1. Spatial coherence of interannual variability in water properties on the U.S. northeast shelf David G. Mountain and Maureen H. Taylor Presented by: Yizhen Li

2. 1. Introduction --Position Chesapeake Bay

3. 1 Introduction – Significance of interannual variation The interannual variability of the water properties as temperature and salinity on the continental shelf off the northeast United States has been proven to be significant during several recent decades The interannual variability of the water properties as temperature and salinity on the continental shelf off the northeast United States has been proven to be significant during several recent decades important for the biological process of the northeast shelf ecosystem. important for the biological process of the northeast shelf ecosystem. the changes in water property will likely be the primary consequence of a change in climate that may occur in future decades (Manabe and Stouffer, 1980). the changes in water property will likely be the primary consequence of a change in climate that may occur in future decades (Manabe and Stouffer, 1980).

4. 1 Introduction — Former research Empirical Orthogonal Function (EOF) analysis to study the interannual variability in sea surface temperature (SST) over a long region from Southern Greenland and Labrador to Cape Hatteras.  two primary modes that account for 44% of the entire variations over a length of over 1000km. Empirical Orthogonal Function (EOF) analysis to study the interannual variability in sea surface temperature (SST) over a long region from Southern Greenland and Labrador to Cape Hatteras.  two primary modes that account for 44% of the entire variations over a length of over 1000km. only four points in the northeast shelf region was represented so the spatial structure within it is unknown. (Thompson et al,1988) only four points in the northeast shelf region was represented so the spatial structure within it is unknown. (Thompson et al,1988) SST interannual variability was largely affected by the surface atmospheric heat flux (Thompson et al,1993); SST interannual variability was largely affected by the surface atmospheric heat flux (Thompson et al,1993); in the Scotian Shelf region : the influx of offshore water at depth on the shelf (Petrie and Drinkwater, 1993). in the Scotian Shelf region : the influx of offshore water at depth on the shelf (Petrie and Drinkwater, 1993). the interannual variability of salinity and temperature within western Gulf of Maine (WGOM) was strongly correlated with those of Georges Bank and Middle Atlantic Bight (MAB). The SST change was due to surface heat flux while salinity is caused by local precipitation and river runoff. (Mountain et al, 1994 ) the interannual variability of salinity and temperature within western Gulf of Maine (WGOM) was strongly correlated with those of Georges Bank and Middle Atlantic Bight (MAB). The SST change was due to surface heat flux while salinity is caused by local precipitation and river runoff. (Mountain et al, 1994 )

5. the main purpose of his paper: the main purpose of his paper: to determine the degree and pattern of spatial coherence in the interannual variation of water properties on the northeast shelf. to determine the degree and pattern of spatial coherence in the interannual variation of water properties on the northeast shelf. 1 Introduction — Objective

6. 2 Data and Methods Data: the Northeast Fisheries Science center (NEFSC) Marine Resources Monitoring, Assessment, and Prediction (MARMAP) program. Data: the Northeast Fisheries Science center (NEFSC) Marine Resources Monitoring, Assessment, and Prediction (MARMAP) program.  3~6 surveys every year during 1977~1987 to measure the plankton and water properties over the continental shelf from Cape Hatteras to the Gulf of Maine (GOM). 160 standard stations  3~6 surveys every year during 1977~1987 to measure the plankton and water properties over the continental shelf from Cape Hatteras to the Gulf of Maine (GOM). 160 standard stations  reversing thermometers at up to 15 standard depths to measure temperature most of the year, with an accuracy of ~0.02°C and ~0.01 in salinity.  reversing thermometers at up to 15 standard depths to measure temperature most of the year, with an accuracy of ~0.02°C and ~0.01 in salinity. Methods: remove the annual cycle of salinity (surface/bottom) and temperature (surface/bottom) of each MARMAP station using a harmonic analysis method Methods: remove the annual cycle of salinity (surface/bottom) and temperature (surface/bottom) of each MARMAP station using a harmonic analysis method EOF analysis (winter (calendar days 304~120) ;summer periods (121~303)  EOFs) & spatial distribution of the correlation between the anomalies at different stations (also include autocorrelation of SST and salinity in the same stations) are used to determine and visualize the spatial structure within the anomaly time series. EOF analysis (winter (calendar days 304~120) ;summer periods (121~303)  EOFs) & spatial distribution of the correlation between the anomalies at different stations (also include autocorrelation of SST and salinity in the same stations) are used to determine and visualize the spatial structure within the anomaly time series. a second station group was selected to focus on GOM to help interpret the results within the gulf from the primary station set. a second station group was selected to focus on GOM to help interpret the results within the gulf from the primary station set. Ancillary data :SST series measured over 6 years (1985~1991) at Ambrose Light Tower ad at five NOAA offshore buoys. Ancillary data :SST series measured over 6 years (1985~1991) at Ambrose Light Tower ad at five NOAA offshore buoys.

7. 2 Data and Methods Asterisk: MARMAP station No clear annual salinity cycle

8. 2 Data and Methods--EOF Example （ ENSO index ） EOF Time Series

9. 3 Results – Standard Deviation/Surface Temperature 0.5°C~2.0°C, larger near the shelf edge and near Cape Hatteras 0.5°C~2.0°C, larger near the shelf edge and near Cape Hatteras The bottom temperature distribution is similar to the surface. The bottom temperature distribution is similar to the surface. 0.5°C~2.0°C Winter Summer

10. generally the deviation of salinity in summer increases north to south generally the deviation of salinity in summer increases north to south Same increase from the north to south for the bottom and winter salinity variability, although the value is a little lower. Same increase from the north to south for the bottom and winter salinity variability, although the value is a little lower. 3 Results – Standard Deviation/Surface Salinity Increase

11. The EOF analysis showed significant first mode in all the parameters. The EOF analysis showed significant first mode in all the parameters. The shelf-wide station EOF shows first mode as low as 26% for the summer SST to 44% for the winter surface. The shelf-wide station EOF shows first mode as low as 26% for the summer SST to 44% for the winter surface. The percentage of GOM ranges from 34%~67%. The percentage of GOM ranges from 34%~67%. 3 Results – EOF results/Percent of Variance

12. 3 Results – EOF results/Surface Temperature/Winter lower value in Eastern Gulf of Maine (EGOM), higher over Georges Bank and the shelf to southward to Delaware Bay, and higher still along the shelf edge and farther south to Cape Hatteras. lower value in Eastern Gulf of Maine (EGOM), higher over Georges Bank and the shelf to southward to Delaware Bay, and higher still along the shelf edge and farther south to Cape Hatteras. The first mode of GOM analysis also shows similar decrease The first mode of GOM analysis also shows similar decrease Generally, the spatial distribution shows similar structure as what the standard deviation indicates. Generally, the spatial distribution shows similar structure as what the standard deviation indicates. Edge Similar Relative Amplitude

13. 3 Results – EOF results/Surface Salinity/Summer Surface Salinity has similar variation as standard variation Surface Salinity has similar variation as standard variation We also found similarity between EOF mode and original data for most occasions except the Summer SST. We also found similarity between EOF mode and original data for most occasions except the Summer SST. Increase

14. 3 Results – EOF results/Surface Temperature/Summer It has high values in MAB off New Jersey, with decreasing values toward Cape Hatteras and toward the east, south of New England, leading to a change in sign in the WGOM. the GOM results show different structure of the shelf-wide EOF It has high values in MAB off New Jersey, with decreasing values toward Cape Hatteras and toward the east, south of New England, leading to a change in sign in the WGOM. the GOM results show different structure of the shelf-wide EOF This is quite different from the standard deviation distribution  This is quite different from the standard deviation distribution  the percentage variance has high values only in the MAB region. the percentage variance has high values only in the MAB region. Change in Sign Larger Value Different The ‘ two modes ’

15. 3 Results – correlations between property anomalies at different stations show results similar to EOF for winter and summer. show results similar to EOF for winter and summer. significant correlation for the shelf-wide SST during winter significant correlation for the shelf-wide SST during winter Winter

16. 3 Results – correlations between property anomalies at different stations Summer only have two localized correlation during summer one in the WGOM and one in MAB.

17. 3 Results--correlation between SST and surface salinity at each station in the summer time at MAB and WGOM. negative correlation between SST and surface salinity at each station in the summer time at MAB and WGOM. negative correlation between SST and surface salinity at each station in the summer time at MAB and WGOM. at the bottom, temperature and salinity show different pattern (positive in most of the region and negative only along a narrow band from Long Island to Chesapeake Bay). at the bottom, temperature and salinity show different pattern (positive in most of the region and negative only along a narrow band from Long Island to Chesapeake Bay). --strong upwelling ; vertical mixing --strong upwelling ; vertical mixing Summer Surface Summer Bottom

18. 3 Results--The autocorrelation for the daily SST from ALT and NOAA buoys as well as the correlation of MARMAP stations MARMAP correlations drop off only slightly rapidly than the buoy autocorrelation MARMAP anomaly correlations may have been influenced as much by the time between the observations as by the spatial separation.

19. 4 Conclusion and Discussion In this paper, the interannual variability of the surface and bottom temperature and salinity on the U.S northeast shelf is carefully described using the 10-year hydrographic data from the NEFSC MARMAP program. In this paper, the interannual variability of the surface and bottom temperature and salinity on the U.S northeast shelf is carefully described using the 10-year hydrographic data from the NEFSC MARMAP program. (1) All parameters show significant first modes in the EOF analysis, with 40~50% variance in winter and 25~35% in the summer period (1) All parameters show significant first modes in the EOF analysis, with 40~50% variance in winter and 25~35% in the summer period (2)Most parameters (except for the summer SST) exhibit coherent variability across the entire shelf region from Cape Hatteras to the central Gulf of Maine. This high degree of coherence and the long coherence length scales indicate that the interannual variability of this shelf region could be derived from observations at relatively few locations. (2)Most parameters (except for the summer SST) exhibit coherent variability across the entire shelf region from Cape Hatteras to the central Gulf of Maine. This high degree of coherence and the long coherence length scales indicate that the interannual variability of this shelf region could be derived from observations at relatively few locations.

20. Conclusion and Discussion (3)The summer SST shows two separate regions of coherent variability (with lower salinity and higher SST) in the central of MAB and WGOM, but compared to the winter SST it ’ s less coherent (25~35%). This regionalization is believed due to the local coastal runoff effect in spring — the less saline coastal water can stabilize the upper water column and inhibit vertical mixing, so the solar insolation accumulates in the surface layer. However, the degree of surface warming depends on a local balance between the run-off induced structure, the surface heating and wind-induced mixing,and the coherence in the MAB and WGOM is according to the heating distribution caused by the local wind and runoff over the water column. (3)The summer SST shows two separate regions of coherent variability (with lower salinity and higher SST) in the central of MAB and WGOM, but compared to the winter SST it ’ s less coherent (25~35%). This regionalization is believed due to the local coastal runoff effect in spring — the less saline coastal water can stabilize the upper water column and inhibit vertical mixing, so the solar insolation accumulates in the surface layer. However, the degree of surface warming depends on a local balance between the run-off induced structure, the surface heating and wind-induced mixing,and the coherence in the MAB and WGOM is according to the heating distribution caused by the local wind and runoff over the water column. (4) Spatially the water property variation in the EGOM is incoherent with the variability of rest of the shelf region. This is because the EGOM water property is less influenced locally but rather dominated by the interannual variability of the inflow (advection process) from Scotian Shelf and Northeast Channel. (4) Spatially the water property variation in the EGOM is incoherent with the variability of rest of the shelf region. This is because the EGOM water property is less influenced locally but rather dominated by the interannual variability of the inflow (advection process) from Scotian Shelf and Northeast Channel.

21. Thank you! Thank you!