Physics of Atmosphere PDF (International Aviation Consulting & Training)

Physics of the ATMOSPHERE Date: 18 Jan 2022 Revision no. 01 Atmosphere It is layers of air envelope the Earth planet, and is held in place by the gravity of the planetary body PHYSICS OF ATMOSPHERE 2 opposing factors determining the extend of the Atmosphere  The thermal solar radiation expands...

Physics of the ATMOSPHERE Date: 18 Jan 2022 Revision no. 01 Atmosphere It is layers of air envelope the Earth planet, and is held in place by the gravity of the planetary body PHYSICS OF ATMOSPHERE 2 opposing factors determining the extend of the Atmosphere  The thermal solar radiation expands the gases of the Atmosphere into the surrounding vacuum of space. While  The earth gravitational attraction contracts the gases of the Atmosphere towards the surface of the Earth. Thus.. The density/ pressure exerted by the atmosphere falls progressively with ascent from the surface of the earth towards outer space. Material of Atmosphere is AIR Air is consist of: With increasing altitude → Rarefaction of Air → Decrease of density → Decrease of Pressure Both density & pressure falls in an exponential manner with altitude. • The density of the Atmosphere at 22,000 feet is half that at sea level & 98% of the mass of the Atmosphere is below 98,000 feet. • The upper limit of the atmosphere is about 430 miles above the surface of the earth • The pressure exerted at sea level by the weight of the atmosphere is 14.7 lb/m2 = 760 mmHg. 0 18,000 feet 33,700 feet 100,000 feet = = = = 760 mmHg 380 mmHg 190 mmHg 1/100 sea level = 7.6 mmHg • As per the differences in characteristics, It is convenient to consider the atmosphere as being made of number of shells or layers, each has its own characteristics. • The layers can be differentiated by its thermal features as follows: LAYERS OF ATMOSPHERE o The Troposphere then Tropopause o The Stratosphere then Stratopause o The Thermosphere 1. TROPOSPHERE o In the Troposphere, the temperature of the air decrease linearly with increasing altitude to the tropopause where it become constant at a value (-56.5 °c) which existed throughout the stratosphere. o This linear decrease is called the lapse rate, o In dry air, the lapse rate is equal to 9.8 °C/km (5.4 °F per 1,000 ft). Or it is approximately 2 C degrees / 1000 feet. So the Troposphere is Characterized by: a. A relatively constant rate of fall of temperature with increasing altitude.  The temperature of air in this layer falls with increase of height because the heating of the lower layers of the atmosphere is primarily by infrared radiation from the surface of the earth.  The radiation is absorbed by the CO2 & water vapor in the air.  The lapse rate varies depending on local conditions. The mean lapse rate is about 2°c per each 1000 feet altitude.  The fall of temperature ceases at the tropopause.  The height of it varies with the seasons & latitude. b. Exponential decrease in barometric pressure with increase altitude. c. The presence of Water Vapor. d. Being in direct contact to the Earth’s terrain, the weather is confined to the troposphere. (Domain of Weather). e. The presence of Large-scale Air Turbulence. WIND FORMATION • Changes of the Earth's surface terrain creates areas of different temperature & moist contents that are known as Air masses. An air mass is any volume of air that moves about the earth & can vary greatly in size. An air mass can be described by properties such as its density, temperature, pressure, & movement. • Winds are currents of air that moves across the earth’s surface & develop when 2 adjacent air masses have different densities. • The movement of air masses above the earth’s surface helps to create wind, & help to move the air mass that predict our weather. CLOUDS & RAIN FORMATION • When the invisible water vapor in the air condenses into visible water droplets or ice crystals, cloud will form → Rain & Snow Height of the Troposphere * The Tropopause is defined as the layer of air next to the Troposphere where the air temperature will unify as -56.5 C degrees. * Since the intensity of the solar energy received at the surface of the earth is greater at the Equator than the poles → The air at the equator is hotter, thus, the altitude of the tropopause is about 60,000 feet at the equator & about 25,000 feet at the poles. So the height of the Troposphere at the beginning of the tropopause is between 25000 – 6000 ft ( highest at the equator & lowest at the poles). 2. STRATOSPHERE Characterized by: a. Uniform Temperature !!! b.Complete absence of Water Vapor c. Extends from tropopause to an altitude of 265,000 feet (82 km) * Actually the temperature is only uniform in the lower part of the stratosphere (Termed as the Isothermal layer). * Above 90,000 feet (30 km), the temperature increases progressively with altitude to reach maximum value of +35°c at 150,000 feet (50 km). This increase is produced by the heat liberated by the dissociation of the ozone that present in this region (the Ozonosphere). • Beyond the Ozonosphere, the temperature of the stratosphere drops value of -35°c at the stratopause (265000 feet/ 80 km). Ozone Layer ozone layer, also called ozonosphere. It is region of the upper atmosphere, containing relatively high concentrations of ozone molecules (O3). Approximately 90 percent of the atmosphere’s ozone occurs in the stratosphere, the region extending from 10–18 km to approximately 50 km above Earth’s surface. In the Ozonosphere the temperature of the atmosphere rises with increasing height, a phenomenon created by the absorption of solar radiation by the ozone layer. The ozone layer effectively blocks almost all solar radiation of wavelengths less than 290 nm from reaching Earth’s surface, including certain types of ultraviolet (UV) and other forms of radiation that could injure or kill most living things. Ozone Layer In 1976, atmospheric research revealed that the ozone layer was being depleted by chemicals released by industry, mainly chlorofluorocarbons (CFCs). Concerns that increased UV radiation due to ozone depletion threatened life on Earth, including increased skin cancer in humans and other ecological problems, led to bans on the chemicals, and the latest evidence is that ozone depletion has slowed or stopped. The United Nations General Assembly has designated September 16 as the International Day for the Preservation of the Ozone Layer. Mesosphere The layer beyond the stratopause is sometimes termed as Mesosphere. It is a layer of Earth's atmosphere which is directly above the stratosphere and below the thermosphere. It extends from about 50 to 85 km (31 to 53 miles) above the sea level. Temperature decreases with height throughout the mesosphere. The coldest temperatures in Earth's atmosphere, about -90° C (-130° F), are found near the top of this layer. 3. THERMOSPHERE • Extends from the stratophere to the exosphere (from 265,000 feet (80 km) to 700 km) above the surface of the earth. a. Progressive rise of temperature with altitude. The temperature of the upper parts of this layer reaches 1000 - 2000°c b. Most of the particles of air are charged (electrons & ions), also termed as Ionosphere. c. The density of the gases is so low that temperature has no thermal significance. STANDARD ATMOSPHERE The pressure/ Altitude relationship General International assumptions in defining the pressure/ altitude relationship standards chart. 1. The Air is dry 2. The gravitational acceleration is constant at 980.665 cm/sec2 (9.8 m/sec2) 3. The pressure at mean sea level is 760 mmHg. 4. The temperature/ altitude profile is: a. b. c. d. e. Mean SL temperature is 15°c Mean Lapse rate 1.98°c/ 1000 feet Height of Troposhpere is 36089 feet Temperature of Isothermal layer of stratosphere is -56.5°c Temperature rises above 65,000 feet to a value of -46°c at 100,000 feet. The International Standard Atmosphere (ISA) is a static atmospheric model of how the pressure, temperature, density, and viscosity of the Earth's atmosphere change over a wide range of altitudes or elevations. It has been established to provide a common reference for temperature and pressure and consists of tables of values at various altitudes, plus some formulas by which those values were derived. The International Organization for Standardization (ISO) publishes the ISA as an international standard, ISO 2533:1975. Other standards organizations, such as the International Civil Aviation Organization (ICAO) and the United States Government, publish extensions or subsets of the same atmospheric model under their own standards-making authority. * The Air is dry * The gravitational acceleration is constant at 980.665 cm/sec2 (9.8 m/sec2) * The pressure at mean sea level is 760 mmHg. * The temperature/ altitude profile is: - Mean SL temperature is 15°c - Mean Lapse rate 1.98°c/ 1000 feet * Height of Troposhpere is 36089 feet * Temperature of Isothermal layer of stratosphere is -56.5°c • Temperature rises above 65,000 feet to a value of - 46°c at 100,000 feet. From all what has been discussed, it has been concluded that the environment of high altitude is encountered with circumstances that are incompatible with human’s life. These stresses can be summarized as: 1. Temperature extremes 2. Low Barometric pressure 3. Low partial pressure of Oxygen 4. Harmful Radiations Composition The composition of the Atmosphere is constant. (Air) →gas mixture Ozone Altitude between 60,000 – 140,000 feet (blue, unstable, triatomic (03)) Temperature: The temp of the Atmosphere varies with altitude The Earth & the Atmosphere are warmed by the sun Thank you 34 Aviation, over the last century, presented a multiplicity of challenges that were encountered on every flight. “International prime meridian is Greenwich” Longitude Meridian Latitude Equator