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DOI: 10.2151/sola. 2019-029.
J-STAGE Advance published date: July 12, 2019
The final manuscript after publication will replace the preliminary version at the above DOI once it is available.
SOLA, XXXX, Vol.X, XXX-XXX, doi: 10.2151/sola.XXXX-XXX 1
1 The “Karakkaze” Local Wind as a Convexity Wind: A Case Study
2 using Dual-Sonde Observations and a Numerical Simulation
3
4 Akifumi NISHI1 and Hiroyuki KUSAKA2
5 1 Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba,
6 Japan.
7 2 Center for Computational Sciences, University of Tsukuba, Tsukuba, Japan
8
9 Corresponding author: Hiroyuki Kusaka, University of Tsukuba, 1-1-1 Tennôdai,
10 Tsukuba, Ibaraki 302-8577, Japan. E-mail: [email protected] © 2019,
11 Meteorological Society of Japan.
12 Abstract
13 In the present study, we conducted dual-sonde observations and a numerical
14 simulation when the “Karakkaze”, a local wind in Japan, blew. The result showed that
15 the basic features of the Karakkaze coincide closely with the characteristics of
16 convexity wind defined as “strong winds in the leeward region of a convex-shaped
17 mountain range”.
18 Firstly, we investigated the horizontal distribution of surface winds during the
19 Karakkaze event on January 24, 2019. The results showed that the Karakkaze blows in
20 the downwind plain of the convexity of the mountain range.
21 Secondly, we compared the vertical distribution of the winds inside and outside
22 the Karakkaze region, using the results of dual-sonde observations and a numerical
1 2 A Case Study of the Karakkaze using Dual-Sonde Observations and a Numerical Simulation
1 simulation. Our results showed that strong winds blew from near ground level to a
2 height of 1.8 km above mean sea level (AMSL) in the Karakkaze region. In contrast,
3 weaker winds were observed and simulated outside the Karakkaze region. The reason of
4 the weaker winds is that a hydraulic jump occurs on the slope of the mountain range and
5 that the area outside the Karakkaze region is located in a more leeward direction than
6 the hydraulic jump. These features closely match the characteristics of convexity winds.
7
8 Keywords: local winds, downslope windstorms, convexity winds, Karakkaze, WRF
9
10 (Citation: Nishi, A., and H. Kusaka, 2019: The “Karakkaze” Local Wind as a
11 Convexity Wind: A Case Study using Dual-Sonde Observations and a Numerical
12 Simulation. SOLA, X, XXX-XXX, doi:10.2151/sola.XXXX-XXX.)
13
14 1. Introduction
15 Due to Japan’s complex terrain, strong local winds blow in many areas (Kusaka
16 and Fudeyasu 2017). For example, the “Hirodo-kaze” (Fudeyasu et al. 2008), the
17 “Kiyokawa-dashi” (Sasaki et al. 2010; Ishii et al. 2007), and “Yamaji-kaze” (Saito and
18 Ikawa 1991; Saito 1993) are called “the three most notorious winds in Japan”. The
19 “Karakkaze”, a local wind in Japan’s Kanto region, is also a well-known strong local
20 wind because the wind sometimes reaches the Tokyo metropolitan area. The Karakkaze
21 tends to blow when the winter monsoon is strong. The strong-wind region has a
22 remarkable fan-shaped horizontal distribution (Yoshino 1986; Kusaka et al. 2011).
23 However, its fundamental mechanism is still under discussion. SOLA, 2010, Vol.6, 000-000, doi: 10.2151/sola.2010-000 3
1 Generally, local winds can be classified into three types. The first type is the
2 “downslope windstorm” that blows down the lee slope of a mountain range, often
3 reaching its peak strength near the foot of the mountains and then weakening rapidly
4 with increasing distance from the mountains (American Meteorological Society 2019).
5 These winds can also be regarded as hydraulic jump phenomena, in which flow
6 becomes supercritical above and to the lee of a mountain barrier. Extensive studies have
7 been conducted using observational, theoretical, and numerical approaches, with the
8 result that the essential mechanism is clearly understood (e.g., Long 1954; Lilly and
9 Zipser 1972; Raymond 1972; Peltier and Clark 1979; Lilly and Klemp 1979; Clark and
10 Peltier 1984; Smith 1985; Pitts and Lyons 1989; Miller and Durran, 1991; Saito and
11 Ikawa 1991; Saito 1993; Lin and Wang 1996; Gohm et al. 2008; Elvidge and Renfrew
12 2016; Miltenberger et al. 2016; Rotunno and Bryan 2018). The Hirodo-kaze is classified
13 as a downslope windstorm.
14 The second local wind type is the “gap wind” that often blows through a gap in
15 a mountain barrier or through a level channel between two mountain ranges (e.g., Scorer
16 1952; Arakawa 1969; Lackmann and Overland 1989; Zängl. 2003; Gaberšek and
17 Durran 2004; Mayr et al 2004; Sasaki et al. 2010; Mass et al. 2014). Gap winds are
18 sub-classified into the upstream-blocking regime and mountain-wave regime types
19 (Gaberšek and Durran 2004). In the case of the upstream-blocking regime, the wind is
20 the strongest in the valley, but in the case of the mountain-wave regime, the wind is
21 strong both in the valley and the exit of the valley. The Kiyokawa-dashi can be
22 classified as a mountain-wave regime type of gap wind.
23 The third local wind type is a combination of downslope windstorm and gap
24 wind that is essentially a downslope windstorm, but in which the strongest wind appears
3 4 A Case Study of the Karakkaze using Dual-Sonde Observations and a Numerical Simulation
1 around the gap exit (e.g., Saito 1993; Gohm and Mayer 2005, Elvidge et al. 2015). This
2 type of wind is sometimes called a “foehn jet” (Elvidge et al. 2015). The Yamaji-kaze is
3 a downslope windstorm but is affected by the col in the mountain range. This wind may
4 be classified as a combination type.
5 Unlike the three “notorious” local winds, the mechanism of the Karakkaze is still
6 not fully understood. Yamagishi (2002), Yomogida and Rikiishi (2004) and Kusaka et
7 al. (2011) reported that the Karakkaze is a part of the winter monsoon and is hence
8 caused by the efficient transfer of momentum from aloft through an evolving
9 convective boundary layer.
10 In contrast, some previous studies considered the Karakkaze as downslope
11 windstorms. Yoshino (1986) considered the Karakkaze as downslope windstorms
12 with cold advection (i.e. Bora type downslope-windstorms). A typical case study
13 showed that the foehn wind can occur in the winter season in the Kanto plain,
14 accompanied with strong northwesterly winds (Watarai et al. 2015).
15 Nishi and Kusaka (2019a) hypothesized that the Karakkaze is a “convexity wind,”
16 a new concept of local wind arrived at by idealized numerical simulations. An essential
17 feature of this type of strong wind, shown in Figure 1, is that they appear only at the exit
18 of a convexity within a mountain range due to downdrafts, even when winds are very
19 weak in the other leeward plain areas of the mountain range due to hydraulic jump over
20 the mountain slope (Nishi and Kusaka 2019a, 2019b). This surface wind pattern is
21 clearly similar to that of the Karakkaze.
22 The present study investigates whether the mechanism of the Karakkaze can be
23 explained based on the concept of a convexity wind. We conducted observations using SOLA, 2010, Vol.6, 000-000, doi: 10.2151/sola.2010-000 5
1 Global Positioning System-Sonde and ran a numerical simulation model with the real
2 topography and atmospheric conditions to achieve the above purpose.
3
4 2. Method
5 We conducted dual-sonde observations at Rissho University, located in Kumagaya
6 City (around Ku in Figure 2b) and in an open area in Kanuma City (around Ka in Figure
7 2b) at 1200 Japan Standard Time (JST) on 24 January 2019 while the Karakkaze was
8 blowing. We also used conventional observational data from the automated
9 meteorological data acquisition system (AMeDAS) and sounding data at the Japan
10 Meteorological Agency (JMA’s) Wajima observatories, marked as Wa in Figure 2b.
11 We also conducted a high-resolution numerical simulation using the Weather
12 Research and Forecasting (WRF) model, version 3.9.1 (Skamarock et al. 2008). The
13 model configuration involved the two-nested domains as shown in Figure 2. The first
14 domain consisted of 133 × 133 grid points in the x and y directions with a horizontal
15 grid spacing of 6.0 km. The second domain consisted of 250 × 250 grid points with a
16 horizontal grid spacing of 2.0 km. Both domains had 58 vertical sigma levels and a
17 model top pressure of 100 hPa. The initial and boundary conditions were created from
18 the National Center for Environmental Prediction Final Analysis dataset. This dataset
19 has a 0.25˚ × 0.25˚ horizontal grid spacing and 6-hour temporal resolution. The model
20 configurations are summarized in Table S1 (see Supplement 1). Using these
21 configurations, we conducted our numerical simulation for 2 day and 3 hours: from
22 2100 JST on 22 January 2019 to 0000 JST on 25 January 2019.
23
5 6 A Case Study of the Karakkaze using Dual-Sonde Observations and a Numerical Simulation
1 3. Results
2 3.1 The Karakkaze on 24 January 2019
3 On 24 January 2019, a mid-latitude cyclone moved to the east while passing over
4 Hokkaido Island. The Siberian high was located in the west and cyclone was located in
5 in the east of Japan islands (see Supplement 2). This pressure pattern is well-known as
6 “typical winter pressure pattern in Japan”. This result shows that a wind component (i.e.
7 northwesterly wind component) across a central mountain range of Japan existed.
8 At 0900 JST on 24 January at Wajima, the cross-mountain wind component (U) is
9 estimated at about 14 m s-1 from Figs. 3a and 3b. In addition, the Brunt-Väisälä
10 frequency (N) is estimated at about 8.4×10-3 s-1 from the vertical-gradient of potential
11 temperature at Wajima (2.0×10-3 K m-1) (Figure 3c). We assume that the average height
12 of a central mountain range of Japan (hm) is about 2.0 km. From these values,
13 dimensionless mountain height (ε=Nhm/U) is estimated at about 1.2 at Wajima. This ε
14 satisfied the formation condition of the convexity wind shown in Nishi and Kusaka
15 (2019a).
16 According to surface observations of AMeDAS, the Karakkaze started to blow
17 around 0000 JST on 24 January (Figure 4a). At this time, the Karakkaze blew only in
18 the semi-basin around Maebashi (36.4N, 139.0E) and the exit of semi-basin around
19 Kumagaya (Figure 5a).
20 The peak time of the Karakkaze event at Kumagaya was recorded around 1200
21 JST. At this time, the strong wind region spread out in a fan-like shape centered on a
22 straight line that connects Maebashi city (around Ma in Figure 2b) to Chôshi city
23 (around Ch in Figure 2b), as shown in Figure 5b. The wind was weak outside the fan
24 shape (Figs. 4b and 5b). Note that Kanuma and Ebina (around Eb in Figure 2b) SOLA, 2010, Vol.6, 000-000, doi: 10.2151/sola.2010-000 7
1 AMeDAS observation stations are located outside the fan shape, although Kumagaya is
2 within it. The strong winds blew at the northern edge of the region (36.8˚N, 140.0˚E)
3 These winds are called “Nasu-Oroshi” that is considered as the different local winds
4 from the “Karakkaze”. In the present study, we focus on only one type of strong winds
5 referred to as Karakkaze.
6 We first confirmed the vertical structure of the winds observed at the Rissho
7 University near Kumagaya. At 1200 JST, the 10 minutes average before 1200 JST was
8 9.4 m s–1 at Kumagaya. At this time, the northwesterly winds blew at the 0.3 - 2.0 km
9 AMSL and at a speed of 20 m s–1 (Figs. 3a and 3b). This value was greater than the
10 wind speed by 5 - 8 m s–1 at 0900 JST at the same altitude over Wajima, located in the
11 upwind region of the mountain range. This implies that the air particles were accelerated
12 when they passed over the mountain range.
13 On the other hand, at Kanuma and Ebina stations, the hourly mean surface wind
14 speeds were 5.6 m s–1 and 1.9 m s–1 at 1200 JST, respectively. These wind speeds
15 appeared to be lower than that at Kumagaya as described above (Figure 5b). At Kanuma,
16 the wind speed in the upper atmospheric layer was also lower than at Kumagaya. This
17 relatively lower wind-speed layer was found up to 1.8 km AMSL, which is close to the
18 height of the upwind mountain range (Figs. 6a and 6b). These results suggest that the
19 weak-wind layer over Kanuma was a result of the upwind mountain effect.
20
21 3.2 Results of numerical simulation
22 In the last section, we analyzed the results of sonde observations and found
23 differences in the vertical profile of the winds between the inside, outside, and upwind
24 regions of the Karakkaze. In this section, we analyze the simulated results and reveal the
7 8 A Case Study of the Karakkaze using Dual-Sonde Observations and a Numerical Simulation
1 three-dimensional structure of the Karakkaze, which is expected to support the spatial
2 structure of the Karakkaze shown by the observations. Figure 4 shows that the wind
3 speed from the onset to the peak time of the Karakkaze at Kumagaya can be reproduced
4 by the WRF model, but the onset time was 3-hours earlier than the observation (at 2100
5 JST on 23 January in the simulation and 0000 JST on 24 January in the observation). In
6 contrast, the lysis time of the Karakkaze cannot be reproduced. Considering these
7 differences between simulation and observation (i.e., the modeling error), we analyzed
8 the results of the simulation from the onset to the peak time of the Karakkaze.
9 The WRF model can reproduce the wind distribution at the onset time of the
10 Karakkaze in which the strong winds blew only in the semi-basin around Maebashi and
11 the exit of semi-basin around Kumagaya (Figs. 5a and 5c). Additionally, the WRF
12 closely reproduced the features of the Karakkaze, in which the wind was strong along
13 the straight line connecting Maebashi and Chôshi, but was weak on both sides (Kanuma
14 and Ebina) (Figs. 5b and 5d). In addition, the northwesterly wind speed at Kumagaya at
15 an altitude of less than 2.2 km AMSL was higher than that of Kanuma (Figs. 3d and 3e).
16 The potential temperature of the mixed layer (280 K) with an altitude of less than 2.2
17 km AMSL can also be reproduced accurately (Figs. 3c and 3f). It can thus be said that
18 WRF can accurately reproduce the vertical structure of the atmosphere at the peak time
19 of the Karakkaze.
20 The wind and potential temperature at the section along the wind direction of the
21 strong wind and passing through Kumagaya (the A – A' section in Figure 2b) show that
22 the wind speed exceeded 15 m s–1 at an altitude of 1.0 km AMSL or less in the leeward
23 plain of the mountain range (139.0˚E - 139.7˚E in Figure 6a). Furthermore, the 280-K
24 isentropic line was located at an altitude of 3.0 km AMSL on the mountain climate, but SOLA, 2010, Vol.6, 000-000, doi: 10.2151/sola.2010-000 9
1 it was located at an altitude of 1.0 - 2.0 km AMSL in the lee of the mountain range.
2 Therefore, the isentropic line descended by more than 1.0 km from the windward to the
3 lee side of the mountain range. In addition, downward flows exceeding 0.5 m s-1
4 occurred in the leeward region (the cross-hatched area between 138.76˚E and 139.64˚E
5 in Figure 6a). This position of downward flows corresponds to inside and exit of the
6 semi-basin (139.0˚E-139.5˚E). This result implied that the grid-scale downward
7 momentum transfer from upper air to near ground surface appears over the semi-basin.
8 On the other hand, wind and potential temperature at the section along the wind
9 direction of the strong wind and passing through Kanuma (the B – B' section in Figure
10 2b) show that the wind speed was less than 10 m s–1 at an altitude of up to 2.0 km
11 AMSL in the leeward part of the mountain range (139.64˚E - 140.0˚E in Figure 6b). The
12 280-K isentropic line rose by 1.0 km toward the leeward side at the foot of the mountain
13 range (139.64˚E). The upward flow was strong in this region (dotted area). In other
14 words, a hydraulic jump occurred on the mountain slope in the B – B' cross-section, and
15 a weak wind appeared at an altitude of less than 1.0 km AMSL on the leeward plain of
16 the mountain range.
17
18 3.3 Comparison between the Karakkaze and convexity winds
19 Nishi and Kusaka (2019a) revealed the following characteristics of convexity
20 wind from idealized numerical simulations: (1) Wind convergence and updrafts appear
21 over the leeward slope of the semi-basin. (2) A relatively strong wind divergence
22 appears near the surface around the leeward plain of the semi-basin. (3) The downdraft
23 transports momentum from the upper air to the ground. In addition, Nishi and Kusaka
24 (2019b) revealed that the strong downward flow does not occur at the gap when the gap
9 10 A Case Study of the Karakkaze using Dual-Sonde Observations and a Numerical Simulation
1 wind occurs, differently from convexity wind.
2 The spatial structure of the Karakkaze shown in the present study is consistent
3 with that of the convexity winds proposed by Nishi and Kusaka (2019a, 2019b) rather
4 than the gap winds. From these, we can conclude the following. (1) The actual
5 conditions of terrain and atmosphere can cause convexity winds to occur. (2) The basic
6 mechanism of the Karakkaze can be explained using the concept of convexity winds.
7 4. Conclusions
8 In the present study, we conducted dual-sonde observations and a numerical
9 simulation. The results revealed that the basic features of the “Karakkaze” local wind in
10 the Kanto region closely match the characteristics of the convexity winds proposed by
11 Nishi and Kusaka (2019a, 2019b).
12 We first investigated the horizontal distribution of surface winds during the
13 Karakkaze event on January 24, 2019, using the surface wind data from the AMeDAS
14 observation network and the simulation data from the WRF model. The results showed
15 that the Karakkaze blows in the downwind plain of the convexity of the mountain range.
16 The Karakkaze region is fan-shaped, with its centerline running from Maebashi to
17 Chôshi.
18 Next, we compared the vertical distribution of the winds inside and outside of the
19 Karakkaze region, using the results of the dual-sonde observations and a numerical
20 simulation. The observation results showed that strong winds blew from near ground
21 level to a height of 1.8 km AMSL at the Kumagaya observation site, located in the
22 Karakkaze region. Weaker winds were observed and simulated at the Kanuma
23 observation site, located outside the Karakkaze region. The reason for this is that SOLA, 2010, Vol.6, 000-000, doi: 10.2151/sola.2010-000 11
1 hydraulic jump occurred on the slopes of the mountain range, and that the area outside
2 the Karakkaze region, including Kanuma, is located in a more leeward region than the
3 hydraulic jump region.
4 There are almost no differences in wind speed approximately 1.8 km AMSL
5 above the area between Kumagaya and Kanuma. It is worth mentioning that the divided
6 height corresponds with the mountain height.
7 A numerical simulation showed that the descent of the isentropic line of 1.0 km or
8 more and the strong downward flow occur over the semi-basin including Maebashi and
9 northwestern plain including Kumagaya. Such a downward flow only appears on
10 convexity winds and do not appear on typical gap winds.
11 These features closely match those of convexity winds. We can thus conclude that
12 the essential mechanism of the Karakkaze can be explained by the concept of a
13 convexity winds.
14
15 Acknowledgments
16 The present study is based on results obtained from a project commissioned by the
17 New Energy and Industrial Technology Development Organization (NEDO). We thank
18 Mr. Yuki Asano and Mr. Yuma Imai at the University of Tsukuba and other students who
19 helped with the observations. We also thank Dr. Asuka Suzuki Parker and Mr. Yusuke
20 Nakamura at the Rissho University who gave advice about with the observations. We
21 used the Generic Mapping Tool (GMT) and NCAR Command Language (NCL) to draw
22 the Figures in the present study.
23
11 12 A Case Study of the Karakkaze using Dual-Sonde Observations and a Numerical Simulation
1 Supplement
2 Table S1 shows the configuration of the numerical simulation (Supplement 1).
3 Figure S1 shows the surface weather charts at 0900 JST on 24 January 2019
4 (Supplement 2).
5
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17 18 A Case Study of the Karakkaze using Dual-Sonde Observations and a Numerical Simulation
1
2 Figure captions
3 Figure 1. Schematic of convexity winds. Arrows indicate the air streams. Blue lines
4 mean hydraulic jumps. Red area indicates strong wind area.
5 Figure 2. Model domains and topographies for the numerical simulation. (a) Domain 1.
6 Shading indicates the terrain height. (b) Domain 2. Shading indicates terrain
7 height. The lines A – A' and B – B' mark the locations of the cross-sections in
8 Figs. 6a and 6b, respectively. The labels “Wa,” “Ma,” “Ku,” “Ka,” and “Eb”,
9 respectively indicate the locations of Wajima, Maebashi, Kumagaya, Kanuma,
10 and Ebina.
11 Figure 3. Vertical profile of (a, d) wind speed, (b, e) wind direction, and (c, f) potential
12 temperature during the Karakkaze event. (a, b, c) observed values; (c, d, e)
13 simulated values. Red and black indicate the values at 1200 JST on 24
14 January 2019 at Kumagaya and Kanuma, respectively. Green shows the value
15 at 0900 JST on 24 January 2019 at Wajima.
16 Figure 4. Time series of wind speed (solid lines) and wind direction (dots) from 0900
17 JST 23 January through 0000 JST 25 January at (a) Kumagaya and (b)
18 Kanuma. Black curves and dots are observations, blue curves and dots are
19 from the WRF model.
20 Figure 5. Surface wind distributions during the peak period of the Karakkaze event. (a)
21 Observed surface wind at 10 m above ground level at 0000 JST on 24 January
22 2019. (b) Same as (a), except for at 1200 JST on 24 January 2019. (c)
23 Simulated surface wind at 10 m above ground level at 2100 JST on 23 SOLA, 2010, Vol.6, 000-000, doi: 10.2151/sola.2010-000 19
1 January 2019. Vectors show the surface winds. (d) Same as (c), except for at
2 1200 JST on 24 January 2019.
3 Figure 6. Simulated horizontal-vertical cross-section of wind speed (shadings),
4 potential temperature (contours) and vertical velocity (cross-hatched and
5 dotted areas) at 1000 JST on 24 January 2019. Cross-hatched area means
6 downdraft exceeding 0.5 m s-1. Dotted area means updraft exceeding 0.5 m s-1.
7 (a) Cross-section A – A' in Figure 2b. (b) Cross-section B – B' in Figure 2b.
8 Figure S1. Surface weather charts at 0900 JST on 24 January 2019 from the Japan
9 Meteorological Agency (2019). The black thin and thick counters indicate the
10 sea level pressure at every 4 and 20 hPa.
11
12 Table captions
13 Table S1. Configuration of the numerical model
14
19 Hydraulic jump Weak wind region
Strong wind region
downdraft
Weak wind region
Figure 1. Schematic of convexity winds. Arrows indicate the air streams. Blue lines mean hydraulic jumps. Red area indicates strong wind area. (a) (b)
(km) (km)
Figure 2. Model domains and topographies for the numerical simulation. (a) Domain 1. Shading indicates the terrain height. (b) Domain 2. Shading indicates terrain height. The lines A ‒ A' and B ‒ B' mark the locations of the cross-sections in Figs. 6a and 6b, respectively. The labels “Wa,” “Ma,” “Ku,” “Ka,” and “Eb”, respectively indicate the locations of Wajima, Maebashi, Kumagaya, Kanuma, and Ebina. (a) (b) (. c) 4
3 ] m [k t h 2 g i e H 1
0 010203040180 270 360 270 280 290 300 Windspeed [m s−1] Wind direction [o] θ [K]
(d) (e) (f). 4
3 ] m [k t h 2 g i e H 1
0 010203040180 270 360 270 280 290 300 Windspeed [m s−1] Wind direction [o] θ [K]
Figure 3. Vertical profile of (a, d) wind speed, (b, e) wind direction, and (c, f) potential temperature during the Karakkaze event. (a, b, c) observed values; (c, d, e) simulated values. Red and black indicate the values at 1200 JST on 24 January 2019 at Kumagaya and Kanuma, respectively. Green shows the value at 0900 JST on 24 January 2019 at Wajima. (a) Kumagaya
2019/1/23 2019/1/24 Japan standard time (b) Kanuma
2019/1/23 2019/1/24 Japan standard time
Figure 4. Time series of wind speed (solid lines) and wind direction (dots) from 0900 JST 23 January through 0000 JST 25 January at (a) Kumagaya and (b) Kanuma. Black curves and dots are observations, blue curves and dots are from the WRF model. a
37˚ 37˚
36˚ 36˚
< 2 m s−1 2 m s−1 5 m s−1 35˚ 35˚ 10 m s−1 138˚ 139˚ 140˚ 141˚ 138˚ 139˚ 140˚ 141˚ (c) WRF 2019/1/23 2100 JST (d) WRF 2019/1/24 1200 JST
Figure 5. Surface wind distributions during the peak period of the Karakkaze event. (a) Observed surface wind at 10 m above ground level at 0000 JST on 24 January 2019. (b) Same as (a), except for at 1200 JST on 24 January 2019. (c) Simulated surface wind at 10 m above ground level at 2100 JST on 23 January 2019. Vectors show the surface winds. (d) Same as (c), except for at 1200 JST on 24 January 2019. (a) [m s-1]
(b) [m s-1]
Figure 6. Simulated horizontal-vertical cross-section of wind speed (shadings), potential temperature (contours) and vertical velocity (cross-hatched and dotted areas) at 1000 JST on 24 January 2019. Cross- hatched area means downdraft exceeding 0.5 m s-1. Dotted area means updraft exceeding 0.5 m s-1. (a) Cross-section A ‒ A' in Figure 2b. (b) Cross-section B ‒ B' in Figure 2b.