View source for Hot tower

{{Short description|Type of tropical cumulonimbus cloud}}
[[File:Global Hawk measures a burst of convection called a Hot Tower.ogv|thumb|upright=1.3|A NASA [[Global Hawk]] detects a hot tower measuring over {{cvt|12|km}} high within the eyewall of [[Hurricane Karl]] on September 16, 2010.|alt=Animation of a drone scanning a hurricane]]
A '''hot tower''' is a tropical [[cumulonimbus cloud]] that reaches out of the lowest layer of the atmosphere, the [[troposphere]], and into the [[stratosphere]].<ref name="DiscoveringHotTowers">{{cite web |last1=Voiland |first1=Adam |title=Discovering Hot Towers |url=https://earthobservatory.nasa.gov/blogs/earthmatters/2012/09/12/discovering-hot-towers/ |website=Earth Observatory |publisher=NASA |access-date=16 March 2021 |date=12 September 2012}}</ref> These formations are called "hot" because of the large amount of [[latent heat]] released as [[water vapor]] that condenses into liquid and freezes into ice within the cloud.  Hot towers in regions of sufficient [[vorticity]] may acquire rotating updrafts; these are known as ''vortical hot towers'' In some instances, hot towers appear to develop characteristics of a [[supercell]], with deep and persistent rotation present in the updraft.<ref name="DiscoveringHotTowers2">{{cite web |last1=Voiland |first1=Adam |title=Discovering Hot Towers |url=https://twitter.com/ReedTimmerAccu/status/1304628666631028738 |publisher=NASA |access-date=16 March 2021 |date=12 September 2012}}</ref> The role of hot towers in [[tropical meteorology|tropical weather]] was first formulated by [[Joanne Simpson]] in 1958. Hot towers dominated discussions in tropical meteorology in the 1960s and are now considered the main drivers of rising air within [[tropical cyclone]]s and a major component of the [[Hadley circulation]]. Although the prevalence of hot towers in scientific literature decreased in the 1970s, hot towers remain an active area of research. The presence of hot towers in [[tropical cyclone]]s is correlated with an increase in the tropical cyclones' intensities.<ref name="Hurricane Monster">{{cite web |last1=Chohan |first1=Rani |title=Scientists Discover Clues to What Turns a Hurricane into a Monster |url=https://www.nasa.gov/vision/earth/environment/Hot_Towers.html |publisher=NASA |access-date=16 March 2021 |location=12 January 2004 |archive-date=28 September 2022 |archive-url=https://web.archive.org/web/20220928020833/https://www.nasa.gov/vision/earth/environment/Hot_Towers.html |url-status=dead }}</ref>

== Observation ==
Hot towers were first detected by [[weather radar|radar]] in the 1950s.<ref name="DiscoveringHotTowers" /> Aerial reconnaissance was used to probe hot towers, though planes avoided the most dangerous cores of hot towers due to safety concerns.{{sfn|Fierro et al. (2009)|p=2731}} The launch of the [[Tropical Rainfall Measuring Mission]] (TRMM) in 1997 provided the resolution and coverage necessary to systematically catalog hot towers and precisely assess their structure globally.<ref name="DiscoveringHotTowers" /> Prior to 1997, the small size and short duration of hot towers limited studies of hot towers to aerial observations as the resolutions of satellite sensors at [[microwave]] and [[infrared]] wavelengths were too coarse to properly resolve details within hot towers.<ref name="Katrina Hot Towers">{{cite web |last1=Perkins |first1=Lori |title=Hurricane Katrina Hot Towers |url=https://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=3253 |website=Scientific Visualization Studio |publisher=NASA |access-date=16 March 2021 |date=15 September 2005}}</ref>

== Structure ==
The term ''hot tower'' has been applied to both rapidly rising parcels of air and the tall [[cumulonimbus cloud]]s that accompany them.<ref name="DiscoveringHotTowers" />{{sfn|Guimond et al. (2010)|p=634}} The regions of rising air are horizontally small and span about {{cvt|2|–|4|km}} across.{{sfn|Guimond et al. (2010)|p=634}}{{sfn|Fierro et al. (2009)|p=2731}} Their greatest extent is in the vertical, reaching altitudes as high as {{cvt|18|km}} and exhibiting high [[reflectivity]].{{sfn|Heymsfield et al. (2010)|p=286}} Hot towers are effectively undilute; as they ascend, the surrounding air does not mix with the rising parcels of air.{{sfn|Montgomery et al. (2006)|p=356}}{{sfn|Anthes (2003)|p=144}} As a result, the [[equivalent potential temperature]] within a hot tower remains nearly constant throughout their entire vertical extent. This allows for efficient transport of heat from the lower [[troposphere]] to the [[stratosphere]]. Hot towers forming within areas of rotation may feature rotating [[updraft]]s; these are known as ''vortical hot towers'' and are associated with localized regions of anomalous vertical [[vorticity]].{{sfn|Anthes (2003)|p=144}}

== Conceptual development ==
[[File:DaisyAug2819580530UTCNavyRecon.png|thumb|left|Aerial studies of [[Hurricane Daisy (1958)|Hurricane Daisy]] in 1958 were pivotal in validating the relationship between hot towers and tropical cyclones]]
Before the 1950s, the mechanism driving atmospheric [[Hadley cell]]s—an air circulation that transports tropical heat and moisture poleward—was poorly understood.<ref name="Hot Tower Hypothesis" /> It was initially believed that the Hadley cell was fueled by the broad, diffuse, and gradual rise of warm and moist air near the equator. However calculations of [[Earth's energy budget]] using data from [[World War II]] showed that the mid-troposphere was an energy deficit region, indicating that the maintenance of the Hadley cell could not be explained by the broad ascent of air.{{sfn|Fierro et al. (2009)|p=2731}} The role of the tropical regions in the global climate system and the development of tropical disturbances were also poorly understood. The 1950s marked a pivotal decade that saw the advancement of [[tropical meteorology]], including the creation of the U.S. [[National Hurricane Research Project]] in 1956.{{sfn|Anthes (2003)|p=139}} In 1958, [[Herbert Riehl]] and [[Joanne Simpson]] proposed that the release of latent heat caused by condensation within hot towers supplied the energy necessary to maintain Hadley cells and the [[trade winds]]; their hypothesis was initially based on aerial observations made by Simpson during her time at [[Woods Hole Oceanographic Institution]].<ref name="Hot Tower Hypothesis" /> This mechanism required the existence of undilute cumulonimbus clouds that did not [[entrainment (meteorology)|entrain]] the surrounding air, allowing for the efficient transfer of heat from the ocean surface into the upper troposphere.{{sfn|Anthes (2003)|p=140}} The existence of 1,500–2,500 of these clouds was required if they were to support the Hadley circulation.{{sfn|Fierro et al. (2009)|p=2731}} The researchers also argued that hot towers helped maintain the warmth present at the center of [[tropical cyclone]]s and that the ascent of moist air within tropical cyclones was concentrated around the hot towers.<ref name="Warm Core Mystery">{{cite web|last1=Weier|first1=John|title=Warm Core Mystery  |url=https://earthobservatory.nasa.gov/features/Simpson/simpson4.php |website=Earth Observatory |publisher=NASA |access-date=16 March 2021 |date=April 28, 2004}}</ref> In their original 1958&nbsp;paper outlining the role of hot towers, Riehl and Simpson described these clouds as "narrow warm towers", but began terming the idea as the "hot tower hypothesis" by 1960.{{sfn|Anthes (2003)|p=140}}<ref name="Hot Tower Hypothesis">{{cite web|last1=Weier|first1=John|title="Hot Tower" Hypothesis |url=https://earthobservatory.nasa.gov/features/Simpson/simpson3.php |website=Earth Observatory |publisher=NASA |access-date=16 March 2021 |date=April 28, 2004}}</ref> For the next two decades, hot towers dominated scientific discussion concerning the interaction between [[cumulus cloud]]s and their larger-scale tropical environments.{{sfn|Anthes (2003)|p=139}}

[[File:Hottower.jpg|thumb|right|Visualization of a hot tower in [[Hurricane Bonnie (1998)]]. Cloud heights are exaggerated.|alt=Visualization of moisture concentrations in a hurricane]]
Aerial observations of [[Hurricane Daisy (1958)|Hurricane Daisy]] in [[1958 Atlantic hurricane season|1958]] suggested that [[atmospheric convection|convection]] within tropical cyclones was limited to a few areas of cumulonimbus clouds, dispelling the idea that rising air was distributed throughout the entire cyclone's envelope and lending support for the hot tower hypothesis.{{sfn|Anthes (2003)|p=140}} In the case of Hurricane Daisy, the convecting cumulonimbus clouds represented only about four percent of the total region of [[precipitation]] associated with the hurricane. A 1961 analysis by Riehl and Simpson using the NHRP data from Hurricane Daisy concluded that hot towers were the principal mechanism by which tropical cyclones move warm air into the upper troposphere. The newfound importance of hot towers in tropical cyclones motivated the development of [[parametrization (atmospheric modeling)|parametrization]]—the representation of small-scale phenomena and interactions, i.e. individual cumulus clouds—in early [[numerical weather prediction|weather models]].{{sfn|Anthes (2003)|p=141}} The hot tower hypothesis also inspired the development of [[convective instability|convective instability of the second kind]] (CISK): a conceptual model that emphasized the [[positive feedback|feedback]]s between the latent heat released by individual cumuli and the convergence associated with tropical cyclones.{{sfn|Anthes (2003)|p=143}} By the 1970s, many of the ideas and predictions put forth by the hot tower hypothesis had been validated by empirical observations.{{sfn|Anthes (2003)|p=144}} Critics of the hot tower hypothesis contended it was implausible that a cumulonimbus cloud could be free of entrainment.<ref name="Hot Tower Hypothesis" /> This facet of the hypothesis remained untested until dropsondes released into hot towers as part of the Convection and Moisture Experiment in 1998 provided the first direct measurements of the thermodynamic structure of hot towers. The data showed that the [[equivalent potential temperature]] within hot towers was virtually constant across their entire vertical extent, confirming the lack of entrainment.{{sfn|Anthes (2003)|p=144}} Other field observations have suggested that some tropical updrafts are diluted by their surrounding environments at altitudes lower than {{cvt|5|km}}, though strong latent heat generated by [[Hurricane dynamics and cloud microphysics|ice within the cloud]] was sufficient to provide the requisite input energy for the Hadley circulation.{{sfn|Fierro et al. (2009)|p=2745}} Scientific research of hot towers experienced a resurgence in the 2000s with a renewed focus on their role in [[tropical cyclogenesis]] and tropical cyclone development.{{sfn|Guimond et al. (2010)|p=634}}

== Effect on tropical cyclones ==
Vortical hot towers aid in the formation of tropical cyclones by producing many small-scale positive anomalies of [[potential vorticity]], which eventually coalesce to strengthen the broader storm.{{sfn|Hendricks et al. (2004)|p=1209}} The high vorticity present in the hot towers traps the latent heat released by those clouds, while the merger of the hot towers aggregates this enhanced warmth.{{sfn|Hendricks et al. (2004)|p=1229}} These processes are the major part of the initial formation of a tropical cyclone's warm core—the anomalous warmth at the center of such a system—and the increased [[angular momentum]] of the winds encircling the developing cyclone.{{sfn|Hendricks et al. (2004)|p=1209}}

In 2007, the [[National Aeronautics and Space Administration]] (NASA) hypothesized that the [[wind shear]] between the eye and the eyewall could enhance updraft through the center of a cyclone and generate convection.<ref>{{cite web|author=National Aeronautics and Space Administration|url=http://svs.gsfc.nasa.gov/vis/a000000/a003400/a003413/index.html|title=Hot towers simulation|year=2007|publisher=NOAA|access-date=2009-09-18|archive-date=2009-08-31|archive-url=https://web.archive.org/web/20090831143057/http://svs.gsfc.nasa.gov/vis/a000000/a003400/a003413/index.html|url-status=dead}}</ref> Hot towers may appear when a cyclone is about to intensify, possibly [[Rapid intensification|rapidly]]. A particularly tall hot tower rose above [[Hurricane Bonnie (1998)|Hurricane Bonnie]] in August 1998, as the storm intensified before striking [[North Carolina]].<ref name="NCDC">{{cite web|author=National Climatic Data Center|url=http://lwf.ncdc.noaa.gov/oa/reports/bonnie/bonnie.html#INTRO|title=Bonnie Buffets North Carolina!|year=1998|publisher=NOAA|access-date=2009-01-07|url-status=dead|archive-url=https://web.archive.org/web/20080916091724/http://lwf.ncdc.noaa.gov/oa/reports/bonnie/bonnie.html#INTRO|archive-date=2008-09-16}}</ref>
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== See also ==
{{Portal|Tropical cyclones}}
* [[List of cloud types]]
* [[Pileus (meteorology)|Pileus]]
* [[Overshooting top]]
* [[Rapid intensification]]

== References ==
{{Reflist}}

== Bibliography ==
{{refbegin|2}}
* {{cite book |last1=Anthes |first1=Richard A. |editor1-last=Tao |editor1-first=Wei-Kuo |editor2-last=Adler |editor2-first=Robert |title=Cloud Systems, Hurricanes, and the Tropical Rainfall Measuring Mission (TRMM) |chapter=Hot Towers and Hurricanes: Early Observations, Theories, and Models |date=2003 |pages=139–148 |doi=10.1007/978-1-878220-63-9_10 |ref={{sfnRef|Anthes (2003)}} |publisher=American Meteorological Society |location=Boston, Massachusetts |via=Springer Link |isbn=978-1-878220-63-9}}
* {{cite journal |last1=Fierro |first1=Alexandre O. |last2=Simpson |first2=Joanne |last3=LeMone |first3=Margaret A. |last4=Straka |first4=Jerry M. |last5=Smull |first5=Bradley F. |title=On How Hot Towers Fuel the Hadley Cell: An Observational and Modeling Study of Line-Organized Convection in the Equatorial Trough from TOGA COARE |journal=Journal of the Atmospheric Sciences |date=September 2009 |volume=66 |issue=9 |pages=2730–2746 |doi=10.1175/2009JAS3017.1 |ref={{sfnRef|Fierro et al. (2009)}} |publisher=American Meteorological Society |location=Boston, Massachusetts|doi-access=free|bibcode=2009JAtS...66.2730F }} {{open access}}
* {{cite journal |last1=Guimond |first1=Stephen R. |last2=Heymsfield |first2=Gerald M. |last3=Turk |first3=F. Joseph |title=Multiscale Observations of Hurricane Dennis (2005): The Effects of Hot Towers on Rapid Intensification |journal=Journal of the Atmospheric Sciences |date=March 2010 |volume=67 |issue=3 |pages=633–654 |doi=10.1175/2009JAS3119.1 |publisher=American Meteorological Society |location=Boston, Massachusetts|ref={{sfnRef|Guimond et al. (2010)}}|doi-access=free |bibcode=2010JAtS...67..633G |hdl=11603/28559 |hdl-access=free }} {{open access}}
* {{cite journal |last1=Hendricks |first1=Eric A. |last2=Montgomery |first2=Michael T. |last3=Davis |first3=Christopher A. |title=The Role of "Vortical" Hot Towers in the Formation of Tropical Cyclone Diana (1984) |journal=Journal of the Atmospheric Sciences |date=June 2004 |volume=61 |issue=11 |pages=1209–1232 |doi=10.1175/1520-0469(2004)061<1209:TROVHT>2.0.CO;2 |ref={{sfnRef|Hendricks et al. (2004)}} |publisher=American Meteorological Society |location=Boston, Massachusetts|doi-access=free |bibcode=2004JAtS...61.1209H }} {{open access}}
* {{cite journal |last1=Heymsfield |first1=Gerald M. |last2=Tian |first2=Lin |last3=Heymsfield |first3=Andrew J. |last4=Li |first4=Lihua |last5=Guimond |first5=Stephen |title=Characteristics of Deep Tropical and Subtropical Convection from Nadir-Viewing High-Altitude Airborne Doppler Radar |journal=Journal of the Atmospheric Sciences |date=1 February 2010 |volume=67 |issue=2 |pages=285–308 |doi=10.1175/2009JAS3132.1 |ref={{sfnRef|Heymsfield et al. (2010)}} |publisher=American Meteorological Society |location=Boston, Massachusetts|s2cid=54697840 |doi-access=free |bibcode=2010JAtS...67..285H |hdl=11603/28558 |hdl-access=free }}
* {{cite journal |last1=Houze |first1=Robert A. Jr. |title=From Hot Towers to TRMM: Joanne Simpson and Advances in Tropical Convection Research |journal=Meteorological Monographs |date=January 2003 |volume=29 |issue=51 |pages=37–47 |doi=10.1175/0065-9401(2003)029<0037:CFHTTT>2.0.CO;2 |ref={{sfnRef|Houze (2003)}} |publisher=American Meteorological Society |location=Boston, Massachusetts|doi-broken-date=1 November 2024 |bibcode=2003MetMo..29...37H }} {{open access}}
* {{cite journal |last1=Leppert |first1=Kenneth D. |last2=Petersen |first2=Walter A. |title=Electrically Active Hot Towers in African Easterly Waves prior to Tropical Cyclogenesis |journal=Monthly Weather Review |date=March 2010 |volume=138 |issue=3 |pages=663–687 |doi=10.1175/2009MWR3048.1 |ref={{sfnRef|Leppert and Petersen (2010)}} |publisher=American Meteorological Society |location=Boston, Massachusetts|doi-access=free |bibcode=2010MWRv..138..663L }} {{open access}}
* {{cite journal |last1=Malkus |first1=Joanne S. |last2=Ronne |first2=Claude |last3=Chaffe |first3=Margaret |title=Cloud Patterns in Hurricane Daisy, 1958 |journal=Tellus |date=January 1961 |volume=13 |issue=1 |pages=8–30 |doi=10.3402/tellusa.v13i1.9439 |via=Taylor & Francis Online |ref={{sfnRef|Malkus et al. (1961)}}|doi-access=free }} {{open access}}
* {{cite book |last1=Malkus |first1=Joanne S. |last2=Williams |first2=R. T. |title=Severe Local Storms |chapter=On the Interaction between Severe Storms and Large Cumulus Clouds |via=Springer Link |date=September 1963 |volume=5 |pages=59–64 |doi=10.1007/978-1-940033-56-3_3 |ref={{sfnRef|Malkus and Williams (1963)}} |publisher=American Meteorological Society |location=Boston, Massachusetts |isbn=978-1-940033-56-3}}
* {{cite journal |last1=Riehl |first1=Herbert |last2=Malkus |first2=Joanne |title=Some Aspects of Hurricane Daisy, 1958 |journal=Tellus |date=January 1961 |volume=13 |issue=2 |pages=181–213 |doi=10.3402/tellusa.v13i2.9495 |via=Taylor & Francis Online |ref={{sfnRef|Riehl and Malkus (1961)}}|doi-access=free }} {{open access}}
* {{cite journal |last1=Montgomery |first1=M. T. |last2=Nicholls |first2=M. E. |last3=Cram |first3=T. A. |last4=Saunders |first4=A. B. |title=A Vortical Hot Tower Route to Tropical Cyclogenesis |journal=Journal of the Atmospheric Sciences |date=January 2006 |volume=63 |issue=1 |ref={{sfnRef|Montgomery et al. (2006)}} |pages=355–386 |doi=10.1175/JAS3604.1 |publisher=American Meteorological Society |location=Boston, Massachusetts|s2cid=20645674 |doi-access=free |bibcode=2006JAtS...63..355M |hdl=10945/36928 |hdl-access=free }} {{open access}}
* {{cite journal |last1=Tao |first1=Cheng |last2=Jiang |first2=Haiyan |title=Global Distribution of Hot Towers in Tropical Cyclones Based on 11-Yr TRMM Data |journal=Journal of Climate |date=February 2013 |volume=26 |issue=4 |pages=1371–1386 |doi=10.1175/JCLI-D-12-00291.1 |ref={{sfnRef|Tao and Jiang (2013)}} |publisher=American Meteorological Society |location=Boston, Massachusetts|doi-access=free |bibcode=2013JCli...26.1371T }}
* {{cite journal |last1=Williams |first1=E. R. |last2=Geotis |first2=S. G. |last3=Renno |first3=N. |last4=Rutledge |first4=S. A. |last5=Rasmussen |first5=E. |last6=Rickenbach |first6=T. |title=A Radar and Electrical Study of Tropical "Hot Towers" |journal=Journal of the Atmospheric Sciences |date=August 1992 |volume=49 |issue=15 |pages=1386–1395 |doi=10.1175/1520-0469(1992)049<1386:ARAESO>2.0.CO;2 |ref={{sfnRef|Williams et al. (1992)}} |publisher=American Meteorological Society |location=Boston, Massachusetts|doi-access=free |bibcode=1992JAtS...49.1386W }} {{open access}}
* {{cite journal |last1=Zhuge |first1=Xiao-Yong |last2=Ming |first2=Jie |last3=Wang |first3=Yuan |title=Reassessing the Use of Inner-Core Hot Towers to Predict Tropical Cyclone Rapid Intensification* |journal=Weather and Forecasting |date=October 2015 |volume=30 |issue=5 |pages=1265–1279 |doi=10.1175/WAF-D-15-0024.1 |ref={{sfnRef|Zhuge et al. (2015)}} |publisher=American Meteorological Society |location=Boston, Massachusetts|doi-access=free |bibcode=2015WtFor..30.1265Z }}
* {{cite book |last1=Zipser |first1=Edward J. |chapter=Some Views on "Hot Towers" after 50 Years of Tropical Field Programs and Two Years of TRMM Data |editor1-last=Tao |editor1-first=Wei-Kuo |editor2-last=Adler |editor2-first=Robert |title=Cloud Systems, Hurricanes, and the Tropical Rainfall Measuring Mission (TRMM) |date=2003 |pages=49–58 |doi=10.1007/978-1-878220-63-9_5 |ref={{sfnRef|Zipser (2003)}} |publisher=American Meteorological Society |location=Boston, Massachusetts |via=Springer Link |isbn=978-1-878220-63-9}}
{{refend}}

==External links==
*[http://www.nasa.gov/vision/earth/lookingatearth/hurricane_multimedia.html Hurricane Multimedia Gallery]&nbsp;– a hurricane multimedia page.
*[https://web.archive.org/web/20051025043644/http://www.ucar.edu/pres/simpson/index.htm UCAR slides: "Hot Towers and Hurricanes: Early Observations, Theories and Models"]

{{Cloud types}}

{{DEFAULTSORT:Hot tower}}
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