Award Abstract # 1129646
Collaborative Research: Microstructure and Mixing Measurements During SPURS

NSF Org: OCE
Division Of Ocean Sciences
Recipient: WOODS HOLE OCEANOGRAPHIC INSTITUTION
Initial Amendment Date: September 26, 2011
Latest Amendment Date: June 17, 2013
Award Number: 1129646
Award Instrument: Standard Grant
Program Manager: Eric C. Itsweire
OCE
 Division Of Ocean Sciences
GEO
 Directorate for Geosciences
Start Date: September 15, 2011
End Date: August 31, 2016 (Estimated)
Total Intended Award Amount: $1,925,975.00
Total Awarded Amount to Date: $1,925,975.00
Funds Obligated to Date: FY 2011 = $1,925,975.00
History of Investigator:
  • Raymond Schmitt (Principal Investigator)
    rschmitt@salientpredictions.com
  • Louis St Laurent (Co-Principal Investigator)
Recipient Sponsored Research Office: Woods Hole Oceanographic Institution
266 WOODS HOLE RD
WOODS HOLE
MA  US  02543-1535
(508)289-3542
Sponsor Congressional District: 09
Primary Place of Performance: Woods Hole Oceanographic Institution
266 Woods Hole Road
Woods Hole
MA  US  02543-1535
Primary Place of Performance
Congressional District:
09
Unique Entity Identifier (UEI): GFKFBWG2TV98
Parent UEI:
NSF Program(s): PHYSICAL OCEANOGRAPHY
Primary Program Source: 01001112DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s):
Program Element Code(s): 161000
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.050

ABSTRACT

Surface salinity variations in the global ocean are caused by freshwater exchange with the atmosphere and land, via evaporation, precipitation and runoff. The expectation that the water cycle will accelerate with global warming has motivated an increased interest in upper-ocean salinity; since the water cycle is predominantly over the ocean, the sea-surface salinity may well be the very best indicator of changes in the water cycle. In considering such ocean-atmosphere interactions, areas of surface salinity extrema are of special interest. A multi-agency field program, the Salinity Processes Upper-ocean Regional Studies (SPURS), to begin to understand the oceanic processes that control upper ocean salinity will be executed in 2012-13. SPURS is focused on the surface salinity maximum in the eastern North Atlantic. The salinity of the upper ocean is controlled by surface freshwater exchange with the atmosphere, mixing and entrainment from below, and mean and eddy advection by horizontal currents, including those due to geostrophic, Ekman and smaller scales of motion. Other elements of SPURS will evaluate many of these processes; here we propose to focus on upper-ocean mixing. Microstructure sensors on profiling and gliding platforms will be used to quantify the mixing processes operating within the salinity maximum region. In addition, model simulations will elucidate both model quality and the physical processes important to the mixing and upper ocean stability structure.

Intellectual Merit: Understanding and prediction of the evolution of the upper-ocean salinity field depends on accurate description and parameterization of the sub grid-scale mixing processes that dissipate the salinity variance created by surface water fluxes. Microstructure measurements will quantify the diabatic flux terms relevant to the temperature and salinity budgets being constrained by the overall SPURS study. The role of surface convection, internal wave processes, and double-diffusive mixing on these fluxes will be assessed. Model simulations, fed by the air-sea interaction buoy data, will help identify the source of the turbulence. Mixing parameterizations for double diffusion will be assessed through alteration of the model implementation to utilize diffusivities as taken from the microstructure based estimates. The combined approach of microstructure measurements and modeling is the most efficient route to provide information that could lead to improved parameterizations. The impact will be multiplied by the synergistic effects of being incorporated into the overall SPURS program, where observations and models of basin, regional and the mesoscale will be undertaken.

Broader Impacts: Improved understanding of ocean mixing processes are essential for advancing climate science, as the representation of sub grid-scale processes in large-scale models continues to be a major unresolved issue. The focus of this project on the salinity is especially relevant to documenting change in the global water cycle, which has tremendous implications for society. As part of this project the investigators will maintain web sites on SPURS and the mixing processes operant in the salinity maximum region. To enhance educational outreach, the investigators will collaborate with The Zephyr Education Foundation's innovative marine science literacy and education program, located in Woods Hole. The Zephyr Foundation is ideally suited for this purpose and attracts school groups from Massachusetts and Rhode Island, including underrepresented and disadvantaged students from inner-city programs in Boston and New Bedford. This project will also involve active roles for full-time graduate students at WHOI/MIT. In addition, a modeling and data analysis module suitable for distribution will be produced.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

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Farrar, J. T., L. Rainville, A. J. Plueddemann, W. S. Kessler, C. Lee, B. A. Hodges, R. W. Schmitt, J. B. Edson, S. C. Riser, C. C. Eriksen, D. M. Fratantoni "Salinity and temperature balances at the SPURS central mooring during fall and winter" Oceanography , v.28 , 2015 , p.56 10.5670/oceanog.2015.06
Li, L. R. W. Schmitt, C. Ummenhofer, K. Karnauskis "Implications of North Atlantic Sea Surface Salinity for Summer Precipitation over the US Midwest: Mechanisms and Predictive Value" Journal of Climate , v.29 , 2016 , p.3143 10.1175/JCLI-D-15-0520.1
Li, L. R. W. Schmitt, C. Ummenhofer, K. Karnauskis "North Atlantic Salinity as a Predictor of Sahel Rainfall" Science Advances , v.2 , 2015 , p.e1501588 10.1126/sciadv.1501588
Lindstrom, E, F. Bryan and R. W. Schmitt "SPURS: Salinity Processes in the Upper-ocean Regional Study, the North Atlantic Experiment." Oceanography , v.28 , 2015 , p.14 10.5670/oceanog.2015.01
R. W. Schmitt "An Old Salt Retires" Oceanography , v.28 , 2015 , p.7
R.W. Schmitt and A. Blair "A River Of Salt" Oceanography , v.28 , 2015 , p.40 10.5670/oceanog.2015.04
R. W. Schmitt et al. "From Salty to Fresh: SPURS-2: Diagnosing the Physics of a Rainfall-Dominated Salinity Minimum" Oceanography , v.28 , 2015 , p.150 10.5670/oceanog.2015.15

PROJECT OUTCOMES REPORT

Disclaimer

This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

The global water cycle is thoroughly dominated by its’ oceanic component.  That is, most of the evaporation and precipitation occurs over the oceans, which contain 97% of the water on the Earth. The ocean is the ultimate source of all rainfall on land. The main signature of the oceanic water cycle is a distinctive pattern of higher and lower salinities, with high salinity found under the mid-latitude subtropical high pressure systems and low salinity found in the tropics and at high latitudes. The subtropical highs are the main source regions for the oceanic supply of water to the atmosphere that supplies precipitation on land and at sea.  Our goal with this project was to develop understanding of how the high salinity regions of the subtropical gyres are maintained by a balance between net evaporation and the oceanic mixing processes, with a particular focus on the North Atlantic. For this work we participated in two cruises, making very detailed measurements of the mixing processes operating in the salinity maximum of the North Atlantic. Several new discoveries were made to contribute to the intellectual merit of the project:

1. Enhanced dissipation in the upper few meters of the ocean was discovered under the stratified conditions of diurnal warming. We hypothesize that this dissipation is associated with internal waves in this thin surface stratified layer. The waves may have "tunneled" across the mixed layer from the thermocline below.

2. Salt finger and turbulent mixing were found to be operative in the thermocline of the region. These vertical mixing processes are estimated to account for about half the mixing necessary to accommodate the net evaporation minus precipitation that maintains the salinity maximum in this region of the North Atlantic. An “isohaline” budgeting approach was used and lateral mixing by eddies accounts for the other mixing.

3. Interannual variations in springtime sea surface salinity were found to be excellent predictors of summer rainfall in the Sahel of Africa and the US Midwest. This new salinity-based prediction technique is superior to all other predictive indices based on SST or Pressure and is generalizable to other regions. It is particularly useful for extremes in rainfall or drought. (See accompanying figures).

The broader impacts of the work can be characterized in several realms:

1. The new type of near-surface mixing discovered here will lead to new understanding of upper-ocean processes and help to improve models of air-sea interaction. Ultimately this will help to improve weather and climate forecasts.

2. The discovery of the predictive utility of seas surface salinity will improve seasonal rainfall forecasts and help prepare communities for extreme rains and flooding or extended drought.  This will be of great benefit to farmers, water system managers, emergency planners, energy providers and for the safety and health of the general public.

3. The graduate students trained on this project will contribute to the future advance of science and technology in the US.


Last Modified: 12/20/2016
Modified by: Raymond W Schmitt

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