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Meteorology classically defined as the science that deals with the phenomena of the atmosphere, especially weather and weather conditions, is a fairly new science that is practiced by Meteorologists. They are people who interpret weather information from local weather observers, balloons, satellites, and weather stations around the world. In more common vernacular, a Meteorologist reads weather maps, predicts and records weather from atmospheric occurrence. The part of Meteorology that will be discussed throughout this paper are: water vapor, precipitation types, cloud types, and fog types. It is important to understand these topics in order to understand how our project, building a fog machine, works and for us to efficiently understand the principles behind building one.
Water vapor is a common term that one probably understands as evaporated water. Essentially this is a correct assumption but this evaporated water makes up our atmosphere and is the most essential element to meteorology. The water vapor is evaporated from the earth s surface from lakes, oceans, rivers, streams, etc. In areas of large amounts of water, it is often noticed that there is a greater occurrence of water vapor. The amount of water vapor in the air is measured in two different methods, relative humidity and dew point. The relative humidity, RH, is a percentage which incorporates the ratio of water vapor which is included in a certain amount of air / space .
It is a measure of how close air is to saturation. Air gets saturated like anything else, i. e. salt and water eventually you can t dissolve any more salt into a give amount of water. One percent relative humidity would be almost completely unsaturated, versus 100 percent saturated would be completely saturated.
The es stands the saturation limit, the most water that the air could hold, and the e stands for the environmental pressure in the following formula. The formula for relative humidity is e / es x 100 %. When e = es the air is completely saturated because looking back at the formula, one times one-hundred equals one-hundred percent which means the air is completely saturated. The relative humidity is dependent upon both temperature and vapor content. To increase the relative humidity it is necessary to increase vapor content and/ or cool the air.
By increasing the vapor content, you are increasing the relative humidity/ saturation percentage. This is simple because your adding more thus making it more saturated. By decreasing the temperature you re simply decreasing the air s ability to saturate. Cold air can t hold as much water vapor as war air. In order to influence the relative humidity negatively it requires the inverse of the former concept. If you decrease the amount of vapor and/ or increase the temperature it decreases the relative humidity.
The problem with using the relative humidity to judge the amount of water vapor is that there could technically be a situation where there is more vapor except the relative humidity is lower. This is because of the influence of temperature on the equation. If there it is a higher temperature then there is more saturation possible than lower temperature. So technically in a condition where there is the same amount of water vapor but there is two different temperatures, the higher temperature would have lower relative humidity then the colder temperate. This is a problem because there is now way to know this with looking at a thermometer. The dew point is considered a more accurate measurement of the vapor in the air, but that is debated over.
The dew point is the temperature at which the water vapor condenses in to liquid. For the most part if the relative humidity is high the dew point will be nearly air temperature. For example if the RH is 100 percent, then the dew point is equal to the air temperature. When the relative humidity is low, then the dew point is lower than the air temperature. The reason that the dew point is more accurate to the telling how much water vapor is found in the air is because it doesn t fluctuate according to the a change in temperature. If the amount of water vapor remains constant then the dew point does not change.
If the dew point rises then the air is absorbing more moisture. All in all, as warm air rises, this becomes colder. Because cold air cannot hold as much moisture as warm air, it becomes saturated. At this saturation point water begins to form and thus the dew point is created.
An important concept is that a net condensation occurs when the rate of condensation is greater than the rate of evaporation. The net evaporation, or evaporation rate, occurs a larger scale when the air is warm. This is based on the principle that warmer air has a greater es. Based on the same principles, a lower air temperature then has a lower es.
This is important to understand because in our project we intend to create fog, clouds by manipulating cold air and warm air. In order for a cloud / fog to form it needs not only water vapor, but also a cooling mechanism, and a condensation nuclei. For clouds the cooling mechanism is simply the rising of the hot air. Fog on the other hand does not rise but is formed by five other forms of cooling mechanisms. The five different kinds of cooling mechanisms which also name of the fog are radiation fog, advection fog, steam fog, up slope fog, and frontal fog.
Radiation fog occurs during clear days, which have calm skies. Normally the infrared rays of radiation, heat, are reflected from the clouds, but on nice days there are no clouds to reflect the rays. The radiation that escapes the upper atmosphere hit the near ground altitude. They heat the air indirectly by rebounding off the ground. Eventually the radiation cools down.
This cooling of the radiation causes the air to fall bellow the dew point temperature, which causes the vapor to condense. This is also called Valley Fog because it is often found in low-lying valleys, and especially riverbeds during the late fall and winter. Advection fog is formed when warm air is cooled to its dew point by a cold surface underneath it. An example of a cold surface would be snow, ice, and cold water. A prominent place that this advection fog is formed is on the Pacific coast because there is a variety of cold and warm water. The warm, moist air from the warmer Pacific Ocean is affected (advection is the horizontal transportation of atmospheric properties) over the cold coastal waters where the warm air is cooled from the bottom and thus brought bellow its saturation limit and condenses into fog.
It is important to remember that advection fog is only affected by the movement of air, unlike radiation fog. Steam fog occurs when cooler air rises above warmer water and the water vapor that evaporates from the warm water into the air, cools to its dew point. An example of this is when cold air runs over a heated pool. The warm air is cooled by the cold air and it precipitates.
The cold air is heated from below and rises; this appears to be steam. Steam Fog is sometimes called Arctic Sea Smoke. Up slope fog happens when air is forced to rise up a slope and the air reduces its temperature to its dew point. This is why there is always fog and snow on the mountainsides. This process occurs adiabatically, which means that it occurs with out gain or loss of heat. Frontal fog, also known as precipitation, evaporation, or mixing fog occurs when two unsaturated air masses with a contrast in temperature mix.
The warm air coming out of your mouth condenses into liquid when it hits the cold air is an example. It happens when raindrops fall on to the cooler unsaturated air, the raindrops evaporate quickly saturating the air, and as a result mist is seen forming fog. One common kind of fog is on a cool summer nigh when one might be driving in their car and suddenly on the top of a small hill there is random fog. This fog is seen there because during the night the warm moist summer air cools and soon becomes saturated.
The saturated now cooler air begins to precipitate and that is the fog. The same principle is used to explain why dew is seen on summer grass in the morning. The cool air precipitates an extremely low altitude and wets the grass as a result. The third aspect to forming a cloud or fog is the condensation nuclei.
This condensation nucleus is the centerpiece to the raindrop, or any condensed water vapor forms a drop. The centerpiece, or condensation nuclei could be anything from smoke, pollen, dust, pollution, etc. There are two theories about how these little droplets actually come about forming rain. The first theory about the formation of rain is the Collision-Coalescence theory.
This is when larger liquid cloud droplets fall through the cloud and collide with smaller droplets that are either suspended in the cloud or falling more slowly than the larger droplets. When the collision takes place, the larger and small droplets coalesce (join) to create a new larger droplet. This larger droplet then repeats the process as it falls even faster through the cloud. The end result is an extremely large droplet called a raindrop leaving the cloud at the bottom. The other theory is the Bergeron Process, which describes how a snowflake is formed. This is a when a cloud is cooled to an extremely low level, or super cooled.
This cloud must contain both liquid droplets and ice crystals and the cloud must be at or bellow freezing for this process to work. It works because the rain droplets prefer to deposit on an ice crystal, or deposition, instead of condensing with other liquid droplets. There are two possible outcomes. One is that the ice crystals grow and cloud droplets evaporate, and the other is that when the ice crystal leaves the cloud it will be large enough to be called a snowflake. There are two forms of Nucleation, which is the process of bringing together into one, that take place when water molecules are condensing into precipitation.
The two forms of Nucleation are homogeneous and heterogeneous. Homogeneous nucleation occurs when the water vapor condenses to form a droplet. In order for this to happen the environmental temperature must be negative forty degrees Celsius, saturated air, and a relative humidity of several hundred percent. The reason this is called homogenous is because it does not condense with a piece of dust for example just pure water. Heterogeneous nucleation occurs because just saturating the air is not enough to form a cloud. A condensation site is needed for the water molecules to condense on.
As said before this site is called the condensation nuclei. There are two different types of condensation nuclei: hygroscopic, water seeking, and hydrophobic, water repelling. Haze is a term used to describe particles in the air. Dry haze is formed from just the condensation nuclei.
Wet haze is condensation which has a relative humidity of 80 % or higher. When the relative humidity hits 100 % the particles grow larger. Soon fog is seen in the air. We plan on creating a fog chamber by influence the temperature, and relative humidity, and dew point in order to trap and force condensation.
One of our goals is to be able to create fog using the five different types of fog, if possible. We will influence the fog by temperature increase, and decrease in order to force saturation. We will try to make the purest fog possible by changing the size of the jar and different amounts of water. We can also experiment with different substances dissolved in the water to see if that has an effect upon the fog.
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