Tim O’Hare
observations, thoughts and useful stuff…Archive for meteorology articles
Fractal forecasting
There’s an interesting piece in New Scientist, No 2733 [07 November 2009] outlining some new published research which has used satellite derived rainfall data to explore how atmospheric processes show the same patterns of variation whatever scale they are examined on. Such behaviour is called multi-fractal and basically means that if you look at something on a large scale you see a certain pattern of variation but then when you look in more detail at a smaller scale the same pattern shows up (an oft-quoted example of this are coastlines which show large-scale undulations/headlands/bays but which, when viewed more closely show similar undulations at smaller scale). Fractal behaviour is starting to show up in all kinds of data and processes.
Anyway, the importance of this finding for meteorology is that currently it is verydifficult to build numerical models which accurate forecast larger scale processes because the resolution of the models prevents accurate description of processes on smaller scales (and so these have to be added into the model as special parameterisations). If atmospheric processes are really fractal (an idea that was first suggested at least 80 years ago by Lewis Fry Richardson) then it will be possible to properly (or at least better) describe the smaller scale processes in numerical weather prediction models.
I’m a believer that much of the complexity that we observe in the real world is governed by relative simple underlying principles and behaviour and this research is an example of this occuring in practice.
Time for Plan B – Geoengineering
There has been a huge amount of coverage of the need to cut Greenhouse Gas emissions as the primary route to slow down, halt and eventually reverse the current global warming trend and rightly so. However, in the background there have been a number of suggestions for actions that mankind could take to directly counter-act global warming. Such measures are collectively known as geoengineering and include such things as the direct removal of carbon dioxide from the atmosphere (e.g. by planting trees or fertilising the oceans) and reflecting incoming solar radiation away from the Earth (e.g. by using mirrors in space or changing the land surface to make it more reflective). These measures have not recevied much public attention, partly because they are all really, really expensive, partly because no-one knows how effective they would be and partly because by discussing the ideas in public we might distract attention from the goal of reducing Greenhouse Gas emissions.
Now, the tide has turned a little. A recent report produced by the Royal Society has highlighted the need to urgently begin considering geoengineering as a Plan B to reducing emissions. The report works through various geoengineering ideas examining their affordability and effectiveness and suggests that there should be a major shift of funding into geoengineering research. The report was widely publicised in the media at the beginning of September and the geoengineering debate is nicely summarised in New Scientist, Issue 2724 [05 September 2009].
Noctilucent clouds
Noctilucent clouds are a rare type of cloud that comprise ice crystals so high up in the atmosphere that they reflect sunlight to the surface of the Earth long after sunset. It seems that noctilucent-like clouds are sometimes observed a few days after space shuttle launches – the shuttle launch creates eddies that carry water into the thermosphere (90-500km altitude). Similar clouds were also recorded as being observed in the days following the Tunguska blast (in Siberia) in 1908. The similarity between the two sets of observations has led to a suggestion that the Tunguska blast was caused by a wet, icy comet crashing to Earth rather than a dry, stone asteroid as had previously been thought. The story is described in New Scientist, Issue 2715 [04 July 2009]
UK weather in the 2080s – or maybe not
Last week, New Scientist, Issue 2714 [27 June 2009] ran a short news item highlighting a new set of climate projections from the UK Met Office for the 2080s (oddly defined as the years 2070-2099). These are presented as a series of maps showing changes in summer mean temperature and summer and winter mean precipitation across the UK based on a 5km grid. The Met Office website also introduces the material and provides a link to the dedicated UK Climate Projections 09 website where the maps can be found. The New Scientist piece points out that some climate scientists feel that the projections are useless, and or misleading, because such fine resolution projections are bound to be upset by processes occuring at the local scale. There is also doubt that the climate models used to make the projections can handle areas of blocking high pressure well enough to make them useful.
So, the projections may or may not be useful or useless depending on who you believe! Nevertheless, I thought I would take a look at the maps and see what they tell me about the likely conditions in Plymouth in the 2080s (I have only just done the mental arithmetic, but I’ll (probably not) be 115 years old in 2080 which has depressed me a little). Anyway, for what it is worth, it looks like it’s going to be 3-4 degrees Celsius warmer and about 40% less wet in the summer and about 10% wettter in the winter…
