Study of the Implications of Whitecap Intermittency on the Uniform Sea-salt Aerosol Source Approximation and Deposition Velocity
Abstract
The source function and deposition velocity of sea-salt particles used in large-scale models assumes that the source and deposition is uniform over areas large compared to the horizontal grid spacing of the model, whereas sea-salt aerosol is overwhelmingly generated by white caps whose surface distribution is usually sparse and sporadic. The analysis presented here uses several puff plume models to study the validity of the underlying assumptions of the horizontally uniform surface source and deposition, and a time series of puff plumes is averaged to obtain the large-scale source and deposition flux. The analysis demonstrates the remarkable difference between (i) the case where deposition results exclusively from non-gravitational deposition processes at the surface (i.e., small particles) and (ii) the case where deposition is solely from gravitational settling (i.e., large particles). For Case (i), the magnitude of the gradient (eddy correlation) flux, initially equal to the source flux, will evolve to an equilibrium state where there is no gradient flux. This can be contrasted to Case (ii) where the upward gradient flux is always equal to the source flux (at a given height) and the transient behavior is governed by the increase of the gravitational flux during the transition to equilibrium (upward gradient (source) flux equals the downward deposition flux). The intermediate case where both the gravitational and deposition fluxes are important is a mixture of the above two cases.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 29, 2007
- Accession Number
- ADA474497
Entities
People
- Peter F. Caffrey
- William A. Hoppel
Organizations
- United States Naval Research Laboratory