The “Karakkaze” Local Wind As a Convexity Wind: a Case Study
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The Meteorological Society of Japan Scientific Online Letters on the Atmosphere (SOLA) EARLY ONLINE RELEASE This is a PDF of a manuscript that has been peer-reviewed and accepted for publication. As the article has not yet been formatted, copy edited or proofread, the final published version may be different from the early online release. This pre-publication manuscript may be downloaded, distributed and used under the provisions of the Creative Commons Attribution 4.0 International (CC BY 4.0) license. It may be cited using the DOI below. The DOI for this manuscript is 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.