Sea salt aerosol (SSA) exerts a major influence over a broad reach of geophysics. It is important to the physics and chemistry of the marine atmosphere and to marine geochemistry and biogeochemistry generally. It affects visibility, remote sensing, atmospheric chemistry, and air quality. Sea salt aerosol particles interact with other atmospheric gaseous and aerosol constituents by acting as sinks for condensable gases and suppressing new particle formation, thus influencing the size distribution of these other aerosols and more broadly influencing the geochemical cycles of substances with which they interact. As the key aerosol constituent over much of Earth's surface at present, and all the more so in pre-industrial times, SSA is central to description of Earth's aerosol burden.

Sea Salt Aerosol Production: Mechanisms, Methods, Measurements, and Models - A Critical Review

The subject of ocean turbulence is in a state of discovery and development with many intellectual challenges. This book describes the principal dynamic processes that control the distribution of turbulence, its dissipation of kinetic energy and its effects on the dispersion of properties such as heat, salinity, and dissolved or suspended matter in the deep ocean, the shallow coastal and the continental shelf seas. It focuses on the measurement of turbulence, and the consequences of turbulent motion in the oceanic boundary layers at the sea surface and near the seabed. Processes are illustrated by examples of laboratory experiments and field observations. The Turbulent Ocean provides an excellent resource for senior undergraduate and graduate courses, as well as an introduction and general overview for researchers. It will be of interest to all those involved in the study of fluid motion, in particular geophysical fluid mechanics, meteorology and the dynamics of lakes.

https://assets.cambridge.org/97805218/35435/frontmatter/9780521835435_frontmatter.pdf

The Turbulent Ocean

Estimates of rain rate from the precipitation radar (PR) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite require a means by which the radar signal attenuation can be corrected. One of the methods available is the surface reference technique in which the radar surface return in rain-free areas is used as a reference against which the path-integrated attenuation is obtained. Despite the simplicity of the basic concept, an assessment of the reliability of the technique is difficult because the statistical properties of the surface return depend not only on surface type (land/ocean) and incidence angle, but on the detailed nature of the surface scattering. In this paper, a formulation of the technique and a description of several surface reference datasets that are used in the operational algorithm are presented. Applications of the method to measurements from the PR suggest that it performs relatively well over the ocean in moderate to heavy rains. An indication of the reliability of...

Use of the Surface Reference Technique for Path Attenuation Estimates from the TRMM Precipitation Radar

In winds approaching hurricane strength, spray droplets proliferate. Once created, these droplets accelerate to the local wind speed in 1 s or less and thereby extract momentum from the wind. Because these droplets have substantial mass, they eventually plunge back into the ocean, delivering their horizontal momentum to the surface in the form of a spray stress. Inadequate information on the production rate and size distribution of spray droplets, however, hampered previous attempts to estimate the magnitude of this spray-mediated momentum exchange. This paper therefore uses recent estimates of the spray generation function to reconsider spray's ability to alter air–sea momentum exchange. Conservation of momentum requires that spray cannot enhance the air– sea stress beyond what the large-scale flow dictates. However, spray can redistribute stress in the near-surface atmosphere since the wind must slow if the spray droplets accelerate. For a wind of 30 m s−1, spray supports about 10% of the surfa...

Spray Stress Revisited

Radar signatures of rain cells are investigated using multifrequency/multipolarization synthetic aperture radar (SAR) images acquired from the space shuttle Endeavour during the spaceborne imaging radar-C/X-band SAR (SIR-C/X-SAR) missions in April and October 1994. In SIR-C/X-SAR images, radar signatures of rain cells over the ocean usually consist of irregularly shaped bright and dark patches that strongly depend on radar frequency and polarization. The radar signatures of rain cells observed in SIR-C/X-SAR imagery of the ocean originate from (1) the scattering and attenuation of the microwaves by raindrops and ice particles in the atmosphere and (2) the modification of the sea surface roughness induced by the impact of raindrops and by wind gusts associated with rain cells. Raindrops impinging on the sea surface generate ring waves, which enhance the sea surface roughness, but they also generate turbulence in the upper water layer, which reduces the sea surface roughness. Depending on the radar wavelength, ocean areas struck by rain can have higher or lower normalized radar cross section (NRCS) than the surrounding rain-free area; in ocean areas where heavy rain is impinging on the sea surface, the X- and C-band NRCS is usually enhanced, and the L-band NRCS is reduced. From the phase difference between the horizontally and vertically copolarized signals, estimates of the rain rate are obtained. The present analysis shows further that the presently used wind speed retrieval algorithms for the scatterometers aboard the ERS and ADEOS satellites may yield biased wind fields if several rain cells lie within a scatterometer resolution cell.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JC00779

Investigation of multifrequency/multipolarization radar signatures of rain cells over the ocean using SIR‐C/X‐SAR data

Effects of rain on surface waves have been investigated in a circulating wind-wave tank. Surface displacement and slope spectra under different wind velocities were measured near the upwind and downwind edges of a region with simulated rains. Spatially uniform rains of varied intensities with drop size of about 2.6 mm and spacing of 3 cm were used. Damping of surface waves by rain was observed in the frequency region of 2–5 Hz, and there was an increase in the damping rate with rain intensity. The effective eddy viscosity in the rain-induced mixed layer was found to be an order of magnitude greater than the molecular viscosity of water. As for rain-induced ripples, spectral densities of the surface slope in the frequency range of 10–100 Hz increased with the rain intensity. However, at the highest wind velocity (6.34 m s−1) of the present experiment, the ripple structure was influenced primarily by wind, with rain introducing no observable effects.

Interactions between Rain and Wind Waves

Previous experiments suggested that rain had dual effects on wind waves: damping in the gravity range and enhancement in the capillary–gravity/capillary range. These results in the frequency domain obtained from fixed-point measurements, however, might be contaminated by the Doppler effect. In the present study, wave slopes were spatially mapped with a scanning laser slope gauge under wind velocities of 3, 5, and 7 m s−1 and rain intensities of 42, 68, and 115 mm h−1. Synthesized spectral densities, which are not affected by the Doppler effect, were obtained by processing the data in both “fixed point” and “spatial scan” modes. The existence of dual effects is clarified with the present results.

Shih Tang

Papers

Interactions between Rain and Wind Waves

An Experimental Study of Rain Effects on Fine Structures of Wind Waves