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Hurricane Modification Study Isaac Ginis GSO/URI

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Hurricane intensity is dependent on many factors Image courtesy of http://hurricanes.noaa.gov Inward component of surface wind Inward component of surface wind Evaporation from ocean INFLOW (Isothermal expansion) OUTFLOW (Isothermal compression) Radiation to space UPDRAFT (Adiabatic expansion & cooling) DOWNDRAFT (Adiabatic compression & warming) DOWNDRAFT (Adiabatic compression & warming)

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Wave-Activated Deep Ocean Pump 1,000 Meters Deep 32ºC Cool deep water is pumped to surface and ejected. The cool deep water and warm surface water mix, reducing sea surface temperatures by several degrees C around the buoy Buoy 6ºC One meter diameter flexible tube Valve in base opens on wave downslope and closes on wave upslope. No external energy source needed.

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Device is deployed by dropping in ocean where heavy rigid base sinks, causing tube to unspool & fill with successively deeper ocean water.

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Deploying Arrays of Wave-Driven Pumps By tethering at base, once deployed the pumps maintain relative position from “sea anchor” effect. Barge Buoy

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Data From Successful Test Of 500’ Deep Prototype – Colder Deep Ocean Water Pumped To Surface and Maintained Overnight. Bermuda 12-11-05

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How efficient is this technology in cooling water at the sea-surface? Let’s assume that a 1-m 3 water volume located at 500-m depth is 10°C cooler than a 1-m 3 water volume located at the surface. The temperature difference causes the volume at 500-m depth to be 2.5 kg heavier that the surface volume. To pump the volume at 500-m depth up to the surface would require about 1250 J/m 3 of energy. On the other hand, cooling the surface volume 10°C by other means would require 4x10 6 J/m 3 of energy – 3,000 times more! Let’s assume that a 1-m 3 water volume located at 500-m depth is 10°C cooler than a 1-m 3 water volume located at the surface. The temperature difference causes the volume at 500-m depth to be 2.5 kg heavier that the surface volume. To pump the volume at 500-m depth up to the surface would require about 1250 J/m 3 of energy. On the other hand, cooling the surface volume 10°C by other means would require 4x10 6 J/m 3 of energy – 3,000 times more!

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This Study I. Theoretical investigation of upper ocean cooling by wave-driven pumps II. Numerical investigation of the impact of the wave pump-induced cooling on hurricanes using a coupled hurricane- ocean model.

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What will happen with cold water after it is released from the pump? What physical processes are responsible for dispersion of the cold water? What are the quantitative estimates of the temperature anomalies, depth of penetration and horizontal size? What processes are responsible for merging the cold water produced by multiple pumps? What are the spatial and time scales involved?

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Theoretical Model of a “Convective Plume” There is a great deal of literature about turbulent convective plumes. Cold water

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Negative buoyancy flux at the sea surface induced by a pump Water heat capacity (c= 4185 J kg -1 K -1 ) Water density (1027 kg m -3 ) Pump rate (P = 1 m 3 /s ) Temperature anomaly at the sea surface (10 K) then Q ~40 MW. This is an enormous power source! then Q ~ 40 MW. This is an enormous power source! By comparison, the world's largest wind turbine delivers up to 6 MW and By comparison, the world's largest wind turbine delivers up to 6 MW and has an overall height of 186 m and a diameter of 114 m (source: Wikipedia). has an overall height of 186 m and a diameter of 114 m (source: Wikipedia).

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Simple Axisymmetric Model - temperature anomaly in the plume; - radius of the plume; - thermal expansion coefficient - ambient vertical temperature gradient - vertical velocity Turner J.S. Buoyancy effects in fluids. University Press, Cambridge, 1973, §6.1.

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Analytic Solutions ( ) Effect of stable stratification ( ) due to salinity gradient is insignificant Then at z=30 m: R= 4.5m, If we assume:

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Temperature and vertical velocity profiles in the plume Depth, m

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Another Theoretical Model: Water is released by discrete volumes – “thermals”

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Basic Equations Conservation of heat: Volume (shape is not spherical) Volume (shape is not spherical) Linear dimension of a single thermal Gebhart B. et al. Buoyancy-Induced Flows and Transport. Hemisphere Publ.Corp., 1988.

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Analytic Solution Temperature anomaly Vertical velocity If P= 1 m 3 /s and T w = 10 s, then = 10 m 3. If we also assume that = 10 K then at Z= 30 m, the temperature anomaly < 0.1 K, which is 10 times smaller that the temperature anomaly of the plume at the same depth!

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Temperature and vertical velocity in the thermal Depth, m

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Horizontal spread of isolated “cold-water intrusion” at the bottom of the mixed Layer h R The intrusion spreads horizontally under its own weight. This process is known as a gravity current. Barenblatt, G.I. Scaling, self-similarity, and intermediate asymptotics. Cambridge University Press, 386 pp. 1996

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Time dependence of the maximum thickness of the intrusion h (1, 2) and its radius R (3,4) for = 100 m 3 and 1000 m 3, correspondingly C=12 Horizontal spread of isolated “cold-water intrusion” at the bottom of the mixed Layer m 2 /s m -1 s -1 R R h h

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Horizontal Spread of a plume-like intrusion at the bottom of the mixed layer m3/s m3/s Assuming continues supply of cold water with constant intensity: R w m m/s

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Time dependence of intusion size (L=2R) for Q= 20 m 3 /s (1) and Q=10 m 3 /s (2). Horizontal spread of the “plume-like intrusion” at the bottom of the mixed layer The cold plume spreads much faster than the intrusion does!

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Multiple-Pump Array There are three mechanisms of the “merger” of cold intrusions produced a pump array: 1.Horizontal diffusion 2.Horizontal spread due to gravity 3.Horizontal advection due to background current

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Horizontal Diffusion Characteristic time of merger: If L 0 = 100 m, K= 0.1 m 2 /s =>= 24 hours

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Horizontal spread due to gravity Characteristic time of merger: If L 0 = 100 m, D= 4 m 2 /s =>< 1 hour C=12

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Horizontal Advection Characteristic time of merger: If L 0 =100 m, = 30 min u=0.05 m/s =>

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Some practical formulas derived from theoretical investigation Formulas for calculating the average cooling of the mixed layer of depth H [m] over the area L 2 (where L [m]– distance between pumps) P [m 3 /s] – pump rate, t [s] – time. H s [m]- significant wave high, T p [s] - wave period, D [m]- diameter of the tube. T p [s] - wave period, D [m]- diameter of the tube.

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II. Numerical investigation of the impact of the wave pump-induced cooling on hurricanes using a coupled hurricane- ocean model

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Case Study: Hurricane Ivan (2004)

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Hurricane Ivan (2004) T=0 hr

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Hurricane Ivan (2004) One pump arrayTwo pump arrays Control

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Hurricane Ivan (2004)

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Case Study: Hurricane Katrina (2005)

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Mixed layer depth and temperature difference from sea-surface to 500 m depth in August 2005 Mixed layer depth is calculated from the GDEM climatology with assimilation of the Loop Current and the warm-core ring as described in Yablonsky and Ginis (2007)

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Surface Wind Data HRD (NOAA’s Hurricane Research Division) winds in Hurricane Katrina are used to force the wave model

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Hs T August 28, 00 UTC Pump rate Pump- induced cooling Sign. wave height Wave period P =0 for Hs > 6 m, 1 pump every 250 meters

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Hs T P θ Pump rate Pump- induced cooling Sign. wave height Wave period August 28, 12 UTC

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Total cooling induced by hypothetical pumps

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Initial ocean temperature field at the beginning of the Katrina Simulation Red – Initial Green – after pump cooling Box indicates location of the pump array Cooling analysis assumes 1 pump every 250 meters Total approx. 600,000 pumps Reduced heat content of upper mixed layer South ern Edge Northern Edge

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Aug 29, 18ZAug 28, 18Z Aug 27, 18Z CONTROLCONTROL P C U O M O P L I N G Sea surface temperature simulation for Katrina

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Blue – Control Red – With Pump Cooling Green box – Cooled Region Black – Observed Reduced intensity from cooling the upper ocean is first evident while Katrina’s eye was more than 500 miles from landfall. This early effect possibly is due to favorable gulf circulation patterns which expanded the cooled water region, producing drier air. This dry air was drawn toward Katrina’s eye by her extensive wind field. Drier air means less evaporation, reducing the energy available to the hurricane.

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Summary Theoretical analysis indicates that an array of wave-driven pumps can be effective at reducing the upper ocean heat content in a large area. Field-verification of these results is being planned Numerical simulations with a coupled hurricane-ocean model indicate that the hurricane intensity can be reduced by placing an array of pumps along the projected track. These are very preliminary results. Practical, economic and environmental implications need to be addressed

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