Andrey Proshutinsky Physical Oceanography Department AOMIP young scientists school Tuesday October 20 2009 1 Major themes Wind blows ice goes synoptic scales of variability Seasonal changes and effects ID: 1039831
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1. Wind-forced dynamics of the Arctic OceanAndrey ProshutinskyPhysical Oceanography DepartmentAOMIP young scientists school. Tuesday October 20, 20091
2. Major themes:Wind blows – ice goes: synoptic scales of variabilitySeasonal changes and effectsInter-annual and decadal variability of wind forcing and ocean conditions
3. Wind blows – ice goes and storm surges
4. There are several environmental issues associated with storm surges which affect human activities in the Alaskan North Slope and Siberian coastal regions is the coastal erosion. The coastal erosion processes are increasing due to: Decline in ice extent and thickness which allow for higher sea levels during storm events Less stable and predictable shore-fast ice, gouging of shelves and coast by sea ice; pile-up of ice on shore; rising in sea level.
5. Coastal regions with low relief are significantly influenced by storm surgesKara SeaLaptev SeaEast SiberianSeaChukchi SeaBeaufort SeaBarents SeaThe combination of waves and high water levels during late summer and fall (during storms) before the development of significant sea-ice cover can be particularly damaging to shorelines
6. Left: Nome - looking toward airport, normal (photo by John Lingaas, WSO Fairbanks); Right: Nome - looking toward airport during flooding (photo by Jerry Steiger, WSO Nome) Left: Shishmaref - abandoned residence long coast; Right: Kivalina - arial view. (photos by John Lingaas, WSO Fairbanks)
7. Sea Level data sourcesSea level data sets were collected by the Arctic and Antarctic Research Institute for 71 stations (see station numbers) located in the Barents and Siberian Seas. The time series of sea level variability generally cover the period between 1948 and 2000 but temporal coverage differs significantly from station to station. Red denotes stations with the most complete datasets.
8. Some data are available for the Beaufort Sea region but the data spatial and temporal coverage is not good enough for purposes of sea level statistics. Therefore, many aspects of storm surge characteristics in the Canada basin and the Beaufort Sea have been done based on numerical modeling.
9. AlaskaSiberiaTypical trajectory of atmospheric cyclones generating significant flooding events along Beaufort Sea shoreline
10. This figure shows distribution of maximum sea surface heights measured by coastal stations in the Siberian sector of the Arctic Ocean. The absolute maximum was observed in the southern part of the Laptev Sea.
11. This figure shows distribution of minimum sea surface heights measured by coastal stations in the Siberian sector of the Arctic Ocean. The absolute minimum was observed in the southern part of the Laptev Sea.
12. Magnitude of the observed variability of sea surface heights from observations in the Siberian sector of the Arctic Ocean. Maximum magnitude reaches 5.5 meters in the southern Laptev Sea
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14. Model calibration and validationDates Experiment conditionsObserved SSH, cmSimulated, SSH cmMean absolute error, cmMSR error,Cm^2Correlation coefficient1-11 01.71No ice76 141 24.929.20.86With ice76 7313.913.90.8913-1612.84No ice109178 32.240.40.89With ice10912920.025.10.859-1909.90No ice11713313.617.40.94With ice11713113.316.90.94500400300200100SSH, cmSolid – observationsDashed - simulatedThe Laptev Sea, station Tiksi:
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19. Sea level variability at the Beaufort Sea stations in August, 2000.Dotted – observations, solid NCAR’s SLP, and dashed – ECMWF’s SLP
20. Simulated SSH under winds of 15 m/sPrescribed 15 m wind directions
21. Simulated SSH under wind of 25 m/sPrescribed 25 m wind directions
22. SSH and currents predicted for 11/12/04
23. Heights of extreme storm surges in the Kara SeaYears with prevailing cyclonic (blue) and anticyclonic (yellow) circulation regimesHigh NAOHigh NAOLow NAOLow NAO
24. Heights of extreme storm surges in the Laptev SeaLow NAOLow NAOHigh NAOHigh NAOYears with prevailing cyclonic (blue) and anticyclonic (yellow) circulation regimes
25. Heights of extreme storm surges in the East-Siberian SeaHigh NAOLow NAO
26. Sea Ice Drift Data Soviet North Pole Stations (1937, 1950, 1954- 1990) NP 1-2, 4, 6-20 from NSIDC NP 3, 5, 21-31 from AARI Int. Geophysical Year Ice Camps (1957-1959) T-3 (Fletcher Ice Island) (1959-1970) ARLIS-II Ice Camp (1961-1965) British Transarctic Expedition (1968-1969) AIDJEX buoys (1972) Int. Arctic Buoy Program (IABP) (1979- present)
27. ICE DRIFT SPEED OBSERVATIONS UPTO 1972ICE DRIFT COLLECTED FROM THE GREY SHADED AREA
28. ICE DRIFT IN WINTER AND SUMMEROBSERVATIONS ARE EVERY 12 HRS, EXCEPT NP 3,5, 21-31 ARE EVERY 4 HRS WINTERSUMMER
29. TRENDS IN THE WIND STRESSNCEP/NCAR 1948-2006T-test values contoured for values > 2 (95%and higher level)
30. NCEP/NCAR SLP VARIANCE AND TRENDS 1948-2006 Daily SLP high-pass filtered with 30-day Papoulis filter to distinguish storms<- Linear trend mb / 58 yrArea average SLPA variance (north of 75N) in a sliding 5 year window
31. Long term trend towards higher ice drift fluctuations over the last 60 years supports other findings of increased storm activity at the high latitudes (Serreze et al. 2002)Upward trend in wind stress fluctuations concentrated over the Transpolar Drift Stream Potential impact on mixing in the upper ocean and on the halocline BUT -- are coupled climate models capable of simulating the increased Arctic storm activity of the warming world and ensuing feedbacks e.g. from halocline erosion ?
32. In the Arctic, the large-scale atmospheric circulation changes from season to season and alternates between cyclonic (summer) and anticyclonic circulation (winter conditions). High atmospheric pressure prevails over the Beaufort Gyre in winter and low pressure dominates in summerSeasonal changes and effects A. Winter SLP and wind B. Summer SLP and wind C. Winter buoy drift D. Summer buoy drift
33. 17,300 km345,000 km312,200 km32,800 km33,800 km32,800 km33,400 km34,000 km377 km3The oceanic Beaufort Gyre (BG) of the Canadian Basin is the largest freshwater reservoir in the Arctic Ocean (Aagaard and Carmack, 1989). Freshwater content: calculated relative to salinity 34.80 according to Aagaard K. and E. Carmack, JGR, vol. 94, C10, 14,495-14,498,1989
34. Salinity distribution in the upper 200-meter layerGreenlandBarents SeaKaraSeaEast-Siberian SeaAlaskaChukchi SeaLaptev SeaBeaufort SeaBeaufort GyreThe upper 400 m low salinity waters are surrounded by relatively more saline waters that rotate anticyclonically following contours of geostrophically balanced dynamical height (Coachman and Aagaard, 1974).
35. Top: Left: water salinity (S) at 10 mRight: S sectionBottom:Left: water salinity (S) at 100 mRight: Dynamic topographyData source: EWG Atlas, 1997, 1998
36. Top: Left: water salinity (S) at 10 mRight: S sectionBottom:Left: water salinity (S) at 100 mRight: Dynamic topographyData source: EWG Atlas, 1997, 1998
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38. Interannual and decadal variability
39. Historically, there were at least two different views on the origin of the Arctic Ocean circulation: Russian scientists, Shokal’skii (1940), Gordienko and Karelin (1945), and Buinitskii (1951, 1958), assumed that the surface circulation in the Arctic Ocean was driven mainly by inflow of Atlantic Water through Fram Strait. They argued that incoming water caused an outflow of surface water and ice along the shorter routes to the Greenland Sea. Data from vessel drifts in the Eurasian sub-basin indicated surface water motion from the Eurasian sub-basin to Fram Strait. Nansen (1902), who discovered waters of Atlantic origin in the Arctic Ocean, claimed that water exchange between the Arctic Ocean and the Greenland and Norwegian Seas was caused by differences in water temperature and salinity, e.g. Nansen assumed that the thermohaline circulation is the major factor forcing observed dynamics of the Arctic Ocean.
40. Historically, there were at least two different views on the origin of the Arctic Ocean circulation: The experiments showed winds to be a principal factor in forming the system of permanent currents in the Arctic Basin such that winds of the Arctic anticyclone generate anticyclonic currents in the Canada basin. The wind system in the Nansen and Amundsen basins, at the periphery of the Arctic anticyclone induces a wide Trans-Arctic current originating in the Chukchi Sea and emerging through Fram Strait. But a physical model of inflow of water to the Arctic Basin from the GIN seas as the only driving factor did not produce a circulation pattern similar to that actually observed. Other views on the nature of the circulation were subsequently proposed by Zubov and Somov (1940), Shuleikin (1941), Shirshov (1944), Treshnikov (1959) where Atlantic Water inflow into the Arctic Basin was caused by wind-forced outflow of surface water to the Greenland Sea. This was supported by experiments undertaken by Gudkovich and Nikiforov (1965) with a hydraulic model simulating the system of wind-driven currents in the Arctic Ocean.
41. Wind-driven circulation regime: Anticyclonic Comparing charts of the SLP distribution with ice drift charts, Gudkovich (1961) concluded that two types of surface water circulation in the Arctic (type A and type B) could be distinguished. Type A circulation usually occurs for years when the winter polar high is prominent. The region of anti-cyclonic surface circulation increases and the region of cyclonic circulation is weakened and reduced in size. The principal Trans-Arctic current occurs along the northern margins of the arctic seas and increases movement of ice into the Greenland Sea. Favorable conditions are created for the movement of ice from the Laptev, East-Siberian, and Chukchi Seas. This circulation pattern generally forms favorable ice conditions on the Northern Sea Route.
42. Wind-driven circulation regime: Cyclonic The B circulation pattern, according to Gudkovich (1961), is characterized by weakening and contraction of the BG circulation system and expansion of the region of cyclonic water circulation. The Trans-Arctic current is reduced, and shifted toward America leading to the development of cyclonic water circulation in the East-Siberian and Chukchi Seas. Sokolov (1962) emphasized that types A and B circulation do not encompass the entire diversity of changes in water circulation pattern of the Arctic Basin. At that time they had data suggesting that the shift of types is cyclic with a period of 3-5 years, and the transition from one cycle to another usually occurs gradually.
43. Proshutinsky and Johnson (1995, 1997), Proshutinsky et al. (1999, 2000) analyzed wind-driven circulation of the Arctic Ocean and re-invented Gudkovich’s idea summarizing model data and atmospheric pressure fields over the Arctic Ocean. They have shown that wind-driven ice motion and upper ocean circulation alternate between anticyclonic and cyclonic states. Shifts between regimes occur at 5- to 7-year intervals, resulting in a 10- to 15-year period. The anticyclonic circulation regime (ACCR) has been observed in the model results for 1946 - 1952, 1958 -1962, 1972 - 1979, and 1984 - 1988, 1997-present. The cyclonic circulation regime (CCR) prevailed during 1953 -1957, 1963 - 1971, 1980 - 1983, and 1989 - 1996.
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75. Circulation regimes1. Circulation2. Ice conditions3.Pacific water4. Atlantic water5. Upwelling/downwelling6. Heat fluxes7. River runoff8. Precipitation regime9. Clouds10. Surface albedo11. Ocean and atmosphere boundary layers (stratification)
76. Circulation regimesNegative index Positive indexSea ice is accumulated in the ocean and is getting thicker Sea ice is removed from the ocean and is getting thinner Arctic is cold and dryArctic is warm and wet
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79. Concluding remarksAtmospheric, ice, and oceanic observational data and the results of numericalexperiments with a coupled sea-ice-ocean model provide evidence that during the ACCR the arctic atmospheric pressure is higher and wind speed is lower compared with the CCR. A mean arctic ACCR winter is colder than a mean CCR winter. When the CCR dominates, precipitation increases over the ocean and decreases over the land. During the CCR, summer wind divergence effectively produces numerous sea-ice openings in the central Arctic Ocean. Repetition of this cyclonic process over several years results in overall thinner ice in the central Arctic, compared with that during the ACCR. Under the CCR, more ice-free summer areas lead to an accumulation of additional heat in the upper ocean, resulting in longer periods of ice melt, increases in fresher water content, and thinner ice. In CCR years both dynamical and thermodynamic factors cause excess ice and freshwater transport through Fram Strait from the Arctic into the Greenland Sea; the water balance in the Arctic Ocean is maintained via an increased inflow of the Atlantic water over the Barents Sea into the Nansen Basin.