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BENHA UNIVERSITY SHOUBRA FACULTY OF ENGINEERING SURVEYING DEPARTMENT METEOROLOGY FIRST YEAR FINAL EXAM - 2nd TERM Date: 23-6-2011 DURATION : 3 HOURS ------------------------------------------------------------------------------------Answer all the following six questions : 1- Complete the following sentences : a- Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location . b-The composition of the atmosphere is made up of three primary gases which are nitrogen, oxygen and argon and other trace gases such as methane and hydrogen . c- When reporting air pressure, meteorologists adjust the pressure readings for sea level so that interpretations of the data are standard. d- Mesosphere layer although it has the same percentage of O2 as the stratosphere layer we cannot breath there because air is very thin and contain far few O2 molecule e-Flood occurs because when a surface becomes less permeable, an increasing amount of water remains on the surface, creating a greater potential for flooding. 2- Give reasons a- A family of compounds known as chlorofluorocarbons (CFC's) are capable of disrupting the cycle of the ozone layer Because of their characteristics that they non-reactive nature, CFC's are able to rise undisturbed into the atmosphere. They are not destroyed by reactions or removed by precipitation in the troposphere layer of the atmosphere, and migrate over several years, eventually reaching as high as the stratosphere. b- The temperature of the air contained in stratosphere layer of Earth increase with an increase in the height because this layer contain ozone layer which absorbs the ultra violt radiation and then emit it in the form of warm heat . c- Ionosphere facilitating radio communication because it reflects radio waves back to the Earth, thus facilitating radio communication. d- The area of high pressure is often accompanied by fair weather because in high pressure area ,as air slowly descends, its temperature rises and be able to hold more water and the warmth of the air prevents water from condensing to form clouds and therefore areas of high pressure are often accompanied by fair weather. e- Clouds may cause cool or warm because a-During the day If skies are cloudy, some of the sun's rays are reflected off the cloud droplets back into space. Therefore, less of the sun's energy is able to reach the earth's surface, which causes the earth to heat up more slowly. This leads to cooler temperatures. b-At night If skies are clear, heat emitted from the earth's surface freely escapes into space, resulting in colder temperatures . If clouds are present, some of the heat emitted from the earth's surface is trapped by the clouds and reemitted back towards the earth. As a result, temperatures decrease more slowly than if the skies were clear . 3- What is meant by : a- Direct radiation is solar radiation received by the Earth’s surface and/or atmosphere that has not been altered by atmospheric scattering. b- 100% albedo is total reflection of solar radiation . c- Photon is The smallest (quantum) unit of light/electromagnetic energy. Photons are generally regarded as particles with zero mass and no electric charge. Each photon contains a certain amount (or bundle) of energy, and all electromagnetic radiation consists of these photons. d- Ozone is made of three oxygen atoms ( ). The oxygen we find in our atmosphere is made up of two oxygen atoms ( stable . is less stable than oxygen atom. ) where it is more , because it wants to return to the diatomic state by giving up an When enough ozone molecules are present, it forms a pale blue gas. Ozone has the same chemical structure whether it is found in the stratosphere or the In the troposphere, the ground-level or "bad" ozone is an air pollutant that damages human troposphere. health, vegetation, and many common materials. It is a key ingredient of urban smog. In the stratosphere, we find the "good" ozone that protects life on earth from the harmful effects of the sun's ultraviolet rays. e-permeability is the rate at which water flows through the soil . 4- a What are the three ways of describing Electromagnetic waves, each with a different set of physical units ? We have three ways of describing electromagnetic wave each with a different set of physical units 1- Frequency A property of a wave that describes how many wave patterns or cycles pass by in a period of time. Frequency is measured in cycles per second (which is called a Hertz), 2- Wave length The distance between adjacent peaks in a series of periodic waves. wavelength is measured in meters, 3- Energy is measured in electron volts Electron volt The change of potential energy experienced by an electron moving from a place where the potential has a value of V to a place where it has a value of (V+1 volt). 4- b What are the three main ingredients that must be present in order for clouds to form ? There must be three main ingredients present in order for clouds to form : 1- Moisture - There must be sufficient water vapor in the air to build a cloud. 2- Cooling air - The air temperature must decrease enough for water vapor to condense. 3- Condensation nuclei - Tiny particles, invisible to the human eye, such as dust, dirt, and pollutants, provide surfaces on which water molecules can gather and condense into water droplets. If the conditions are right, then a cloud will form 5- Wind is the result of a limited number of accelerated and decelerating forces, and that the action of these forces are controlled by specific fundamental natural laws . a- What are these forces ? b- In detail explain the effect of these forces on the direction and the speed of the wind . Driving Forces are : 1- Pressure gradient Pressure gradient force is the primary force influencing the formation of wind from local to global scales. This force is determined by the spatial pattern of atmospheric pressure at any given moment in time. Figure below illustrates two different pressure gradient scenarios and their relative effect on wind speed. The two diagrams display the relative relationship between pressure gradient and wind speed. This relationship is linear and positive. As a result, quadrupling the pressure gradient increases wind speed by a factor of four. This is what we would expect according to Newton's second law of motion, assuming the mass of the wind is unchanged. Figure : Effect of pressure gradient on wind speed. 2- Coriolis force The rotation of the Earth creates another force, termed Coriolis force, which acts upon wind and other objects in motion in very predictable ways. According to Newton's first law of motion, air will remain moving in a straight line unless it is influenced by an unbalancing force. The consequence of Coriolis force opposing pressure gradient acceleration is that the moving air changes direction. Instead of wind blowing directly from high to low pressure, the rotation of the Earth causes wind to be deflected off course. In the Northern Hemisphere, wind is deflected to the right of its path, while in the Southern Hemisphere it is deflected to the left. The magnitude of the Coriolis force varies with the velocity and the latitude of the object Coriolis force is absent at the equator, and its strength increases as one approaches either pole. Furthermore, an increase in wind speed also results in a stronger Coriolis force, and thus in greater deflection of the wind. Coriolis force only acts on air when it has been sent into motion by pressure gradient force. Finally, Coriolis force only influences wind direction and never wind speed. 3- Centripetal acceleration Centripetal acceleration is the third force that can act on moving air. It is a force that can influence the direction of wind. Centripetal acceleration creates a force directed at right angles to the flow of the wind and inwards towards the centers of rotation It acts only on air that is flowing around centers of circulation. (e.g., low and high pressure centers). This force produces a circular pattern of flow around centers of high and low pressure. Centripetal acceleration is much more important for circulations smaller than the mid-latitude cyclone. 4- frictional deceleration. The last force that can influence moving air is frictional deceleration. Friction can exert an influence on wind only after the air is in motion. Frictional drag acts in a direction opposite to the path of motion causing the moving air to decelerate. Frictional effects are limited to the lower one kilometer above the Earth's surface. 6- Differentiate between geostationary operational environmental satellites (GOES ) and polar orbiting satellite (POES ) with respect to : a- their orbits b-their height c- their coverage area GOES satellites orbit the earth above the equator at the same speed as the earth rotates so they can transmit a continuous picture of the region below. They hover over a single point above the earth at an altitude of about 36,000 kilometers . To maintain constant height and momentum , a geostationary satellite must be located over the equator .Scientists determine this position by using Newton ,s law of gravity . The same force that makes apples fall from trees on earth is the force that keeps the satellite in its orbit . Polar orbiting satellites travel in a circular orbit moving from pole to pole . These satellites collect data in a swath beneath them as the earth rotates on its axis . In this way, a polar orbiting satellite can see the entire planet twice in a 24 hour period . The basic operational mode deploys two polar orbiting satellites continuously ,one passing north to south (descending) and the other passing south to north (ascending) , circling the earth every 12 hours . Polar Orbiting Satellites are inserted into sun-synchronous orbits which place the spacecraft in a relatively constant relationship to the sun so that the ascending node will remain at a constant solar time, permitting images and data to be received by direct broadcast at the same time each day . Polar Operational Environmental Satellites (POES) are significantly closer to earth than GOES, orbiting at altitude of only 879 kilometers so it only takes one hour and 42 minutes to complete a full orbit . This proximity results in high resolution images and atmospheric profiles .