共查询到20条相似文献，搜索用时 31 毫秒
1.
The global electrical circuit, which maintains a potential of about 280 kV between the earth and the ionosphere, is thought to be driven mainly by thunderstorms and lightning. However, very few in situ measurements of electrical current above thunderstorms have been successfully obtained. In this paper, we present dc to very low frequency electric fields and atmospheric conductivity measured in the stratosphere (30–35 km altitude) above an active thunderstorm in southeastern Brazil. From these measurements, we estimate the mean quasi-static conduction current during the storm period to be 2.5 ± 1.25 A. Additionally, we examine the transient conduction currents following a large positive cloud-to-ground (+ CG) lightning flash and typical − CG flashes. We find that the majority of the total current is attributed to the quasi-static thundercloud charge, rather than lightning, which supports the classical Wilson model for the global electrical circuit. 相似文献
2.
Cosmic rays and the electric field of thunderclouds: Evidence for acceleration of particles (runaway electrons) 总被引：1，自引：0，他引：1
We present the data on correlations of the intensity of the soft component of cosmic rays with the local electric field of the near-earth atmosphere during thunderstorm periods at the Baksan Valley (North Caucasus, 1700 m a.s.l.). The large-area array for studying the extensive air showers of cosmic rays is used as a particle detector. An electric field meter of the ‘electric mill’ type (rain-protected) is mounted on the roof of the building in the center of this array. The data were obtained in the summer seasons of 2000–2002. We observe strong enhancements of the soft component intensity before some lightning strokes. At the same time, the analysis of the regression curve ‘intensity versus field’ discovers a bump at the field sign that is opposite to the field sign corresponding to acceleration of electrons. It is interpreted as a signature of runaway electrons from the region of the strong field (with opposite sign) overhead. 相似文献
3.
Kevin E. Trenberth 《Dynamics of Atmospheres and Oceans》1979,4(1):57-64
A survey is made of the published estimates of the components of the poleward flux of energy by the atmosphere in the Southern Hemisphere in order to determine the total atmospheric transport. Together with recent measurements by satellite of the Earth's radiation budget this allows a new estimate of the required poleward energy transport by the oceans in the Southern Hemisphere for mean annual conditions. Results show that the ocean and atmosphere each contribute similar amounts for 0–30°S and that the ocean probably also transports about one third of the total at 60°S. The latter is in contrast to similar latitudes in the Northern Hemisphere where the ocean transport is negligible, but consistent with the different distribution of land and sea in the two hemispheres. 相似文献
4.
We examined microsecond- and submicrosecond-scale pulses in electric field records of cloud and cloud-to-ground lightning discharges acquired in summer 2006, in Gainesville, Florida. A total of 12 cloud and 12 ground flashes were analyzed in detail, with the electric field record length being 96 or 200 ms and sampling interval being 4 or 10 ns. The majority of pulses in both cloud and ground discharges analyzed in this study were associated with the initial breakdown process and were relatively small in amplitude and duration. The typical durations were an order of magnitude smaller than tens of microseconds characteristic of “classical” preliminary breakdown pulses. We estimated that 26% of the pulses in the 12 cloud discharges and 22% of the pulses in the 12 cloud-to-ground discharges had total durations less that 1 µs. 相似文献
5.
6.
Sounding-derived indices for neural network based short-term thunderstorm and rainfall forecasts 总被引：1，自引：0，他引：1
A neural network-based scheme to do a multivariate analysis for forecasting the occurrence and intensity of a meteo event is presented. Many sounding-derived indices are combined together to build a short-term forecast of thunderstorm and rainfall events, in the plain of the Friuli Venezia Giulia region (hereafter FVG, NE Italy).For thunderstorm forecasting, sounding, lightning strikes and mesonet station data (rain and wind) from April to November of the years 1995–2002 have been used to train and validate the artificial neural network (hereafter ANN), while the 2003 and 2004 data have been used as an independent test sample. Two kind of ANNs have been developed: the first is a “classification model” ANN and is built for forecasting the thunderstorm occurrence. If this first ANN predicts convective activity, then a second ANN, built as a “regression model”, is used for forecasting the thunderstorm intensity, as defined in a previous article.The classification performances are evaluated with the ROC diagram and some indices derived from the Table of Contingency (like KSS, FAR, Odds Ratio). The regression performances are evaluated using the Mean Square Error and the linear cross correlation coefficient R.A similar approach is applied to the problem of 6 h rainfall forecast in the Friuli Venezia Giulia plain, but in this second case the data cover the period from 1992 to 2004. Also the forecasts of binary events (defined as the occurrence of 5, 20 or 40 mm of maximum rain), made by classification and regression ANN, were compared. Particular emphasis is given to the sounding-derived indices which are chosen in the first places by the predictor forward selection algorithm. 相似文献
7.
M. W. Moncrieff 《Atmospheric Research》1995,35(2-4)
This essay concerns precipitating convective cloud systems and convectively-driven mesoscale circulations (“mesoscale convection”) and their role in the large-scale structure of the atmosphere. Mesoscale convection is an important and ubiquitous process on scales of motion spanning a few kilometers to many hundreds of kilometers. It plays a role in the input of energy to the climate system through the radiative effect of upper-tropospheric cloud and water vapor, and enhanced surface fluxes. This is in addition to its important effect on energy, heat and momentum transport within the atmosphere. However, mesoscale convection is neither parameterized nor adequately resolved in atmospheric general circulation models. Its representation in mean-flow terms raises issues that are quite distinct from classical approaches to sub-grid scale convection parameterization.Cloud-resolving modeling and theoretical concepts pertinent to the transport properties and mean-flow effects of organized convection are summarized, as are the main convective parameterization techniques used in global models. Two principal themes that are relevant to the representation of organized mesoscale systems are discussed. First, mesoscale transports and their sub-grid scale approximation with emphasis on dynamical approaches. Second, long time-scale modeling of mesoscale cloud systems that involves the collective effect of convection, boundary and surface layers, radiation, microphysics acting under the influence of large-scale forcing.Finally, major research programs that address the role of precipitating convection and mesoscale processes in global models are summarized. 相似文献
8.
The global energy cycle of stationary and transient atmospheric waves: Results from ECMWF analyses 总被引：3，自引：0，他引：3
Summary The role of stationary (monthly mean) and transient (departure from monthly mean) waves within the atmospheric energy cycle is examined using global analyses from the European Centre for Medium Range Weather Forecasts (ECMWF) for the period 1980–1987. Only January and July averages are considered.It is confirmed that planetary stationary waves are basically baroclinic. Their contribution to the globally averaged energy cycle of the atmosphere is comparable to that of the transient waves. In January they contribute about 40% to the baroclinic conversion (CA) from zonal mean to eddy available potential energy. Local values for the northern hemisphere even show a predominant role of the stationary wave conversions over those originating from transient waves. Part of the available potential energy of stationary waves (A
SE) is converted to kinetic energy by warm air rising and cold air sinking. Nonlinear energy conversion, which can be interpreted as destruction of stationary temperature waves by transients, is the second sink forA
SE. The order of magnitude of these two processes is similar.Barotropic nonlinear conversions, though negligible in the global average, reveal large conversion rates between the mean positions of the polar and the subtropical jets. Their orientation is suggestive of a tendency to increase stationary wave kinetic energyK
SE at its local minimum between the jets at the expense of the synoptic scale transients.While all terms of the energy cycle related to stationary waves reveal a predominance of the planetary scale (zonal wave numbers 1–3) transient waves are governed by synoptic scale waves (zonal wave numbers 4–9) only with respect to the baroclinic and barotropic conversions: a significant amount of transient wave energy (50% for the global average ofA
TE) is due to planetary scale waves.With 15 Figures 相似文献
9.
Stanislav S. Davydenko Thomas C. Marshall Maribeth Stolzenburg 《Atmospheric Research》2009,91(2-4):165-177
This study examines the electricity in two thunderstorms, typical for their respective locales (the Great Plains and the New Mexico mountains), by modeling them as a set of steady-state horizontal layers of external currents. The model electric sources, corresponding to the charge separation processes in the thundercloud, are embedded in an exponential conducting atmosphere. The source parameters are determined by fitting the model electric field to measured profiles. The resulting currents to the ionosphere (i.e., the Wilson current) from the two storms are 0.53 A and 0.16 A, while the calculated electrical energies of the storms are 2.3 × 1010 J and 2.8 × 109 J, respectively. The more vigorous storm is estimated to transfer 16 000 C in the global circuit during 8.5 h of its lifetime, while the weaker mountain storm transferred about 1200 C in its entire 2-h lifetime. Removal of the screening charge layer from above the updraft region in one modeled storm leads to only a small increase in the net Wilson current of less than 3%, while it provides a substantial local disturbance of the electric field. Overall, the model findings indicate that differences in the Wilson currents and electrical energies of the two storms result from differences in their internal dynamical and electrical structures as well as their geographical locations. 相似文献
10.
Methanol has been recognised as an important constituent of the background atmosphere, but little is known about its overall cycle in the biosphere/atmosphere system. A model is proposed for the production and emission to the atmosphere of methanol by flowering plants based on plant structure and metabolic properties, particularly the demethylation of pectin in the primary cell walls. This model provides a framework to extend seven sets of measurements of methanol emission rates to the global terrestrial biosphere. A global rate of release of methanol from plants to the atmosphere of 100 Tg y–1 is calculated. A separate model of the global cycle of methanol is constructed involving emissions from plant growth and decay, atmospheric and oceanic chemical production, biomass burning and industrial production. Removal processes occur through hydroxyl radical attack in the atmosphere, in clouds and oceans, and wet and dry deposition. The model successfully reproduces the methanol concentrations in the continental boundary-layer and the free atmosphere, including the inter-hemispheric gradient in the free atmosphere. The model demonstrates a new concept in global biogeochemistry, the coupling of plant cell growth with the global atmospheric concentration of methanol. The model indicates that the ocean provides a storage reservoir capable of holding at least 66 times more methanol than the atmosphere. The ocean surface layer reservoir essentially buffers the atmospheric concentration of methanol, providing a physically based smoothing mechanism with a time constant of the order of one year. 相似文献
11.
以发展基于奇异向量技术为初值扰动的GRAPES全球集合预报系统为目的,在GRAPES模式及其干动力框架下的切线性、伴随模式基础上开展了以总能量模为权重算子的奇异向量计算技术研究,建立奇异向量的计算求解模块,并通过奇异向量检验方法和切线性近似方法验证了奇异向量求解的正确性.通过对中高纬度的GRAPES奇异向量水平结构的线性演变分析,证实了在最优时间间隔内GRAPES奇异向量能够快速增长,并能描述中高纬度大气的斜压不稳定特征.分析在初始时刻和最优化时间间隔时刻的GRAPES奇异向量总能量及其分量(动能和势能)的垂直分布特征,发现在中高纬度区域,GRAPES奇异向量能够描述对流层不同层次的斜压不稳定增长特征. 相似文献
12.
L. D. Danny Harvey 《Climatic change》1995,29(1):53-89
The relative costs and CO2 emission reduction benefits of advanced centralized fossil fuel electricity generation, hybrid photovoltaic-fossil fuel electricity generation, and total solar electricity generation with hydrogen storage are compared. Component costs appropriate to the year 2000–2010 time frame are assumed throughout. For low insolation conditions (160 W m–2 mean annual solar radiation), photovoltaic electricity could cost 5–13 cents/kWh by year 2000–2010, while for high insolation conditions (260 W m–2) the cost could be 4–9 cents/kWh. Advanced fossil fuel-based power generation should achieve efficiencies of 50% using coal and 55% using natural gas. Carbon dioxide emissions would be reduced by a factor of 2 to 3 compared to conventional coal-based electricity production in industrialized countries. In a solar-fossil fuel hybrid, some electricity would be supplied from solar energy whenever the sun is shining and remaining demand satisfied by fossil fuels. This increases total capital costs but saves on fuel costs. For low insolation conditions, the costs of electricity increases by 0–2 cents/kWh, while the cost of electricity decreases in many cases for high insolation conditions. Solar energy would provide 20% or 30% of electricity demand for the low and high insolation cases, respectively. In the solar-hydrogen energy system, some photovoltaic arrays would provide current electricity demand while others would be used to produce hydrogen electrolytically for storage and later use in fuel cells to generate electricity. Electricity costs from the solar-hydrogen system are 0.2–5.4 cents/kWh greater than from a natural gas power plant, and 1.0–4.5 cents/kWh greater than from coal plant for the cost and performance assumptions adopted here. The carbon tax required to make the solar-hydrogen system competitive with fossil fuels ranges from $70–660/tonne, depending on the cost and performance of system components and the future price of fossil fuels.Leakage of hydrogen from storage into the atmosphere, and the eventual transport of a portion of the leaked hydrogen to the stratosphere, would result in the formation of stratospheric water vapor. This could perturb stratospheric ozone amounts and contribute to global warming. Order-of-magnitude calculations indicate that, for a leakage rate of 0.5% yr–1 of total hydrogen production -which might be characteristic of underground hydrogen storage - the global warming effect of solarhydrogen electricity generation is comparable to that of a natural gas-solar energy hybrid system after one year of emission, but is on the order of 1% the impact of the hybrid system at a 100 year time scale. Impacts on stratospheric ozone are likely to be minuscule. 相似文献
13.
Serge Soula Oscar van der Velde Joan Montany Torsten Neubert Olivier Chanrion Michal Ganot 《Atmospheric Research》2009,91(2-4):514-528
During the summers of 2003 to 2006 sprites were observed over thunderstorms in France by cameras on mountain tops in Southern France. The observations were part of a larger coordinated effort, the EuroSprite campaigns, with data collected simultaneously from other sources including the French radar network for precipitation structure, Meteosat with images of cloud top temperature and the Météorage network for detection of cloud-to-ground (CG) flash activity. In this paper two storms are analyzed, each producing 27 sprite events. Both storms were identified as Mesoscale Convective Systems (MCS) with a trailing stratiform configuration (ST) and reaching a maximum cloud area of ~ 120,000 km2. Most of the sprites were produced while the stratiform area was clearly developed and during periods of substantial increase of rainfall in regions with radar reflectivity between 30 and 40 dBZ. The sprite-producing periods followed a maximum in the CG lightning activity and were characterized by a low CG flash rate with a high proportion of + CG flashes, typically around 50%. All sprites were associated with + CGs except one which was observed after a − CG as detected by the Météorage network. This − CG was estimated to have − 800 C km charge moment change. The peak current of sprite-producing + CG (SP + CG) flashes was twice the average value of + CGs and close to 60 kA with little variation between the periods of sprite activity. The SP + CG flashes were further characterized by short time intervals before a subsequent CG flash (median value < 0.5 s) and with clusters of several CG flashes which suggest that SP + CG flashes often are part of multi-CG flash processes. One case of a lightning process associated with a sprite consisted of 7 CG flashes. 相似文献
14.
Intracloud discharge and the correlated basic charge structure of a thunderstorm in Zhongchuan, a Chinese Inland Plateau region 总被引：1，自引：0，他引：1
The intracloud (IC) discharge is closely related to the charge structure of thunderstorms. The location, charge moment and polarity of intracloud discharges have been analyzed by using the electric field changes from a 7-site network of slow antennas synchronized by GPS with 1 μs time resolution in the area of Zhongchuan in the Chinese Inland Plateau. Ten IC flashes, from a storm on August 20, 2004, have been fitted by using the non-linear least-square solution. The results show that five IC flashes occurred between the main negative charge region and the lower positive charge region and other five between the main negative charge region and the upper positive charge region during the mature stage of the thunderstorm. The centers of discharge were 3.2–5.6 km and 6.8–7.7 km above sea level. The neutralized moments were about 4.56–61.0 C km and 1.06–15.9 C km. It suggests that the charge structure related to the lightning discharge can be represented by a tripole but with a strong positive charge region in the lower part of the thunderstorm, with the lower positive charge region taking an active role in the discharge. 相似文献
15.
The influence of an idealized moving wavy surface on the overlying airflow is investigated using direct numerical simulations (DNS). In the present simulations, the bulk Reynolds number is Re = 8000 (; where U0 is the forcing velocity of the flow, h the height of the domain and v the kinematic viscosity) and the phase speed of the imposed waves relative to the friction velocity, i.e., the wave age varies from very slow to fast waves. The wave signal is clearly present in the airflow up to at least 0.15λ (where λ is the wave length) and is present up to higher levels for faster waves. In the kinetic energy budgets, pressure transport is mainly of importance for slow waves. For fast waves, viscous transport and turbulent transport dominate near the surface. Kinetic energy budgets for the wave and turbulent perturbations show a non-negligible transport of turbulent kinetic energy directed from turbulence to the wave perturbation in the airflow. The wave-turbulent energy transport depends on the size, tilt, and phase of the wave-induced part of the turbulent Reynolds stresses.According to the DNS data, slow waves are more efficient in generating isotropic turbulence than fast waves.Despite the differences in wave-shape as well as in Reynolds number between the idealized direct numerical simulations and the atmosphere, there are intriguing similarities in the turbulence structure. Important information about the turbulence above waves in the atmosphere can be obtained from DNS—the data must, however, be interpreted with care. 相似文献
16.
Rainer Bleck 《Dynamics of Atmospheres and Oceans》1985,9(1):17-37
Equations for the mean and eddy kinetic energy and for the mean and eddy potential energy in isopycnic and isentropic coordinates are derived, and conversion terms between the four energy forms are identified. Contrary to Lorenz' isobaric formulae, a conversion term between mean kinetic and eddy potential energy is found in the isopycnic/isentropic framework; furthermore, no term governing direct conversion between eddy and mean potential energy exists in isopycnic coordinates. The option of “re-routing” some energy conversion processes to eliminate the formal difference between the isopycnic/isentropic and the isobaric viewpoint is discussed. A numerical simulation of baroclinic instability in an isentropic coordinate model is used to illustrate the energy conversion processes. 相似文献
17.
Charge source of cloud-to-ground lightning and charge structure of a typical thunderstorm in the Chinese Inland Plateau 总被引：1，自引：0，他引：1
Tinglong Zhang Xiushu Qie Tie Yuan Guangshu Zhang Tong Zhang Yang Zhao 《Atmospheric Research》2009,92(4):475-480
GPS-synchronized measurements of electric (E) field changes induced by lightning flashes were recorded at six stations in the northeastern verge of the Tibetan Plateau. The height and magnitude of charge neutralized by 65 return strokes, including 16 negative cloud-to-ground (CG) flashes and 2 positive CG flashes, have been fitted with the nonlinear least-square method based on the E field changes of CG flashes observed in a typical thunderstorm with larger-than-usual lower positive charge center (LPCC). Results show that the height of the charge region neutralized by negative CG flashes ranges from 3 km to 5 km above the ground, corresponding to an ambient temperature between − 2 °C and − 15 °C. For the two positive CG flashes, the neutralized charge regions are located at a height of about 5.5 km and the ambient temperature is about − 18 °C, indicating the existence of upper positive charge in the thunderstorm. 相似文献
18.
Study of the total lightning activity in a hailstorm 总被引：1，自引：0，他引：1
Joan Montany Serge Soula Nicolau Pineda Oscar van der Velde Pere Clapers Glria Sol Joan Bech D. Romero 《Atmospheric Research》2009,91(2-4):430-437
A thunderstorm that developed over northeastern Spain on 16 June 2006 is analyzed. This severe thunderstorm produced hailstones as large as 40 mm and had a lifetime of 3 h and 30 min. Radar cross-sections show strong vertical development with cloud echo tops reaching an altitude of 13 km. The specific characteristics of the lightning activity of this storm were: (i) a large amount (81%) of negative cloud-to-ground (−CG) flashes with very low peak currents (< 10 kA in absolute value), (ii) a very large proportion of intra-cloud (IC) flashes with an IC/CG ratio reaching about 400, (iii) a large number of “short” IC flashes (with only 1-VHF source according to SAFIR detection), (iv) a large increase of the −CG flash rate and of the CG proportion near the end of the storm. The rate of −CG flashes with a low peak current were observed to evolve similarly to the rates of IC flashes. Most of them have been assumed to be IC flashes misclassified by the Spanish Lightning Detection Network (SLDN). They have been filtered as it is usually done for misclassified +CG flashes. After this filtering, CG flash rates remained very low (< 1 min− 1) with +CG flashes sometimes dominant. All the particular lightning activity characteristics similar to those observed in the Severe Thunderstorm Electrification and Precipitation Study (STEPS) campaigns support the hypothesis that this thunderstorm could have had an inverted-polarity or complex charge structure. The maximum IC flash rate (67 min− 1) peaked 24 min before the presence of reflectivity higher than 60 dBZ. The IC activity abruptly decreased during the period when reflectivity was dramatically increasing. The time of maximum reflectivity observed by radar was consistent with the times of reported hail at the ground. 相似文献
19.
Individual bacterial cells occur in many samples that were collected at Cape Grim, Tasmania and during the Lagrangian “B” experiment of the Aerosol Characterization Experiment 1 (ACE-1) campaign that was conducted above the Southern Ocean. They are present in samples from altitudes as high as 5.4 km. Morphologically, almost all bacteria are rod-shaped, about 1 μm long or smaller, have one polar flagellum, and contain inclusions that are rich in P and K. Their morphological features suggest that these bacteria are motile, marine species. It seems likely that the cells became airborne by the same bubble-bursting mechanism that ejects sea-salt aerosol particles into the atmosphere; however, the bacteria and sea-salt particles are typically not aggregated with one another. The estimated number ratio of bacteria and the dominant aerosol species, sea salt, varies in the samples and averages about 1%. The aerosol bacteria seem to represent an important atmospheric reservoir of P and organic compounds; on the other hand, since they are externally mixed with sea salt, they are unlikely to be effective as cloud condensation nuclei. 相似文献
20.
利用总体平均经验模态分解算法(EEMD),对南京地区2010—2011年6—8月近地面大气电场资料进行分析,研究了晴天、弱雷暴和强雷暴天气条件下大气电场的振荡特征。在单站电场仪观测范围内,以晴天大气为背景场,根据固有模态函数(IMF)方差最大值对应层数的动态特性,建立并验证了两种强度的雷暴临近预报模型。结果表明:弱雷暴发生前IMF方差最大值对应层数跳变幅度较平稳,而强雷暴跳变幅度逐渐加剧。对IMF方差最大值对应层数进行三次样条插值,可直观地表征雷暴发生发展过程,延长预报时间至1 h。利用这些特征对92个独立样本进行预报效果检验,预报的准确率为73.3%,虚警率为14.5%。 相似文献