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Hyodae Seo, Arthur J. Miller, and Joel R. Norris

flux, stability of the MABL, and downward turbulent momentum transfer. The coherent wind response to mesoscale SST has been broadly observed in the global oceans (e.g., Park and Cornillon 2002 ; Xie 2004 ; Chelton and Xie 2010 ; O’Neill et al. 2010 , 2012 ; Frenger et al. 2013 ; among many others). Using this positive correlation between T e and W e , Chelton et al. (2004) developed an empirical relation that the spatial derivative of wind (vorticity or divergence) is linearly

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Thomas Kilpatrick, Niklas Schneider, and Bo Qiu

regions with alongfront surface winds (red area) and strong wind stress divergence is found in regions with cross-front surface winds (blue area). The two physical mechanisms typically cited for this oceanic influence on the MABL are the “vertical mixing mechanism” ( Wallace et al. 1989 ; Hayes et al. 1989 ) and the “pressure adjustment mechanism” ( Lindzen and Nigam 1987 ). According to the vertical mixing mechanism, a destabilizing air–sea heat flux over warm SST increases the turbulent mixing and

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Satoru Okajima, Hisashi Nakamura, Kazuaki Nishii, Takafumi Miyasaka, Akira Kuwano-Yoshida, Bunmei Taguchi, Masato Mori, and Yu Kosaka

studies, because of their rather coarse horizontal resolution. Tanimoto et al. (2003) and Taguchi et al. (2009 , 2012 ) have found that, unlike in most of the North Pacific basin where surface heat flux anomalies due to changes in near-surface wind, air temperature, and humidity force SST anomalies, warm (cold) SST anomalies along the SAFZ tend to enhance (reduce) heat release into the atmosphere, which can be regarded as thermodynamic forcing by the SAFZ variability on the overlying atmosphere

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James F. Booth, Young-Oh Kwon, Stanley Ko, R. Justin Small, and Rym Msadek

a reasonable proxy for climatological activity of extratropical cyclones ( Hoskins and Hodges 2002 ), and their maxima occur over the oceans, in the vicinity of ocean western boundary currents (WBCs) and their extensions (e.g., Fig. 1b ). WBCs are unique regions of air–sea coupling: ocean currents in these regions generate strong ocean heat flux convergence, which can dictate spatial and temporal variability in air–sea fluxes [see reviews by Kwon et al. (2010) and Kelly et al. (2010) ]. The

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Atsuhiko Isobe, Shin’ichiro Kako, and Shinsuke Iwasaki

, in line with Qiu and Kelly (1993) . Also, Q denotes net heat flux through the sea surface, and this was computed using the bulk formulas in Kondo (1975) with modeled SST, gridded wind speeds using daily data of the Advanced Scatterometer (ASCAT; Kako et al. 2011 ; downloaded from http://mepl1.riam.kyushu-u.ac.jp/~kako/ASCAT/NetCDF/ ), and other atmospheric properties furnished by the National Centers for Environmental Prediction (NCEP)–National Center for Atmospheric Research (NCAR

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Kohei Takatama, Shoshiro Minobe, Masaru Inatsu, and R. Justin Small

closure scheme for vertical diffusion and a modified Monin–Obukhov scheme for turbulent fluxes at the ocean surface. We conducted two experiments: a standard experiment with a 0.5° × 0.5° horizontal grid and a high-resolution experiment with a 0.25° × 0.25° horizontal grid. For both the experiments, the vertical layers are 28 sigma layers. The model domain fully covers the western North Atlantic (5°–65°N, 100°–20°W). We used the National Centers for Environmental Prediction (NCEP) Reanalysis-1 with a

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Niklas Schneider and Bo Qiu

winds, frontally induced air–sea fluxes of heat, and their impact on the momentum budget. In the process, we provide a unified framework for all processes put forth in the context of frontal air–sea interaction, cast frontal air–sea interaction as a classical Rossby adjustment problem, and explore its scale and parameter dependence. Two mechanisms are invoked to explain the response of boundary layer winds and surface stresses to fronts of SST: adjustments of vertical mixing and of baroclinic

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Hyodae Seo, Young-Oh Kwon, Terrence M. Joyce, and Caroline C. Ummenhofer

1. Introduction Air–sea interaction over the western boundary currents is one of the fundamental processes of extratropical climate variability ( Kwon et al. 2010 ; Kelly et al. 2010 ). In the North Atlantic, the largest surface heat flux and its strongest interannual variability are found over the Gulf Stream (GS). The variations in the location and strength of the GS modify the cyclogenesis and the North Atlantic storm track ( Cione et al. 1993 ; Booth et al. 2012 ; Small et al. 2014

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Yuta Ando, Masayo Ogi, and Yoshihiro Tachibana

studies. Fig . 1. The 5-day running means of (a) the AO index as defined by Ogi et al. (2004) , (b) the WP index, (c) SAT anomalies over Japan from AMeDAS station data (°C), (d) air temperature anomalies (°C) as a function of time and pressure level, (e) the heat flux anomaly index (W m −2 ), and (f) SST anomalies (°C). In (d)–(f) areal averages over the Sea of Japan (36.0°–43.5°N, 130.0°–140.0°E; inside the orange box in Fig. 4 ) are shown. Daily anomalies were calculated relative to daily climatic

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Bunmei Taguchi, Niklas Schneider, Masami Nonaka, and Hideharu Sasaki

; Nonaka et al. 2008 ; Taguchi et al. 2010 ; Sasaki and Schneider 2011 ). Besides the major oceanic datasets, we use an atmospheric reanalysis and an oceanic index: the Japanese 55-year Reanalysis (JRA-55; Kobayashi et al. 2015 ) for surface sensible and latent heat fluxes, and the Oyashio Extension index (OEI; Frankignoul et al. 2011 ). The OEI represents meridional shift of the Oyashio Extension (or SAFZ) and is the first principal component of the Oyashio Extension position in latitude for the

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