The blanket of "air" that surrounds the solid Earth up to a height of about 150 miles provides protection from cosmic rays, ultraviolet radiation and permits the visible wavelengths through.
Composition of the atmosphere is 78.1% Nitrogen, 20.9% Oxygen, 0.03% Carbon dioxide and other gases. The water vapor in the Atmosphere is counted separately.
- The weight of the atmosphere is 14.7 pounds at the bottom of a one inch square column.
- Three-fourths of the air is in the lower 6-7 miles; density decreases as you go up. 5 miles up, density is 1/2 sea level. 12 miles up density is 1/13 sea level.
- The density of air at sea level is ~2.75 pounds/cubic yard (1300 grams/m3), but it halves every 5 kilometers above the surface.
- The atmosphere is about 150 miles thick.
- Temperature decreases as you go up, until you get to the outermost part of the atmosphere which is the hottest.
- Electromagnetic waves have wavelength, crest, trough and wave height. Shorter wavelengths always have more energy than longer wavelengths.
High energy rays like gamma rays and x-rays are followed by ultraviolet rays, then the visible spectrum, then low energy infrared, microwaves and radio waves. To remember the order of visible light, recall "ROY-GBV." The red wavelengths are longer and curve around the outside of the rainbow, while the violet waves are shorter and curve the shortest part of the rainbow.
- The color of a material may change as its temperature changes. The blue part of the flame is hottest; the red part is coolest. Red-hot metal or red-hot lava is too hot to touch; more dangerous is black lava or metal emitting violet which cannot be seen, yet can burn instantly.
- Clouds tend to insulate the surface; clear nights are usually cooler than cloudy ones.
- Only one-half of incoming radiation reaches the surface.
- Changing the concentration of CO2 and other gases may increase the "greenhouse effect" and raise surface temperatures.
Temperature changes in response to:
- Elevation -- temperature and altitude change in the different layers of the atmosphere: troposphere, stratosphere, mesosphere and thermosphere.
- Latitude and Season -- the angle of Earth's axial tilt affects the amount of sunlight reaching the earth, and the amount reflected. This results in our seasons.
- Heat Transport and Storage
- Conduction is heat transfer between two things that touch.
- Convection as heat is applied from below, material cools from above; sets off convection cells of heat flow.
- Advection is the movement of a fluid as an integral entity due to temperature differences.
- Latent heat is "stored" in water and other fluids and is released at phase changes.
|Changing directly from steam/vapor to ice is called "sublimating." The opposite, from ice to steam, is common in volcanic eruptions on mountains covered with snow and produces much energy for the eruption. |
- Specific heat = energy needed to raise 1 g/1 degree C. It takes more energy to heat water than rocks!
- Evaporation is a cooling process; water loses heat and cools by evaporation.
- Freezing water releases energy; this energy can help ice melt itself under certain circumstances.
Land and water react differently to these factors.
|Land takes less calories needed to heat per unit||Water takes more calories to heat per unit|
|Land heats faster than water||Water heats more slowly than land|
|Land loses heat faster than water||Water retains heat longer than land|
dark colored soil absorbs 5-15%
water reflects more at low angles, absorbs more when sun overhead
|Land is opaque||Water is transparent
light penetrates into photic zone
|Land - no heat mixing||Water - mixing by currents|
|Land loses less water vapor to the air than standing water||Water loses more water vapor than land|
We use instruments to monitor conditions in the atmosphere. We use Thermometers for temperature, hygrometers to measure relative humidity, barometers for air pressure, anemometer for wind speed, vanes for wind direction and observe cloud cover directly or calculate it from satellite images.
From these we have learned how to predict weather = what is happening now.
And to infer climate, defined as the average of weather.
Humidity is the amount of water vapor in the air.
- Absolute humidity (g/m3)
- Relative humidity percent = (actual h/max possible h)100
- Saturation is when relative humidity = 100 percent
- Warm air can hold more water vapor than cold air.
- Without the addition or removal of heat, air can change temperature:
- Compressed air heats up (ex. bike pump gets hot).
- When pressure is released on air, gas cools (ex: spray can ice).
- Changing the temperature of air packet changes relative humidity. As a unit of air cools, it approaches saturation, even though the amount of vapor does not change per unit.
- The dew point is the temperature at which saturation occurs.
- The flat bottom of cumulus clouds can show us the "elevation of the dew point." When it touches ground, we get "fog."
- Supersaturation & supercooling occur in nature.
Cooling and Condensation
- Radiation cooling occurs as land and water lose heat gained in sunlight.
- Contact cooling - dew and frost are more common on surfaces. Bridge freezes before road.
- Cooling of rising air leads to adiabatic temperature changes
- Remember: compressing a gas makes the temperature go up
- releasing pressure on a gas makes the temperature go down.
- The dry adiabatic lapse rate = 5.5 F/1000 feet
- The wet adiabatic lapse rate is cooling after the beginning of condensation. It varies from 2.7 F (moist) to 5 (drier) F/1000 feet. Cooling slows with elevation.
- Sinking air masses always become warmer at the dry adiabatic rate due to compression of the air.
- Convection -- warms, expands, less dense, rises
- Orographic lifting -- air rises over mountains
- Frontal wedging -- cool air slips below warm air, forcing warm air to rise.
- Air is colder as you go up.
- As rising air goes up, it encounters colder air, cools at the appropriate lapse rate and clouds condense.
- Cloud types:
- Stratus: altostratus
- Cumulus: stratocumulus, cumulonimbus, nimbostratus
- Snow, sleet, glaze
- Fog: advection fog, radiation fog, evaporation fog, upslope fog
Lows and Highs attempt to equalize the weather.
- Low pressure sucks air from near the ground and releases it in the upper atmosphere. Lows are known as cyclones in the southern hemisphere and anti-cyclones in the northern hemisphere. To state it another way, in both hemispheres, winds associated with Lows run away from the spin.
- High pressure blows the air back down, cooled and dried from its passage in the upper atmosphere. High pressure winds blow spinward in both hemispheres.
- To put it another way:
- In the Northern Hemisphere, Lows suck air counterclockwise, while Highs blow air clockwise.
- In the Southern Hemisphere, Lows suck air clockwise, while Highs blow air counterclockwise.
- Storm troughs are found under extreme Highs, while storm surges occur under Lows.
- This creates a pressure gradient -- winds blow from high to low.
- We draw maps with isobars and connect lines of even pressures.
Winds create waves and come in many forms:
- Surface winds are slowed by friction.
- Prevailing winds is a term for the average direction from which local winds come. For the western U.S., the prevailing winds are off the Pacific Ocean.
- High altitude jet streams first discovered in WWII tend to flow from the poles and toward the spin in both hemispheres, dipping south to nearly the equator before being deflected back up to the pole. Much weather rides the jet stream, especially in winter.
Air masses are large bodies of air, of nearly uniform temperature and humidity at a similar altitude.
|There are four types of air masses:|
|Continental||continental/polar cp||continental/tropical ct|
|Marine ||marine polar mp||marine tropical mt|
|These abbreviations are used on weather maps and in weather reports.|
There are four types of weather fronts:
- Warm front -- moving warm air collides with slower (or stationary) cold air. Warm air rises over cold air; light rain along sloping boundary.
- Cold front -- moving cold air collides with slower (or stationary) warm air. Cold air pushes under warm air; steeper leading edge and bigger storms.
- Occluded front -- faster moving cold air traps warm air against another cold air mass. (Warm air is filling in "oreo" cookie.) Storms form on both cold air/warm air intersections and produces both light and heavy rains in a large band of nasty weather.
- Stationary front -- two non-moving air masses just sit there; rain, drizzle and fog may result.
Topography & Weather
- Convergence of air flows across peninsulas like Florida can blow up clouds which bring rain upwind.
- Convection cells cause troughs and surges in large bodies of water and cause wind storms in advance of any rain events.
- Orographic rise causes higher elevations to receive precipitation even when lower elevations stay dry.
- Frontal thunderstorms can sweep across many states; some even generate tornados.
- Air lifted over mountain ranges loses its moisture going uphill. This creates rain shadow deserts such as that from the Sierras to about the 100th Meridian.
- sea and land breezes cause the wind to reverse daily as the temperature creates local lows and highs which are sometimes referred to as day and night winds. The Fremantle Doctor, a landward breeze felt most afternoons in Perth, brings needed cool air to an otherwise hot city.
- El Nino has a global effect. It is a temperature oscillation in the southern Pacific Ocean with far reaching effects around the globe.
Fast moving weather includes:
- Monsoons -- in winter, the cold heart of the continent makes dry dense air that sinks and flows over the ocean. In summer, the continent heats rapidly, its air rises and sucks cool, moist ocean air on land. The wind directions are controlled by cyclones and anticyclones.
- Thunderstorms -- occur in the midwestern U.S. when warm, moist air from the Gulf of Mexico meets cool dry air from the pole. Driven by anticyclonic winds, rising air creates cumulonimbus clouds which reach heights of 10,000 feet or more. Over water, they may make storm surges.
- Lightning is generated in thunderstorm clouds. (Time of Flash minus Time of Thunder) divided by five is distance in miles to epicenter.
- Tornados -- horizontal energy to vertical rotation, use bottle/soap demonstrator to see how this works.
- Tropical Cyclones and Hurricanes (Hurikan of central America) can flow either toward the spin or against it and can blow up in either the Pacific or the Atlantic. Towering clouds surround a central eye. A giant low pressure system sits in the middle generating a storm surge which can overtop islands and shorelines. Once overland, they lose energy as their supply of warm, moist water is shut off.
- Mid-latitude cyclones cause much North American weather. Snowstorms blowing from the plains states (about 100th meridian) east to the Atlantic in winter are blowing along this storm track.
Climate is the average of weather. Factors which influence climate include but are not limited to:
- Oceans/large lakes
- Global winds & climate.
- Ocean currents and climate
- Climate zones of earth.
- Urban climates -- heat islands and local storms
- Watch the T.V. weather maps. Hop channels and see the different images used by each broadcaster.
- Visit my California Links page to see near live time Eureka satellite images, river gages, tide information, and weather.
- Don't miss the Weather Underground and look way down at the bottom of the left hand column at the near real time visible satellite image. If it's a clear night, the picture shows you the glow from U.S. cities.