Effects of Salinity Variability in a low wind speed Environment in the BVW Model

1. Effects of Salinity Variability in a low wind speed Environment in the BVW Model Danielle Niles & Steven Martinaitis Physics of the Air-Sea Boundary Layer OCP 5551 Dr. Mark Bourassa The Florida State University

2. Outline • Introduction • Problem and Background • Data & Methodology • Results • Concluding Remarks • References

3. Introduction:Description of the problem & its relevance • What effect(s) do salinity variations in a low wind speed environment have on sea fluxes and oceanic modeling? • Salinity in the ocean varies globally due to a number of factors • Precipitation and Evaporation • Prevalent areas of rising and sinking air • Episodic forcing (e.g., high-frequency winds like land breezes) • Salinity influences density of water, thus influencing circulation patterns, and moisture fluxes

4. Introduction Continued… • Although density changes slightly with salinity variations, LHF depends on the difference between specific humidity at the surface and observation height (Edwards, 2006) • Surface stress is a function of frictional velocity, found in most boundary layer parameterization • Consider wave age for roughness length of a near smooth surface and also consider capillary waves

5. Introduction: Background Information Image Courtesy of NOAA Image Courtesy of USGS SOFIA

6. Previous Studies • Lagerloefet al., 1992, 1995; Le Vine et al., 1998 • Use of remotely sensed salinity and comparison to observational values • Cronin and McPhaden, 1999 • Analysis of diurnal cycles of rainfall and salinity in the western Pacific warm pool • Michel et al., 2007 • Use of bi-dimensional mixed layer model to investigate sea surface salinity balance and variability over different temporal ranges

7. Dataset • Pan American Climate Studies (PACS) • Objective was to link sea surface temperature variability in the tropical oceans and climate over the American continents (Trasket al., 1998) • Two buoys from the Upper Ocean Processes (UOP) Group at the Woods Hole Oceanographic Institute (WHOI) deployed over an eight month period in 1997 and redeployed in 1998 • Averaged hourly observations are used to calculated other parameters using TOGA COARE Bulk Flux Algorithm (Fairallet al., 1996a) based on methods by Liu et al. (1979) with low wind regime modifications and cool skin, warm layer adjustments based on Fairallet al. (1996b) (Anderson et al., 2000)

8. Methodology PARAMETERS • PACS ‘98 North Data • 9.96° N, 125.40° W • Filtering procedure • Missing data, wind speeds > 6 ms-1 not used • 1715 hourly observations • Varied salinity from 0-40 parts per thousand or Practical Salinity Units (PSU) in the BVW model on an interval of 1 PSU • Represents the effect of salinity in reducing vapor pressure over water

9. Salinity Effects

10. Notes on Salinity Effects • Most trends appear to be near linear with increase in salinity (some are nonlinear) • Changes in most parameters are very small • SHF increases ~ 1.7 × 10-4 Wm-2 per 1 PSU • τ1 (surface stress) changes ~ 1 × 10-6 Nm-2 per 1 PSU • Zref/L (dimensionless Obukhov scale length where Zref is the observation height and L is the Obukhov scale length; related to frictional velocity) decreases ~ 0.001 per 1 PSU) • |U*| (frictional velocity) increases ~ 1 × 10-5 ms-1 per 1 PSU • Focus on LHF for this presentation • Decreases ~ 0.05 Wm-2 per 1 PSU

11. Results – LHF • Visually similar spatial distribution with nearly identical R2 values, but the overall latent heat flux values tend to be smaller with increased salinity • This could explain the decrease in the RMSE with more data points near the one-to-one line

12. Results – LHF Difference • Displays difference of LHF with 40.0 PSU salinity versus LHF with 0.0 PSU salinity (0.0 PSU has higher LHF values) • Near perfect correlation but displaced over 5 Wm-2 from the one-to-one line

13. Concluding Remarks • Salinity has a minor effect on calculated parameters in the BVW model • Analysis of the LHF shows an overall decrease of LHF as salinity increases in a near linear fashion • This agrees with Edwards (2006), stating that LHF decreases slightly with salinity due to differences in vapor pressure over water • The change of q’ due to change of q at the surface due to salinity is greater than the change of fluid density due to salinity • As qsfc decreases with increases salinity, q’ decreases • Edwards (2006) states that the difference between qsfc and q10 can be as much as 8 gkg-1

14. References • Anderson, S. P., K. Huang, N. J. Brink, M. F. Baumgartner, and R. A. Weller, 2000: Pan American Climate Studies (PACS) data report. [available online at https://darchive.mblwhoilibrary.org/bitstream/1912/351/1/WHOI-2000-03.pdf.] • Cronin, M. F., and M. J. McPhaden, 1999: Diurnal cycle of rainfall and surface salinity in the western Pacific warm pool. Geophys. Res. Let., 26, 3465-3468. • Edwards, J. M., 2006: Simulation of marine latent heat fluxes in the unified model. Preprints, 17th Symposium on Boundary Layers and Turbulence, San Diego, CA, Amer. Meteor. Soc., P4.1. • Fairall, C.W., E.F. Bradley, D.P. Rogers, J.B. Edson and G.S.Young, 1996a: Bulk parameterization of air-sea fluxes for TOGA COARE. J. Geophys. Res., 101, 3747-3764. • ——, ——, J.S. Godfrey, G.A. Wick, J.B. Edson and G.S.Young, 1996b: The cool skin and the warm layer in bulk flux calculations. J. Geophys. Res., 101, 1295-1308. • Lagerloef, G. S. E., C. T. Swift, and D. M. Le Vine, 1992: Remote sensing sea surface salinity: Airborne and satellite concepts. Proc. Ocean Sciences Meeting, New Orleans, LA. Amer. Geophys. Union. • ——, ——, and ——, 1995: Sea surface salinity: The next remote sensing challenge. Oceanography,8, 44–50. • Liu, W.T., K.B. Katsaros and J.A. Businger, 1979: Bulk parameterization of air-sea exchanges of heat and water vapor including the molecular constraints at the interface. J. Atmos. Sci., 36, 1722-1735. • Michel, S., Chapron, B., Tournadre, J., and Reul, N., 2007: Sea surface salinity variability from a simplified mixed layer model of the global ocean. Ocean Science Discussions, 4, 41-106. • Trask, R. P., R. A. Weller, W. M. Ostrom, and B. S. Way, 1998: Pan American Climate Studies (PACS). Mooring recovery and deployment cruise report, R/V Thomas Thompson cruise number 73, WHOI-98-18, 107 pp.

15. Questions?