“Expect the cold weather to continue for the next ten days, followed by a warm spell.” This might have been the fourteen- day weather forecast for Montreal on December, 31, 2006 (Fig. 5.1, top). But imagine what it might have been if Earth rotated about its axis ten times more slowly, so that the length of the day coincided with the ten- day weather– macroweather transition scale— an alignment of scales almost achieved on Mars. In that case (Fig. 5.1, bottom) we would have heard, “Expect mild weather on Monday, followed by freezing temperatures, until a warm spell on Thursday, followed by a brisk Friday and Saturday, a warming on Sunday and Monday, followed by freezing on Tuesday, then a four- day warm period followed by freezing and then warming.” Although long- term trends in weather can persist for up to ten days or so, in macroweather, the upshifts tend to be followed immediately by downshifts (and vice versa) and, although longer term trends exist, they are much more subtle, resulting from imperfect cancelations of successive fluctuations. The tendency of macroweather fluctuations to cancel rather than to accumulate is its defining feature, and cancelation is synonymous with stability. Quantitatively, it implies that the temporal fluctuation exponent H is negative. In the weather regime with positive H, the temperature, wind, and other variables wander up and down with prolonged swings. The weather is a metaphor for instability. If we average macroweather over longer and longer times, its variability is reduced systematically so that it appears to converge to a well-defined value. In that sense, macroweather is what you expect, the weather is what you get. But what about macroweather’s spatial properties? As usual, forecasts can be explained with recourse to maps. For example, Plate 5.1 (left) shows the day- to-day evolution of the daily temperatures corresponding to the forecast in Figure 5.1 (top).
Long-term trends in helminth infections of wood mice (Apodemus sylvaticus) from the vicinity of Malham Tarn in North Yorkshire, England
