book13fronts - Weather Observation and Analysis John...

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Weather Observation and Analysis John Nielsen-Gammon Course Notes These course notes are copyrighted. If you are presently registered for ATMO 251 at Texas A&M University, permission is hereby granted to download and print these course notes for your personal use. If you are not registered for ATMO 251, you may view these course notes, but you may not download or print them without the permission of the author. Redistribution of these course notes, whether done freely or for profit, is explicitly prohibited without the written permission of the author. Chapter 13. FRONTS AND FRONTOGENESIS 13.1 Fronts as Temperature Gradients Fronts were first discovered during World War I, and the name was adopted by analogy to the fronts of battle during the war. Until data from a weather network covering a significant hunk of territory was regularly transmitted and plotted at a central location, it was difficult to recognize the patterns behind the sudden weather changes at different stations. Today, fronts, along with highs and lows, are the most common features of weather maps, and even children are able to recognize the symbols. Nonetheless the working definition of a front remains somewhat elusive, and the decision about where a front lies is a judgment call that experienced weather analysts can disagree about. The basic definition of a front is a narrow, elongated zone with a locally strong temperature gradient. But how narrow is narrow, how elongated is elongated, and how strong is strong? Some have argued that, because of this ambiguity, we should dispense with the concepts of fronts entirely and simply let the analyses of temperature, wind, pressure, etc. speak for themselves. Such an approach is attractive in its intellectual purity, but in practice, people expect to see fronts, and fronts are intimately related to weather patterns. The non-front folks would argue that the relationship between fronts and weather patterns is anything but simple, and that the mere presence of a frontal symbol without a depiction of the underlying weather elements is likely to be misleading. ATMO 251 Chapter 13 page 1 of 22
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Even the basic definition of a front includes many non-fronts. For example, imagine a coastline separating a warm land surface from a cold ocean. The air above the coastline would meet the criterion of a narrow, elongated zone of locally strong temperature gradient. Yet nobody would consider it to be a true front. While this argument rages, we will attempt to construct a working definition of fronts that will serve us well enough for the time being. A synoptic-scale front is an air mass boundary that extends up into the troposphere. It includes at least a locally enhanced temperature gradient and a vector wind shift. A vector wind shift means that the horizontal wind vectors on one
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This note was uploaded on 04/02/2008 for the course ATMO 251-501/50 taught by Professor Alcorn during the Fall '07 term at Texas A&M.

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book13fronts - Weather Observation and Analysis John...

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