MAR 110: Lecture 18 Outline – Hurricane Dynamics

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MAR110 LECTURE #18

Hurricane Dynamics

Hurricane and Typhoon Distribution The locations of historical hurricanes/typhoons (red dots) and the tropical regions where they are formed and found most frequently. (ItO)

Geostrophic Flow – A REVIEW With geostrophic flow (red), the pressure gradient force (blue) and Coriolis force (aqua) are perpendicular to the flow and in balance.

MAR 110: Lecture 18 Outline – Hurricane Dynamics

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Geostrophic Ocean Flow With geostrophic Gulf Stream (red), the sea surface slope induces the pressure gradient force (blue) which balances the Coriolis force (aqua) .

Geostrophic Atmospheric Winds With geostrophic Jet Stream (red), the temperature contrasts induce the pressure gradient force (blue) which balances the Coriolis force (aqua) .

MAR 110: Lecture 18 Outline – Hurricane Dynamics

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Cloud Structure of a Typical Hurricane and Earth Rotation (a) Warm (pink), wet air spirals inwards over the warm ocean towards the eye of the hurricane, where it begins spirals upward around the outside of the eye - called the “eyewall”. (b) Because the rising air cools, it becomes increasingly more humid (that is the air becomes saturated with water vapor - a gas). (c) At 100% humidity the water vapor condenses to form water droplets (liquid) that make up the clouds and rain. (c) At the top of the troposphere the very cool (blue), dry air spirals outward and begins to descend toward the sea surface. (d)This cool, dry air descends in the eye and the various spiral bands, warming and becoming even less humid (i.e. dryer) as it encounters the higher pressures at lower levels. (e) Upon reaching the sea surface this very warm and dry air able to absorb both heat and moisture from the ocean – re-energizing it so that it can feed the heat engine (i.e., power) of the hurricane. (??)

MAR 110: Lecture 18 Outline – Hurricane Dynamics

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Temperature Structure of a Typical Hurricane Warm moist air heated by the ocean rises through the center of the hurricane through convection and spreads out once it reaches a certain elevation where it cools and the moisture in the air condenses and becomes rain. (??, NH)

Hurricane Wind Dynamics

MAR 110: Lecture 18 Outline – Hurricane Dynamics

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Hurricane Trajectories

Hurricane Wind Structure In the northern hemisphere the highest winds are on the right hand side of the leading edge of the hurricane (here the upper right quadrant). The speed of the hurricane itself is added to the speed of the wind around the storm when they are both going in the same direction while it is subtracted when going in opposite directions as on the left side of

MAR 110: Lecture 18 Outline – Hurricane Dynamics

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Saffir-Simpson Scale Ocassionally a extratropical coastal storm will interact with a tropical storm and morph into a powerful hybrid –such as the so-called “Perfect Storm” that stayed relatively stationary off the northeast coast for several days in and around Halloween October 1991. (NH)

MAR 110: Lecture 18 Outline – Hurricane Dynamics

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Hurricane Measurements The “Hurricane Hunter” trajectories are indicated in the

schematics of the spiral-banded hurricanes.

MAR 110: Lecture 18 Outline – Hurricane Dynamics

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Hurricane Rita (2005) Evolution (ABOVE) A time series composite of wind speed and air pressure measurements are compared to an inverted version of the trajectory . Note the color-coded Saffir Simpson scale categories.

Hurricane Rita (2005) Wind Structure

MAR 110: Lecture 18 Outline – Hurricane Dynamics

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Hurricane Rita (2005) Rain

Hurricane Sizes

MAR 110: Lecture 18 Outline – Hurricane Dynamics

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Hurricane Damage