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The current study investigates the recurrence of fog phenomenon in Northern Borders area of Saudi Arabia according to the Synoptic International Scale in terms of its types, causes, and the annual, seasonal, and monthly recurrence. The study also classifies the climate conditions co-occurring with the formation of fog in the area, as well as the potential traffic and health risks ensuing. For data resources, the researcher relies on the monthly weather data of climate phenomenon in Northern Borders in the areas of Tiraifand Arar in the period 20002015. The study adopts the descriptive-analytic approach and some statistical models for achieving the aims of the research.The research findings indicated that fogs in Tiraif occur most in the months of December and January, whereas in Ararfog occurs in November and February, the matter that led to numerous health and traffic problems in the area. Hence, the research recommends that the authors concerned take the measures and precautions required for dealing with accidents resulting from the fog. Introduction Fog is formed when water vapour is condensed on the surface of the atmosphere in the form of small drops the diameter of each is no more than 100 micron. Because of the smallness of these drops, they remain suspended in the air, the thing that limits visibility hence causing traffic accidents. In fog days, there are more incidents of traffic accidents which aggravates the economic situation since they necessitate exceptional measures and continuous lighting of streets ,to say nothing of the cost of repairs due to damages incurred. Visibility, on fog formation, is correlated with the rate of watervapour in the air: the higher the relative humidity, the less the visibility. Fog is different from Shaboorain that visibility in fog is less than 1000 metres, whilst in Shaboora, or light fog, it is more than 1000 metres (NaumanShahata, 135:1998).Problem of the Study The Northern Borders area of Saudi Arabia is characterized by annual occurrences of fog formations, the thing that reflects on man’s life and health. Fog is one of the causes of chest diseases. Further, it blocks visibility, which leads to numerous traffic accidents since the suspended water drops work to disperse the light, which sometimes causes visibility to be as low as a few metres, thus arresting traffic and causing accidents. Therefore, this fog phenomenon has become the concern of traffic and transport system planners in most of world areas including the Northern Borders of Saudi Arabia. Aims of the Study 1. Identifying the types of fog conditions according to the Synoptic Scale in Northern Borders area. 2. Determining the fog recurrence in the area. 3. Specifying the weather conditions attending fogs in the area. 1 Associate professor of geography and climate,Department of Geography, Faculty of Arts ,Nourah bint Abdulrahman University,dr.motirh@hotmail.com, Mobile:00966-541167114 Motirh Kueetm Al-Mutairi 65 4. Finding out about the connection between the fog and traffic accidents, and its impact on human health in the area. Methodology The study adopted the descriptive-analytic approach, using the statistical modes following:  The Descriptive Statistics for calculating fog frequency and the means of climate conditions accompanying fog.  The One-way Anovaanalysis for specifying the differences in fog frequency in the area of study.  The K-Mean Cluster analysis for classifying fog in the study areas according to rainfall and the climate conditions accompanying.  The use of Pearson Correlation coefficient for identifying the correlation between the fog phenomenon and the number of traffic accidents as well as the rates of chest infections.  Drawing and analyzing the GISmaps, using Arc Map. Data Resources The monthly climate data for the weather phenomena in the areas of Tiraifand Ararin the period 20002015 has been provided by the General Directorate for Meteorology and Environmental Protection, Department of Information Supply, for studying the fog phenomenon and the distribution thereof in Northern Borders area (Table 1). Station No. station latitude (north),) longitude (east)) Height (m) Tiraif 40356 31.69 38.73 852 Arar 41357 30.91 41.14 555 The Study Area The area lies to the north of Saudi Arabia as a northwest, south-east strip between latitudes 29,37’17” and 31,41’16” to the north, and longitudes 38,44’22” and 43,29’41” to the east. It is bordered from the north by Iraq and Jordan; from the east by Iraq; by the Eastern Region and Qaseemfrom south, and by Aljoaf andHaelfrom the west (Figure 1). Administratively it is divided to: the main area of Ararand three provinces: Rafhaa, Tiraiff, andArar. The area is characterized by a tropical climate. Maximum summer temperatures are 46, turning to as low as a littlebelow zero in winter. The annual rainfall, however, is so low it does not exceed 10m. Figure 1: The study area 66 Journal of Geography and Earth Sciences, Vol. 5(1), June 2017 Definition of “Fog” The fog phenomenon can be defined as the “low visibilityin the air to less than, or equal to, 1000 metres, because of water droplets or snow particles suspended in the air.”The fog is a natural, climatic condition in the form of clouds coming close to ground surface, formed by warm air currents touching cold surfaces or vice versawhen cold air currents blow on warm surfaces. It is a form of condensation, containing minute water drops the diameter of each is no more than 1m. Fog dissipates at sunrise when air temperature begins to increase. It isthicker in cities than in rural areas due to dust and grime pollution where dust and grime cling to the water drops. As a rule, upon formation of fog, visibility becomes low which leads to accidents, particularly in the event of thick fogs. Owing to the risks involved in fogs, scientists have developed an international fog measure (from 0 to 9) relying on the naked eye for observation (Table 1-4) (Abu-alainain, 1985: 334-335). There is a number of factors that collectively work towards the formation of fog. These are: 1. The high level of humidity in the air. Fog is formed in relative-humidity areas, especially in bodies of water and dense vegetation. 2. Light winds that help speed up the process of air cooling. 3.Sufficient condensation molecules. 4. Clear weather leading to dispersion of earth radiation which cools the air down to a dew form or below until condensation occurs (Iessa, 2006: 124-125). Table (2): visibility through the various types of fog Fog International number Maximum distance kind of see where things clearly Opaque fog 0 50 m Heavy fog 1 200 m Show is very poor 2 500 m Show poor 3 1 km Rusk (Ajaj) 4 2 km Show weak 5 4 km Show moderate 6 10 km Opaque fog 7 20 km Heavy fog 8 50 km Show is very poor 9 More than 50 km Source: Abu-alainain, 1985: 334-335. Causes of Fog Formation Fog occurrence is correlated with the relative humidity, temperature, wind velocity, cloud cover, and weather thermal stability. The dew point occurs when air temperature is saturated with water vapour. This takes place when air, or the water drops clinging thereto, takes in more humidity. Water vapour enters the air in different ways: either through evaporation from water bodies or wet ground because of heat from sunlight, or because of water vapour resulting from vegetation, or when a cold or dry air current passes above a warm water surface. Water vapour may also enter the atmosphere by way of some human activities such as industry and transport (Nolan, 2010: 1-5).When air temperature nears the dew point, a little humidity condenses on the particles suspended in the air ,such as dust and snow, and turns into liquid state the matter that results in the fog or shaboora or dew phenomenon and may lead to cloud formation. On the whole, fog begins to form when air temperature is warmer than dew point (Environment Canada, 2014:65). Fog is formed when water vapourso condenses in the atmosphere that it takes the form of water drops or snow crystals, becoming visible and having a basis linked to the ground. Therefore, air saturation with vapour, and the condensation of minute water particles are two major conditions for fog formation (Nolan, 2010: 1-5). Thickness of fog layer is measured according to how higher its peak than the sea or ground level. Motirh Kueetm Al-Mutairi 67 This thickness can be more accurately measured by how high the warmest or driest mass of air which is above the cold air layer closest to the ground surface. This varies according to the air pressure above, since the fog mass can be dense if the air pressure above is high. Fog mass can also be less dense if the air pressure above begins to drop (Environment Canada, 2014: 65). Fog formation and density on ground surface is not easily predictable, since it does not have to occur in completely quiet winds. Some fog cases, studied at the end of the 18th century, were associated with troubled winds (Gultepe, 2007: 1122). Analysis and Discussion Types of Fog in Northern Borders Area: Outer land fog comes in various types, according to the location it is formed in: for example, the valleys fog, the mountain slopes fog, and cities fog. Peter Nolan (2010) classifies fog according to the manner it is formed: it can occur as a result of the air being saturated with water vapour, or through cooling the air until it has reached saturation point. So the agents causing air saturation with vapour, the speed of evaporation, and the factors affecting the cool air that is close to ground surface, are the determinants for classifying fog types which are as follows: A. Fog of Evaporation: This includes: 1. Steam Fog It is a fog resultant from intense evaporation from water to relatively cool air, so the state turns from saturation to condensation to fog. Evaporation fog can be noticed over water bodies and in tropical areas. Sometimes it occurs in warm areas or wet lands, or immediately after rains as is the case in N

Fog: Its Causes, Types, and Dangers in Saudi Northern Borders (A Climatic Study)