Tropical cyclone hazard mitigation
Tropical cyclones are powerful storm systems that are fueled by the thermal energy stored in warm ocean waters. Strong sustained winds pushing on the ocean surface can give rise to storm surge and hence significant floods, potentially leading to fatalities and property damage. The 2005 and 2012 tropical cyclone seasons were particularly devastating in the North Atlantic Basin following an ongoing era of high hurricane activity [1, 2]. Hurricanes Katrina and Sandy, which hit the Louisiana and New Jersey coasts of the United States, are reported to have caused more than 1800 and 120 fatalities respectively, together with overall losses exceeding $US 135 billion and $US 50 billion, respectively [3, 4].
While considered traditionally as acts of fate and out of reach of human influence, researchers have started considering possible methods to weaken tropical cyclones to mitigate future catastrophic impacts of tropical cyclones on cities and civilians. Several techniques have been suggested in recent years, such as hurricane cloud seeding, marine cloud brightening, offshore wind turbines, ocean upwelling, and microwave energy transfer [5-11]. This project investigates potential space contributions to currently conceived tropical cyclone hazard mitigation concepts.
In this project, we are performing an overview of ground-based methods and means for threat reduction and investigating potential space contributions including remote sensing instrumentation. We also investigating space-based concepts for tropical cyclone hazard mitigation. Two different mechanisms are considered here: atmospheric heating based on microwave irradiation and laser-induced cloud seeding based on laser power transfer. Technology roadmaps for cyclone mitigation based on two space platform types will be introduced. To improve their mitigation efficiency a high-accuracy and high-resolution forecast system would be needed, described as the Earth Meteorological Forecast System.
|Concept||Physical process||Space or Ground|
|Hurricane cloud seeding||Internal dynamics||Ground|
|Marine cloud brightening||Energy exchange at air-sea interface||Ground|
|Offshore wind turbines||Energy exchange at air-sea interface||Ground|
|Ocean upwelling||Energy exchange at air-sea interface||Ground|
|Compressible free jets||Energy exchange at air-sea interface||Ground|
|Microwave energy transfer||Large-scale interactions with troposphere||Space|
|Laser-induced condensation||Internal dynamics||Space|
Tropical cyclone formation and dissipation are governed by the following physical mechanisms:
- Energy exchange at air-sea interface
Tropical cyclones are fuelled by warm moist air evaporating from the sea surface, hence natural or anthropogenic decreases of sea surface temperature values will very likely cause dissipation within a cyclone. In addition when tropical cyclones make landfall they are deprived of their energy source (i.e. latent heat from warm ocean waters) and will quickly weaken. To a lesser extent, the surface roughness of the land increases friction, reduces the circulation pattern hence weakens the storm.
- Large-scale interactions with the troposphere
Tropical cyclones feed on latent heat released during condensation. Moist warm air parcels rising in the cyclone will adiabatically expand and cool at the moist adiabatic lapse rate according to several °C per km. An air parcel will continue rising provided its adiabatic lapse rate is higher than the environment lapse rate. In other words the water vapour contained inside the cooling air parcel condenses, releasing latent heat and allowing that air parcel to stay warmer relative to the environment so that it continues its ascension in the unstable atmosphere. Theoretically, a rising air parcel would tend to be impeded by warm tropospheric temperatures, as it would be colder and denser than its surroundings, preventing further intensification of the storm. Measurements of the difference between tropospheric temperatures and SSTs are of primary importance in tropical cyclone intensification theory.
- Internal dynamics (cloud microphysics and eyewall replacement cycles)
Tropical cyclones gain energy from the large amounts of latent heat released during condensation and precipitation. One could expect that the redistribution of precipitation patterns induced by changing the cloud microphysical properties could redistribute latent heating leading to changes in the cyclone’s internal dynamics and circulation patterns. Specifically targeting the convection outside the inner eyewall might rob the latter of its moisture and energy, leading to the formation of an outer eyewall with reduced surface wind speeds.
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