A Preliminary Assessment of Inducing Anthropogenic Tropical Cyclones Using Compressible Free Jets and the Potential for Hurricane Mitigation

We have conceptually studied the potential for mitigation of natural hurricanes by inducing anthropogenic perturbations prior to or in front of an advancing hurricane. We propose actual hardware for the task. It consists of multiple jet engines mounted on barges or ships that will be dispatched to strategic locations in the ocean where the sea surface temperature is high and the vertical temperature profile and atmospheric conditions are such that the potential for development of a hurricane or tropical storm is high. The engines will direct compressible high momentum, high-speed free jets skyward causing entrainment of even larger amounts of additional air to form plumes and updrafts. The unstable humid updraft will itself produce conditions for additional entrainment and evolution of tropical cyclones. These anthropogenic perturbations will extract enthalpy from the ocean, cooling the ocean surface and depriving the advancing natural hurricane of its needed thermal energy. The barrage of hurricanes and adverse impacts on human life and property in the Southeastern United States and Caribbean Basin during 2004-2005 has revived an interest in hurricane mitigation (Hoffman 2004, 2002). Reputable atmospheric scientists have developed a few ideas for hurricane mitigation over the past 60 years (Gray et al. 1976; Simpson 1981). Only two programs have involved actual field or laboratory experiments (Willoughby et al. 1985; Alamaro 2001). The most well known was the Stormfury project that lasted for more than 20 years, under which NOAA used cloud seeding by silver iodide to try to nucleate supercooled water in the hurricane's clouds. The hypothesis was that the heat of fusion released upon nucleation would increase the hurricane eyewall diameter, leading to a decrease in the maximum wind speed. Through radar observations it was eventually discovered that the clouds contain ice and little or no supercooled water, so the project was abandoned (Willoughby et al. 1985). Another attempt was undertaken at the Air-Sea Interaction Laboratory at the Massachusetts Institute of Technology, where a monolayer film was used to retard evaporation in a wind wave tank in which the airflow over the water surface was comparable to that of hurricane (Alamaro 2001). The hypothesis was that spreading a monolayer film on the ocean in the front of the hurricane would retard the evaporation that fuels the hurricane with latent heat. Unfortunately, at a wind speed of about 10 m/sec or higher the film tends to break apart and becomes immersed in the water due to high-speed airflow and wave action, and loses its effectiveness (See: http://alamaro.home.comcast.net/Evaporationretardati on.htm). We propose to induce atmospheric perturbations in front of or prior to an advancing hurricane or potentially dangerous cyclone. These induced perturbations will extract enthalpy from the ocean surface, leading to a decrease in the sea surface temperature (SST). As such, the approaching naturally occurring hurricane will be deprived of its source of enthalpy. It is hypothesized that the hurricane intensity will then be much reduced prior to landfall. Compressible free jets generated by multiple jet engines mounted on barges or ships will induce the perturbations. They will be dispatched to strategic locations in the ocean during an advancing hurricane. Alternatively, the jet generator vessels will continuously patrol the western Tropical Atlantic, inducing cyclones during the hurricane season to reduce the SST up to a few hundred miles from the shoreline. The proposed method is analogous to backfires created by firefighters when confronting an advancing firewall. Small and controlled fires are started in front of the advancing, uncontrolled and larger fire. By the time the main fire advances, its fuel supply has been consumed causing it to be reduced in intensity and if properly executed, extinguished. Just as firefighters maintain distance between the backfires and the larger fire so they do not merge, it would be necessary to keep a distance between the induced cyclones and the natural hurricane so they do not merge to form a larger hurricane. Compressible Free Jets and Plumes. A free jet is an unbounded flow of one fluid into another and is April 2006 ALAMARO ET AL.