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  • Author or Editor: Na Wen x
  • Journal of Applied Meteorology and Climatology x
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Na Wen, Zhengyu Liu, and Qinyu Liu

Abstract

Most previous studies have proven the local negative heat flux feedback (the surface heat flux response to SST anomalies) in the midlatitude areas. However, it is uncertain whether a nonlocal heat flux feedback can be observed. In this paper, the generalized equilibrium feedback assessment (GEFA) method is employed to examine the full surface turbulent heat flux response to SST in the North Atlantic Ocean using NCEP–NCAR reanalysis data. The results not only confirm the dominant local negative feedback, but also indicate a robust nonlocal positive feedback of the Gulf Stream Extension (GSE) SST to the downstream heat flux in the subpolar region. This nonlocal feedback presents a strong seasonality, with response magnitudes of in winter and in summer. Further study indicates that the nonlocal effect is initiated by the adjustments of the downstream surface wind to the GSE SST anomalies.

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Dian Wen, Ying Li, Da-Lin Zhang, Lin Xue, and Na Wei

Abstract

A statistical analysis of tropical upper-tropospheric trough (TUTT) cells over the western North Pacific Ocean (WNP) during 2006 to 2015 is performed using the NCEP Final reanalysis. A total of 369 TUTT-cell events or 6836 TUTT cells are identified, with a peak frequency in July. Most TUTT cells form to the east of 150°E and then move southwestward with a mean speed of 6.6 m s−1 and a mean life span of 4.4 days. About 75% of the TUTT cells have radii of <500 km with 200-hPa central heights of <1239.4 dam. In general, TUTT cells exhibit negative height anomalies above 450 hPa, with their peak amplitudes at 200 hPa, pronounced cold anomalies in the 650–200-hPa layer, and significant cyclonic vorticity in the 550–125-hPa layer. A comparison of the composite TUTT cells among the eastern, central, and western WNP areas shows the generation of an intense cold-cored vortex as a result of the southward penetration of a midlatitude trough into a climatological TUTT over the eastern WNP region. The TUTT cell with pronounced rotation is cut off from the midlatitude westerlies after moving to the central WNP region, where it enters its mature phase, under the influence of northeasterly flow. The TUTT cell weakens in rotation and shrinks in size, diminishing within the TUTT after arriving at the western WNP region. Results suggest that, although most TUTT cells may diminish before reaching the western WNP, their vertical influences may extend to the surface layer and last longer than their signals at 200 hPa.

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