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1.
中国华北雾霾天气与超强El Ni?o事件的相关性研究   总被引：1，自引：1，他引：0       下载免费PDF全文
2015年11—12月,全国接连发生七次大范围、持续性雾霾天气过程,其中,11月27日—12月1日的雾霾天气过程持续时间长达五天,成为2015年最强的一次重污染天气过程;12月19-25日重度雾霾再次发展,影响面积一度达到35.2万km~2.本文利用多种数据资料通过个例对比和历史统计详细分析了超强El Ni?o背景下雾霾天气频发的天气气候条件.其结果清楚表明:2015年11—12月欧亚中高纬度以纬向环流为主,东亚冬季风偏弱,使得影响我国的冷空气活动偏少,我国中东部大部地区对流层低层盛行异常偏南风,大气相对湿度明显偏大,并且大气层结稳定,对流层底层存在明显逆温.上述大气环流条件使得污染物的水平和垂直扩散条件差,因此在有一定污染排放的情况下,造成了重度雾霾天气过程的频发.由此,超强El Ni?o事件所导致的大尺度大气环流异常是我国中东部,尤其华北地区冬季雾霾天气频发的重要原因之一.  相似文献   

2.
In January 2013,a long-lasting episode of severe haze occurred in central and eastern China,and it attracted attention from all sectors of society.The process and evolution of haze pollution episodes were observed by the"Forming Mechanism and Control Strategies of Haze in China"group using an intensive aerosol and trace gases campaign that simultaneously obtained data at 11 ground-based observing sites in the CARE-China network.The characteristics and formation mechanism of haze pollution episodes were discussed.Five haze pollution episodes were identified in the Beijing-Tianjin-Hebei(Jing-Jin-Ji)area;the two most severe episodes occurred during 9–15 January and 25–31 January.During these two haze pollution episodes,the maximum hourly PM2.5mass concentrations in Beijing were 680 and 530μg m 3,respectively.The process and evolution of haze pollution episodes in other major cities in the Jing-Jin-Ji area,such as Shijiazhuang and Tianjin were almost the same as those observed in Beijing.The external cause of the severe haze episodes was the unusual atmospheric circulation,the depression of strong cold air activities and the very unfavorable dispersion due to geographical and meteorological conditions.However,the internal cause was the quick secondary transformation of primary gaseous pollutants to secondary aerosols,which contributed to the"explosive growth"and"sustained growth"of PM2.5.Particularly,the abnormally high amount of nitric oxide(NOx)in the haze episodes,produced by fossil fuel combustion and vehicle emissions,played a direct or indirect role in the quick secondary transformation of coal-burning sulphur dioxide(SO2)to sulphate aerosols.Furthermore,gaseous pollutants were transformed into secondary aerosols through heterogeneous reactions on the surface of fine particles,which can change the particle’s size and chemical composition.Consequently,the proportion of secondary inorganic ions,such as sulphate and nitrate,gradually increased,which enhances particle hygroscopicity and thereby accelerating formation of the haze pollution.  相似文献   

3.
—?The hydrostatic Naval Research Laboratory/North Carolina State University (NRL/NCSU) model was used to study the mesoscale dynamics and diurnal variability of the Intertropical Convergence Zone (ITCZ) over the Indian Ocean in the short-range period. To achieve this objective the initial conditions from two northeast monsoon episodes (29 January, 1997 and 29 January, 1998) were run for 48-hour simulations using a triple-nested grid version of the model with 1.5°?×?1.5°, 0.5°?×?0.5° and 0.17°?×?0.17° resolutions. The 1997 case represents a typical northeast monsoon episode, while the 1998 case depicts an abnormal monsoon episode during an El Niño event.¶Comparisons between the model-produced and analyzed mean circulation, wind speed, and associated rainfall for different spatial scales are presented. During the active northeast monsoon season in 1997, the major low-level westerly winds and associated high rainfall rates between 0° and 15°S were simulated reasonably well up to 24 hours. During the 1998 El Niño event, the model was capable of simulating weak anomalous easterly winds (between 0° and 15°S) with much lower rainfall rates up to 48 hours. In both simulations, the finest grid size resulted in largest rainfall rates consistent with Outgoing Longwave Radiation data.¶The model performance was further evaluated using the vertical profiles of the vertical velocity, the specific humidity and temperature differences between the model outputs and the analyses. It is found that during a typical northeast monsoon year, 1997, the water vapor content in the middle troposphere was largely controlled by the low-level convergence determined by strong oceanic heat flux gradient. In contrast, during the 1998 El Niño year moisture was present only in the lower troposphere. Due to strong subsidence associated with Walker circulation over the central and eastern Indian Ocean, deep convection was not present. Finally, the diurnal variations of the maximum rainfall, vertical velocity and total heat flux were noticeable only during the 1997 northeast monsoon year.  相似文献   

4.
The diurnal variations in electrical (quasistatic electric field and electrical conductivity) and meteorological (temperature, pressure, relative humidity of the atmosphere, and wind speed) parameters, measured simultaneously before strong earthquakes in Kamchatka region (November 15, 2006, М = 8.3; January 13, 2007, М = 8.1; January 30, 2016, М = 7.2), are studied for the first time in detail. It is found that a successively anomalous increase in temperature, despite the negative regular trend in these winter months, was observed in the period of six–seven days before the occurrences of earthquakes. An anomalous temperature increase led to the formation of “winter thunderstorm” conditions in the near-surface atmosphere of Kamchatka region, which was manifested in the appearance of an anomalous, type 2 electrical signal, the amplification of and intensive variations in electrical conductivity, heavy precipitation (snow showers), high relative humidity of air, storm winds, and pressure changes. With the weak flow of natural heat radiation in this season, the observed dynamics of electric and meteorological processes can likely be explained by the appearance of an additional heat source of seismic nature.  相似文献   

5.
New observations from buoys and soundings reveal the discrepancies in air–sea interface and in vertical structures between spring (April to May) and summer (July) fogs in the Yellow Sea. Spring fogs are shallow with a robust temperature inversion, dry layer and cold phase (surface air temperature or SAT is lower than sea surface temperature or SST); summer fogs are deep with weaker stability, indistinct fog top and warm phase (SAT?>?SST). Along with numerical simulations, conceptual models for the mechanisms of temperature inversion are suggested. The land–sea contrast is responsible for the robust temperature inversion in spring, and the deep southerlies derived from the east Asian summer monsoon and the adiabatic sinking from the western Pacific subtropical high contributes to the weaker inversion in summer. The dry layer above the sea fog top intensifies the longwave radiative cooling effect to lead to the cold phase in spring fogs. The radiative cooling is weaker in summer fogs resulting in SAT?>?SST.  相似文献   

6.
Low Visibility Formation and Forecasting on the Northern Coast of Brazil   总被引：1，自引：0，他引：1  
Visibility analysis and forecast at the Maceio International Airport in the Brazilian Northeast (NEB) was the principal goal of this investigation. Surface meteorological data of the Maceio International Airport were used for low visibility frequency study. Low visibility in NEB was provoked more frequently by light fog (LF) formation (1,098 or 92 h month?1 on average). Haze and fog were very rare (81 h and one event per year, respectively on average). Light fog with a visibility less than 2 km usually was detected together with rain or drizzle. Low visibility was observed more frequently at night and during the rainy season. Applications of the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model for light fog forecast were tested. Thermodynamic processes were studied by vertical profile, elaborated by: (1) National Centers for Environmental Prediction (NCEP) reanalysis data for Maceio (because of some radiosonde absence) and (2) forecast vertical temperature and humidity profiles were produced, using Air Parcels Trajectories of the HYSPLIT model at the pattern levels. The synoptic situations before and during low visibility phenomena were analyzed using different products of NCEP reanalysis, the high resolution (10 km) ETA model and infrared satellite images. Wave disturbance in the trade winds field, localized on the northwest periphery of the South Atlantic subtropical High, usually accompanied the phenomena. A humidity advection, weak ascendant movement and thermal inversion absence at the low levels were created by these waves. The middle level’s descendent movement provoked the humidity accumulation at levels below. Satisfactory results of the HYSPLIT model applications for light fog forecast were obtained with 12 h antecedence. In particular, stable level forecast by the ETA model was forecast satisfactorily with 12 h antecedence; vertical movements were predicted better with up to 48 h antecedence. The PSU/NCAR mesoscale model (MM5) and PAFOG models were tested for analysis and forecast of an intensive fog event. Intensive fog provoked a fatal accident of a small airplane near the Maceio Airport in 2007. These fog formation processes were studied by NCEP reanalysis data, the high resolution regional model MM5, and satellite and radar data. Fog formation was simulated by PAFOG model and satisfactory results were obtained with 10 h antecedence.  相似文献   

7.
Sea fog is typically formed and developed under a set of favorable environmental conditions, which are associated with the station pressure changes, sea level pressure, winds, temperature, water vapor supply, and sea surface temperature. Understanding of these environmental factors during the evolution of a sea fog episode is crucial for forecasting the occurrence and severity of sea fogs over the ocean and adjacent coastal areas. In this study, the large-scale environment variability of six fog events over the Yellow Sea was investigated. It was realized in the present study that the northwest Pacific Ocean high (NPH) is vital to fog formation over the Yellow Sea. In our study, six fog cases can be basically divided into two types: (1) pressure-weakening type, (2) pressure-strengthening type. The former type happened in spring and the latter type in summer. Prevailing southerly winds, accompanied with the well-positioned NPH, may supply a large amount of warm water vapor for the fog formation and maintenance. The intensity of the air temperature inversion is stronger in summer cases than that in spring ones. The wind direction change from south to north and the unstable lower atmosphere may lead to fog’s dissipation. This study may provide a comprehensive understanding of sea fog’s onset, maintenance, and dissipation over the Yellow Sea.  相似文献   

8.
Our analysis of fog and haze observations from the surface weather stations in China in recent 50 years(from 1961 to 2011)shows that the number of fog days has experienced two-stage variations,with an increasing trend before 1980 and a decreasing trend after 1990.Especially,an obvious decreasing trend after 1990 can be clearly seen,which is consistent with the decreasing trend of the surface relative humidity.However,the number of haze days has demonstrated an increasing trend.As such,the role of reduction of atmospheric relative humidity in the transition process from fog into haze has been further investigated.It is estimated that the mean relative humidity of haze days is about 69%,lower than previously estimated,which implies that it is more difficult for the haze particles to transform into fog drops.This is possibly one of the major environmental factors leading to the reduction of number of fog days.The threshold of the relative humidity for transition from fog into haze is about82%,also lower than previously estimated.Thus,the reduction of the surface relative humidity in China mainly due to the increase of the surface temperature and the saturation specific humidity may exert an obvious impact on the environmental conditions for the formations of fog and haze.In addition,our investigation of the relationship between haze and visibility reveals that with the increase of haze days,the visibility has declined markedly.Since 1961,the mean visibility has dropped from 4–10to 2–4 km,about a half of the previous horizontal distance of visibility.  相似文献   

9.
Based on satellite data and the estimated inversion strength (EIS) derived by Wood et al. (2006), a feasible and uncomplicated stratocumulus scheme is proposed, referred to as EIS scheme. It improves simulation of cloud radiative forcing (CRF) in the Grid-point Atmospheric Model of IAP/LASG version 2 (GAMIL2.0) model. When compared with the original lower troposphere stability (LTS) scheme, the EIS scheme reproduces more reasonable climatology distributions of clouds and CRF. The parameterization partly corrects CRF underestimation at mid and high latitudes and overestimation in the convective region. Such improvements are achieved by neglecting the effect of free-tropospheric stratification changes that follow a cooler moist adiabat at middle and high latitude, thereby improving simulated cloudiness. The EIS scheme also improves simulation of the CRF interannual variability. The positive net CRF and negative stratiform anomaly in the East Asian and western North Pacific monsoon regions (EAWNPMR) are well simulated. The EIS scheme is more sensitive to sea surface temperature anomalies (SSTA) than the LTS. Therefore, under the effect of a warmer SSTA in the EAWNPMR, the EIS generates a stronger negative stratiform response, which reduces radiative heating in the low and mid troposphere, in turn producing strong subsidence and negative anomalies of both moisture and cloudiness. Consequent decreases in cloud reflection and shading effects ultimately improve simulation of incoming surface shortwave radiative fluxes and CRF. Because of the stronger subsidence, a stronger anomalous anticyclone over the Philippines Sea is simulated by the EIS run, which leads to a better positive precipitation anomaly in eastern China during ENSO winter.  相似文献   

10.
The Nested Air Quality Prediction Model System(NAQPMS)was used to investigate the temporal and spatial variations of PM2.5over tropospheric central eastern China in January 2013.The impact of regional transport and its implications on pollution prevention and control were also examined.Comparison between simulated and observed PM2.5showed NAQPMS was able to reproduce the evolution of PM2.5during heavy haze episodes.The results indicated that regional transport of PM2.5played an important role in regional haze episodes in the city cluster including Hebei,Beijing and Tianjin(HBT).The cross-city clusters transport outside HBT and transport among cities inside HBT contributed 20%–35%and 26%–35%of PM2.5as compared with local emission,in HBT respectively.To meet the Air Quality Standards for Grade II,90%,90%and65%of emissions would have to be cut down in Hebei,Tianjin and Beijing,if non-control strategy was taken in the surrounding city clusters of HBT.This implicated that control of emissions in one city cluster is not sufficient to reduce regional haze events,and joint efforts among city clusters are essential.Besides regional transports,two-way feedback between boundary-layer evolution and PM2.5also significantly contributed to the formation of heavy hazes,which contributed 30%of monthly average PM2.5concentration in HBT.  相似文献   

11.
Lushan MS7.0 earthquake occurred in Lushan county, Ya'an city, Sichuan province of China, on 20 April 2013, and caused 196 deaths, 23 people of missing and more than 12 thousand of people injured. In order to analyze the possible seismic brightness temperature anomalies which may be associated with Lushan earthquake, daily brightness temperature data for the period from 1 June 2011 to 31 May 2013 and the geographical extent of 25°E-35°N latitude and 98°E-108°E longitude are collected from Chinese geostationary meteorological satellite FY-2E. Continuous wavelet transform method which has good resolution both in time and frequency domains is used to analyze power spectrum of brightness temperature data. The results show that the relative wavelet power spectrum (RWPS) anomalies appeared since 24 January 2013 and still lasted on 19 April. Anomalies firstly appeared at the middle part of Longmenshan fault zone and gradually spread toward the southwestern part of Longmenshan fault. Anomalies also appeared along the Xianshuihe fault since about 1 March. Eventually, anomalies gathered at the intersection zone of Longmenshan and Xianshuihe faults. The anomalous areas and RWPS amplitude increased since the appearance of anomalies and reached maximum in late March. Anomalies attenuated with the earthquake approaching. And eventually the earthquake occurred at the southeastern edge of anomalous areas. Lushan earthquake was the only obvious geological event within the anomalous area during the time period, so the anomalous changes of RWPS are possibly associated with the earthquake.  相似文献   

12.
The Ebro river basin, in the northeastern part of the Iberian Peninsula in Europe, very often experiences radiation fog episodes in winter that can last for several days. The impact on human activities is high, especially on road and air transportation. The installation in July 2009 of a WindRASS in the area, which is able to work in the presence of fog, now allows inspecting the vertical structure of the temperature and wind profiles across the roughly 300-m-thick fog layer. We present a case study of a long-lasting (60 h) deep radiation fog that took place in December 2009 to obtain a deeper understanding of the dynamic processes governing such persistent fog. Field observations of vertical profiles of temperature, wind and turbulent kinetic energy are compared with a high-resolution mesoscale simulation, satellite imagery of fog distribution and observations taken in the area to understand why the fog is so persistent and how it dissipates only for a short period in the afternoon despite intermittent turbulence within the fog deck. The confinement of the fog inside a practically closed basin allows us to study the relevant physical processes in the establishment and subsequent evolution of the fog episode using a limited-area mesoscale model. The contribution of the WindRASS measurements allowed us to validate the numerical simulations, particularly inspecting the role of turbulence that can link the bottom and top of the fog through moderate episodic mixing. The fog layer has very weak winds inside, but is well mixed and experiences intermittent top-bottom turbulence generated in its upper part by convection due to radiative cooling and by wind shear due to the topographically generated flows that blow just above the top of the fog.  相似文献   

13.
In this study an attempt has been made to examine the evolutionary features of the dynamic and thermodynamic characteristics of the marine atmosphere over the South-East Arabian Sea near 9.22°N, 74.51°E just two to three days prior to the onset of southwest monsoon over Kerala during 2003 and seek the linkages with the large-scale flow in the lower and middle troposphere at that time over the region. The marine meteorological data collected onboard ORV Sagarkanya as part of the experiment ARMEX-2003 for 4–8 June, 2003 are used. The monsoon onset over Kerala occurred on 8 June, 2003. The observed changes in the marine atmospheric boundary layer (MABL) characteristics just two days prior to the onset are discussed. It is observed that the MABL increased in height up to 4 km on 6 June from an initial height 2.8 km on 5 June. The top of the MABL dried up (Relative Humidity RH ~ 30–40%) with weak and variable winds throughout the day on 6 June while the air at 850 hPa is relatively humid (RH ~ 50–80%) but not saturated. A sequential increase in RH is associated with a change in the winds from southwesterly to westerly from 6 June onwards until the onset date. The changes in the lower and middle troposphere flow patterns over the Arabian Sea and Indian region are highlighted.  相似文献   

14.
副热带急流对中国南部地区对流层中上层臭氧浓度的影响程度及地理范围目前还研究较少,且缺乏综合使用常规气象资料及卫星资料来判识对流层中上层臭氧浓度增高的方法.本文利用NCEP再分析与最终分析资料、日本GMS-5地球静止卫星水汽云图资料,以2001年3月27~29日中国南部的临安、昆明、香港臭氧探测个例为基础,结合1996年3月29日香港与2001年4月13日临安对流层中上层高浓度臭氧分布个例对副热带急流对中国南部对流层中上层臭氧浓度的影响进行了详细分析,提出根据气象要素场判识春季中国南部对流层中上层臭氧浓度增高的充分条件为根据卫星水汽图像上的暗区、高空急流入口区的左侧辐合区、高空锋区、对流层中上层≥1 PVU的向下伸展的舌状高位涡区来综合判断.本文的分析结果表明,本文个例中对流层中上层高浓度臭氧来自平流层;香港对流层中上层低浓度臭氧来自热带海洋地区.不仅臭氧垂直廓线的多个极小与极大值表明臭氧垂直分布的多尺度变化特征,而且对流层中上层PV分布以及卫星水汽图像分析也表明大气中的多尺度运动对臭氧垂直分布特征有显著影响.本文的结果表明与副热带高空急流相联系的平流层空气侵入不仅发生在中国大陆的较高纬度地区,较低纬度的昆明与香港地区也有平流层空气侵入导致对流层中上层臭氧浓度升高.  相似文献   

15.
Nearshore currents of the southern Namaqua shelf were investigated using data from a mooring situated three and a half kilometres offshore of Lambert's Bay, downstream of the Cape Columbine upwelling cell, on the west coast of South Africa. This area is susceptible to harmful algal blooms (HABs) and wind-forced variations in currents and water column structure are critical in determining the development, transport and dissipation of blooms. Time series of local wind data, and current and temperature profile data are described for three periods, considered to be representative of the latter part of the upwelling season (27 January–22 February), winter conditions (5–29 May) and the early part of the upwelling season (10 November–12 December) in 2005. Differences observed in mean wind strength and direction between data sets are indicative of seasonal changes in synoptic meteorological conditions. These quasi-seasonal variations in wind forcing affect nearshore current flow, leading to mean northward flow in surface waters early in the upwelling season when equatorward, upwelling-favourable winds are persistent. Mean near-surface currents are southward during the latter part of the upwelling season, consistent with more prolonged periods of relaxation from equatorward winds, and under winter conditions when winds were predominantly poleward. Within these seasonal variations in mean near-surface current direction, two scales of current variability were evident within all data sets: strong inertial oscillations were driven by diurnal winds and introduced vertical shear into the water column enhancing mixing across the thermocline, while sub-inertial current variability was driven by north–south wind reversals at periods of 2–5 days. Sub-inertial currents were found to lag wind reversals by approximately 12 h, with a tendency for near-surface currents to flow poleward in the absence of wind forcing. Consistent with similar sites along the Californian and Iberian coasts, the headland at Cape Columbine is considered to influence currents and circulation patterns during periods of relaxation from upwelling-favourable winds, favouring the development of a nearshore poleward current, leading to poleward advection of warm water, the development of stratification, and the creation of potentially favourable conditions for HAB development.  相似文献   

16.
Zonal mean data and amplitudes and phases of planetary zonal waves were derived from daily hemispheric maps for tropospheric and stratospheric levels, for the four winters 1975–76 to 1978–79. Important year-to-year fluctuation in zonal means and wave activity are described, most notable of which are the changes from 1975–76 to 1976–77. Comparison of the relative strengths of the stratospheric and tropospheric jet streams shows a strong negative correlation (–0.8) between monthly mean zonal stratospheric winds (at 10 mb, 65°N) and zonal tropospheric winds (at 200 mb, 32.5°N, in the jet core) and a positive correlation (+0.7) between the stratospheric 10 mb winds and the tropospheric 200 mb winds at 65°N. Parameters correlated were the departures from the climatological mean zonal winds. The structure of correlation between wave amplitudes in the same wave number (1, 2) at different altitudes and between wave numbers 1 and 2 is investigated. We find a high correlation (+0.93) between wave 1 in the stratosphere (10 mb height) and wave 2 (height) in the troposphere at 65°N; but only a weak correlation (+0.2) between wave 1 amplitudes in the stratosphere and troposphere. These results suggest the possible importance of wave-wave interactions in processes linking the stratosphere and troposphere. The wave correlations presented here are based on comparisons of monthly means of daily amplitudes; the correlation structure in individual wave developments may differ, in view of the likelihood of altitudinal lags in wave amplification.  相似文献   

17.
Based on the theory of potential vorticity(PV),the unstable development of the South Asia High(SAH)due to diabatic heating and its impacts on the Indian Summer Monsoon(ISM)onset are studied via a case diagnosis of 1998.The Indian Summer Monsoon onset in 1998 is related to the rapidly strengthening and northward moving of a tropical cyclone originally located in the south of Arabian Sea.It is demonstrated that the rapid enhancement of the cyclone is a consequence of a baroclinic development characterized by the phase-lock of high PV systems in the upper and lower troposphere.Both the intensification of the SAH and the development of the zonal asymmetric PV forcing are forced by the rapidly increasing latent heat released from the heavy rainfall in East Asia and South East Asia after the onsets of the Bay of Bengal(BOB)monsoon and the South China Sea(SCS)monsoon.High PV moves southwards along the intensified northerlies on the eastern side of the SAH and travels westwards on its south side,which can reach its northwest.Such a series of high PV eddies are transported to the west of the SAH continuously,which is the main source of PV anomalies in the upper troposphere over the Arabian Sea from late spring to early summer.A cyclonic curvature on the southwest of the SAH associated with increasing divergence,which forms a strong upper tropospheric pumping,is generated by the anomalous positive PV over the Arabian Sea on 355 K.The cyclone in the lower troposphere moves northwards from low latitudes of the Arabian Sea,and the upper-layer high PV extends downwards and southwards.Baroclinic development thus occurs and the tropical low-pressure system develops into an explosive vortex of the ISM,which leads to the onset of the ISM.In addition,evolution of subtropical anticyclone over the Arabian Peninsula is another important factor contributing to the onset of the ISM.Before the onset,the surface sensible heating on the Arabian Peninsula is very strong.Consequently the subtropical anticyclone which dominated the Arabian Sea in spring retreats westwards to the Arabian Peninsula and intensifies rapidly.The zonal asymmetric PV forcing develops gradually with high PV eddies moving southwards along northerlies on the eastern side of the anticyclone,and a high PV trough is formed in the middle troposphere over the Arabian Sea,which is favorable to the explosive barotropic development of the tropical cyclone into the vortex.Results from this study demonstrate that the ISM onset,which is different from the BOB and the SCS monsoon onset,is a special dynamical as well as thermodynamic process occurring under the condition of fully coupling of the upper,middle,and lower tropospheric circulations.  相似文献   

18.
Numerical experiments are performed with a comprehensive one-dimensional boundary layer/fog model to assess the impact of vertical resolution on explicit model forecasts of an observed fog layer. Two simulations were performed, one using a very high resolution and another with a vertical grid typical of current high-resolution mesoscale models. Both simulations were initialized with the same profiles, derived from observations from a fog field experiment. Significant differences in the onset and evolution of fog were found. The results obtained with the high-resolution simulation are in overall better agreement with available observations. The cooling rate before the appearance of fog is better represented, while the evolution of the liquid water content within the fog layer is more realistic. Fog formation is delayed in the low resolution simulation, and the water content in the fog layer shows large-amplitude oscillations. These results show that the numerical representation of key thermo-dynamical processes occurring in fog layers is significantly altered by the use of a grid with reduced vertical resolution.  相似文献   

19.
本文以拉格朗日观点分析北极涛动(Arctic Oscillation,AO),也被称为北半球环状模(Northern Hemisphere Annular Mode,NAM)的指数异常事件中北极近地面冷气团的活动路径,直接地表现出了异常事件中冷气团运动的优势路径,从而反映出AO/NAM对地面气温的直接调控作用.在正AO/NAM指数异常事件中,极区近地面冷气团活动轨迹以纬向环流为主,表现为环绕北半球中高纬地区的冷气团活动轨迹特征明显.而在负AO/NAM指数异常事件中,极区冷气团以反气旋式轨迹流出极区后,流入中纬度海洋上的低气压区,这种由极区向中纬度地区流动的经向运动轨迹特点显著.并且在指数下降的中后期出现两种强烈影响欧亚大陆的运动轨迹.正负事件中冷气团运动轨迹很好地解释了传统公认的AO/NAM对北半球不同地区冬季气温的影响.特别是对中国冬季气温的影响上,正AO/NAM指数异常事件中的中低层冷气团活动有利于南支槽加深,进而为南方地区冰冻雨雪天气提供了有利条件;而负事件中的极地近地面冷气团可直接影响东北地区,形成寒潮降温天气.  相似文献   

20.
Haze and fog are both low visibility events, but with different physical properties. Haze is caused by the increase of aerosol loading or the hygroscopic growth of aerosol at high relative humidity, whereas visibility degradation in fog is due to the light scattering of fog droplets, which are transited from aerosols via activation. Based on the difference of physical properties between haze and fog, this study presents a novel method to distinguish haze and fog using real time measurements of PM2.5, visibility, and relative humidity. In this method, a criterion can be developed based on the local historical data of particle number size distributions and aerosol hygroscopicity. Low visibility events can be classified into haze and fog according to this criterion.  相似文献   

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