河套干旱地区夏季边界层结构特征观测分析

利用2013年夏季7月爱尔达K/LLX802J型机动式边界层风廓线雷达获取的三维风场资料和银川站高空气象探测资料,对河套干旱地区夏季边界层日变化特征进行了分析.结果表明:爱尔达K/LLX802J型机动式风廓线雷达能较好的反映并分辨出夏季河套干旱地区边界层内大气湍流和风场的演变过程.夏季7月河套干旱地区边界层高度白天平均为2127.2 m,夜间平均为1760.7 m,白天边界层高度比夜间平均高366.5 m.河套干旱区夏季地表非绝热加热对边界层的影响主要集中在800 m以下,800~2000 m高度边界层则主要受昼夜交替和大尺度天气系统的影响.夏季7月河套干旱地区边界层风速在300 m以下随高度增加而增大,离地500 m以下边界层易在北京时间07:00-11:00和18:00-21:00时段发生风速切变;300 m以下边界层白天盛行西南偏南风、夜间盛行南风,300~2000 m高度边界层白天和夜间均盛行东南风;离地300 m以下边界层易在夜间21:00-23:00时出现风向切变.夏季7月白天河套干旱地区边界层大气垂直速度在300 m高度以下随高度增加而增大,由0.3 m·s^-1增大到0.6 m·s^-1,夜间边界层大气垂直速度在200 m高度以下随高度增大而增大;300 m高度以上边界层大气垂直速度无论昼夜随高度变化均较小.     

Olivine dissolution in basaltic melt

The main purpose of this work is to understand and quantify diffusive and convective olivine dissolution in basaltic melt. Crystal dissolution and growth in a magma chamber is often accompanied by the descent or ascent of the crystal in the chamber due to gravity. The motion induces convection that enhances mass transport. Such convective dissolution and growth rates have not been quantified before. MgO diffusivity in the melt (D_MgO), MgO concentration of the interface melt (C₀) and the effective thickness of the compositional boundary layer (δ) are necessary parameters to model the convective dissolution. Experiments of non-convective olivine dissolution in a basaltic melt were conducted at 1271-1480 °C and 0.47-1.42 GPa in a piston-cylinder apparatus. At specific temperature and pressure conditions, multiple experiments of different durations show that the interface melt reaches near-saturation within 2 min. Therefore, diffusion, not interface reaction, is the rate-controlling step for non-convective olivine dissolution in basaltic melt. The compositional profile length and olivine dissolution distance are proportional to the square root of experimental duration, consistent with diffusive dissolution. D_MgO and C₀ are obtained from the experimental results. D_MgO displays Arrhenian dependence on temperature, but the pressure dependence is small and not resolved. C₀ increases with increasing temperature and decreases with increasing pressure. Comparison with literature data shows that D_MgO depends strongly on the initial melt composition, while C₀ does not. δ is estimated from fluid dynamics. D_MgO/δ, which characterizes the kinetic and dynamic aspects of convective crystal dissolution, is parameterized as a function of temperature, pressure, and olivine composition. Convective olivine dissolution rate in basaltic melt can be conveniently calculated from the model results. Application to convective crystal growth and xenolith digestion is discussed.     

Forces acting on a subducting oceanic plate

Free conductive flows in the asthenosphere, layer C, and subduction zone are considered on the basis of experimental and theoretical simulation. The main forces acting on the oceanic lithospheric plate in the subduction zone are described. The horizontally directed forces arising due to free convection in the asthenosphere and transferring the oceanic lithospheric plate toward subduction zone have been estimated. These are friction force F_a and force of gravitational sliding F _rd. Thermogravitational force F _tg, which is created because the subducting lithospheric plate has a lower average temperature than the ambient mantle, is estimated. The force created owing to phase transitions in the subducted plate has been estimated as well. The tangential stress at the contact of the subducting plate with the continental lithosphere and underlying upper mantle has been determined. The horizontal force arising due to different lateral temperature gradients in the upper mantle on the left and on the right of the subducting plate has been estimated. The results of experimental modeling of the effect exerted upon subduction by counter free convective flows developing in the asthenosphere are considered. The experiments show that the position of the descending free convective flow and thus of the subduction zone depends on the ratio of the thermal power of astehnospheric countercurrents. The pressure arising near the 670 km boundary gives rise to spreading of the subducting plate over this boundary.     

Extreme carbon monoxide pollution of the atmospheric boundary layer in Moscow region in the summer of 2010

Using data of spectroscopic measurements in Moscow and Moscow region and data of ecological monitoring from Ostankino TV Tower, it has been found that, in the period of intense smoke blanketing of the atmosphere in summer 2010 due to large-scale forest-peat fires on the territory of the European part of the Russian Federation, the carbon monoxide content in the boundary layer and in the atmospheric depth of Moscow region reached the extremely high level of 8 g/m², or 17 ×10¹⁸ mol/cm², and the carbon monoxide concentration in the near-ground atmospheric layer increased to 37.5 mg/m³, i.e., an unprecedentedly large value for Moscow and more than a factor of 7 larger than the one-time maximum permissible concentration for carbon monoxide MPC_ot = 5 mg/m³. In the first decade of August, when intense smoke blanketing of the Moscow region was observed, the average carbon monoxide concentrations varied in the range from approximately 3 to 7 m/g³, i.e., an order of magnitude larger than the annual average concentrations calculated according to data of measurements in 2009. The probabilities of exceeding MPC_ot and multiples of MPC_ot are calculated. Analysis of data of thermal sensing showed that an important feature of the atmospheric boundary layer over the city was a high stability of the lower atmospheric layer with the thickness of 150–200 m, and also long-term nighttime and morning inversions of the air temperature in this layer.     

Application and Verification of Joint Probability Method in Potential Forecast for Severe Convective Weather in Anhui Province

In consideration of large uncertainties in severe convective weather forecast, ensemble forecasting is a dynamic method developed to quantitatively estimate forecast uncertainty. Based on ensemble output, joint probability is a post-processing method to delineate key areas where weather event may actually occur by taking account of the uncertainty of several important physical parameters. An investigation of the environments of little rainfall convection and strong rainfall convection from April to September (warm season) during 2009-2015 was presented using daily disastrous weather data, precipitation data of 80 stations in Anhui province and NCEP Final Analysis (FNL) data. Through ingredients-based forecasting methodology and statistical analysis,four convective parameters characterizing two types of convection were obtained, respectively, which were used to establish joint probability forecasting together with their corresponding thresholds. Using the ECMWF ensemble forecast and observations from April to September during 2016-2017, systematic verification mainly based on ROC and case study of different weather processes were conducted. The results demonstrate that joint probability method is capable of discriminating little rainfall convection and non-convection with comparable performance for different lead times, which is more favorable to identifying the occurrence of strong rainfall convection. The joint probability of little rainfall convection is a good indication for the occurrence of regional or local convection, but may produce some false alarms. The joint probability of strong rainfall convection is good at indicating regional concentrated short-term heavy precipitation as well as local heavy rainfall. There are also individual missing reports in this method, and in practice, 10% can be roughly used as joint probability threshold to achieve relative high TS score. Overall, ensemble-based joint probability method can provide practical short-term probabilistic guidance for severe convective weather.     

极端干旱荒漠区典型晴天大气热力边界层结构分析

利用极端干旱区敦煌野外观测试验资料,分析了极端干旱荒漠区夏季典型晴天位温、风速、比湿等主要物理要素的垂直结构特征及其地表热力和近地层大气运动特征的日变化规律。发现在极端干旱地区夏季晴天大气热力边界层结构十分独特。在夜间,贴地逆温层最低在900 m以上,最厚可以达到1 750 m,逆温层上面的残余层一般能达到4 000 m左右的高度。在白天,位温超绝热递减层高达1 000 m,超绝热递减层上面的混合层最高达3 700 m,混合层顶上还有大约450 m甚至更厚的夹卷层。当白天对流层发展达到残余层以后,混合层的发展明显加快。风速和比湿垂直廓线特征很好地印证了大气热力边界层独特的结构特征,地表热力和近地层大气运动特征也为这种独特的大气热力边界层结构提供了较好的物理支持。     

Seasonal changes in stable carbon isotopic composition of n-alkanes in the marine aerosols from the western North Pacific: Implications for the source and atmospheric transport

To constrain seasonal changes in the long-range atmospheric transport of land-derived lipid biomarker compounds, we investigated the compound-specific stable isotopic composition of marine aerosol n-alkanes collected from 1990 to 1993 at a remote island, Chichi-Jima (27°04′N, 142°13′E), in the western North Pacific. Compound-specific isotope analysis revealed, in particular, strong seasonal changes in the δ¹³C values of the C₂₉ and C₃₁n-alkanes (biomarkers for higher plants). Lighter δ¹³C values were observed in winter (typically −32 to −34‰), with a transition to heavier values in summer (typically −28 to −31‰). Using a mixing equation and typical end members for C₃ and C₄ plants, we found that this is due to relative increases in the contributions from C₄ plants in the summer season. Using backward air-mass trajectory analyses, it was shown that the Asian continent was the major source region for C₃ plant material during winter/spring, whereas Indonesia/Australia and possibly the Americas were the major source regions for C₄ material during the summer/autumn. Also observed was an enhanced atmospheric transport of n-alkanes from C₄ plants in 1991 summer/autumn during a strong El Nino event, which was associated with forest and bushfires in Indonesia and Australia. In addition to providing information on contemporary processes, this study also provides a base for future paleoclimatological work in ocean sediments.     

Estimation of urban mixed layer height in Zanjan using LIDAR observations and numerical modeling

Air pollution predictions often require the height of atmospheric mixed layer in time especially in big cities. Here, the variation of the height of this layer is estimated from direct measurements and also from a numerical forecast model with a high resolution boundary layer scheme. The height of the daytime mixed layer for the city of Zanjan (48.5°N, 36.7°E, 1700m above sea level) is measured using a LIDAR (532 nm) system, which works based on aerosols scattering of laser light. The mixed layer height (z _i ) for Zanjan city, well above mean sea level compared to other major cities in the world, is found to be between 1.4 km typically in spring and 2.2 km in summer, for synoptic calm conditions. Also, the MM5 forecast model with a proper boundary layer scheme (MRF) is used to estimate z _i which shows rather good agreement with direct observations using the LIDAR system. The entrainment zone of the mixed layer was also found to undergo some occasional temporal growth that may be attributed to shear instability that led to more mixed layer growth.     

A case study of atmospheric boundary layer features during winter over a tropical inland station — Kharagpur (22.32°N, 87.32°E)

The local weather and air quality over a region are greatly influenced by the atmospheric boundary layer (ABL) structure and dynamics. ABL characteristics were measured using a tethered balloon-sonde system over Kharagpur (22.32°N, 87.32°E, 40m above MSL), India, for the period 7 December 2004 to 30 December 2004, as a part of the Indian Space Research Organization-Geosphere Biosphere Program (ISRO-GBP) Aerosol Land Campaign II. High-resolution data of pressure, temperature, humidity, wind speed and wind direction were archived along with surface layer measurements using an automatic weather station. This paper presents the features of ABL, like ABL depth and nocturnal boundary layer (NBL) depth. The sea surface winds from Quikscat over the oceanic regions near the experiment site were analyzed along with the NCEP/NCAR reanalysis winds over Kharagpur to estimate the convergence of wind, moisture and vorticity to understand the observed variations in wind speed and relative humidity, and also the increased aerosol concentrations. The variation of ventilation coefficient (V C), a factor determining the air pollution potential over a region, is also discussed in detail.     

The C20 highly branched isoprenoid biomarker – A new diatom-sourced proxy for summer trophic conditions?

The exact biological source of the C₂₀ highly branched isoprenoid (HBI) present in sediments from aquatic systems is unclear. We therefore examined the relationship between the distribution of fossil diatoms and the concentration of the C₂₀ HBI in a Late Glacial sedimentary record from the Hässeldala Port paleolake in southern Sweden. Using Bayesian multiple linear regression analysis, we show that its concentration is linked primarily to the production of the diatom taxon Gomphonema acuminatum, which accounts for the largest proportion of the temporal variability in the biomarker. By analogy with modern observations, we argue that an increasing amount of G. acuminatum biomass in our sedimentary record reflects increasing oligotrophy in the paleolake during the summer growing season, especially at times defined by subdued hydrologic flow. Our conclusions are corroborated by the δ¹³C composition of the C₂₀ HBI biomarker, which points to a negative photosynthetic fractionation between atmospheric CO₂ and the pool of dissolved inorganic carbon during diatom bloom, a distinct phenomenon at times of inhibited hydrological flow. Accordingly, we suggest that the C₂₀ HBI biomarker can be effectively used to reconstruct the trophic state of the paleolake at Hässeldala Port, while its stable isotope composition can provide physicochemical information about the lake conditions during the dry summer season.Moreover, we note that the major hydrological shifts recorded in the G. acuminatum-C₂₀ HBI stratigraphy do not coincide with the pollen zone boundaries. We thus infer that aquatic and terrestrial environmental responses to climate change are substantially decoupled through the hydrological system, which highlights the necessity for multi-proxy investigations to decipher past climate events.     

Summary and Prospects of Numerical Simulation Research of the Atmospheric Boundary Layer

As an important bridge between the underlying surface and the free atmosphere, the atmospheric boundary layer is not only closely related to the development of various weather processes, but also plays a key role in local and regional weather and climate changes. In view of the complexity of the atmospheric boundary layer, the numerical simulation of the atmospheric boundary layer has always been a hotspot and difficulty in the numerical simulation research of the atmosphere. In this paper, the three numerical model development stages of the atmospheric boundary layer in recent decades were summarized and the important advances in arid and semi-arid areas, Tibet Plateau, urban complex underlying surface, and special typhoon boundary layer were reviewed. At present, there are still five scientific problems to be solved urgently, including cloud and boundary layer interaction, boundary layer parameterization, model resolution, boundary layer data assimilation and boundary layer development mechanism. Moreover, it was pointed out that in this field we need to strengthen the understanding of different types of atmospheric boundary layer processes, boundary layer bottom and top interface exchange, boundary layer development mechanism in special regions, improve boundary layer parameterization scheme and give full play to the advantages of LES in boundary layer simulation.     

Experimental and theoretical simulation of the thermal and hydrodynamic structure of a subducting plate

The presented scenario of free convection flows in a subduction zone is based on experimental and theoretical simulation. The experimental simulation of free convection flows is carried out under various conditions of heat transfer that occurs between the oceanic and continental limbs of the subduction zone. The experiments show that to provide insights into subduction zones, it is necessary to estimate the horizontal forces acting on the left and right sides of the plunging plate, as well as the resulting horizontal force and its direction. The vector sum of horizontal and gravity forces of the subducting plate determines the slope angle of this plate at different depths. Heat transfer in the subducting plate has been considered. The y _min coordinate of the temperature minimum in a plate and the value of minimum temperature have been estimated. The forces that arise due to phase transition and owing to the horizontal temperature gradient along the thickness of the descending lithosphere in the transitional mantle layer C are estimated as well. These forces are directed in opposite direction from the y _min coordinate and induce spreading of the subducting lithosphere along the boundary between the upper and lower mantle. Theoretical simulation of the hydrodynamics and heat transfer in combination with experimental simulation of convection flows in a subduction zone indicates that a significant part of the upper mantle material of the plunging plate circulates in the oceanic limb of the subduction zone owing to spreading from the region of minimum temperature along a 670 km boundary.     

Sediment and carbon storages in the Yahagi River Delta during the Holocene,central Japan

We estimated stored sediment and carbon during the Holocene for each layer of the Yahagi River Delta, central Japan and discussed the provenance of stored carbon. To estimate the bulk density and the carbon content of each layer, we collected two 30 m deep undisturbed cores. The volume of each layer was calculated using ArcView 3D analyst. Although the volume ratio of each layer to the total volume was calculated to be 9.5% for the top mud layer, 34.9% for the upper sand layer, 32.8% for the middle mud layer and 22.9% for the lower sand layer, the mass ratio of each layer to the total mass was calculated to be 8.5, 40.9, 25.2 and 25.4%, respectively, and the stored carbon ratio in each layer to the total stored carbon was 20.4, 4.7, 55.9 and 18.9%, respectively. These results suggest that the top mud and middle mud layers have a significant role as a place for carbon sequestration during postglacial time. Total stored carbon in the study area of only 92.1 km² was estimated at 26 Tg C, which is equivalent to 0.003% of atmospheric carbon. This suggests that deltas on the globe have accumulated a massive amount of carbon during the evolution. The inorganic carbon ratio to total carbon reached more than 45% around the boundary between the middle mud and lower sand layers. The increasing trend in the C_org/N_total ratio accompanied with a decrease in δ¹³C from the bottom to the top horizon in the middle mud layer indicates a gradual increase in terrestrial organic matter contribution. The relative proportion of terrestrially derived materials decreases with increasing distance seaward.     

Characterization of the atmospheric boundary layer from radiosonde observations along eastern end of monsoon trough of India

In this paper, a comparison of two methods for the calculation of the height of atmospheric boundary layer (ABL), using balloon-borne GPS radiosonde data is presented. ABL has been characterized using vertical profiles of meteorological parameter. The gradient of virtual potential temperature (?? _v ) profile for the determination of mixed layer heights (MLH) and the mean value of turbulent flow depth (TFD) obtained from the vertical profile of Bulk Richardson Number (R _{i B} ) have been used in this study. One-year data have been used for the study. There is large seasonal variability in MLH with a peak in the summer and winter whereas the TFD remained steady throughout the year. Results from the present study indicate that the magnitudes of TFD are often larger than the MLH.     

末次盛冰期太平洋赤道辐合带对暖池外热带海表温度变化的敏感性

利用美国NCAR CAM3大气环流模式,分析了末次盛冰期（LGM）两个不同的热带海表温度重建方案中,北半球冬季热带中、西太平洋对流活动及大气环流对暖池外（赤道东太平洋和热带大西洋）热带SST异常的敏感性。结果表明：  1）SST异常首先引起大气环流的改变。  赤道东太平洋对流层下沉增强,而作为经向补偿,副热带东太平洋上升运动增强,其中南半球尤为明显,同时南半球热带中、西太平洋上升运动增强,加剧了该区纬向逆时针环流,说明冰期热带海气耦合过程受气候背景场（如SST）影响很大;   2）大气环流格局改变引起热带中西太平洋的大气加热、对流活动、表层风场及降雨的巨大变化。  140°E以西的婆罗洲和菲律宾区域,总的大气加热减少是由于对流与辐射加热减少所致,对应于该区风场辐散和降雨减少;   而140°E以东的南半球热带中、西太平洋,大气吸收热量增加,对流与辐射加热均增强,总降雨量也随之增加,反映该区赤道辐合带南移并增强。该项研究为探索热带太平洋在冰期/间冰期旋回中的古海洋学变化提供了新的数据支撑。此外,不同重建SST对赤道辐合带的影响比较大,因此利用重建SST进行数值模拟或者利用耦合模式研究LGM热带海气相互作用时,应该十分重视全球热带SST分布特征。     

Doppler SODAR observations of the temperature structure parameter during monsoon season over a tropical rural station,Gadanki

Doppler SODAR (Sound Detection and Ranging) measurements over a tropical Indian station at National Atmospheric Research Laboratory (NARL), Gadanki (13.5°N, 79.2°E) during two consecutive monsoon seasons, 2007 and 2008, are investigated to study the influence of mechanically generated turbulence on temperature structure parameter (C_T²)_{\rm T}^{2}) in the convective boundary layer. Increase in the C_T²_{\rm T}^{2} is observed after the arrival of monsoon for both seasons. Contribution of vertical wind shear in horizontal wind component to C_T²_{\rm T}^{2} due to zonal winds is responsible for the increase observed in the temperature structure parameter which is inferred from the results obtained. C_T²_{\rm T}^{2} is found to be increased by an order of 2 in both the lower and upper altitudes, respectively. Magnitude of wind speed is reported to be doubled with the arrival of monsoon. It is also observed that, southwest monsoon wind modulates the day-to-day variations of wind pattern over this station during the onset phase of monsoon season. The lower variability observed at lower height is attributed to the complex topography surrounding this region.     

Numerical simulation of the marine boundary layer characteristics over the Bay of Bengal as revealed by BOBMEX-98 Pilot experiment

An attempt has been made to study the marine boundary layer characteristics over Bay of Bengal using BOBMEX (Bay of Bengal and Monsoon Experiment) pilot experiment data sets, which was conducted between 23rd October and 12th November 1998 on board ORV Sagar Kanya. A one-dimensional multilevel atmospheric boundary layer with TKE-ε closure scheme is employed to study the marine boundary layer characteristics. In this study two synoptic situations are chosen: one represents an active convection case and the other a suppressed convection. In the present article the marine boundary layer characteristics such as temporal evolution of turbulent kinetic energy, height of the boundary layer and the airsea exchange processes such as sensible and latent heat fluxes, drag coefficient for momentum are simulated during both active and suppressed convection. Marine boundary layer height is estimated from the vertical profiles of potential temperature using the stability criterion. The model simulations are compared with the available observations.     

A study of turbulent characteristics of atmospheric boundary layer over monsoon trough region using Kytoon and Doppler sodar

As a part of the MONTBLEX-90 observational programme, Kytoon and Doppler sodar observations were taken at Kharagpur. These data are analysed to study the turbulent characteristics of the atmospheric boundary layer in terms of stability, temperature structure function (C _T ² ) and velocity structure function (C _v ² ).C _T ² follows aZ ^−4/3 law on most of the days, whereas the variation ofC _V ² is not systematic.C _V ² andC _T ² values are found to vary between 10⁻⁵−10⁻¹ m^4/3s⁻² and 10⁻⁵−10⁻²°C² m^−2/3 respectively.     

Mechanisms of orthopyroxene dissolution in silica-undersaturated melts at 1 atmosphere and implications for the origin of silica-rich glass in mantle xenoliths

Experiments dissolving orthopyroxene (En₉₃) in a variety of Si-undersaturated alkaline melts at 1 atmosphere and variable f _O2 demonstrate that orthopyroxene dissolves to form olivine, Si-rich melt and clinopyroxene. These phases form a texturally and chemically distinct boundary layer around the partly dissolved orthopyroxene crystals. The occurrence of clinopyroxene in the boundary layer is due to inward diffusion of Ca from the solvent melt to the boundary layer causing clinopyroxene saturation. Compositional profiles through the solvent and the boundary layer for a number of experiments demonstrate rapid diffusion of cations across the boundary layer – solvent interface. SiO₂ diffuses outward from the boundary layer whereas CaO and Al₂O₃ diffuse toward the Si-enriched boundary layer melt. The rate of Al diffusion is slower under reducing conditions compared to the rates in experiments performed in air. Concentrations of FeO and MgO in the boundary layer and solvent are approximately equal indicating rapid diffusion and attainment of equilibrium despite ongoing crystallisation of clinopyroxene within the boundary layer. The behaviour of Na₂O and K₂O is strongly affected by f _O2. Under reducing conditions Na₂O and K₂O concentrations are approximately equal in the boundary layer and solvent indicating normal diffusion down the concentration gradient and attainment of equilibrium. Under oxidising conditions, K₂O and to a lesser extent Na₂O, have compositional profiles indicative of uphill diffusion likely due to their preference for more polymerised Si- and Al-rich melts. Under reduced conditions Al-enrichment in the boundary layer melt is not as extreme and uphill diffusion did not occur. The composition of the solvent melt after the experiments indicates that it was contaminated by the boundary layer by convective mixing due to the onset of hydrodynamic instabilities brought on by density and viscosity contrasts between the two melts. Despite using a wide variety of solvent melt compositions we find that the boundary layer melts converge toward a common composition at high SiO₂ contents. The composition of glass generated by orthopyroxene dissolution at 1 atmosphere is similar in many respects to Si-rich glass found in many orthopyroxene-rich mantle xenoliths that have been attributed to high pressure in situ processes including mantle metasomatism. The results of this study suggest that at least some Si-rich melts are likely to have formed by dissolution of xenolith orthopyroxene at low pressure possibly by their Si-undersaturated host magmas. Received: 30 August 1996 / Accepted: 15 April 1998     

An analysis of MONTBLEX data on heat and momentum flux at Jodhpur

Parameterization of sensible heat and momentum fluxes as inferred from an analysis of tower observations archived during MONTBLEX-90 at Jodhpur is proposed, both in terms of standard exchange coefficientsC _H andC _D respectively and also according to free convection scaling. Both coefficients increase rapidly at low winds (the latter more strongly) and with increasing instability. All the sensible heat flux data at Jodhpur (wind speed at 10 m Ū₁₀ < 8 ms⁻¹) also obey free convection scaling, with the flux proportional to the ‘4/3’ power of an appropriate temperature difference such as that between 1 and 30 m. Furthermore, for Ū₁₀ < 4 ms⁻¹ the momentum flux displays a linear dependence on wind speed.