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Physics News Preview: The Persistence Of Weather

What Is The News?

• A new study, to be published in the 20 July issue of Physical Review Letters, shows that the correlation between the temperature today and that for x days from now is not exponential in nature (e raised to the -x power) but more like a power law (x raised to an exponent gamma).
  
• The value of gamma, -0.65, is the same for all 14 sites in the worldwide study, suggesting that some universal effect is operating.
  
• The persistence of this behavior seems to hold over at least a decade and possibly for as long as a century or more.
  

Although there seems to be nothing reliable about the weather, especially when planning a picnic, there is actually a (very) long range consistency at work. Scientists have sought to find the mathematical relation between the temperature today and the temperature after x days. The degree of correlation can be indicated to by an appropriate function,the correlation function C(s). Such an inquiry will be more robust if more data, stretching over decades and even centuries, can be brought into account.

The purpose behind such studies is to furnish a tool for testing state-of-the-art climate models.

The New Study

Armin Bunde (011-49-641-993-3360, armin.bunde@theo.physik.uni-giessen.de) at the University of Giessen (Germany), and his colleagues from Milan, Potsdam, and the Bar-Lan University (Israel) have now conducted the most thorough multi-year study yet of correlations in daily temperature records by applying techniques from modern statistical physics. What they do in effect is to ask: if the weather is sunny and warm today, what will be the likelihood that it will be sunny and warm tomorrow, and the next day, and after x days? Choosing randomly 14 meteorological stations worldwide and factoring out seasonal effects by comparing not temperatures but departures from the average daily temperature, they were able to tease out the persistent rhythms of temperature.

As expected, the researchers observed that after x days the weather is less and less likely to be similar to that on day one. But the particular mathematical shape did not conform to previous expectations. The falloff is not exponential but power-law (the number of days raised to a specific exponent) in nature. This behavior (with one universal exponent) seems to occur worldwide, and may be regarded as a "global weather law."

The Sites Used In The Study

Fourteen sites were chosen randomly from many possible meteorological stations from around the world. The cities, and number of years of data, are as follows: Albany, NY (90 years), Brookings, SD (99), Huron, OH (55), Luling, TX (90), Melbourne (136), New York City (116), Pendleton, OR (57), Prague (218), Sidney (117), Spokane, WA (102), Tuscon (97), Vancouver (93), Moscow (115), and St. Petersburg (111).

Applicability

The researchers hope to check the persistence of weather in still more places to determine whether any spot on Earth is exempt from the pattern. Since the global weather law they find does not depend on characteristic geographic details of the diverse meteorological stations, it can be used as an ideal tool for testing highly complicated state-of-the-art climate models.

Could this new finding be applied to studying weather on Venus or Jupiter? Probably not because of the absence of an ocean, which acts as a great moderator of temperature.

More Information

Outside experts:

• Michael E. Shlesinger, Office of Naval Research, 703-696-4220
• Eugene Stanley, Boston University, 617-353-2617; he is an expert in applying statistical physics methods to various scientific disciplines---e.g., modeling urban growth patterns, Nature, vol 377, p 608, (1995); long-range anti-correlations and non-gaussian behavior of the heartbeat, Physical Review Letters, vol 70, p 1343 (1993)
• Klaus Hasselmann, Max-Planck Institute for Meteorology, Hamburg, 011-49-4117-3236; he is head of the Institute.

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