Environmental Engineering Reference
In-Depth Information
Figure 7.15
Formation areas and mean tracks of tropical
cyclones.
Source: After Barry and Chorley (1998).
the United Kingdom monthly forecasts of temperature and precipitation used to be
prepared on the basis of previous weather analogues. For example, if the atmospheric
circulation and sea surface temperature patterns in, say, July 2002 were very similar to
those of July 1964, it could be assumed that the weather in August 2002 should be the
same as that in August 1964. Other controlling factors such as ice cover, the state of the
El Niño-Southern Oscillation and the Quasi-biennial Oscillation (a feature of the wind
circulation in the tropical upper troposphere and lower stratosphere) are also included to
improve the accuracy of the forecast. However, even if the basic circulation pattern is
correctly predicted, slight errors in the tracks of cyclones or anticyclones can produce
markedly different weather. Future developments in monthly forecasting are likely to be
built around numerical ensemble methods, used to generate probability forecasts. The
ensembles are produced as a set of runs from a global numerical model, all slightly
different. Their output is interpreted in terms of the probability of the occurrence of
particular circulation types.
WEATHER PREDICTION AND HAZARDS
It is possible to predict many of the weather hazards discussed earlier, but we have to
distinguish between large-scale and small-scale hazards. The longer is the time scale of
development, the larger will be the area affected. Major
