Andreas E. L., K. F. Jones and C. W. Fairall (December 2010): Production velocity of sea spray droplets. J. Geophys. Res. Oceans, 115, C12065. doi:10.1029/2010JC006458

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The sea spray generation function dF/dr0 predicts the rate at which droplets of initial radius r0 are produced at the sea surface. Because this function is not readily measurable in the marine environment, however, it is often inferred from measurements of the near-surface droplet concentration, C(r0), through an assumed velocity scale, the effective spray production velocity. This paper proceeds in reverse, though: It uses a reliable estimate of dF/dr0 and 13 sets of measurements of C(r0) over the ocean to calculate the implied effective production velocity, Veff, for droplets with initial radii r0 from 5 to 300 μm. It then compares these Veff values with four candidate expressions for this production velocity: the dry-deposition velocity, VDh; the mean wind speed at the significant wave amplitude (A1/3), the standard deviation in vertical droplet velocity, σwd; and laboratory measurements of the ejection velocity of jet droplets, Vej. The velocity scales and Vej agree best with the implied Veff values for 20 ≤ r0 ≤ 300 μm. The deposition velocity, VDh, which is the velocity most commonly used in this application, agrees worst with the Veff values. For droplets with r0 less than about 20 μm, the analysis also rejects the main hypothesis: that dF/dr0 and C(r0) can be related through a velocity scale. These smaller droplets simply have residence times that are too long for spray concentrations to be in local equilibrium with the spray production rate.

Item Type: Article
Subjects: PSD Publications
Divisions: Physical Sciences Division
DOI: 10.1029/2010JC006458