Ocean vector winds are important for ocean-atmosphere interaction and modes of climate variability. Similarly winds play an important role in spatial patterns of climate change. Maintaining a long, consistent, well-calibrated wind dataset is critical for climate change research. FIGURE 7.27 In diagram (a), under ordinary conditions higher pressure over the southeastern Pacific and lower pressure near Indonesia produce easterly trade winds along the equator. These winds promote upwelling and cooler ocean water in the eastern Pacific, while warmer water prevails in the western Pacific. The trades are part of a circulation that typically finds rising air and heavy rain over the western Pacific and sinking air and generally dry weather over the eastern Pacific. When the trades are exceptionally strong, water along the equator in the eastern Pacific becomes quite cool. This cool event is called La Niña. During El Niño conditions—diagram (b)—atmospheric pressure decreases over the eastern Pacific and rises over the western Pacific. This change in pressure causes the trades to weaken or reverse direction. This situation enhances the countercurrent that carries warm water from the west over a vast region of the eastern tropical Pacific. The thermocline, which separates the warm water of the upper ocean from the cold water below, changes as the ocean conditions change from non-El Niño to El Niño. 1

Surface wind trend based on ship obs. Increased ship size & anemometer height t Spurious increase in measured wind Visual observations of wind wave height  correct wind biases Tokinaga, H., and S.-P. Xie, 2011: Wave and Anemometer-based Sea-surface Wind (WASWind) for climate change analysis. J. Climate, 24, 267-285.

SST Uncorrected ICOADS wind (oC/60yr) (ms-1/60yr) Trend for 1950 - 2009 SST (oC/60yr) Uncorrected ICOADS wind (ms-1/60yr) 3

SST WASWind (oC/60yr) (ms-1/60yr) Trend for 1950 - 2009 Tokinaga, H., and S.-P. Xie, 2011: Weakening of the equatorial Atlantic cold tongue over the past six decades. Nature Geosci., 4, 222-226 4

Interannual variability of high-wind occurrence over ocean Shang-Ping Xie1 X. Cheng2,1, T. Sampe3, H. Tokinaga1 & Y. Du2 1 IPRC, University of Hawaii 2 South China Sea Institute of Oceanology, China 3 Aizu University, Japan

QuikSCAT wind velocity on 0.25o grid (Sept 1999 - Nov 2009) Data & Methods QuikSCAT wind velocity on 0.25o grid (Sept 1999 - Nov 2009) SSM/I wind speed on 0.25o grid (1988-2009) Map high-wind ( >20 m/s) frequency (HWF) Sampe, T., and S.-P. Xie, 2007: Mapping high sea winds from space: A global climatology. Bull. Amer. Meteor. Soc., 88, 1965-1978. Cheng, X., S.-P. Xie, H. Tokinaga, and Y. Du, 2011: Interannual variability of high-wind occurrence over the North Atlantic. J. Climate, revised.

Dec-Jan-Feb high-wind frequency (%) frequent in wintertime midlatitudes (storm track region) winter summer This figure show the high-wind freq in percentage in boreal winter, Dec to Feb. Clearly high winds are frequent in wintertime midlatitudes in the storm track region, and far less in most of the tropics.

North Atlantic storm track South tip of Greenland In this map, you’ll see the freq. exhibits small-scale features. small patches of frequent high winds, associated with orography (around south-east coast of Greenland, Norway, to the south of France --- known as mistral) * Strong winds over these two regions cause strong cooling of sea water and they are regarded to be involved in deep convection in the ocean. (2) High-wind freq. is strongly influenced by SST. The freq. is less than 6% near the east coast, more over warm the Gulf Stream here. And this meandering of SST contour corresponds remarkably well to the variability of high-wind frequency. This bend of the Gulf Stream makes the gap in high wind frequency there. Color: High wind frequency (%) Contour: SST Orography (Greenland, Norway, France-“mistral”) SST frontal effects (more frequent over warmer waters)

North Atlantic 2%~17% Color: High wind frequency (%) Contour: SST In this map, you’ll see the freq. exhibits small-scale features. small patches of frequent high winds, associated with orography (around south-east coast of Greenland, Norway, to the south of France --- known as mistral) * Strong winds over these two regions cause strong cooling of sea water and they are regarded to be involved in deep convection in the ocean. (2) High-wind freq. is strongly influenced by SST. The freq. is less than 6% near the east coast, more over warm the Gulf Stream here. And this meandering of SST contour corresponds remarkably well to the variability of high-wind frequency. This bend of the Gulf Stream makes the gap in high wind frequency there. Color: High wind frequency (%) Contour: SST Orography (Greenland, Norway, France-“mistral”) SST frontal effects (more frequent over warmer waters)

Momentum-mixing mechanism low static stability over warm waters  enhanced mixing  increased surface wind u u cold warm The SST influence on surface winds can be explained by momentum-mixing mechanism. [explanation] December 2010 Special Issue on the Future of Oceanography from Space

Interannual variability in high-wind frequency (HWF) DJF 1988-2009 High variance A, B & C: Gulf Stream front D: Cape Farewell E: Open ocean band

North Atlantic Oscillation (NAO) effect DJF high wind frequency anomaly (color) and wind anomaly (vector) regressed upon the NAO Index, superimposed on correlation between storm-track intensity and NAO index (black contours).

Interannual variations off Cape Farewell Tip jet Reversed tip jet Westerly & easterly HWF; NAO Winter high-wind occurrence (%) associated with (a) westerly and (b) easterly wind 13

SST front effect DJF HWF, SST-SAT, and cross-frontal advection HWF and 10-m wind b/w positive and negative phases of cross-front advection Correlation with the Eastern Atlantic pattern = 0.64

HWF trend NAO Local trend of high-wind frequency (color) and 10-m wind (vector) over 1988-2009, superimposed on climatological seasonal means of AVHRR SST.

Factors for high-wind occurrence Climatology Storm tracks Sea surface temperature fronts Coastal orography Interannual variability North Atlantic Oscillation East Atlantic pattern SST fronts and orography Rough Sea by Claude Oscar Monet 1881

Jun-Jul-Aug Tropical cyclones do not emerge in climatology Typhoon summer winter Typhoon This shows the frequency in boreal summer. Again high winds are frequent in the storm track region in the winter hemisphere. High winds associated with tropical cyclones are slightly seen in the western Pacific, but far less in number compared to wintertime midlatitudes. Color: High wind frequency (%)

Enhanced eddy-kinetic energy  Increased instability  Cross-frontal advection (black contours) Winter climatology

Interannual variations off Cape Farewell Tip jet Reversed tip jet Interannual standard deviation of winter HWF (unit: %) associated with (a) westerly and (b) easterly wind From Moore and Renfrew, 2005 Westerly & easterly HWF; NAO