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supercells are rotating thunderstorms

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that can cause tornadoes and hail the

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most widely accepted theory for storm

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spin up produces a pair of counter

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rotating supercells but such pairs are

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rarely observed in the troposphere and a

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theory is needed that produces a single

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supercell a new mathematical model

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called vertical rotating draft has been

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developed that includes the gross

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features of a supercell in highly

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idealized form this new model produces a

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single supercell principal ingredients

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of the model include rotation about a

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vertical axis horizontal convergence in

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the middle troposphere caused by the

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buoyancy

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and the Coriolis force

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when these ingredients are used in fluid

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dynamic equations the horizontal

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pressure gradient is found to be zero

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and air parcels move along inertial

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circles projected on a horizontal

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surface this circular motion gives the

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model and inertial oscillation that

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appears to have been overlooked in

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previous supercell models the inertial

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oscillation consists of a long quiescent

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phase when the draft diameter is large

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and rotates anti cyclonic Lee and a

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short intense phase when the draft

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diameter is small and rotates cyclonic

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ly one cycle of mathematically driven

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animation represents 13 hours of

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quiescent phase and five hours of

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intense phase during the intense phase

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of the inertial oscillation the rotating

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draft resembles a supercell rising

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parcels of air expand causing the draft

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to expand and rotate anti cyclonic Li

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the updraft changes to a downdraft

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downdraft is driven by evaporative

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cooling and updraft by condensation

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aletan expanding flow interacts with the

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Coriolis force to produce anti cyclonic

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contracting flow interacts with the

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Coriolis force to produce cyclonic

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additional physical ingredients of the

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model include translation of the

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rotating draft and vertical wind shear

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the rotating draft moves at a constant

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height above the surface of the earth

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the intense phase has a small buoyant

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draft cyclonic rotation marked by a

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track that turns to the right this right

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turn is a salient feature of actual

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supercells the quiescent phase has a

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large negatively buoyant draft with

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antipsychotic rotation latent heating

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changes the downdraft to an updraft in

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the middle of the intense phase this

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flow reversal interacts with the

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vertical wind shear to cause the right

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turn the latent energy required to

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support this inertial oscillation is

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greatest during the quiescent phase when

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the draft diameter is large a supercell

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storm that produced one and one half

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centimeter hail is documented by radar

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echoes spaced 30 minutes apart these

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echoes become increasingly stronger as

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the supercell bills the track turns to

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the right hail is produced and strong

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echoes are recorded the echoes then

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weaken as the supercell dissipates

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application of the mathematical model

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starts in the middle of the quiescent

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phase the first week radar echoes are in

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theory created by a growing up draft in

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a predominantly downward airflow after

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the turning point the strong echoes and

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hail are created in theory by a

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predominantly upward airflow data from

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the documented supercell storm generally

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support the intense phase of the model

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however the quiescent phase of the model

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is not supported by the storm data

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possibly because the quiescent phase

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requires too much latent energy the new

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mathematical model called vertical

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rotating draft has an inertial

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oscillation with an intense phase that

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resembles a single supercell

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this intense phase starts with a

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predominantly downward flow that causes

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the draft to contract and spin up partly

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by action of the Coriolis force more

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research remains to be done they

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predominantly downward flow that

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theoretically occurs before the turning

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point in a supercell track needs to be

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detected and measured this down flow if

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confirmed by measurements would strongly