Intense Summer Heat in Tokyo and Its Suburban Areas Related with Variation in the Synoptic-Scale Pressure Field: a Statistical Analysis

SEPTEMBER 2013 Y O S H I K A D O 2065

Intense Summer Heat in Tokyo and Its Suburban Areas Related with Variation in the Synoptic-Scale Pressure Field: A Statistical Analysis

HIROSHI YOSHIKADO Graduate School of Science and Engineering, Saitama University, Saitama, Japan

(Manuscript received 21 November 2012, in ﬁnal form 18 April 2013)

ABSTRACT

Intense summer heat in Tokyo, Japan, and its suburban areas between 1990 and 2010 was statistically analyzed. Sample days were selected from among days with a sea breeze and sufficient sunshine duration, because sea breeze is the dominant summertime meteorological system in the region. Excess in the daily maximum temperature of an inland urban site in Tokyo over a site facing the outer sea where the sea breeze originates was selected as a key index. A comparison of a group of days for which the temperature excess was large with an opposing group of days for which it was small revealed a distinct difference in diurnal wind variations: persistent southwesterly winds overwhelmed the sea breeze in areas facing the outer sea in the former case, whereas in the latter case a diurnal sea-breeze cycle was typically observed in those areas as well as in the inland areas. This difference could furthermore be connected to differences in the pressure gradient in the region, that is, differences in the synoptic-scale pressure field. As a result, slight shifts in the pressure field affect urban heat, suggesting that, in addition to general warming, changes in the pressure field resulting from future climate change can be of great importance.

1. Introduction effects remain at the present levels. The response of the urban climate to global warming requires analysis to Increased air temperature in urban areas compared cope with these problems. with surrounding rural areas is a well-known phenom- Urban climate is influenced by larger-scale meteoro- enon called the urban heat island (UHI). This phe- logical factors. First of all, global warming is expected to nomenon is most clearly observed in large cities. In the raise base temperatures in urban areas as in most regions case of Tokyo, the annual average temperature has in- 2 of the world. More specifically, however, global climate creased at a rate of 3.28C (100 yr) 1 for the period be- change is an aggregate of changes in synoptic-scale sys- tween 1931 and 2011 (JMA 2012). For the same period, tems such as pressure distributions and accompanying 17 observatories in remote small towns recorded an 2 weather characteristics in each season. These changes average temperature increase of 1.58C (100 yr) 1. This furthermore influence local wind patterns around urban increase is considered to be mainly a response to global areas of interest. Therefore, UHIs are influenced by climate change in the Japan region, and the difference in synoptic-scale meteorology through local meteorology. Tokyo’s temperature is attributed to the UHI effect. Many studies have been devoted to local winds and Special attention is paid to daily maximum tempera- thermal structures dominated by synoptic-scale systems. tures T in summer because the peak electric power max The Kanto Plain, with the Tokyo metropolitan area in demand for air conditioning is directly dependent on it. the southern part, has been the most important region in Also, there is a marked increase in the number of cases Japan for such studies. For example, Fujibe (1985) an- of heat stroke in hot summers. Global warming will alyzed deviations in local winds over the south Kanto possibly aggravate these circumstances, even if the UHI region under the influence of a synoptic-scale pressure gradient. Furthermore, Fujibe (1998) examined extremely hot days in the Kanto Plain in relation to the Corresponding author address: Hiroshi Yoshikado, Graduate School of Science and Engineering, Saitama University, Saitama, pressure gradient. Nevertheless, few researchers have 338-8570, Japan. analyzed the two-stage reaction, between synoptic-scale E-mail: [email protected] and local-scale systems as the first stage and between

DOI: 10.1175/JAMC-D-12-0315.1

Ó 2013 American Meteorological Society Unauthenticated | Downloaded 09/30/21 09:21 AM UTC 2066 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 52 local-scale and urban-scale systems as the second stage, The present study statistically analyzes data observed specifically for the UHI around Tokyo. This is probably in Tokyo and its suburban areas with the aim to detect due to the preconception that urban-scale phenomena a two-stage relationship that connects synoptic-scale are not sufficiently clear to be detected under dynamic structure with intense summer heat through local-scale changes in larger-scale systems. In reality, however, the systems, while synoptic-scale structures predominant in UHI observed in the Tokyo area persists under the the future will be predicted by GCMs. Automated Me- predominant summertime sea-breeze system and in- teorological Data Acquisition System (AMeDAS) data fluences the downwind suburban climate (Yoshikado from the Japan Meteorological Agency (JMA) for 21 1990). Shifts in the prevailing pressure field under the summers between 1990 and 2010 are employed for this influence of global climate change may therefore distort purpose, with ‘‘summer’’ defined as July and August. major sea-breeze patterns, and furthermore may alter urban and suburban climate in a more intricate way than mere warming. 2. Methodology and data used Future urban climates under global warming are a. Hypotheses currently investigated using general circulation models (GCMs) and dynamical downscaling. Kusaka et al. Some factors and mechanisms can presumably in- (2012) made detailed climate predictions, namely tem- tensify summer heat in urban areas. First, air tempera- poral and spatial variations in temperature and other tures increase when a particularly hot synoptic-scale air meteorological factors, in major Japanese urban areas mass covers the area (hypothesis 1). Second, sunshine for the 2070s. They incorporated the best estimate cur- will heat land air more on clear days (hypothesis 2). It is rently available for future local climates by a pseudo– also empirically known that successive clear-sky days global warming method (PGW) developed by Kimura result in increased daily maximum temperatures (hy- and Kitoh (2007). The PGW uses averaged temperature pothesis 2a). These are direct effects of synoptic-scale rises predicted by GCMs instead of direct GCM output meteorology on urban climate. for future climate. Iizuka et al. (2010, 2011) applied The third factor is variations in local wind patterns, a similar approach to the Nagoya region. In their work, which contribute to the above-mentioned two-stage re- however, the magnitude of urban warming is mainly action and are of major interest in the present study. presented without discussion of the specifics of change Tokyo is located in the coastal area of the Kanto Plain, in synoptic-scale effects on local-scale or urban-scale and the sea breeze penetrates there mostly on fine climate. Analyzing this two-stage reaction with statis- summer days. As the sea breeze generally cools the tical reliability, even from past data, would improve coastal areas, a delay in its inflow can promote urban understanding of future summer heat. As an example heat. Note that the time and direction of the sea-breeze of the statistical analysis of synoptic-scale data to re- inflow depends on the synoptic-scale pressure gradient search local warming, Fujibe (1998) reported an in- (Fujibe 1985). Therefore, some pressure patterns are crease in the number of days characterized by an expected to promote urban heat, and other pressure extremely warm air mass and sufficient sunshine after patterns to moderate it (hypothesis 3). the 1980s as a cause of the increase of extremely hot We confine the analyses to days on which the sea days in the Kanto Plain. breeze developed in Tokyo and its suburban areas (SB Another insufficiency in the current modeling ap- days, below) as the most representative summertime proach, as well as in statistical analysis, is the lack of meteorological system, although another notable system a relationship between year-to-year variations in larger- promoting summer heat in the Kanto Plain has also been scale climate and urban summer heat. There were ir- investigated (Takane and Kusaka 2011). The relation regularly hot summers in the past several decades. between SB days and urban summer heat is clarified in Fujibe (1996) examined the hot summer experienced in section 3a. Japan in 1994 and concluded that UHI was a minor b. Region and data used factor in the intense heat observed that year. This im- plies that a larger-scale meteorological structure was the The Tokyo metropolitan area is most heavily urban- main cause. We suppose that not only synoptic-scale ized along the shore of Tokyo Bay and landward, mainly structures but also local systems developing under their to the northwest. Approximately 18 million people live influence, such as land and sea breezes, play an impor- in this region. Downtown Tokyo is located on the tant role, and thus that combined synoptic-scale and northwest coast of the bay, where three AMeDAS sta- local-scale structures will dominate the intensity of tions are located (see Fig. 1): Shinkiba near the shore at summer heat every summer, and ultimately every day. the north end of the bay, Tokyo in the central area about

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FIG. 2. Numbers of days in the groups of days deﬁned in the study.

There are exceptional sites in urbanized areas, which FIG. 1. The southern Kanto region and targeted AMeDAS sta- are not surrounded by wide fields. To compensate for tions: Shinkiba (S), Tokyo (T), Nerima (N), Urawa (U), Kumagaya this, for example, the anemometer of the Tokyo station (K), and Tateyama (Ta). Shading level indicates the percentage of is placed on the roof of a high-rise building, 35 m above built-up areas in a 1-km grid, and gray lines are boundaries of prefectures. the ground, and therefore the wind direction can be representative of the area even if a representative wind speed cannot be defined. Air temperatures are mea- suredataunifiedheightof1.5m,andeventhoughthe 8 km northwest of Shinkiba (note that in the remainder Nerima station is located in a built-up residential area, of this paper, in most cases ‘‘Tokyo’’ refers to the its data are representative of the conditions in such monitoring station), and Nerima on the inland side of areas. downtown. Nerima is 12 km northwest of Tokyo, and the next station is Urawa, in a suburban area 15 km north- c. Selection of sea-breeze days northwest of Nerima. Days during July and August between 1990 and 2010 Another station of special importance in this analysis were classified as SB days according to the following is Tateyama, 70 km south of Shinkiba. For examining conditions for Tokyo and Urawa. hypothesis 1, this station was selected as representative of the sea air temperature unaffected by the landmass, 1) Northerly wind or calm at dawn: Wind direction although local land effects are of course included to- between 0400 and 0600 LT was WSW to E clockwise, 2 gether with local sea surface temperatures. Several or calm with wind speeds of 1 m s 1 or less. For other stations not indicated in Fig. 1 are referred to as Tokyo, however, we replace the ‘‘calm’’ condition 2 needed. with ‘‘wind speed of 4 m s 1 or less,’’ accounting for These AMeDAS stations provide hourly readings the fact that pressure gradients decreasing toward of air temperature (resolution 0.18C), wind direction the north tend to persist in summer along the 2 (16 directions), wind speed (resolution 1 m s 1), and southern shores of the Kanto region. Note that even sunshine duration (0–10; e.g., 0.1 h of sunshine is ex- with this alternative condition, condition 3 below pressed by 1). The AMeDAS network, maintained by must not be satisfied at least at 0700 LT for a day to the JMA, monitors mesoscale phenomena in real time be classified as an SB day. and consists of stations distributed with an average 2) Clear skies during midday: Total sunshine duration spacing of 20 km, with attention paid to the represen- (SS) for 0900–1500 LT $ 30 (maximum value 5 60). tativeness of each area in conformity to a guideline. 3) Steady southerly wind during midday: Wind di- Every site is selected on pervious ground covered with rectionwasESEtoSWclockwise,withwindspeeds 2 grass in an open field; the anemometer is installed at of 2 m s 1 or greater for 2 consecutive hours after the top of a pole whose height is generally 6.5–10 m. 0800 LT.

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FIG. 3. Trends in intensely hot days at Nerima in July–August, 1990–2010, and the number of Tokyo and typical SB days within these days.

Two additional conditions were applied to narrow down SB days to those typical of the area of interest: 4) Onset time of the sea breeze at Tokyo was between 0800 and 1300 LT. 5) Onset time of the sea breeze at Urawa was the same as, or later than, that at Tokyo. No sea-breeze arrival

at Urawa was also accepted, but cases in which the FIG.4.TheTmax at Tateyama vs Tmax at Nerima on typical SB days time lag exceeds 6 h were considered irregular and for different classes of SS at Tokyo. Linear regression lines are also therefore excluded. drawn, each corresponding to the SS class shown in the legend box. 2 These conditions are kept simple because it is un- geostrophic wind speeds were .10 m s 1. As most sea- 2 necessary for this study to classify SB days based on breeze days occurred at wind speeds , 10 m s 1 (cf. Fig. strict definitions. 8), these days were considered to be characterized by steep pressure gradients, under which no sea breeze can develop, and some other pressure patterns. 3. Data analysis a. Intense summer heat and SB days The conditions described in section 2c resulted in 400 typical SB days in the 42 months examined (Fig. 2). Here, a ‘‘typical SB’’ day means one satisfying conditions 4 and 5 in addition to conditions 1–3. We define an intensely hot (IH) day as one with the daily maximum temperature Tmax $ 358C, following the JMA’s definition. There were 46 IH days at Tokyo, 194 at Nerima, and 143 at Urawa during the same period, suggesting that cool sea breeze affects Tokyo more strongly and earlier than Nerima on the inland side of downtown Tokyo. Figure 3 indicates that many IH days were SB days, especially in those years when many IH days occurred; 120 of the 194 IH days at Nerima were typical SB days, and 143 days were Tokyo SB days (which means that SB conditions 1–3 are satisfied at Tokyo). We therefore focus our analysis on the SB days described in section 2a and consider the factors promoting or suppressing heating in areas such as Nerima. FIG. 5. As in Fig. 4, but only for cases in which SS $ 51. Data are For the remaining days, of the 51 IH days that were further separated into P, M, and N days by color [and by two not SB days, nearly half of them (24) occurred un- imaginary lines corresponding to linear regression lines (not drawn der steeper pressure gradient whose corresponding but same as one denoted as 51- in Fig. 4) 618C].

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FIG. 6. Scatterplots of Tmax between Tateyama and other stations for typical SB days with SS $ 51 with each plot separated into P, M, and N days.

b. Tmax at Nerima on SB days similar Tmax values at Tateyama? Second, where does such dispersion as observed at Nerima develop: only in

Figure 4 compares Tmax at Nerima and Tateyama on the vicinity of Nerima, or gradually from further upwind? typical SB days. At Tateyama, we expect to observe We suspect that hypothesis 3 in section 2a answers the temperatures near that of the outer sea air before sea ﬁrst question, and examine detailed sea-breeze patterns breeze advances over the land, although some land in- in the following section. However, ﬁrst we attempt to

fluence is certainly present. We find a positive correla- answer the second question by analyzing Tmax at several tion between the two stations, probably corresponding stations, as we do for Nerima in Fig. 5, with the symbol to hypothesis 1 in section 2a. The graph furthermore for each sample day retained (Fig. 6). suggests that larger values for SS raise Tmax at Nerima Dispersion is reasonably small at Miura because its relative to Tateyama. This corresponds to hypothesis 2 position is similar to that of Tateyama, reflecting the in section 2a. temperatures of outer sea air. Shinkiba, at the north end However, dispersion along the vertical axis is as large of Tokyo Bay, unexpectedly gives similar results. This as approximately 58C, even when only days with SS $ 51 probably indicates that sea breezes from the outer sea are sampled (see Fig. 5). Sample days in Fig. 5 were penetrate the bay almost without being influenced by simply separated into three groups by two lines parallel the heated land. to the linear regression line (not drawn in Fig. 5). We On the western coast of the bay (Miura, Yokohama, refer to these groups as positive (P), medium (M), and and Tokyo in Fig. 6), however, Tmax exceeds that at negative (N) bias days. In this study, there were 43 P, Tateyama more frequently on P days than on N days, 109 M, and 57 N days. and their distribution is similar to that at Nerima. The

We are faced with two questions. First, what factor so increase in Tmax on P days is perceived even at Yokohama, widely disperses Tmax at Nerima, even for days with which is much closer to Tateyama and Miura than is

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FIG. 7. Average wind hodographs on P and N days for (a) Nerima, (b) Shinkiba, (c) Tokyo, and (d) Tateyama. A wind vector at every hour (LT; numerals beside symbols) would be indicated by an arrow (not drawn) from the origin to every time marker. The W–E and S–N components of wind are u and y, respectively.

Shinkiba, and the increase approaches the magnitude at and night on P days, whereas nocturnal calm condi- Nerima (Fig. 5) with the distance from the southern tions and diurnal sea-breeze developments alternate coast facing the outer sea. on N days. The southwesterly component is noticeable also in P-day hodographs for Shinkiba and Tokyo c. Wind hodographs for P and N days (Figs. 7b,c). Diurnal variations in winds averaged for each of P and The southwesterly wind on P days can be associated N day were obtained ﬁrst for Nerima, but no substantial with a synoptic-scale pressure ﬁeld. Corresponding difference was found between them (Fig. 7a). Both ho- geostrophic winds are shown in Fig. 8. The geostrophic dographs are characterized by nearly calm conditions at winds on P days are westerly overall, meaning that the night and a southerly sea breeze during the daytime. pressure decreases toward the north. Similarly to Nerima, hodographs for P and N days are d. Diurnal temperature variations for P and N days quite similar for the inland suburban areas to the west and north of Tokyo (not shown). In addition to Tmax, which was used in section 3b as the In contrast, those for Tateyama exhibit remarkable basic indicator of heat for each sample day, we examined differences (Fig. 7d). A southwesterly wind persists day diurnal temperature variations for P and N days. As

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FIG. 8. Surface geostrophic winds at 0900 LT on P and N days, calculated from the two pressure gradients shown in the map. The length and direction from the origin to each symbol defines a wind vector. shown in Fig. 9, the most conspicuous is a small tem- extremely high as seen in Fig. 5, they did not rise as much perature rise at Tateyama on P days, which might be during the advance to Nerima. consistent with the persistent southwesterly winds seen The predominant high corresponding to P days, cov- in Fig. 7d. Southwesterly winds supply sea air with ering the Kanto region from the south, is presumably smaller diurnal temperature variation more actively accompanied by a subsidence inversion. A more stable than sea breeze. potential temperature profile is correspondingly detected On the other hand, the temperature rise at Nerima is for P days at Tateno, located in the central region of the certainly more substantial on P days than on N days. We Kanto Plain (Fig. 12). The more stable stratification can ask why this is the case on P days than on N days at Nerima, in spite of the similar winds (Fig. 7a) in both cases. This is discussed in the final section after some further analyses. e. Pressure systems characterizing P and N days We have already found multiple factors characterizing P days that are mutually consistent: a local pressure gradient decreasing toward the north, southwesterly wind, and a small temperature rise at Tateyama facing the outer sea. Some specific synoptic-scale pressure distributions are expected to promote these features. Examining the numbers of P and N days (Fig. 10), their occurrence frequencies were extremely one sided in years where summer heat was particularly intense. For example, 20 and 21 typical SB days occurred in 1994 and 1995, and the ratios of P and N days for those years were 1:12 and 9:1, respectively. During the summer of 1995, when there were many P days, the predominant North Pacific high tended to extend from the east of Japan to the south of the Kanto region (Fig. 11a). In contrast, the Pacific high rarely prevailed in the 1994 summer

(Fig. 11b), and N days were more frequent. In the latter FIG. 9. Diurnal temperature variations averaged for (a) P days and case, even when the temperatures at Tateyama were (b) N days at Nerima, Tokyo, and Tateyama.

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the same (a P day after a P day) or increase in magnitude (a P day after an M day), since a P day (and an M day) means large (moderate) temperature rise over land with large SS ($ 51); few N days occurred after P or M days although N days are included in clear-sky days with SS $ 51. These results support hypothesis 2a, which suggests that serial clear-sky days tend to result in a P day.

4. Discussion and conclusions Urbanization promotes summer heat. Increase in base air temperature caused by future climate change may enhance its severity. Not only averaged temperature increase but changes in local meteorological systems induced by synoptic-scale climate change can affect the FIG. 10. (top) Number of typical SB days with SS $ 51 for July– severity. To detect this kind of two-stage reaction, me- August each year 1990–2010. (bottom) Composition ratios with teorological factors associated with intense summer heat respect to P, M, and N days. in the Tokyo metropolitan area were analyzed statistically using AMeDAS data. Here, the focus was on in- generally results in a larger temperature rise if the tense heat on sea-breeze days because the sea breeze heating is equivalent, and promotes the intense heat on is the dominant wind pattern during summer days in P days. the Kanto region, which includes the Tokyo area. In- tense heat is most frequently observed at Nerima, on f. Successive P and N days the inland side of downtown Tokyo. For comparison, As a final data analysis, we briefly examined hy- Tateyama was selected as a reference point represen- pothesis 2a in section 2a. On the day before each of the tative of the sea air temperature prior to sea-breeze 43 P days, there were 11 P days, 13 M days, no N days, inflow to the land, in particular to the urban areas. and 4 typical SB days with SS , 51, as well as 14 days The positive correlation between daily maximum without typical SB. One case could not be determined temperatures at the two points in Fig. 4 supports hy- because of insufficient data. On the other hand, on the pothesis 1, namely that an increase in the temperature of day before each of the 57 N days, there were no P days, synoptic-scale air mass promotes summer heat. Fur- 6 M days, 10 N days, and 19 typical SB days with SS , 51 thermore, the upward shift of the linear regression line were observed, as well as 21 days without typical SB. following the increase in accumulated sunshine duration This suggests that daily temperature rise tends to stay suggests the validity of hypothesis 2, namely that an

FIG. 11. Typical pressure patterns (a) in the summer of 1995 associated with P days and (b) in the summer of 1994 associated with N days.

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side of downtown Tokyo and areas further inland (Fig. 7a). Only on the southern coast and further east of the shore of Tokyo Bay, southwesterly winds from the predominant Pacific high extending to the south of the Kanto region are occasionally stronger than the sea breeze, intensifying inland heat. In the opposite case, when sea breeze is also observed on the east of Tokyo Bay, inland heat is relatively moderate. The two groups of typical sample days are respectively denoted as P and N days in the present study. Regarding the question of how synoptic-scale southwesterly winds lead to intense inland heat, in spite of the small temperature rise at the southern shore area (Fig. 9a), the answer can probably be obtained by an exami- nation of diurnal variations of winds in a broader region than that covered by the sites in Fig. 7. Figure 13a suggests that, on the P days, a fragment of the southwesterly wind landing at the west of the mouth of Tokyo Bay FIG. 12. Vertical potential temperature profiles averaged for advances by land along the west shore of the bay, and P and N days. The profile with clear symbols is a horizontal reaches the inland side of downtown Tokyo. The air translation of the N days for comparison. The data are from Tateno along this trajectory experiences long active heating by Aerological Observatory for 0900 LT and interpolated every 50 m in the vertical direction. the land. An opposite wind pattern for the N days (Fig. 13b) seems to cause the onshore sea breeze near the north end of the bay to advance downtown. In this case, increase in sunshine increases land air temperatures. It is the sea air is supplied from the bay, and its temperature also true that successive days with long sunshine dura- is almost the same as that at Tateyama (cf. the Shinkiba tions promote temperature rises. case in Fig. 6). This discriminating heating process seems In addition to these synoptic-scale factors, variations to be similar to that investigated by Zhang et al. (2011). in the sea-breeze pattern related to the synoptic-scale It should also be noted that wind speeds to the northwest pressure distribution (hypothesis 3) also proved to be an of downtown are rather low in both cases, a phenome- important factor for particularly intense heat. Signifi- non that is often referred to (e.g., Yoshikado 1990) and cant variations, however, are not detected on the inland that may intensify local heating.

FIG. 13. Surface winds at 1400 LT averaged for (a) P days and (b) N days.

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In conclusion, the factors mentioned in hypotheses 1 ——, 1998: An increasing trend of extremely hot days in the inland and 2 certainly contribute to the intense heat in the Tokyo of the Kanto plain and its relation to urban effects (in Japanese area, and static stability (Fig. 12) structurally influences it. with English abstract). Tenki, 45, 643–653. Iizuka, S., K. Kinbara, H. Kusaka, M. Hara, and Y. Akimoto, 2010: Also of great significance is the fact that slight shifts in the A numerical simulation of current status of summer and an synoptic-scale pressure field can influence the intensity of attempt to project a future thermal environment combined urban heat. Depending on what type of pressure field with pseudo global warming data—Numerical study on ther- becomes prevalent under future climate change, the in- mal environment in the Nagoya metropolitan area by using tense summer heat in urban areas can become more se- WRF (Part 1) (in Japanese with English abstract). J. Environ. Eng., 75, 87–93. vere than the averaged effects of warming, or vice versa. ——, ——, ——, and ——, 2011: A long-term projection of As far as recent tendencies are examined (Fig. 10), N a thermal environment in summer of the 2070s—Numerical days, which occurred with considerable frequency in the study on thermal environment in the Nagoya metropolitan 1990s, have not been as frequent in recent years, whereas area by using WRF (Part 2) (in Japanese with English ab- the frequency of occurrence of P days tends to be con- stract). J. Environ. Eng., 76, 425–430. JMA, cited 2012: Climate change monitoring report 2011 (in stant. Over the total sample number, however, the Japanese). Japan Meteorological Agency, 62 pp. [Available sea-breeze days with the longest sunshine duration di- online at http://www.data.kishou.go.jp/climate/cpdinfo/ minished to several days in most of the period of 2002–09, monitor/2011/pdf/ccmr2011_all.pdf.] and therefore future trends should be monitored. Kimura, F., and A. Kitoh, 2007: Downscaling by pseudo global The intense summer heat associated with the Tokyo warning method. Research Institute for Humanity and Nature ICCAP Final Rep., 4 pp. [Available online at http://www. metropolitan area in fact extends beyond the city, es- chikyu.ac.jp/iccap/ICCAP_Final_Report/2/4-climate_kimura. pecially to the northwest, which is the downwind di- pdf.] rection of the sea breeze in the area. The connection Kusaka, H., M. Hara, and Y. Takane, 2012: Urban climate pro- between this and summer heat in the inland areas will be jection by the WRF model at 3-km horizontal grid increment: discussed in another study. Dynamical downscaling and predicting heat stress in the 2070’s August for Tokyo, Osaka, and Nagoya metropolises. J. Meteor. Soc. Japan, 90B, 47–63. Acknowledgments. The author thanks the JMA for Takane, Y., and H. Kusaka, 2011: Formation mechanisms of the providing the AMeDAS data. This study was supported extreme high surface air temperature of 40.98C observed by JSPS KAKENHI Grant 22246074. in the Tokyo metropolitan area: Considerations of dynamic foehn and foehnlike wind. J. Appl. Meteor. Climatol., 50, 1827–1841. REFERENCES Yoshikado, H., 1990: Vertical structure of the sea breeze pene- trating through a large urban complex. J. Appl. Meteor., 29, Fujibe, F., 1985: An effect of pressure gradient on the diurnal vari- 878–891. ation of wind in the atmospheric boundary layer. J. Meteor. Zhang, D., Y. Shou, and R. R. Dickerson, 2011: Impact of upstream Soc. Japan, 63, 52–59. urbanization on the urban heat island effects along the ——, 1996: Boundary layer features of the 1994 hot summer in Washington–Baltimore corridor. J. Appl. Meteor. Climatol., Japan. J. Meteor. Soc. Japan, 74, 259–272. 50, 2012–2029.

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