Meteorology at Armagh

Meteorology – the study of the weather – has been carried out in Armagh since 1795. The Observatory archives include the longest series of continuous weather records in Ireland and the United Kingdom. They are a very valuable resource for studying long-term changes in the weather. Climatology has recently become very important because it is thought that the Earth’s atmosphere is slowly heating up. This global warming may be a consequence of the release of greenhouse gases from power stations, cars, homes and factories into the Earth’s atmosphere. Carbon dioxide (CO₂) and methane (CH₄) are two of the most important greenhouse gases.

The Earth’s weather systems are driven by energy from the Sun. It is therefore no surprise that astronomers have been investigating how small changes on the Sun can effect our climate.

 The best example of solar variability is an 11 year cycle in the number of spots on the surface of the Sun. These sunspots are regions that are slightly cooler than the average temperature on the solar surface (5500° C). Approximately every 11 years, the number of sunspots rises to a maximum and then falls to near zero. There is a close match between the length of the sunspot cycle and the average northern hemisphere temperature. There may also be a link between the maximum sunspot number and the length of the cycle. From the late 17th to the early 18th centuries there were very few sunspots and a very long cycle length. This was a time of generally cold temperatures world-wide, known as the Little Ice Age and famous for ‘Frost Fairs ‘ on the frozen Thames in London.
 
 

Other objects in the solar system can also effect the Earth and its weather – sometimes catastrophically. Small dust particles – meteors – and rocks – meteorites – strike the Earth quite frequently. Some examples of meteorites can be seen in the Planetarium. On rare occasions a much larger objects, such as a comet or asteroid may collide with the Earth. The collision can result in an explosion equivalent to the power of several million nuclear warheads. The explosion and resulting fires release massive amounts of dust and gas into the atmosphere.

The dust reduces the amount of sunlight reaching the Earth’s surface, causing plants to die and lowering temperatures. Severe damage to global weather systems can last for many years.

65 million years ago a large comet about 12km in diameter struck the Yucatan peninsula, off the coast of Mexico, and triggered a mass extinction of the dinosaurs. Such catastrophes are rare, but in 1908 a large meteorite exploded over Tunguska, a remote region of Siberia, flattening trees over thousands of square miles and producing beautiful sunsets for years. If that meteorite had arrived 6 hours later it could have exploded over Ireland.

Dendrochronology is the dating of wood samples from the pattern of tree-ring growth. Each growing season, a tree adds a layer of wood to its trunk and branches, creating annual growth rings. In good growing seasons (wet and warm), certain tree species produce wide rings, but in poor years (dry and cold), the rings are much narrower. The unique pattern of wet and dry growing seasons creates a corresponding pattern of tree rings.

 A sequence of ring-patterns can be built up from timber of many different ages, and this allows each tree-ring to be dated exactly. Samples may be taken from very old living trees such as the Bristlecone pines found in California, which can be over 4,500 years old! They can also make use of wood that has been dead for a long time, for example the Irish 'bog oaks' that are kept in a near-perfect condition in peat bogs, or petrified forests in which tree remnants have been turned to stone. Wood that has been used in buildings or other artefacts can also be used.

 Climatologists use dendrochronology to build up a picture of climate patterns in the past. This is a way of measuring local weather conditions over hundreds or thousands of years, even where no other weather records exist. More information about dendrochronology and its uses may be found at the Navan Centre, 2 miles west of Armagh.