Presentation on theme: "Hurricanes and the Carnot cycle"— Presentation transcript:
1 Hurricanes and the Carnot cycle We are going to show that hurricanes are (in good approximation) anatural realization of the Carnot cycle.rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004.
2 Some basics about tropical cyclones for details readtropical cyclones: a storm system with a closed circulation (cyclonic)around a center of low pressure that originates over tropical oceansand is driven principally by heat transfer from the oceancounterclockwise circulation in the Northern HemisphereCategorization of tropical cyclones: maximum averaged wind speed17 m/s or lesstropical depression18 to 32 m/stropical stormcalled hurricanesin the western North Atlanticand eastern North Pacific regions33 m/s or greatertyphoons in thewestern North Pacificsevere tropical cycloneselsewhere
3 Structural elements of a tropical cyclone Basic flowsPrimary circulationorigin of circulation is the Coriolis forceFictitious force in the rotating reference frame of the earthvelocity in the rotating frameangular velocity of rotating frame (earth)Low pressure regionBrief reminder to the Coriolis force:Exact:Intuitive for :acCoriolis force
4 Secondary circulation Eye, Eyewall andRainbandsSecondary circulationVery high wind speed due toconservation of angular momentumclick for animation
5 The hurricane as a Carnot heat engine see for detailsAB:air undergoes isothermal expansion as it flows toward the lower pressureof the storm center while in contact with the surface of the ocean (heat Ts300K)BC:Adiabatic (very fast) ascent of the airCD:air flows out at the top of its trajectory and is incorporated from the extreme low pressureregion into other weather systems via an isothermal compression (heat T0200K)DA:air undergoes an adiabatic compression when loosing altitude fast
6 PV-Diagram of the hurricane Carnot engine BCDTs=300KT0=200K
7 City of Huntington Beach Where does the work go which the hurricane produces from the heat of the oceanWork drives the windwith surface speedDevastation byhurricane Katrina,City of Huntington Beachstationary state:Generated work per time dissipated (friction)( )becausedissipationrate of heat transfer from the ocean to the atmospherequantifies the thermodynamic disequilibriumbetween the ocean and atmosphere
8 We know the textbook efficiency of a Carnot engine: important difference to textbook Carnot cycletextbook Carnot cycletropical cyclones=work done on environmentwork used for turbulent dissipationtransformed back intoback into the front endof the Carnot cycleheat from the oceanandHeat from turbulent dissipationwhere E:=b/atheoretical upper bound on hurricane wind speednote T0 <Ts
Your consent to our cookies if you continue to use this website.