Sensitivity of Southern Ocean circulation to wind stress changes: Role of relative wind stress

The influence of different wind stress bulk formulae on the response of the Southern Ocean circulation to wind stress changes is investigated using an idealised channel model. Surface/mixed layer properties are found to be sensitive to the use of the relative wind stress formulation, where the wind stress depends on the difference between the ocean and atmosphere velocities. Previous work has highlighted the surface eddy damping effect of this formulation, which we find leads to increased circumpolar transport. Nevertheless the transport due to thermal wind shear does lose sensitivity to wind stress changes at sufficiently high wind stress. In contrast, the sensitivity of the meridional overturning circulation is broadly the same regardless of the bulk formula used due to the adiabatic nature of the relative wind stress damping. This is a consequence of the steepening of isopycnals offsetting the reduction in eddy diffusivity in their contribution to the eddy bolus overturning, as predicted using a residual mean framework.     

Seasonal response of surface wind to SST perturbation in the Northern Hemisphere

The seasonal response of surface wind speed to sea surface temperature (SST) change in the Northern Hemisphere was investigated using 10 years (2002-2011) high-resolution satellite observations and reanalysis data. The results showed that correlation between surface wind speed perturbations and SST perturbations exhibits remarkable seasonal variation, with more positive correlation is stronger in the cold seasons than in the warm seasons. This seasonality in a positive correlation between SST and surface wind speed is attributable primarily to seasonal changes of oceanic and atmospheric background conditions in frontal regions. The mean SST gradient and the prevailing surface winds are strong in winter and weak in summer. Additionally, the eddy-induced response of surface wind speed is stronger in winter than in summer, although the locations and numbers of mesoscale eddies do not show obvious seasonal features. The response of surface wind speed is apparently due to stability and mixing within the marine atmospheric boundary layer (MABL), modulated by SST perturbations. In the cold seasons, the stronger positive (negative) SST perturbations are easier to increase (decrease) the MABL height and trigger (suppress) momentum vertical mixing, contributing to the positive correlation between SST and surface wind speed. In comparison, SST perturbations are relatively weak in the warm seasons, resulting in a weak response of surface wind speed to SST changes. This result holds for each individual region with energetic eddy activity in the Northern Hemisphere.     

南半球热带外气候变量与两种ENSO的联系

This study uses the Climate Forecast System Reanalysis(CFSR) to investigate the responses of the Southern Hemisphere(SH) extratropical climate to two types of El Ni?o–Southern Oscillation(ENSO)—the eastern Pacific(EP) type and the central Pacific(CP) type in different seasons. The responses are denoted by the anomalies of climate variables associated with one-standard-deviation increase in the Ni?o3 or Ni?o4 index. The results show that in austral spring the differences in the ENSO-related anomaly(ERA) patterns of atmospheric circulation between the EP ENSO period(1979–1998) and CP ENSO period(1999–2010) are mainly associated with the change in the ENSO-PSA2 relationship. Such differences affect the ERA fields of surface air temperature and mixed layer temperature, and finally result in significant differences in sea-ice concentration anomalies in the Atlantic sector. In austral summer, significant correlation exists between the variations of SAM and both of the variations of Ni?o3 and Ni?o4 in 1979–1998, while the correlation between SAM and Ni?o4 disappears in 1999–2010. For all seasons, the strength of the climate ERAs depend on if there are close relationship between ENSO and the major climate variation modes of the SH extratropics. For the climate variables, the ERA patterns of surface air temperature are generally controlled by surface wind anomalies and mirrored by the mixed layer temperature anomalies. The mixed layer depth anomalies are primarily modulated by surface heat flux anomalies and occasionally by anomalous wind. There are strikingly strong anomalies of surface heat flux in the autumn of 1979–1998 related to the Ni?o3 variation, the period when there is only significant correlation between ENSO and PSA2. There are no evidence that the SH extratropical climate variability induced by Ni?o3 variations are stronger in the EP-ENSO period, and that variability induced by Ni?o4 variations are stronger in the CP-ENSO period.     

南半球平流层大气环流的若干特点

利用欧洲中期预报中心(ECMWF)5°×5°格点场南北半球6层位势高度场资料计算分析了南半球平流层100hPa平均地转西风随纬度的分布特点、平均地转西风季节变化特点、厄尔尼诺年前后西风廓线形态差异计算分析了南半球位势高度对纬向平均的偏差,分析了超长波的分布特征.以上结果均与北半球同期计算结果作了对比比较,指出了南北半球大气环流在这几方面的异同点.     

Responses of humpback whales to a changing climate in the Southern Hemisphere: Priorities for research efforts

Globally, baleen whales were severely depleted by historic whaling. Recovering populations have been observed to alter their behaviour. These changes have been attributed to climate change in some cases and raise concerns over the successful recovery of baleen whale populations. Current data-driven statistical habitat and behavioural models have proven useful for addressing questions of whale distribution changes within their limitations. Given observed changes in oceanic conditions, a new approach to managing baleen whale population recovery is necessary. Model predictions of future whale movements and distributions under climate change scenarios are vital to enable adequate conservation management. This paper presents a new perspective on understanding the impacts of climate change on humpback whales, arguing the need for a system-based multidisciplinary research approach. Our approach includes coupled, mechanistic models based upon robust ecological principles, and integrates key physical, biogeochemical, biological and ecological modules to address long-term changes associated with climate change. To illustrate the need for this system-based multidisciplinary approach, we focus on Southern Hemisphere humpback whales, the recovery of which may be impacted by rapid changes in habitat conditions brought about by anthropogenic climate change.     

南半球海平面大气环流的若干特点

利用欧洲中期天气预报中心 (ECMWF) 5°× 5°格点场南北半球位势高度场资料 ,计算并分析了南半球海平面平均地转西风及其随纬度的分布特点和季节变化特点 ,计算了南半球位势高度对纬向平均的偏差 ,分析了超长波的分布特征。以上结果均与北半球同期计算结果作了比较 ,指出了南北半球大气环流的异同点     

Cross-equatorial flow and its effects on the hurricanes occurrence over the Southern Hemisphere

Channels of cross - equatorial flow and their characteristics Winds at every 5 deg. grid point from 30°E to 180° over the equator at 850 hPa and 200hPa from December 1984 to February 1985 have been separated into U(zonal wind) andV(meridional wind).The V component has been used to represent cross- equatorial flow. FromFig. 1 we obtained that as during the Northern summer,there are also severa1 regions in which     

Multidecadal climate variability in the subtropics/mid‐latitudes of the Southern Hemisphere oceans

Observations of multidecadal variability in sea surface temperature (SST), surface air temperature and winds over the Southern Hemisphere are presented and an ocean general circulation model applied towards investigating links between the SST variability and that of the overlying atmosphere. The results suggest that the dynamical effect of the wind stress anomalies is significant mainly in the neighbourhood of the western boundary currents and their outflows across the mid‐latitudes of each Southern Hemisphere basin (more so in the South Indian and South Atlantic than in the South Pacific Ocean) and in the equatorial upwelling zones. Over most of the subtropics to mid‐latitudes of the Southern Hemisphere oceans, changes in net surface heat flux (particularly in latent heat) appear to be more important for the SST variability than dynamical effects. Implications of these results for modelling and understanding low frequency climate variability in the Southern Hemisphere as well as possible links with mechanisms of decadal/interdecadal variability in the Northern Hemisphere are discussed.     

Estimating Contributions of Natural Climate Variability Modes and Greenhouse Gases to Surface Temperature Trends in the Southern Hemisphere from Observations

Izvestiya, Atmospheric and Oceanic Physics - Contributions of the anthropogenic influence characterized by variations in the atmospheric greenhouse gas radiative forcing and of the key modes of...     

On the reliability of millennial reconstructions of variations in surface air temperature in the Northern Hemisphere

The reliability of the recently published reconstructions of the surface air temperature variability in the Northern Hemisphere over the past 2000 yr is discussed. For this purpose, the power spectra of the two best known reconstructions (Mann et al.[10–12] and Moberg et al. [13]) are calculated and compared to the spectra of the 150-yr temperature series based on instrumental observations and simulated 1000-yr series. It is found that the Mann et al. reconstruction drastically underestimates low-frequency temperature variations, whereas the Moberg et al. reconstruction reproduces them much better, although with a certain underestimation rather than overestimation, as Mann et al. have recently argued.     

"凤凰"台风模拟对陆面方案敏感性的分析

为研究台风模拟对不同陆面过程方案的敏感性,本文以0808号登陆台风"凤凰"为例,采用中尺度数值模式WRFv3及NCEP同化资料,进行了48 h的数值研究。结果表明,每一陆面方案与大气模式耦合模拟时台风中心位置及台风最大风速都呈现出该耦合系统独特的模拟特征,如与观测台风中心位置相比,NOAH方案模拟移动路径平均偏差最小,PX模拟偏差最大,NOAH-PX两方案差异可达NOAH方案模拟移动路径平均偏差的40%,可见台风模拟可因陆面方案的不同而呈现系统性的差异,且台风模拟对陆面方案的选择是敏感的;不同陆面方案通过模拟地表通量的差异导致温压场差异,并进一步影响模拟台风路径及台风强度。这些结果都表明了在台风的模式预报中,选择适当陆面方案的重要性。     

A method to determine the incident wave boundary conditions and its application

When studying the harbor water tranquility, cases are often confronted as that the verification point is not located on the generation line or that the angle between the generation line and the isobath is so large that the differences of the wave climates along the generation line can not be ignored. For these cases, the incident boundary conditions are difficult to evaluate. In order to solve this problem, a combined wave model is developed in the present paper based on the Boussinesq equation and the wave action balance equation. Instead of the one-line wave generation method, a multi-line generation method is proposed for the combined model. Application of this method is given to a case that the harbor is designed with two entrances and the angle between the generation line and the isobath is large and the results are shown reasonable. We suggest that the wave generation method on multi-lines might also be introduced to the wave physical model as the replacement for the one-line generation method.     

区域海洋模式中的开边界问题

因研究对象不同,目前的海洋环流模式常分为全球模式和海盆尺度(区域)模式,各个模式考虑的物理过程、参数化方法、数值解法和分辨率都不尽相同,因此不同模式的计算结果存在差异,尤其区域尺度上的差异更为明显,这就对发展区域性的海盆尺度环流模式提出了要求.海盆尺度模式可以使用更高的分辨率,考虑更精细的物理和生化过程,从而对区域的刻画更为准确和真实,而且,在碳循环的研究中,陆架边缘海碳循环是新的研究热点,这也需要进一步发展海盆尺度的碳循环模式.另外从计算方面来说,限于目前的计算条件,在未来很长时间内海盆尺度碳循环模式都将与全球模式同时存在并互为补充.