Hurricane Frances

MODIS view of Hurricane Frances(Note that eye is present but clouds at base of eye make it look cloudy throughout)

FRANCES TRACK

Hurricane frequency

Frances

Hurricane Structure• Major Components

– Eye – Eyewall(s) – Rainbands (primary, secondary, outer)

• Regions– Core region – Outer region

• Other Components (not always present)– Eyewall mesovortices and swirls– Fine-scale rainbands

From Willoughby (1988)

Structure of a hurricane: View from the top

Structure of a Hurricane in cross section

Theta-e fromSimulation(Liu et al 1997)

Conceptual

Light-shading: cloud and precipitationDark regions: convective eyewall and spiral rainbandsEIL: : Eye inversion layer (slash- hatched areas)OEA: occluded eye air with low e

(cross-hatched regions)MTD: moist downdrafts between the convective bandsSR: Spiral rainband updraftsRO: Return outflowSU: Sloping updraft of eyewallMI: Main inflowMO: Main outflowRI: Return inflowDF: Divergent flowVC: Forced vertical circulationLX: Lateral mixingGO: Gravity wave oscillationsMD: Mean decent in eyeDashed line: Freezing level

Schematic (radial–height) conceptual model of a mature hurricane in the inner-core region

Types of eyewall structure observed in hurricanes with radar

Symmetric single ring eyewall

The double eyewall of Hurricane Gilbert (1988)(most intense Category 5 storm in western hemisphere)

Asymmetric eyewall of Hurricane Georges

From Willoughby et al. (1984)

Inner Core Region:

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PGF balancesCentrifugal acceleration

Inside eye, Rankine vortexApprox. (v(r) = VoR/r).

Outside gradient wind approx. is valid: (v2/r + fv –fvg = 0)

Parcels orbit eye inside core region

From Willoughby et al. (1984)

Outside Core Region:

Coriolis force Important

Air passes around hurricane without orbiting

Convergent airflow alongthe right flank relativeto direction of motion(motion here to top ofpage)

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Principal Band: primary band of precipitation - typically extendingsoutheast from eyewall toward perimeter of hurricane

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Connecting Band: Sometimes connects Eyewall to Principal Band

Compare the conceptual model to Hurricane Frances

Inner core of Frances

Principal band

Radial velocity from Hurricane FrancesConceptual diagram

The inner core winds of Hurricane Frances

Eyewall Mesovortices

Wright and Bennett (1997)

Bertha 1996

Isabel 2003

No suggestion of vortices in eye of Frances from satellite

Eye vortex

Gall et al. (1998)

Hurricanes also contain many fine scale bands

Hurricane Andrew (1992)

Hurricanes also contain many fine scale bands

Hurricane Hugo (1989)Gall et al. (1998)

Note the fine scale bands in Andrew

Fine scale bands in Frances