Tephigram

(meteorology) A thermodynamic diagram designed by Napier Shaw with temperature and logarithm of potential temperature as coordinates; isobars are gently curved lines and the chart is rotated so that pressure increases downward; vapor lines and saturation adiabats are curved; on this chart, energy is proportional to the area enclosed by the curve representing the process.

An aerological diagram, of two axes aligned at 45° to each other. The nearly horizontal lines show atmospheric pressure, together with the heights at which they are found; the lines at 45° to the isobars show temperatures, running from bottom left to top right.

Superimposed upon these two are three sets of guide-lines: those running from bottom right to top left show the dry adiabatic lapse rate (DALR); those running from bottom left to top right, at about 60° to the base, show constant humidity (mixing ratio lines); and convex, curved lines, indicate the saturated adiabatic lapse rate (SALR). With the help of these lines, the behaviour of a rising parcel of air may be predicted.

First, the readings from a radiosonde are plotted to show the environmental lapse rate. Next, from the same source, dew point temperatures are plotted against height. From the temperature and height of the air parcel under investigation, a plot is made of its temperature fall at the DALR, parallel to the DALR guide-lines. Similarly, the dew point change of the air parcel with height is plotted, parallel to the mixing ratio lines. Where these two plots intersect, the parcel will begin to cool at the SALR, and a plot is made of the parcel parallel to the SALR guide-lines. At the point where this plot intersects the environmental lapse rate line (above), the height of the top of any cloud formed by the parcel may be established.

Tephigram

Annotated Tephigram

A tephigram is one of four thermodynamic diagrams commonly used in weather analysis and forecasting. The name evolved from the original name "T-φ-gram" to describe the axes of temperature (T) and entropy (φ) used to create the plot. Usually, temperature and dew point data from radiosondes are plotted on these diagrams to allow calculations of convective stability or convective available potential energy (CAPE). Wind barbs are often plotted at the side of a tephigram to indicate the winds at different heights.

The tephigram was invented by Napier Shaw in 1915 and is used primarily in the United Kingdom and Canada. Other countries use similar thermodynamic diagrams for the same purpose however the details of their construction vary. In the tephigram, isotherms are straight and have a 45 degree inclination to the right while isobars are horizontal and have a slight curve. Dry adiabats are also straight and have a 45 degree inclination to the left while moist adiabats are curved. The principal reason that tephigrams are used by the British Met Office is the property that areas contained by the curves have equal energies for equal areas, leading to better comparisons of CAPE and hence convective systems.

Contents 1 See also 2 References 3 Bibliography 4 External links

See also

• Thermodynamic diagrams
• SkewT
• Emagram
• Stüve diagram

References

• Thermodynamic diagrams

Bibliography

• M K Yau and R.R. Rogers, Short Course in Cloud Physics, Third Edition, published by Butterworth-Heinemann, January 1, 1989, 304 pages. EAN 9780750632157 ISBN 0-7506-3215-1
• J.V. Iribarne and W.L. Godson, Atmospheric Thermodynamics, 2nd Edition, published by D. Reidel Publishing Company, Dordrecht, Holland, 1981, 278 pages, ISBN 9027712972, ISBN978-902771297

External links

• Department of Meteorology, University of Reading page about tephigrams including pdfs of blank printable colour and monochrome tephigrams.

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