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Journal ArticleDOI

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

31 Mar 2015-Monthly Weather Review (American Meteorological Society)-Vol. 143, Iss: 4, pp 1122-1141

AbstractThis 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...

Topics: Extratropical cyclone (54%)

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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Faculty and Researchers Faculty and Researchers' Publications
2015-04
A Composite Perspective of the Extratropical
Flow Response to Recurving Western North
Pacific Tropical Cyclones
Archambault, Heather M.; Keyser, Daniel; Bosart, Lance
F.; Davis, Christopher A.; Cordeira, Jason M.
Montly Weather Review, Volume 143, pp. 1122-1141, April 2015
http://hdl.handle.net/10945/45742
This publication is a work of the U.S. Government as defined in Title 17, United
States Code, Section 101. Copyright protection is not available for this work in the
United States.
Downloaded from NPS Archive: Calhoun

A Composite Perspective of the Extratropical Flow Response to Recurving
Western North Pacific Tropical Cyclones
HEATHER M. ARCHAMBAULT*
Department of Meteorology, Naval Postgraduate School, Monterey, California
DANIEL KEYSER AND LANCE F. BOSART
Department of Atmospheric and Environmental Sciences, University at Albany, State
University of New York, Albany, New York
CHRISTOPHER A. DAVIS
National Center for Atmospheric Research, Boulder, Colorado
JASON M. CORDEIRA
Department of Atmospheric Science and Chemistry, Plymouth State University, Plymouth, New Hampshire
(Manuscript received 22 August 2014, in final form 18 December 2014)
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 asso-
ciated with the TC. The 2.58 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 2408 of longitude and persists for approximately 10 days. Recurving TCs associated with
strong TC–extratropical ow interactions are associated with a stronger extratropical flow response than those
associated with weak TC–extratropical flow interactions. Compared with weak interactions, strong interactions
feature a more distinct upstream trough, stronger and broader divergent outflow associated with stronger midlevel
frontogenesis and forcing for ascent over and northeast of the TC, and stronger upper-level PV frontogenesis that
promotes more pronounced jet streak intensification. During strong interactions, divergent outflow helps anchor
and amplify a downstream ridge, thereby amplifying a preexisting RWT from Asia that disperses downstream to
North America. In contrast, during weak interactions, divergent outflow weakly amplifies a downstream ridge,
such that a RWT briefly amplifies in situ before dissipating over the western-central North Pacific.
1. Introduction
Tropical cyclones (TCs) undergoing extratropical tran-
sition (ET), a change from a warm-core, axisymmetric
system to a cold-core, asymmet ric system (e.g ., Klein et al.
2000; Jones et al. 2003; Harr and Archambault 2015), may
significantly perturb their environment as they recurve into
the midlatitudes (e.g., McTaggart-Cowan et al. 2007; Harr
and Dea 2009; Cordeira and Bosart 2010). The poleward
and upward transport of low potential vorticity (PV) air
associated with TC recurvature tends to amplify a ridge and
intensify a jet streak along the meridional PV gradient
marking the jet stream (e.g., Agustí-Panareda et al. 2004,
Publisher’s Note: This article was revised on 10 June 2015 in order
to include an updated acknowledgements section.
* Current affiliation: NOAA/OAR Climate Program Office,
Modeling, Analysis, Predictions and Projections Program, Silver
Spring, Maryland.
Corresponding author address: Heather M. Archambault, 1315
East–West Hwy., Silver Spring, MD 20910.
E-mail: heather.archambault@noaa.gov
1122 MONTHLY WEATHER REVIEW VOLUME 143
DOI: 10.1175/MWR-D-14-00270.1
Ó 2015 American Meteorological Society

2005; Riemer et al. 2008; Riemer and Jones 2010; Cordeira
2011; Grams et al. 2013a; Archambault et al. 2013).
Ridge amplification and jet streak intensification are
enhanced by diabatic heating associated with the recurv-
ing TC (e.g., Atallah and Bosart 2003) and attendant
frontogenesis in its northeast quadrant (e.g., Torn 2010).
Above the level of maximum diabatic heating associated
with clouds and precipitation, PV is reduced in conjunc-
tion with diabatic vertical redistribution. In addition, the
divergent outflow generated by diabatic heating advects
low PV toward the PV gradient/jet stream (Archambault
et al. 2013, their Fig. 4).
Given a strong, continuous meridional PV gradient
(i.e., waveguide; Martius et al. 2010), ridge amplification
and jet streak intensification will excite or amplify a baro-
clinic Rossby wave train (RWT) that disperses eddy
kinetic energy downstream while initia ting surfa ce cy-
clogenesis downstream (e.g., Riemer et al. 2 008; Harr
and Dea 2009; Keller et al. 2014). Thus, a recurving TC
may indirectly reconfigure the extratropical flow pattern
and influence the sensible weather thousands of kilome-
ters downstream within a few days (e.g., Archambault
et al. 2013, their Fig. 1).
On average, the North Pacific flow pattern becomes
significantly amplified for approximately four days fol-
lowing western North Pacific (WNP) TC recurvature
(Archambault et al. 2013). However, the extratropical flow
response to TC recurvature may range from a marked flow
amplification [e.g., with TC Oscar (1995); Archambault
et al. (2013),theirFig.1;Harr and Archambault (2014)], to
a strengthened jet stream without substantial flow amplifi-
cation [e.g., with TC Jangmi (2008); Grams et al. (2013a,b)],
to little change in the flow pattern [e.g., with TC Opal
(1997); Harr and Elsberry (2000)]. Anticipating the
extratropical flow response to TC recurvature is crucial
given that flow amplification downstream of a recurving
TC may induce extreme weather (e.g., Cordeira and
Bosart 2010; Grams et al. 2011; Chaboureau et al. 2012;
Pantillon et al. 2014) and contribute to reduced mid-
latitude predictability (e.g., Harr et al. 2008; Anwender
et al. 2008; Reynolds et al. 2009; Keller et al. 2011;
Pantillon et al. 2013, 2014; Harr and Archambault 2015).
The primary factors influencing the downstream flow
response to TC recurvature are (i) the large-scale flow
pattern into which the TC is moving (e.g., Harr and Dea
2009; Riemer et al. 2008; Riemer and Jones 2010,
2014),
and (ii) the interaction between the TC and an extra-
tropical disturbance such as a trough or jet streak (e.g.,
Klein et al. 2002; Ritchie and Elsberry 2007; Riemer and
Jones 2010, 2014; Grams et al. 2013b; Keller et al. 2014).
Characteristics of the recurving TC, such as size and
intensity, are thought to be secondary factors (e.g., Harr
and Dea 2009; Archambault et al. 2013).
The large-scale extratropical flow pattern into which
a TC recurves varies by time of year and by ocean basin.
Compared with August–November, June and July are
relatively unfavorable for the North Pacific flow pattern to
become significantly amplified following WNP TC re-
curvature (Archambault et al. 2013,theirFig.15),con-
sistent with the tendency for the North Pacific waveguide/
jet stream to be relatively weak in June and July com-
pared with August–November. A compositing study by
Quinting and Jones (2014) indicates that, whereas RWT
activity is significantly above average following WNP TC
recurvature, it is not significantly above average following
North Atlantic TC recurvature. Based on case studies
(e.g., Grams et al. 2011; Pantillon et al. 2013, 2014), anti-
cyclonic Rossby wave breaking instead of Rossby wave
dispersionmaybemoretypicalfollowingNorthAtlantic
TC recurvature, perhaps owing to the climatologically
short and weak waveguide/jet stream over the North At-
lantic compared with over the North Pacific.
The large-scale extratropical flow response to TC
recurvature also depends on the interaction of the TC
with disturbances in the extratropical flow. The TC–
extratropical flow interaction, or phasing, can be con-
sidered favorable or unfavorable. An example of an
unfavorable phasing between the TC and extratropical
flow is the recurvature of WNP TC Jangmi (2008). As
the TC recurved into the base of a WNP trough, the jet
stream was enhanced downstream but Rossby wave
amplification and dispersion did not occur (Grams et al.
2013a,b). Through numerical modeling experiments,
Grams et al. (2013a) demonstrate that had TC Jangmi
recurved ahead of the trough rather than into the base of
the trough, a high-amplitude RWT likely would have
been induced. They find that the shift in TC position
required to discriminate between RWT and no-RWT
scenarios is only 130 km, which they note is the average
48-h TC position error for ensemble mean ECMWF
forecasts (Lang et al. 2012).
In a recent climatological study (Archambault et al.
2013), the top quintile of TC–extratropical interactions,
defined by the magnitude of negative PV advection by
the irrotational wind associated with the recurving TC, is
found to be associated with a sustained, highly statisti-
cally significant amplification of the North Pacific flow.
In contrast, the bottom quintile of TC–extratropical flow
interactions is found to be associated with a shorter-
lived, less statistically significant amplification of the
North Pacific flow. In the present study, the climato-
logical study of Archambault et al. (2013) is used as the
basis for a comprehensive composite analysis of the
extratropical flow response to WNP TC recurvature. In
particular, key synoptic–dynamic differences are illus-
trated between strong and weak TC–extratropical flow
APRIL 2015 A R C H A M B A U L T E T A L . 1123

interactions, which are important to understanding dif-
ferences in the downstream extratropical flow response
to TC recurvature.
The remainder of this paper is organized as follows.
Section 2 describes the methodology. Section 3 presents
composite analyses of the midlatitude flow response to
recurving WNP TCs and compares composite analyses
of strong and weak TC–extratropical flow interactions
during WNP TC recurvature. Section 4 provides a dis-
cussion, and section 5 contains a summary and an
overview of future work.
2. Methodology
a. Recurvature-relative compositing methodology
To examine the extratropical flow response to recurv-
ing WNP TCs, all 292 recurving WNP TCs identified
during 1979–2009 from the Japan Meteorological Agency
best track dataset by Archambault et al. (2013) are com-
posited. Tropical cyclone recurvature is defined following
Archambault et al. (2013) as a change in TC heading from
westward to eastward as a TC moves poleward. The re-
curvature point corresponds to the most westward posi-
tion of the recurving TC. All recurving TCs are required
to be at tropical storm intensity or greater at the time of
recurvature (i.e., T 1 0 h), and to eventually become ex-
tratropical (i.e., complete ET). The recurving TCs mainly
occur during May–December, with a peak in activity
during August–October. September has the highest in-
cidence of TC recurvature of any month, with 82 cases
identified in 31 years, a frequency of 2.6 yr
21
.
Composite analyses of the recurving WNP TCs are
constructed in a recurvature-relative framework. That is,
fields for each case are shifted such that the recurvature
point is collocated with the mean recurvature point at the
time of recurvature (T 1 0 h). As illustrated by a compar-
ison of conventional geography-relative and recurvature-
relative TC tracks (Figs. 1a,b), the recurvature-relative
framework reduces composite smearing that would arise
from the spatial variability of the recurving TC tracks
(Fig. 1a). The track variability partially reflects the in-
fluence of the time of year: Between May and August, TC
recurvature shifts poleward as the North Pacific jet stream
weakens and shifts poleward, and thereafter shifts equa-
torward through December as the jet stream strengthens
and shifts equatorward (e.g., Archambault et al. 2013,
section 3e).
The 6-hourly 2.58 NCEP–NCAR reanalysis fields
(Kalnay et al. 1996; Kistler et al. 2001)areusedtocon-
struct the composite analyses. Although higher-resolution
reanalyses such as the 0.58 Climate Forecast System Re-
analysis (Saha et al. 2010) are available, the NCEP–NCAR
reanalysis is used for consistency with the Archambault
et al. (2013) climatology. As discussed in Archambault
et al. (2013, their section 2d), the 2.58 NCEP–NCAR re-
analysis is able to capture synoptic signatures of TC–
ext ratropical flow interactions.
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).
The climatology is produced from 1979–2009 21-day
running means of recurvature-relative 2.58 NCEP–
NCAR reanalysis fields.
b. Interaction-relative compositing methodology
Composite analysis is used to compare the extratropical
flow response to strong and weak TC–extratropical
FIG. 1. Recurving WNP TC tracks (2000–09 only; N 5 101) for T 2
48 to T 1 72 h plotted in (a) geography-relative and (b) recurvature-
relative frameworks. The thick black curve denotes the composite
track of all recurving TCs (N 5 292) for T 2 48 to T 1 72 h. The TC
symbol denotes the composite recurvature point (24.98N, 134.08E) for
all recurving TCs.
1124 MONTHLY WEATHER REVIEW VOLUME 143

flow interactions during WNP TC recurvature. For each
recurving TC, the strength of the interaction (i.e., the
interaction metric) is defined as the magnitude of the
spatially and temporally averaged 250–150-hPa layer-
averaged PV advection by the irrotational wind associ-
ated with the TC computed from 6-hourly 2.58 NCEP–
NCAR reanalysis (Archambault et al. 2013, their section
2d). The spatial (1583158) and temporal (48 h) averaging
is centered on the point and time (i.e., T 1 0 h), re-
spectively, of maximum interaction, which is defined as
the highest instantaneous magnitude of negative PV ad-
vection by the irrotational wind associated with the TC.
As noted by Archambault et al. (2013, their Fig. 5a) for
the case of WNP TC Oscar (1995) and by Cordeira (2011,
p. 111) for the case of WNP TC Dale (1996), the region
of strongest negative PV advection by the irrotational
wind generally tends to be closely aligned with the up-
stream edge of the TC cirrus shield. A point of maximum
interaction is not identified for 20 of the 292 recurving TC
cases because the negative PV advection by the irrotational
wind associated with the TC never exceeds an arbitrary
threshold of 1 PVU day
21
(1 PVU 5 10
6
Kkg
21
m
2
s
21
).
These cases are considered no-interaction cases. For the
remaining 272 recurving TC cases, those associated with an
interaction metric in the top quintile are categorized as
strong interactions (N 5 54), whereas those associated with
an interaction in the bottom quintile are categorized as
weak interactions (N 5 54).
As discussed in Archambault et al. (2013, their section
2d), the negative PV advection by the irrotational wind is
useful for diagnosing the strength of the TC–extratropical
flow interaction because divergent outflow impinging
upon the PV waveguide/jet stream is a key signature of
Rossby wave amplification induced by a TC (e.g., Harr
et al. 2008; Riemer et al. 2008; Hodyss and Hendricks
2010; Pantillon et al. 2013, 2014; Grams et al. 2013a,b).
Ridge amplification and jet streak intens ification
occur in conjunction with Rossby wave amplification
as the divergent outflow of the TC deforms PV con-
tours poleward and strengthens the PV gradient
(Archambault et al. 2013, their Fig. 4). T he effect s of
diabatic heating are included in this framework, as
upper-level low-PV air that arises from diabatic
heating is advected by diabatically driven divergent
outflow toward the waveguide/jet stream.
To examine strong and weak TC–extratropical flow
interactions, composites are constructed such that they
are centered on the point of maximum TC–extratropical
flow interaction. This ‘‘interaction-r elative’’ framework
is used to maximize the sharpness of the composite
synoptic features associated with the TC–extratropical
flow interactions. To construct these composites, the 2.58
NCEP–NCAR fields for a given case are shifted such
that the point of maxi mum TC–e xtratro pical flow in-
teraction is collocated with the mean point of maxi-
mum interaction (Fig. 2). The statistical significance of
the composite fields with respect to climatology is
evaluated using a two-sided Student’s t test. The cli-
matology is produced from 1979–2009 21-day running
means of interacti ve-r elative 2.58 NCEP–NCAR re-
analysis fields.
For all WNP TCs undergoing recurvature, the point of
maximum interaction tends to be located approximately
68–148N of the TC center (Fig. 2). However, for strong
interaction cases the location of the mean point of
maximum interaction is significantly farther northward
(11.68 vs 8.18 latitude) and westward (21.18 vs 1.58 lon-
gitude) relative to the TC compared with weak in-
teraction cases (Fig. 2; Table 1).
The synoptic signatures and dynamics of strong and
weak TC–extratropical flow interactions are compared
using a variety of plan-view composite analyses pro-
duced at the time of maximum interaction (i.e., T 1 0 h).
The irrotational and nondivergent wind fields are com-
puted for each individual case prior to compositing. All
derived variables, including PV advection, Q vectors,
and Q-vector divergence (described subsequently in
section 2d), and PV frontogenesis
1
[i.e., the rate of
change of the magnitude of the horizontal PV gradi-
ent; e. g., Davies and Rossa (1998), Cordeira (2011,
p. 105)], are computed on isobaric l evels from the
composite fields.
c. Assessment of characteristic magnitudes of various
quantities for composite cases
Although useful for identifying common synoptic fea-
tures, composite analyses have limited utility in de-
termining the characteristic magnitudes of these features
(e.g., Archambault et al. 2008). To compensate for this
limitation, the maximum values of various quantities for
the individual cases that constitute the composites are
analyzed for strong and weak TC–extratropical flow in-
teractions. For each case, the maximum magnitude of
a given quantity in the NCEP–NCAR reanalysis is ob-
tained by searching within a 208 latitude 3 208 longitude
box centered on the point of maximum interaction.
Whether the mean of the maximum magnitude 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).
1
The PV frontogenesis is calculated by replacing potential
temperature with PV in the simplified 2D form of the Miller (1948)
frontogenesis equation [e.g., Novak et al. 2004, their Eq. (1)].
A
PRIL 2015 A R C H A M B A U L T E T A L . 1125

Figures (16)
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Abstract: Recurving tropical cyclones (TCs) undergoing extratropical transition (ET) may substantially modify the large-scale midlatitude flow pattern. This study highlights the role of diabatic outflow in midlatitude flow amplification within the context of a review of the physical and dynamical processes involved in ET. Composite fields of 12 western North Pacific ET cases are used as initial and boundary conditions for high-resolution numerical simulations of the North Pacific–North American sector with and without the TC present. It is demonstrated that a three-stage sequence of diabatic outflow associated with different weather systems is involved in triggering a highly amplified midlatitude flow pattern: 1) preconditioning by a predecessor rain event (PRE), 2) TC–extratropical flow interaction, and 3) downstream flow amplification by a downstream warm conveyor belt (WCB). An ensemble of perturbed simulations demonstrates the robustness of these stages. Beyond earlier studies investigating PREs, recurv...

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Cites background or methods or result from "A Composite Perspective of the Extr..."

  • ...The maximum interaction point is defined as the largest magnitude of instantaneous 250–150-hPa layer-averaged negative PV advection by the irrotational wind over the entire model domain (Archambault et al. 2013, 2015)....

    [...]

  • ...As noted in Archambault et al. (2013, 2015), strong interactions tend to be associated with Rossby wave amplification and dispersion across the North Pacific to North America....

    [...]

  • ...…Rossby wave dispersion due to ET is highly sensitive to the phasing of the recurving TC and midlatitude flow features (Ritchie and Elsberry 2007; Archambault et al. 2013, 2015) and showed the existence of a bifurcation point for the track of the TC in the trough-relative steering flow during ET…...

    [...]

  • ...…building (e.g., Bosart and Lackmann 1995; Riemer et al. 2008; Archambault et al. 2013), in addition to the balanced flow, and triggers downstream dispersion of Rossby waves (e.g., Riemer and Jones 2010; Grams et al. 2013a; Archambault et al. 2015; Torn and Hakim 2015; Quinting and Jones 2016)....

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  • ...…of low-PV air by the TC divergent outflow anchors the midlatitude jet, resulting in initial ridge building, a reduction of the phase speed, and a retardation in the eastward propagation of Rossby waves (e.g., Riemer et al. 2008; Riemer and Jones 2010; Grams et al. 2013a; Archambault et al. 2015)....

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Abstract: Many studies have highlighted the importance of recurving tropical cyclones (TCs) in triggering Rossby waves. This study investigates the impact of western North Pacific (WNP), south Indian Ocean, and North Atlantic recurving TCs on the amplitude and frequency of synoptic-scale Rossby wave packets (RWPs) over a 30-yr period. The results indicate a significant increase of RWP frequency downstream of WNP and south Indian Ocean TCs. A statistically significant RWP amplitude anomaly downstream of these TCs suggests that RWPs, which are associated with TCs, are stronger than those that generally occur in midlatitudes. North Atlantic TCs do not seem to be associated with a statistically significant increase in RWP frequency and amplitude downstream.Processes that contribute to Rossby wave amplification are identified by creating composites for WNP TCs with and without downstream development. Potential vorticity, eddy kinetic energy, and quasigeostrophic forcing diagnostics highlight dynamical mechanisms...

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  • ...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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Book
03 Jun 2011
Abstract: Praise for the First Edition: 'I recommend this book, without hesitation, as either a reference or course text...Wilks' excellent book provides a thorough base in applied statistical methods for atmospheric sciences' - "BAMS" ("Bulletin of the American Meteorological Society"). Fundamentally, statistics is concerned with managing data and making inferences and forecasts in the face of uncertainty. It should not be surprising, therefore, that statistical methods have a key role to play in the atmospheric sciences. It is the uncertainty in atmospheric behavior that continues to move research forward and drive innovations in atmospheric modeling and prediction. This revised and expanded text explains the latest statistical methods that are being used to describe, analyze, test and forecast atmospheric data. It features numerous worked examples, illustrations, equations, and exercises with separate solutions. "Statistical Methods in the Atmospheric Sciences, Second Edition" will help advanced students and professionals understand and communicate what their data sets have to say, and make sense of the scientific literature in meteorology, climatology, and related disciplines. This book presents and explains techniques used in atmospheric data summarization, analysis, testing, and forecasting. Chapters feature numerous worked examples and exercises. Model Output Statistic (MOS) includes an introduction to the Kalman filter, an approach that tolerates frequent model changes. It includes a detailed section on forecast verification, including statistical inference, diagrams, and other methods. It provides an expanded treatment of resampling tests within nonparametric tests. It offers an updated treatment of ensemble forecasting. It provides expanded coverage of key analysis techniques, such as principle component analysis, canonical correlation analysis, discriminant analysis, and cluster analysis. It includes careful updates and edits throughout, based on users' feedback.

6,604 citations


Journal ArticleDOI
Abstract: The National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR) have cooperated in a project (denoted “reanalysis”) to produce a retroactive record of more than 50 years of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involved the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data. These data were then quality controlled and assimilated with a data assimilation system kept unchanged over the reanalysis period. This eliminated perceived climate jumps associated with changes in the operational (real time) data assimilation system, although the reanalysis is still affected by changes in the observing systems. During the earliest decade (1948–57), there were fewer upper-air data observations and they were made 3 h later than the current main synoptic times (e.g., 0300 UTC), and primarily in the Northern Hemisphere, so that the reanalysis is less reliable than for th later 40 years. The reanalysis data assimilation system continues to be used with current data in real time (Climate Data Assimilation System or CDAS), so that its products are available from 1948 to the present. The products include, in addition to the gridded reanalysis fields, 8-day forecasts every 5 days, and the binary universal format representation (BUFR) archive of the atmospheric observations. The products can be obtained from NCAR, NCEP, and from the National Oceanic and Atmospheric Administration/ Climate Diagnostics Center (NOAA/CDC). (Their Web page addresses can be linked to from the Web page of the NCEP–NCAR reanalysis at http:// wesley.wwb.noaa.gov/Reanalysis.html.) This issue of the Bulletin includes a CD-ROM with a documentation of the NCEP–NCAR reanalysis (Kistler et al. 1999). In this paper we present a brief summary and some highlights of the documentation (also available on the Web at http://atmos.umd.edu/ ~ekalnay/). The CD-ROM, similar to the one issued with the March 1996 issue of the Bulletin, contains 41 yr (1958–97) of monthly means of many reanalysis variables and estimates of precipitation derived from satellite and in situ observations (see the appenThe NCEP–NCAR 50-Year Reanalysis: Monthly Means CD-ROM and Documentation

4,106 citations


Journal ArticleDOI
Abstract: The NCEP Climate Forecast System Reanalysis (CFSR) was completed for the 31-yr period from 1979 to 2009, in January 2010. The CFSR was designed and executed as a global, high-resolution coupled atmosphere–ocean–land surface–sea ice system to provide the best estimate of the state of these coupled domains over this period. The current CFSR will be extended as an operational, real-time product into the future. New features of the CFSR include 1) coupling of the atmosphere and ocean during the generation of the 6-h guess field, 2) an interactive sea ice model, and 3) assimilation of satellite radiances by the Gridpoint Statistical Interpolation (GSI) scheme over the entire period. The CFSR global atmosphere resolution is ~38 km (T382) with 64 levels extending from the surface to 0.26 hPa. The global ocean's latitudinal spacing is 0.25° at the equator, extending to a global 0.5° beyond the tropics, with 40 levels to a depth of 4737 m. The global land surface model has four soil levels and the global sea ice m...

3,978 citations


Related Papers (5)
Frequently Asked Questions (2)
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. 

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 ).