Thermodynamic diagrams are diagrams used by scientists and engineers to represent the thermodynamic states of a material (typically fluid) and the consequences of manipulating this material. For instance, a temperature-entropy diagram (T-s diagram) may be used to demonstrate the behavior of a fluid as it is changed by a compressor. Thermodynamics (Greek: thermos = heat and dynamic = change) is the physics of energy, heat, work, entropy and the spontaneity of processes. ... A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ...

Especially in meteorology they are used to analyze the actual state of the atmosphere derived from the measurements of radiosondes, usually obtained with weather balloons. In such diagrams, temperature and humidity values (represented by the dew point) are displayed with respect to pressure. Thus the diagram gives at a first glance the actual atmospheric stratification and vertical water vapor distribution. Further analysis gives the actual base and top height of convective clouds or possible instabilities in the stratification. Satellite image of Hurricane Hugo with a polar low visible at the top of the image. ... View of Jupiters active atmosphere, including the Great Red Spot. ... radiosonde with measuring instruments A radiosonde (Sonde is German for probe) is a unit for use in weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver. ... A hydrogen filled balloon at Cambridge Bay Upper Air station, Nunavut, Canada Close up of a hydrogen filled balloon at Cambridge Bay Upper Air station, Nunavut, Canada Rawinsonde weather balloon just after launch. ... This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... This article or section is not written in the formal tone expected of an encyclopedia article. ... Dew on a spider web The dew point or dewpoint of a given parcel of air is the temperature to which the parcel must be cooled, at constant barometric pressure, for the water vapor component to condense into water, called dew. ... Diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure at any point in the Earths atmosphere. ... Atmospheric stratification is the division of the atmosphere into distinct layers, each with specific properties such as temperature or humidity. ... This article or section does not adequately cite its references or sources. ...

By assuming the energy amount due to solar radiation it is possible to predict the 2 m (6.6 ft) temperature, humidity, and wind during the day, the development of the boundary layer of the atmosphere, the occurrence and development of clouds and the conditions for soaring flight during the day. Solar irradiance spectrum at top of atmosphere. ... The metre, or meter (symbol: m) is the SI base unit of length. ... A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, ′ – a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. ... The planetary boundary layer (PBL) is also known as the atmospheric boundary layer (ABL). ...

The main feature of thermodynamic diagrams is the equivalence between the area in the diagram and energy. When air changes pressure and temperature during a process and prescribes a closed curve within the diagram the area enclosed by this curve is proportional to the energy which has been gained or released by the air.

There are mainly three different types of thermodynamic diagrams used by the different weather services:

• Skew-T log-P diagram
• Tephigram
• Emagram

These all are derived from the physical P-alpha-diagram which combines pressure and specific volume (alpha) as basic coordinates. The P-alpha-diagram shows a strong deformation of the grid for atmospheric conditions and is therefore not useful in atmospheric sciences. The three diagrams are constructed from the P-alpha-diagram by using appropriate coordinate transformations. Black and White Skew-T log-P Color Skew-T log-P diagram, SVG/ PDF format A Skew-T Log-P diagram is one of four thermodynamic diagrams commonly used in weather analysis and forecasting. ... A tephigram is one of four thermodynamic diagrams commonly used in weather analysis and forecasting. ... Wikipedia does not have an article with this exact name. ... Atmospheric sciences is an umbrella term for the study of the atmosphere, its processes, the effects other systems have on the atmosphere, and the effects of the atmosphere on these other systems. ...

Not a thermodynamic diagram in a strict sense since it does not display the energy - area equivalence is the

• Stüve diagram

Due to its simpler construction it is preferred in education. A Stüve diagram is one of four thermodynamic diagrams commonly used in weather analysis and forecasting. ...

Thermodynamic diagrams usually show a net of five different lines:

• isobars = lines of constant pressure
• isotherms = lines of constant temperature
• dry adiabats = lines of constant potential temperature representing the temperature of a rising parcel of dry air
• saturated adiabats or pseudoadiabats = lines representing the temperature of a rising parcel saturated with water vapour
• mixing ratio = lines representing the dewpoint of a rising parcel

The lapse rate, dry adiabatic lapse rate (DALR) and moist adiabatic lapse rate (MALR), are obtained. With the help of these lines, parameters such as cloud condensation level, level of free convection, onset of cloud formation. etc. can be derived from the soundings. The word isobar derives from the two ancient Greek words, ισος (isos), meaning equal, and βαρος (baros), meaning weight. In meteorology, an isobar is a line of equal or constant pressure on a graph, plot, or map; an isopleth of pressure. ... An isotherm is a line of equal or constant temperature on a graph, plot, or map; an isopleth of temperature. ... The lapse rate is the rate at which an atmospheric variable (usually temperature) decreases with altitude. ... The lifted condensation level or lifting condensation level (LCL), represents the height at which an air parcel being lifted dry adiabatically will become saturated because of adiabatic cooling (caused by expansion) and condense into cloud. ... The level of free convection (LFC) is any point in the atmosphere where the temperature of the environment decreases faster than the moist adiabatic lapse rate of a saturated air parcel at the same level. ...

References

• 'The Physics of Atmospheres' by John Houghton, Cambridge University Press 2002

Especially chapter 3.3. deals solely with the tephigram.

• 'Handbook of meteorological forecasting for soaring flight' WMO Technical Note No. 158. ISBN 92-63-10495-6 especially chapter 2.3.

External links

• radarmet.atmos.colostate.edu/../AT620_ch4.ppt A PowerPoint presentation with a very good mathematical description about the derivation of the different diagrams.
• www.met.tamu.edu/../aws-tr79-006.pdf A very large technical manual (164 pages) how to use the diagrams.
• www.comet.ucar.edu/../sld010.htm A course on how to use diagrams at comet the 'Cooperative Program for Operational Meteorology, Education and Training'.
• www.raob.com RAOB analysis software for radio soundings.
• www.ultx.de/thermik/60Tempanalyse.ppt a PowerPoint presentation about the use of the Stuve diagram (in German).
• Tephigram page, University of Reading Blank colour and monochrome tephigrams as pdf from the Department of Meteorology, University of Reading.
• maths.ucd.ie/../blank_tephigram.pdf Blank black and white Tephigram as pdf from UCD School of Mathematical sciences in Dublin.
• http://www.meteo.uni-koeln.de/meteo.php?show=En_We_We Radio soundings from all over the world from the 'Institut für Geophysik und Meteorologie' at the University of Cologne/Germany
• weather.uwyo.edu/upperair/sounding.html Radio soundings from all over the world from the Department of Atmospheric sciences at the University of Wyoming/USA