How to Parameterize the Sea-Spray Effect in the ESRL sea-spray Parameterization Scheme

1. A Numerical Investigation of Feedback Processes in the Droplet Evaporation Layer for Tropical Cyclones L. Bianco, J.-W. Bao, C. W. Fairall, and S.A. Michelson NOAA/Earth System Research Laboratory, Boulder, CO CIRES, University of Colorado and NOAA/Earth System Research Laboratory, Boulder, CO (email contact: Laura.Bianco@noaa.gov) 1,2 1,2 1 1 1 2 Large droplets feedback E = -300 (1.2x10 kg) Small droplets feedback E = -300 (1.2x10 kg) -4 -4 • Large droplets feedback • E = -30000 (1.2x10 kg) • A&E considers the impact on momentum at the level the spray is introduced (7m) • Barenblatt considers the reduction in • Small droplets feedback • E = -30000 (1.2x10 kg) • A&E considers the impact on momentum at the level the spray is introduced (7m) • Barenblatt considers the reduction in -2 -2 • Conclusions • A bulk parameterization of the sea-spray effect on momentum flux has been developed and is added to the ESRL sea-spray parameterization developed by Fairall et al. (1994). • The parameterization is capable of reproducing the observed variation of with wind speed. • The behavior of the scheme suggests that the impact of sea spray on momentum flux may explain the differences between the variation of at high wind speed derived from the surface-wave dynamics (Moon et al. 2004) and that derived from observations (Powell et al. 2003, Jarosz et al. 2007). A21C-0644 Motivation High winds generate large re-entrant sea-spray droplets which tend to increase the sea-air enthalpy transfer and, thus, have positive feedback to the intensification of hurricanes. On the other hand, sea spray is generated at the expense of the momentum, which in effect causes the turbulent momentum flux to decrease. The parameterization of the feedback effect of sea spray to the overall air-sea momentum and enthalpy fluxes is still a subject of research. • Numerical Results of the Kepert et al. (1999) Model • Feedback effects on wind and thermal profiles as seen in the Kepert et al (1999) 1-D explicit sea spray model: • Thermal feedback diminished as the droplet size increases • Wind speed reduced with more and bigger droplets; different treatment of the momentum feed leads to significant differences in the resulting wind and temperature profiles (Andreas and Emanuel, 2001; Barenblatt et al., 2005): • However, these results are limited by the lack of spray effect in the TKE equation! Results What happens if the Spray Effect is Included in the TKE equation of the Kepert et al. (1999) Model? The increase in stability and TKE dissipation due to spray suspension reduces turbulence that is responsible for momentum and heat fluxes in the wave boundary layer. How to Parameterize the Sea-Spray Effect in the ESRL sea-spray Parameterization Scheme (Fairall et al. 1994)? One way to parameterize the spray effect on momentum flux is to follow the similarity theory by assuming a constant and steady state in the wave-boundary layer. (Makin, 2005) • References: • Andreas EL, and KA Emanuel, 2001: Effect of sea spray on tropical cyclones intensity, J. Atmos. Sci., 58, 3741-3751. • Barenblatt GI, AJ Chorin, and VM Prostokishin, 2005: A note concerning the Lighthill “sandwich model” of tropical cyclones, Proceedings Of the National Academy of Science of the United States of • America, 102, 11148-11150. • Fairall CW, JD Kepert, and GJ Holland, 1994: The effect of sea spray on surface energy transports over the ocean, The Global Atmospheric Ocean System, 2, 121-142. • Jarosz E, DA Mitchell, DW Wang, and Teague WJ, 2007: Bottom-up determination of air-sea momentum exchange under a major tropical cyclone, Science, 315, • 1707-1709. • Kepert JD, CW Fairall, and JW Bao, 1999: Modeling the interaction between the atmospheric boundary layer and evaporating sea spray droplets, Air–Sea Exchange: • Physics, Chemistry and Dynamics, G.L. Geernaert, Ed., Kluwer. • Makin VK, 2005: A note on the drag of the sea surface at hurricane winds, Bound.-Layer Meteorol., 115, 169-176. • Moon IJ, I Ginis, and T Hara, 2004: Effect of surface waves on Charnock coefficient under tropical cyclones, Geophysical Research Letters, 31, Art. No. 20302. • Powell MD, PJ Vickery, TA Reinhold, 2003, Reduced drag coefficient for high wind speeds in trolical cyclones, Nature, 422, 279-283.