Journal of Heat Island Institute International Vol. 12-2 (2017)

Academic Article

Estimation of sea breeze fronts using satellite imagery
Kosuke Kittaka*1Hiroshi Miyazaki*2*1 Graduate School of Engineering, Kobe University*2 Faculty of Environmental and Urban Engineering, Kansai University
Corresponding author: Kosuke KITTAKA, kittaka@bear.kobe-u.ac.jp
ABSTRACTSea breezes can mitigate the effects of heat islands in Japan, where most big cities are located in coastal areas.
It is important to know the locatiom of the sea breeze front in order to define the regions affected by sea breezes.
Although this locatiom can be simulated, in this study we examined the use of satellite imagery to define the sea
breeze front through its relationship to cumulus cloud cover. Particularly in the summer season, it is possible toeasily estimate the location of the sea breeze front by visual observation of satellite imagery.
Key Words : Urban heat island, Sea breeze front, Satellite imagery, Cumulus clouds

１. Introduction

observation and simulation6,7). There are also studies on therelationship between the local wind and movement of cloud forIn Japan where many major cities are located in coastal areas,

Shikoku and considering movement of cloud involving local

sea breezes can act as countermeasures against the heat island

winds such as valley winds and sea breeze8). These studies

effect. Regarding the effect of sea breeze, there are studies thatsuggest that there is a possibility to estimate the locatiom of thereported on the effect of sea breeze by actually measuring for

sea front fronts from the distribution of cumulus clouds; in thisHiroshima City and Nagoya City and studies on the effect ofstudy we investigate a method for more easily estimating thewind on the river from invasion of the sea breeze front1,2,3).

locatiom of sea breezes using the satellite-derived distribution of

There are also studies on the effect of high temperature

cumulus clouds, and examine the frequency of cumulus clouds

mitigation when sea breezes are planarly captured in Sendai anddistributions that can estimate the locatiom of sea breezes.

Hiroshima4,5). In order to obtain such a temperature mitigation
effect of the sea breeze, it is important to define areas where this２. Comparison of satellite images and observed wind

can happen. On the other hand, There are studies that clarified

speed and direction

the cause of the occurrence of a row of cumulus clouds (circleYakumo) appearing above the Tokyo Route 8 Route using

Fig.1, The relationship between sea breeze, updrafts, andFig.2, Satellite imagary showing the sea breeze front defined by acumulus clouds.

cloud-free belt along the coast.

- 73 -

These data were collected from 6 locations of the JapanThe circulation of sea breezes is caused by the difference in

Meteorological Agency’s Automated Meteorological Data

surface temperature between the sea and land. Updrafts are

Acquisition System (AMeDAS) and 60 locations of the Osakagenerated over land where the temperature becomes higher in

Atmosphere Observatory.

daytime. Generally, when these moisture-containing updrafts

sea breeze front using observation data is confirms the wind

Identification of the locatiom of thereache a certain height, water vapor condenses to form cumulus

direction of the observation point in order from the sea side toclouds. In areas affected by a sea breeze, such updrafts are

the inland side, and assumption there are sea breeze until theweakened, and cumulus clouds often disappear (Fig. 1).

observation point on the inland side of the observation point

For example, in AVNIR-2 imagery from the ALOS satellite

where the westward wind is continuous, and the line connecting(taken at 11:03 on August 13, 2006) a belt-like area without

the observation points was taken as the sea breeze front. We also

cumulus clouds is clearly visible along the coastline (Fig. 2). In

used satellite images observed by the MODIS sensor on thethis study, we assumed that this pattern is a result of the sea

Earth Observation Satellites Aqua and Terra (specifications

breeze, and thus that the boundary between the clear and cloudy

shown in Table 1). With two satellites, two to three daytime

areas can be considered the sea breeze front.

images can be obtained almost daily. It is assumed that the sea
breeze has entered until the cumulus cloud located on the sea

2.1Methodsside, and the line connecting the cumulus clouds was taken asthe sea breeze front.

We chose the Osaka Plain for this analysis and compared thecumulus cloud line derived from satellite imagery with thelocatiom of the sea breeze front obtained from observational

2.2

Results

data for wind speed and direction. The locatiom of the sea

We superimposed wind speed and direction onto the satellite

breeze front can be simulated using various methods with theseimages as shown in Figs. 3-8.

data; we used data which easily obtained the sea breeze front atIn Fig. 3, the wind speed is weakest in the eastern andthe shooting date and time of the satellite image.

northeastern areas. The wind direction is also disturbed: no sea

Fig.3, Sea breeze front from meteorological data (Yellow Line)

Fig.4, Sea breeze front from meteorological data (Yellow Line)and cumulus cloud line (Blue Line), 2006/08/04 13:00

and cumulus cloud line (Blue Line), 2006/08/05 10:00

Table 1, The main specifications of each satellite- 74 -

breeze is entering but in other areas the sea breeze is in the end

Osaka Plain. The wind direction is disturbed in the northwestof the Osaka Plain. In this case, the sea breeze front appears toand the entry of the sea breeze cannot be confirmed, but in thebe located behind about 2-3 km (Max. 5-6 km in central north)

northeast a westerly wind is blowing and the sea breeze isthe cumulus cloud line, but there is agreement in the generalentering. We interpret this pattern to be influenced by the seapattern.

breeze running up the river. The sea breeze front is located

In Fig. 4, the sea breeze cannot be seen other than outside thebehind about 2-5 km the cumulus cloud line in the south, butsouthern part of the coastal area. The cumulus clouds arethey generally agree. In the northeast the cumulus clouds are

distributed in the southeastern part of the Osaka Plain. In thisgone, but we cannot judge whether the sea breeze is entering.

case, it seems that the sea breeze front is located behind about

Using the cumulus distribution alone, it is difficult to capture the2-3 km the cumulus cloud line in the southern part of the Osaka

projecting sea breeze front running up the river, although it isPlain, but they roughly conform.

shown by observational data. The distance between sea breeze

In Fig. 5, the sea breeze is entering the southern part of thefront from meteorological data and cumulus cloud line is more

Fig.5, Sea breeze front from meteorological data (Yellow Line)

Fig.6, Sea breeze front from meteorological data (Yellow Line)and cumulus cloud line (Blue Line), 2006/08/09 13:00

and cumulus cloud line (Blue Line), 2006/08/25 13:00

Fig.7, Sea breeze front from meteorological data (Yellow Line)

Fig.8, Sea breeze front from meteorological data (No Line)and cumulus cloud line (Blue Line), 2008/08/12 10:00

and cumulus cloud line (No Line), 2009/08/02 12:00- 75 -than 10 km away.

disappearance of the cumulus clouds, the sea breeze front isIn Fig. 6, the sea breeze has entered the coastal area of the Osaka

located somewhat behind the cumulus cloud line.

Plain, but the wind direction is disordered in the eastern part, so
３. Frequency of cumulus cloud line occurrence

the sea breeze has not penetrated deeply. The sea breeze does
reach further into the southern part. The cumulus clouds aremostly distributed in the northern and eastern parts of the Osaka

In order to confirm the frequency of the cumulus cloud line’s

Plain. In this case, it seems that the sea breeze front is locatedoccurrence, we studied this visually from 2006 to 2009 (48behind about 2-3 km the cumulus cloud line, but they generallymonths); the frequency of occurrence for each month is shownagree.

in Table 2. A cumulus cloud line could be confirmed in 399 ofIn Fig. 7,the sea breeze has entered the coastal area of the Osaka

2884 images, at a rate of about 13.8%. Gray highlights indicate

Plain, but the wind direction is disturbed in most other areas, somonths in which the cumulus cloud line occured in more than

the sea breeze has not penetrated further. The cumulus clouds are

20% of that month. The highest frequencies of occurrence weredistributed throughout the non-coastal areas. The sea breeze

found in the summer: 24.2% in July and 31.5% in August. On

front and the cumulus cloud line generally agree.

the other hand, the frequency of cumulus cloud line occurrence

In Fig. 8, the wind direction is disturbed in most areas of thewas lowest in winter: 8.9% in January and 4.5% in December.

Osaka Plain, and the sea breeze is not entering. The cumulus

The frequency of cumulus cloud line occurrence in 2009 wasclouds are distributed in most areas from the coast to deep inland.

lower than in the other three years. This confirms a tendency for

Both data sets show no sea breeze at this time.

the cumulus cloud line to be better-confirmed in the summer andless-well confirmed in the winter. It is thought that the summer

2.3Considerations

season is due to the strong updraft and high humidity the easy

In most of these images, the cumulus cloud line and the sea

cumulus appearance.

breeze front generally agree, with a tendency for the latter to be
４. Conclusions

located somewhat behind the former (The distances are about
2-3 km). As the air warmed on the ground surface forms updrafts,
it is cooled at higher elevations and becomes cumulus clouds.

We proposed and investigated a method to estimate theWhile the updraft exists, cumulus clouds gradually grow, but

relationshipwhen the updraft is weakened by the sea breeze entering, itobservational data) and the cumulus cloud line (obtained from

gradually dissipates and finally disappears. Since there is a timesatellite imagery). In general, the sea breeze front was locatedlag between the entrance of the sea breeze enters and thesomewhat behind the cumulus cloud line, but they generally

betweentheseabreeze(determined

Table 2, Frequency of cumulus cloud line occurrence per month○ Yes cumulus cloud line
× No cumulus cloud line- 76 -by(3)agreed in location. Thus it is possible to easily estimate theT. Fukuda, M. Kasima, J. Suzuki and M. Kanda,

location of the sea breeze front by visual observation of satellite

Verification of Wind Channel Effect around an Urbanimagery.

River by the Map of Sea Breeze Front Line, Proceedingsof Hydraulic Engineering, Vol. 42 (1998), pp. 49-54

In addition, we studied satellite images from 2006 to 2009 and(4)documented a tendency for the cumulus cloud line to be

Y. Junimura and H. Watanabe, Study on The Effects of Sea

comparatively well-confirmed in the summer and less-well

Breeze for Decreasing Urban Air Temperatures in Summer

confirmed in the winter. Our methods will be of most use for-Analyses based on long-term multi-point measurements

estimating the location of the sea breeze front in the summer

and observed wind conditions-, Journal of Environmental

season. Observation point networks such as AMeDAS can not

Engineering, AIJ, Vol.73 No.623, pp.93-99

necessarily ensure sufficient spatial distribution, but this method(5)K. Matsuo and T. Tanaka, Analysis on The Effect of Seais possible to complement grasp more detailed spatial

Breeze on Summer Diurnal Temperature Distribution

distribution.

Pattern in Hiroshima Plain: Mapping the sea breeze effects
for mitigating urban warming, Journal of Environmental

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(Received Apr. 28, 2017, Accepted Jul. 7, 2017)- 77 -