The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, JapanINLAND AIR-HEATING INDUCED BY A SEA-BREEZE PENETRATION
Yukitaka Ohashi*, Atsuko Sano*, and Yukihiro Kikegawa***Okayama University of Science, Okayama, Japan; **Meisei University, Hino, TokyoAbstract
To clarify the heating mechanism of Nara Basin in Japan, we simulated local circulations developed over theKansai area, with mesoscale meteorological numerical model, WRF. Since Osaka Prefecture is more urbanizedthan surroundings, the urban canopy structure and anthropogenic heat emission will affect not only the local
thermal environment there but also the mesoscale atmosphere of surroundings. Our simulations revealed that thetwo heating mechanisms: a dry-foehn phenomenon due to the dry adiabatic process with the mountain-passing
sea breeze, and a sensible-heat transport from Osaka urban area by the sea-breeze penetration. These effects
induced the air-heating at Nara Basin about 0.5~2.0℃.
Key words: sea breeze, heat transport, Osaka Plain

1. INTRODUCTION
The Kansai area (Fig.1) of Japan, which includes Osaka, Kyoto, and Nara Prefectures, is an interesting field
which two sea-breezes penetrate inland from Osaka Bay: one penetrates into the northeastern Kyoto Basinthrough a plain, the other does into the eastern Nara Basin through over a mountain (600 m in height). Featuresof these sea breezes have been investigated by Iishii et al. (2000), Ohashi and Kida (2002; 2004), Yamazaki(2004) and so on, using a numerical model. Athough the dynamics of sea-breeze circulations were clarified bythese studies, no simultanous comparison have been discussed yet. Therefore, the role of each sea breeze onthe climate of Kansai area sould be distincted through the comparison between two sea-breeze. Especially, thesea breeze through over Mt. Ikoma plays an important role of the climate in Nara Basin where a typical basin
climate is formed.
Using a meso-scale meteorological model, we investigated the effect of sea-breeze which penetrated into Nara
Basin on the basin temperature, as the first step of our aims.
2. AIR-HEATING DUE TO SEA BREEZE DETECTED FROM METEOROLOGICAL DATA
We measured surface air-temperature at some sites during the period of summer season, July 27 to August 17in 2007. As shown in Fig.1, the two lines were assigned for observation; the “KH (Keihan) LINE” is along Osakaand Kyoto points, and the “I (Ikoma) LINE” is along Osaka and Nara points. Figure 2 indicates that the temporalvariations of surface air-temperature measured over the I LINE on (a) non-sea-breeze day and (b) sea-breeze
day. The temperatures were averaged every 10 minutes and separating non-sea-breeze and sea-breeze days
during the observation period. The daytime temperature measured at the site of I③, which is located within Nara
Basin, was lower than those of I① and I② on non-sea-breeze day, whereas the temperature of I③ became thehighest of the three sites on sea-breeze day; this feature was detected after the arrival time of sea breeze. Thus,
the sea breeze, which penetrated into Nara Basin through over Mt. Ikoma, seems to rise the Nara temperature.
On the other hand, the daytime maximum temperatures at the sites of KH LINE (Fig.3) were delayed with inland
on sea-breeze day, whereas no such a feature appears on non-sea-breeze day.
The above features were also confirmed from the AMeDAS (Automated Meteorological Data AcquisitionSystem) stations which were established by Japan Meteorological Agency.
3. NUMERICAL MODEL3.1. WRF
We used a numerical meteorological model, WRF (Weather Research and Forecasting model) -AWR Ver. 2.2
which was developed by NCAR and so on. The WRF is a compressible fluid and non-hydrostatic model. The
Noah-LSM (Chen and Dudhia, 2001) is adopted as a land surface model, which includes plant and urban canopylayers (Kusaka et al., 2001). The TKE prognostic equation (the Mellor-Yamada-Janjic scheme; Janjic, 2001) isadopted for the parametarization of the atmospheric boundary layer. Also, the Lin scheme (Lin et al., 1983) waschosen for the micropyisic calculations.

The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, JapanThe horizontal computational domain was divided into the three, and each domain was connected by the twoway nesting method. The domain, which had a finest mesh (1 km in horizontal), included the Osaka and Kyoto
urban areas, and includes 79×91 grids. The initial and boundary conditions were given from the use of the mesoscale objective analysis data and RTG_SST data which were provided by the Japan Meteorological Agency andNCEP, respectively. The calculation started from 20 July, 2007 and ended on 31 August, 2007. Thus, thesimulation results during the period of 42 days except the first day were analyzed.
3.2. Treatments of Osaka urban effects
Urban canopy effects are introduced by the single-layer urban model. Because the anthropogenic heat emittedfrom the Osaka urban area can be neglected to impact the atmospheric heating, we inputted the mesh data of theanthropogenic heat flux estimated from the urban energy consumption. Additionally, we improved the model asthat the heat intruded into building rooms (windows and walls) was pumped to the outside atmosphere by airconditioning operations.
4. SIMULATION RESULTS
Figure 4 shows the temporal variations of surface air-temperatures measured and calculated within Nara Basin.
The calculated temperature well corresponds to the measured that, especially compared with the simulation casewithout urban canopy and anthropogenic heat.
To investigate the urban and mountain effects on Nara temperature, we calculated four assumptions with WRF:
①CASE ALL includes urban canopy layer, anthropogenic heat emission, and real terrain (mountains), ②CASE
SLAB without urban canopy and anthropogenic heat, ③CASE FLAT with flat plain without mountains, and ④
CASE NO without all.
Figure 5 indicates the differences in daily maximum temperatures between CASES ALL, SLAB, FLAT and
CASE NO, at Nara Basin. The Nara temperature difference between CASE SLAB and CASE NO implies
mountain effects; in many days of sea breeze arrival at Nara, the temperatures in CASE SLAB were 0.5℃ or overhigher than those in CASE NO. We consider that a dry-foehn appears due to a descending sea breeze from Mt.
Ikoma. On the other hand, the temperature difference between CASE FLAT and CASE NO represents an
influence of the Osaka urban heat transported by sea breeze on Nara temperature. In the almost sea-breeze days
at Nara, the temperatures in CASE FLAT were 0.5~1.5℃ higher than those in CASE NO. This heating at Nara isinduced by the horizontal advection of the Osaka urban heat. Finally, the temperature difference between CASE
ALL and CASE NO is provided by the above both works. The temperatures in CASE ALL were higher than thosein CASE NO in all sea-breeze days. Additionally, these temperature differences were, to some extent, higher thanthose between CASE FLAT and CASE NO. It is worthy of note that the temperature differences between CASE
ALL and CASE NO become to be smaller than sum of “CASE SLAB minus CASE NO” and “CASE FLAT minus
CASE NO.” That is, the coexistence of the Osaka urban area and Mt. Ikoma weakens the air-heating at Nara
Basin. This results from the fact that Mt. Ikoma works as the “wall” which makes the Osaka urban heat transportdifficult.
References
Chen, F. And Dudhia, J., 2001. Coupling an advanced land surface-hydrology model with the Penn State-NCAR
MM5 modeling system. Part Ⅰ: model implementation and sensitivity. Monthly Weather Review, 129, 569-585.
Ishii, Y., Tamai, M., and Muraoka, K., 2000. An Interaction between heat-island and sea breeze in the Osaka plain.
Nagare, 19, 139-142 (in Japanese).
Janjic, Z.I., 2001. Nonsingular implementation of the Mellor-Yamada level 2.5 scheme in the NCEP meso model.
NCEP Office Note #437.
Kusaka,H., Kondo, H., Kikegawa, H., and Kimura, F., 2001. A simple single-layer urban canopy model foratmospheric models: comparison with multi-layer and slab models. Boundary-Layer Meteorology, 101, 392-358.
Lin, Y.-L., Farley, R.D., and Orville, D., 1983. Bulk parameterization of the snow field in a cloud model. Journal of
Climate and Applied Meteorology, 22, 1065-1092.
Ohashi, Y. and Kida H., 2002. Effects of mountains and urban areas on daytime local-circulations in the Osakaand Kyoto regions. Journal of the Meteorological Society of Japan, 80, 539-560.
Ohashi, Y. and Kida H., 2004. Local circulations developed in the vicinity of both coastal and inland urban areas.
PartⅡ: effects of chain-flow and mountains on heat transports. Journal of Applied Meteorology, 43, 119-133.
Yamazaki, R., 2004. Mechanical and thermal effects of Ikoma mountain on local circulations in Hanna region.
Thesis of Kyoto University, Japan (in Japanese).

The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, JapanKyoto
Basin

Kyoto

(a)

36・I LINE (NO SEA‐BREEZE DAY)I①34I②32

Osaka
Plain

Mt.
Ikoma

Osaka・Nara・

22

Nara
Basin

Osaka
Bay

I③j･ٛ
iٛ 30･ertu
rae 28pm
26
teir
A
24

00 0:0

020:2

040:4

060:6

0
0
00
0
0
0
080:8 100:0 120:2 140:4 160:6 180:8 200:0 220:211
11122hours(b)

36

I LINE (SEA‐BREEZE DAY)

M
I①

3430km
Fig.1 The Kansai area which are a field of ourstudy. The dashed lines indicate a penetration
direction of the sea breeze.

I②32j･ٛ
iٛ 30･ertu
rae 28
pm
et 26
ir
A
24

I③

22000:0

020:2

040:4

060:6

080:8

00:
100
10120:2
10140:4
10160:6
10180:8
10200:020220:22hours(a)

36

KH LINE (NO SEA‐BREEZE DAY)

KH①

34

KH②32j･ٛiٛ 30･er
u
ta 28
repm
et 26ri
A
24

KH③

22
00:00

02:02

04:04

06:06

08:08

010:0010012:02 14:04
11hours

016:06
1018:08
10020:00 22:02
22(b)

36

KH LINE (SEA‐BREEZE DAY)

M
KH①
KH②
KH③

3432
j･ٛ
iٛ 30･eruta 28
repmet 26ri
A
24
2200 :00

02:02

04:04

06:06

08:08

000
000
0
10:00 12:02 14:04 16:06 18:08 20:00 22:02
1
11
1
1
22hours

Fig.3 Same as Fig.2 but KH (Keihan) LINE.

Fig.2 Temporal variations of surface air-temperature
measured over the I LINE (Ikoma Line) at (a) nonsea-breeze day and (b) sea-breeze day. Thetemperatures are averaged every 10 minutes andseparating non-sea-breeze and sea-breeze days
during our observation period.

The seventh International Conference on Urban Climate,
29 June - 3 July 2009, Yokohama, Japan

Observation
Calculation

Surface air-temperature (℃)

3836
34
3230

Fig.4 Surface air-temperatures
measured and calculated atNara Basin.

2826
2422
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20

Date

Fig.5 Four simulation cases: ①CASE ALL includes urban canopy layer, anthropogenic heat emission, andreal terrain (mountains), ②CASE SLAB without urban canopy and anthropogenic heat, ③CASE FLAT with flat
plain without mountains, and ④CASE NO without all.

○ CASE ALL minus CASE NO＊ CASE FLAT minus CASE NO

2.0△ CASE SLAB minus CASE NO

1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0

7/20
7/22
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8/31

Temperature difference (℃)

1.5DateFig.6 Differences in daily maximum
temperatures between
CASES ALL, FLAT, SLAB
and CASE NO, at NaraBasin. The arrow indicates aday when sea breeze seems
to arrive at Nara Basin.