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[机构公布] 北极冰监测

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匿名  发表于 2012-3-19 23:42 |阅读模式
February ice extent low in the Barents Sea, high in the Bering Sea
二月冰面积在巴伦支海低,白令海高

As in January, sea ice extent in February was low on the Atlantic side of the Arctic, but unusually high on the Pacific side of the Arctic, remaining lower than average overall. At the end of the month, ice extent rose sharply, as winds changed and started spreading out the ice cover.
正如一月份,在大西洋一侧的北极地区海冰面积低,但太平洋一侧的北极地区却异常的高,其余低于总平均水平。在本月底,由于风力改变,海冰面积急剧上升,并且冰盖开始蔓延。
Sea ice extent in late winter can go up and down very quickly, getting pushed together or dispersed by strong winds. Ice extent usually reaches its annual maximum sometime in late February or March, but the exact date varies widely from year to year.
冬末的海冰面积上升和下降的速度可以非常快,被强风吹袭挤到一起或分散。海冰面积达到全年最高通常在二月下旬或三月的某个时候,但确切日期每年差异很大。
1.png
Arctic sea ice extent for February 2012 was 14.56 million square kilometers (5.62 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data.
Credit: National Snow and Ice Data Center High Resolution Image
2012年2月北冰洋冰面积为1456万平方公里(562万平方英里)。粉红色线条显示1979年至2000年该月的正中程度。黑色十字指示地理北极。
海冰指数数据
来源:国家冰雪数据中心的高分辨率图像

Overview of conditions
条件概述

Arctic sea ice extent in February 2012 averaged 14.56 million square kilometers (5.62 million square miles). This is the fifth-lowest February ice extent in the 1979 to 2012 satellite data record, 1.06 million square kilometers (409,000 square miles) below the 1979 to 2000 average extent.
2012年2月北冰洋的冰程度平均1456万平方公里(562万平方英里)。这是在1979年至2012年的卫星数据记录中第五低的2月,冰面积低于1979年至2000年平均程度106万平方公里(40.9万平方英里)。
Continuing the pattern established in January, conditions differed greatly between the Atlantic and Pacific sides of the Arctic. On the Atlantic side, especially in the Barents Sea, air temperatures were higher than average and ice extent was unusually low. February ice extent for the Barents Sea was the lowest in the satellite record.  Air temperatures over the Laptev, Kara and Barents seas ranged from 4 to 8 degrees Celsius (7 to 14 degrees Fahrenheit) above average at the 925 hectopascal (hPa ) level (about 3000 feet above sea level).  In contrast, on the Pacific side, February ice extent in the Bering Sea was the second highest in the satellite record, paired with air temperatures that we
re 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) below average at the 925 hPa level.

持续在一月建立的模式,北极在大西洋一侧和太平洋一侧之间的条件差异很大。在大西洋一侧,尤其是在巴伦支海,气温高于平均水平和冰的程度非常低。 2月在巴伦支海的冰面积是卫星记录的最低水平。在925百帕(hPa)(海拔约3000英尺)层面上, Laptev, Kara和巴伦支海的气温高于平均4至8摄氏度(7至14华氏度)。相比之下,在太平洋一侧,2月在白令海冰面积是卫星记录的第二位,并且在925 hPa层面空气温度低于平均水平的3至5摄氏度(5至9华氏度)。
2.png
The graph above shows daily Arctic sea ice extent as of March 5, 2012, along with the ice extents for the previous four years. 2011 is shown in light blue, 2010 is in pink, 2009 in dark blue, 2008 is in purple, and 2007, the year with the record low minimum, is dashed green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center High Resolution Image
上述图表显示在2012年3月5日,每天北极海冰的面积,与过去四年的冰面积。 2011年淡蓝色显示,2010年是粉红色,深蓝色2009,2008年是紫色,和创历史新低最低的一年2007年是绿色虚线。平均线周围的灰色区域显示数据的两个标准偏差范围。海冰指数数据。
来源:国家冰雪数据中心的高分辨率图像
Conditions in context
环境条件

Overall, the Arctic gained 956,000 square kilometers (369,000 square miles) of ice during the month. This was 486,000 square kilometers (188,000 square miles) more than the average ice growth for February 1979 to 2000. The overall low ice extent for the month stemmed mostly from the low ice extent in the Barents Sea: the extensive ice in the Bering Sea was not enough to compensate. On average, the Barents Sea has 865,000 square kilometers (334,000 square miles) of ice for the month of February. This year there were only 401,000 square kilometers (155,000 square miles) of ice in that region, the lowest recorded in the satellite data record.
总体来说,北极地区在一个月期间增加了95.6万平方公里(36.9万平方英里)的冰。超过了1979年至2000年48.6万平方公里(18.8万平方英里)一般的2月冰增长。该月总体低冰程度是因为大多是在巴伦支海的低冰程度:白令海广泛冰是不足以弥补。平均而言,在巴伦支海地区的冰,二月份86.5万平方公里(33.4万平方英里)。而今年只有40.1万平方公里(15.5万平方英里),是卫星数据记录的最低记录。
At the end of February, ice extent rose sharply. Data from the NSIDC Multisensor Analyzed Sea Ice Extent (MASIE) showed that the rise came mainly from the Bering Sea and Baffin Bay. In the Bering Sea and Baffin Bay, winds pushed the ice extent southward. Ice growth in the Kara Sea also contributed to the rise in ice extent. In the Kara Sea, westerly winds that had been keeping the area ice-free shifted, allowing the open water areas to freeze over. During late winter, ice extent can change quickly as winds push extensive ice cover together, or spread out ice floes over a greater area.
在二月底,冰面积急剧上升。 NSIDC多传感器分析海冰面积(MASIE)的数据表明,上升主要来自白令海和Baffin湾。在白令海和Baffin湾,强风推动冰面积向南。冰在喀拉海的增长也促进了冰程度上升,在喀拉海,西风一直保持该地区的无冰区转移,使得开阔的水域冻结。冬末,强风一起推动广泛的冰盖或使浮冰分散于更大的面积,冰面积可以迅速改变。

3.png
Monthly February ice extent for 1979 to 2012 shows a decline of 3.0% per decade.
Credit: National Snow and Ice Data Center
High Resolution Image
1979年至2012年二月月度冰面积显示为每十年下降3.0%。
来源:全国冰雪数据中心
高分辨率图像
February 2012 compared to past years
2012年2月相比于过去几年

Arctic sea ice extent for February 2012 was the fifth lowest in the satellite record. Including the year 2012, the linear rate of decline for February ice extent over the satellite record is 3.0% per decade. Based on the satellite record, through 2003, average February ice extent had never been lower than 15 million square kilometers (5.79 million square miles). February ice extent has not exceeded that mark eight out of the nine years since 2003.
2012年2月的北冰洋冰面积是卫星记录的第五低。包括2012年,卫星记录二月冰面积的线性率下降是每十年3.0%。基于卫星的记录,到2003年二月份,冰平均面积从来没有低于1500万平方公里(579万平方英里)。2003年以来, 二月份冰面积不超过标记8、9年。
4.jpg
This photograph of sea ice near Greenland was taken on March 18, 2011 from the NASA P3 aircraft. The Ice Bridge mission is collecting data on ice thickness, an important measure of the health of sea ice.

Credit: NASA/ATM automatic Cambot system
High Resolution Image
这是从NASA的P3飞机2011年3月18日拍摄的格陵兰岛附近的海冰照片。 IceBridge任务是收集海冰厚度的数据,是保护海冰的一个重要举措。
来源:NASA/ ATM机器人自动拍摄系统
高分辨率图像
IceBridge thickness data
IceBridge厚度数据

Measuring ice thickness is critical to assessing the overall health of Arctic sea ice. The passive microwave data that NSIDC presents here provide only ice extent, a two-dimensional measure of ice cover. But ice can vary in thickness from a few centimeters to several meters, and scientists want to know if the ice pack is thinning overall as well as declining in extent. A new study by NASA scientist Ron Kwok compared ice thickness data collected by airplanes during the ongoing Operation IceBridge with thickness data from the NASA Ice, Cloud and Land Elevation Satellite (ICESat), which ended its mission in 2009. IceBridge is an airborne data-collection mission that started in 2009, in order to bridge the data gap between the first ICESat and ICESat-2, which is scheduled to launch in 2016.
冰层厚度测量是评估北极海冰总体健康状况的关键。 NSIDC这里介绍的被动微波数据提供的仅是冰面积,一种冰盖的两维测量。但冰的厚度可以不同,从几厘米到几米,并且科学家想知道,如果整体浮冰变薄以及程度下降。由NASA的科学家Ron Kwok一个新的研究正在进行,将IceBridge飞机收集冰层厚度数据与从NASA的冰、云和陆地高度卫星(ICESat)收集的数据对比,在2009年结束其使命。 IceBridge是一种机载的数据收集任务,在2009年开始,以便弥补第一代ICESat和ICESat-2之间的数据差距,该计划在2016年推出。
Kwok found good agreement between simultaneous IceBridge and ICESat freeboard measurements made in 2009. Freeboard is the elevation of sea ice above the ocean surface, and provides a measure of ice thickness. These results show that IceBridge measurements will be able to bridge the gap between the ICESat and ICESat-2 satellite missions and add to other ice thickness data from the European Space Association (ESA) Cryosat-2. Satellite measurements of ice thickness provide a third dimension of information on the changing sea ice cover, helping scientists to more accurately assess the amount of sea ice in the Arctic.
Kwok在2009年发现在IceBridge和ICESat之间同时进行超高测量有很好的一致性。超高是指露出海面以上的海冰,并提供了冰厚度的测量。这些结果表明,IceBridge测量将能够弥合ICESat和ICESat-2卫星飞行任务之间的差距,并由欧洲航天协会(ESA)Cryosat-2添加其他冰厚度数据。卫星测量冰厚度提供了海冰变化上的第三维度信息,帮助科学家更准确地评估在北极的海冰量。
Data collected by the IceBridge mission is archived and distributed by the NSIDC IceBridge Data program.
由IceBridge收集数据任务, NSIDC IceBridge数据库计划归档和分发。
5.png
These images show the general effects of the positive phase (left) and negative phase (right) of the NAO. Red dots show the location of harp seal breeding grounds.
Credit: Johnston, et. al., 2012
High Resolution Image
这些图像显示NAO正相位(左)和负相位(右)的总体效果。红点显示的是海豹繁殖地的位置。
来源:Johnston等人。 2012年
高分辨率图像
Regional ice conditions and harp seals
区域冰情和海豹

Many animals rely on sea ice as part of their habitat. Harp seals, for example, give birth to and care for their young on floes of sea ice. Recent research by David Johnston and colleagues at Duke University showed that harp seals in the northwest Atlantic have higher mortality rates during years when the North Atlantic Oscillation (NAO) is in its negative phase, a pattern that favors low ice cover in the Labrador Sea and Gulf of St. Lawrence, where harp seals breed.
由于许多动物它们栖息地的一部分依靠海冰。例如,海豹出生和照护他们年幼在海冰浮冰上。在Duke大学的David Johnston和他的同事们最近的研究表明,当西北大西洋的海豹在年内有较高的死亡率时,北大西洋涛动(NAO)是其负相位的阶段,在拉布拉多海圣劳伦斯海湾冰盖低的格局,有利于海豹的繁殖。
This winter, the NAO has mostly been in a positive phase and ice conditions in the Labrador Sea and Gulf of St. Lawrence have been at near-normal levels. However, in recent years, ice conditions in the region have been very low. The study showed a longer-term decline in sea ice cover of up to 6% per decade across all North Atlantic harp seal breeding grounds since 1979. While harp seals are well-suited to deal with natural short-term shifts in ice conditions, they may not be able to adapt to the combined effects of both short-term variability and long-term climate change.
这个冬天,NAO大多在正相位,并且拉布拉多海和圣劳伦斯海湾的冰情,已接近正常水平。然而,近年来,在该地区的冰层状况一直非常低。研究表明,自1979年以来,在所有北大西洋海豹繁殖地,海冰盖长期下降每十年高达6%。虽然海豹非常适合于应对自然短期的冰情变化,但他们未必能够适应短期变化和长期气候变化的两种综合影响。
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 楼主| 发表于 2012-4-9 18:49 | 显示全部楼层
Apr 4, 2012
Arctic sea ice enters the spring melt season
北极海冰进入春融季节

Arctic sea ice reached its annual maximum extent on March 18, after reaching an initial peak early in the month and declining briefly. Ice extent for the month as a whole was higher than in recent years, but still below average.
3月18日,北极海冰达到其年度最大程度,在本月初达到初步峰值后并短暂的下降。整个月的冰程度高于近几年,但仍低于平均水平。
As the melt season begins, researchers look at a variety of factors that may contribute to summer ice melt. While the maximum extent occurred slightly later than average, the new ice growth is very thin and likely to melt quickly. Ice age data indicate that despite the higher extent compared to recent years, the winter sea ice continues to be dominated by younger and thinner sea ice.
由于融化季节开始,研究人员寻找可能有利于夏季冰融化的各种影响因素。虽然出现最大程度时比平均水平稍晚,新冰增长却非常薄,很可能迅速融化。冰期的数据表明,与近年相比尽管程度较高,但冬季海冰继续以年轻与海冰变薄为主。
1.png

Figure 1. Arctic sea ice extent for March 2012 was 15. 21 million square kilometers (5.87 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data Credit: National Snow and Ice Data Center
图1。2012年3月北冰洋海冰面积为1521万平方公里(587万平方英里)。洋红色线条显示1979年至2000年该月的正中程度。黑色十字指示地理北极。海冰指数数据。有关数据来源:国家冰雪数据中心


Overview of Conditions
条件概述


Arctic sea ice extent in March 2012 averaged 15.21 million square kilometers (5.87 million square miles). Ice extent this March ranked ninth lowest out of the 34 years of satellite data for the month, but it was the highest March average ice extent since 2008 and one of the higher March extents in the past decade. Ice extent was 530,000 kilometers (205,000 square miles) below the 1979 to 2000 average extent, and 780,000 square kilometers (301,000 square miles) above the record low for the month, which happened in 2006.
2012年3月的北极海冰面积,平均为1521万平方公里(587万平方英里)。今年三月冰面积位列34年卫星数据中最低的第九,但它是自2008年以来最高的3月平均海冰面积和过去十年中较高的三月程度之一。海冰面积为530,000平方公里(205,000平方英里),低于1979年至2000年的平均程度,并高于该月的记录最低点78万平方公里(30.1万平方英里)以上。该月最低点发生在2006年。
Ice cover remained extensive in the Bering Sea, where it has been above average all winter. Ice extent was also higher than average in Baffin Bay, between Greenland and Canada, and the Sea of Okhotsk, north of Russia. These conditions stemmed from a combination of wind patterns and low temperatures. Air temperatures were 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) below average over the Bering Sea, Baffin Bay, and parts of the Sea of Okhotsk, at the 925 millibar level (about 3,000 feet above sea level).
白令海的冰盖依然保持广泛,整个冬季那里一直高于平均水平,巴芬湾、格陵兰岛和加拿大之间、鄂霍次克海和俄罗斯北部的冰程度也高于平均。这些条件源于风模式和低温的组合。气温为6至8摄氏度(11至14华氏度)低于平均水平,在925MB水平(海拔约3000英尺)超过巴芬湾,白令海和部分的鄂霍次克海。
In the Kara Sea, where ice extent had been below average during January and February, ice extent rebounded to near-average levels in March. Winds that had been pushing the ice cover back shifted, allowing areas of open water in the Kara Sea to freeze over and the ice to spread out. Ice extent in the Barents Sea remained well below normal. In both the Barents and Kara seas, temperatures remained above normal by 4 to 6 degrees Celsius (7 to 11 degrees Fahrenheit).
喀拉海一月和二月期间海冰面积已低于平均水平,海冰面积回升接近至三月平均水平。大风一直推动冰盖退缩,使喀拉海开阔水域地区的冰冻结束和散开。巴伦支海的冰程度仍远低于正常值。巴伦支海和喀拉海两者的温度为4至6摄氏度(7至11华氏度),仍然高于正常。
2.png

Figure 2. The graph above shows daily Arctic sea ice extent as of April 2, 2012, along with the ice extents for the previous four years. The current year is shown in light blue, 2010-11 is in pink, 2009-10 in dark blue, 2008-09 is in purple, and 2006-2007, the year with the record low minimum, is dashed green. The gray area around the average line shows the two standard deviation range of the data.Sea Ice Index data.
Credit: National Snow and Ice Data Center
图2。上述图表表示北极海冰每天的程度,2012年4月2日连同过去四年的冰程度。本年度的显示淡蓝色,2010-11年度是粉红色, 2009-10年度深蓝色,2008-09年度和2006-2007年是紫色,记录最低的一年是绿色虚线。平均线左右灰色区域显示的是海冰指数数据标准的两个偏差范围。
来源:国家冰雪数据中心
Conditions in context
背景条件


Overall, the Arctic gained 140,000 square kilometers (54,000 square miles) of ice during March. Typically, March has been a month of net ice loss (an average of 260,000 square kilometers [100,000 square miles] for 1979 to 2000), but the last three Marches have had net ice growth. At its maximum extent on March 18, Arctic sea ice extent was within two standard deviations of the average, a measure that scientists look at as an estimate of the natural range of variability for the data.
整体而言,北极3月期间获得14万平方公里(54,000平方英里)的冰。通常,3月一直是净冰减少的一个月(1979年至2000年平均26万平方公里[100,000平方英里]),但过去三年过程中有净冰增长。3月18日达到最大程度,北极海冰范围的两个平均标准偏差,是衡量科学家们寻找自然范围内变异数据的一种估算。
Over the past thirty years of satellite data, the day of the maximum has varied by over six weeks, occurring as early as mid-February and as late as the end of March. However, even with so much variability, there is a small trend towards later maximum ice extents. This year’s maximum ice extent continued that trend, occurring 12 days later than average.
越过过去30年的卫星数据,最大的日际变化跨越六个星期, 在2月上、中旬发生,三月底结束。然而,这么多的变化是相当于这些小趋势走向后的最大冰程度。今年的最大冰程度继续这一趋势,比平均晚12天发生。
It is not clear why the maximum ice extent would happen later, given that in general, ice extent is decreasing. One possibility is that the lower winter ice extents might make it easier for ice to continue growing later in the season. With lower winter extents, a late cold snap or northerly wind could spread ice southward over ocean that would normally be ice-covered at that point. Researchers do not expect the late maximum ice extent to strongly influence summer melt. The ice that grew late this winter is quite thin, and will melt rapidly as the sun rises higher in the sky and the air and water get warmer.
目前尚不清楚为什么最大冰程度会发生稍后,考虑到海冰面积普遍减少的情况。一种可能是,在本季时间的稍后,冬季冰程度较低,冰可能更容易持续增长。随着冬季程度较低,后期的寒流或偏北风波及南方海洋,通常令冰覆盖该点。研究人员别指望后期强烈影响的最大冰程度在夏季融化。今年冬天晚期增长的冰相当薄,而且会迅速融化,由于天空中太阳升起时,空气和水得到温暖。
3.png

Figure 3. Monthly March ice extent for 1979 to 2012 shows a decline of 2.6% per decade.
Credit: National Snow and Ice Data Center
图3。1979年至2012年每个3月份显示年代际冰面积线性率下降2.6%。
来源:国家冰雪数据中心
March 2012 compared to past years
2012年3月与过去几年相比


Arctic sea ice extent for March 2012 was the 9th lowest in the satellite record, but the highest since 2008 and one of the highest March extents in the past decade. Including the year 2012, the linear rate of decline for March ice extent over the satellite record is 2.6% per decade.
2012年3月北冰洋海冰面积位列卫星记录最低点的第九,但它是自2008年以来最高的3月平均海冰面积和过去十年中较高的三月程度之一,包括2012年。3月海冰面积年代际线性率下降2.6%。超过卫星的记录。
4.jpg

Figure 4. This image, from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS), shows extensive sea ice cover in the Bering Sea on March 18, 2012. For more details and a full-resolution image, visit the NASA Earth Observatory Web site.
Credit:NASA image by Rob Simmon based on data from Jeff Schmaltz, NASA GSFC.
图4。这图像,来自美国宇航局的中分辨率成像光谱仪(MODIS),显示了2012年3月18日白令海上广泛的海冰盖。对于更多的细节和全分辨率图像,访问美国航空航天局地球观测网站。
来源:NASA图像根据来自Jeff Schmaltz, NASA GSFC数据,由Rob Simmon提供。
High ice extent in the Bering Sea
白令海的冰程度高


In the Bering Sea, off Alaska, ice extent reached a record high for the month of March. Persistent winds pushed the sea ice southward and froze more seawater into ice.
在白令海,阿拉斯加,冰面积三月份达到该月度记录的高位。持续性大风推动海冰南下并冻结了更多的海水变成冰。
As winds from the north pushed Arctic ice southward through the Bering Strait, the ice locked together and formed a structurally continuous band known as an ice arch, which acts a bit like a keystone arch in a building. The ice arch temporarily held back the ice behind it, but as the winds continued, the arch failed along its southern edge, and ice cascaded south through the strait into the Bering Sea. Sea ice also piled up on the northern coast of St. Lawrence Island, streaming southward on either side of it.
由于大风从北方推动北极冰向南通过白令海峡,冰叠在一起,形成一个结构连续的频带,因此称为冰拱,就像大厦的基石拱位。冰拱暂时阻碍了其背后的冰,但由于大风持续下去,拱未能沿着其南部边缘,而且冰向南层叠通过海峡进入白令海。海冰也堆积在圣劳伦斯岛的北部海岸,它两侧的其中一侧向南分流。
5.png

Figure 5. Ice age data show that first-year ice made up 75% of the Arctic sea ice cover this March. Thicker multiyear ice used to make up around a quarter of the Arctic sea ice cover. Now it constitutes only 2%.
Credit: NSIDC courtesy J. Maslanik and M. Tschudi, University of Colorado
图5。冰期数据显示,今年三月北极海冰盖的首年冰占75%。较厚的多年期冰占北极海冰的四分之一左右。现在它仅占2%。
来源: NSIDC的J. Maslanik和美国科罗拉多大学的M. Tschudi,友情提供。
Ice age data shows thin ice cover
冰期数据显示薄冰盖


One key predictor for summer ice melt is the amount of old, thick ice in the Arctic at the end of the winter. Some ice thickness data are available from satellites, but these records are short and discontinuous. Data from the NASA ICESat satellite covers only 2003 to 2009, and the new European Space Agency CryoSat satellite began collecting data in 2011. So researchers look at ice age data as one indicator of Arctic sea ice thickness. Older ice that has survived multiple melt seasons tends to be thicker than newly formed ice.
夏季冰雪融化的关键指标之一,是旧冰的数量。北极地区的厚冰在冬季结束,有些冰厚度是从卫星数据中获得,但这些记录是短而不连续。美国宇航局ICESat卫星数据仅包括2003年至2009年,而欧洲航天局CryoSat卫星在2011年开始收集数据。所以研究人员看冰期北极海冰厚度的一项指标数据,年长的冰已存活多个融化季节,往往比新形成的冰厚。
Ice age data this year show that the ice cover remains much thinner than it was in the past, with a high proportion of first-year ice, which is thin and vulnerable to summer melt. After the record low minimum of 2007 the Arctic lost a significant amount of older, thicker ice, both from melting and from movement of ice out of the Arctic the following winter. In the last few years, the melt and export of old ice was less extreme than in 2007 and 2008, and multiyear ice started to regrow, with second and third-year ice increasing over the last three years.
冰期数据表明,今年的冰盖仍然非常薄,相比过去,首年冰的比例很高,其中薄和脆弱的到夏季会融化。2007年记录最低点后,下面的冬季,冰无论是融化和从北极地区移动出来,北极失去了相当数量的旧厚冰。在过去的几年里,旧冰的融化和出来比2007年和2008年的极端少,以及随着第二和第三年的冰在过去三年的增长,多年积冰开始再生。
After the near-record melt last summer, second-year ice declined again, but some of the ice that had survived the previous few summers made it through another year, increasing the proportion of third- and fourth-year ice. However the oldest, thickest ice, more than four years old, continued to decline. Ice older than four years used to make up about a quarter of the winter sea ice cover, but now constitutes only 2%. First-year ice (0 to 1 years old) this year makes up 75% of the total ice cover, the third highest at this time of year in the satellite record. In 2008 the proportion of first-year ice was 79%, and in 2009 it was 76%.
去年夏天接近记录高位的融化后,第二年的冰再次下降,但前几个夏天有些幸存的冰又经过了一年,第三和第四年的冰比例增加。然而,比四年更老、更厚的冰继续下降。超过四年的旧冰约占冬季海冰盖的四分之一,但现在仅占2%。首年冰(0至1岁)占今年总冰盖的75%,卫星记录这季节的第三高。2008年的首年冰的比例为79%,2009年为76%。
6.png

Figure 6. The top image shows a decline in upper-atmosphere winds (solid line) over the last 30 years that mirrors the decline in sea ice over the same time period (dashed line). The bottom image shows the expected change in trajectory of the jet stream (dotted line) compared to the current jet stream trajectory (solid line).
Credit: Jennifer Francis, Rutgers University
图6。最上面的图片显示对流层上层大气大风(实线)在过去的30年期间(虚线)减少,反映出了海冰在同一时间下降。底部的图像显示当前的急流轨迹(实线)与预测急流轨迹(虚线)的变动。
来源:罗格斯大学的Jennifer Francis
Rapid Arctic warming and mid-latitude weather
迅猛的北极变暖与中纬度天气


The Arctic has warmed about twice as fast as the rest of the Northern Hemisphere in recent decades. Summer Arctic sea ice has declined by 40%, and snow is melting earlier in spring on the surrounding land. This dramatic change in the climate system is expected to affect weather patterns well beyond the confines of the Arctic—but researchers are working to understand exactly how those changes are affecting other regions.
近几十年来,北极地区变暖比北半球其他地区快约两倍。夏季北极海冰已经下降了40%,周围的土地上早在春天雪就已融化。这在气候系统中戏剧性的天气模式变化,预计的影响将远远超出北极地区范围,但研究人员正在努力了解这些变化究竟是如何影响到其他地区。
New research by Jennifer Francis of Rutgers University and Steve Vavrus of the University of Wisconsin suggests that warming in the Arctic is causing weather patterns in mid-latitudes to become more persistent. This persistence can lead to conditions like heat waves, cold spells, drought, flooding, and heavy snows. The researchers found that as temperatures in the Arctic warm and become closer to temperatures in lower latitudes, the waves of the jet stream tend to spread out, and west-to-east winds slow down in the upper level of the atmosphere (where storm tracks form). Both of these effects tend to slow the progression of weather patterns, which means that a weather pattern, whether hot or cold, is more likely to stick around.
由罗格斯大学的Jennifer Francis和美国威斯康星大学的Steve Vavrus新的研究表明,北极地区的气候变暖会导致中纬度的天气模式变得更持久。这种持久性,可导致如热浪、寒流、干旱、洪水、大雪。研究人员发现,北极地区的温暖温度和低纬度地区的温度关系非常密切,急流波趋向于分散,在大气层上层从西到东的大风减缓(如风暴轨迹的位置)。上述两个因素的这些效应往往延缓气候模式的恶化,这意味着天气模式,无论是热或冷更容易持续留下来。
帖子中涉及地图来源广泛,图中所涉及的行政区域以中国官方认定的为准。
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 楼主| 发表于 2012-5-10 22:25 | 显示全部楼层
Arctic sea ice reaches near-average extent in April
北极海冰到达接近四月的平均程度

Arctic sea ice extent declined slowly through the first three weeks of April, compared to recent years. The slow decline through March and the first few weeks of April meant that by mid-April, ice extent was at near-average levels. However, much of the extensive ice cover is thin ice that will melt quickly once temperatures rise in the Arctic. Over the past week, extent has started to fall sharply.
与近年相比,北极海冰面积经过四月的前三个星期缓慢下降。通过3月和4月的头几个星期的缓慢下降,意味着4月中旬冰面的范围接近平均水平。然而,许多广泛的冰盖是薄薄的冰层,在北极地区的一次气温上升中将迅速融化。在过去的一周,程度已开始大幅下降。

Figure 1. Arctic sea ice extent for April 2012 was 14.73 million square kilometers (5.69 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole.Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
图1。2012年4月北冰洋冰面的范围为1473万平方公里(569万平方英里)。洋红色线条显示1979年至2000年该月的平均值程度。黑色的十字架指示地理北极 ,海冰指数数据及有关数据

来源:全国冰雪数据中心
Overview of Conditions
条件概述

Arctic sea ice extent in April 2012 averaged 14.73 million square kilometers (5.69 million square miles). Because of the very slow rate of ice loss through the last half of March and the first three weeks of April, ice extent averaged for April ranked close to average out of 34 years of satellite data.  It was the highest average ice extent for the month since 2001, only 270,000 square kilometers (104,000 square miles) below the 1979 to 2000 average extent. April ice extent was 860,000 square kilometers (330,000 square miles) above the record low for the month, which happened in 2007.
2012年4月北极海冰程度平均为1473万平方公里(569万平方英里)。由于通过三月下旬的一半和四月的头三个星期冰损失非常缓慢,四月海冰面积平均值接近34年卫星数据的平均值。这是自2001年以来,该月平均海冰面积最高,只有27万平方公里(104,000平方英里),低于1979年至2000年的平均程度。 4月海冰面积为860,000平方公里(330,000平方英里)创该月在2007年发生的历史新低。
In April, ice cover remained unusually extensive in the Bering Sea, continuing a pattern that persisted over the winter.  Ice extent was also slightly higher than average in Baffin Bay and part of the Sea of Okhotsk.  As in recent winters, ice extent was well below normal in the Barents Sea, compensating for the extensive ice in the Bering Sea.
今年四月在白令海继续坚持在冬季的模式,冰雪覆盖仍然异常丰富。在巴芬湾和鄂霍次克海的一部分,冰面的范围也比平均略高。因为最近的冬季在巴伦支海冰程度远低于正常值,弥补了白令海丰富的冰。
As discussed in previous posts, the high Bering Sea ice extent this winter stemmed from unusually low air temperatures and persistent winds that helped to push ice southwards. During April, atmospheric conditions changed, warming the air to near-average temperatures for this time of year and slowing the strong southerly winds.
正如在先前的文章中所讨论的,白令海今年冬天的高海冰面积源于异常低的气温和持续的大风,有助于推动冰南移。今年四月间,大气条件发生变化,暖空气接近每年这个时候的平均温度,强劲的偏南风放缓。
During April, air temperatures over most of the Arctic were higher than usual, particularly over the central Arctic Ocean.  Over the Bering Sea and parts of the East Greenland and Norwegian seas, temperatures ranged from average to slightly below average.
在4月期间,北极大部分的气温比正常高,特别是在北冰洋中部。在白令海和东格陵兰岛的部分地区以及挪威海,温度介于平均到稍低于平均水平之间。

Figure 2. The graph above shows Arctic sea ice extent as of May 1, 2012, along with daily ice extent data for the previous five years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
图2。上述图表显示2012年5月1日的北冰洋海冰面积,连同过去五年的每天冰程度数据。 2012年蓝色显示,2011年橙色,2010年粉红, 2009年深蓝色,2008年紫色和2007年绿色。平均线周围的灰色区域显示数据的两个标准偏差范围。海冰指数数据。

来源:全国冰雪数据中心

Note: That image originally published on May 3 contained an error in the climatology. The image has been replaced with the correct image.
注:最初公布的5月3日图像中包含一个出错的气候映像现已被准确的图像替换。
Conditions in context
背景条件

Overall, the Arctic lost 1.07 million square kilometers (413,000 square miles) of ice during April, somewhat less than the 1979 to 2000 average April loss of 1.21 million square kilometers (467,000 square miles). The average daily rate of ice loss was 35,600 square kilometers (13,700 square miles) per day.  On April 24, ice extent was only 118,000 square kilometers (45,6000 square miles) below the 1979 to 2000 average for that day, although the difference has increased since then.
总体而言,北极地区在四月失去了107万平方公里(413,000平方英里)的冰,略少于1979年至2000年4月期间平均损失121万平方公里(467,000平方英里)。每天平均冰损失率为35,600平方公里(13,700平方英里)。 4月24日,海冰面积只有118,000平方公里(45,6000平方英里),低于1979年至2000年期间这一天的平均,虽然自那时起,差异增加。(译者注:可能数据有误)
While ice conditions approached the 1979 to 2000 average levels for this time of year, the high ice extent will have little influence on how much ice melts this summer. Much of the ice cover is recently formed thin ice that will melt out quickly. Research has shown that sea ice extent in spring does not tell us much about ice extent the following summer. More important to the summer melt is the thickness of the ice cover, and summer weather.
虽然冰情接近1979年至2000年期间这个季度的平均水平,在今年夏天将有多少冰融化对高冰程度影响不大。大部分的冰盖是由最近形成的迅速融化的薄冰组成。研究表明,春季海冰程度不会告诉我们很多关于之后夏天的冰程度。更重要的是夏季融化的冰盖厚度和夏季天气。

Figure 3. Monthly April ice extent for 1979 to 2012 shows a decline of 2.6% per decade.

Credit: National Snow and Ice Data Center
图3。1979年至2012年期间4月份显示冰的跌幅程度为每十年2.6%。

来源:全国冰雪数据中心
April 2012 compared to past years
2012年4月相比过去几年

Arctic sea ice extent for April 2012 was near average for the month in the satellite record, but was the highest since 2001. Including the year 2012, the linear rate of decline for April ice extent over the satellite record is 2.6% per decade.
2012年4月北极海冰面积接近该月卫星记录的平均值,是2001年以来最高的。包括2012年,卫星记录上4月冰面积下降的线性率是每十年2.6%。

Figure 4. This graph shows Antarctic sea ice extent as of May 1, 2012 (light blue line), along with the average ice extent and the ice extent from last year (dark blue). The average Southern Annular Mode (SAM) index number for each month is overlaid on the image. A stronger SAM correlates to stronger winds, which help to spread the sea ice and increase ice extent.

Credit: National Snow and Ice Data Center
图4。本图显示2012年5月1日(淡蓝色线)南极海冰的程度,连同平均冰程度和来自去年的冰程度(深蓝色)。平均南半球环状模(SAM)的索引号每月在图像上是重叠的。SAM更强的相关因素到强风,有助于传播海冰和增加冰面积。

来源:全国冰雪数据中心
Antarctic sea ice spread by strong winds
强风导致南极海冰扩散

The sea ice cover that surrounds the continent of Antarctica has been higher than average through most of the Southern Hemisphere summer (December to March). Ice extent declined much more slowly than usual in late November and remained above average through December and January, although it did not reach record highs for those months. At its minimum extent in March, Antarctic sea ice remained above average. Ice extent was the highest in the Weddell Sea and the northwestern Ross Sea.
围绕南极大陆高于平均水平的海冰覆盖面积已经占据了南半球夏季(12月至3月)的大部分时间。 11月下旬的海冰面积下降较正常慢得多,去年12月和今年1月虽然它没有创这段时间的历史新高,仍保持高于平均水平。南极海冰在3月的最低程度,持续高于平均水平。在威德尔海和罗斯海西北部的海冰范围最高。
The high ice extent likely stemmed from unusually strong winds that circled the continent of Antarctica during most the southern summer. These circumpolar winds tend to push the ice out from the continent, increasing the extent of the ice, although not necessarily the volume. Air temperatures in December and January were close to average over most of the sea ice-covered water. Researchers approximate the circumpolar wind intensity by an index called the Southern Annular Mode (SAM). A positive value for SAM indicates strong circumpolar winds around the continent; negative values indicate weaker winds. This index was at a record high for the two months of December 2011 and January 2012, at the same period of the higher-than-normal seasonal extents. For more information on Antarctic sea ice, see the NSIDC Icelights article: Sea ice down under: Antarctic sea ice and climate.
高冰程度可能源于不寻常的强风,夏季期间盘旋在南极大陆的最南部。这些极地风往往从大陆推出冰增加了冰的程度,虽然不一定在体积上增加。大部分的海冰覆盖水域在去年12月和今年1月的气温已接近平均。研究绕极风大致强度的称为南半球环状模(SAM)指数。一个SAM正值表示大陆各地的强大的极地风;负值表示较弱的风。该指数是2011年12月, 2012年1月两个月同期的历史新高,高于季节性正常的程度。南极海冰上的更多信息,请参阅NSIDC高冰文章:Sea ice down under: Antarctic sea ice and climate。

Figure 5. This map shows Arctic sea ice thickness, as well as the elevation of the Greenland Ice Sheet, for March 2011. The data come from the European Space Agency CryoSat-2 satellite. For the sea ice, green shades indicate thinner ice, while the yellows and oranges indicate thicker ice.

Credit: NSIDC courtesy CPOM/UCL/Leeds/ESA/PVL
图5。这张地图显示了北极海冰的厚度,以及2011年3月格陵兰冰原的高度。来自欧洲航天局CryoSat-2卫星的数据。对海冰,绿色表明较薄的冰,而黄色和橙色表示冰厚。

来源:NSIDC courtesy CPOM/UCL/Leeds/ESA/PVL
帖子中涉及地图来源广泛,图中所涉及的行政区域以中国官方认定的为准。
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 楼主| 发表于 2012-6-8 17:59 | 显示全部楼层



Jun 6, 2012

Arctic sea ice variable, ends May below average


Analysis
After reaching near-average levels in late April, sea ice extent declined rapidly during the early part of May. The rest of the month saw a slower rate of decline. Ice extent in the Bering Sea remained above average throughout the month.

Figure 1. Arctic sea ice extent for May 2012 was 13.13 million square kilometers (5.07 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High Resolution Image
Overview of conditions
Arctic sea ice extent for May 2012 averaged 13.13 million square kilometers (5.07 million square miles). This was 480,000 square kilometers (185,000 square miles) below the 1979 to 2000 average extent. This May’s extent was similar to the May 2008 – 2010 extent, but it was higher than May 2011. May ice extent was 550,000 square kilometers (212,000 square miles) above the record low for the month, which happened in the year 2004.
Ice cover remained extensive in the Bering Sea, continuing the pattern observed this past winter and spring. The anomalously heavy ice conditions were countered by unusually low extents in the Barents and Kara Seas, resulting in Arctic-wide ice conditions that remained below normal. By the end of the month, open water areas had begun to form along some parts of Arctic Ocean coast.
While the ice extent for May is not especially low this year, there is little correlation between the extent of the ice cover in May and that at the end of the melt season in September.


Figure 2. The graph above shows Arctic sea ice extent as of June 4, 2012, along with daily ice extent data for the previous four years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High Resolution Image
Conditions in context
For May, the Arctic as a whole lost 1.62 million square kilometers (625,000 square miles) of ice, which was 180,000 square kilometers (69,500 square miles) more than the 1979 to 2000 average. The average daily rate of ice loss was 52,000 square kilometers (20,000 square miles) per day, which was slightly faster than the long-term average of 46,000 square kilometers (18,000 square miles) per day. However, the rate of ice loss for the month was composed of two distinct periods: a rapid loss of ice during the first part of the month, followed by near-average rates during the latter part of the month.
Air temperatures for May were higher than usual over the central Arctic Ocean and the Canadian Archipelago. Over the Bering Sea, Hudson Bay, and parts of the East Greenland and Norwegian seas, temperatures were slightly below average.


Figure 3. Monthly May ice extent for 1979 to 2012 shows a decline of 2.3% per decade.

Credit: National Snow and Ice Data Center
High Resolution ImageMay 2012 compared to past years
Arctic sea ice extent for May 2012 was below average for the month, compared to the satellite record from 1979 to 2000. However, the ice extent this May was not as low as it has been in some recent years. Including the year 2012, the linear rate of decline for May ice extent over the satellite record is 2.3% per decade.
May and April have the smallest trends of the year, indicating that spring is a period during the year when there is less variability and conditions tend to converge. It also demonstrates that spring extents are not necessarily indicative of conditions later in the summer.


Figure 4. This map of sea level pressure anomalies for May 2012 shows that low pressure continued to dominate off of southern Alaska, resulting in northerly winds in the Bering Sea.

Credit: NSIDC courtesy NOAA/ESRL PSD
High Resolution ImageA persistent pattern of extensive ice in the Bering Sea
Continuing the pattern of the past six months, ice cover remained unusually extensive in the Bering Sea. Normally by the end of May, the Bering is largely ice-free, but this year, 350,000 square kilometers (135,000 square miles) of ice remained. As was also the case for February through April, May 2012 had the highest average Bering Sea ice extent for the month in the satellite record.
The higher than normal extent and late spring break up of the ice cover in the Bering Sea are mainly due to unusually low air temperatures and persistent winds from the north, related to a region of low atmospheric pressure centered over Kodiak, Alaska. As these cold winds slowed ice melt, they also pushed the ice edge to the south. The heavy ice in the region may delay the start of Shell Alaska’s Arctic drilling this summer, which will be the first exploratory drilling in the Arctic Ocean in 20 years.
With the overall springtime warming of the Arctic, the ice has nevertheless started to break up and large areas of open water are now present in the northern part of the Bering Sea.


Figure 5. In this Moderate Resolution Imaging Spectroradiometer (MODIS) Arctic Mosaic image for the Beaufort Sea on May 29, 2012, open water is apparent between fast ice along the coast and the broken-up floes off-shore. Toward the bottom of the image, thin clouds can be seen over the open water.

Credit: NASA/GSFC, Rapid Response
High Resolution ImageOpen water areas within the Arctic Ocean
Although ice extent has remained high in the Bering Sea, open water areas have developed in parts of the Arctic Ocean, notably along the coasts of the Beaufort and Laptev seas. These openings are largely driven by winds pushing the ice away from fast ice, ice that is attached to the coast and that does not move with the winds. That the open water areas have not refrozen points to the relatively warm conditions over the Arctic, particularly in the Beaufort Sea.
The ice cover in the southern Beaufort Sea is also substantially broken up, with many individual ice floes instead of a consolidated pack. This makes the ice in this region vulnerable to enhanced melt during summer, as the sun rises higher in the sky and the dark open water areas between the floes readily absorb solar energy.


Figure 6. Snow depth on Arctic sea ice (top) and Arctic sea ice thickness (bottom), derived from the 2012 Operation IceBridge “quick-look” data products, spanning 14 March to 02 April 2012.

Credit: S. Farrell and N. Kurtz, NASA Goddard Space Flight Center.
High Resolution Image: Figure 6a, Figure 6bQuicker thickness data from NASA IceBridge
As we discussed last month, thickness information is extremely important for understanding the state of the ice cover. It is particularly important to seasonal forecasts (such as the SEARCH Sea Ice Outlook that will be released later this month), because thinner ice is more likely to melt completely during summer.
Sea ice age can be inferred from satellite data, and can help indicate the locations of relatively thin versus relatively thick ice. But direct measurements of ice thickness have been limited. Satellite missions such as ICESat and CryoSat, which measure ice thickness with altimeters, have been extremely valuable in better understanding overall changes in Arctic sea ice volume.
Currently, the NASA IceBridge mission supplies both sea ice thickness and snow depth measurements in spring, providing timely information on the state of the ice cover as the melt season begins. IceBridge data are collected from aircraft that fly over the ice cover carrying a suite of instruments, including altimeters that can directly measure ice thickness above the surface. These measurements are at high spatial resolution that can also be used to validate satellite data.
This year, the IceBridge Arctic sea ice campaign collected data in late March and early April, and provided data to NSIDC for distribution shortly thereafter. The data, collected from the North American side of the Arctic, indicate thick ice north of Greenland due to wind and ocean current patterns piling ice into thick ridges. In the Beaufort Sea, the offshore ice is fairly thin (1 to 2 meters, or 3 to 6 feet), indicative of first-year ice. Such thin ice will be prone to melt out completely this summer.
Ice along the Alaskan coast is thicker. Thicker ice tends to have a deeper overlying snow cover. The amount of snow is an important factor in the summer melt, because the snow reflects solar energy. The snow must melt away before surface melting of the ice can begin in earnest


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 楼主| 发表于 2012-7-12 13:59 | 显示全部楼层
Rapid sea ice retreat in June


July 5, 2012

Arctic sea ice extent declined quickly in June, setting record daily lows for a brief period in the middle of the month. Strong ice loss in the Kara, Bering, and Beaufort seas, and Hudson and Baffin bays, led the overall retreat. Northern Hemisphere snow extent was unusually low in May and June, continuing a pattern of rapid spring snow melt seen in the past six years.


Figure 1. Arctic sea ice extent for June 2012 was 10.97 million square kilometers (4.24 million square miles). The magenta line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image
Daily data files

Overview of conditions
Arctic sea ice extent for June 2012 averaged 10.97 million square kilometers (4.24 million square miles). This was 1.18 million square kilometers (456,000 square miles) below the 1979 to 2000 average extent. The last three Junes (2010-2012) are the three lowest in the satellite record. June 2012 ice extent was 140,000 square kilometers (54,000 square miles) above the 2010 record low. Ice losses were notable in the Kara Sea, and in the Beaufort Sea, where a large polynya has formed. Retreat of ice in the Hudson and Baffin bays also contributed to the low June 2012 extent. The only area of the Arctic where sea ice extent is currently above average is along the eastern Greenland coast.
The ice extent recorded for 30 June 2012 of 9.59 million square kilometers (3.70 million square miles) would not normally be expected until July 21, based on 1979-2000 averages. This puts extent decline three weeks ahead of schedule.


Figure 2. The graph above shows Arctic sea ice extent as of July 2, 2012, along with daily ice extent data for the previous five years. 2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy, 2008 in purple, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image
Daily data files

Conditions in context
In June, the Arctic lost a total of 2.86 million square kilometers (1.10 million square miles) of ice. This is the largest June ice loss in the satellite record. Similar to May, the month was characterized by a period of especially rapid ice loss (discussed in the mid-month entry, June 19th) followed by a period of slower loss. Warm conditions prevailed over most of the Arctic; temperatures at the 925 hPa level (about 3000 feet above the ocean surface) were typically 1 to 4 degrees Celsius (1.8 to 7.2 degrees Fahrenheit) above the 1981 to 2010 average, and as much as 7 to 9 degrees Celsius (12.6 to 16.2 degrees Fahrenheit) above average over northern Eurasia and near southern Baffin Bay. Weather patterns over the Arctic Ocean varied substantially through the month.


Figure 3. Monthly June ice extent for 1979 to 2012 shows a decline of 3.7% per decade.

Credit: National Snow and Ice Data Center
High-resolution image

June 2012 compared to recent years
Arctic sea ice extent for June 2012 was well below average for the month compared to the satellite record from 1979 to 2000. It was the second lowest in the satellite record, behind 2010. Through 2012, the linear rate of decline for June Arctic ice extent over the satellite record is 3.7% per decade.


Figure 4. These photographs show sea ice on the fast ice near Barrow, Alaska. (a) Chris Polashenski stands in a melt pond with instrumentation, (b) honeycombed sample of rotten ice taken from the bottom of a melt pond, (c) sea ice rubble field after winds pushed the weakened sea ice onto the shore.

Credit: National Snow and Ice Data Center, courtesy Chris Polanshenski of CRREL as part of the SIZONET project.
High-resolution image

A report from the field
Dr. Chris Polashenski of the Cold Regions Research Lab (CRREL) recently returned from making sea ice measurements on landfast ice a few kilometers offshore near Barrow, Alaska as part of the National Science Foundation and NASA funded Seasonal Ice Zone Observing Network (SIZONET) project. He and his fellow researchers made some interesting observations. Prior to the onset of melt, the ice was thicker than observed in recent years – around 1.8 meters (5.9 feet) as compared to typical conditions of around 1.4 meters (4.6 feet). Despite this thick ice at the beginning of the season, melt proceeded relatively rapidly. Melt ponds began forming on June 4—a typical timing for recent years, but high temperatures, sunny afternoons, and foggy nights combined to speed the melt of ice thereafter.
On June 17-18, a confluence of weather conditions, including a daytime high of 19 degrees Celsius (66 degrees Fahrenheit), overnight condensing fog, and bright sun in the afternoon combined to produce exceptional surface melt of just under 11 centimeters (4.3 inches) in a 24-hour period, according to preliminary lidar data. By June 18, ice conditions had deteriorated significantly and with strong winds forecast out of the west, safety dictated it was time to get off the ice. Collisions of the pack with the weakened shore fast ice on June 21-23 resulted in substantial deformation and a series of ice pushes onto the beach, an amazing process to watch from the safety of land.Such field observations may only be representative of the local area. However, they provide context for basin-wide observations and a better understanding of local processes.


Figure 5. June 2012 set a record low for Northern Hemisphere snow cover extent. Figure 5 (a) graphs snow extent for Junes from 1967 to 2012. Figure 5 (b) maps snow cover anomalies in the Northern Hemisphere.

Credit: National Snow and Ice Data Center courtesy Rutgers University Snow Lab.

High-resolution image: June snow cover anomalies graph
High-resolution image: June snow cover anomalies map
Graph of May snow cover anomalies
Map of May snow cover anomalies

Low June snow extent
Snow cover over Northern Hemisphere lands retreated rapidly in May and June, leaving the Arctic Ocean coastline nearly snow free. June 2012 set a record low for snow extent (for a 45-year period of record spanning 1967-2012) by a significant margin. Snow extent for June 2012 was more than 1 million square kilometers (386,000 square miles) below the previous record set in 2010. Snow extent for 2011 was a close third lowest. May 2012 had third lowest snow extent for the period of record. This rapid and early retreat of snow cover exposes large, darker underlying surfaces to the sun early in the season, fostering higher air temperatures and warmer soils.

A note on the daily sea ice data
NSIDC has published the underlying data used for the Daily Sea Ice Extent image and the Daily Sea Ice Extent 5-Month Time Series graph. Please see the links below for documentation for the Sea Ice Index and links to the data:Documentation–Daily extent data file
Documentation–Climatology file
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 楼主| 发表于 2012-8-8 10:15 | 显示全部楼层
A most interesting Arctic summer


August 6, 2012

Arctic sea ice extent declined quickly in July, continuing the pattern seen in June. On August 1, ice extent was just below levels recorded for the same date in 2007, the year that saw the record minimum ice extent in September. Low sea ice concentrations are present over large parts of the western Arctic Ocean. Warm conditions dominated the weather for most of the Arctic Ocean and surrounding lands. For a brief period in early July, nearly all of the Greenland ice sheet experienced surface melt, a rare event.

Overview of conditions




Figure 1. Arctic sea ice extent for July 2012 was 7.94 million square kilometers (3.07 million square miles). The orange line shows the 1979 to 2000 median extent for that month. The black cross indicates the geographic North Pole. Sea Ice Index data. About the data

Credit: National Snow and Ice Data Center
High-resolution image


Arctic sea ice extent for July 2012 averaged 7.94 million square kilometers (3.07 million square miles). This was 2.12 million square kilometers (819,000 square miles) below the 1979 to 2000 average extent. July 2012 ice extent was 20,000 square kilometers (7,700 square miles) above the 2011 record July low.
As throughout the summer, the low ice extent for the Arctic as a whole is primarily due to extensive open water on the Atlantic side of the Arctic (Kara, Laptev and East Siberian seas) and the Beaufort Sea. By August 1, open water in the Laptev Sea, along the Siberian coast, had reached nearly 80[sup]o[/sup]N latitude. Ice extent remains near average in the Chukchi Sea, and ice continues to block sections of the both the Northern Sea Route and the Northwest Passage. The ice extent recorded for August 1 of 6.53 million square kilometers (2.52 million square kilometers) is the lowest in the satellite record. The previous record for the same date was set in 2007 at 6.64 million square kilometers (2.56 million square miles), when the current record low September ice extent was set.

Conditions in context




Figure 2. The graph above shows Arctic sea ice extent as of August 5, 2012, along with daily ice extent data for the 2011 and for 2007, the record low year. 2012 is shown in blue, 2011 in orange, and 2007 in green. The gray area around the average line shows the two standard deviation range of the data. Sea Ice Index data.

Credit: National Snow and Ice Data Center
High-resolution image


In July, the Arctic lost a total of 2.97 million square kilometers (1.15 million square miles) of ice. The largest July total loss, 3.53 million square kilometers (1.36 million square miles) occurred in the year 2007. Warm conditions prevailed over most of the Arctic Ocean; temperatures at the 925 hPa level (about 3,000 feet above the ocean surface) were typically 1 to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) above the 1981 to 2010 average over the Beaufort Sea and regions to the north, as well as over Baffin Bay. By contrast, temperatures were 1 to 3 degrees Celsius below average over the Norwegian Sea. Weather patterns over the Arctic Ocean varied substantially through the month, as they have done throughout the melt season.

July 2012 compared to recent years




Figure 3. Monthly July ice extent for 1979 to 2012 shows a decline of 7.1% per decade.

Credit: National Snow and Ice Data Center
High-resolution image

Arctic sea ice extent for July 2012 was the second lowest in the satellite record, behind 2011. Through 2012, the linear rate of decline for July Arctic ice extent over the satellite record is 7.1% per decade.

MODIS data shows low concentration ice





Figure 4. This image from the Moderate Resolution Imaging Spectroradiometer (MODIS), taken in late July, shows areas of low concentration sea ice in the Beaufort Sea, north of Alaska. Barrow, Alaska is at the top left. The resolution is 500 meters. The cloud band covering much of the lower right part of the image is associated with an approaching storm.

Credit: NASA Goddard Space Flight Center, Rapid Response
High-resolution image


In our last post (July 24, 2012) we commented on large areas of low ice concentration depicted in Special Sensor Microwave Imager/Sounder (SSMIS) data in the Beaufort and Chukchi seas, the Canadian Archipelago, the East Greenland Sea, and north of Siberia. These areas of low ice concentration ice can be seen clearly in visible-band data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua and Terra satellites.
The MODIS image shows polygonal floes of multi-year ice, as well as thin, gray first-year ice, and dark open water in the Beaufort Sea, north of Alaska. Most of these areas of low concentration ice will likely melt over the next month. Because MODIS senses light reflected from the surface as opposed to the emission of microwave radiation, its ability to see the surface depends on cloud cover.

Comparisons between observed and modeled September sea ice trends




Figure 5. This figure shows the observed September sea ice extent for 1952 to 2011 (bold black line) and extents for 1900 to 2100 from the CMIP3 models using the “business as usual” SRESA1B greenhouse gas emissions scenario (the blue line averaging results from all of the model runs with the blue shading showing the +/- 1 standard deviation of the different model runs) and from the CMIP5 archive, using the RCP 4.5 scenario (pink line and pink shading). The darker pink shading shows where the simulations from CMIP3 and CMIP5 overlap each other.

Credit: National Snow and Ice Data Center courtesy Stroeve et al. 2012
High-resolution image


Previous research at NSIDC documented that September Arctic ice extent has declined faster than models predicted it would. The comparison was between observations and simulated trends from models participating in the World Climate Research Programme Coupled Model Intercomparison Project Phase 3 (CMIP3). These climate models were used in the 2007 4[sup]th[/sup] Assessment report of the Intergovernmental Panel on Climate Change (IPCC). In a new paper, Stroeve et al. (2012) compared the observed 1979-2011 September trend for the Arctic against trends over the same period from the next generation of models in the CMIP5 archive. While the newer CMIP5 models do a better job of simulating the observed trend, most of the modeled ice extent trends are still smaller than the observed downward trend. NSIDC is working with researchers to further improve the models, which help extend and refine our understanding of the climate system.

Extensive melt over the Greenland Ice Sheet




Figure 6. This figure shows the daily, cumulative area of the Greenland ice sheet showing surface melt for 2012, 2011, 2010 and for the 1980 to 1999 mean. While melt was unusually extensive through May and June of 2012, the melt area increased rapidly in early July in response to an unusually warm weather event.

Credit: National Snow and Ice Data Center courtesy Marco Tedesco, CUNY
High-resolution image


This summer, the ocean has not been the only place where unusual melt has been observed in the Arctic. NASA researchers reported that for several days in early July, nearly the entire Greenland ice sheet experienced a brief period of surface melt, including at the summit of the ice sheet. Typically, about half of the ice sheet sees some surface melting during summer, but this tends to be confined to the lower elevations. The 2012 event was associated with a high-pressure weather pattern bringing unusually warm temperatures over the higher elevations of the ice sheet. While the event has not been seen previously in the 34-year satellite record, there is evidence in ice core data from Summit, Greenland of similar events occurring several times over the past few thousand years. These melt events recorded in the ice cores from Summit show an overall average frequency of about once every 150 years since the end of the last ice age. Perhaps more important, however, is the extraordinary high melting occurring this year around the lower elevations in Greenland. Figure 6 shows that the first few months of melt exceeded past higher-than-average melt seasons. Flooding and damage to structures has been reported in some areas where this melt runs off the ice sheet and fills streams and rivers along the Greenland coast. The surface melt runoff, as well as the flow of ice and the resulting calving of icebergs, are contributors to sea level rise. Along with the substantial summer sea ice extent decline and the early Northern Hemisphere snow melt, the pace of Greenland surface melt suggests that 2012 is yet another interesting summer in the Arctic.
For more information and images, visit Greenland Melting.
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