View source for Physics:Overshooting top

{{Short description|Part of the convective tower of a thunderstorm}}
[[File:Cumulonimbus13 - NOAA.jpg|thumb|right|An '''overshooting top''' protruding above the anvil at the top of a thunderstorm]]
An '''overshooting top''' (or '''penetrating top''') is a dome-like protrusion shooting out of the top of the [[Earth:Cumulonimbus incus|anvil]] of a [[Physics:Thunderstorm|thunderstorm]] and into the lower [[Earth:Stratosphere|stratosphere]].<ref>{{cite journal|last1= Shenk|first1= W. E.|date= 1974|title= Cloud top height variability of strong convective cells|journal= Journal of Applied Meteorology|volume = 13|issue= 8|pages= 918{{ndash}}922| doi=10.1175/1520-0450(1974)013<0917:cthvos>2.0.co;2 |bibcode = 1974JApMe..13..917S |doi-access= free}}</ref><ref name="Overshooting Tops">{{cite web|url=https://www.eumetsat.int/website/home/Data/Training/TrainingLibrary/DAT_2042700.html|title=Overshooting Tops – Satellite-Based Detection Methods|publisher=[[Organization:EUMETSAT|EUMETSAT]]|date=9 June 2011|access-date=10 May 2019}}</ref> When an overshooting top is present for 10 minutes or longer, it is a strong indication that the storm is severe.<ref name="Training">Chance Hayes, National Weather Service Wichita, Kansas. "Storm Fury on the Plains." Storm Spotter Training. 4H Building, Salina, Kansas. 22 Feb. 2010. Lecture.</ref>

== Formation ==
[[File:Top of cumulo nimbus viwed from an airplane above DRC.jpg|thumb|right|Overshooting top of a cumulonimbus viewed from a plane crossing the Democratic Republic of Congo. Airliners typically fly at an altitude ranging from 10 km to 13 km, at the tropopause.]]

When a thunderstorm forms, clouds build vertically into the atmosphere until the storm's [[Earth:Vertical draft|updraft]] (warm rising air) has reached an [[Earth:Equilibrium level|equilibrium level (EL)]]; the point where the surrounding air is about the same temperature or even warmer.<ref name=nssl>{{cite web  | title = Thunderstorm Detection  | publisher = National Severe Storms Lab (NSSL) | url = http://www.nssl.noaa.gov/primer/tstorm/tst_detecting.html  | access-date = 2009-02-28}}</ref> This point of equilibrium is often marked by the [[Earth:Tropopause|tropopause]]. Rather than continuing to rise into the stratosphere, the vertical cloud growth abruptly stops, and instead clouds spread horizontally, forming an "anvil" shape on top of the thunderstorm.<ref name="Training"/>

An overshooting top forms when a thunderstorm's updraft, due to [[Physics:Momentum|momentum]] from rapid ascent and strength of lifting through the [[Earth:Free convective layer|free convective layer]] (FCL), protrudes its equilibrium level, forming a dome-like structure above the anvil.<ref name=glossary>{{cite web  | title = Overshooting Top definition  | publisher = NSSL  | url = http://www.nssl.noaa.gov/primer/defs/overshooting.html  | access-date = 2009-02-28  | archive-url = https://web.archive.org/web/20110927165205/http://www.nssl.noaa.gov/primer/defs/overshooting.html  | archive-date = 2011-09-27  | url-status = dead  }}</ref> This can occur with any [[Earth:Cumulonimbus cloud|cumulonimbus cloud]] when instability is high. Whereas anvils form at the equilibrium level, overshooting tops continue to the [[Earth:Maximum parcel level|maximum parcel level (MPL)]].

=== Above-anvil cirrus plume ===
[[File:AS09-22-3375 (21413692423).jpg|thumb|left|Cirrus plumes in the wake of overshooting tops may be indicators of severe weather|alt=Photograph of the top of a cumulonimbus cloud]]
The strong updrafts delineated by overshooting tops can act as a barrier against the surrounding flow of air. Fast stratospheric winds may rise slightly upon encountering overshooting tops, cooling and producing a turbulent wake of cooler temperatures downstream of the updraft. This interaction also sheds ice and water vapor from the anvil cloud, forming a plume of [[Earth:Cirrus cloud|cirrus]] emanating from the updraft region,<ref name="ShowOffPlumage" /><ref name="BetterUnderstandingIcyPlumes" /> though this is most evident in mid-latitude environments where the tropopause is typically lower and the associated [[Astronomy:Inversion (meteorology)|inversion]] wider.<ref name="Murillo and Homeyer 2022">{{cite journal |last1=Murillo |first1=Elisa M. |last2=Homeyer |first2=Cameron R. |title=What Determines Above-Anvil Cirrus Plume Infrared Temperature? |journal=Journal of the Atmospheric Sciences |date=December 2022 |volume=79 |issue=12 |pages=3181–3194 |doi=10.1175/JAS-D-22-0080.1|doi-access=free }}</ref> These cirrus plumes may be warmer than the underlying anvil cloud due to the mixing of air from the warmer [[Earth:Stratosphere|stratosphere]]. Termed above-anvil cirrus plumes (AACP), the emergence of such features on satellite imagery have been associated with severe weather events.<ref name="ShowOffPlumage">{{cite web |title=Severe Storms Show off their "Plume-age" |url=https://www.nasa.gov/feature/langley/severe-storms-show-off-their-plume-age |publisher=NASA |access-date=September 14, 2023 |date=August 15, 2018}}</ref><ref name="BetterUnderstandingIcyPlumes">{{cite web |last1=Phillips |first1=Jean |title=Scientists gain better understanding of icy plumes associated with violent tornadoes |url=https://news.wisc.edu/scientists-gain-better-understanding-of-icy-plumes-associated-with-violent-tornadoes/ |publisher=University of Wisconsin&ndash;Madison |access-date=September 14, 2023 |location=Madison, Wisconsin |date=September 9, 2021}}</ref> A 2018 study published in ''Weather and Forecasting'' found that 73&nbsp;percent of significant severe weather reports in the United States were associated with storms producing AACPs and that AACPs emerged an average of 31&nbsp;minutes before the issuance of severe weather warnings.<ref name="Bedka et al. 2018">{{cite journal |last1=Bedka |first1=Kristopher |last2=Murillo |first2=Elisa M. |last3=Homeyer |first3=Cameron R. |last4=Scarino |first4=Benjamin |last5=Mersiovsky |first5=Haiden |title=The Above-Anvil Cirrus Plume: An Important Severe Weather Indicator in Visible and Infrared Satellite Imagery |journal=Weather and Forecasting |date=October 2018 |volume=33 |issue=5 |pages=1159–1181 |doi=10.1175/WAF-D-18-0040.1|doi-access=free }}</ref> Simulations suggest that overshooting tops behave like [[Physics:Hydraulic jump|hydraulic jump]]s in the presence of strong winds aloft, allowing the transport of over {{cvt|7|tonne}} of water vapor into the lower stratosphere per second.<ref name="O'Neill et al. 2021">{{cite journal |last1=O’Neill |first1=Morgan E |last2=Orf |first2=Leigh |last3=Heymsfield |first3=Gerald M. |last4=Halbert |first4=Kelton |title=Hydraulic jump dynamics above supercell thunderstorms |journal=Science |date=September 10, 2021 |volume=373 |issue=6560 |pages=1248–1251 |doi=10.1126/science.abh3857|pmid=34516791 |s2cid=237473018 |url=https://repository.library.noaa.gov/view/noaa/54242 }}</ref>

== Severe weather ==
[[File:Tornadic supercell.jpg|thumb|upright=1.5|Diagram of a supercell thunderstorm, which shows the overshooting top rising above the anvil cloud.]]
Many thunderstorms exhibit an overshooting top at some point in their life cycle.<ref name=nssl/> In weaker thunderstorms, the overshooting top is short-lived, and often takes on a wispy appearance.<ref name=glossary/> If the overshooting top is rising and falling in a cyclical fashion with each protrusion persisting only a few minutes, then it could indicate the storm is pulsing and not as strong as a storm with a continuous overshooting top.<ref name=nws>{{cite web  | title = JetStream - Glossary  | publisher = [[Earth:National Weather Service|National Weather Service]]  | date = August 29, 2007  | url = http://www.srh.noaa.gov/jetstream//append/glossary_o.htm  | access-date = 2008-02-28}}</ref>

An overshooting top lasting for more than 10 minutes is a sign of a strong updraft in a thunderstorm, indicating a strong likelihood the storm is producing [[Earth:Severe weather|severe weather]].<ref name=nssl/> If the overshooting top is continuous, it's an indication of enhanced probability that the storm is a [[Earth:Supercell|supercell]], i.e. a rotating storm.<ref name=glossary/> During a strong [[Earth:Tornado|tornado]], the overshooting top may roll or fold over as new activity climbs up the back while the front of the overshooting top collapses into the storm. During a long-track tornado, the entire top of the storm, including the overshooting top, may drop by thousands of feet.{{cn|date=May 2019}}

== Storm features ==
A storm powerful enough to produce a lasting overshooting top typically produces the following{{cn|date=May 2019}}:
* Heavy rain; a deluge of rain could fall from this storm in a short amount of time.
* Strong straight-line [[Earth:Wind|wind]] from [[Earth:Downburst|downburst]]s; the storm clouds have powerful winds churning inside them. These winds are likely to be felt at the surface and also a threat to aviation aloft.
* Sometimes a [[Earth:Tornado|tornado]] may form; most strong tornadoes are associated with [[Earth:Mesocyclone|mesocyclone]]s located near the interchange of the rotating updraft and the rear flank downdraft (RFD).
* [[Earth:Hail|Hail]]; if the updraft is strong enough to produce an overshooting top it can also carry large [[Earth:Hail|hail]].
* A storm that features an overshooting top is a [[Physics:Thunderstorm|thunderstorm]], and is thus likely to produce [[Astronomy:Lightning|lightning]].

== See also ==
* [[Earth:Atmospheric convection|Atmospheric convection]]
* [[Earth:Atmospheric thermodynamics|Atmospheric thermodynamics]]

== References ==
{{Reflist}}

== External links ==
* [http://www.theweatherprediction.com/habyhints/352/ http://www.theweatherprediction.com/habyhints/352]

{{Cloud types}}

[[Category:Severe weather and convection]]
[[Category:Cloud and fog physics]]
[[Category:Cumulus]]

{{Sourceattribution|Overshooting top}}