The spatial and temporal variability of fog and its relation to fog oases in the Atacama Desert, Chile

Fog has been studied in the Atacama Desert of Chile for the past ten years. This paper analyzes its temporal and spatial variability, relying in part on satellite images (GOES) to analyze the frequent orographic fog and the low cloud deck (stratocumulus, Sc) that generates advective fog in the area. Fog water fluxes were measured with Standard Fog Collectors (SFC). Field trips and observers provided information on cloud top and base and the presence of fog. Vegetation in fog oases were used to confirm the results of these surveys.The Sc moves onshore into the continent with different intensities depending on season and time of day. The maximum spatial extent occurs during winter and at night. Fog is frequent in the coastal cliffs, where fog water fluxes of 7.0 L m^− 2 day^− 1 were measured using a SFC. It is less frequent 12 km inland, where the collection rates were less than 1 L m^− 2 day^− 1. The height of the fog collector above the ground affected the collection rate. The highest fog water fluxes were recorded at Alto Patache at altitudes of between 750 and 850 m a.s.l. The growth or thickness of the cloud is important in the collection of fog water. The information that GOES provides on the altitude of the top of low clouds is used to analyze this factor. Fog oases are described and analyzed in relation to how the geographical location of fog influences the growth of vegetation.     

Temporal characteristics and fog water collection during summer in Tenerife (Canary Islands, Spain)

The study of fog dynamics in the island of Tenerife began in 1993 at six sites. The analysis of the relationship between fog and several meteorological parameters was conducted at the site located at Anaga. Anaga is located at the summit of a mountain range, at an altitude of 842 m and 3.5 km away from the north-western coastline of the island. The study uses hourly data of the three summer months (June, July and August) that were collected over a period of nine years — from 1996 to 2005. The mean summer (June–August) rainfall was found to be 21.2 mm whilst the total volume of fog water collected was 879.9 l m^− 2; the daily average fog water collection was 9.5 l m^− 2 day^− 1, and the hourly average about 0.4 l m^− 2 h^− 1. Although these amounts were recorded with wind speeds of between 8 and 12 m s^− 1, the correlation between water collected and wind speed is not statistically significant. In spite of this, the volume of fog water collected and wind speed showed a very distinct daily behavioural pattern, their frequency and speed reaching their minimum at 12 a.m. and their maximum from 7 p.m. to 8 a.m. GMT. The importance of this research is that it shows that the fog in the Canary Islands occurs more frequently and makes a more significant contribution to the growth of vegetation in the summer (the dry season) than in the winter, when fog accompanies rainfall.     

The climate of the coast and fog zone in the Tarapacá Region, Atacama Desert, Chile

In the Atacama Desert, the narrow littoral plain and the adjacent mountain range have a unique climate. This area is locally called the “coastal desert with abundant cloudiness”, and extends from the coastline up to an elevation of 1000 m. The climate is designated as being BWn according to Köppen's Climate Classification as adapted for Chile. In the original classification the acronym (Bn) is used for foggy environments. Toward the east a “normal desert” climate (BW) is found. This is known as one of the most extreme deserts of the world. In the BWn areas there are meteorological differences between low and high elevation zones. The climate of the coastal plains and the mountains is described in this paper in order to show that there is an area where the climate differs from those classified as BWn and BW in the Chilean Climate Classification. This area is located between 650 and 1200 m a.s.l. and contains several fog oases or lomas vegetation, rich in biodiversity and endemism.The weather is warmer near sea level, with an annual average temperature of 18 °C. At high elevation sites like Alto Patache, the temperature decreases at a rate of 0.7 °C for every 100-m increase in altitude. The average annual minimum temperature often approaches 1 °C in winter, while the mean annual temperature range is significant (8.3 °C in Los Cóndores). The mean monthly relative humidity in Alto Patache is over 80%, except during the summer months. During autumn, winter and spring high elevation fog is present in the study area at altitudes ranging from 650 m up to 1060 m, giving annual water yields of 0.8 to 7 L m^− 2 day^− 1. If vegetation is used as an indicator, the foggy zone lies between 650 m a.s.l. and 1200 m a.s.l. About 70% of the mountain range experiences the foggy climate, as opposed to the coastal plains that are characterized by a cloudy climate.     

Ion fluxes from fog and rain to an agricultural and a forest ecosystem in Europe

The deposition fluxes of inorganic compounds dissolved in fog and rain were quantified for two different ecosystems in Europe. The fogwater deposition fluxes were measured by employing the eddy covariance method. The site in Switzerland that lies within an agricultural area surrounded by the Jura mountains and the Alps is often exposed to radiation fog. At the German mountain forest ecosystem, on the other hand, advection fog occurs most frequently. At the Swiss site, fogwater deposition fluxes of the dominant components SO₄²⁻ (0.027 mg S m⁻² day⁻¹), NO₃⁻ (0.030 mg N m⁻² day⁻¹) and NH₄⁺ (0.060 mg N m⁻² day⁻¹) were estimated to be <5% of the measured wet deposition (0.85, 0.70 and 1.34 mg m⁻² day⁻¹, respectively). The corresponding fluxes at the forest site (0.62, 0.82 and 1.16 mg m⁻² day⁻¹, respectively) were of the same order of magnitude as wet deposition (1.04, 1.01 and 1.36 mg m⁻² day⁻¹), illustrating the importance of fog (or occult) deposition. Trajectory analyses at the forest site indicate significantly higher fogwater concentrations of all major ions if air originated from the east (i.e. the Czech Republic), which is in close agreement with earlier studies.     

Pollutant concentrations in fog and low cloud water at selected sites of the Czech Republic

In this paper, the basic composition of fog and low cloud water are presented, resulting from the analyses of water samples from 111 fog/cloud events. The samples were collected at five sites located in various regions of the Czech Republic. Two sampling sites are in mountainous regions and three sites represent various urban areas. The mountain stations are located in two regions of the Czech Republic with different industry types. At all the sites, active fog collectors were employed. In the water samples, the conductivity, acidity (pH), cations (H⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺) and anions (F⁻, Cl⁻, NO₃⁻, SO₄²⁻) were determined.A mean pH value of about 4.5 was obtained at mountain sites whereas the measurements in urban areas showed mean pH values from 4.9 to 6.4. The mean conductivity values in the samples from the two mountain stations were 137 and 191.5 μS cm⁻¹. The samples from urban sites showed mean values between 127.7 and 654.4 μS cm⁻¹. The maximum concentration means for the three dominant pollutants (expressed by the ratio mountain sites/urban sites) are 32.9/99.6 mg l⁻¹ for NO₃⁻, 32.5/192.9 mg l⁻¹ for SO₄²⁻ and 18.5/52.7 mg l⁻¹ for NH₄⁺. As expected, we found higher ion concentrations in the northern part of the Czech Republic where larger numbers of lignite-burning power plants, chemical factories and opencast lignite mines are located. A decrease in ion concentrations was observed at higher altitude sites, probably reflecting at least in part higher liquid water contents at these locations.     

The implementation of fog water collection systems in South Africa

Two fog water collection systems (FWCS) have been implemented in South Africa. Both are located in areas where communities experience acute water shortages but which are prone to frequent fog episodes. The first was located at a high elevation site at the Tshanowa Junior Primary (JP) School in the Soutpansberg located in the Northern Province and the other near a small rural community at Lepelfontein along the West Coast. The former represents a mountainous site, while the latter is located on a low level coastal plain. The principal aim of the projects was to implement operational FWCSs to supply the communities with water. During the period 1999 to 2001 the total recorded cloud water yields at the Tshanowa JP School and Lepelfontein water collection sites were in the region of 72 422 and 148 691 l, respectively. This is equivalent to just over 2 l m⁻² day⁻¹ at the Tshanowa JP School and 4.6 l m⁻² day⁻¹ at the Lepelfontein site. Despite the relatively low average daily yields recorded, the total water volume collected on a particular day may be considerable. In fact, at both sites the maximum daily yield exceeded 3800 l. Fog deposition accounted for around 25% and 88% of the total water yield measured at the Tshanowa JP School and Lepelfontein sites, respectively. Both experiments indicated that fog water collection holds considerable potential as an alternative water source in the mountainous regions and along the West Coast of South Africa.     

Thermal effect of the sea breeze on the structure of the boundary layer and the heat budget over land

The daytime boundary-layer heating process and the air-land heat budget were investigated over the coastal sea-breeze region by means of observations over the Sendai plain in Japan during the summer. In this area, the onset of the sea breeze begins at the coast around 0900 LST, intruding about 35 km inland by late afternoon. The cold sea breeze creates a temperature difference of over 10°C between the coastal and inland areas in the afternoon. On the other hand, warm air advection due to the combination of the counter-sea breeze and land-to-sea synoptic wind occurs in the layer above the cold sea breeze in the coastal region. Owing to this local warm air advection, there is no significant difference in the daytime heating rate over the entire atmospheric boundary layer between the coastal and inland areas. The sensible heat flux from the land surface gradually decreases as distance from the coastline increases, being mainly attributed to the cold sea breeze. The daytime mean cold air advection due to the sea breeze is estimated asQ _adv ^local =–29 W m^–2 averaged over the sea breeze region (035 km from the coastline). This value is 17% of the surface sensible heat fluxH over the same region. The results of a two-dimensional numerical model show that the value ofQ _adv ^local /H is strongly affected by the upper-level synoptic wind direction. The absolute value ofQ _adv ^local /H becomes smaller when the synoptic wind has the opposite direction of the sea breeze. This condition occurred during the observations used in the present study.     

Exploring fog as a supplementary water source in Namibia

Namibia is an arid country where many rural and urban centres depend on ephemeral rivers for their water supply. These water sources are, however, limited and display seasonal salinisation. Fog occurs along the coast and extends for some distance inland, and it could be used as a source of drinking water. Data on groundwater salinisation and fog deposition were collected at villages of the indigenous communities and at the Gobabeb Training and Research Centre (GTRC) in the Central Namib Desert. Fog collection experiments were done with Standard Fog Collectors (SFCs) and 1-m² fog collectors made from the Raschel mesh that is used in SFCs from 1996 onwards. The results indicate that fog occurs throughout the year and that it has low major ion concentrations (chemical composition). The period of high fog deposition coincides with that of high groundwater salinity and would suit mixing of the two waters to provide water of good drinking quality to people in these areas. In conclusion, fog is a viable source of water in the Namib and could supplement traditional sources in rural settlements and perhaps also in urban water supply schemes in this region as in other parts of the world where it is used as a source of drinking water.

Full-size image (24K)

Fog measurements at the site “Falda Verde” north of Chañaral compared with other fog stations of Chile

Fog collection data registered through a Standard Fog Collector (SFC) installed by a local fishermen's association at a height of 600 m at the “Falda Verde” site, north of the Chilean harbor Chañaral (26°17′S/70°36′W), from November 1998 to November 2000, are analyzed. Trying to give new lights on the dynamics of fog along the Chilean northern coast, this article compares, for the first time, the data obtained at Falda Verde with those obtained at five other Chilean fog stations. The total time period runs from 1987 to 2001. A mean of 1.46 l/m²/day was registered at the Falda Verde site after 2 years of measurements, one of the lowest yields along the north Chilean coast. After a brief historical recapitulation of fog researches in the study area, geographical explanations of the water yields obtained in different sites are discussed. The annual mean collection from Cerro Moreno and Paposo shows a clearly different behavior from all other sites, showing a greater stability throughout the year. Other stations have a marked difference between extreme seasons. Alto Patache yields, if not the best in Chile, are very high and offer unexpected possibilities for future applications in the coast. Stations located away from the seashore (Cerro Guatalaya) are clearly less productive. Ocean proximity, altitude, south and southwest orientations of the coastal ranges and local relief explain some of the differences noted.     

Fog and rain water chemistry at Mt. Fuji: A case study during the September 2002 campaign

Measurements of fog and rain water chemistry at the summit of Mt. Fuji, the highest peak in Japan, as well as at Tarobo, the ESE slope of Mt. Fuji in September 2002. The pH of fog and rain water sampled at Mt. Fuji varied over a range of 4.0–6.8. Acidic fogs (pH < 5.0) were observed at the summit when the air mass came from the industrial regions on the Asian continent. The ratio of [SO₄²⁻]/[NO₃⁻] in the fog water was lower at Tarobo than at the summit. High concentrations of Na⁺ and Cl⁻ were determined in the rain water sampled at the summit, possibly because of the long-range transport of sea-salt particles raised by a typhoon through the middle troposphere. The vertical transport of sea-salt particles would influence the cloud microphysical properties in the middle troposphere. Significant loss of Mg²⁺ was seen in the rain water at the summit. The concentrations of peroxides in the fog and rain water were relatively large (10–105 μM). The potential capacity for SO₂ oxidation seems to be strong from summer to early autumn at Mt. Fuji. The fog water peroxide concentrations displayed diurnal variability. The peroxide concentrations in the nighttime were significantly higher than those in the daytime.     

Changes of cloud water chemical composition in the Western Sudety Mountains, Poland

The changing chemical composition of cloud water and precipitation in the Western Sudety Mountains are discussed against the background of air-pollution changes in the Black Triangle since the 1980s until September 2004. A marked reduction of sulphur dioxide emissions between the early 1990's and the present (from almost 2 million tons to around 0.2 million tons) has been observed, with a substantial decline of sulphate and hydrogen concentration in cloud water (SO₄²⁻ from more than 200 to around 70 μmol l^− 1; H⁺ from 150 to 50 μmol l^− 1) and precipitation (SO₄²⁻ from around 80 to 20–30 μmol l^− 1; H⁺ from around 60 to 10–15 μmol l^− 1) samples. At some sites, where fog/cloud becomes the major source of pollutants, deposition hot spots are still observed where, for example, nitrogen deposition can exceed 20 times the relevant critical load. The results show that monitoring of cloud water chemistry can be a sensitive indicator of pollutant emissions.     

Estimation of fog deposition on epiphytic bryophytes in a subtropical montane forest ecosystem in northeastern Taiwan

The fog meteorology, fog chemistry and fog deposition on epiphytic bryophytes were investigated from July 2000 to June 2001 in the Yuanyang Lake forest ecosystem. The elevation of the site ranges from 1650 to 2420 m, at which the high frequency of fog occurrence throughout the year has been thought to be of benefit to the establishment of the primary Taiwan yellow cypress forest [Chamaecyparis obtusa var. formosana (Hayata) Rehder] and to the extensive growth of the epiphytic bryophytes. A weather station including a visibility sensor and an active fog collector was installed for fog meteorological and chemical study. The fog deposition rate on epiphytic bryophytes was estimated by measuring the increase rate in plant weight when exposed to fog. Average fog duration of 4.7 and 11.0 h per day was measured in summer months (June to August) and the rest of the year, respectively. November 2000 was the foggiest month in which the average fog duration reached 14.9 h per day. The ionic composition of fog water revealed that the area was less polluted than expected from literature data. The in situ exposure experiments done with the dominant epiphytic bryophytes showed an average fog deposition rate of 0.63 g H₂O g⁻¹ d. w. h⁻¹, which approximated 0.17 mm h⁻¹ at the stand scale. The nutrient fluxes estimated for February 2001 showed that for all ions, more than 50% of the ecosystem input was through fog deposition. These results demonstrate the importance of epiphytic bryophytes and fog deposition in nutrient cycling of this subtropical montane forest ecosystem. The incorporation of fog study in the long-term ecosystem research projects is necessary in this area.     

The degree of Cl-loss for the particulate matter (PM) and fog water sampled at the same air mass at the Hachimantai mountain range in northern Japan

It is well known that sea-salt aerosols in particulate matter (PM) react with acids such as H₂SO₄ and HNO₃ during transportation and thereby lose chloride ions (Cl-loss). The PM and fog were sampled concurrently at different altitudes in the Hachimantai mountain range, northern Japan. The PM and fog sampled at different altitudes had nearly identical properties for the ion components. However, the PM was in a Cl-depleted state (more than 80% of all samples), but the fog water was not in so Cl-depleted state (less than 29%). As a result, it could be explained that this phenomenon caused because the fog droplets took up the gaseous state HCl other than sea-salt PM. After all Cl^- in the fog water recovered and was rather rich compared with the sea-salt or the PM by the uptake of the gaseous state HCl. Moreover, it was found that for PM_coarse(2.5 < D < 10), 86% of the acid (H₂SO₄ and HNO₃) was consumed for Cl-loss reactions and/or for dissolution of Ca and Mg in soil particles.     

A satellite-based climatology of fog and low-level stratus in Germany and adjacent areas

A 10-year fog climatology of Germany and adjacent areas, based on NOAA-Advanced Very High-Resolution Radiometer (AVHRR) data, is presented. Maximum fog frequency is obtained for the Lake Constance area; minimum fog occurrence, accounting for basins and river valleys, is located in the Lower Rhine area. This is a transition zone between coastal advection fog and the more continental radiation fog of the lower mountain range. Fog persistence is estimated by a comparison of night and day maps. Using the bispectral approach of Nakajima and Nakajima [J. Atmos. Sci. 52, (1995) 4043], the potential of weather satellite data for climatologies of fog's optical and microphysical properties is examined. Maps of fog optical depth, effective radius and liquid water path (LWP) are computed from well-illuminated noon images and the resulting data set is statistically evaluated. Typical features of advection fog are obtained for the coastal areas of the North and Baltic Seas, while the fog of the pre-Alpine basins reveals characteristics of continental radiation fog. The results are in general accordance with field observations of various sources.     

Local Meteorological and Synoptic Characteristics of Fogs Formed over Incheon International Airport in the West Coast of Korea

Fogs observed over Incheon international airport (IIA) in the west coast of Korea from January 2002 to August 2006 are classified into categories of coastal fog, cold sea fog, and warm sea fog based on the areal extent of the fogs and the difference between the air temperature (T) and the SST, i.e., cold sea fog if TSST = T-SST>0^oC and warm sea fog if TSST <0^oC. The numbers of coastal, cold, and warm sea fog cases are 64, 26, and 9. Coastal fogs form most frequently in winter, while cold sea fogs occur mostly in summer and warm sea fogs are observed from January to May but not in November and December. On average the air gets colder by 1.6^oC during the three hours leading up to the coastal fog formation, and an additional cooling of 1.1^oC occurs during the fog. The change in the dew point temperature (T_d) is minimal except during the fog (0.6^oC). Decreases in T for the cold and warm sea fogs are relatively smaller. The average T_d is higher than SST during the cold sea fog periods but this T_d is more than 4^oC higher than that for the corresponding non-fog days, suggesting that cold sea fogs be formed by the cooling of already humid air (i.e., T_d>SST). Increases of T_d are significant during the warm sea fog periods (1.4^oC), implying that efficient moisture supply is essential to warm sea fog formation. Four major synoptic patterns are identified in association with the observed fogs. The most frequent is a north Pacific high that accounts for 38% of cases. Surface or upper inversions are present in 77%, 69%, and 81% of the fog periods for coastal, cold, and warm sea fogs, respectively.     

近53年辽宁雾的时空分布及成因分析

利用1951～2003年辽宁12个代表站的雾资料,分析了雾的时空分布特征及形成条件。结果表明:辽宁年平均雾日地域分布呈现两高三低的形势。雾日的年际变化曲线较平稳,雾日最多的年份和最少的年份相差17d。沈阳与大连雾日变化相反,大连呈下降趋势,沈阳则在平稳中略有上升。辽宁大雾每个月都可形成,但沿海地区和内陆又有所差异,沿海地区主要出现在5～8月,而内陆地区主要出现在8～11月。雾日的天气形势可分为5～7种类型,其中以倒槽型、锋面气旋型、地形槽型、冷高压前部型最为典型。     

基于MTSAT卫星遥感监测的浙江省及周边海区大雾分布特征

利用日本静止气象卫星MTSAT逐时资料,综合地面气象观测数据,对浙江省及其周边海区陆地和海上2008—2012年的大雾进行了专题信息提取,并给出了浙江省陆域、周边海域0.05°×0.05°网格点的小时尺度的遥感大雾产品,结果表明:(1)基于MTSAT卫星观测数据,采用分级判识太阳高度角阈值和归一化大雾指数的方法,构建的浙江及其周边地区陆地和海上遥感大雾监测模型,大雾判识精度总体超过75%,基本满足使用需求。(2)浙江省陆域近5年大雾年平均累计为411.7 h,约占全年的4.7%,基本呈南多北少,山区多平原少的格局,其中浙江南部高山区、舟山和温州部分海岛及西部山区为大雾多发区,且大雾季节分布为冬秋季较多,春夏季较少,22时至09时是浙江省陆域大雾的高发时段,10时以后大雾逐渐消散,至后半夜、凌晨前后,大雾频次逐渐增多。(3)研究区海雾主要发生在大陆近海,呈现由近海向外海减少的空间格局,东海海域年大雾累计为311.7 h,以东海西南部地区大雾出现最多,浙江省沿海大雾的高发区位于温州海域及钱塘江口。研究区海域大雾具有明显的季节特征,主要表现为春季较多,夏季次之,秋冬季较少的分布格局,且海上主要受平流雾影响,大雾不易消散,持续时间较长。从各海区大雾发生频次从高到低依次为:东海东南部、台湾以东洋面、东海中东部、黄海西南部、东海中西部、台湾海峡、东海西北部、黄海东南部、东海西南部和东海东北部。     

江苏省雾的集中程度及其气候趋势研究

引入雾的集中期和集中度的方法,对江苏省59个地面观测站1961—2007雾的发生频次资料进行了分析研究,得出了近47 a来江苏雾的时空分布特征及其相关统计结果。研究表明,集中度和集中期能够明显地分辨江苏省雾的时空分布非均匀特性。江苏省雾集中度呈现南北高、中间低的特点;集中期在47 a中出现较大波动。采用EOF方法分别对雾日数、集中度和集中期的距平值进行分析,其第一特征向量表现为同相位;其中雾日数的第一时间系数在1980s前后出现峰值,集中度和集中期距平值的第一时间系数表现为先减小后增大的总体趋势。通过气候趋势系数的计算表明苏北地区除4站点外均呈上升趋势。     

沈大高速公路雾气候特征与气象要素分析

利用1958—2007年沈大高速公路沿线6站雾日资料对沈大高速公路雾的气候特征及气象要素进行分析。结果表明：沿海地区雾日偏多,且总体呈上升趋势,内陆地区雾日偏少,且呈下降趋势。内陆地区雾多出现在秋冬季,沿海地区多出现在夏季。雾多在凌晨至日出前后时段生成,日出后逐渐消散,持续时间多为1—3 h。相对湿度、气温、风速和风向对雾的预报有较好指示意义：当相对湿度在90%—100%时,春季气温为-5—15 ℃、夏季为16—24 ℃、秋季为-3~19℃、内陆冬季为-20~2 ℃,沿海冬季为-7~4 ℃范围内,内陆风速为0—3 m&#8226;s-1,沿海风速为0—6 m&#8226;s-1,且沿海地区为偏南风时,雾易发生。     

南海西北部一次海上海雾的微物理及化学特性分析

利用2017年3月MICAPS资料、欧洲气象中心再分析ERA-Interim数据及在南海西北部海上的海雾观测数据,分析了南海西北部一次海上海雾的微物理特征和雾水化学特性,并将海上海雾与南海岸边海雾进行对比分析。结果表明:此次海雾为南海偏南暖气流移至冷海面发生冷却并达到饱和而形成。海雾过程中气压与气温变化趋势相反,相对湿度不断增加,雾滴数浓度、液态含水量和平均直径的平均值分别为198 cm-3、0.116 g/cm3和5.6 μm。相比广东湛江东海岛和广东茂名博贺地区岸边海雾个例,本次海上海雾水汽充足,雾滴偏大。本次海雾属于酸性海雾,pH值变化范围为2.51~3.50,海雾后的雨水样本pH值则为4.05。海雾发生初期电导率比其它阶段高很多,说明海雾发生的初始阶段雾水溶解了大量的气溶胶。海上雾水中Na+和Cl-浓度最高,浓度分别为32 535 μmol/L和53 466 μmol/L,K+浓度远高于Mg2+和Ca2+,而东海岛岸边海雾相反。