Report

Climate Implications of Frontal Scale Air-Sea Interaction (August 5-7, 2013 / NCAR) Northern Hemisphere Atmospheric Transient Eddy Fluxes and their Co-variability with the Gulf Stream and Kuroshio-Oyashio Extensions Young-Oh Kwon and Terrence M. Joyce (Woods Hole Oceanographic Institution) Support from the NASA Physical Oceanography Program is gratefully acknowledged. Meridional heat transport by ocean and atmosphere Trenberth and Caron (2001) Large heat is handed over to the atmosphere from ocean near the western boundary current regions Data: atmospheric transient eddy heat fluxes • Source: NASA MERRA (Modern Era Retrospective-analysis for Research and Applications) • Period and temporal resolution: Daily mean for 1979-2009 (31 years) • Season: Winter (JFM: all the analysis shown here is for the winter only!) • Spatial domain and resolution: 1/2lat 2/3long in the Northern Hemisphere only. • Levels: Sea-level, 850 hPa, 500 hPa, 250 hPa, 200 hPa, and 100 hPa • Variables: Winds (u, v), temperature (T), and specific humidity (q) Calculation: atmospheric transient eddy heat fluxes (1) Two time scales: synoptic (2-8days) and intra-seasonal (8days-3months) Daily variables for each winter (e.g. JFM 1979) at each level v v v ' v ' s T T T ' T ' s where i a : individual JFM mean , a ' : synoptic ( 2 8 day ) transient anomaly s i a ' : intraseaso nal ( 8 day 3 month ) transient anomaly i (2) Covariances: for each winter (JFM) and for the two time scales: vT v T v ' T ' v ' T ' v ' T ' v ' T ' s s Synoptic transient eddy flux i i s i i s Intra-seasonal transient eddy flux (3) 31-yr time-series: sensible (<vT>) and latent (<vq>) for each time scale. Climatological mean and interannual standard deviation. Variables examined (1) Northward heat flux by transient eddies (Vertically integrated from the surface to 50 hPa) 1 psurface (C p < v¢T ¢ > +L < v¢q¢ >)dp ò g 50hPa = [unit: W m-1] (2) Northward heat transport by transient eddies (Vertically and zonally integrated) = ò 360 0 1 psurface [ ò (Cp < v¢T ¢ > +L < v¢q¢ >)dp] dx g 50hPa [unit: PW] (3) Lateral divergence of vertically integrated eddy heat fluxes = 1 g ¶u¢T ¢ ¶v¢T ¢ ¶u¢q¢ ¶v¢q¢ -2] [W m (C < + > +L < + > )dp ò 50hPa p ¶x ¶y ¶x ¶y psurface JFM mean northward heat flux by transient eddies (1) (sensible+latent, vertically integrated from surface to 50 hPa) Synoptic (2-8 days) Intra-seasonal (8-90 days) Contour Interval : 2 107 W m-1 Mean WBC positions: Gulf Stream / Kuroshio Extension / Oyashio Extension (from Joyce et al. 2009 & Frankignoul et al. 2011) Vertical structures of northward heat flux by transient eddies (Average over a zonal band in 30-50N) Zonally integrated northward heat transport by transient eddies (2) (Climatological JFM mean and interannual standard deviation) Lateral divergence of transient eddy heat fluxes (3)(Vertically integrated climatological mean for JFM) 1 g Synoptic ò psurface 50hPa (C p < ¶u¢T ¢ ¶v¢T ¢ ¶u¢q¢ ¶v¢q¢ + > +L < + >)dp ¶x ¶y ¶x ¶y Intra-seasonal Synoptic+Intra-seasonal Black contours: SST isotherms for 6, 8, 10C Interannual standard deviation of JFM lateral divergence of heat flux by transient eddies (3) Synoptic Intra-seasonal Synoptic+Intra-seasonal Northward heat transport by synoptic transient eddies regressed on the GSI, KEI, OEI GSI KEI OEI Bjerknes Compensation or Coupled Oscillation? Summary • Synoptic and intra-seasonal time scales contribute comparably to the zonally integrated northward heat transport by transient eddies, though with very distinct spatial patterns. • Lateral divergence of transient eddy heat fluxes : synoptic+intraseasonal mean distribution and interannual variability are remarkably coincident with the ocean fronts. • Greater than 50% of the interannual variance of the winter northward heat flux and transport by transient eddies in the synoptic bands are correlated with interannual variability for the positions of the KE, OE and GS as the forcing as well as the response to the ocean front changes. Thank you Regression of intra-seasonal daily 850 hPa variables on the Pacific-North America (PNA) teleconnection index v regression (C.I.= 0.5 m s-1) T regression (C.I.=0.5 K) = v regression T regression (C.I.=0.5 106 W m-2) H regression (C.I. 10m / gray: negative ) Red: positive regressions / Blue: negative regressions Regression of intra-seasonal daily 850 hPa variables on the Arctic Oscillation (AO) index v regression (C.I.= 0.5 m s-1) T regression (C.I.=0.5 K) = v regression T regression (C.I.=0.5 106 W m-2) H regression (C.I. 10m / gray: negative ) Red: positive regressions / Blue: negative regressions Indices for the meridional position of the Gulf Stream, Kuroshio Extension & Oyashio Extension Gulf Stream Index: 15C at 200 m (1954-2006; Joyce et al. 2000) Kuroshio Extension Index: 14C at 200 m (1980-2006; Joyce et al. 2009) Oyashio Extension Index: maximum dSST/dy based on 1/4 SST (1983-2007; Frankignoul et al. 2011) Interannual standard deviation of JFM northward heat fluxes by transient eddies (1) Synoptic Intra-seasonal Mean contour interval: 4 107 W m-1