Melt Pond Scheme Parameter Estimation Using an Adjoint Model

Melt ponds significantly affect Arctic sea ice thermodynamic processes. The melt pond parameterization scheme in the Los Alamos sea ice model(CICE6.0) can predict the volume, area fraction(the ratio between melt pond area to sea ice area in a model grid), and depth of melt ponds. However, this scheme has some uncertain parameters that affect melt pond simulations. These parameters could be determined through a conventional parameter estimation method, which requires a large number of sensitivity simulations. The adjoint model can calculate the parameter sensitivity efficiently. In the present research, an adjoint model was developed for the CESM(Community Earth System Model) melt pond scheme. A melt pond parameter estimation algorithm was then developed based on the CICE6.0 sea ice model, melt pond adjoint model,and L-BFGS(Limited-memory Broyden-Fletcher-Goldfard-Shanno) minimization algorithm. The parameter estimation algorithm was verified under idealized conditions. By using MODIS(Moderate Resolution Imaging Spectroradiometer)melt pond fraction observation as a constraint and the developed parameter estimation algorithm, the melt pond aspect ratio parameter in CESM scheme, which is defined as the ratio between pond depth and pond area fraction, was estimated every eight days during summertime for two different regions in the Arctic. One region was covered by multi-year ice(MYI) and the other by first-year ice(FYI). The estimated parameter was then used in simulations and the results show that:(1) the estimated parameter varies over time and is quite different for MYI and FYI;(2) the estimated parameter improved the simulation of the melt pond fraction.     

Multi‐year sea‐ice conditions in the western Canadian arctic archipelago region of the northwest passage: 1968–2006

Abstract

Numerous studies have reported decreases in Arctic sea‐ice cover over the past several decades and General Circulation Model (GCM) simulations continue to predict future decreases. These decreases — particularly in thick perennial or multi‐year ice (MYI) — have led to considerable speculation about a more accessible Northwest Passage (NWP) as a transit route through the Canadian Arctic Archipelago (CAA). The Canadian Ice Service Digital Archive (CISDA) is used to investigate dynamic import/export and in situ growth of MYI within the western CAA regions of the NWP from 1968 to 2006. This analysis finds that MYI conditions in the western CAA regions of the NWP have remained relatively stable because the M'Clintock Channel and Franklin regions continuously operate as a drain‐trap mechanism for MYI. Results also show that in addition to the Queen Elizabeth Islands (QEI) region, the Western Parry Channel and the M'Clintock Channel are also regions where a considerable amount of MYI forms in situ and combined with dynamic imports contributes to heavy MYI conditions. There is also evidence to suggest that more frequent dynamic import of MYI appears to have occurred since‐1999 compared to the formation of more MYI in situ before 1999. As a result, the drain‐trap mechanism that has historically maintained heavy MYI conditions in the NWP is perhaps operating faster now than it was in the past. Based on the 38‐year MYI record examined in this study, it is likely that the mechanisms operating within the western CAA regions of the NWP can facilitate the continued presence of MYI for quite some time.     

Changes in Arctic clouds during intervals of rapid sea ice loss

We investigate the behavior of clouds during rapid sea ice loss events (RILEs) in the Arctic, as simulated by multiple ensemble projections of the 21st century in the Community Climate System Model (CCSM3). Trends in cloud properties and sea ice coverage during RILEs are compared with their secular trends between 2000 and 2049 during summer, autumn, and winter. The results suggest that clouds promote abrupt Arctic climate change during RILEs through increased (decreased) cloudiness in autumn (summer) relative to the changes over the first half of the 21st century. The trends in cloud characteristics (cloud amount, water content, and radiative forcing) during RILEs are most strongly and consistently an amplifying effect during autumn, the season in which RILEs account for the majority of the secular trends. The total cloud trends in every season are primarily due to low clouds, which show a more robust response than middle and high clouds across RILEs. Lead-lag correlations of monthly sea ice concentration and cloud cover during autumn reveal that the relationship between less ice and more clouds is enhanced during RILEs, but there is no evidence that either variable is leading the other. Given that Arctic cloud projections in CCSM3 are similar to those from other state-of-the-art GCMs and that observations show increased autumn cloudiness associated with the extreme 2007 and 2008 sea ice minima, this study suggests that the rapidly declining Arctic sea ice will be accentuated by changes in polar clouds.     

Trans-Arctic shipping routes expanding faster than the model projections

Rapid declines in Arctic sea ice coverage over the past four decades have increased the commercial feasibility of trans-Arctic routes. However, the historical changes in navigability of trans-Arctic routes remain unclear, and projections by global circulation models (GCMs) contain large uncertainties since they cannot simulate long-term Arctic sea ice changes. In this study, we determined the changes in trans-Arctic routes from 1979 to 2019 by combining two harmonized high-quality daily sea ice products. We found that the trans-Arctic routes are becoming navigable much faster than projected by the GCMs. The navigation season for open water (OW) vessels along the Northeast Passage (NEP) has lengthened from occasionally navigable in the 1980 s to 92 ± 15 days in the 2010 s. In contrast, previous GCM projections have suggested that navigability would not be achieved until the mid-21st century. The 90-day safety shipping area for OW vessels expanded by 35% during 1979–2018, reaching 8.28 million km² in 2018, indicating an increasing rate of 0.08 ± 0.01 million km² per year. The shortest trans-Arctic routes were also shifted further north than the model projections. Regular ships have been able to safely travel north along the islands in the NEP and transit through the M’Clure Strait in the Canadian Arctic Archipelago during the 2010 s, while previous studies have projected that this would not be feasible until the mid-21st century. We also found that the improved navigability of trans-Arctic routes enables commercial ships to transport approximately 33–66% (at the same load factor) more goods from East Asia to Europe during the Arctic shipping season than by the traditional Suez Canal route. These findings highlight the need for aggressive actions to develop mandatory rules that promote navigation safety and strengthen environmental protection in the Arctic.     

The International polar year (IPY) circumpolar flaw lead (CFL) system study: Overview and the physical system

Abstract

The Circumpolar Flaw Lead (CFL) system study is a Canadian‐led International Polar Year (IPY) initiative with over 350 participants from 27 countries. The study is multidisciplinary in nature, integrating physical sciences, biological sciences and Inuvialuit traditional knowledge. The CFL study is designed to investigate the importance of changing climate processes in the flaw lead system of the northern hemisphere on the physical, biogeochemical and biological components of the Arctic marine system. The circumpolar flaw lead is a perennial characteristic of the Arctic throughout the winter season and forms when the mobile multi‐year (MY) pack ice moves away from coastal fast ice, creating recurrent and interconnected polynyas in the Norwegian, Icelandic, North American and Siberian sectors of the Arctic. The CFL study was 293 days in duration and involved the overwintering of the Canadian research icebreaker CCGS Amundsen in the Cape Bathurst flaw lead throughout the annual sea‐ice cycle of 2007–2008.

In this paper we provide an introduction to the CFL project and then use preliminary data from the field season to describe the physical flaw lead system, as observed during the CFL overwintering project. Preliminary data show that ocean circulation is affected by eddy propagation into Amundsen Gulf (AG). Upwelling features arising along the ice edge and along abrupt topography are also detected and identified as important processes that bring nutrient rich waters up to the euphotic zone. Analysis of sea‐ice relative vorticity and sea‐ice area by ice type in the AG during the CFL study illustrates increased variability in ice vorticity in late autumn 2007 and an increase in new and young ice areas in the AG during winter. Analysis of atmospheric data show that a strong northeast–southwest pressure gradient present over the AG in autumn may be a synoptic‐scale atmospheric response to sensible and latent heat fluxes arising from areas of open water persisting into late November 2007. The median atmospheric boundary layer temperature profile over the Cape Bathurst flaw lead during the winter season was stable but much less so when compared to Russian ice island stations.     

全球气候变暖中南北半球海冰变化的差异

应用海冰面积资料,分析在全球气候变暖下,南北半球海冰季节和年际变化的差异,结果表明:冬季南半球海冰面积为北半球的1.13倍,而夏季仅为北半球的2/5,南半球海冰的季节变化比北半球更为显著,其季节振幅为北半球的1.6倍.1979--2006年,北半球海冰总面积呈显著减少趋势,夏秋季最快,特别在1990年代中后期以来,减少尤为迅速;夏秋季,整个区域海冰为均一的减少趋势,北冰洋靠近北太平洋的近海变化最为迅速,冬春季,主要发生在北太平洋海域.南半球海冰自1980年代初以来有所增多,四季整个区域海冰并未呈均一的减少趋势,而是有一显著减少中心,位于南极半岛附近,两个增多中心,分别位于罗斯海外围和西南印度洋一带.随夏一秋一冬一春的季节转换,3个中心区域位置存在东移和返回的过程.     

Properties of adjoint sea ice sensitivities to atmospheric forcing and implications for the causes of the long term trend of Arctic sea ice

Based on adjoint sensitivities of the coupled Massachusetts Institute of Technology ocean–sea ice circulation model, the potential influence of thermodynamic atmospheric forcing on the interannual variability of the September sea ice area (AREA) and volume (VOLUME) in the Arctic is investigated for the three periods 1980–1989, 1990–1999 and 2000–2009. Sensitivities suggest that only large forcing anomalies prior to the spring melting onset in May can influence the September sea ice characteristics while even small changes in the atmospheric variables during subsequent months can significantly influence September sea ice state. Specifically, AREA close to the ice edge in the Arctic seas is highly sensitive to thermodynamic atmospheric forcing changes from June to July. In contrast, VOLUME is highly sensitive to atmospheric temperature changes occurring during the same period over the central parts of the Arctic Ocean. A comparison of the sea ice conditions and sensitivities during three different periods reveals that, due to the strong decline of sea ice concentration and sea ice thickness, sea ice area became substantially more sensitive to the same amplitude thermodynamic atmospheric forcing anomalies during 2000–2009 relative to the earlier periods. To obtain a quantitative estimate of changes that can be expected from existing atmospheric trends, adjoint sensitivities are multiplied by monthly temperature differences between 1980s and two following decades. Strongest contributions of surface atmospheric temperature differences to AREA and VOLUME changes are observed during May and September. The strongest contribution from the downward long-wave heat flux to AREA changes occurs in September and to VOLUME changes in July–August. About 62 % of the AREA decrease simulated by the model can be explained by summing all contributions to the thermodynamic atmospheric forcing. The changing sea ice state (sensitivity) is found to enhance the decline and accounts for about one third of the explained reduction. For the VOLUME decrease, the explained fraction of the decrease is only about 37 %.     

夏、秋季北极海冰异常与秋、冬季青藏高原极端低温日数的关系及影响机理

利用1979~2012年青藏高原125个基本、基准站观测日最高及最低气温数据、Hadley中心月平均海冰覆盖率资料、ERA-Interim的风场、高度场等再分析资料,根据相关统计分析、合成分析等方法系统地分析了青藏高原地区秋、冬季冷昼和冷夜日数(低温日数)与关键影响海区海冰的关系及影响机理。结果表明,夏、秋季关键海区海冰偏少时,秋、冬季极地和青藏高原地区500 h Pa位势高度减小,中高纬西伯利亚地区位势高度增强,北极至青藏高原有明显由北向南波动通量,高压反气旋系统在西伯利亚地区形成与壮大,青藏高原以北风场呈现明显偏北风,Rossby波在青藏高原及其以北地区呈现由北向南波动形式,青藏高原以北的西风带地区Rossby波东传减缓,导致经向活动加强,北部冷空气易于通过气流向高原侵袭,秋、冬季青藏高原低温日数将偏多。     

Projected 21st-century changes to Arctic marine access

Climate models project continued Arctic sea ice reductions with nearly ice-free summer conditions by the mid-21st century. However, how such reductions will realistically enable marine access is not well understood, especially considering a range of climatic scenarios and ship types. We present 21st century projections of technical shipping accessibility for circumpolar and national scales, the international high seas, and three potential navigation routes. Projections of marine access are based on monthly and daily CCSM4 sea ice concentration and thickness simulations for 2011–2030, 2046–2065, and 2080–2099 under 4.5, 6.0, and 8.5 W/m² radiative forcing scenarios. Results suggest substantial areas of the Arctic will become newly accessible to Polar Class 3, Polar Class 6, and open-water vessels, rising from ~54 %, 36 %, and 23 %, respectively of the circumpolar International Maritime Organization Guidelines Boundary area in the late 20th century to ~95 %, 78 %, and 49 %, respectively by the late 21st century. Of the five Arctic Ocean coastal states, Russia experiences the greatest percentage access increases to its exclusive economic zone, followed by Greenland/Denmark, Norway, Canada and the U.S. Along the Northern Sea Route, July-October navigation season length averages ~120, 113, and 103 days for PC3, PC6, and OW vessels, respectively by late-century, with shorter seasons but substantial increases along the Northwest Passage and Trans-Polar Route. While Arctic navigation depends on other factors besides sea ice including economics, infrastructure, bathymetry, and weather, these projections are useful for strategic planning by governments, regulatory agencies, and the global maritime industry to assess spatial and temporal ranges of potential Arctic marine operations in the coming decades.     

The Arctic Amplification Debate

Rises in surface air temperature (SAT) in response to increasing concentrations of greenhouse gases (GHGs) are expected to be amplified in northern high latitudes, with warming most pronounced over the Arctic Ocean owing to the loss of sea ice. Observations document recent warming, but an enhanced Arctic Ocean signal is not readily evident. This disparity, combined with varying model projections of SAT change, and large variability in observed SAT over the 20th century, may lead one to question the concept of Arctic amplification. Disparity is greatly reduced, however, if one compares observed trajectories to near-future simulations (2010–2029), rather than to the doubled-CO₂ or late 21st century conditions that are typically cited. These near-future simulations document a preconditioning phase of Arctic amplification, characterized by the initial retreat and thinning of sea ice, with imprints of low-frequency variability. Observations show these same basic features, but with SATs over the Arctic Ocean still largely constrained by the insulating effects of the ice cover and thermal inertia of the upper ocean. Given the general consistency with model projections, we are likely near the threshold when absorption of solar radiation during summer limits ice growth the following autumn and winter, initiating a feedback leading to a substantial increase in Arctic Ocean SATs.     

Mechanism of an Abrupt Decrease in Sea-Ice Cover in the Pacific Sector of the Arctic during the Late 1980s

The recent decline in Arctic sea-ice cover (SIC) shows seasonal and regional characteristics. The retreat of summer sea ice has occurred mainly in the Pacific sector of the Arctic. In this study, using the moving t-test, we found an abrupt change event in the long-term sea-ice area in the Pacific sector in summer 1989. This event was linked to the phase shift of the Arctic Oscillation (AO) or the Northern Annular Mode (NAM). Corresponding with the AO/NAM phase shift from negative to positive, the area of the northern hemisphere stratospheric polar vortex decreased abruptly in winter 1988/89. Comparisons of two periods before (1979–1988) and after (1989–1993) the abrupt decrease in sea ice show that an anomalous winter sea level pressure (SLP) was induced by changes in the polar vortex leading to an anomalous cyclonic ice drift in the Pacific sector. The changes in SLP and wind field persisted into the following spring, resulting in a decrease in SIC and warming of the surface air temperature (SAT). The influence of the spring SLP and SAT on ice persisted into the following summer. Meanwhile, the increased summer net surface heat flux over the ocean and sea ice as a result of the decreased spring ice cover further contributed to the summer sea-ice melt.     

极冰对南方涛动的影响

分析南、北极冰量与南方涛动序列作月、季和年尺度的变化过程线性相关关系，发现北极冰量与南方涛动指数是反相关关系，而南极冰量与南方涛动是正相关。比较而言，南极冰量与南方涛动的关系在月和季尺度上似乎较北极与大气的关系密切些。在各时间尺度序列中以太平洋地区南极极冰的影响表现最明显。分析发现极冰与南方涛动之间存在较复杂的非线性关系。在前期极冰的强信号寻找中，发现极冰与南方涛动在月序列的相关关系上存在周期变化现象。进一步选择相关极值的对应步长建立前期极冰状态激发大气变化的预测统计动力模式，模式对大气序列的解释方差可达０．９０以上。文中还进一步探讨了月序列存在的周期变化的共同因素的影响     

冬季北极海冰运动主模态的构成及其与海平面气压变化的关系

利用国际北极浮冰运动观测资料（IABP）（1979-1998）以及NCEP／NCAR月平均海平面气压再分析资料（1960-2002）,通过求解海冰运动异常的复斜方差矩阵,研究了冬季北极海冰运动主模态构成及其与海平面气压变化的关系。冬季海冰运动主模态是由两个海冰运动优势模态的一个线性组合构成,与这两个运动优势模态有直接关系的海平面气压变化主要发生在北极海盆及其边缘海区。尽管北极涛动（北大西洋涛动）通过影响海平面气压进而影响北极海冰运动,但是,北极涛动（北大西洋涛动）并不是决定海冰运动主模态的关键性因素。     

南、北极海冰的长期变化趋势及其与大气环流的联系

采用南、北极海冰面积指数 1°× 1°经纬度格点资料及海平面气压资料 ,运用多种统计方法 ,研究了南、北极海冰的长期变化趋势、突变特征及其与大气环流的联系 ,发现近年来南极冬、春、秋季海冰逐渐减少 ,夏季海冰逐渐增加 ;北极春、夏、秋季海冰均不同程度地减少 ,冬季海冰变化趋势不明显 ;南、北极各季海冰的年际变化均存在一定的突发性 ,大气环流在海冰突变年前后有显著的差异     

深度学习方法在北极海冰预报中的应用

在全球气候变暖背景下,北极海冰呈现出逐年消融的趋势.海冰的消融给北极的开发利用带来了重要机遇,例如北极航道通航潜力的显现.但北极航道开通还面临着诸多困难,尤其是海冰变化机理的复杂性和海冰预报的不确定性以及由此带来的航行安全风险.近年来,深度学习因其强大的非线性拟合能力,逐渐在海冰预报领域中崭露头角.本文对近年来深度学习...     

Evaluation of pan-Arctic melt-freeze onset in CMIP5 climate models and reanalyses using surface observations

The seasonal melt-freeze transitions are fundamental features of the Arctic climate system. The representation of the pan-Arctic melt and freeze onset (north of 60°N) is assessed in two reanalyses and eleven CMIP5 global circulation models (GCMs). The seasonal melt-freeze transitions are retrieved from surface air temperature (SAT) across the land and sea-ice domains and evaluated against surface observations. While monthly averages of SAT are reasonably well represented in models, large model-observation and model–model disparities of timing of melt and freeze onset are evident. The evaluation against surface observations reveals that the ERA-Interim reanalysis performs the best, closely followed by some of the climate models. GCMs and reanalyses capture the seasonal melt-freeze transitions better in the central Arctic than in the marginal seas and across the land areas. The GCMs project that during the 21st century, the summer length—the period between melt and freeze onset—will increase over land by about 1 month at all latitudes, and over sea ice by 1 and 3 months at low and high latitudes, respectively. This larger summer-length increase over sea ice at progressively higher latitudes is related to a retreat of summer sea ice during the 21st century, since open water freezes roughly 40 days later than ice-covered ocean. As a consequence, by the year 2100, the freeze onset is projected to be initiated within roughly 10 days across the whole Arctic Ocean, whereas this transition varies by about 80 days today.     

Changes in the climate of the Alaskan North Slope and the ice concentration of the adjacent Beaufort Sea

A reliable data set of Arctic sea ice concentration based on satellite observations exists since 1972. Over this time period of 36 years western arctic temperatures have increased; the temperature rise varies significantly from one season to another and over multi-year time scales. In contrast to most of Alaska, however, on the North Slope the warming continued after 1976, when a circulation change occurred, as expressed in the PDO index. The mean temperature increase for Barrow over the 36-year period was 2.9°C, a very substantial change. Wind speeds increased by 18% over this time period, however, the increase were non-linear and showed a peak in the early 1990s. The sea ice extent of the Arctic Ocean has decreased strongly in recent years, and in September 2007 a new record in the amount of open water was recorded in the Western Arctic. We observed for the Southern Beaufort Sea a fairly steady increase in the mean annual amount of open water from 14% in 1972 to 39% in 2007, as deduced from the best linear fit. In late summer the decrease is much larger, and September has, on average, the least ice concentration (22%), followed by August (35%) and October (54%). The correlation coefficient between mean annual values of temperature and sea ice concentration was 0.84. On a monthly basis, the best correlation coefficient was found in October with 0.88. However, the relationship between winter temperatures and the sea ice break-up in summer was weak. While the temperature correlated well with the CO₂ concentration (r?=?0.86), the correlation coefficient between CO₂ and sea ice was lower (r?=??0.68). After comparing the ice concentration with 17 circulation indices, the best relation was found with the Pacific Circulation Index (r?=??0.59).     

从2011/2012和2015/2016年冬季大气环流异常看北极海冰以及前期夏季北极大气环流异常的作用

利用美国NCEP/NCAR、欧洲中心ERA-Interim再分析资料,以及英国哈得来中心海冰密集度资料,通过诊断分析和数值模拟试验,研究了2011/2012和2015/2016年两个冬季大气环流异常的主要特征和可能原因。结果表明,尽管热带太平洋海温背景截然不同（分别为弱的拉尼娜事件和强厄尔尼诺事件）,但这两个冬季西伯利亚高压均异常偏强,自1979年以来其强度分别排第1和第5位。前期秋季北极海冰异常偏少是导致这两个冬季西伯利亚高压偏强的主要原因。更为重要的是,前期夏季北冰洋表面反气旋风场,以及其上空对流层中、低层平均气温偏高,加强了北极海冰偏少对冬季大气变率的负反馈,进一步促进了西伯利亚高压的加强,从而有利于东亚地区冬季阶段性强严寒的出现。因此,夏季北极大气环流的动力和热力状态不仅影响夏、秋季北极海冰,而且对海冰偏少影响亚洲冬季气候变率有重要调节作用。2015/2016年冬季强厄尔尼诺事件并不能掩盖来自北极海冰和大气环流的影响。      

20世纪90年代以来北极海冰减少的热动力分析——基于PIOMAS模式结果

本文利用美国华盛顿大学的PIOMAS海冰模式输出结果,分析了20世纪90年代以来北极海冰减少的动力和热力过程的特征,并探讨了海冰减少与北极大气环流模态之间的关系。结果表明:（1）通过弗拉姆海峡输出的多年冰的厚度自1995年以来有显著减少;（2）海冰的热力过程在20世纪90年代以后特别是21世纪以来是海冰减少的主导因素;（3）大气模态中的北极涛动（AO）和北极偶极子（AD）均对北极海冰的动力输出有影响,各自与海冰输出量的相关关系显著,并且AO和AD的多元线性回归能很好的拟合出海冰输出量的减少。     

Climate tendencies of changes in multiyear sea ice thickness in the Arctic Basin (1970–2005)

The area integral of the sea ice thickness in the Arctic Basin is estimated from the measurements of sea ice surface fluctuations at drift-ice stations. The 1970–1990 linear trend is indicative of an approximately 10-cm reduction in the average sea ice thickness over the entire Arctic Basin, which makes 3% of the average ice thickness (about 3 m). Seasonal changes made 40 cm. The amplitude of variations of the average ice thickness in that period is 20 cm with a period of changes of approximately 6–8 years. The observations were interrupted during 1991–2003 and then resumed in 2004. During 1990–2005, the old ice thickness over the entire Arctic Basin decreased, on average, by 110 cm.