Sensitivity of sea ice to wind-stress and radiative forcing since 1500: a model study of the Little Ice Age and beyond

Three different reconstructed wind-stress fields which take into account variations of the North Atlantic Oscillation, one general circulation model wind-stress field, and three radiative forcings (volcanic activity, insolation changes and greenhouse gas changes) are used with the UVic Earth System Climate Model to simulate the surface air temperature, the sea-ice cover, and the Atlantic meridional overturning circulation (AMOC) since 1500, a period which includes the Little Ice Age (LIA). The simulated Northern Hemisphere surface air temperature, used for model validation, agrees well with several temperature reconstructions. The simulated sea-ice cover in each hemisphere responds quite differently to the forcings. In the Northern Hemisphere, the simulated sea-ice area and volume during the LIA are larger than the present-day area and volume. The wind-driven changes in sea-ice area are about twice as large as those due to thermodynamic (i.e., radiative) forcing. For the sea-ice volume, changes due to wind forcing and thermodynamics are of similar magnitude. Before 1850, the simulations suggest that volcanic activity was mainly responsible for the thermodynamically produced area and volume changes, while after 1900 the slow greenhouse gas increase was the main driver of the sea-ice changes. Changes in insolation have a small effect on the sea ice throughout the integration period. The export of the thicker sea ice during the LIA has no significant effect on the maximum strength of the AMOC. A more important process in altering the maximum strength of the AMOC and the sea-ice thickness is the wind-driven northward ocean heat transport. In the Southern Hemisphere, there are no visible long-term trends in the simulated sea-ice area or volume since 1500. The wind-driven changes are roughly four times larger than those due to radiative forcing. Prior to 1800, all the radiative forcings could have contributed to the thermodynamically driven changes in area and volume. In the 1800s the volcanic forcing was dominant, and during the first part of the 1900s both the insolation changes and the greenhouse gas forcing are responsible for thermodynamically produced changes. Finally, in the latter part of the 1900s the greenhouse gas forcing is the dominant factor in determining the sea-ice changes in the Southern Hemisphere.

广州气温与厄尔尼诺的多尺度相互联系

通过对广州气温距平和Ｎｉｎｏ　３、Ｎｉｎｏ　１＋２区ＳＳＴＡ序列做小波变换,研究了广州气温变化与ＥＮＳＯ振荡过程之间的多尺度联系,发现它们都存在着强的十年际振荡。年际尺度的振荡为正相关,十年际风度为负相关。由于ＳＳＴＡ的十年际变率是由强厄尔尼诺事件的韵律产生的,因此;广州气温对强烈厄尔尼诺的响应性质上不同于对普通厄尔尼诺的响应．     

北京地区地基辐射计与卫星云特性参数对比研究

利用2019年MODIS卫星数据、葵花-8卫星数据和天空辐射计观测数据分析北京城区云光学特性的时空分布特征。结果表明,北京地区的云光学厚度(Cloud optical depth,COD)和云滴有效半径(Cloud drop effective radius,CER)呈现明显的季节变化特征。北京地区COD主要分布特征为南部地区较高而北部地区较低,且夏季COD值明显高于其他季节,最高值为20左右。CER在春季和夏季呈现相反的区域分布特征,春季北京地区南低北高,夏季北京地区南高北低,而秋冬季CER明显低于春夏两季。通过将天空辐射计观测数据与卫星观测结果对比分析发现二者在COD方面一致性较高, r分别为0.69和0.66,MODIS对于CER数据的一致性较差,r值为0.053而葵花-8一致性较好r值为0.53。     

Transfer processes in a simulated urban street canyon

The transfer processes within and above a simulated urban street canyon were investigated in a generic manner. Computational fluid dynamics (CFD) was used to aid understanding and to produce some simple operational parameterisations. In this study we addressed specifically the commonly met situation where buoyancy effects arising from elevated surface temperatures are not important, i.e. when mechanical forces outweigh buoyancy forces. In a geophysical context this requires that some suitably defined Richardson number is small. From an engineering perspective this is interpreted as the important case when heat transfer within and above urban street canyons is by forced convection. Surprisingly, this particular scenario (for which the heat transfer coefficient between buildings and the flow is largest), has been less well studied than the situation where buoyancy effects are important. The CFD technique was compared against wind-tunnel experiments to provide model evaluation. The height-to-width ratio of the canyon was varied through the range 0.5–5 and the flow was normal to the canyon axis. By setting the canyon’s facets to have the same or different temperatures or to have a partial temperature distribution, simulations were carried out to investigate: (a) the influence of geometry on the flow and mixing within the canyon and (b) the exchange processes within the canyon and across the canyon top interface. Results showed that the vortex-type circulation and turbulence developed within the canyon produced a temperature distribution that was, essentially, spatially uniform (apart from a relatively thin near-wall thermal boundary layer) This allowed the temperatures within the street canyon to be specified by just one value T _can , the canyon temperature. The variation of T _can with wind speed, surface temperatures and geometry was extensively studied. Finally, the exchange velocity u _E across the interface between the canyon and the flow above was calculated based on a heat flux balance within the canyon and between the canyon and the flow above. Results showed that u _E was approximately 1% of a characteristic wind velocity above the street canyon. The problem of radiative exchange is not addressed but it can, of course, be introduced analytically, or computationally, when necessary.     

1957～2004年盘锦芦苇湿地的气候变化特征分析

利用1957～2004年盘锦湿地常规气象资料,分析了盘锦湿地的日照、温度、降水和风速的变化特征。结果表明:日照时数的月变化呈双峰曲线,5月和9月表现为日照高峰,7月为日照低谷;近48 a盘锦湿地的年平均气温呈显著的上升趋势,冬季增温最明显,其次为春季,夏季增温最弱,年平均极端最低温度呈显著的上升趋势;近48 a的年平均风速呈显著的下降趋势,月平均风速变化趋势呈双峰曲线。     

一种插值相似方法作温度预测的应用研究

将插值方法运用到短期气象预测中，其基本原理是按照相似原理将产生相似结果来作预报。对云南昆明等四站温度进行了九年定性和定量预报检验，结果表明：这种方法具有良好的预报能力，可以作要素预报应用。     

Spectra of poorly resolved ocean data

Standard temperature and pressure sensors on Aanderaa RCM8 current meters have a resolution of 0.024 °C and 0.6 bar, each equal to 1 digital number (value) over a range of 1024. It is shown that an 11-month deep-ocean temperature record using only four values can contain useful spectral information on internal wave motions. This is partially due to the modulation of high-frequency data by non-zero low-frequency (subinertial) variations. This result follows from the comparison of this record with artificial three- and four-value data constructed from temperature records observed in stronger stratified waters nearby. These artificial records show main features of the internal wave band similar to those observed in the original data spectra. Peaks at tidal harmonic frequencies and enhancements at sum-tidal-inertial interaction frequencies are preserved in the artificial data, but overall noise level (and thus the continuum spectral slope) is enhanced with respect to the properly resolved records (using 15 and 100 values). As a demonstration of the stable accuracy of the temperature sensors, the poorly resolved records provided an estimate of mean stratification to within 5% of the estimate using Seabird CTD data.Responsible Editor: Hans Burchard     

Modelling the effect of an assumed cosmic ray-modulated global cloud cover on the terrestrial surface temperature

We have used the thermodynamic model of the climate to estimate the effect of variations in the oceanic cloud cover on the surface temperature of the Earth in the North Hemisphere (NH) during the period 1984–1990. We assume that the variations in the cloud cover are proportional to the variation of the cosmic ray flux measured during the same period. The results indicate that the effect in the temperature is slightly noticeable when we consider the surface hemispheric temperature on July 1987, finding an average temperature anomaly between −0.06°C and −0.14°C, along a latitudinal band between 20° and 40°. The surface temperature averaged globally in the NH presents a decrease of 0.01°C in average, which is almost the same for continents and oceans. However, these values are not significant when compared to the overall variability of the time series with and without forcing.     

蒸发波导对GNSS海面反射信号有效散射区域的影响

蒸发波导在海洋低空的发生概率高达90%,对舰船雷达、通信等电磁系统具有重要影响.为了分析利用GNSS卫星海面反射信号的时延-相关功率波形反演蒸发波导的可行性,本文提出了GNSS卫星海面反射信号的有效散射区域的概念,并将有效散射区域内的GNSS反射信号区分为GNSS标准反射信号和GNSS波导反射信号;然后,利用射线追踪方法,仿真分析了GNSS卫星海面反射信号的有效散射区域大小对蒸发波导的关键参数——波导高度的敏感性,并分析了在时延-相关功率波形上利用反射信号的传播时延将二者分离开的可行性.结果表明,GNSS卫星海面反射信号的有效散射区域对蒸发波导高度非常敏感,对于2~25 m高的GNSS反射信号接收天线,当蒸发波导的高度由0 m增加至20 m时,GNSS反射信号有效散射区域半径的均值可由约14 km迅速扩展至约160 km;采用高度角足够大的GNSS卫星可以将有效散射区内的GNSS标准反射信号与GNSS波导反射信号在时延-相关功率波形上分离开.

     

断层失稳错动热场前兆模式：雁列断层的实验研究

在实验室使用红外热像仪和接触式测温仪同步观测记录了压性和张性雁列断层失稳错动前后的热场变化过程.从实验记录中发现,在断层失稳引起温度场和热红外辐射亮温温度场上升之前,在两断层段之间的岩桥区发生降温变化.断层带开始升温发生在失稳前2～3 s内,岩桥区的降温却发生在失稳前约20s,这两个超前时间长度相差近一个量级.此类热场先降后升变化过程在雁列构造变形中有一定的普遍性,可能作为雁列断层失稳错动的热场前兆模式.根据实验观测结果,详细描述了上述热场变化的时间过程及其空间分布特征,分析了产生此种失稳前兆模式的机制,显著异常出现的条件及有利观测部位,讨论了它在地震前兆探索等研究中的意义.