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2009年豫南一次强暴雨过程的位涡方程诊断分析 总被引：1，自引：0，他引：1
利用中尺度WRF模式、NCEP/NCAR再分析格点资料及常规气象观测资料,对2009年8月28—30日河南省南部一次强暴雨过程进行中尺度数值模拟,借助模式输出的模拟数据计算位势涡度及位势涡度方程收支,并利用位涡收支方程对此次暴雨过程进行诊断分析。结果表明,WRF模式对此次暴雨过程的模拟效果较好,模拟暴雨强度及落区与实况较一致,位势涡度能够较好地反映此次暴雨过程的动力及热力特征。位涡异常高值区与暴雨中心有较好的对应关系,暴雨中心大致位于位涡高值中心东南侧。位涡收支方程中各收支项同样能够反映此次暴雨过程的动力、热力性质。暴雨发展过程中大气中低层位涡局地增加,位涡局地变化大值中心驿应暴雨中心。各收支项中,引起中低层位涡局地变化的贡献主要来源于潜热加热作用、水平平流作用、垂直输送作用及摩擦作用。其中潜热加热与水平平流作用对暴雨中低层正变位涡起正贡献作用,潜热加热作用有利于位涡局地增加,水平平流作用易于低层位涡向流场辐合区聚集,引起局地位涡增加;垂直输送及摩擦作用对中低层位涡变化表现为负贡献作用,垂直作用易于将中低层位涡向高层输送,使得低层位涡减小,高层位涡增加。在摩擦作用下,低层位涡被大量耗散,使得中低层位涡局地减小。 相似文献
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A.M. Le Brocq M.J. Bentley A. Hubbard C.J. Fogwill D.E. Sugden P.L. Whitehouse 《Quaternary Science Reviews》2011,30(19-20):2422-2432
The Weddell Sea Embayment (WSE) sector of the Antarctic ice sheet has been suggested as a potential source for a period of rapid sea-level rise – Meltwater Pulse 1a, a 20 m rise in ～500 years. Previous modelling attempts have predicted an extensive grounding line advance in the WSE, to the continental shelf break, leading to a large equivalent sea-level contribution for the sector. A range of recent field evidence suggests that the ice sheet elevation change in the WSE at the Last Glacial Maximum (LGM) is less than previously thought. This paper describes and discusses an ice flow modelling derived reconstruction of the LGM ice sheet in the WSE, constrained by the recent field evidence. The ice flow model reconstructions suggest that an ice sheet consistent with the field evidence does not support grounding line advance to the continental shelf break. A range of modelled ice sheet surfaces are instead produced, with different grounding line locations derived from a novel grounding line advance scheme. The ice sheet reconstructions which best fit the field constraints lead to a range of equivalent eustatic sea-level estimates between approximately 1.4 and 3 m for this sector. This paper describes the modelling procedure in detail, considers the assumptions and limitations associated with the modelling approach, and how the uncertainty may impact on the eustatic sea-level equivalent results for the WSE. 相似文献
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《Journal of Atmospheric and Solar》1999,61(3-4):329-350
Many satellite and ground-based observations from 2–11 November 1993 werecombined in the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure toderive realistic time dependent global distributions of the auroral precipitation and ionosphericconvection. These were then used as inputs to the Thermosphere–Ionosphere–ElectrodynamicsGeneral Circulation Model (TIEGCM) to simulate the thermospheric and ionospheric responseduring the storm period. The November 1993 storm was an unusually strong storm associatedwith a recurring high speed stream of solar plasma velocity in the declining phase of the solarcycle. Significant gravity waves with phase speeds of about 700 m/s caused by Joule heating werepresent in the upper thermosphere as perturbations to the neutral temperature and wind fields,especially on 4 November. The observed gravity waves in the meridional wind and in the height ofthe electron density peak at several southern hemisphere stations were generally reproduced bythe model using the AMIE high latitude inputs. Both model and observed equatorward windswere enhanced during the peak of the storm at Millstone Hill and at Australian ionosondestations. The observed neutral temperature at Millstone Hill increased about 400 K during thenight on 4 November, returning to normal on 9 November, while the model increased 300 K thefirst night at that location but was still elevated on 11 November. Enhanced westward windsduring the storm were evident in the UARS WIND Imaging Interferometer (WINDII) data. Theenhanced westward winds in the model were largest around 40–45° magnetic latitude at night,and also tended to be largest in the longitudes containing the magnetic poles. The peak westwardwind enhancements at 0 LT reached about 250 m/s at 300 km, and about 100 m/s at 125 km thefirst day of the storm at 40° magnetic latitude. At 20° magnetic latitude, the maximum westwardwind enhancements at 125 km at 0 LT appeared 2–4 days after the major part of the storm,indicating very long time constants in the lower thermosphere. The model showed global averageneutral temperature enhancements of 188 K after the peak of the storm that decayed with time,and which correlated with variations 8 h earlier in the Dst index and in the electric potential dropinput from AMIE. The global average temperature enhancement of 188 K corresponded to apotential drop increase of only about 105 kV. The results showed that the TIEGCM usingrealistic AMIE auroral forcings were able to reproduce many of the observed time dependentfeatures of this long-lived geomagnetic storm. The overall global average exospheric temperaturevariation correlated well with the time variation of the cross-tail potential drop and the Dst indexduring the storm period. However, the enhanced westward winds at mid-latitudes were stronglyrelated to the corrected Joule heating defined by the time dependent AMIE inputs. 相似文献
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《Marine Chemistry》2001,73(1):65-81
Radiocarbon (Δ14C) abundance and stable carbon isotope (δ13C) compositions were measured for total lipid, total hydrolyzable amino acids (THAA), total carbohydrates (TCHO), and acid-insoluble organic fractions separated from phytoplankton, zooplankton, and sediment cores collected from two abyssal sites, one in the northeast (NE) Pacific Ocean and one in the Southern Ocean. These results are compared with those obtained for a separate core from the NE Pacific and reported by Wang et al. [Geochim. Cosmochim. Acta 62 (1998) 1365.]. An uncharacterized acid-insoluble fraction dominated (43–57%) the sediment TOC pool at both sites. Sediment collected from the NE Pacific exhibited higher TOC, TN. and higher Δ14C values and contained both labile (THAA and TCHO) and refractory (lipid and acid-insoluble) fractions. In contrast, sediment from the Southern Ocean had much lower TOC and Δ14C values, which indicated that organic matter was extremely refractory. Sedimentation rates calculated from 14C ages of TOC for both sites indicate that the differences in the organic composition and Δ14C signatures of organic matter in the sediments likely resulted from the differences in production and deposition of organic matter to the sediment, and the diagenetic stages of sedimentary organic matter in the two oceans.Unlike Δ14C, stable carbon isotopic (δ13C) compositions of TOC in the sediments of the two oceans had similar values, which reflect not only the organic matter input from marine-derived sources but also the nature of degraded, predominately uncharacterized organic fraction in these sediments. The differences in δ13C values among the compound classes in sediments at both sites can be attributed to the carbon isotopic signatures in original sources during photosynthesis and associated environmental factors. Preferential degradation of organic matter and heterotrophic effects may also play important roles for the observed δ13C variations and these effects need to be further investigated. 相似文献
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