Formation of Clouds and Their Causes - Essay Example

Running Head METEREOLOGY METEREOLOGY Formation of clouds and their causes Cloud can be defined as a collection of minute water or ice particles which are sufficiently numerous to be seen (Sloane and Tesche 1991). The size of cloud droplets ranges from a few microns to as large as 100 microns. The main causes of clouds formation are orographic uplift, convectional lifting, convergence, radiactive cooling. It is important note that from one place and time to another place and time in the same cloud, there are large differences in the droplet characteristics. Although the processes of increasing the relative humidity which lead to fog formation are effective, by far the most important cause for cloud formation is upward movement of bodies of air. When a body of air rises, it moves from higher pressure to lower pressure. In so doing it must expand, and as it does so, its temperature is reduced. One can calculate the amount of cooling to be expected when the air is lifted by a fixed amount. If the air is dry and no heat is added or taken away as the air ascends, it cools at the rate of 1.0C per 100 meters. This is known as the dry adiabatic lapse rate. Once a cloud has begun to form, the cooling effects caused by the expansion of the rising air are partially offset by the heat released during the condensation process. Evaporation causes cooling. When condensation occurs, the reverse is true; heat is added. If the rate of ascent of air, which may be called the updraft speed (Sloane and Tesche 1991), is quite high, the air may cool so fast that condensation cannot proceed fast enough to keep the air at saturation. In this case the air may become supersaturated. The equations show that once this happens the smaller droplets grow more rapidly than the large ones. The final condition is one with clouds having a narrow range of droplet sizes. The main processes which influences cloud formation are condensation or deposition (Brasseur et al 1999). Weather Fronts The difference in temperature always causes a difference in atmospheric pressure, which in turn causes the wind. When the resulting winds are confined to small areas, not more than a few miles in extent, they blow directly from high pressure to low pressure, as one would expect. Weather front can be identified as a boundary between air masses of hot and cold air (Brasseur et al 1991). The main types of fronts are cold front and warm front, stationary front and occluded front. The typical wind circulation about a well-developed low or a well-developed stationary high is often useful in predicting lower-level winds. Several hundred feet above the ground, these circulatory winds blow nearly parallel to the isobars. Fronts are always described as zones of transition, the types of the front depends upon the direction and air masses (Sloane and Tesche 1991). The cold front, extending southward and southwestward from the low center, is also a wedge of cold air underlying warm air -but an active, undercutting wedge, a steeper wedge than the warm front, a wedge that is steadily advancing eastward and southeastward in such a way as to crowd out the warm air more or less violently and to thrust it aloft. The warm front extends east and southeast from the low center, with the warm sector advancing behind it from the southwest and the colder air retreating slowly ahead of it towards the north (Sloane and Tesche 1991). Occlusion is the combination of warm and cold fronts where the latter has overtaken the former. The occlusion itself usually extends gradually southward as more and more of the warm sector is forced above the surface by the closing wedges of colder air. Stationary front is defined as a front which does not move (Sloane and Tesche 1991). Weather Systems: hurricanes, tornadoes, thunderstorms The term hurricane is usually used to describe tropical storms and cyclones. Also, hurricane can be defined as the strongest level of wind according to the Beaufort scale. Unstable air above these steaming areas of warm and azure sea is continually building up into towering showers and squalls marked by violent updrafts extending to high altitudes. If the rising currents happen to extend over a fairly large area at one time, and if the general aerological conditions are favorable, the latent heat released by large-scale condensation may cause a local drop in atmospheric pressure, which in turn induces a further inward flow of warm, moist air. Swayed by the earth's rotation, these inflowing currents soon assume a spiral or circular form (Sloane and Tesche 1991). The result is a destructive hurricane. For in the actual hurricane, likewise, the width of the whole whirl (a hundred miles or more) is much greater than its thickness or depth (less than ten miles), and the speed of rotation (say one hundred miles per hour) is much greater than its speed of translation (say ten miles per hour) (Sloane and Tesche 1991). Thunderstorm can be explained as a thunder accomplishment by lightening and cumulonimbus clouds (Sloane and Tesche 1991). Lightening builds up inside the storm. Thunderstorms occur most frequently in the warm, moist, and unstable air masses within the tropics, where they are a daily afternoon occurrence, and sometimes so regular that they serve as a convenient time indicator for human affairs. In arctic regions, where the air is cold and comparatively dry, thunderstorms may not occur oftener than once in several years. Temperate regions experience their share of storms in the late spring and summer. Thunderstorms are classed, according to their apparent severity, as 'mild,' involving few if any ground-strikes and relatively light winds; 'moderate,' involving fairly frequent groundstrikes, moderate to heavy rain, and moderate to strong winds; and 'severe,' attended by nearly incessant lightning, torrential rain, and severe squalls. Air-mass thunderstorms occur entirely within one air mass, and without aid from any frontal action between air masses. They arise where the characteristics of the air mass, aided by wind and topography, favor them (Sloane and Tesche 1991). Tornadoes are the smallest of all true storm whirls, but they are by long odds the most fearful and the most violent. Also, tornadoes are defined as rotating column of air. For the great air whirls likewise originate as vortices between conflicting currents -- currents in the flow of the upper air. These strongly opposed upper winds arise oftenest in the more turbulent portions of a large and vigorous cyclone, either temperate or tropical, a cyclone that is usually some hundreds of miles wide. The column of whirling dust is usually not more than a few feet wide, and its progress is slow enough so that anyone on foot or on horseback can easily avoid it. The dust whirl is limited in size and intensity by the limited amount of energy present in its atmospheric causes (Sloane and Tesche 1991). Unstable air and conflicting air currents, in some form, are responsible for all whirlwinds, dust whirls, waterspouts, and tornadoes alike. But in the case of dust whirls both these causes operate on a small and limited scale (Sloane and Tesche 1991). Lightening Lightening is defined as "an atmospheric discharge of electricity" (Seinfeld and Pandis 20006, p. 76). Lightening is usually white in color, combining the spectrum of nitrogen with that of oxygen. But it may appear bluish in contrast to yellowish artificial lights, and may appear yellowish if viewed through haze, fog and clouds. Occasionally a reddish or pinkish flash occurs, when air rich in water vapor is ionized so as to give the spectrum of hydrogen. Usually Lightening strikes from thundercloud to ground, from ground to cloud -- or, even more commonly, between clouds. But on rare occasions it flickers or glows out of a clear sky, as charged masses of air pass near each other or the ground. Several kinds of lightening have been observed, of which by far the most common is 'streak' lightening, the ordinary bolt. A streak of lightening is not a zigzag, as commonly drawn, but sinuous in shape, like a river in broken country. The streak may be single, but more commonly, part of it splits off into smaller downward branches that may or may not reach the ground. Occasionally a bolt splits into 'forked' lightening -- two or more main branches that each strike home (Seinfeld and Pandis 20006). Precipitation and the Hydrolic Cycle Precipitation occurs when the atmosphere is saturated with water. Though all rain results from rising moist air, the gentleness and uniformity or violence and variability of the formative updrafts go far to determine what form the precipitation will take. Rain out of stable (stratus) cloud layers, gently rising, say, along a warm front, is light, steady, and continuous. But rain out of unstable cumulus along a cold front (where updrafts are patchy but powerful) is likely to be heavy, variable, and showery. Precipitation is a core of the Hydrolic Cycle. Precipitation can be liquid (drizzle and rain), freezing (freezing drizzle and rain) and frozen (snow, hail, ice pellets, graupel, etc.). Precipitation occurs because of air cooling and adding moisture (Brasseur et al 1999). The Hydrolic Cycle is defined as a continuous movement of water. The main stages are water storage in ice and water storage in atmosphere, precipitations, snowmelt run off to streams, ground water discharge to oceans and rivers, evaporation and condensation, etc. this cycle is contentious, and has no a stating point or ending (Brasseur et al 1999). Climate Zones The temperate zone is, in a climatic sense, nothing better than a battleground between weather forces, between warm and cold air masses. Nevertheless the temperate zone is that part of the earth in which civilized man evolved, and is probably the region most favorable to his continued progress and development. On the Earth there are five climate zones according to the Kppen Climate Classification System (temperature and rainfalls): Moist Tropical Climates, Dry Climates, Humid Middle Latitude Climates, Continental Climates, Cold Climates (Sloane and Tesche 1991). The temperate zone can have no stable and typical weather of its own. To southward (in the northern hemisphere) is the steady, warm, moist climate of the tropics. To northward is the fairly steady, mostly cold, fairly dry climate of the arctic. The temperate zone is a buffer region between tropic and arctic climates, a battleground on which the gigantic atmospheric forces of heat and moisture advance and retreat, an unstable compromise between irreconcilable extremes, swayed this way and that in its evanescent weather as tropic forces (warm air masses) or arctic forces (cold air masses) momentarily gain ascendancy (Sloane and Tesche 1991). Jet Stream and El Nino Jet stream is defined as fast flowing narrow air currents (Brasseur et al 2996). They are formed in the regions with significant differences in temperature (polar or southern regions). Jet streams are caused by two different masses of air (cold and warm) as a result of pressure difference (Seinfeld and Pandis 2006). El-Nino is an ocean atmosphere phenomenon. Since these regions are strongly influenced by winds, there are certain months of the year when droughts or heavy flooding occur, usually once or twice a decade, and other months when these extreme events are much less common. El-Nino is caused by temperature changes on the surface water. It is an anomaly defined as a cooling or warming of the water. Usually, occurs in the equatorial Pacific Ocean. Even in normal years, unaffected by El Nino events, these relatively seasonless zones experience shifts in wind speed and direction (Seinfeld and Pandis 2006). References 1. Brasseur, G. P., Orlando, J.J. Tyndall, G.S. (1999). Atmospheric Chemistry and Global Change. Oxford University Press, USA; 1st edition. 2. Seinfeld, J.H., Pandis, S.N. (2006). Atmospheric Chemistry and Physics: From Air Pollution to Climate Change. John Wiley & Sons; 2nd Edition edition. 3. Sloane, Ch., S. Tesche, T.W. (1991). Atmospheric Chemistry: Models and Predictions for Climate and Air Quality. CRC. Read More