Tornado: In the Eye of the Storm

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Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to [email protected]. Eyewall replacement cycles, also called concentric eyewall cycles, naturally occur in intense tropical cyclones, generally with winds greater than 185 km/h (115 mph), or major hurricanes (Category 3 or higher on the Saffir–Simpson hurricane scale). When tropical cyclones reach this intensity, and the eyewall contracts or is already sufficiently small (see above), some of the outer rainbands may strengthen and organize into a ring of thunderstorms–an outer eyewall–that slowly moves inward and robs the inner eyewall of its needed moisture and angular momentum. Since the strongest winds are located in a cyclone's eyewall, the tropical cyclone usually weakens during this phase, as the inner wall is "choked" by the outer wall. Eventually the outer eyewall replaces the inner one completely, and the storm can re-intensify. [8]

Lee, Julian J.; Samaras, Timothy P.; Young, Carl R. (2004-10-07). "Pressure Measurements at the ground in an F-4 tornado". Preprints of the 22nd Conf. Severe Local Storms. Hyannis, Massachusetts: American Meteorological Society. Yes, if one takes the common meaning of the term "eye of the storm" to be the area of relatively low wind speed near the center of the vortex, most tornadoes can be said to have eyes. Cyclostrophic balance describes a steady-state, inviscid flow with neglected Coriolis force:Tornado occurrence is highly dependent on the time of day, because of solar heating. [89] Worldwide, most tornadoes occur in the late afternoon, between 15:00 (3pm) and 19:00 (7pm) local time, with a peak near 17:00 (5pm). [90] [91] [92] [93] [94] Destructive tornadoes can occur at any time of day. The Gainesville Tornado of 1936, one of the deadliest tornadoes in history, occurred at 8:30am local time. [24] Eyewall mesovortices are a significant factor in the formation of tornadoes after tropical cyclone landfall. Mesovortices can spawn rotation in individual convective cells or updrafts (a mesocyclone), which leads to tornadic activity. At landfall, friction is generated between the circulation of the tropical cyclone and land. This can allow the mesovortices to descend to the surface, causing tornadoes. [21] These tornadic circulations in the boundary layer may be prevalent in the inner eyewalls of intense tropical cyclones but with short duration and small size they are not frequently observed. [22] Stadium effect [ edit ] View of Typhoon Maysak's eye from the International Space Station displaying a pronounced stadium effect The size of the eye varies, depending on the size of the hurricane. Some eyes are as small as five miles across, while others are as big as 60 miles. It is hard to gage – when the eye of the hurricane is above you – just when the storms will start up again.

While direct measurement of the most violent tornado wind speeds is nearly impossible, since conventional anemometers would be destroyed by the intense winds and flying debris, some tornadoes have been scanned by mobile Doppler radar units, which can provide a good estimate of the tornado's winds. The highest wind speed ever measured in a tornado, which is also the highest wind speed ever recorded on the planet, is 301±20mph (484±32km/h) in the F5 Bridge Creek-Moore, Oklahoma, tornado which killed 36 people. [117] The reading was taken about 100 feet (30m) above the ground. [3] While typical mature storms have eyes that are a few dozen miles across, rapidly intensifying storms can develop an extremely small, clear, and circular eye, sometimes referred to as a pinhole eye. Storms with pinhole eyes are prone to large fluctuations in intensity, and provide difficulties and frustrations for forecasters. [7] Detail of Hurricane Isabel's eye, as viewed from the International Space Station Also under study are the low-level mesocyclone and the stretching of low-level vorticity which tightens into a tornado, [87] in particular, what are the processes and what is the relationship of the environment and the convective storm. Intense tornadoes have been observed forming simultaneously with a mesocyclone aloft (rather than succeeding mesocyclogenesis) and some intense tornadoes have occurred without a mid-level mesocyclone. [134] While normally quite symmetric, eyes can be oblong and irregular, especially in weakening storms. A large ragged eye is a non-circular eye which appears fragmented, and is an indicator of a weak or weakening tropical cyclone. An open eye is an eye which can be circular, but the eyewall does not completely encircle the eye, also indicating a weakening, moisture-deprived cyclone or a weak but strengthening one. Both of these observations are used to estimate the intensity of tropical cyclones via Dvorak analysis. [5] Eyewalls are typically circular; however, distinctly polygonal shapes ranging from triangles to hexagons occasionally occur. [6] Hurricane Wilma with a pinhole eye Tornadoes in the dissipating stage can resemble narrow tubes or ropes, and often curl or twist into complex shapes. These tornadoes are said to be "roping out", or becoming a "rope tornado". When they rope out, the length of their funnel increases, which forces the winds within the funnel to weaken due to conservation of angular momentum. [28] Multiple-vortex tornadoes can appear as a family of swirls circling a common center, or they may be completely obscured by condensation, dust, and debris, appearing to be a single funnel. [29]Monteverdi, John (2003-01-25). "Sunnyvale and Los Altos, CA Tornadoes 1998-05-04". Archived from the original on 2013-06-13 . Retrieved 2006-10-20. Another striking feature reported by some eyewitnesses is the 'sound of a tornado'. On the outside, tornadoes are often described as generating a sound similar to a freight train or a roaring jet engine. However, inside the eye, the noise is muffled, replaced by an eerie quiet. Ben-Amots, N. (2016). "Dynamics and thermodynamics of tornado: Rotation effects". Atmospheric Research. 178–179: 320–328. Bibcode: 2016AtmRe.178..320B. doi: 10.1016/j.atmosres.2016.03.025. The winds of the tornado vortex and of constituent turbulent eddies, as well as airflow interaction with the surface and debris, contribute to the sounds. Funnel clouds also produce sounds. Funnel clouds and small tornadoes are reported as whistling, whining, humming, or the buzzing of innumerable bees or electricity, or more or less harmonic, whereas many tornadoes are reported as a continuous, deep rumbling, or an irregular sound of "noise". [44]