A Composite Perspective of the Extratropical Flow Response to Recurving Western North Pacific Tropical Cyclones
Summary (1 min read)
1. Introduction
- Tropical cyclones (TCs) undergoing extratropical transition (ET), a change from a warm-core, axisymmetric system to a cold-core, asymmetric system (e.g., Klein et al.
- On average, the North Pacific flow pattern becomes significantly amplified for approximately four days following western North Pacific (WNP) TC recurvature (Archambault et al. 2013).
- The large-scale extratropical flow response to TC recurvature also depends on the interaction of the TC with disturbances in the extratropical flow.
2. Methodology
- A. Recurvature-relative compositing methodology A point of maximum interaction is not identified for 20 of the 292 recurving TC cases because the negative PVadvection by the irrotational wind associated with the TC never exceeds an arbitrary threshold of 1PVUday21 (1PVU 5 106Kkg21m2 s21).
- For the remaining 272 recurving TC cases, those associated with an interaction metric in the top quintile are categorized as strong interactions (N5 54), whereas those associatedwith an interaction in the bottom quintile are categorized as weak interactions (N 5 54).
- The climatology is produced from 1979–2009 21-day running means of interactive-relative 2.58 NCEP–NCAR reanalysis fields.
- The Q vector describes the time rate of change of the vector horizontal potential temperature gradient due to the nondivergent wind.
3. Results
- A. Extratropical flow response to recurving TCs Recurvature-relative composite analyses of the upperlevel flow for all 1979–2009 recurving WNP TCs are displayed for T 2 72 to T 1 144h relative to recurvature time at 36-h intervals (Fig. 3).
- Between T 1 36 and T 1 144h (Figs. 3d–g), the RWT disperses across the North Pacific and alters the flow pattern over North America.
- Subtle differences exist in the configurations of the extratropical flow pattern relative to the recurving TC for strong and weak TC–extratropical flow interactions at the time of maximum interaction.
- During weak interactions (Fig. 9d), the patterns ofQs vectors and Qs-vector divergence are similar to the strong interaction composite (Fig. 9c), but less pronounced.
- In addition, the negative PV advection by the irrotational wind within the ridge on its western side promotes an amplification of the ridge.
4. Discussion
- The tendency for a preexisting RWT to amplify and migrate downstream in association with the recurvature of a WNP TC corroborates findings of a recent climatology (Archambault et al. 2013), case studies (e.g., Harr and Dea 2009; Reynolds et al.
- The tendency for strong interactions to exhibit stronger ascent in conjunction with stronger and broader divergent outflow than weak interactions is consistent with the tendency for strong interactions to be associated with larger and more intense TCs at recurvature than weak interactions noted by Archambault et al. (2013, their section 4e).
- It should be recognized that a strong interaction is not necessarily sufficient to induce a sustained, spatially extensive RWT response.
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Cites background or methods from "A Composite Perspective of the Extr..."
...Another 36 h later (+108 h, Figure 1c), an upper-level RWT developed and propagated downstream, resulting in a prominent ridge-trough-ridge pattern over the central and eastern North Pacific....
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...Due to a wrong amplitude and phase of a resulting RWT, ΔeqFH can reach more than 5 days after only 72 forecast hours, in these scenarios....
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...This perturbation of the midlatitude upper-level waveguide may continue downstream and trigger the formation or amplification of a Rossby wave train (RWT) [e.g., Harr and Dea, 2009; Agustí-Panareda et al., 2004; Riemer et al., 2008; Archambault et al., 2015; Quinting and Jones, 2015; Torn and Hakim, 2015]....
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...…flow have been explored in detail by various authors [e.g., Thorncroft and Jones, 2000; Harr and Elsberry, 2000; Harr et al., 2000; McTaggart-Cowan et al., 2001; Atallah and Bosart, 2003; Agustí-Panareda et al., 2004; Riemer et al., 2008; Grams et al., 2011, 2013a, 2013b; Archambault et al., 2015]....
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...MIDLATITUDE FLOW RESPONSE TO TROPICAL CYCLONES 9525 and initial ridgebuilding, resulting in a strong modification and shift of the midlatitude RWT (Choi-Wan, Lupit, Malakas, and Sandy; Text S4 and Figures S3–S5 and S9), ΔeqFH remains high or even increases at longer lead times....
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"A Composite Perspective of the Extr..." refers methods in this paper
...Whether the mean of the maximummagnitude of a given quantity is significantly different for strong versus weak interactions is tested using a nonparametric two-sided Wilcoxon–Mann–Whitney rank-sum test (e.g., Wilks 2006, section 5.3.1)....
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...The statistical significance of the composite fields with respect to climatology is assessed using a two-sided Student’s t test (e.g., Wilks 2006, see section 5.2.1)....
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Frequently Asked Questions (2)
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 ).