Monthly Archives: May 2011

Fuel Mix and CO2

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Since 2005 UK electricity suppliers have been legally obliged by Ofgem to provide information about the fuel mix they use to generate electricity and the carbon dioxide they produce in the process.

The UK average fuel mix; heavy on gas and coal.

The “Big 6” energy suppliers supply 99% of the UK population between them; most have a fairly similar energy mix, but one stands out from all the rest.

Most of the Big 6 are heavily reliant on natural gas and coal; but EDF stands out by generating more than 60% of its electricity from nuclear power. The effect that this has on the amount of CO2 that it creates for every kilowatt-hour of energy produced is very noticeable.

EDF Energy is a subsidiary of Électricité de France, so it’s no surprise to see it relying on nuclear power; France generates 78% of its electricity from nuclear power and is the world’s largest electricity exporter. This has enabled Électricité de France to become the world’s largest utility company.

Source for fuel mix data: ElectricityInfo.org

What’s the time?

(This post was prompted by Samoa’s decision to jump forward a day by moving the international date line.)

“What’s the time?” seems like a simple question, but it’s not. There are many different ways of measuring time.

Universal Time is based on the rotation of the Earth, measured using observations by the International Earth Rotation and Reference Systems Service (IERS); it replaced Greenwich Mean Time (GMT) in 1928. The IERS uses a network of stations across the globe to perform Very Long Baseline Interferometry (VLBI) of 212 distant objects (mainly quasars) outside our Milky Way galaxy. During VLBI simultaneous readings from stations a long distance apart are compared and the differences between them used to calculate the distance to, and position of these extra-galactic objects. By combining the VLBI readings with lunar ranging and GPS satellite orbit data the principal form of Universal Time, UT1 is calculated.

Coordinated Universal Time (UTC) is the world’s time standard; if you want to know what the current time is, you want to know what UTC is. It is based on International Atomic Time (TAI) and is always kept to within ± 0.9 seconds of UT1. If it ever falls outside of this range a leap second is introduced by IERS to correct the difference. The difference between the two arises because TAI assumes that a day is a perfect 86400 seconds long (24×60×60) whereas in reality the Earth’s rotation is irregular, overall slowing by about 1.7 milliseconds every century.*

The last ten years’ of data is shown above; a sharp vertical line indicates the introduction of a leap second. The last leap second was at the end of 2008, taking the difference between UTC and UT1 from -0.591 to +0.409 seconds. Since 1999 there have been far fewer leap seconds (two in the ten year afterwards, eight in the ten years before). The Earth’s rotational speed increased in 1999 for some unknown reason, though there may be some link with earthquakes.

TAI is the average time from more than two hundred caesium atomic clocks at about seventy laboratories across the world; every month the data from these clocks is gathered by the International Bureau of Weights and Measures Bureau (BIPM) and published to participating organisations (e.g. May’s data). TAI and UTC were synchronised in 1958 but since TAI never includes leap seconds it is gradually moving away from universal time and is currently 34 seconds ahead of UTC.

Each GPS satellite contains four caesium atomic clocks that were synchronised with UTC in 1980. Leap second corrections are never applied to GPS clocks so GPS time is now 19 seconds behind TAI, putting it 15 seconds ahead of UTC. This offset is included in the GPS time signal and receivers usually apply the correction automatically.

* The pull of the Moon increases the length of the day by 2.3 ms/century but the increase in the height of land due to the melting of glaciers decreases it by 0.6 ms/cy.

Japan’s atmosphere heated before earthquake struck

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For a long time there have been reports of “earthquake lights”, aurora-like lights or colours that appear in the sky during, or just before, earthquakes. Their existence is not widely accepted, but a group of US and Russian researchers claim to have discovered a different earthquake-related atmospheric effect.

After the March 11 quake in Japan the researchers looked at atmospheric data from the days before the quake struck, and their data appears to show a noticeable heating effect in the atmosphere beginning three days before the quake.*

Red lines indicate tectonic fault lines and the star indicates the location of the March 11 earthquake.

The article claims that this heating is due to a complex mechanism called the lithosphere-atmosphere-ionosphere coupling mechanism, in which the lithosphere (the rocky crust of the Earth), the atmosphere (the layers of gas surrounding the Earth) and the ionosphere (a layer of the atmosphere that contains particles that have been ionised by the Sun, where aurora occur) interact with each other.

They posit that small movements of the crust that occurred before the earthquake released radioactive radon gas (created by the radioactive decay of uranium and thorium in the crust) that was trapped there. This radon gas (either Rn-220 or Rn-222) is a highly-ionising alpha emitter. The researchers propose that the radon creates ionised particles in the air that cause water molecules to condense out of their vapour state. This condensation process releases energy, causing the surrounding atmosphere to increase in temperature.

Dimitar Ouzounov et al. 2011. “Atmosphere-Ionosphere Response to the M9 Tohoku Earthquake Revealed by Joined Satellite and Ground Observations. Preliminary results” arXiv:geo-ph/1105.2841v1

* Not everyone agrees with their data.

How to hide a Nobel medal

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In the run up to World War II Niels Bohr’s Institute in Copenhagen had become a refuge for Jewish physicists. The Jewish physicist James Franck and the anti-Nazi physicist Max von Laue, concerned for their gold Nobel Prize medals, both left them there for safekeeping. When Hitler’s army invaded Denmark, Bohr was worried that the invading German soldiers would steal the medals but his friend, the Hungarian physicist George de Hevesy, came up with an ingenious solution.

de Hevesy dissolved both medals in aqua regia, a highly corrosive 1:3 mixture of nitric acid and hydrochloric acid. This formed a transparent yellow liquid, chloroauric acid, that he hid in plain site, simply leaving the jar on a shelf in the Niels Bohr Institute.

When he returned in 1945, after World War II had ended, the jar was still there. The gold was recovered from solution and the medals were restruck by the Nobel Foundation and returned to their rightful owners.