A Composite Perspective of the Extratropical Flow Response to Recurving Western North Pacific Tropical Cyclones

TLDR: In this paper, the authors investigated the composite extratropical flow response to recurving western North Pacific tropical cyclones (WNP TCs), and the dependence of this response on the strength of the TC-extrropical interaction as defined by the negative potential vorticity advection (PV) by the irrotational wind associated with the TC.

Abstract: This study investigates the composite extratropical flow response to recurving western North Pacific tropical cyclones (WNP TCs), and the dependence of this response on the strength of the TC–extratropical flow interaction as defined by the negative potential vorticity advection (PV) by the irrotational wind associated with the TC. The 2.5° NCEP–NCAR reanalysis is used to construct composite analyses of all 1979–2009 recurving WNP TCs and of subsets that undergo strong and weak TC–extratropical flow interactions.Findings indicate that recurving WNP TCs are associated with the amplification of a preexisting Rossby wave train (RWT) that disperses downstream and modifies the large-scale flow pattern over North America. This RWT affects approximately 240° of longitude and persists for approximately 10 days. Recurving TCs associated with strong TC–extratropical flow interactions are associated with a stronger extratropical flow response than those associated with weak TC–extratropical flow interactions...

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TABLE 1. The means and standard deviations of the latitudinal and longitudinal distance of the maximum TC–extratropical flow interaction point from the recurving WNP TC at the time of maximum interaction for strong (N 5 54) and weak (N 5 54) interactions, and the differences between themeans of the strong and weak interactions (degrees). The confidence levels for the significance of the differences based on a two-sided Student’s t test are given in parentheses.

FIG. 2. Points ofmaximumTC–extratropical flow interaction plotted relative to the recurving WNPTC at the time ofmaximum interaction for strong TC–extratropical flow interactions (red diamonds; N 5 54), weak TC–extratropical flow interactions (blue circles; N 5 54), and interactions classified as neither strong nor weak (purple triangles;N5 164). The large diamond and circle represent the mean points of maximum TC–extratropical flow interaction for strong and weak interactions, respectively.

FIG. 8. Interaction-relative composite analyses showing (a) strong (N 5 54) and (b) weak (N 5 54) TC– extratropical flow interactions at the time ofmaximum interaction.Analyses show 500-hPa ascent (dashed green, every 23 1023 hPa s21, negative values only), total-column precipitable water (shaded according to grayscale, mm), 200-hPa PV (blue, every 1 PVU), irrotational wind (vectors,.2m s21; purple vectors,.8m s21), negative PV advection by the irrotational wind (dashed red, every 2 PVUday21 starting at22 PVUday21), and total wind speed (shaded according to color bar, m s21). The star denotes the point of maximum interaction. The TC symbol denotes the composite TC position.

FIG. 11. Interaction-relative composite analyses for (a),(c),(e) strong (N5 54) and (b),(d),(f) weak (N5 54) TC– extratropical flow interactions at the time of maximum interaction. Analyses show 250–150-hPa layer-averaged PV advection (shaded according to color bar, PVUday21), PV (contours, every 2 PVU), and wind (vectors, m s21). The TC symbol denotes the composite TC position. In (a),(b) the total and (c),(d) the nondivergent wind are used to compute PV advection and are plotted for values .18m s21, whereas in (e),(f), the irrotational wind is used to compute PV advection and is plotted for values .2m s21.

FIG. 3. Recurvature-relative composite analyses of all recurving WNP TCs (N 5 292) at 36-h intervals for (a)–(g) T 2 72 to T1 144 h. Analyses show 250-hPa meridional wind anomalies (shaded according to the color bar, m s21; enclosed by black contours where significant at the 99% confidence level) and PV (blue, every 1 PVU). The TC symbol denotes the composite TC position, which is plotted for (a)–(f) T 2 72 to T 1 108 h. Solid and dashed black lines denote subjectively identified 250-hPa ridges and troughs, respectively.

FIG. 7. Interaction-relative composite analyses of strong TC– extratropical flow interactions (N 5 54) for (a) T 2 48, (b) T 1 0, and (c) T 1 48 h. Analyses show total-column precipitable water (shaded according to grayscale,mm), sea level pressure (black, every 4 hPa), 1000–500-hPa thickness (dashed red, except dashed blue for values,540 dam; every 6 dam), and 250-hPa wind speed (solid blue, every 10m s21 starting at 20m s21). The TC symbol denotes the composite TC position, which is plotted for (a) T 2 48 and (b) T 1 0 h. The ‘‘L’’ symbol denotes the location and minimum sea level pressure (hPa) of a downstream surface cyclone.

Frequently asked questions

Q1. What are the contributions mentioned in the paper "A composite perspective of the extratropical flow response to recurving western north pacific tropical cyclones" ?

This study investigates the composite extratropical flow response to recurving western North Pacific tropical cyclones ( WNP TCs ), and the dependence of this response on the strength of the TC–extratropical flow interaction as defined by the negative potential vorticity advection ( PV ) by the irrotational wind associated with the TC. 

Q2. What are the future works mentioned in the paper "A composite perspective of the extratropical flow response to recurving western north pacific tropical cyclones" ?

The findings of this study suggest a variety of avenues for future research. For example, the onset of a trough over centralNorthAmerica following WNP TC recurvature indicated by the composite analysis of all recurving WNP TCs suggests a possible connection between recurving TCs and outbreaks of severe convection over the U. S. central plains. Although this study did not directly address predictability, it provides a potential framework in which to evaluate numerical model forecast error and uncertainty associated with the TC–extratropical flow interaction for recurving TC cases and other weather phenomena associated with divergent outflow that may impinge strongly upon the PV waveguide [ e. Many studies suggest that large numerical model forecast errors may result from a failure of the numerical model to adequately capture diabatically driven ridge amplification ( e. g., Davies and Didone 2013 ; Gray et al. 2014 ), whether associated with recurving TCs ( e. g., Henderson et al. 1999 ; Torn 2010 ), mesoscale convective systems ( e. g., Dickinson et al. 1997 ; Rodwell et al. 2013 ), or warm conveyor belts of explosively deepening extratropical cyclones ( e. g., Doyle et al. 2014 ).