A report discusses ASAP (Air-sea Spray Airborne Profiler), a dual-wavelength radar profiler that provides measurement information about the droplet size distribution (DSD) of sea-spray, which can be used to estimate heat and moisture fluxes for hurricane research. Researchers have recently determined that sea spray can have a large effect on the magnitude and distribution of the air-sea energy flux at hurricane-force wind speeds.
To obtain information about the DSD, two parameters of the DSD are required; for example, overall DSD amplitude and DSD mean diameter. This requires two measurements. Two frequencies are used, with a large enough separation that the differential frequency provides size information. One frequency is 94 GHz; the other is 220 GHz. These correspond to the Rayleigh and Mie regions. Above a surface wind speed of 10 m/s, production of sea spray grows exponentially. Both the number of large droplets and the altitude they reach are a function of the surface wind speed.
This work was done by Stephen L. Durden and D. Esteban-Fernandez of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com /tsp under the Physical Sciences category. NPO-46537
This Brief includes a Technical Support Package (TSP).
Air-Sea Spray Airborne Radar Profiler Characterizes Energy Fluxes in Hurricanes
(reference NPO-46537) is currently available for download from the TSP library.
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Overview
The document outlines the development of the Air-Sea Spray Airborne Radar Profiler (ASAP), a high-resolution radar system designed to characterize energy fluxes in hurricanes. Led by Principal Investigator Daniel Esteban-Fernandez at NASA's Jet Propulsion Laboratory, the project aims to enhance understanding of the role of sea spray in air-sea interactions during hurricane events, which is crucial for predicting hurricane intensity changes.
The ASAP utilizes a dual-frequency radar system operating at 94 GHz and 220 GHz. This dual-frequency approach allows for the measurement of sea spray droplets, particularly in the size range of 100 μm to 600 μm, by leveraging different scattering regimes. The 94 GHz frequency operates primarily in the Rayleigh scattering region, while the 220 GHz frequency enters the Mie scattering region, enabling the retrieval of a two-variable distribution of drop-size (DSD) of the scatterers. This capability is essential for accurately assessing the concentration of sea spray and its impact on energy fluxes.
The document details the methodology employed in the radar system, including the coupling of Fairall’s model of the spray source function with Prandtl’s solution of the transport equation. Verification of the model is achieved through Monte-Carlo Lagrangian simulations and numerical solutions of stochastic differential equations, demonstrating good agreement for particles of various sizes.
Key specifications of the radar system include a minimum detectable reflectivity of -24 dBZ at 94 GHz and -35 dBZ at 220 GHz, with a dynamic range of 90 dB to accommodate returns from both sea spray and the ocean surface. The radar is designed to operate from a platform altitude of 2000 m, ensuring effective observation of spray while maintaining safety.
The project aims to provide insights into the air-sea exchange of heat, moisture, and momentum, which are critical for understanding how hurricanes derive energy from the ocean. By improving the accuracy of hurricane intensity forecasts, the ASAP has the potential to significantly enhance disaster preparedness and response efforts.
Overall, the ASAP represents a novel and unique approach to studying sea spray dynamics in hurricane environments, contributing to the broader field of atmospheric science and improving our understanding of extreme weather phenomena.
