Geopitential Height

8/10/2019 Geopitential Height

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GEOPITENTIAL HEIGHT

The height of a given point in the atmosphere in units proportional to the potential energy of unit

mass (geopotential) at this height relative to the sea level.

(http://tigge.ecmwf.int/tigge/d/show_object/table=parameters/name=geopotential_height/levtype

=pl/)

Geopotential height approximates the actual height of a pressure surface abovemean sea-level. Therefore, a geopotential height observation represents the height

of the pressure surface on which the observation was taken.

Since cold air is more dense than warm air, it causes pressure surfaces to be lowerin colder air masses, while less dense, warmer air allows the pressure surfaces to behigher. Thus, heights are lower in coldair masses, and higher in warmair masses.

A line drawn on a weather map connecting points of equal height (in meters) iscalled a height contour. That means, at every point along a given contour, the valuesof geopotential height are the same. An image depicting the geopotential height fieldis given below.

Source: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cyc/upa/trgh.rxml

Geopotential Height

height of a given pressure

Geopotential height approximates the actual height of a pressure surface above mean sea-

level. Therefore, a geopotential height observation represents the height of the pressure

surface on which the observation was taken. A line drawn on a weather map connecting

points of equal height (in meters) is called a height contour. That means, at every point along

a given contour, the values of geopotential height are the same. An image depicting the

geopotential height field is given below.
http://tigge.ecmwf.int/tigge/d/show_object/table=parameters/name=geopotential_height/levtype=pl/http://tigge.ecmwf.int/tigge/d/show_object/table=parameters/name=geopotential_height/levtype=pl/http://tigge.ecmwf.int/tigge/d/show_object/table=parameters/name=geopotential_height/levtype=pl/http://tigge.ecmwf.int/tigge/d/show_object/table=parameters/name=geopotential_height/levtype=pl/http://tigge.ecmwf.int/tigge/d/show_object/table=parameters/name=geopotential_height/levtype=pl/http://tigge.ecmwf.int/tigge/d/show_object/table=parameters/name=geopotential_height/levtype=pl/


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Height contours are represented by the solid lines. The small numbers along the contours are

labels which identify the value of a particular height contour (for example 5640 meters, 5580

meters, etc.). This example depicts the 500 mb geopotential height field and temperatures

(color filled regions). The height field is given in meters with an interval of 60 meters.

Geopotential height is valuable for locatingtroughsandridgeswhich are the upper level

counterparts of surfacecyclonesandanticyclones.

(http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/cyc/upa/hght.rxml)

Geopotential is the potential energy acquired by unit mass on being raised through unit

distance in a field of gravitational force of unit strength. The Geopotential meter is related tothe Dynamic meter by the expression one geopotential meter=0.98 dynamic meter. It is

roughly the height of a pressure surface in the atmosphere above mean sea level.

The equation which defines the relationship between geopotential height (Z) and geometric

height (z) is Z=gz/980. Thus when gravity g has its near average value of 980 cm/sec2,

heights in geopotential meters and and geometric meters are the same; for g < 980 cm/sec2

the height in geopotential meters is the smaller, for g > 980 cm/sec2it is bigger.

Geopotential (from the dynamic point of view) is a better measure of height in the

atmosphere than is geometric height since energy is in general lost or gained when air moves

along a geometrically level surface but not when it moves along an equigeopotential surface.

(http://disc.sci.gsfc.nasa.gov/data-holdings/PIP/geopotential_height.shtml)
http://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/trough.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/trough.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/trough.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/ridge.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/ridge.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/ridge.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/cyclone.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/cyclone.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/cyclone.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/anticyclone.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/anticyclone.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/anticyclone.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/cyc/upa/hght.rxmlhttp://disc.sci.gsfc.nasa.gov/data-holdings/PIP/geopotential_height.shtmlhttp://disc.sci.gsfc.nasa.gov/data-holdings/PIP/geopotential_height.shtmlhttp://disc.sci.gsfc.nasa.gov/data-holdings/PIP/geopotential_height.shtmlhttp://disc.sci.gsfc.nasa.gov/data-holdings/PIP/geopotential_height.shtmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/anticyclone.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/cyclone.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/ridge.rxml?hret=/guides/mtr/cyc/upa/hght.rxmlhttp://ww2010.atmos.uiuc.edu/%28Gh%29/wwhlpr/trough.rxml?hret=/guides/mtr/cyc/upa/hght.rxml


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( Holton, J.R., 1992,An Introduction to Dynamic MeteorologyAcademic Press, 166-175

Singh & Rathor, 1974, Reduction of the Complete Omega Equation to the Simplest Form,

Pure and Applied Geophysics, 112, 219-223)

OmegaA term used to describe vertical motion in the atmosphere. The "omega equation"

used in numerical weather models is composed of two terms, the "differential

vorticity advection" term and the "thickness advection" term. Put more simply, omega

is determined by the amount of spin (or large scale rotation) and warm (or cold)

advection present in the atmosphere. On a weather forecast chart, high values of

omega (or a strong omega field) relate to upward vertical motion (UVV) in the

atmosphere. If this upward vertical motion is strong enough and in a sufficiently moist

airmass, precipitation results.(http://w1.weather.gov/glossary/index.php?letter=o)

Vertical velocity

A measure of the upward motion ofairin theatmosphere.Vertical velocities are in general

around 1 cm.s-1 (compared to 10 m.s-1 for horizontal velocities), but can reach several m.s-1

inthunderstormupdrafts. Often the vertical velocity is displayed in hectopascals per hour.

Sincepressuredecreases with height, negative values of the vertical velocity indicate rising

motion in theatmosphere,and positive values indicate sinking air). Large values of the

vertical velocity on these charts can (when combined with high moisture level) indicate the

potential for heavyrainfall.

(http://www.weatherzone.com.au/help/glossary.jsp?l=v)

Wind flows in the horizontal at a much higher average wind speed than in the vertical. Vertical

motion is roughly two orders of magnitude smaller than horizontal motion. Wind speeds in the

horizontal are commonly over 50 knots at some point in the atmosphere above a location. The

average vertical wind speed is only a few centimeters per second! This seems unusual considering

thunderstorm updraftscan have vertical velocities over 100 miles per hour. The deal is,

thunderstorms only encompass a tiny surface area of the earth compared to regions not having

thunderstorms. Well less than 1% of the time are vertical velocities greater than 1 mile per hour
http://w1.weather.gov/glossary/index.php?letter=ohttp://w1.weather.gov/glossary/index.php?letter=ohttp://w1.weather.gov/glossary/index.php?letter=ohttp://www.weatherzone.com.au/help/glossary.jsp?l=a#airhttp://www.weatherzone.com.au/help/glossary.jsp?l=a#airhttp://www.weatherzone.com.au/help/glossary.jsp?l=a#airhttp://www.weatherzone.com.au/help/glossary.jsp?l=a#atmospherehttp://www.weatherzone.com.au/help/glossary.jsp?l=a#atmospherehttp://www.weatherzone.com.au/help/glossary.jsp?l=a#atmospherehttp://www.weatherzone.com.au/help/glossary.jsp?l=t#thunderstormhttp://www.weatherzone.com.au/help/glossary.jsp?l=t#thunderstormhttp://www.weatherzone.com.au/help/glossary.jsp?l=t#thunderstormhttp://www.weatherzone.com.au/help/glossary.jsp?l=p#pressurehttp://www.weatherzone.com.au/help/glossary.jsp?l=p#pressurehttp://www.weatherzone.com.au/help/glossary.jsp?l=p#pressurehttp://www.weatherzone.com.au/help/glossary.jsp?l=a#atmospherehttp://www.weatherzone.com.au/help/glossary.jsp?l=a#atmospherehttp://www.weatherzone.com.au/help/glossary.jsp?l=a#atmospherehttp://www.weatherzone.com.au/help/glossary.jsp?l=r#rainfallhttp://www.weatherzone.com.au/help/glossary.jsp?l=r#rainfallhttp://www.weatherzone.com.au/help/glossary.jsp?l=r#rainfallhttp://www.weatherzone.com.au/help/glossary.jsp?l=vhttp://www.weatherzone.com.au/help/glossary.jsp?l=vhttp://www.weatherzone.com.au/help/glossary.jsp?l=vhttp://www.theweatherprediction.com/habyhints/319/http://www.theweatherprediction.com/habyhints/319/http://www.theweatherprediction.com/habyhints/319/http://www.weatherzone.com.au/help/glossary.jsp?l=vhttp://www.weatherzone.com.au/help/glossary.jsp?l=r#rainfallhttp://www.weatherzone.com.au/help/glossary.jsp?l=a#atmospherehttp://www.weatherzone.com.au/help/glossary.jsp?l=p#pressurehttp://www.weatherzone.com.au/help/glossary.jsp?l=t#thunderstormhttp://www.weatherzone.com.au/help/glossary.jsp?l=a#atmospherehttp://www.weatherzone.com.au/help/glossary.jsp?l=a#airhttp://w1.weather.gov/glossary/index.php?letter=o


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above any point location. All the uplift from low pressure and fronts only produce vertical upglide

of a few to sometimes greater than 20 centimeters per second on the synoptic scale. That's it. Why

then does it rain? Well, an uplift of 6 centimeters per second leads to a pretty significant distance

given enough time. In fact, moving 6 centimeters per second in one hour produces 216 meters of

vertical distance. Give it a few hours, and that parcel of air can rise in the vertical over a kilometer.

An upward vertical velocity of just 6 centimeters per second can produce a large volume of

precipitation if themoistureis present to be condensed. Let's apply upward vertical velocity to

interpreting the synoptic scale forecast models (NAM,GFS etc.). Upward vertical velocity is plotted

on the 700-mb prog. Go ahead and look at a 700 mb forecast panel on your computer. This prog is

available on UNISYS weather at:

http://weather.unisys.com/nam/700.php
http://www.theweatherprediction.com/habyhints/113/http://www.theweatherprediction.com/habyhints/113/http://www.theweatherprediction.com/habyhints/113/http://weather.unisys.com/nam/700.phphttp://weather.unisys.com/nam/700.phphttp://weather.unisys.com/nam/700.phphttp://www.theweatherprediction.com/habyhints/113/

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Geopitential Height