Journal of Heat Island Institute International Vol. 9-2 (2014)

Academic Article

Relationship between wind direction and air temperature in theOsaka center city determined using fixed point observation
Kosuke Kittaka*1

Hiroshi Miyazaki*2*1 Dept. of Science and Engineering, Kansai University* Dept. of Architecture, Faculty of Environmental and Urban Engineering, Kansai University
2Corresponding author : Kosuke KITTAKA, kosuke.kittaka@gmail.com
ABSTRACTIn 2009, we have carried out traverse observation in the central area of Osaka. These results suggested that thewind direction was the dominant factor in controlling air temperature in this built-up area. Thus, we now investigate
the thermal and meteorological environment using several fixed-point observation systems in the same area. The
aim of this research is to clearly show the relationship between air temperature and wind direction. The subject area
was the same area in the central part of Osaka, where we conducted our previous observations in 2009. We installed
observation devices at 34 locations in this area over 23 days in 2011 summer. We found that the air temperature
differences on the river side area were lower when the wind blew from the west and the air temperature differenceswere higher when the wind blew from the north to the east. The air temperature differences in the business districts
were higher than the air temperature difference in other areas and the influence of wind direction was not clear inthese areas. The traverse observation in the park showed that the temperatures were lower than the temperatures inother areas with any wind direction. However, the fixed-point observations showed that even in the park, winddirections influenced the temperature, similar to the river area.
Key Words : Urban heat island, Wind direction, Fixed-point observation, Traverse observation

used.

1. Introduction

However, detailed observation in a small area is not often
The urban air temperature is rising, which results from the urban

performed, because observation methods are not standardized atheat island effect (UHI). Today, several events such as anevery management organization and there are few observation

increasing number of hot nights, danger of heat stroke and airpoints.

pollution are serious social problems. UHI is a local climaticIn this study, we performed fixed-point observation in the central

effect, which depends on local conditions. Even though UHI is aarea of Osaka, the same area that we used for our previous

local effect, it is important to measure and understand thisobservations in 2009. We installed observation devices at 34

phenomenon to determine an effective countermeasure.

locations in this area over 23 days in the summer of 2011.

Before this investigation, we performed a traverse observation,
where we used a bicycle as an observation platform in the2. Traverse observation

central area of Osaka in 2009. The results of this investigation
illustrated that wind direction was the dominant factor that

In our former investigation in 2009, we performed traverse

controlled the air temperature in this area. Although the traverseobservations 6 times using 10 bicycles over 2 days (3 and 7observation by bike has the advantage of allowing detailed

August). Table 1 shows the time schedule of this research. It wasobservation, this method can only take a snapshot. This meansa clear day on 3 August 2009, and on 7 August 2009, it wasthat the traverse method needs further research and othercloudy until noon and then became clear in the afternoon. Table

methods to confirm its repeatability.

2 shows the average, maximum, and minimum air temperatures

A commonly-used method is fixed-point observation. Whenthat we found in the traverse research. The days were hot andfixed-point observation is performed, air temperature data fromhad no precipitation.

meteorological agencies and the local government are often

Of the six observations, RUN2 and RUN5 are shown.
-1-RUN2: Observations on 3 August included no sea breeze, and aland breeze blew during the observation. Critical air temperature
distribution information was obtained on the day that a landbreeze dominated. A WNW wind began to blow in Osaka at
15:30 (this is an estimated sea breeze). Along the Midousuji andChuoOdori rivers, it has become a severely hot environment(Fig.2).
RUN5: On 7 August, the situation was dominated by a seabreeze. The sea breeze developed more over time and the airtemperature near the river was low. The air temperature on thewest side of the Honmachi area was low and on the east side,
there was a higher temperature trend (Fig.3).
Fig.2 RUN2 From 15:15 to 15:45 3 August 2009
Table 1 Observation dates and times
Observation dayObservation time
RUN13 August 200913:15-13:45
RUN2
3 August 2009
15:15-15:45
RUN3
14:30-15:00
7 August 2009
RUN4
7 August 2009
16:00-16:30
RUN5
7 August 2009
18:00-18:30
RUN6
7 August 2009
20:00-20:30

Table 2 Air temperature on the observation day in JMA Osaka
Min airMax airAvg. airtemp.
temp.
temp.
Day(°C)(°C)(°C)
3 Aug. 2009

28.7

33.9

24.2

7 Aug. 2009

29.6

33.9

27.2

Fig.3 RUN5 From 18:00 to 18:30 7 August 2009
2.1 Traverse observation considerations
In Utsubo Park, the temperature was lower the entire time
regardless of the presence or absence of a sea breeze, which
seemed to play a role in cool spots in the city.
On 7 August, there was a blowing sea breeze all day, and the airtemperature was low along the river, but on 3 August, was noowing sea breeze,and the air temperature was high along theriver.
From 15:15 to 15:45 on 3 August, the highest temperature wasJapanobserved along the rivers. The river’s cool spot effect was

Osaka Pref.

strongly influenced by the sea breeze.
The RUN5 wind speed doubled compared with RUN4,
significantly decreaing the Nakanoshima area temperature.

Approximately 1km

Because the wind speed dropped below the 2 m/s, the winddirection during RUN2 changed from the northeast to thewest-northwest, but it is possible that this did not lead to thetemperature reduction in Nakanoshima.
3. Fixed-point observation
Osaka center city
The subject area was the central part of Osaka, which was theFig.1 Observation areasame area as for the traverse observation in 2009. We installed
observation devices at 34 locations in this area. Each observation-2-device was installed at a height of 2,500 mm on street telephone

E when the wind blew from the north to the southeast (1.2°C)

poles that were 250-300 meters apart. Fig.4 shows thecompared with when the wind blew from the south to theobservation area and location of the observation points.

northwest (0.5°C).

The observation interval time was 10 minutes. The observation

The air temperature differences were higher in areas D and F

period was from 19 August to 10 September 2011. Conditions

when the wind blew from the north to the southeast (1.5°C)

during the observation included cloudy weather for 7 days, clear

compared with when the wind blew from the south to theweather for 10 days, and cloudy and partly rainy weather for 6

northwest (0.8°C).

days. A radiation shelter made of stainless steel, and with a

The air temperature difference was higher in area G when wind

natural ventilation system, was placed on each thermometer

blew from even most directions (1.5°C). In addition, areas A, B,(Fig.5)

C and E were approximately 0.3°C lower when wind blew fromeven most directions, compared with areas D, F and G.
Table 3 Area classifications

Approximately 1kmArea

Area classifications

Obs. points

A

West of the river coast

8

B

Western business district

4

C

Around park

3

DWest of avenue

3

E

East of the river coast

5

F

Eastern business district

8

G

East of avenue

3Fig.4 Observation area and points
3.2 Fixed-point observation considerations
In area A, a difference of approximately 1.0°C was observed
Approximately 100mm

when the wind blew from the north and west.
Fixed-point observations in area C showed different resultscompared with the former bicycle traverse observation. Thismay be a result of our ability to observe inside of the park withtraverse observation but not with fixed-point observation, which
was near, but not in, the park.

Time constant
15 seconds

In area G, the temperature difference is large. This may beRadiation shelter with natural Thermistor sensor andventilation
Data logger T&D Co. RTR-52

caused by the heavy traffic in the area between the Streets.

Fig.5 Observation device

when wind blew from the south. However, a local characteristic

In all areas, the temperature difference tended to be smaller
may have been missed because the south wind was infrequent
during the observation period.

3.1 Result of fixed-point observation
We excluded 2 of 36 points from the analysis because of theft. Inaddition, an air conditioner that was close to the observation

4. Comparison between traverse observation and fixed-point

device caused outlier values, which were also excluded.

observation

We classified the observation area into 7 areas for the analysis.
Fig.6 shows the differences between the observed average air

For areas A and E, both the traverse and the fixed-pointtemperature at each point and the JMA's (Japan Meteorologicalobservation methods confirmed the same tendencies that the airAgency)

Data

temperature was lower when the wind blew from the west, butAcquisition System) Osaka air temperature. A positive value

the air temperature tendancies were higher when the wind blewmeans that the observed temperature was higher than AMeDAS.

from the north to the east.

The graph shows how air temperature changed in each wind

For area C, traverse observation in 2009 showed that the airdirection. Fig.7 shows the zone map, and Table 3 shows thetemperature difference was smaller when the wind blew fromurban categories.

the north and the west.

The air temperature differences were higher in areas A, B, C andHowever, fixed-point observation showed that the airAMeDAS(AutomatedMeteorological-3-°C°C°C

Area A°C

Area D

Area CArea B°C°C

Area E

Area F°C

Area G
Fig.6 Relationship wind direction and air temperature difference area A-G

Fig.7 Zone map

temperature difference was smaller when the wind blew fromfixed-point observations have advantages and disadvantages thatthe west, but it was larger when wind blew from the north andshould be determined.

the east. In addition, we could not confirm differences in areas A

In the test area, the air temperature decreased when the wind

and D because the air temperature difference was larger byblew from the west. This wind direction corresponds to theapproximately 1.2°C when wind blew from the north.

direction of a large local river. The air temperature increased

There was no clear influence of the wind direction in area D, as

when wind blew from the north to the east.

assessed using either traverse or fixed-point observation.

Compared with other areas, the air temperature differences in thebusiness districts were higher and the influence of winddirection was not clear in these areas.

5. Conclusion

Our traverse observation in the park showed that temperatures
In this study, we performed fixed-point observation to follow up

were lower with any wind direction. However, the fixed-point

our former traverse observations that were performed using aobservation showed that, even in the park, wind directions had

bicycle in the central area of Osaka. Both the traverse and thean influence on temperature, similar to that along the river area.

-4-References(1) K. Masumoto, I. Taniguchi, T. Nomura, Characteristics ofAir Temperature Distribution in 2005 and Situation of Heat
Island in Osaka City, 10 July 2006, Journal of Heat Island
Institute International Vol.1, 30-35 (2006)(2) Y. Kimura, H. Miyazaki, Urban Heat Island in Summer in
the Northern Part of Osaka, summaries of technical papersof annual meeting architectural institute of Japan D-1,895-896 (2009)(Received Nov. 13, 2014, Accepted Dec. 27, 2014)-5-