CEE 1030 1st Edition Lecture 21 Atmosphere Origin of Earth’s Atmosphere- gases trapped in planet interior released by volcanic eruptions - ancient atmosphere consisted mostly of water vapor and carbon dioxide- without atmosphere, earth’s surface would be ~60of colder Earth’s modern atmosphere- gas layers surrounding the planet, retained by gravity- modern atmosphere composed of a mix of gases, mostly nitrogen (78%) and oxygen (21%)Atmosphere layers exosphere, thermosphere, mesosphere, stratosphere, troposphere - no distinct upper limit: atmosphere gradually becomes thinner and fades into space - 90% of gases are concentrated in the troposphere (0-10km) - denser gases (nitrogen, oxygen) sink, so composition varies with altitude Ozone layer - layer in stratosphere with high concentration of ozone molecules - absorbs ultraviolet light- thickness varies (thinner at poles) and from year to year Temperature of atmosphere- troposphere cools with altitude (ground absorbs solar energy, heats air) - ozone layer absorbs ultraviolet light, heats upper stratosphere - mesosphere cools with altitude (uppermost layer is coldest place on earth) Thermosphere and exosphere - upper layers These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- oxygen molecules in thermosphere absorb solar radiation, temperature increases with altitude until gas is too thin to have effect - solar winds drive charged particles into upper atmosphere, resulting in colorful lights in nigh sky (=Auroras) Atmospheric pressure = barometric pressure= force per unit area exerted by atmosphere on surface beneath or within it - pressure decreases as altitude increases - average sea level pressure= 1013 mbar Air in the troposphere- warm air is less dense than cold air - dense air masses sink, less dense air rises, warm air= rise, cold air= sink Pressure zones - high pressure zone: sinking air mass causes diverging winds; associated with clear, cool weather - low pressure zone: converging winds to rising air mass; associated with cloud formation and precipitation Atmospheric convection 1.) air masses move from areas of high pressure to areas of low pressure, creating winds2.) moving air mass creates a low pressure zone where it began and a high pressure zone where it is going Why coastal breezes change direction land breeze: - during day, sun warms land more quickly than water - warm air rises, low pressure area forms on land - draws cooler air from sea to fill void over land - water warming air Cloud formation by convection  cloud: visible mass of condensed water droplets or ice crystals in atmosphere - air mass at earth’s surface is warmed and rises (like hot air balloon) - at higher altitudes, air mass expands and cools, causing water vapor to precipitateThunder storms - thunderstorms form when an air mass with significant condensation is forced upward rapidly in an unstable atmosphere, where temperature drops Lightning - lightning: atmospheric discharge of electricity resulting from differently charged particles in air masses; typical feature of thunderstorms Weather fronts  front: transition zone between air masses of difference densities - front extend both horizontally and vertically and are often marked by cloud formation Cloud formation  frontal lifting: convergence of air masses (fronts) - warmer, moister air mass will override cooler, dryer air masses- clouds form where warm, moist air rises and cools  orographic uplift: moist winds forced upwards by hills or mountains cool and precipitate on windward side - dry air descends on leeward side (rain shadow desert)  radiative cooling: when sun sets and no longer warms air and ground, air just above ground cools, forming fog Precipitation  precipitation: condensation of atmospheric water vapor that falls to earth’s surface (rain, snow, hail, etc.) Liquid precipitation- rain or drizzle (differentiated by droplet size): forms when drops of water fall to earth’s surface Frozen precipitation - frozen precipitation (e.g., snow) forms when atmospheric water is cooled below its freezing point - when it comes into contact with a dust particle, supercooled water condenses around a nucleus Global wind patterns- global wind patterns results primarily from:  temperature- driven convection  adiabatic effects (evaporation and condensation)  coriolis effect seasonal shifts in solar heating Global wind patterns part 1:1. connection circulates air by unequal warming at different latitudes: - at poles, dense cool air descends and moves toward equator - at equator, less dense warm air rises - air moves from surface high pressure near the poles toward a belt of low pressure along the equator Global wind patterns part 2: 2. variation in moisture levels resulting from evaporation and condensation patters cause cool, dry air to sink at 30o north and 30o south of equator - descending cool, dry air forms high pressure belts to subtropical latitudes - descending cold, dry air near poles creates another convection loop at high latitudes Global wind patterns part 3: 3. coriolis effect (resulting from Earth’s rotation) deflects air currents to right in northern hemisphere and to left in southern hemisphere Jet streams - fast narrow air currents found near stratosphere/troposphere transition - caused by atmospheric heating (solar radiation) and planet’s rotation on axis - major jets flow west to east - subtropical jets tend to be higher and weaker than polar jets Global wind patterns part 4: - seasonal changes in solar heating of earth’s surface affects distribution of high and low pressure areas - seasonal differences in surface heating and air pressure cause changes in wind directions during the year Low-latitude deserts- band of deserts and steppes concentrated between 20oSeasonal variations- seasonal temperature changes result from variation in solar radiation reaching the ground - variation results from tilt of earth’s axis as it rotates around the sun - at any given time, one part of planet is exposed to more direct rays of the sun Seasons- mid-latitude and polar regions: seasonal cycle marked by changes in temperature - equatorial and subequatorial regions: little temperature variation, seasons defined by changes inprecipitation equatorial seasons- tropical and subtropical regions: amount of precipitation often varies more than