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DOI: 10.2151/sola. 2020-010.
J-STAGE Advance published date: Mar. 3, 2020
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SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 1
1 Future Changes of Tropical Cyclones in the Midlatitudes in
2 4-km-mesh Downscaling Experiments from Large-Ensemble
3 Simulations
4 Sachie Kanada1, Kazuhisa Tsuboki1, and Izuru Takayabu2
5 1Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan
6 2Meteorological Research Institute, Tsukuba, Japan
7
8 Corresponding author: Sachie Kanada, Nagoya University, Furo-cho, Chikusa-ku,
9 Nagoya 464-8601, Japan. E-mail: [email protected]. © 2020, Meteorological
10 Society of Japan.
11 Abstract
12 To understand the impacts of global warming on tropical cyclones (TCs) in
13 midlatitude regions, dynamical downscaling experiments were performed using a
14 4-km-mesh regional model with a one-dimensional slab ocean model. Around 100
15 downscaling experiments for midlatitude TCs that traveled over the sea east of Japan
16 were forced by large-ensemble climate change simulations of both current and warming
17 climates. Mean central pressure and radius of maximum wind speed of simulated
18 current-climate TCs increased as the TCs moved northward into a baroclinic
19 environment with decreasing sea surface temperature (SST). In the warming-climate
20 simulations, the mean central pressure of TCs in the analysis regions decreased from
21 958 hPa to 948 hPa: 12% of the warming-climate TCs were of an unusual central
22 pressure lower than 925 hPa. In the warming climate, atmospheric conditions were
1 2 Kanada et al., Future Changes of Tropical Cyclones in the Midlatitudes
23 strongly stabilized, however, the warming-climate TCs could develope, because the
24 storms developed taller and stronger eyewall updrafts owing to higher SSTs and larger
25 amounts of near-surface water vapor. When mean SST and near-surface water vapor
26 were significantly higher and baroclinicity was significantly smaller, unusual intense
27 TCs with extreme wind speeds and large amounts of precipitation around a small eye,
28 could develop in midlatitude regions, retaining the axisymetric TC structures.
29 (Citation: Kanada, S., K. Tsuboki, and I. Takayabu, XXXX: Future Changes of
30 Tropical Cyclones in the Midlatitudes in 4-km-mesh Downscaling Experiments
31 from Large-Ensemble Simulations. SOLA, X, XXX-XXX,
32 doi:10.2151/sola.XXXX-XXX.)
33 1. Introduction
34 Tropical cyclones (TCs) often bring torrential rainfall, gales, and storm surges that
35 sometimes cause severe disasters in midlatitudinal coastal regions. Sea surface
36 temperature (SST) is projected to increase as a result of anthropogenic greenhouse
37 warming, and the maximum intensity (the maximum wind speed or central pressure) of
38 future TCs will likely increase as well (e.g., IPCC 2012; Mizuta et al. 2014; Murakami
39 et al. 2012), because the TC intensity generally increases as SST increases (e.g.,
40 DeMaria and Kaplan 1994; Emanuel 1986).
41 In the present climate, TCs that travel to higher latitudes tend to weaken as SST
42 decreases north of 30°N. However, Kossin et al. (2014) reported that the average
43 latitude at which TCs reach their lifetime-maximum wind speed has been shifting
44 poleward over the past 30 years. A number of future projection studies have implied that
45 higher-latitude occurrences of intense TCs will increase (e.g., Kanada et al. 2013; SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 3
46 Tsuboki et al. 2015; Yoshida et al. 2017) because the projected future increase in SST is
47 larger at higher latitudes (Mizuta et al. 2017). Furthermore, case studies of TCs that
48 caused record-breaking heavy rainfalls in eastern coastal regions of northern Japan have
49 shown that precipitation amounts associated with a TC’s landfall increased in the
50 warming-climate simulations (Kanada et al. 2017a, 2019). These results suggest that
51 large numbers of people living in mid-to-high latitudes may be exposed to unusually
52 intense TCs and associated winds and precipitation in the future, warmer climate.
53 In midlatitude regions, TCs undergo an extratropical transition and structural changes
54 as they move poleward into a baroclinic environment characterized by a temperature
55 gradient, increased vertical wind shear (VWS), and decreased SST (Evans et al., 2017;
56 Wada 2016). To simulate the detailed inner-core structure of a TC, it is necessary to use
57 models with a horizontal resolution not larger than 5 km (e.g., Gentry and Lackmann
58 2010; Kanada and Wada 2016).
59 Regional TC changes include large uncertainty caused mainly by SST warming
60 patterns (Knutson et al. 2010; Murakami et al. 2012). In addition, the projected TC
61 changes vary greatly among individual storms (Gutmann et al. 2018). Therefore, to
62 understand changes in TC activity in the future climate, it is important to use a large
63 ensemble to model storms.
64 The present study aimed to understand the impact of global warming on TCs likely to
65 affect the large number of people living in eastern midlatitude coastal regions. Changes
66 in TCs traveling over the sea east of Japan were investigated by conducting dynamical
67 downscaling experiments with a 4-km-mesh regional model. The downscaling
68 experiments were forced by large-ensemble climate simulations for both current and
69 4-K-warming climates (Mizuta et al. 2017). Around 100 dynamical downscaling
3 4 Kanada et al., Future Changes of Tropical Cyclones in the Midlatitudes
70 experiments for both the current and warming climates were conducted to explore
71 changes in the intensity and structures of midlatitude TCs.
72 2. Models and methodology
73 Dynamical downscaling experiments of TCs traveling over the sea east of Japan were
74 performed by using the Policy Decision-Making for Future Climate Change (d4PDF)
75 database (Mizuta et al. 2017). This database comprises results of a large ensemble of
76 climate change simulations with a 60-km-mesh atmospheric global circulation model
77 (MRI-AGCM3.2H; Mizuta et al. 2012) and a 20-km-mesh atmospheric regional model
78 (NHRCM; Sasaki et al. 2011). All TCs that made landfall in eastern Hokkaido in
79 northern Japan (142°E–146°E and 42°N–46°N) from the western North Pacific Ocean
80 with no previous landfalls were targeted. Only eight TCs met those criteria according to
81 the Regional Specialized Meteorological Center Tokyo (RSMC) best-track dataset from
82 1951 to 2018, but 98 and 125 storms were selected from the 3,000 years of
83 current-climate and 5,400 years of 4-K warming-climate runs, respectively, in the
84 d4PDF database. Tracks of the targeted storms are shown in Fig. 1.
85 Downscaling experiments for all targeted storms were conducted with a
86 high-resolution non-hydrostatic regional model, the Cloud Resolving Storm Simulator
87 version 3.4 (CReSS; Tsuboki and Sakakibara 2002), which has a horizontal resolution
88 of 0.04° (approximately 4 km). The computational domain of CReSS spans
89 128°E–152°E and 24°N–48°N (Fig. 1a and b). SST cooling associated with storm
90 passage is considered by a simple thermal diffusion model. Initial and lateral boundary
91 conditions were provided every 6 h from the NHRCM results. Detailed information on
92 the models and methodology are given in Supplement 1. SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 5
93 3. Results
94 3.1 Changes in midlatitude TCs with increasing latitude
95 In the RSMC best-track dataset for 1951–2018, the lowest central pressure over the
96 sea east of Japan between 30°N and 45°N was 925 hPa, during Typhoon Oscar (1995),
97 and that in the current simulation was 922 hPa. In the warming climate, the lowest
98 central pressure in the region dropped to 869 hPa. The mean central pressure of TCs in
99 the analysis regions decreased from 958 hPa to 948 hPa in the warming-climate
100 simulation: 12% of the warming-climate TCs were of an unusual central pressure lower
101 than 925 hPa. The warming-climate TCs tended to travel northward at slower
102 translation speeds than the current-climate TCs. Mean translation speed of the current-
103 and warming-climate TCs between 30°N and 45°N was 9.2 (8.8 in the RSMC TCs) and
104 8.0 m s−1, respectively. A similar slowdown in the translation speed of midlatitude TCs
105 under a warming climate has been reported by Kanada et al. (2017a) and Yamaguchi et
106 al. (2020).
107 Changes in the simulated midlatitude TCs with increasing latitude were investigated
108 (Fig. 2) for all storms whose center was located in the region shown in Figs. 1 and S1.
109 List of abbreviations and the definitions in this study were summarized in Table S1. TCs
110 tend to weaken and their radius of maximum wind speed (RMW) increases as they
111 move poleward (Evans et al. 2017). The current-climate simulations showed both a
112 decrease in the maximum wind speed and increases in the central pressure and RMW
113 under the increasing VWS and decreasing SST associated with latitude increases (Figs.
114 1 and 2). In the warming-climate simulations, mean SST in the inner core of the storms
115 increased in all analysis regions, whereas baroclinicity and VWS decreased (Fig. 1).
116 Mean central pressure decreased in the regions south of 40°N (Fig. 2) were statistically
5 6 Kanada et al., Future Changes of Tropical Cyclones in the Midlatitudes
117 significant at the 95% confidence level (Welch’s t-test). Mean precipitation amounts and
118 wind speeds in the inner core were enhanced in warming-climate storms, but they
119 tended to have a smaller RMW than current-climate storms (Fig. 2).
120 Changes in TC structure were investigated by examining storm-centered composite
121 structures of all storms whose centers were located in 142°E–147°E and 35°N–40°N in
122 the current and warming climates (Fig. 3). Mean central pressures of the storms in this
123 region were 963 hPa and 955 hPa in the current and warming climates, respectively (Fig.
124 2a). Areas of high winds appeared on the right side of the storm center (‘A’ in Fig. 3),
125 because the storms were moving northward. Although wind speeds around the eye
126 increased, the horizontal extent of moderate wind speeds (16–24 m s−1) decreased in the
127 warming climate (‘B’ in Fig. 3). The increases in wind speed in the warming-climate
128 TCs, compared with wind speeds in current-climate TCs, were large in the inner core
129 and on the left side of the storm center (Fig. 3c). Mean symmetry of a TC (SY; see
130 Supplement 1) of the current- and warming-climate TCs was 0.69 and 0.28, respectively.
131 SY of a mature, axisymmetric TC is less than 0.85, whereas that of a cyclone with
132 mature or developing frontal structures exceeds 0.85 (Evans et al. 2017). The mean SY
133 of current-climate TCs in the northernmost analysis region (C40) of 0.90 indicates that
134 these TCs have undergone extratropical transition; in contrast, the mean SY of
135 warming-climate TCs was relatively low at 0.5.
136 Figure 4 depicts the horizontal distributions of SST and air temperature when the
137 storm centers were located in 142°E–147°E and 35°N–40°N. Because SST and air
138 temperature increases in the vicinity of Japan under a warming climate are larger in the
139 higher latitudes and the Sea of Japan than in the lower latitudes (Fig. 4), temperature
140 gradients (baroclinicity) around Japan are reduced in the warming climate. The reduced SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 7
141 temperature gradients are attributable to decrease in thermal wind and hence decreases
142 in northward and westward winds (Figs. 3 and 4), which is a possible factor
143 contributing to the slower northward translation speed. Decreased SST causes a
144 reduction of surface heat fluxes and a TC begins to interact with the midlatitude
145 baroclinic environment to transform into an extratropical cyclone (Jones et al. 2003).
146 However, in the warming climate, SSTs was significantly high, and the jet stream was
147 weakened, and the altitude of it increased and was farther from the TC inner core (‘C’ in
148 Fig. 3). Thus, the warming-climate storms could retain the axisymmetric TC structures
149 even they arrived around northern Japan.
150 3.2 Changes in intensity and structure of midlatitude TCs
151 Changes in the structures of TCs were explored in relation to TC intensity (Fig. 5).
152 Changes in the environmental sea level pressure (SLP) from the current to the warming
153 climates can affect the central pressure. Therefore, we used the decrease in the central
154 pressure from the environmental SLP (hereafter, pressure decrease: PD) as an index of
155 TC intensity (see Supplement 1). To avoid topographic effects, TCs whose centers were
156 located in 142°E–147°E and 30°N–40°N were selected (Fig. S2).
157 Mean PDs increased from 51 hPa to 41 hPa from the current to the warming climate.
158 Furthermore, TCs of unusual intensity, with a mean PD exceeding 70 hPa (central
159 pressure approximately 928 hPa), appeared in the warming climate. In general, MWS,
160 WS200, PR200, and IKE (see Supplement 1)) increased and RMW decreased as the PD
161 increased in both the current and warming climates (Fig. 5). The largest difference
162 between current- and warming-climate storms was in SY; SY of warming-climate
163 storms was smaller than 0.4 regardless of PD, whereas SY of current-climate TCs
164 tended to be large.
7 8 Kanada et al., Future Changes of Tropical Cyclones in the Midlatitudes
165 The appearance of extremely intense TCs and more axisymmetric TC structures in
166 the warming climate can be attributed to more favorable environmental conditions (i.e.,
167 significantly high SST, large amounts of near-surface water vapor, smaller VWS and
168 baroclinicity for TC development as well as to slower translation speeds and a weaker
169 upper-level jet. The only exception was an increase in the mean static stability (N2) in
170 the inner core (Supplement 1). In the warming climate, the increase in air temperature in
171 the upper troposphere is projected to be large (e.g., Hill and Lackmann 2011; Kanada et
172 al. 2017b) and atmospheric conditions stabilize (Fig. 5l). The significant stabilization
173 inhibited convective activity and suppressed TC development. When mean SST (Fig.
174 5h) and near-surface water vapor (Fig. 5i) were significantly higher and baroclinicity
175 (Fig. 5k) was significantly smaller, however, unusual intense TCs with extreme wind
176 speeds and large amounts of precipitation around a small eye, could develop in
177 midlatitude regions despite the strong stabilization.
178 How do the warming-climate TCs develop to have the same PD as current-climate
179 TCs despite the stabilization? Storm-centered composite azimuthally averaged
180 structures of TCs with a PD between 40 and 60 hPa in the current and warming climates
181 were compared (Fig. 6). The vertical moisture flux and eyewall updrafts of the
182 warming-climate TCs were considerably stronger and located within a smaller RMW at
183 all altitudes, compared with those of the current-climate TCs (Figs. 6a, 6b, 6d and 6e).
184 Furthermore, regions with high inertial stability appeared inside the RMW where the
185 intense updrafts developed. Theoretical studies have shown that the fraction of thermal
186 forcing Q (i.e., heating by latent heat release in the eyewall updrafts), which contributes
187 to TC development, increases when the horizontal extent of Q is small and close to the
188 region of high inertial stability (Schubert and Hack 1982). In other words, the simulated SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 9
189 warming-climate TCs exhibited structures of a TC in the developing stage that
190 efficiently uses Q in the eyewall updrafts. The heating by latent heat release induces
191 near-surface inflow around the eyewall region (Stern et al. 2015), and this enhancement
192 of heating-induced near-surface inflow as well as the reduction of the RMW intensified
193 horizontal wind speeds in the vicinity of the smaller eye in the warming-climate TCs. In
194 contrast, current-climate TCs, which had weaker eyewall updrafts that tilted outside the
195 larger RMW, entered a post-mature stage as losing axisymmetric structures of a TC
196 under conditions of lower SSTs and relatively large baroclinicity. The extremely intense
197 TCs in the warming-climate simulations had even stronger and taller eyewall updrafts
198 inside a smaller RMW, where the inertial stability was very high, compared with the
199 updrafts of TCs with a PD between 40 and 60 hPa in both climates (Figs. 6c and 6f).
200 4. Discussion: Changes in RMW and storm size
201 Using a 14-km-mesh model, Yamada et al. (2017) found that future TCs would
202 become larger because of deeper secondary circulation. However, the results of the
203 present study obtained with a 4-km-mesh regional model showed a reduction in IKE.
204 There were no large differences in the horizontal extent of near-surface wind speeds in
205 TCs with the same PD between the current and warming climates (Fig. 6). A reduction
206 in the RMW was also found in future change experiments of intense TCs conducted
207 with high-resolution non-hydrostatic models with horizontal resolutions of 2–5 km
208 (Kanada et al. 2013, 2017b; Wang et al. 2015). In addition, an atmosphere-ocean couple
209 model with a horizontal resolution of 6 km projected a reduction in the size of western
210 North Pacific storms under future warming (Knutson et al. 2015). According to
211 Schubert and Hack (1982), heating-induced tangential wind acceleration at low levels is
9 10 Kanada et al., Future Changes of Tropical Cyclones in the Midlatitudes
212 larger inside the RMW and leads to a reduction of the RMW. The significantly increased
213 near-surface water vapor in the warming climate can be attributed to the reduction in the
214 RMW by enhancement of the eyewall updrafts (Fig. 6) and hence heating by latent heat
215 release. Furthermore, a delay in the extratropical transition is attributable to the
216 reduction in the RMW of midlatitude TCs in the warming climate. Thus, to project
217 changes to the inner-core structures of TCs, high-resolution models with a horizontal
218 resolution of several kilometers should be used.
219 5. Summary
220 The impacts of global warming on TCs in midlatitude regions were investigated by
221 analyzing the results of around 100 dynamical downscaling experiments conducted with
222 a 4-km-mesh regional model forced by a large ensemble of climate simulations for both
223 current and 4-K-warming climates. All TCs that struck eastern Hokkaido in northern
224 Japan from the western North Pacific Ocean without previous landfalls were targeted. In
225 total, 98 and 125 storms were selected from the 3,000 years of current and 5,400 years
226 of 4-K-warming climate runs, respectively.
227 The results of the downscaling experiments showed increases in the frequency of
228 intense TCs with strong horizontal winds and large precipitation amounts around a
229 smaller eye under a future, warmer climate (Fig. 2). Extremely intense TCs with a mean
230 pressure decrease (PD) exceeding 70 hPa (central pressure approximately 928 hPa),
231 appeared in midlatitude regions. The mean PD was 41 hPa (approximately 964 hPa) in
232 the current-climate TCs and 51 hPa (approximately 953 hPa) in the warmer-climate TCs.
233 Although the RMW and asymmetric property of the current-climate TCs increased as
234 they moved poleward into a more baroclinic environment, the warming-climate TCs SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 11
235 exhibited axisymmetric structures and a smaller RMW. The decreased temperature
236 gradients and increased SST caused a delay in the extratropical transition of midlatitude
237 TCs in a warming climate.
238 In the warming climate, most environmental conditions such as SST, VWS, and
239 baroclinicity, as well as the slower TC translation speed and weaker upper-level jet,
240 were more favorable for TC development. However, significant increases in static
241 stability indicated stabilization of atmospheric conditions (Fig. 5l), which inhibited TC
242 development. To overcome the enhanced stability, the warming-climate TCs required
243 significantly high SSTs (Fig. 5h) and large amounts of water vapor in the lower
244 troposphere (Fig. 5i).
245 The results of the present study suggested a slowdown in the translation speed of TCs
246 under a warming climate. The impact of the SST cooling associated with the storm
247 passage is large in midlatitude regions, because TC heat potential is smaller than in
248 low-latitude regions (Wada 2016). Atmosphere-ocean coupled models that include
249 cold-wake effects should be used for more accurate future projections of TC activity.
250 Furthermore, environmental conditions and TC size differ greatly among ocean basins
251 (Wada et al. 2012). Studies of TCs in each basin using high-resolution models that can
252 capture structural changes in the storm inner cores will be required to gain deeper
253 insights into TC changes in a warming climate.
254 Acknowledgements
255 The authors are grateful to two reviewers and an editor for instructive comments.
256 This study was supported by the Ministry of Education, Culture, Sports, Science and
257 Technology of Japan under the framework of the TOUGOU Program. Numerical
11 12 Kanada et al., Future Changes of Tropical Cyclones in the Midlatitudes
258 simulations were performed using the Earth Simulator (JAMSTEC).
259 Supplement
260 Supplement 1 describes detailed information on the models and methodology.
261
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279 SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 13
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366 Wang, C.-C., B.-X. Lin, C.-T. Chen, and S.-H. Lo, 2015: Quantifying the effects of
367 long-term climate change on tropical cy-clone rainfall using a cloud-resolving model:
368 Examples of two landfall typhoons in Taiwan. J. Climate, 28, 66–85.
369 Yamada, Y., M. Satoh, M. Sugi, C. Kodama, A. T. Noda, M. Nakano, and T. Nasuno,
370 2017: Response of tropical cyclone activity and structure to global warming in a
371 high-resolution global nonhydrostatic model. J. Climate, 30, 9703-9724.
372 Yamaguchi, M., J. C. L. Chan, I. Moon, K. Yoshida, and R. Mizuta, 2020: Global
373 warming changes tropical cyclone translation speed. Nat. Commun. 11, 47.
374 https://doi.org/10.1038/s41467-019-13902-y SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 17
375 Yoshida, K., M. Sugi, R. Mizuta, H. Murakami, and M. Ishii, 2017: Future changes in
376 tropical cyclone activity in high-resolution large-ensemble simulations. Geophys. Res.
377 Lett., 44, 9910-9917.
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17 18 Kanada et al., Future Changes of Tropical Cyclones in the Midlatitudes
397 Figure Captions
398 Fig. 1. The downscaling experiment domain showing the tracks of the targeted TCs
399 (thin black lines) in the (a) current- and (b) warming-climate simulations. The
400 rectangles outlined in red show the regions used for composite analyses.
401 Box-and-whisker plots of (c) mean sea surface temperature in the TC inner core
402 (SST200: °C), (d) mean water vapor at an altitude of 10 m in the inner core
403 (QVS200: g kg−1), (e) vertical wind shear (VWS: m s−1), and (f) baroclinicity (BA:
404 K). Outliers are excluded. Pink (cyan) shading indicates that the increase (decrease)
405 in the mean value in the warming climate compared with the current climate is
406 statistically significant at the 95% confidence level (Welch’s two-sided t-test). Boxes
407 with bold outlines indicate that the difference in the mean value between analysis
408 regions is statistically significant at the 95% confidence level (Welch’s two-sided
409 t-test).
410
411 Fig. 2. Box-and-whisker plots of (a) central pressure (hPa), (b) maximum 10-m wind
412 speeds (MWS: m s−1), (c) mean 10-m wind speeds in the inner core (WS200: m
413 s−1), (d) mean hourly precipitation in the inner core (PR200: mm), (e) radius of the
414 maximum 10-m wind speed (RMW: km), and (f) symmetry (SY: K). A green line
415 with an asterisk in (a) indicated ranges of central pressure of the relevant TCs in
416 the RSMC best-track dataset. Other information is the same as in Fig. 2c–f.
417
418 Fig. 3. Storm-centered composite horizontal distributions of 10-m wind speeds when the
419 storm centers were located in 142°E–147°E and 35°N–40°N in the (a) current and
420 (b) warming climates, and (c) changes in the warming climate compared with the SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 19
421 current climate. (d)–(f) Same as (a)–(c), but for meridional vertical cross sections
422 of horizontal wind speed. (g)–(i) Same as (a)–(c), but for latitudinal vertical cross
423 sections. ‘A’, ‘B’, and ‘C’ denote areas of high winds, areas of moderate wind
424 speeds, and the jet stream, respectively.
425
426 Fig. 4. Mean horizontal distributions of SST when the storm centers were located in
427 142°E–147°E and 35°N–40°N (dashed green rectangles) in the (a) current and (b)
428 warming climates. (c) and (d) Same as (a) and (b), but for mean temperature at an
429 altitude of 5.1 km. (e) and (f) Same as (a) and (b), but for mean horizontal wind
430 speed at an altitude of 12.3 km in the current climate and 13.3 km in the warming
431 climate. Black arrows in (c) and (d) indicate horizontal winds in the current climate
432 and changes in horizontal winds from the current to the warming climates
433 ([warming]-[current]) at an altitude of 5.1 km, respectively.
434
435 Fig. 5. (a) Frequency distribution of pressure decrease (PD) in 10-hPa bins when the
436 storm centers were located in 142°E–147°E and 30°N–40°N (Fig. S2) in the
437 current (cyan bars) and warming (orange bars) climates. Mean values of (b) MWS
438 (m s−1), (c) RMW (km), (d) WS200 (m s−1), (e) PR200 (mm), (f) integrated
439 kinematic energy (IKE: m2 s−2), (g) SY (K), (h) SST200 (°C), (i) QVS200 (g kg−1),
440 (j) VWS (m s−1), (k) baroclinicity (BA: K), and (l) static stability (N2: s−2) in the
441 same region for each PD bin in the current (cyan circles) and warming (orange
442 circles) climates. Mean values in the warming climate indicated by orange-filled
443 circles are significantly different from those in the current climate at the 95%
444 confidence level (Welch’s two-sided t-test).
19 20 Kanada et al., Future Changes of Tropical Cyclones in the Midlatitudes
445
446 Fig. 6. Storm-centered composite azimuthally averaged radial–vertical cross sections of
447 the TCs when the storm centers were located in 142°E–147°E and 30°N–40°N (Fig.
448 S2) showing the vertical moisture flux in (a) the current climate for TCs with a PD
449 between 40 and 60 hPa, (b) the warming climate for TCs with a PD between 40
450 and 60 hPa, and (c) the warming climate for TCs with a PD between 70 and 140
451 hPa. The black dotted line denotes the radius of the maximum tangential wind
452 speed at each altitude. Cyan lines denote water vapor mixing ratios of 20 and 24 g
453 kg−1. (d)–(f) Same as (a)–(c), but for vertical wind velocity. Black lines denote
454 tangential wind speeds of 25 and 35 (m s−1). Green lines denote inertial stability of
455 3, 6, 9, 12, and 15 (10−6 s−1). (g)–(i) Same as (a)–(c), but for storm-centered
456 composite horizontal distributions of 10-m wind speeds.
457
458
459
460
461
462
463
464
465 SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 1
1
2 Fig. 1. The downscaling experiment domain showing the tracks of the targeted TCs 3 (thin black lines) in the (a) current- and (b) warming-climate simulations. The 4 rectangles outlined in red show the regions used for composite analyses. 5 Box-and-whisker plots of (c) mean sea surface temperature in the TC inner core 6 (SST200: °C), (d) mean water vapor at an altitude of 10 m in the inner core 7 (QVS200: g kg−1), (e) vertical wind shear (VWS: m s−1), and (f) baroclinicity (BA: 8 K). Outliers are excluded. Pink (cyan) shading indicates that the increase 9 (decrease) in the mean value in the warming climate compared with the current 10 climate is statistically significant at the 95% confidence level (Welch’s two-sided 11 t-test). Boxes with bold outlines indicate that the difference in the mean value 12 between analysis regions is statistically significant at the 95% confidence level 13 (Welch’s two-sided t-test). SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 1
1
2 Fig. 2. Box-and-whisker plots of (a) central pressure (hPa), (b) maximum 10-m wind
3 speeds (MWS: m s−1), (c) mean 10-m wind speeds in the inner core (WS200: m
4 s−1), (d) mean hourly precipitation in the inner core (PR200: mm), (e) radius of the
5 maximum 10-m wind speed (RMW: km), and (f) symmetry (SY: K). A green line
6 with an asterisk in (a) indicated ranges of central pressure of the relevant TCs in
7 the RSMC best-track dataset. Other information is the same as in Fig. 1c–f.
8 SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 1
1
2 Fig. 3. Storm-centered composite horizontal distributions of 10-m wind speeds when the
3 storm centers were located in 142°E–147°E and 35°N–40°N in the (a) current and
4 (b) warming climates, and (c) changes in the warming climate compared with the
5 current climate. (d)–(f) Same as (a)–(c), but for meridional vertical cross sections
6 of horizontal wind speed. (g)–(i) Same as (a)–(c), but for latitudinal vertical cross
7 sections. ‘A’, ‘B’, and ‘C’ denote areas of high winds, areas of moderate wind
8 speeds, and the jet stream, respectively.
9 SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 1
1
2 Fig. 4. Mean horizontal distributions of SST when the storm centers were located in
3 142°E–147°E and 35°N–40°N (dashed green rectangles) in the (a) current and (b)
4 warming climates. (c) and (d) Same as (a) and (b), but for mean temperature at an
5 altitude of 5.1 km. (e) and (f) Same as (a) and (b), but for mean horizontal wind
6 speed at an altitude of 12.3 km in the current climate and 13.3 km in the warming
7 climate. Black arrows in (c) and (d) indicate horizontal winds in the current climate
8 and changes in horizontal winds from the current to the warming climates
9 ([warming]-[current]) at an altitude of 5.1 km, respectively. SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 1
1
2 Fig. 5. (a) Frequency distribution of pressure decrease (PD) in 10-hPa bins when the
3 storm centers were located in 142°E–147°E and 30°N–40°N (Fig. S2) in the
4 current (cyan bars) and warming (orange bars) climates. Mean values of (b) MWS
5 (m s−1), (c) RMW (km), (d) WS200 (m s−1), (e) PR200 (mm), (f) integrated
6 kinematic energy (IKE: m2 s−2), (g) SY (K), (h) SST200 (°C), (i) QVS200 (g kg−1),
7 (j) VWS (m s−1), (k) baroclinicity (BA: K), and (l) static stability (N2: s−2) in the
8 same region for each PD bin in the current (cyan circles) and warming (orange
9 circles) climates. Mean values in the warming climate indicated by orange-filled
10 circles are significantly different from those in the current climate at the 95%
11 confidence level (Welch’s two-sided t-test).
12 SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 1
1
2 Fig. 6. Storm-centered composite azimuthally averaged radial–vertical cross sections of
3 the TCs when the storm centers were located in 142°E–147°E and 30°N–40°N (Fig.
4 S2) showing the vertical moisture flux in (a) the current climate for TCs with a PD
5 between 40 and 60 hPa, (b) the warming climate for TCs with a PD between 40
6 and 60 hPa, and (c) the warming climate for TCs with a PD between 70 and 140
7 hPa. The black dotted line denotes the radius of the maximum tangential wind
8 speed at each altitude. Cyan lines denote water vapor mixing ratios of 20 and 24 g
9 kg−1. (d)–(f) Same as (a)–(c), but for vertical wind velocity. Black lines denote
10 tangential wind speeds of 25 and 35 (m s−1). Green lines denote inertial stability of
11 3, 6, 9, 12, and 15 (10−6 s−1). (g)–(i) Same as (a)–(c), but for storm-centered
12 composite horizontal distributions of 10-m wind speeds.