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1.
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
2.
《中国科学:地球科学(英文版)》2015,(8)
This paper revealed the climatic change characteristics of fog and haze of different levels over North China and Huang-Huai area(NCHH).It was found that the haze-prone period has changed from winter into a whole year,and the haze days(HD)in winter have increased significantly.The foggy days(FD)are half of HD.There are little difference on the number of days and trends of fog at various levels.The HD and FD show no obvious positive correlation until the 1980s.Fog has larger spatial scale,showing more in the south than in the north.Haze occurs mainly around large cities with a discrete distribution.In the background of weakened East Asian Winter Monsoon(EAWM)and sufficient particulate matter,the negative correlation between haze and wind speed is weakened,but the positive correlation between haze and moisture conditions(precipitation and humidity)is significantly strengthened.In recent years,small wind and variability appear frequently.Meanwhile,as the stable source and strong moisture absorption of the aerosol particles,the moisture condition becomes one key control factor in the haze,especially wet haze with less visibility.In contrast,the FD presents a stable positive correlation with precipitation and relative humidity,but has no obvious negative correlation with wind speed. 相似文献
3.
Meteorological conditions for the persistent severe fog and haze event over eastern China in January 2013 总被引：11，自引：0，他引：11
In January 2013,a severe fog and haze event(FHE)of strong intensity,long duration,and extensive coverage occurred in eastern China.The present study investigates meteorological conditions for this FHE by diagnosing both its atmospheric background fields and daily evolution in January 2013.The results show that a weak East Asian winter monsoon existed in January2013.Over eastern China,the anomalous southerly winds in the middle and lower troposphere are favorable for more water vapor transported to eastern China.An anomalous high at 500 hPa suppresses convection.The weakened surface winds are favorable for the fog and haze concentrating in eastern China.The reduction of the vertical shear of horizontal winds weakens the synoptic disturbances and vertical mixing of atmosphere.The anomalous inversion in near-surface increases the stability of surface air.All these meteorological background fields in January 2013 were conducive to the maintenance and development of fog and haze over eastern China.The diagnosis of the daily evolution of the FHE shows that the surface wind velocity and the vertical shear of horizontal winds in the middle and lower troposphere can exert dynamic effects on fog and haze.The larger(smaller)they are,the weaker(stronger)the fog and haze are.The thermodynamic effects include stratification instability in middle and lower troposphere and the inversion and dew-point deficit in near-surface.The larger(smaller)the stratification instability and the inversion are,the stronger(weaker)the fog and haze are.Meanwhile,the smaller(larger)the dewpoint deficit is,the stronger(weaker)the fog and haze are.Based on the meteorological factors,a multi-variate linear regression model is set up.The model results show that the dynamic and thermodynamic effects on the variance of the fog and haze evolution are almost the same.The contribution of the meteorological factors to the variance of the daily fog and haze evolution reaches 0.68,which explains more than 2/3 of the variance. 相似文献
4.
A vertical sounding of severe haze process in Guangzhou area 总被引：1，自引：0，他引：1
We detected a severe haze process in Guangzhou area with lidar and microwave radiometer, performed an inversion to get boundary layer height by wavelet covariance transform, and analyzed the correlation between meteorological factors of boundary layer and visibility from the perspective of dynamical and thermodynamic structures. Our results indicate that the boundary layer height shows significant daily changes, consistent with ground visibility variation. During the cleaning process, the boundary layer height exceeded 1 km; during severe haze, the height was only 500 m. Temperature gradient of 50–100 m, which was 30 h lag, was remarkably correlated with visibility, with the correlation coefficient of 0.77. High layer visibility(255 m) and low layer stability were significantly anticorrelation, and the maximum anticorrelation coefficient was up to-0.76 in cleaning days and-0.49 in haze days. In the related boundary layer meteorological factors, surface ventilation coefficient was linearly correlated with ground visibility, with the greatest correlation coefficient of 0.88. The correlation coefficients of boundary layer height, ground wind velocity, relative humidity and ground visibility were 0.76, 0.67, and-0.77, respectively. There was a strong correlation between different meteorological factors. The dominant meteorological factor during this haze process was surface ventilation coefficient. In the area without boundary layer height sounding, ground visibility and wind velocity could be used to estimate boundary layer height. 相似文献
5.
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
6.
Martial Haeffelin Jean-Charles Dupont Neda Boyouk Darrel Baumgardner Laurent Gomes Greg Roberts Thierry Elias 《Pure and Applied Geophysics》2013,170(12):2283-2303
Fog is an atmospheric phenomenon that has important environmental consequences related to visibility, air quality and climate change on local and regional scales. The formation of radiation fog results from a complex balance between surface radiative cooling, turbulent mixing in the surface layer, aerosol growth by deliquescence and activation of fog droplets. During the ParisFog field experiment, out of 16 events forecasted for radiation fog, activated fog materialized in seven events, while in five other events the visibility dropped to 1–2 km but haze particle size remained below the critical size of activation. To better understand the conditions that lead to or do not lead to sustained fog droplet activation, we performed a comparative study of dynamic, thermal, radiative and microphysical processes occurring between sunset and fog (or quasi-fog) onset. We selected two radiation fog events and two quasi-radiation fog events that occurred under similar large-scale conditions for this comparative study. We identified that aerosol growth by deliquescence and droplet activation actually occurred in both quasi-fog events, but only during <1 h. Based on ParisFog measurements, we found that the main factors limiting sustained activation of droplets at fog onset in the Paris metropolitan area are (1) lack of mixing in the surface layer (typically wind speed <0.5 ms?1), (2) relative humidity exceeding 90 % throughout the residual layer, (3) low cooling rate in the surface layer (typically less than ?1 °C per hour on average) due to weak radiative cooling (0 to ?30 Wm?2) and near zero sensible heat fluxes, and (4) a combination of the three factors listed above during the critical phase of droplet activation preventing the transfer of cooling from the surface to the liquid layer. In addition, we found some evidence of contrasted aerosol growth by deliquescence under high relative humidity conditions in the four events, possibly associated with the chemical nature of the aerosols, which could be another factor impacting droplet activation. 相似文献
7.
针对2011年12月初北京及华北持续近一周的严重大雾天气这一热点事件,从城市群大雾过程气溶胶区域影响的视角,基于"973"项目"北京及周边地区大气-水-土环境污染机理与调控原理"的研究工作,就北京及周边地区大雾天气与大气气溶胶区域影响的关系等方面进行了讨论.研究表明,北京城市大雾前低空SO2和NO2浓度存在"积聚"与"突增"现象.北京及周边地区冬季雾日数和气溶胶光学厚度则呈正相关,并具有"同位相"的年际变化趋势.研究同时发现北京及其南部周边的冬季气溶胶高值区呈南北向带状分布,其与北京周边居民户数高值区有所吻合,反映了冬季北京城市气溶胶颗粒物的远距离影响源区及大尺度输送效应.统计分析指出,冬季北京气溶胶颗粒物PM10、PM2.5主要影响成分是SO2和NOX,且有关研究也表明,电厂、采暖和工业面源是SO2的三大本地排放源,而机动车、电厂、工业为NOX的三大本地排放源,上述大气PM10、PM2.5主成分污染源亦与雾水样本化学分析结果相吻合,即冬季由于燃煤在生活能源中的比例较大,北京雾水中硫元素和碳元素的含量都较高.因此,北京冬季大雾不仅与北京城区气溶胶及其污染排放影响存在相关关系,而且与北京周边天津、河北、山东等地气溶胶及大气污染物的远距离输送和气溶胶区域影响效应有着重要的联系.因此,北京雾霾天气及相关大气污染的治理工作首先要着眼于局地污染物的减排,但同时如何做好区域大气污染的协同治理也是不容忽视的问题. 相似文献
8.
Thierry Bergot 《Pure and Applied Geophysics》2007,164(6-7):1265-1282
Short-term forecasting of fog is a difficult issue which can have a large societal impact. Fog appears in the surface boundary
layer and is driven by the interactions between land surface and the lower layers of the atmosphere. These interactions are
still not well parameterized in current operational NWP models, and a new methodology based on local observations, an adaptive
assimilation scheme and a local numerical model is tested. The proposed numerical forecast method of foggy conditions has
been run during three years at Paris-CdG international airport. This test over a long-time period allows an in-depth evaluation
of the forecast quality. This study demonstrates that detailed 1-D models, including detailed physical parameterizations and
high vertical resolution, can reasonably represent the major features of the life cycle of fog (onset, development and dissipation)
up to +6 h. The error on the forecast onset and burn-off time is typically 1 h. The major weakness of the methodology is related
to the evolution of low clouds (stratus lowering). Even if the occurrence of fog is well forecasted, the value of the horizontal
visibility is only crudely forecasted. Improvements in the microphysical parameterization and in the translation algorithm
converting NWP prognostic variables into a corresponding horizontal visibility seems necessary to accurately forecast the
value of the visibility. 相似文献
9.
Implementation of a Single-Column Model for Fog and Low Cloud Forecasting at Central-Spanish Airports 总被引：1，自引：0，他引：1
Operations at Central-Spanish airports are often, especially in winter, affected by visibility reduction. The Instituto Nacional de Meteorología (INM), the Spanish Weather Service, has developed a single-column model (SCM) in order to improve short-term forecasts of
fog, visibility and low-clouds. The SCM, called H1D, is a one-dimensional version of the HIRLAM limited-area model. It is
operationally run for three airports in the region: Madrid-Barajas, Almagro and Albacete-Los Llanos. Since SCMs cannot deal
with horizontal heterogeneity, the terms that depend on the horizontal structure of the atmosphere are estimated from the
outputs of the three-dimensional (3-D) model and introduced into the SCM as external forcings. The systematic analysis of
the meteorological situations has evidenced the existence of a close relationship between fog formation and the presence of
drainage winds in the region. Since the 3-D model docs not have the necessary resolution to correctly simulate the main features
of the drainage flow caused by the complex topography in the proximity of Madrid-Barajas, it cannot provide the SCM with the
correct forcings. This problem has been partially overcome through the introduction of a module that, under certain conditions,
substitutes the values computed from the 3-D model outputs by others that are based on a conceptual model of the phenomenon
and have been empirically derived from climatological knowledge. This module improves the H1D verification scores for the
basic meteorological variables—wind, temperature and humidity—and reduces the false alarm rate in fog forecast. 相似文献
10.
Seasonal and annual trends of changes in rainfall, rainy days, heaviest rain and relative humidity have been studied over the last century for nine different river basins in northwest and central India. The majority of river basins have shown increasing trends both in annual rainfall and relative humidity. The magnitude of increased rainfall for considered river basins varied from 2–19% of mean per 100 years. The maximum increase in rainfall is observed in the Indus (lower) followed by the Tapi river basin. Seasonal analysis shows maximum increase in rainfall in the post‐monsoon season followed by the pre‐monsoon season. There were least variations in the monsoon rainfall during the last century and winter rainfall has shown a decreasing trend. Most of the river basins have experienced decreasing trends in annual rainy days with a maximum decrease in the Mahanadi basin. The heaviest rain of the year has increased from 9–27 mm per 100 years over different river basins with a maximum of 27 mm for the Brahamani and Subaranrekha river basins. A combination of increase in heaviest rainfall and reduction in the number of rainy days suggest the possibility of increasing severity of floods. Such information is useful in the planning, development and management of water resources in the study area. Further, the majority of river basins have also experienced an increasing trend in relative humidity both on seasonal and annual scales. An increase in annual mean relative humidity for six river basins has been found in the range of 1–18% of mean per 100 years, while a decrease for three river basins from ? 1 to ? 13% of mean per 100 years was observed, providing a net increase in the study area by 2·4% of mean per 100 years. It is understood that an increase in areal extent of vegetation cover as well as rainfall over the last century has increased the moisture in the atmosphere through enhanced evapotranspiration, which in turn has increased the relative humidity. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
11.
12.
The variation of potential gradient in mist, haze, and fog has been studied. During the formation of these hydrometers the
potential gradients were found to increase. Large positive potential gradients were observed during dense fog conditions.
Possible charge generation mechanisms responsible for these potential gradients during fog formation are discussed. 相似文献
13.
Microphysical Observations and Mesoscale Model Simulation of a Warm Fog Case during FRAM Project 总被引：3，自引：0，他引：3
The objective of this work is to apply a new microphysical parameterization for fog visibility for potential use in numerical
weather forecast simulations, and to compare the results with ground-based observations. The observations from the Fog Remote
Sensing And Modeling (FRAM) field which took place during the winter of 2005 – 2006 over southern Ontario, Canada (Phase I)
were used in the analysis. The liquid water content (LWC), droplet number concentration (Nd), and temperature (T) were obtained from the fog measuring device (FMD) spectra and Rosemount probe, correspondingly. The visibility (Vis) from a visibility meter, liquid water path from microwave radiometers (MWR), and inferred fog properties such as mean volume
diameter, LWC, and Nd were also used in the analysis. The results showed that Vis is nonlinearly related to both LWC and Nd. Comparisons between newly derived parameterizations and the ones already in use as a function of LWC suggested that if models can predict the total Nd and LWC at each time step using a detailed microphysics parameterization, Vis can then be calculated for warm fog conditions. Using outputs from the Canadian Mesoscale Compressible Community (MC2) model,
being tested with a new multi-moment bulk microphysical scheme, the new Vis parameterization resulted in more accurate Vis values where the correction reached up to 20 –50%. 相似文献
14.
The relationship between liquid water content (LWC) and visibility (VIS) in a fog was examined by a field measurement of LWC values at a clean location of the meteorological observatory Sodankylä (Finland) and in a polluted region at the meteorological observatory Mile?ovka (Czech Republic). Furthermore, the use of a simple regression fog model to determine LWC from VIS is examined by comparing well-known relationships with the measurement results. The results show that the verbal characterization of environment (clean, mild polluted, polluted) is insufficient to calculate the LWC values from visibility. It is necessary to establish an additional criterion based on quantitative fog characteristics or to determine the site-related equation from the previous LWC and VIS measurement. 相似文献
15.
Fog Research: A Review of Past Achievements and Future Perspectives 总被引：20，自引：0，他引：20
I. Gultepe R. Tardif S. C. Michaelides J. Cermak A. Bott J. Bendix M. D. Müller M. Pagowski B. Hansen G. Ellrod W. Jacobs G. Toth S. G. Cober 《Pure and Applied Geophysics》2007,164(6-7):1121-1159
The scientific community that includes meteorologists, physical scientists, engineers, medical doctors, biologists, and environmentalists
has shown interest in a better understanding of fog for years because of its effects on, directly or indirectly, the daily
life of human beings. The total economic losses associated with the impact of the presence of fog on aviation, marine and
land transportation can be comparable to those of tornadoes or, in some cases, winter storms and hurricanes. The number of
articles including the word ``fog' in Journals of American Meteorological Society alone was found to be about 4700, indicating
that there is substantial interest in this subject. In spite of this extensive body of work, our ability to accurately forecast/nowcast
fog remains limited due to our incomplete understanding of the fog processes over various time and space scales. Fog processes
involve droplet microphysics, aerosol chemistry, radiation, turbulence, large/small-scale dynamics, and surface conditions
(e.g., partaining to the presence of ice, snow, liquid, plants, and various types of soil). This review paper summarizes past
achievements related to the understanding of fog formation, development and decay, and in this respect, the analysis of observations
and the development of forecasting models and remote sensing methods are discussed in detail. Finally, future perspectives
for fog-related research are highlighted. 相似文献
16.
Analysis of Fog Probability from a Combination of Satellite and Ground Observation Data 总被引：1，自引：0，他引：1
The Cloud Type product, developed by the Satellite Application Facility to support to nowcasting and very short-range forecasting
(SAFNWC) of EUMETSAT and based on Météosat-8/SEVIRI, identifies cloud categories, and especially low and very low clouds which
are first estimates of areas where fog is likely to occur. This cloud type is combined with precipitation information from
radar data and with hourly diagnostic analyses of 2-metre relative humidity and 10-metre wind to elaborate an hourly analysis
of fog probability. This analysis provides four levels of fog probability with a 3-kilometre horizontal resolution: No risk,
low-level risk, medium-level risk and high-level risk. An evaluation of such fog probability analyses versus a one-year set
of French hourly SYNOP reports shows encouraging results (potential of detection = 0.73 for low and medium and high-level
risks), even if false alarm ratios remain high. Most of the non-detections occur at twilight and are due to satellite non-detections.
Eventually, we show case studies that clearly illustrate the high potential of the method. 相似文献
17.
A. H. C. Stalenhoef 《Pure and Applied Geophysics》1972,98(1):213-226
Summary Transmissometer records at Schiphol-Airport, Amsterdam have been analyzed to show the frequencies of visibility changes, in periods between 1 and 16 minutes, on occasions that the visibility is below 1000 metres for at least 30 minutes. Tables are presented for the frequencies of visibility changes in shallow and in deep fog, both for increasing and decreasing visibilities, with an initial visibility in the range of 60–1000 metres (the lower limit of this range is connected with the length of the transmissometer-baseline in use).In deep fog the probability of a visibility change surpassing 25 percent is about 1 percent after 1 minute and 20 percent after 16 minutes if the initial visibility is between 100 and 200 metres. The corresponding figures in shallow fog are 7 and 55 percent. If the initial visibility is between 200 and 400 metres, the corresponding figures in deep fog are 5 and 45 percent and in shallow fog 26 and 84 percent. 相似文献
18.
Visibility and Incidence of Respiratory Diseases During the 1998 Haze Episode in Brunei Darussalam 总被引：6，自引：0，他引：6
A.K. Yadav K. Kumar Awg Makarimi bin Hj Awg Kasim M.P. Singh S.K. Parida M. Sharan 《Pure and Applied Geophysics》2003,160(1-2):265-277
— Air pollution episodes as a result of forest fires in Brunei Darussalam and neighbouring regions have reached hazardous levels in recent years. Such episodes are generally associated with poor visibility and air quality conditions. In the present study, data on PM10 (particulate matter of size less than 10 microns) and CO in Brunei Darussalam have been considered to study the incidence of respiratory diseases whereas data on relative humidity (RH) in addition to PM10 have been used to explain the visibility with a particular emphasis on haze episode during 1998.¶Initial exploratory analysis indicates significant correlation of visibility with PM10 and RH. An attempt has been made to explain visibility on the basis of PM10 and RH using multiple linear regression analysis. The regression model shows that PM10 and RH are two significant factors affecting the visibility at a given site. Further, canonical correlation, a multivariate method of analysis, has been used to explain the incidence of respiratory diseases as a function of air quality during the haze period. The results indicate that PM10 and CO levels during the haze period have a significant bearing on the incidence of respiratory diseases (Asthma, Acute Respiratory Infections and Influenza (ARII)). 相似文献
19.
Based on the visibility analysis data during November 2009 through April 2010 over North America from the Aviation Digital Database Service (ADDS), the performance of low visibility/fog predictions from the current operational 12?km-NAM, 13?km-RUC and 32?km-WRF-NMM models at the National Centers for Environmental Prediction (NCEP) was evaluated. The evaluation shows that the performance of the low visibility/fog forecasts from these models is still poor in comparison to those of precipitation forecasts from the same models. In order to improve the skill of the low visibility/fog prediction, three efforts have been made at NCEP, including application of a rule-based fog detection scheme, extension of the NCEP Short Range Ensemble Forecast System (SREF) to fog ensemble probabilistic forecasts, and a combination of these two applications. How to apply these techniques in fog prediction is described and evaluated with the same visibility analysis data over the same period of time. The evaluation results demonstrate that using the multi-rule-based fog detection scheme significantly improves the fog forecast skill for all three models relative to visibility-diagnosed fog prediction, and with a combination of both rule-based fog detection and the ensemble technique, the performance skill of fog forecasting can be further raised. 相似文献