初始扰动对静力适应过程的影响

本文从描述非静态、可压缩、等温干大气静力适应过程的线性模型出发,利用均匀介质中的波动理论,研究了初始扰动对静力适应过程中物理量场适应方向的影响;从能量分配和转换的角度探讨了静力平衡破坏后大气运动的物理本质.理论结果显示,当大气静力平衡被破坏后,垂直气压梯度场和密度场、垂直气压梯度场和水平流场u分量之间相互适应的因果关系...     

Driving energy losses for constant diameter and tapered submerged monopiles

Large monopiles are used as foundations for offshore wind turbines and are generally designed with a tapered section or conical shape. Some loss of driving energy is expected to occur during installation of these structures due to the submerged section of the tapered monopile. The current literature on this subject is limited and indicates rather large losses compared to field observations.A numerical model of the monopile–water–soil system was set up in the general-purpose finite element package Abaqus. By simulating the hammer impact and the resulting stress wave propagation through the monopile and water, the energy losses to be expected can be calculated accurately. The model was verified against independent finite element analyses and experimental data.A parametric study was performed and the effect of hammer characteristics, submerged monopile length and monopile geometry on the driving energy losses were quantified. The results enable a simple relationship between the energy losses and the monopile geometry to be proposed which increases linearly with pile diameter, taper angle, and submerged length. The losses are typically on the order of 0.15–0.3% per metre submerged length for large tapered monopiles.     

南大西洋副热带偶极子的年际变化

南大西洋副热带偶极子(South Atlantic Subtropical Dipole;SASD)为南大西洋海洋与大气相互作用的主要模态。它的空间型为海表面温度异常呈现东北-西南偶极子分布。当SASD指数大于1,为SASD正事件,小于-1,为负事件。根据1960-2016年HadISST(Hadley Center Global Sea Ice and Sea Surface Temperature)数据,本文鉴别出57年中共发生6次正事件和9次负事件。SASD存在显著的5~8年周期的年际变化特征。本文进一步利用1992-2016年ECCO2(Estimating the Circulation and Climate of the Ocean,PhaseⅡ)模式数据,根据温度倾向方程分别诊断了SASD西南极和东北极的混合层温度变化。诊断结果表明,SASD的年际变化主要来自于表面热力强迫项的年际变化。考虑到表面热力强迫项主要由短波辐射项控制,SASD的年际变化最终来源于短波辐射项的年际变化。     

Examining the impacts of urbanization on surface radiation using Landsat imagery

Metropolitan Beijing is facing many environmental problems such as haze and urban heat island due to the rapid urbanization. Surface shortwave, longwave, and net radiations are key components of the surface-atmosphere radiation budget. Since megacities are affected by the thermal radiation of complex landscape structures and atmospheric environments, quantitative and spatially explicit retrieval from remotely sensed data remains a challenge. We collected the surface radiation fluxes from seven fixed sites representing different land-use types to calibrate the local parameters for remotely sensed retrieval of net radiation. We proposed a remote sensing–based surface radiation retrieval method by embedding the underlying land covers and integrating the observational data. The improved method is feasible to accurately retrieve surface radiation and delineate spatial characteristics in metropolitan areas. The accuracy evaluation indicated that the difference between remotely sensed and in situ observed net radiation ranged within 0~± 40 W· m^?2. The root mean squared error of the estimated net surface radiation was 32.71 W· m^?2. The strongly spatial heterogeneity of surface radiation components in metropolitan Beijing was closely related to land-cover patterns from urban area to outskirts. We also found that the surface net radiation had a decreasing trend from 1984 to 2014, and the net radiation in the urban area was lower than that in the outskirts. According to the surface radiation budgets, urbanization resulted in the cooling effect in net radiation flux in the daytime, which was stemmed from low atmospheric transmittances from massive aerosol concentration and high surface albedo from light building materials.     

Argo时代东南印度洋上层盐度变化对海平面年代际演变的影响

In the past nearly two decades, the Argo Program has created an unprecedented global observing array with continuous in situ salinity observations, providing opportunities to extend our knowledge on the variability and effects of ocean salinity. In this study, we utilize the Argo data during 2004–2017, together with the satellite observations and a newly released version of ECCO ocean reanalysis, to explore the decadal salinity variability in the Southeast Indian Ocean(SEIO) and its impacts on the regional sea level changes. Both the observations and ECCO reanalysis show that during the Argo era, sea level in the SEIO and the tropical western Pacific experienced a rapid rise in 2005–2013 and a subsequent decline in 2013–2017. Such a decadal phase reversal in sea level could be explained, to a large extent, by the steric sea level variability in the upper 300 m. Argo data further show that, in the SEIO, both the temperature and salinity changes have significant positive contributions to the decadal sea level variations. This is different from much of the Indo-Pacific region, where the halosteric component often has minor or negative contributions to the regional sea level pattern on decadal timescale. The salinity budget analyses based on the ECCO reanalysis indicate that the decadal salinity change in the upper 300 m of SEIO is mainly caused by the horizontal ocean advection. More detailed decomposition reveals that in the SEIO, there exists a strong meridional salinity front between the tropical low-salinity and subtropical high salinity waters. The meridional component of decadal circulation changes will induce strong cross-front salinity exchange and thus the significant regional salinity variations.     

2010—2018碳收支的变化分析年海南东寨港红树林湿

红树林生态系统在全球气候变化和碳循环过程中发挥着很重要的作用,准确评估红树林湿地的碳收支,对于保护和恢复海洋蓝色碳汇以及全球气候治理工作具有重要的意义。本研究以海南东寨港国家级自然保护区的红树林湿地为研究对 象,采用 《对 2006 IPCC 国家温室气体清单指南的 2013 增补：湿地》 （简称 《湿地指南》） 中的计算方法,利用野外现场调查数据及已有的研究成果作为参数,评估和量化海南东寨港红树林湿地在 2010—2018 年期间的碳收支情况。研究表明：（1） 2010 年红树林面积为 1 627.21 hm2,全部为成熟红树林,碳储量为 5.85*105t C;2018 年红树林面积为 1 665.42 hm2,其中 1 625.84 hm2为成熟红树林,碳储量为 6.71*105t C,39.58 hm2为过渡期红树林,碳储量为 4.36*103t C,总碳储量为6.75*105t C。 （2） 2010—2018 年期间红树林碳储量增加了 9.0*104t C。另外,有 1.37 hm2的红树林湿地退化为水域,释放了81.36 t 的碳储量。因此,2010—2018 年期间东寨港红树林湿地碳收支为+8.99*104t C,整体上表现为净碳汇生态系统。本研究结果可为气候变化背景下海南红树林湿地的保护与恢复、风险评估以及气候治理提供科学参考。     

盐度和氨氮对方斑东风螺存活和能量收支的影响

为了探究盐度和氨氮对方斑东风螺生理代谢的影响,本文采用实验生态学方法,研究了不同盐度和氨氮浓度条件下方斑东风螺(Babylonia areolata)的存活以及能量收支变化。结果显示,方斑东风螺的存活率随着盐度上升呈现先上升后下降的趋势,当盐度为25和30时,方斑东风螺的存活率为100%,低盐96hLC50为10.14,高盐为44.36;方斑东风螺存活率随氨氮浓度上升逐渐下降,当氨氮质量浓度为0～20 mg/L时,存活率均为100%;氨氮96 h LC50为253.83 mg/L。盐度和氨氮对方斑东风螺的摄食率、排粪率、耗氧率和排氨率均具有显著影响(P<0.05)。盐度实验中,方斑东风螺的摄食率、排粪率和排氨率在盐度30时达到最大值,分别为20.50、8.62和0.07 mg/(g·h),耗氧率在盐度35时达到最大值,为1.84 mg/(g·h)。氨氮实验中,摄食率和排粪率在10 mg/L时达到最大值,分别为23.58和10.42 mg/(g·h),耗氧率和排氨率在20 mg/L时达到最大值,分别为2.49和0.13 mg/(g·h)。通过能量收支方程发现,随着盐度和氨氮浓度的上...     

芜湖市一次引发严重内涝暴雨过程的水汽输送特征

基于自动气象观测站降水数据、中国降水数据集、ERA5再分析资料及NCEP/NCAR再分析数据,使用水汽收支分析、HYSPLIT后向轨迹追踪和水汽输送贡献率等方法对2022年6月5日凌晨芜湖市一次引发严重内涝暴雨过程的水汽输送特征进行了分析。结果表明:此次暴雨过程出现在200 hPa分流区和850 hPa低空急流左前方,500 hPa冷空气在低空急流出口北侧不断激发对流云团,形成强降水。高层辐散和低层辐合增强了水汽的水平辐合和垂直输送,西南低空急流持续加强,将水汽不断输送至暴雨区,为暴雨的出现提供了必要的水汽条件,使芜湖市在强降水发生前水汽充沛,湿层深厚且持续增湿。暴雨出现时大气可降水量、850 hPa比湿、水汽通量和水汽通量散度分别达到71.0 kg·m^-2、16.0 g·kg^-1、15.0 g·hPa^-1·cm^-1·s^-1和-3.0×10^-6 g·cm^-2·hPa^-1·s^-1。850 hPa水汽通量散度的变化与暴雨的出现和强度变化有较好的对应关系,雨强最强时段可达-8.0×10^-6 g·cm^-2·hPa^-1·s^-1。水汽收支和追踪分析结果显示:水汽流入主要发生在对流层低层的西边界和南边界,暴雨发生前流入层深厚,有向上的水汽垂直输送。整层水汽流入量约为56.0×10⁷ t·h^-1,主要流入高度为850～700 hPa,单层流入量最大可达9.0×10⁷ t·h^-1,水汽主要源自孟加拉湾和南海,其水汽通道轨迹占比为32.0％,水汽输送贡献率达55.4％。暴雨出现时水汽流入层降低,流入量减少,水汽垂直输送减弱,总水汽净流入集中在850 hPa,净流入量为1.0×10⁷ t·h^-1左右,水汽主要源自南海,其水汽通道轨迹占比为46.0％,水汽输送贡献率达60.3％。     

基于CMIP6模式的东南亚极端降水未来预估及热动力成因研究

本文利用26个CMIP6全球气候模式,研究了21世纪末东南亚极端降水事件的变化,通过分解水汽收支方程分析降水变化的动力和热力效应。结果表明,21世纪末(2071—2100年)相对历史参考期(1985—2014年),东南亚大部分地区的气候态降水、极端降水事件的发生频率和强度均显著增加。除大于10 mm降水日数(R10mm)外,其他极端降水指数在SSP5-8.5情景下的变化幅度比SSP2-4.5情景更大。其中强降水量贡献率(R95pTOT)的增长幅度最大,在SSP2-4.5(SSP5-8.5)情景下增加22％(41％)。极端降水变化对气候变暖的响应存在明显的区域性差异。加里曼丹岛将出现更短时集中的极端降水。苏门答腊岛南部的极端降水频率略有减小,且可能发生较强的持续性干旱事件。进一步分析水汽收支方程可知,SSP2-4.5(SSP5-8.5)情景下,热力作用项对P-E(降水减蒸发)的变化贡献为65％(64％),并且模式间一致性更高。而动力作用项对P-E的变化呈抵消趋势,贡献为35％(36％)。这说明相比大尺度环流变化,大气比湿变化引起的水汽辐合是未来东南亚降水量增多的主要因子。     

节理岩体能量损伤本构模型与工程应用

本文根据Betti能量互易定理,节理岩体能量损伤演化方程,广义正交法则和塑性损伤一致性条件建立了节理岩体的能量损伤本构模型,并将该模型编制成三维非线性有限元计算程序应用于溪洛渡地下厂房洞室群施工开挖稳定性分析,获得了较为满意的计算结果。