On the interannual variability of arctic sea‐level pressure and sea ice

Abstract

Monthly mean sea‐level pressure (SLP) data from the Northern Hemisphere for the period January 1952‐December 1987 are analysed. Fluctuations in this field over the Arctic on interannual time‐scales and their statistical association with fluctuations farther south are determined. The standard deviation of the interannual variability is largest compared with that of the annual cycle along the seaboards of the major land masses. The SLP anomalies are generally in phase over the entire Arctic Basin and extend south over the northern Russia and Canada, but tend to be out of phase with fluctuations at mid‐latitudes. The anomalies are most closely associated with fluctuations over the North Atlantic and Europe except near the Chukchi Sea to the north of Bering Strait. The associations with the North Pacific fluctuations become increasingly more prominent at most Arctic sites (e.g. the Canadian Arctic Archipelago) as the time‐scale increases.

Associations between the SLP fluctuations and atmospheric indices that represent processes affecting sea‐ice drift (wind stress and wind stress curl) are determined. In every case local associations dominate, but some remote ones are also evident. For example, changes in the magnitude of the wind stress curl over the Beaufort Sea are increased if the atmospheric circulation over the North Pacific is intensified; wind stress over the region where sea ice is exchanged between the Beaufort Gyre and the Transpolar Drift Stream is modulated by both the Southern and North Atlantic Oscillations.

Severe sea‐ice conditions in the Greenland Sea (as measured by the Koch Ice Index) coincide with a weakened atmospheric circulation over the North Atlantic.     

秋季北极海冰对EP型ENSO的非线性响应

利用1961—2015年Hadley中心逐月海表温度资料、海冰密集度资料以及NCEP/NCAR再分析资料,探讨了秋季北极海冰对于EP型ENSO事件的异常响应,并进一步研究了这种异常响应的可能原因。结果表明,秋季北极海冰对EP型ENSO的响应具有非线性,特别是喀拉海海域(60°～90°E,70°～80°N)海冰无论在EP型El Ni?o或是La Ni?a位相,均表现为显著的负异常。进一步研究发现,不同ENSO位相造成该区域海冰异常偏少的机制有明显不同。EP型El Ni?o年秋季菲律宾附近海域对流活动被抑制,所激发的经向波列在高纬地区形成异常反气旋环流,其南风分量向喀拉海输送暖平流,造成海冰异常偏少。而EP型La Ni?a年喀拉海海域则主要受到来自大西洋开放性海域西风异常的影响,合成结果和个例年均显示EP型La Ni?a年秋季北大西洋上空存在一个显著的西风急流中心,有利于北大西洋开放性海域较暖海水向下游输送,进而影响喀拉海海冰。这些结果表明,热带外地区大气环流场对EP型ENSO的非线性响应导致了喀拉海海冰对EP型ENSO事件的响应也表现出明显的非线性。     

On the role of the Arctic sea ice in seasonal variability of carbon dioxide concentration in Northern latitudes

For the first time, based on direct observations of carbon dioxide concentration at modern Russian drifting stations, the role of the Arctic sea ice in maximum seasonal changes in carbon dioxide distribution is considered. Carbon dioxide is generated during growth of ice mass at the sea ice undersurface and is absorbed at the surface of melting sea ice. The time of ice growth is three or four times greater than that of its melting in summer months, and, as result, the time of carbon dioxide generation is longer that that of its uptake. Consequently, the Arctic Ocean is a source of carbon dioxide on the mean annual scale (the effect of Arctic “breathing”). Experiments in a freezing chamber confirm these conclusions.     

秋季北极海冰对中国冬季气温的影响

利用海冰资料、中国地面气候资料、环流特征量资料及NCEP/NCAR再分析资料,研究了秋季北极海冰变化对中国冬季平均气温、日气温变率以及异常低温天气的影响。分析结果表明,秋季北极海冰异常偏多年中国冬季常为暖冬;异常偏少年中国冬季常为冷冬,且异常低温天气出现频率更高,常发生低温灾害事件。秋季北极海冰通过影响后期的北半球极涡、东亚冬季风和西伯利亚高压进而影响中国冬季的平均气温,且通过影响冬季异常强西伯利亚高压的出现频次,影响中国冬季异常低温天气的发生频次。合成分析结果表明,秋季北极海冰异常偏少年的冬季,中国以北亚欧大陆高纬度的偏北风较强,且中国及其以北的中高纬度地区空气异常偏冷,导致极地和高纬度的冷空气易向南爆发,造成中国冬季气温偏低,异常低温天气频发。     

北极海冰及其与气象要素年际关系的年代际变化

利用Hadley海冰密集度资料和NCEP/NCAR再分析资料,分析了北极海冰融冰量及其与大气变量年际关系的年代际变化。结果表明,北极海冰存在显著的年代际变化,且有较强的区域性。东西伯利亚海和波弗特海海冰融冰量的平均值变大且方差增大,格陵兰岛以东洋面海冰融冰量的量值和变率均在减弱。对3个不同气候时段内北极海冰融冰量进行EOF分解,前两个模态均在3个气候时段发生显著的年代际变化,东西伯利亚海海冰融冰量的增加与EOF第一模态年代际变化相关,而EOF第二模态则明显造成了波弗特海海冰的年代际消融。并且,与之相应的大气环流也出现了明显的年代际变化,它们与AO/NAO的年际关系也存在年代际转折,融冰量第二模态与AO的年际关系更为紧密,1960—1990年第二模态与AO的相关系数仅为0.186,而1980—2010年相关系数已升高至0.367。整个北冰洋的海冰融冰量与AO的年际关系也出现了年代际增强,尤其是东西伯利亚地区海冰融冰量与AO的年际关系发生了年代际增强,1980—2010年两者相关达到了0.4以上。而波弗特海融冰量与AO相关系数变化较大,1960—1990年其的相关系数高达-0.488,1980年后却减少至0.161。然而AO却未发生明显的年代际变化。造成北极海冰融冰量及其与大气变量年际关系发生年代际变化的主要因子之一是波弗特高压,其年代际减弱使得极区向东西伯利亚海和波弗特海的海冰输送减弱,导致这两个区域海冰减少,使得AO与北极海冰的年际关系发生了年代际转折。     

冬季北半球大气对秋冬季巴伦支海海冰异常的敏感性研究

基于ERA-Interim再分析资料,借助大气模式CAM4,分析了北半球冬季不同月份的平均大气对巴伦支海不同振幅及不同季节海冰扰动的敏感性,并考察了中高纬度典型大气模态的分布变化情况.结果表明,冬季巴伦支海海冰的减少,会导致湍流热通量异常向上、局地异常变暖及水汽含量的异常升高,且相关异常的强度和范围随着海冰减少幅度的减...     

Ensemble of sea ice initial conditions for interannual climate predictions

Polar climate studies are severely hampered by the sparseness of the sea ice observations. We aim at filling this critical gap by producing two 5-member sea ice historical simulations strongly constrained by ocean and atmosphere observational data and covering the 1958–2006 and 1979–2012 periods. This is the first multi-member sea ice reconstruction covering more than 50 years. The obtained sea ice conditions are in reasonable agreement with the few available observations. These best estimates of sea ice conditions serve subsequently as initial sea ice conditions for a set of 28 3-year-long retrospective climate predictions. We compare it to a set in which the sea ice initial conditions are taken from a single-member sea ice historical simulation constrained by atmosphere observations only. We find an improved skill in predicting the Arctic sea ice area and Arctic near surface temperature but a slightly degraded skill in predicting the Antarctic sea ice area. We also obtain a larger spread between the members for the sea ice variables, thus more representative of the forecast error.     

Investigating the variability of the Arctic sea ice thickness in response to a stochastic thermodynamic atmospheric forcing

The natural low frequency variability of the sea-ice thickness in the Arctic is investigated based on a 10 000 years simulation with a one-dimensional thermodynamic sea-ice model forced by random perturbations of the air surface temperature and solar radiation. The simulation results suggest that atmospheric random perturbations are integrated by the sea-ice. Moreover those perturbations occurring at the onset of ice melting force the largest ice thickness anomalies, which are successively amplified in summer by the albedo feedback and damped in winter by the feedback of the heat conduction through the ice. They also result in a global shift of the melting season which, in the mean annual cycle, leads to earlier melting as compared to the mean climatological cycle. The power spectrum of the ice anomalies suggests that the thickness of the perennial ice should vary preferentially on a time scale of approximately 20 years. The shape of the spectrum is consistent with that of a first order Markov process in which the characteristic time scale of the ice fluctuations would be the relaxation time scale associated with the linear feedback. The equivalent Markov model is constructed by linearizing the ice growth rate anomaly equations and allows us to derive an analytical expression of the feedback and of the forcing of the anomalies. The characteristic time scale depends explicitly on those model parameters involved in the atmosphere-ice interaction but also on the mean seasonal characteristics of the forcing and of the ice thickness. Received: 18 August 1999 / Accepted: 10 May 2000     

Climate-driven chlorophyll-a concentration interannual variability in the South China Sea

Physical forcing and biological response are highly variable over a wide range of scales in the South China Sea. The present paper analyzed interannual variability of the surface chlorophyll-a concentration of the South China Sea using NASA standard SeaWiFS monthly products from 1997 to 2007. Time series of monthly data were first smoothed using a 12-month running mean filter. An empirical orthogonal function (EOF) analysis was performed to evaluate the interannual variability. The first EOF mode is characterized by a higher surface chlorophyll-a concentration in the deep basin of the South China Sea with a maximum value southwest of Luzon Strait. The corresponding time coefficient function is highly correlated with the multivariate ENSO index (MEI). The correlation coefficient is ?0.61 when the time coefficient function lags the MEI by 9?months. The second EOF mode is characterized by a northwest lower chlorophyll-a concentration. The corresponding time coefficient function correlates with the MEI at a correlation coefficient equal to 0.88, with a lag of 1?month. The third EOF mode shows the interannual variability of the chlorophyll-a concentration has some relationship with Indian Ocean dipole mode as well. The link between the climate and ocean biological states in the South China Sea is due to changes in upper-ocean temperature and wind field, which influence the availability of nutrients for phytoplankton growth.     

On the Association between Spring Arctic Sea Ice Concentration and Chinese Summer Rainfall： A Further Study

In our previous study,a statistical linkage between the spring Arctic sea ice concentration(SIC)and the succeeding Chinese summer rainfall during the period 1968–2005 was identified.This linkage is demonstrated by the leading singular value decomposition(SVD)that accounts for 19%of the co-variance.Both spring SIC and Chinese summer rainfall exhibit a coherent interannual variability and two apparent interdecadal variations that occurred in the late 1970s and the early 1990s.The combined impacts of both spri...     

Boundary-layer modification in wintertime cold-air outbreaks from the Arctic sea ice

During the field experiment ARKTIS 1993 ten cases of boundary-layer modification in wintertime cold-air outbreaks from the Arctic sea ice in the Spitsbergen region were observed by aircraft over a distance ranging from about 50 km over the ice to about 300 km over the water. The modification depends decisively on the initial conditions over the ice, the boundary conditions at the bottom and top of the boundary layer and on the conditions of the large-scale flow. The modification of the bulk boundary-layer characteristics in relation to these conditions is presented.Besides the air-sea temperature contrast, the most important role for the boundary-layer modification is played by the stability on top of the boundary layer and by the divergence of the large-scale flow. According to the high variability of these conditions the observed boundary-layer modifications were very variable ranging from 100 to 300 m thick boundary layers with air temperatures between -32 and -22 °C over the ice to thicknesses between 900 and 2200 m and air temperatures between -15 and -5 °C after 300 km fetch over the open water. In most cases the large-scale flow was anticyclonic and divergent over the ice and changed to cyclonic and convergent over the water and an ice-sea breeze was superimposed on it.The sensible and latent heat fluxes are the dominant terms in the surface energy budget over the open water and ranged between 200 and 700 W m^-2 whereas the net longwave radiation is the dominating term over the ice with the heat fluxes only about 10 W m^-2.     

Temperature and snow-melt controls on interannual variability in carbon exchange in the high Arctic

Summary Net Ecosystem CO₂ Exchange (NEE) was studied during the summer season (June–August) at a high Arctic heath ecosystem for 5 years in Zackenberg, NE Greenland. Integrated over the 80 day summer season, the heath is presently a sink ranging from −1.4 g C m⁻² in 1997 to −23.3 g C m⁻² in 2003. The results indicate that photosynthesis might be more variable than ecosystem respiration on the seasonal timescale. The years focused on in this paper differ climatically, which is reflected in the measured fluxes. The environmental conditions during the five years strongly indicated that time of snow-melt and air temperature during the growing season are closely related to the interannual variation in the measured fluxes of CO₂ at the heath. Our estimates suggest that net ecosystem CO₂ uptake is enhanced by 0.16 g C m⁻² per increase in growing degree-days during the period of growth. This study emphasises that increased summer time air temperatures are favourable for this particular ecosystem in terms of carbon accumulation.     

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 %.     

1981—2018年中国东北地区秋冬季霾日变化及其与北极海冰的关系

利用中国东北地区1981—2018年166个地面气象观测站资料,定义了中国东北地区秋冬季霾日指数,分析了年际尺度上该地区霾日数与同期大气环流异常的内在关系。结果表明：中国东北地区秋冬季霾日指数存在显著的年际变化特征,欧亚—太平洋遥相关型(Eurasia-Pacific Teleconnection Pattern, EUP)负位相、东亚大槽偏弱等大气环流异常配置导致中国东北地区秋冬季霾的发生频次增加。巴伦支海与喀拉海北部海域是影响中国东北地区秋冬季霾日年际变化的海冰关键区,该区域海冰面积与霾日数呈显著负相关,北极海冰通过改变大气环流间接影响中国东北地区秋冬季霾日发生频次,当北极海冰异常偏少时,东亚冬季风偏弱,近地面风速偏低,环境湿度偏高,中国东北地区受东北亚异常反气旋西侧的异常偏南风控制,且受“EUP”负位相模态影响,东亚大槽减弱,有利于大气污染物和水汽向中国东北地区输送,该地区秋冬季霾的发生频次增加。     

A comparison of the effects of interannual Arctic sea ice loss and ENSO on winter haze days: Observational analyses and AGCM simulations

This study compares the impacts of interannual Arctic sea ice loss and ENSO events on winter haze days in mainland China through observational analyses and AGCM sensitivity experiments. The results suggest that (1) Arctic sea ice loss favors an increase in haze days in central–eastern China; (2) the impact of ENSO is overall contained within southern China, with increased (reduced) haze days during La Niña (El Niño) winters; and (3) the impacts from sea ice loss and ENSO are linearly additive. Mechanistically, Arctic sea ice loss causes quasi-barotropic positive height anomalies over the region from northern Europe to the Ural Mountains (Urals in brief) and weak and negative height anomalies over the region from central Asia to northeastern Asia. The former favors intensified frequency of the blocking over the regions from northern Europe to the Urals, whereas the latter favors an even air pressure distribution over Siberia, Mongolia, and East Asia. This large-scale circulation pattern favors more frequent occurrence of calm and steady weather in northern China and, as a consequence, increased occurrence of haze days. In comparison, La Niña (El Niño) exerts its influence along a tropical pathway by inducing a cyclonic (anticyclonic) lower-tropospheric atmospheric circulation response over the subtropical northwestern Pacific. The northeasterly (southwesterly) anomaly at the northwestern rear of the cyclone (anticyclone) causes reduced (intensified) rainfall over southeastern China, which favors increased (reduced) occurrence of haze days through the rain-washing effect.     

不同类型ENSO事件对初冬北极海冰的影响

基于1951—2019年NCEP/NCAR再分析资料、Hadley环流中心海温、海冰密集度资料,通过合成分析和诊断温度异常方程,研究不同类型ENSO对初冬北极海冰的影响。结果表明,EP La Ni1a发展年初冬(11—12月),巴伦支—喀拉海海冰异常减少;CP La Ni1a发展初冬,巴伦支—喀拉海海冰异常增加。EP和CP型El Ni1o对初冬北极海冰的影响类似：格陵兰海海冰异常减少,而哈德逊—巴芬湾海冰异常增加。不同类型ENSO对初冬北极海冰的影响主要通过产生不同的大气遥相关,引起同期和前期的海表气温异常而实现。