The Hurricane Aerosol and Microphysics Program (HAMP): A HAMP Contribution

The Department of Homeland Security asked NOAA/ESRL in Boulder to organize a workshop on possible new scientific theory and approaches to hurricane modification in February, 2008. Nearly two dozen scientists from around the world attended and there were a number of hypotheses and new ideas presented. We shall summarize the workshop results here and the development of the new DHS-funded HAMP Program that arose from the Workshop. HAMP is only the first Phase in a planned three-phase program. There will be no actual seeding trials unless one or more of the modification hypotheses is confirmed in Phase 1, through an interactive program of high-resolution coupled models and new aircraft observations. HAMP will focus on the effects of aerosols on cloud microphysics within the hurricane and on the effects of aerosols on hurricane structure and behavior, especially changes in hurricane intensity. This will be done through observations of aerosols and resulting cloud microphysical structure within the hurricane and simulating their effects using high-resolution, coupled, ocean-atmosphere models that treat cloud microphysical processes explicitly and incorporate the effects of sea spray.

If HAMP is successful and can provide the community with the data, forecasting should take a giant leap ahead. With this in mind, the thrust of the HAMP program was modified to focus first on understanding cloud and hurricane microphysical structure prior to undertaking any examination of hurricane modification. NOAA has been kept appraised with this process to ensure the work remains complementary to and supportive of their efforts with HFIP and is not duplicative of that work. The PI's in HAMP include the authors and colleagues Drs. Daniel Rosenfeld and Alexander Khain of Hebrew University, Dr. William Cotton of Colorado State and Dr. Isaac Ginis of the University of Rhode Island and their students.

HAMP has 3 overarching objectives. The first one is to establish a strong theoretical foundation to determine the effects on cloud microphysical processes of utilizing pollution-sized hygroscopic aerosol seeding and/or black carbon seeding. A second objective is to determine the effects of aerosols on hurricane intensity. Recently-published research suggests that seeding hurricanes with small (pollution-sized) hygroscopic aerosol concentrations can lead to significant reductions in hurricane intensity (Rosenfeld et al., 2007; Cotton et al., 2007). A third objective is to specify quantitatively the effects of carbon black seeding within the storm circulation. This will involve broadcast seeding of black carbon aerosol either in the boundary layer on the storm periphery or alternatively over the anvil tops of the hurricane. Both hypotheses are viable, physically plausible scenarios but neither has been explored quantitatively. Later phases of HAMP may examine the effects of artificially-induced ocean cooling in advance of hurricanes on their possible weakening.

HAMP will capitalize on the contributions of various researchers providing independent yet collaborative research. The ultimate goal is to test quantitatively mitigation hypothesis by means of rigorous numerical simulation, supported by the necessary observations.

We shall also briefly summarize HAMP Program status, including some exciting new microphysical observations acquired during a field campaign in India this past summer.