Now that Typhoon Haiyan has passed and left thousands of dead and massive damage to the infrastructure in the Philippines and Viet Nam, questions are being asked about the possibility of reducing the strength of such massive tropical cyclones including both typhoons and hurricanes. According to the National Oceanic and Atmospheric Administration (NOAA), there are several methods that have been attempted or considered in recent decades. Let's look at a few of them:
1.) Using nuclear devices to destroy tropical cyclones: While there is an obvious problem with the release of radioactive fallout over land masses that would move with the storm, there is an even more scientific explanation that would preclude this method. The amount of energy in a tropical cyclone is massive from both the release of rain and the kinetic energy of the wind produced.
Let's start by looking at the energy release from the condensation of water droplets from clouds; according to NOAA, an average hurricane produces about 0.6 inches or 1.5 centimetres of rain per day inside a radius of 360 nautical miles or 665 kilometres. This results in total rainfall volume of 2.1*10E16 cubic centimetres of water with one cubic centimetre of rain water weighing one gram. Using the latent heat of condensation, this amount of rain produced 6.0*10E14 Watts of power or 200 times the total worldwide electrical generating capacity. The amount of kinetic energy created by an average windspeed of 90 miles per hour wind over a storm with a radius of 40 nautical miles or 60 kilometres is 1.5*10E12 Watts of power, equal to roughly half of the world's total electrical generating capacity. It is this amount of energy that would have to be overcome. The heat released by a fully developed tropical cyclone is equivalent to a 10-megaton nuclear bomb exploding every 20 minutes
To raise the barometric pressure in a tropical cyclone using a nuclear device would require a massive number of nuclear bombs, particularly since the high pressure pulse that emanates from the site of a nuclear explosion would travel at the speed of sound and the barometric pressure would quickly return to the pre-explosion level once the shock wave had passed, negating its impact. To change a Category 5 hurricane or typhoon into a Category 2 storm, you would have to add about half a ton of air for each square metre inside the eye of the storm or a bit more than half a billion tons for a 20 kilometre eye. To move that amount of air around is totally impractical.
2.) Using surface water cooling techniques to destroy tropical cyclones: Tropical cyclones draw their energy from the warm surface waters of the ocean so it has been suggested that cooling the oceanic surface waters could reduce the strength of tropical storms. This could be done by towing icebergs into the storm track or by pumping deeper cooler ocean water to the surface. The problem with this method is the size of an average tropical cyclone. If the eyewall of a storm is 30 miles in diameter, the area of the eye of the storm is nearly 2000 square miles. If the tropical depression is moving at 10 miles per hour, it will cover a total oceanic surface area of 7200 square miles in just 24 hours. As well, since the final track of the tropical depression is uncertain, it would be very difficult for scientists to predict where either icebergs or pumping systems should be placed to be most effective. On top of this, the environmental impact of sudden cooling and freshening of the ocean's surface waters would be substantial, causing damage to the sea life in the area.
4.) Using silver iodide to destroy tropical cyclones: Silver iodide is commonly used in parts of the United States and Canada to reduce the intensity of hail storms. For twenty years between 1962 and 1983, NOAA experimented with the use of silver iodide by injecting it into the rain bands of hurricanes to reduce the strength of the winds in the inner core of the hurricane by reducing the energy transfer to the core of the storm from the storm periphery. The project called Stormfury, used silver iodide to enhance the thunderstorms of the rain band by causing the supercooled water in the band to freeze, freeing the latent heat of fusion and helping the rain band to grow and another eyewall to form as shown in this diagram:
Through this mechanism, the eyewall of the storm would reform at a larger radius, reducing the windspeed. It was felt that a reduction in wind speed of as little as 10 percent would have made the intervention worthwhile. The problem with the method was that there is not much supercooled water and a great deal of natural ice in hurricane convection and updrafts are relatively small. As the understanding of hurricanes grew during the twenty year period, it also became apparent that hurricanes naturally change as the storms mature, resulting in the development of outer rain bands that rob the inner eyewall of the moisture that it needs to exist. Interestingly, scientists at the Institute of Earth Sciences at the Hebrew University of Jerusalem are still researching the use of aerosols from pollution and dust to redistribute both precipitation and heat transfer in tropical cyclones and, as shown here, claim to have had some success as shown in this diagram:
From this article, we can see that humanity is basically helpless in the face of such massive storms. The advantage that we have today is generally better storm prediction methodology; meteorologists in the 21st century have a distinct advantage over their mid-20th century counterparts. The use of both satellites and computer modelling have given those of us who live in coastal areas advance warning of coming storm events, however, even with the great strides made, the one day advance error in establishing the landfall position of a tropical cyclone is still 100 miles. Predicting the actual intensity of a given storm at a point in time is even more uncertain as is predicting the scope of the damage resulting from both wind and storm surges.
No one knows that better than the people of the Philippines.
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