No. 33

Summer 2013
ContentsPage

Urban Heat Island Effect Enhancement caused by Hot Summer Conditions

1

Summary of Kosa (Aeolian dust) Events over Japan in 2013

3

Sea Ice in the Sea of Okhotsk for the 2012/2013 Winter Season

4

Introduction of New Climate Monitoring Products on the TCC Website

5

JM A’s Contribution to improving Climate Risk Management

5

Urban Heat Island Effect Enhancement caused by Hot Summer Conditions
Urban heat island (UHI) varies in intensity depending on
synoptic atmospheric conditions and becomes more pronounced in extremely hot summers, a new research into theUHI effects over Japan’s metropolitan area shows. This article gives a summary of the findings from “Heat Island Monitoring Report 2012”, the latest of a series of reports on monitoring and analysis of urban climatology published by theJapan Meteorological Agency.

The striking distinction between the long-term rate ofwarming in urban cities and that in non-urban areas arises
from the gradually intensified urban heat island (UHI) effect. In the temperate moist climate zone of the Japanese
mainland, pristine land surfaces are typically covered withrich vegetation. Grassland or forests in their natural conditions have the capacity to hold large amounts of moisture,
which is released with latent heat into the upper atmosphere through evaporation and transpiration on days whenstrong summer sunlight parches the ground, thereby moderating land surface temperatures. However, in modern
developed cities such as Tokyo, houses, buildings, paved
roadways and other man-made structures proliferate in away that gradually encroaches upon vegetation. On dry,impermeable and lifeless urban surfaces with little vegetation left, the natural cooling thermostat based on evaporation and transpiration ceases to work.
The proliferation of high-rise buildings in city centers
increases urban canopy roughness and hinders ventilation,
leading to lower efficiency in the upward turbulent diffusion of near-surface heat. During nocturnal hours, urban
canyons impede cooling caused by the emission of infrared
radiation into space because less open sky is visible from agiven point on the urban surface. Adding to theseheat-trapping effects, waste heat emission from air conditioners, automobiles and other energy-consuming equipment cannot be underestimated in densely populated citycenters. These factors are all known to contribute in varying degrees to the formation of UHI.

Ever since modern cities began to develop in the early
20th century, urban dwellers have experienced increasingly warmer climates than those living in rural surroundings.
Figure 1 shows long-term changes in monthly mean temperatures for August as observed in Japan’s three mostpopulous cities (Tokyo, Osaka and Nagoya) comparedwith temperatures averaged across non-urban stations.
Non-urban station temperature records generally indicate along-term warming trend at a rate of around 1°C per century, largely reflecting global warming caused by increased
atmospheric concentrations of greenhouse gases. In contrast, temperatures at urban stations show warming at asignificantly higher rate. This is especially true for Tokyo,
where the monthly mean temperature for August has risen
at around 2.5°C per century.

Figure 1 Long-term changes in monthly mean surface airtemperatures for August as recorded at urban stations inTokyo (red solid), Osaka (blue) and Nagoya (green)
Temperatures averaged over non-urban stations (black solid) arealso shown for comparison. The red and black dashed lines indicate the long-term trends for Tokyo and for non-urban stations,
respectively. Each sequence of temperatures is presented as thedeviation from the 1901 – 1930 average.

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1No. 33 | Summer 2013

across the region.
Extremely hot summer conditions in Japan are closely
associated with the intensity, extent and persistency of theNorthwestern Pacific High. In summers when thishigh-pressure system dominantly influences the easternpart of Japan, daylight hours are longer, southerly winds
prevail and temperatures soar. These synoptic weather
conditions also happen to be factors that contribute to theevolution of UHI intensity in the Kanto region. The longer-than-normal sunshine duration leads to greater diurnal
heat uptake into the urban canopy. Southerly winds blowing from the sea, which is relatively cool and helps to dissipate heat accumulated across regions, weaken before
reaching areas inland due to the presence of metropolitan
areas on the coast of Tokyo Bay.
These research results suggest that the UHI effect in theKanto region acts like a type of positive feedback, exacerbating scorching heat in summers when synoptic atmospheric circulation patterns cause extremely high temperatures.
For more details, a full report is available on the JMA
website at
http://www.data.kishou.go.jp/climate/cpdinfo/himr/2013/in
dex.html (in Japanese).

The effects of UHI, which in general gradually build in
intensity and extent over decades as cities develop, may
manifest themselves in different degrees depending on
individual years’ weather conditions on meso- to synoptic
scales, including sunshine duration and dominant windvelocity. This raises the question of how much UHI has
affected urban temperatures in the summers of past years.
To address this issue, the JMA Urban Climate Model(UCM) was run to reproduce observed temperatures under
actual urban ground conditions as well as to illustrate how
the climate might have been under hypothetical pristine
ground conditions before mankind started to build cities.
Comparison between the results of these two simulations
provides a clear picture of annual variability in UHI intensity.
The observed monthly mean temperatures were thehighest on record since the end of the 19th century forAugust 2010 at all seven meteorological observatories
across the Kanto Plain, and were the second highest forAugust 2012 at the four inland observatories. Figure 2
shows the spatial distribution of UHI intensity over theKanto Plain defined as differences in monthly mean temperature between the simulations carried out under urban
ground conditions and hypothetical pristine ground conditions for August 2009, 2010, 2011 and 2012. In the extremely hot summers of 2010 and 2012, the effects of UHI
were significantly enhanced both in intensity and in extent(Yoshinori Oikawa, Climate Prediction Division)

Figure 2 Spatial distribution of UHI intensity over the Kanto Plain for August 2009 (a), 2010 (b), 2011 (c) and 2012 (d)UHI intensity is defined as differences in monthly mean temperature between simulations with urban ground conditions andpristine ground conditions.

TCC News2No. 33 | Summer 2013

Summary of Kosa (Aeolian dust) Events over Japan in 2013
Characteristics of Kosa events in 2013
From January to June 2013, the number ofdays on which meteorological stations inJapan observed Kosa (referred to belowsimply as the number of days) was 13,
which was below the 1981 – 2010 normal of
23.1. The number of days was lower than thenormal after April, while it was higher inJanuary and March (Figure 3, left).
The total number of stations observing
Kosa (referred to here simply as the total
number of stations) over the same period
was 130, which was also below the normalof 208.3. The total number of stations wasalso much lower than the normal after April,while it was twice as high as the normal in
March (Figure 3, right).

Figure 3 Monthly number of days when meteorological stations inJapan observed Kosa (left), and the monthly total number of stations
observing Kosa (right) from January to June 2013
The red and yellow bars show the values for 2013 and the 1981 – 2010
normals, respectively.

Significant Kosa event in early March
Kosa was observed at many stations in western and eastern Japan from 8to 10 March (Figure 4).
A large dust storm arose around the Ocher Plateau from 6 to 7 March.
Massive volumes of dust particles were blown up into the atmosphere andcarried over to Japan by upper-air westerly winds. The Kosa moved overJapan as low-pressure systems passed over the country from 8 to 10 March(Figure 5). Based on results from JMA’s Kosa prediction model, the Kosawas expected to move across the East China Sea and prevail over westernJapan on 9 March (Figure 6). Using this forecast and surface observation
reports from meteorological stations in Japan, JMA released informationon the Kosa event to the public in order to call attention to potential traffic
hazards due to visibility degradation on 9 March.

Figure 4 Meteorological stations observing Kosa and minimum visibility on9 March(Nozomu Ohkawara, Atmospheric Environment Division)

Figure 5Surface weather analysis charts at 09 JST (00 UTC) from 8 to 10 March

Figure 6 Forecasts of surface dust concentration and surface wind by JMA’s Kosa prediction
model at 09 JST (00 UTC) from 8 to 10 March (initial time: 21 JST (12 UTC) on 7 March)
The Kosa was expected to reach western Japan on 8 March and prevail over western Japan the following day.

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3No. 33 | Summer 2013

Sea Ice in the Sea of Okhotsk for the 2012/2013 Winter Season
The sea ice extent in the Sea of Okhotsk was near or lessthan normal from December 2012 to April 2013, and greaterthan normal in May 2013.
The sea ice extent in the Sea of Okhotsk was near orless than normal from December 2012 to April 2013, andbecame greater than normal due to slow melting of ice inMay (Figure 7). It reached its seasonal maximum of
107.13 x 104 km2 (less than the normal of 116.92 x 104km2) on 15 March (Figures 7 and 8). Figure 9 shows
overall trends for the period from 1971 to 2013. Although the sea ice extent in the Sea of Okhotsk showslarge interannual variations, there is a long-term downward trend of 175 [71 – 279] x 104 km2 per decade (thenumbers in square brackets indicate the two-sided 95%
confidence interval) in the accumulated sea ice extent,
and another long-term downward trend of 5.8 [2.2 – 9.5]
x 104 km2 (equivalent to 3.7% of the area of the Sea ofOkhotsk) per decade in the maximum extent.
(Ryohei Okada, Office of Marine Prediction)
Figure 7 Seasonal variation of sea ice extent at five-day
intervals in the Sea of Okhotsk from November 2012 toJuly 2013

Figure 9 Interannual variations in the maximum sea ice extent (redline) and the accumulated sea ice extent (blue line) in the Sea ofOkhotsk from 1971 to 2013
Accumulated sea ice extent: the sum of all five-day sea ice extent values
from December to May

Figure 8 Sea ice situation on 15 March 2013
The white area shows the observed sea ice extent, and the red line indicates the extent of normal coverage (1981 – 2010).

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No. 33 | Summer 2013

Introduction of New Climate Monitoring Products on the TCC Website
In July 2013, TCC started providing new climate monitoring products called Regional Maps on its website. Theseresources enable users to easily monitor the regional distribution of 10-day and half-monthly mean temperatures
and total precipitation in Africa, Asia, South America,
North America, Oceania and Europe.
Regional Maps are produced using data from SYNOP
messages received via GTS from WMO Members aroundthe world, and represent 10-day or half-monthly mean
temperatures, total precipitation amounts and their anomalies from the normal. In addition, time-series graphs ofmean temperatures and total precipitation are available forstations selected by JMA (see Figures 10 and 11 as examples).
The 10-day maps are updated on the 1st, 11th and 21stof the month, and the half-monthly maps are updated on
the 1st and 16th of the month. These maps are available on
the World Climate page of the TCC website at
http://ds.data.jma.go.jp/tcc/tcc/products/climate/rmap/rmap.php.

Figure 10 Ten-day mean temperatures in Asia from 1 to10 July 2013

Figure 11 Time-series of ten-day total precipitation in Beijing, China from April to July 2013

(Hiroaki Minematsu, Tokyo Climate Center)

JMA’s Contribution to improving Climate Risk Management
Introduction
Daily life and economic activity are greatly affected byanomalous climatic conditions. The potential for adverse
effects from such conditions is referred to as climate risk,
and climate risk management (CRM) involves understanding and taking effective measures against it. The Global
Framework for Climate Services (GFCS) aims to enable
better management of climate-related risks. To promote
improved use of climate information in CRM in Japan,
JMA has launched a dedicated website at
http://www.data.jma.go.jp/gmd/risk/index.html (in Japanese).

based on dialogue. Secondly, it is necessary to assess climate risk quantitatively by analyzing climate-related dataand industrial data on variables such as agricultural production and sales. To this end, JMA provides an accessible
and user-friendly climate database on the website to facilitate assessment of climate risk. Finally, climate-affected
sectors can reduce adverse influences and increase benefits
by taking action for adaptation to climate risk using various
climate forecast products on the site. In addition to the current provision of the latest forecast products for adaptation,
JMA also plans to output hindcast products enabling users
to perform verification of their practical actions.

New website to assist CRM
The new website provides the following content to support approaches to CRM in Japan:• Clarification of the basic CRM concept and the relatedprocess• Information on good practices in CRM conducted by
JMA together with partner organizations• Historical data (observations and statistics) and prediction data to support CRM
The CRM process involves the steps of awareness, assessment and adaptation. JMA provides public- and private-sector operators with extensive support for and advice
on better management of climate risk for each step. Firstly,
it is necessary for each sector to be individually aware of
the influence of the climate. In this context, JMA works todevelop awareness of climate risks in various user sectors

Good practices in CRM
JMA has developed four good practices in CRM in collaboration with its partners. Good practices in CRM for theagriculture, health, energy and retail sectors are outlined on
the website.

TCC News

Poster presented at IBCS-1
JMA presented a poster (see next page) introducing thenew website supporting CRM in Japan to publicize its activities in relation to GFCS on a national level at the firstsession of the Intergovernmental Board on Climate Services (IBCS) and the Dialogue on “Operational Climate
Services: Dialogue on Practical Action” held in Geneva,
Switzerland from 1 to 5 July 2013.
(Akira Itoh, Climate Prediction Division)

5No. 33 | Summer 2013

Tokyo Climate Center (TCC), Climate Prediction Division, JMA
Address: 1-3-4 Otemachi, Chiyoda-ku, Tokyo 100-8122, Japan
TCC Website: http://ds.data.jma.go.jp/tcc/tcc/index.html

Any comments or inquiry on this newsletter and/or the TCC
website would be much appreciated. Please e-mail to
tcc@met.kishou.go.jp.
(Editors: Teruko Manabe, Ryuji Yamada and Kenji Yoshida)

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6No. 33 | Summer 2013