Meteorology The Study of Atmosphere and its Processes
Weather vs. Climate Weather is the day-to-day atmospheric conditions in a specific time and place. Climateis the average weather conditions in a specific location over a long period of time. To be classified as climate the weather conditions are usually recorded over a 30 year period.
History of the Atmosphere Like everything else in the natural universe, Earth’s atmosphere has been continually evolving since its birth approximately 4.6 billion years ago. It is theorized that Earth is now in its fourth major atmosphere.
Earth’s First Atmosphere Earth’s first atmosphere was believed to be composed mainly of hydrogen and helium. However, due to Earth’s small size and low gravitational pull, scientists suggest that the gases were not able to be held in place and were simply lost to space.
Earth’s Second Atmosphere As Earth grew in size and mass so did its gravitational pull. The second atmosphere is believed to be composed mainly of CO2, Sulfur Dioxide (SO2), H2O vapor, and Nitrogen (N2) that came from the “outgassing” of volcanoes that covered Earth’s newly formed crust.
Earth’s Third Atmosphere In this atmosphere it is theorized that cyanobacteria multiplied, converting a CO2 rich atmosphere into a oxygen rich atmosphere. In this new atmosphere, single cell organisms would have begun to evolve into more advanced multicellular organisms. The biodiversity of life on our planet began.
Fourth Atmosphere The fourth atmosphere is our atmosphere. Our atmosphere is composed of two classes of gases: Permanent Gases which remain relatively constant and Variable gases which are mainly associated with atmospheric cycles.
Earth’s Permanent Gases Some of earth’s atmospheric gases are considered to be permanent because their percentages are stable and constant. The three main gases include: • Nitrogen – 78% • Oxygen - 21% • Argon - .93%
Variable Gases Some of Earth’s gases are considered to be variable because they are constantly changing in cycles. The main variable gases include: 1. Water Vapor - .25% (Hydrologic Cycle) 2. Carbon Dioxide - .036% (Carbon Cycle) 3. Ozone - .01% 4. Methane - .01% (normal level, currently1.7%)
Aerosols Aerosols are Small solid particles and liquid droplets in the air. (Not including: water vapor and precipitation) Forms from natural and human processes In a normal human breath, our lungs takes in approx. 1000 cm3 ,(1 Liter), of air. As a result, approx. 1 million aerosols are taken into our lungs several times a minute, or about 2 tablespoonsof solids each day. Condensation Nuclei: Necessary for Cloud formation, and precipitation to form.
Layers of the Atmosphere There are 4 main layers of Earth’s atmosphere. • Thermosphere • Mesosphere • Stratosphere • Troposphere
Thermosphere The thermosphere is the fourth and highest layer of our atmosphere. The thermosphere begins at approximately 90 km above the surface and ends at 2400 km. The thermosphere is divided into 4 sub-layers. 1. Lowest layer: Nitrogen 2. Ionosphere:Layer of charged particles. (Auroras) 3. Middle layer: Helium 4. Highest Layer: Hydrogen
Mesosphere The third layer is the mesosphere. This layer is at an altitude of 50 to 90 km above the surface.
Stratosphere The second layer is the stratosphere. This layer is at an altitude of 16 to 50 km above the surface. Located within this layer is the ozone layer. The ozone layer protects earth’s surface from excessive ultraviolet solar radiation by converting UV radiation into heat.
Troposphere The first layer of the atmosphere is the Troposphere which is 0 – 16 km thick at the equator and only 0 – 9km at the poles) The troposphere accounts of 80% of the total atmosphere. All life on Earth in contained within the troposphere.
Earth’s Energy Balance In order for Earth to maintain its stable temperature, 100% of the incoming solar radiation must be balanced with an equal amount of outgoing energy. A mere 100 F change in temperature up or down could melt the ice caps and raise ocean levels 200 ft or send Earth into an ice age with glaciers covering 70% of the surface.
Earth’s Major Air Masses Air masses are large bodies of air in the lower troposphere which have similar characteristics throughout. Types of air masses: cA– Continental Arctic – Very Cold and Dry cP– Continental Polar – Cold and Dry cT – Continental Tropical – Hot and Dry mP– Maritime Polar – Cool and Moist mT– Maritime Tropical – Warm and Moist
Global Wind Patterns Three Cell Model Polar Cells Ferrell Cells – Mid-Latitudes Hadley Cell – IntertropicalConvergence Zone (ITCZ)
High Pressure Systems • CoriolisEffect deflects air to the right in the northern hemisphere • Winds rotate clockwise in the northern hemisphere (Anticyclone) • High pressure systems blow cool, dry air from the upper atmosphere down toward the surface H
Low Pressure Systems Low pressure systems rotate Counterclockwise in the northern hemisphere. (Cyclone) • Low pressure system drawwarm moist air from the surface and blow up into the upper atmosphere where it cools and condenses from a gas to a liquid. L
Fronts A Frontis the boundary that separates two opposing air masses. Symbol Key:
Cold Front A Cold Front is the boundary between an advancing cold air mass and the warmer air mass it is displacing. Characteristics of a cold front: • Fast moving: Average speed 10 - 30 mph • Normally in a steep wedge shape • Cloud cover will usually be cumuliform • Associated with heavy precipitations • Dramatic decrease in temperature: 10 degrees or more • High winds
Warm Front A Warm Front is the leading edge of advancing warm air that rises above the denser cold air mass in a process known as overrunning. • The wedge shape is much more gradual than a cold front. • Signs of an approaching warm front: 1. Fair weather 2. Cloud Formation 3. Associated with light steady rain
Stationary Front A stationary front is a non-moving boundary between a cold front and a warm front. • If there is no movement of air masses in a three hour period, then the front is considered stationary.
Occluded Front Since cold fronts move twice as fast as a warm front, the warm front is typically overtaken by the cold front.When this occurs, warm air gets trapped and forced upward which cools and often causes cloudiness and precipitation.
Life Cycle of a Mid-latitude Cyclone • Cyclogenesis: the birth of a mid-latitude cyclone • Occurs only in the temperate zones • Largest weather system on the planet, ranging from 100 – 1500 miles in diameter
Phase 1 A polar front separates the cold easterlies and the warmer westerlies.
Phase 2 • A minor kink develops along the boundary. The cold air north of the front begins to push southward behind the cold front, and air behind the warm front advances northward. • This creates a counterclockwise rotation around a weak developed low pressure system. Continued uplift leads to cloud formation.
Phase 3 • A band of cumuliform cloud cover runs along and ahead of the cold front, caused by the displacement of the warm air by the cold denser air. • Because of the high moisture content, intense rain, snow, and hail could occur.
Phase 4 The system becomes occluded and loses it warm, moist air fuel. The system begins to shut down.
Cloud Formation Adiabatic Process: • Parcel: A pocket of air which is heated by the earth’s surface by the process of conduction. • Relative Humidity: The amount of water vapor in the air at a given temperature compared to the total amount of water vapor that the air could hold (saturation: 100%) • Inverse relationship: As the temperature decreases, the relative humidity increases.
Adiabatic Process cont. • Normal Lapse Rate: Ambient air temperature will decrease at an average of 6.50 C per every 1000 m. • Dry Adiabatic Lapse Rate: As the parcel of air rises the warmer air inside will decrease at a rate of 100 C per 1000 m. • Wet Adiabatic Lapse Rate: When the parcel of air reaches 100% relative humidity, the lapse rate will decrease to 50 C per 1000 m