Origin, Composition & Structure The Atmosphere Origin, Composition & Structure

Origin of Atmosphere Atmosphere evolved in 4 steps: primordial gases, later lost due to sun's radiation exhalations from the molten surface (volcanic venting); bombardment from icy comets steady additions of carbon dioxide, water vapor, carbon monoxide, nitrogen, hydrogen, hydrogen chloride, ammonia, and methane from volcanic activity addition of oxygen by plant/bacterial life

Formation of the Atmosphere & Oceans: Prevailing Theory The major trapped volatile was water (H2O). Others included nitrogen (N2), the most abundant gas in the atmosphere, carbon dioxide (CO2), and hydrochloric acid (HCl), which was the source of the chloride in sea salt (mostly NaCl). The volatiles were probably released early in the Earth's history, when it melted and segregated into the core, mantle, and crust. This segregation occurred because of differences in density, the crust being the "lightest" material. Volcanoes have released additional volatiles throughout the Earth's history, but probably more during the early years when the Earth was hotter. Probably, the oceans formed as soon as the Earth cooled enough for water to become liquid, about 4 billion years ago. The oldest rocks on the earth's surface today are 3.96 billion years old.

ATMOSPHERE Present Composition Atmosphere Unique Among Other Planets 78% Nitrogen; 21% Oxygen; trace amounts of CO2, Argon, ect. Atmosphere Unique Among Other Planets Venus & Mars CO2 Gaseous planets H, He, CH4 Pressure in Venus 100x Earth on Mars 1/100 Surface Temperature 450-500oC Venus; -130-25oC Mars Atmospheric Gases Controlled by volcanoes and interactions between gases and the solid Earth & Oceans as well as biotic component Ozone (O3): produced by photochemical Rx absorbs harmful UV radiation

Oxygen in the Atmosphere Earth only planet in solar system with oxygen thus only planet able to sustain higher forms of life Oxygen produced by Photosynthesis- algae and plants Photolysis-fragmentation of water molecules into Hydrogen and Oxygen Oxygen consumed by Respiration Decay Weathering (chemical oxidation)

Structure of the Atmosphere The atmosphere is a reasonably well-mixed envelope of gases roughly 80 km (54 mi) thick called the HOMOSPHERE. Above 80 Km the gases are stratified such that the heavier gases decrease much more rapidly than the lighter ones; this is the HETEROSPHERE In addition, we can identify four layers in the atmosphere that have distinct characteristics. The four layers of the atmosphere, in order from lowest to highest elevation, are: the troposphere, the stratosphere, the mesosphere, the thermosphere

The Troposphere The density of the atmosphere decreases rapidly with increasing height. The troposphere has the following characteristics: it is about 12 km (7 mi) thick, the temperature decreases rapidly with altitude, the mean temperatures at the bottom and top are 16°C & -60°C, it is heated from below by conduction and from condensation of water vapor, it is the region where you find precipitation, evaporation, rapid convection, the major wind systems, and clouds, and it is the densest layer of the atmosphere.

The Tropopause/Stratosphere Above the troposphere is a region of relatively constant temperature, -60°C, about 10 km (6 mi) thick called the tropopause. This is where high velocity winds (jet streams) occur. The stratosphere has the following characteristics: it is about 28 km (17 mi) thick, the temperature increases with altitude from about -60°C to 0°C, this is where ozone, an unstable form of oxygen, appears, it is heated as the ozone absorbs incoming ultraviolet radiation.

Stratosphere/Stratopause The stratosphere offers clear, smooth conditions for flying No air exchange between it and troposphere Gases and aerosols can persist for months or years triggering short term climatic variations A constant temperature condition is described as isothermal The stratopause is at 0oC

Mesosphere/Mesopause/Thermosphere Mesosphere temperatures fall with increasisng altitude until they reach the Mesopause at 80Km and -95oC Above the mesopause is the Thermosphere where temperatures are isothermal for 10Km then rise rapidly with increasing altitude The thermosphere is very sensitive to incoming solar radiation

The Ionosphere From between 70 and 80Km in the Thermosphere to an indefinite altitude in the Thermosphere High concentration of ions of Oxygen and Nitrogen Solar wind strips electrons from these atoms and molecules

Ionosphere

Aurora Australis NASA Images from Space

Exosphere Outermost atmospheric layer No definite outer limit, as it merges with space Many satellites orbit within this layer, usually at altitudes of from 300 to 600 miles above sea level

Monitoring the Atmosphere

Upper Air Observations A three-dimensional picture of temperature, pressure, relative humidity, and wind speed and direction in the atmosphere is essential for weather forecasting and meteorological research During the latter part of the 19th century and the first quarter of the 20th century, this information was obtained mainly by meteorographs sent aloft on tethered kites, which automatically recorded, on a single sheet, the measurements of two or more meteorological parameters such as air pressure, temperature, and humidity

Monitoring the Atmosphere Kites & the Radiosonde

The Radiosonde The radiosonde is a small, expendable instrument package that is suspended below a large balloon filled with hydrogen or helium. The radiosonde consists of sensors coupled to a radio transmitter and assembled in a lightweight box. The meteorological sensors sample the ambient temperature, relative humidity, and pressure of the air through which it rises. As the radiosonde is carried aloft, sensors on the radiosonde measure profiles of pressure, temperature, and humidity. These sensors are linked to a battery powered, 300 milliwatt radio transmitter that sends the sensor measurements to a sensitive ground receiver.

Worldwide, there are more than 900 upper-air observation stations using 15 major types of radiosondes. Most stations are located in the Northern Hemisphere and all observations are taken at the same times each day at 00:00 and 12:00 UTC (Greenwich Mean Time), 365 days per year. Observations are made by the NWS at 93 stations - 72 in the conterminous United States, 13 in Alaska, 10 in the Pacific, and 1 in Puerto Rico

The Radiosonde During the flight train's ascent, the radiosonde continuously transmits temperature, relative humidity, and pressure readings to the ground-based Radiosonde Tracking System which is housed in a fiberglass dome above the inflation shelter. Wind speed and direction are determined for each minute of the flight, generally 90 minutes. They are determined from changes in the position and direction of the flight train as detected by the Radiosonde Tracking System. When winds are incorporated into the observation, it is termed a rawinsonde observation, and all National Weather Service upper air stations take rawinsonde observations

Monitoring the Atmosphere Those observations that reach the bursting altitude of the regular 600-gram balloon attain an average height slightly in excess of 90,000 feet. The average bursting altitude for stations using the larger 1,200-gram balloon exceeds 100,000 feet

Radiosonde Approximately one-third of the radiosondes released by the National Weather Service are found and returned to the Instrument Reconditioning Branch in Kansas City, Missouri, They are repaired and reissued for further use, some as many as seven times. Instructions printed on the radiosonde explain the use of the instrument, state the approximate height reached, and request the finder to mail the radiosonde, postage free

Other Monitoring Radar Satellites