Danielle Niles & Steven MartinaitisPhysics of the Air-Sea Boundary Layer

OCP 5551Dr. Mark Bourassa

The Florida State University

Introduction Problem and Background

Data & Methodology Results Concluding Remarks References

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

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

''qwLE v

'3'uuii 5.0'3'* uuu ii

2*

0 uz

g

u

ucz

poM

2*

*/

48.0

Image C

ourt

esy

of

NO

AA

Image C

ourt

esy

of

USG

S

SO

FIA

Lagerloef et 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

Pan American Climate Studies (PACS) Objective was to link sea surface

temperature variability in the tropical oceans and climate over the American continents (Trask et 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 (Fairall et al., 1996a) based on methods by Liu et al. (1979) with low wind regime modifications and cool skin, warm layer adjustments based on Fairall et al. (1996b) (Anderson et al., 2000)

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

wv_ang 90°

dyn_p 0 (wind speed)

ss_prm 2 (wave age)

wv_age 43.64

a_moist_p 1 (relative humidity)

s_moist_p 1 (relative humidity)

CON_P 0.6

neutral 1

z_ref 3.26 m

t_ref 1.99 m

rhum (for s_moist_p) 0.98+(0.02*(1-(salin/0.04)))

PARAMETERS

Represents the effect of salinity in reducing vapor pressure over water

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

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

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

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

''qwLE v

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.