4Sea Ice and Climate٨֔ȁဢਏςκȜΠȆΓϋΏϋΈܿ੅ΓϋΗȜୌ๶ȁ໲຃୷ဩఱ‫ڠ‬۪‫ޏ‬ςκȜΠΓϋΏϋΈࡄ‫ݪ‬ΓϋΗȜ
Hiroki Kai
Remote Sensing Technology Centerof Japan
Fumihiko Nishio
Center for Environmental Remote Sensing,Chiba University

4.1 ζͼ·υ෨༶ৣࠗͥ͢ͅ٬ຕ۷௶

Sea Ice Observation by Microwave Radiometer٬ຕ͉٬͈ນ࿂͈٬କ̦ൄ̹͈̽́͜Ȃཤޭ٬͞ධޭ٬͈͕̥΂γȜΜ·٬̈́̓ཤޭ֖ਔ༏͈٬́͜ࡉ̳ͣͦ͘ȃ౷‫ݩ‬஠ఘ͈٬͈̠̻ࠫຕ̳ͥ࿂ୟ͉࿩1‫ͤ̈́͜ͅڬ‬̳͘ȃ٬ຕ͉٬࿂ͅ๤͓ͺσαΡ̦̩ࣞȂକȆ΀ΥσΆȜ੏۪͈൲ႁ࡙̜́ͥఊု༶ৣ͈ఉ̩ͬ฽ৣ̱̳͘ȃ̹͘٬ຕ͉ఱ‫ٮޏܨ‬௄͂٬ဢນ௄͈͂୪૘ͬ৭౯̱Ȃࡐ෎Ȇஆ෎͈࿶௣ͬཐ̬̳͘ȃ̯ͣͅȂ٬ဢఱ੏۪̤̞̀ͅਹါ̈́ධޭೲ௄କ͈ࠁ଼ͅ٬ຕ͈୆଼ً೾̦‫۾‬ဓ̱̞̀ͥ͂ࣉ̢ͣͦͥ̈́̓Ȃ٬ຕ͉౷‫ܰͬ࢓ܨ͈ݩ‬೰̳ͥέ͹·ΗȜ͈̱֚̾͂̀ఱ୨̈́࿨‫ͬڬ‬౜̞̳̽̀͘ȃ٬ຕ͉̹͘Ȃ஑ต͈࣐࣎̈́̓Ȃ૽‫͈ۼ‬୆‫ͬޣג͜ͅڰ‬ဓ̢̳͘ȃ଎4.1.1͉2002ාոࣛൃ͈‫ྀۼ‬඾௸༭̱͂̀࢖‫̞̱ͥ̀ٳ‬ȂAMSR-E͂MODISͥ͢ͅ΂γȜΜ·٬͈٬ຕ໦ື̳́ȃAMSR-E͉‫͈׌‬ခྫͅ‫̴ͣͩ۾‬۷௶̧͈́ͥ́Ȃ඾ș͈٬ຕ͈အঊͬ෤՜̳̭̦ͥ͂‫خ‬ෝ̳́ȃ
ζͼ·υ෨༶ৣࠗͥ͢ͅ٬ຕ͈۷௶͉1970ාయ̧̥࣐̱̹̦ͣͩͦ̀͘Ȃુ̵̥̞͈̦ࠧ̈́ͅ۷௶ΟȜΗ͈࠿બ̳́ȃAMSR/AMSR-E̞̾̀͜ͅȂNASA͞٬ષ༗հ಩͂‫ވ‬൳́࣎ߗ‫͞ܥ‬஑ตͬဥ̞̹࠿બ۷௶̧࣐̱̹ͬ̽̀͘ȃ଎4.1.2̷͉͈֚႕̳́ȃ
Sea ice, which is simply frozen sea-surface water, is seen in the Arctic Ocean, the Antarctic(a) AMSR-E Sea Ice Concentration(b) MODIS 3 Channels Composite Image

46

46

45

45

44

44

43

43

42

42
141

142

143
0

144

145

146

147

148

149

100 [%]

141

142

143

144

145

146

147

148

149

B : Ch.2 (841 - 876nm) G : Ch.5 (1,230 - 1,250nm) R : Ch.4 (545 - 565nm)

଎ġġġ4.1.1ȁ΂γȜΜ·٬͈٬ຕ 2005ා3࠮2඾
ȪaȫAMSR-E ٬ຕྟ୪ഽȪbȫMODIS 3ΙλϋΥσ଼ْࣣ௨Fig. 4.1.1ȁSea ice in the Sea of Okhotsk, March 2, 2005(a) AMSR-E sea ice concentration (b) MODIS 3 channels composite image

Ocean and the oceans surrounding the Arctic region such as the Sea of Okhotsk. The area
where sea ice forms comprises 10% of the Earth's total sea surface.
Compared with the unfrozen sea surface, the albedo of sea ice is significantly higher andreflects the incoming solar radiation, which is the power source of the water and energy
cycles. Sea ice interrupts contact between the atmospheric boundary layer and the sea
surface, and blocks transportation of both sensible and latent heat. The process of sea-ice
development may also contribute to formation of the Antarctic Bottom Water, which is an
important component of ocean general circulation. Thus, sea ice is an essential factor
affecting the global climate.
Sea ice also influences human activities, such as the movement of cruise vessels. Fig.
4.1.1 depicts the sea-ice distribution on the Sea of Okhotsk from AMSR-E and MODIS. Those
images have been released every day in the winter seasons since 2002. AMSR-E canobserve sea-ice conditions from day to day regardless of clouds.
Sea ice has been observed by microwave radiometer since the 1970s. Validation of data isalways a basic requirement, and validation observations for AMSR and AMSR-E wereperformed in collaboration with NASA and the Japan Coast Guard, using both airplanes andocean vessels. Fig. 4.1.2 illustrates an example of such an observation.

଎ġġġ4.1.2 ධޭαςϋΈΑΧ;Δϋ٬͈́࠿બ۷௶Fig. 4.1.2 Observation for validation at the Bellingshausen Sea in the Antarctic23

4.2 ཤޭ֖͈٬ຕ͂‫࢓ܨ‬་൲
Arctic Sea Ice and the Climate ChangeAug. 2002

Aug. 2003

Feb. 2003

Aug. 2004

Feb. 2004

Feb. 2005

no data1000[%]଎ġġġ4.2.1 ཤޭ֖͈٬ຕྟ୪ഽ͈‫ܬ‬୯་‫ا‬Fig. 4.2.1 Seasonal variation of sea ice concentration in the Arctic region24

2

଎4.2.1͉AMSR-Eͤ͢ͅ۷௶̯̹ͦཤޭ֖Ȫཤޭ٬̷͈͂ਔ༏٬֖ȫ͈٬ຕྟ୪ഽ͈‫ܬ‬୯་‫ا‬̳́ȃཤޭ֖͉́٬ຕ͉3࠮ͅडఱȂ9࠮ͅड઀̳͂̈́ͤ͘ȃ̷͈ํս͉डఱশ́࿩1,450ྔkm2Ȃ
ड઀শ́࿩780ྔkm2̳́ȃཤޭ٬͉ਔսͬၘͅս̞̹ͦ̀ͥ͛͘Ȃ‫́͜ذ‬ဏ̴̫ͅॼͥఉාຕ
̦ఉ̩Ȃ٬ຕํս͈डఱশ́࿩฼໦ͬ୸̞̳͛̀͘ȃ̹͘΂γȜΜ·٬͉Ȃ٬ຕ͈ࡉͣͦͥड͜֌ഽ͈೩̞٬֖̳́ȃ
଎4.2.2͉ཤޭ֖͈٬ຕ͈໹޳౵̥͈ͣ༊ओ͂ΠτϋΡͬা̱̹͈̳́͜ȪJ. C. ComisoȂIGARSS 2005ȫȃȪaȫ͉٬ຕํսȪྟ୪ഽ̦15%ոષ͈ํսȫȂȪbȫ͉٬ຕ࿂ୟȪྟ୪ഽ100%۟ͅॳ̱̹৘ৗഎ̈́٬ຕ͈࿂ୟȫȂȪcȫ͉٬ຕྟ୪ഽͬນ̱̳͘ȃ୤͈໐໦͉SMMRȂࣱ͈໐໦͉SSM/I͈ΟȜΉ̳ȃ̭ͦͣඵ͈̾Γϋ΍ͥ͢ͅ౵̥ͣ໹޳౵Ȃ༊ओ‫͍ݞ‬ΠτϋΡͬॳ੄̱Ȃ̯ͣͅ
ႂ́AMSR-E͈ΟȜΗͬਹ͇̞̳̀͘ȃ̭͈଎̥ͣྶ̥̠ͣ̈́͢ͅȂཤޭ֖͉́1978ාո࡛ࣛह́͘Ȃ٬ຕ͉ࡘઁ̳ͥ߹̜̳࢜ͤ͘ͅȃ̷͈‫͉ࣣڬ‬Ȃ٬ຕํս͉10ා̧̾ͅ࿩2.7%Ȃ٬ຕ࿂ୟ͉10ා̧̾ͅ࿩3.4%̳́ȃඅͅఉාຕ͈ࡘઁ̦ࡐಠ́Ȃ٬ຕ̦ड઀͂̈́ͥ9࠮͉́ఉාຕ͈
࿂ୟ̦10ා̧̾ͅ9.2%͈‫̞ͥ̀̽ࡘࣣ́ڬ‬Ȃ͈͂༭̜̳࣬ͤ͘͜ȃཤޭ֖͈ນ࿂‫أ‬ഽً͉‫ݲ‬20ා‫ͅۼ‬࿩1ɋCષઌ̱̹̭̦͂౶̤ͣͦ̀ͤȂཤޭ֖̤̫ͥͅ٬ຕ͈ࡘઁ̭ͦ͜ͅచ؊̳͈ͥ͂͜ࣉ̢̞̳ͣͦ̀͘ȃ(a) Ice Extent Anomalies
Area (106 km2)

10-1

Trend : -33493.4 r 2329.0 km2/year(-2.711 r 0.189 %/dec)-22(b) Ice Area Anomalies
Area (106 km2)

10Fig. 4.2.1 presents the seasonal variation of sea-ice concentration in the Arctic region (the Arctic Ocean-1and its surrounding oceans). In this region, sea ice reaches its maximum in March and its minimum in
Trend : -36873.6 r 2120.9 km2/year(-3.434 r 0.198 %/dec)

September. The ice extends from a minimum of 7.8 million km2 to a maximum of 14.5 million km2. The Arctic-2
10Ocean is surrounded by land, and the multi-year (perennial) ice remains throughout the summer season,

Ice Concentration (%)(c) Ice Concentration Anomalies

covering about half of the total maximum extent of sea ice. The Sea of Okhotsk is located at the lowest
latitude that we can find sea ice.

5Fig. 4.2.2 plots the deviation from the average and the trend of sea ice in the Arctic region (J. C. Comiso,
IGARSS 2005). In the figure, (a) indicates sea-ice extent (total area of 15% or more of the concentration);(b) indicates sea-ice area (converted into 100% of the concentration); and (c) indicates the concentration of

0sea ice. The red line represents SMMR data, and black represents SSM/I. These two data were used forderiving the average, deviation and trend. AMSR-E data was added as the green line. Clearly revealed in-5these figures, sea ice steadily decreased since 1978 at a rate of 3.4% per decade in extent, and 2.7% in

Trend : -0.082 r 0.011 %/year(-0.953 r 0.125 %/dec)
-10
1978

1980

1982

1984

1986

1988

1990

area. Reduction of multi-year ice is especially remarkable, with reports that the extent of multi-year ice in1992

1994

1996

1998

2000

Year
଎ 4.2.2ȁཤޭ֖͈٬ຕ͈ಿ‫ܢ‬ΠτϋΡ

2002

2004

September, the minimum time, is decreasing at 9.2% per decade. We know that the surface temperature of
the Arctic region rose approximately 1q
C over the past 20 years. We think that decreased sea ice in theregion is a corresponding phenomenon.

Fig. 4.2.2ȁLong-term trends of sea ice in the Arctic region(J. C. Comiso, IGARSS 2005)25

4.3 ධޭ֖͈٬ຕ͂‫࢓ܨ‬་൲
Antarctic Sea Ice and the Climate ChangeAug. 2002

Aug. 2003

Feb. 2003

Aug. 2004

Feb. 2004

Feb. 2005
no data
1000[%]

଎ġġġ4.3.1 ධޭ֖͈٬ຕྟ୪ഽ͈‫ܬ‬୯་‫ا‬Fig. 4.3.1 Seasonal variation of sea ice concentration in the Antarctic region

26

2

଎4.3.1͉AMSR-Eͤ͢ͅ۷௶̯̹ͦධޭ֖Ȫධޭ٬ȫ͈٬ຕྟ୪ഽ͈‫ܬ‬୯་‫̳́ا‬ȃධޭ֖́
͉٬ຕ͉9࠮ͅडఱȂ2࠮ͅड઀̳͂̈́ͤ͘ȃ̷͈ํս͉डఱশ́࿩2,000ྔkm2Ȃड઀শ́࿩
360ྔkm2̳́ȃධޭ٬͉ཤޭ٬͉͂చચഎͅၘͅս̞̞͈ͦ̀̈́́͘Ȃ٬ຕ͉ఱၘ‫ٸ̥ͣ܅״‬̧࢜ͅ‫ڐ‬ఱ଼̱̾̾ಿ̧̳̭̦̳ͥ͂́͘ȃ̷͈̹͛Ȃධޭ٬͉́٬ຕ͈ఉ̩̦֚ාຕ́Ȃ٬ຕํս͈डఱশ͈࿩8‫̳̞̀͛͘୸ͬڬ‬ȃ
଎4.3.2͉ධޭ֖͈٬ຕ͈໹޳౵̥͈ͣ༊ओ͂ΠτϋΡͬা̱̹͈̳́͜ȪJ. C. ComisoȂIGARSS 2005ȫȃ଎4.2.2͂൳အͅȂȪaȫ͉٬ຕํսȂȪbȫ͉٬ຕ࿂ୟȂȪcȫ͉٬ຕྟ୪ഽͬນ̱̳͘ȃධޭ֖͈٬ຕ͉1978ාո࡛ࣛह͈́͘‫ͅۼ‬Ȃ஠ఘ̱͉͂̀৹͈ۙ௩‫̳̜ͤ࢜͘ͅ߹ح‬ȃ̷͈‫ڬ‬ࣣ͉Ȃ٬ຕํս͉10ා̧̾ͅ࿩0.7%Ȃ٬ຕ࿂ୟ͉10ා̧̾ͅ࿩1.3%̳́ȃ̱̥̱൐ධޭ͂ୌධޭ͉́߹̦࢜։̈́ͤȂୌධޭ͈αςϋΈΑΧ;Δϋ٬͞ͺθϋΔϋ٬̺̫͙ͬͥ͂Ȃ٬ຕํ
ս͉10ා̧̾ͅ࿩6.7%Ȃ٬ຕ࿂ୟ͉10ා̧̾ͅ࿩6.0%͈ࡘઁ߹࢜ͬা̱̞͈̀ͥ͂ࠫ‫੄̦ض‬̯̞̳ͦ̀͘ȃධޭ֖͈ນ࿂‫أ‬ഽً͈‫ݲ‬20ා‫͈ۼ‬ΠτϋΡ͉Ȃ‫͇ٽ‬൐ධޭ͉́ඤၘ໐ͬಎ૤ͅ೩‫ئ‬Ȃୌධޭ͉́ධޭ฼ോ̥ͣαςϋΈΑΧ;Δϋ٬ȆͺθϋΔϋ٬̥̫̀ͅષઌͬা̱̤̀ͤȂ٬ຕ͈ΠτϋΡ͂ເࣣ̱̞̳̀͘ȃ̭͈̠͢ͅȂζͼ·υ෨༶ৣࠗͥ͢ͅ٬ຕ͈۷௶͉Ȃ‫࢓ܨ‬་൲͈ΏΈ΢σͬ௴̢ͣͦͥ‫خ‬ෝ଻̦̜̳ͤ͘ȃ̷͈̹͛͜ͅȂ੿ြ̹ͩͥͅಿ‫ܢ‬എ‫ࠑ̾ڶ‬௽എ̈́۷௶̦๱ુͅਹါ̳́ȃ

Area (106 km2)

10-1

Trend : 8886.0 r 3142.5 km2/year(0.719 r 0.254 %/dec)-22

Area (106 km2)

10-1

Fig. 4.3.1 depicts the seasonal variation of sea-ice concentration in the Antarctic region (the Antarctic

Trend : 12430.5 r 2878.2 km2/year(1.313 r 0.304 %/dec)

Ocean). In this region, sea ice reaches its maximum in September and its minimum in February. Its-2
10approximate extent is a maximum of 20.0 million km2 and a minimum of 3.6 million km2. The Antarctic

Ice Concentration (%)

Ocean, in contrast to the Arctic, is not surrounded by land, so sea ice can expand outward from thecontinent. Therefore, most sea ice in this region is first-year ice, and it covers about 80% of the extent at its

5maximum time.
Fig. 4.3.2 presents the deviation from the average and the trend of sea ice in the Antarctic region (J. C.
0Comiso, IGARSS 2005). Similar to Figure 4.2.2, it indicates (a) extent, (b) area, and (c) concentration of sea
ice. In the Antarctic region, sea ice increased slightly since 1978. The percentage was 0.7% per decade inextent, and 1.3% in area. However, the trend differs between the east and west Antarctic. At the-5

Bellingshausen Sea and the Amundsen Sea in the west Antarctic, reports indicate that sea ice decreased

Trend : 0.067 r 0.014 %/year(0.920 r 0.192 %/dec)
-10
1978

1980

1982

1984

1986

19881990

6.7% per decade in extent and 6.0% in area. The trend of surface temperatures over the past 20 years was1992

1994

1996

1998

2000

Year
଎ 4.3.2ȁධޭ֖͈٬ຕ͈ಿ‫ܢ‬ΠτϋΡ
Fig. 4.3.2ȁLong-term trends of sea ice in the Antarctic region(J. C. Comiso, IGARSS 2005)

2002

2004

a decline in the inland of the east Antarctic, and a rise in the Antarctic Peninsula, the Bellingshausen Sea
and the Amundsen Sea of the west Antarctic, consistent with the sea ice trend.
Through sea-ice observation using microwave radiometers, we can detect the signals of climate change.
For that future objective, long-term and continuous observations are essential.

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