- Lifted index
The lifted index (LI) is the
temperaturedifference between an air parcellifted adiabatically Tp(p) and the temperature of the environment Te(p) at a given pressure height in the troposphere(lowest layer where most weather occurs) of the atmosphere, usually 500 hPa (mb). When the value is positive, the atmosphere (at the respective height) is stable and when the value is negative, the atmosphere is unstable.
LI can be computed using computer algorithms but can also be determined graphically. To do this, generally, the parcel is lifted from the portion of the
planetary boundary layer(PBL) that lies below the morning inversion. The air here should be about 60 to 65% RH, which is then lifted along the dry adiabat (see also adiabatic process) to the lifting condensation level (LCL), which is the intersection of that curve with the average mixing ratioin the boundary layer. Once the LCL is found, the parcel is lifted along the moist adiabat to 500 mb. It is then that one finds LI = Te(p) - Tp(p).
LI is generally scaled as follows:
* LI 6 or Greater, Very Stable Conditions
* LI Between 1 and 6 : Stable Conditions, Thunderstorms Not Likely
* LI Between 0 and -2 : Slightly Unstable, Thunderstorms Possible, With Lifting Mechanism (i.e., cold front, daytime heating, ...)
* LI Between -2 and -6 : Unstable, Thunderstorms Likely, Some Severe With Lifting Mechanism
* LI Less Than -6: Very Unstable, Severe Thunderstorms Likely With Lifting Mechanism
Significance to thunderstorms
The lifted index can be used in
thunderstormforecasting, however, convective available potential energy(CAPE) is considered by most as a superior measurement of instability and is preferred by many meteorologists for convection forecasting.cite journal |last= Blanchard |first= David O. |title= Assessing the Vertical Distribution of Convective Available Potential Energy |journal= Weather and Forecasting|volume= 13 |issue= 3 |pages= 870–7 |publisher= American Meteorological Society|date= Sept 1998 |url= http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0434(1998)013%3C0870%3AATVDOC%3E2.0.CO%3B2 |year= 1998 |doi= 10.1175/1520-0434(1998)013<0870:ATVDOC>2.0.CO;2 ] However, LI is easier and faster to determine without using a computer, as determining CAPE requires integration from one level to another.
* [http://ww2010.atmos.uiuc.edu/(Gl)/guides/maps/wupa/upa0lift.rxml Lifted Index] (
University of Illinois)
* [http://www.theweatherprediction.com/habyhints/300/ A look at LI]
* [http://www.crh.noaa.gov/lsx/science/indices.php Convective indices] (NWS St. Louis)
* [http://amsglossary.allenpress.com/glossary/search?id=stability-index1 AMS Glossary stability indices, including LI]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Lifted Music — Infobox record label name = Lifted music founded = 2006 founder = Chris Renegade genre = Drum and bass/ Avant garde country = England location = St Albans url = [http://www.liftedmusic.co.uk] Lifted music is a drum and bass concept label mainly… … Wikipedia
Lifted (film) — Infobox Film name = Lifted image size = caption = Lifted poster director = Gary Rydstrom producer = Katherine Sarafian Osnat Shurer and John Lasseter (executive producers) writer = Jeff Pideon Max Brace narrator = starring = music = Michael… … Wikipedia
Lifted Research Group — Infobox Company company type = Private company name = Lifted Research Group company foundation = 1999 location = Lake Forest, California industry = Fashion products = Streetwear clothing and accessories homepage = [http://www.l r g.com LRG… … Wikipedia
Index card — An index card is heavy paper stock cut to a standard size. Index cards are often used for recording individual items of information that can then be easily rearranged and filed. The most common size in the United States and Russia is 3 in by 5 in … Wikipedia
Thunderstorm — Electrical storm redirects here. For other uses, see Electrical storm (disambiguation). A typical thunderstorm A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather… … Wikipedia
Convective available potential energy — A skew T plot showing a morning sounding with a large hydrolapse followed by an afternoon sounding showing the cooling which occurred in the mid levels resulting in an unstable atmosphere as surface parcels have now become negatively buoyant. The … Wikipedia
Wind — For other uses, see Wind (disambiguation). Wind, from the … Wikipedia
Precipitation (meteorology) — Long term mean precipitation by month In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under… … Wikipedia
Convective instability — For a more general discussion of the same phenomenon, see Convective available potential energy. This article incorporates public domain text created by the US government. In meteorology, convective instability or stability of an airmass refers… … Wikipedia
Palm Sunday tornado outbreak of 1920 — Infobox tornado outbreak|name=Palm Sunday (1920) Tornado Outbreak date=March 28, 1920| duration= 9 hours fujitascale=F4 tornadoes= > 38 total damages (USD)=Unknown total fatalities=380+ areas affected=Alabama, Georgia, Illinois, Indiana, Michigan … Wikipedia