others worry so loudly about the inevitable rise of traditional electricity costs.

    Third, Monbiot gets the precedent for the British government’s solar “cash-back” scheme – the German feed-in tariff – upside down. He says the “German government decided to reduce sharply the tariff it pays for solar PV, on the grounds that it is a waste of money”.

    But all feed-in tariffs are supposed to decline, and indeed reduce to zero within some years – that is the whole point. They are not like the market-building schemes for the nuclear technologies that Monbiot advocates, where subsidies – open and hidden – are needed for decades. Most Germans are rightly proud of their feed-in tariff regime. They have, after all, created over 50,000 jobs in solar PV alone.

    Fourth, Monbiot has it wrong about who pays the cash back. “The government is about to shift £8.6bn from the poor to the middle classes,” he says. But the number is not the cost to “the poor”. It’s not even the cost to all electricity consumers over the next two decades. The cumulative cost to all consumers – including all non-domestic industrial, public sector, and commercial users and covering all technologies in the scheme – is £6.7bn, and is spread over 20 years.

    The average household levy in 2013, when tariff rates are all up for review, is likely to be less than £3. This is far less than the average saving from the government’s various domestic energy efficiency measures over the same period. So there is no net subsidy. The levy is not “regressive” at all.

  • Batten down the hatches, a political storm is brewing

    Batten down the hatches, a political storm is brewing

    Climate change in Australia — of the political variety — is real and happening now. As a fresh opinion poll rolls in every few days, the underlying trend is moving inexorably against Labor. Here’s a sampling over the past week:

    Federal: Newspoll, published today, shows little change in party polling (government ahead on two-party-preferred terms 52-48), but Tony Abbott’s satisfaction rating jumped four points to 48. Yesterday’s Essential Research has Labor’s lead at a new low of 53-47, down from 54-46 last week and 55-45 a week before.

    Victoria: Nine months out from a state election, yesterday’s Morgan Poll puts Liberal and National support at 50.5, leading the ALP (49.5) for the first time on a two-party preferred basis. And although John Brumby (50.5) is clearly preferred as the “better Premier ” ahead of Opposition Leader Ted Baillieu (30.5), 47% disapprove of Brumby’s handling of the job compared to only 37% who approve.

    South Australia: A Sunday Mail poll over the weekend showed a swing of around 10 per cent against Labor in the key marginal seat of Morialta, weeks out from a state election.

    Tasmania: Last Wednesday’s EMRS poll had Labor are down two points since November to 31, the Liberals down five to 39 and the Greens are up six to 27 — which would give the Greens the balance of power in this month’s state election.

    Even allowing for local factors, margins of error, temporary issues and blips, you’d be hard pressed not to conclude that the punters are uneasy and the mood is running against the incumbents everywhere.

    Batten down the hatches.

  • Caltech Researchers Create Highly Absorbing, Flexible solarCells with Silicon Wire Arrays,

     

    This is a photomicrograph of a silicon wire array embedded within a transparent, flexible polymer film. [Credit: Caltech/Michael Kelzenberg]

    The light-trapping limit of a material refers to how much sunlight it is able to absorb. The silicon-wire arrays absorb up to 96 percent of incident sunlight at a single wavelength and 85 percent of total collectible sunlight. “We’ve surpassed previous optical microstructures developed to trap light,” he says. 

    Atwater and his colleagues — including Nathan Lewis, the George L. Argyros Professor and professor of chemistry at Caltech, and graduate student Michael Kelzenberg — assessed the performance of these arrays in a paper appearing in the February 14 advance online edition of the journal Nature Materials.

    Atwater notes that the solar cells’ enhanced absorption is “useful absorption.”

    “Many materials can absorb light quite well but not generate electricity — like, for instance, black paint,” he explains. “What’s most important in a solar cell is whether that absorption leads to the creation of charge carriers.”

    The silicon wire arrays created by Atwater and his colleagues are able to convert between 90 and 100 percent of the photons they absorb into electrons — in technical terms, the wires have a near-perfect internal quantum efficiency. “High absorption plus good conversion makes for a high-quality solar cell,” says Atwater. “It’s an important advance.”

    The key to the success of these solar cells is their silicon wires, each of which, says Atwater, “is independently a high-efficiency, high-quality solar cell.” When brought together in an array, however, they’re even more effective, because they interact to increase the cell’s ability to absorb light.

    “Light comes into each wire, and a portion is absorbed and another portion scatters. The collective scattering interactions between the wires make the array very absorbing,” he says.

    This is a schematic diagram of the light-trapping elements used to optimize absorption within a polymer-embedded silicon wire array. [Credit: Caltech/Michael Kelzenberg]

    This effect occurs despite the sparseness of the wires in the array — they cover only between 2 and 10 percent of the cell’s surface area.

    “When we first considered silicon wire-array solar cells, we assumed that sunlight would be wasted on the space between wires,” explains Kelzenberg. “So our initial plan was to grow the wires as close together as possible. But when we started quantifying their absorption, we realized that more light could be absorbed than predicted by the wire-packing fraction alone. By developing light-trapping techniques for relatively sparse wire arrays, not only did we achieve suitable absorption, we also demonstrated effective optical concentration—an exciting prospect for further enhancing the efficiency of silicon-wire-array solar cells.”

    Each wire measures between 30 and 100 microns in length and only 1 micron in diameter. “The entire thickness of the array is the length of the wire,” notes Atwater. “But in terms of area or volume, just 2 percent of it is silicon, and 98 percent is polymer.”

    In other words, while these arrays have the thickness of a conventional crystalline solar cell, their volume is equivalent to that of a two-micron-thick film.

    Since the silicon material is an expensive component of a conventional solar cell, a cell that requires just one-fiftieth of the amount of this semiconductor will be much cheaper to produce.

    The composite nature of these solar cells, Atwater adds, means that they are also flexible. “Having these be complete flexible sheets of material ends up being important,” he says, “because flexible thin films can be manufactured in a roll-to-roll process, an inherently lower-cost process than one that involves brittle wafers, like those used to make conventional solar cells.”

    Atwater, Lewis, and their colleagues had earlier demonstrated that it was possible to create these innovative solar cells. “They were visually striking,” says Atwater. “But it wasn’t until now that we could show that they are both highly efficient at carrier collection and highly absorbing.”

    The next steps, Atwater says, are to increase the operating voltage and the overall size of the solar cell. “The structures we’ve made are square centimeters in size,” he explains. “We’re now scaling up to make cells that will be hundreds of square centimeters — the size of a normal cell.”

    Atwater says that the team is already “on its way” to showing that large-area cells work just as well as these smaller versions.

    In addition to Atwater, Lewis, and Kelzenberg, the all-Caltech coauthors on the Nature Materials paper, “Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications,” are postdoctoral scholars Shannon Boettcher and Joshua Spurgeon; undergraduate student Jan Petykiewicz; and graduate students Daniel Turner-Evans, Morgan Putnam, Emily Warren, and Ryan Briggs.

    Their research was supported by BP and the Energy Frontier Research Center program of the Department of Energy, and made use of facilities supported by the Center for Science and Engineering of Materials, a National Science Foundation Materials Research Science and Engineering Center at Caltech. In addition, Boettcher received fellowship support from the Kavli Nanoscience Institute at Caltech.

    Lori Oliwenstein is Senior Science Writer in the Media Relations office at Caltech.

  • Green fuels cause more harm than fossil fuels, accordind to report

     

    The Renewable Transport Fuels Obligation this year requires 3¼ per cent of all fuel sold to come from crops. The proportion is due to increase each year and by 2020 is required to be 13 per cent. The DfT commissioned E4tech, a consultancy, to investigate the overall impact of its biofuel target on forests and other undeveloped land.

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    The EC has conducted its own research, but is refusing to publish the results. A leaked internal memo from the EC’s agriculture directorate reveals its concern that Europe’s entire biofuels industry, which receives almost £3 billion a year in subsidies, would be jeopardised if indirect changes in land use were included in sustainability standards. A senior official added to the memo in handwriting: “An unguided use of ILUC [indirect land use change] would kill biofuels in the EU.”

    The EC hopes to protect its biofuel target by issuing revised standards that would give palm plantations the same status as natural forests. Officials appear to have accepted arguments put forward by the palm oil industry that palms are just another type of tree.

    A draft of the new rules, obtained by The Times, states that palm oil should be declared sustainable if it comes from a “continuously forested area”, which it defines as areas where trees can reach at least heights of 5m, making up crown cover of more than 30 per cent. “This means, for example, that a change from forest to oil palm plantation would not per se constitute a breach of the criterion,” it adds.

    Clearing rainforest for biofuel plantations releases carbon stored in trees and soil. It takes up to 840 years for a palm oil plantation to soak up the carbon emitted when the rainforest it replaced was burnt. The expansion of the palm oil industry in Indonesia has turned it into the third-largest CO2 emitter, after China and the US. Indonesia loses an area of forest the size of Wales every year and the orang-utan is on the brink of extinction in Sumatra.

    Last year, 127 million litres of palm oil was added to diesel sold to motorists in Britain, including 64 million litres from Malaysia and 27 million litres from Indonesia. Kenneth Richter, biofuels campaigner for Friends of the Earth, said: “The billions of subsidy for biofuels would be better spent on greener cars and improved public transport.”