Weather is today! Climate is history!
The composition and structure of EarthÕs atmospheric layers
EarthÕs atmosphere is the layer of gases that surrounds the planet and makes conditions on Earth suitable for living things.
EarthÕs atmosphere is divided into several different atmospheric layers extending from
EarthÕs surface outward
á the troposphere, where all weather occurs, where we live!
á the stratosphere, where the ozone layer is contained
á the mesosphere -meteors or shooting stars are seen here.
á the thermosphere
á the exosphere
Nitrogen and Oxygen
á the two most common gases; found throughout all the layers, nitrogen makes up 78% of the atmosphere and oxygen makes up 21%
á a form of oxygen found in the stratosphere, shields us from dangerous ultraviolet radiation.
Water vapor and
á important gases for weather conditions; found in the
Trace gases, argon
á play an insignificant role
Differences in temperature
separate the layers
á As altitude increases, temperature decreases in the
troposphere . Air pressure and temperature get lower and lower as we go higher.
á The stratosphere is cold except in its upper region where ozone is located
á The mesosphere is the coldest layer
á Even though the air is thin in the thermosphere, The individual air molecules are very hot but are spread so far apart that you couldn't feel the heat.
á The cold regions of outer space extend from the exosphere
The air pressure, caused by the mass of the gases pushing on an object, is greatest near the surface of Earth, in the troposphere.
á Air pressure decreases
through the layers farther out from the surface as EarthÕs pull of gravitydecreases.
Troposphere pressure-greatest pressure
decreases as we go higher.
Exosphere - least pressure
The water cycle (including precipitation, evaporation, transpiration, condensation, surface-water flow, and groundwater flow).
Water is always moving between the atmosphere (troposphere) and surface of Earth. Each components of the water cycle process has certain conditions under which each form of precipitation develops:
á After condensation occurs (forming clouds), water droplets fall in various forms of precipitation – rain, snow, freezing rain, sleet, or hail, depending upon weather conditions.
á Temperature variations within clouds and/or within the region between the cloud and Earth allows for the various forms of precipitation.
. liquid water changing into a gas called water vapor.
á Water enters the atmosphere as water vapor through evaporation and transpiration(plants releasing water vapor.)
áCooling causes condensation! Cool air cannot hold as much water vapor so it changes back into water droplets!
.Condensation happens in the atmosphere as water vapor changes to water droplets.
á Clouds are condensation, water droplets NOT Water vapor!!!
á Dew forms when water vapor condenses directly onto a surface;
á Frost forms when water vapor changes from gas directly to ice crystals on a surface when the temperature at which condensing would take place is at the freezing point or below.
á If precipitation falls on land surfaces, it always attempts to move back toward sea level as surface-water flow or groundwater flow.
á The type of surface that the precipitation falls onto determines its flow back towards sea level.
á Water will remain on the surface when the surface is not permeable or the precipitation is falling too fast for the water to sink(or infiltrate) into the ground. This water becomes runoff and can become streams which flow into rivers which then flow back into the ocean.
á Water will sink into the ground when the surface is permeable and there is lots of space in the soil to hold the water. Permeable soil forms an aquifer. Aquifers are important sources of freshwater for most parts of the world. Wells are drilled into the aquifer.
Types of clouds according to elevation and their associated weather conditions and patterns.
Clouds that form from the condensation of water vapor are classified by a basic shape and associated weather conditions and patterns. Clouds can be classified in three major groups:
Cumulus is cottony
á Clouds formed at medium or low elevation.
á Cumulus clouds are puffy with flat bottoms, like cotton balls.
á When cumulus clouds are white they often signal fair weather, but when they are darker, they may signal rain or thunderstorms.
Cirrus are "see through"
á Clouds formed at high elevations; wispy clouds usually consisting of ice crystals that signal fair weather or may also signal an approaching warm front.
Stratus are "spread out"
á Clouds formed at medium or low elevation; spread out layer upon layer covering a large area
á As stratus clouds thicken, precipitation usually occurs over that area.
. Fog is a stratus cloud on the ground.
The names of many clouds are a combination of one of the three basic shapes and a prefix or suffix. The basic shape name can be combined with the appropriate prefix or suffix listed below as clues to the weather conditions that may result.
á Combinations of those shapes can be used with nimbus or nimbo, which means ÒrainÓ, for example, cumulonimbus or nimbostratus.
á A cumulonimbus cloud, also called a thunderhead, is often part of thunderstorm conditions that may accompany a cold front.
á The prefix alto- may also be used to indicate medium-level clouds formed at about 2-6 kilometers up into the atmosphere, for example, altocumulus or altostratus.
Clouds that form when condensation occurs at or near the ground are called fog.
The movement of air masses, high and low pressure systems, and frontal boundaries to storms (including thunderstorms, hurricanes, and tornadoes) and other weather conditions.
Interactions between air masses, fronts, and pressure systems result in various weather conditions.
á Air masses are huge bodies of air that form over water or land in tropical or polar regions.
á Temperature and humidity conditions (for example, warm or cold air, humid or dry air) within the air masses as they form are important to the resulting weather conditions when air masses move.
. Continental air masses are dry and form over land. Maritime air masses form over the ocean and contain lots of moisture. tropical air masses are warm and polar air masses are cold.
. 4 types of air masses; cP, cT, mP, mT
á As these air masses move and collide with each other, fronts form at the boundaries between the air masses.
á Depending upon the air masses involved, a warm front, cold front, stationary front, or occluded front can develop.
á When a warm air mass collides and rides over a cold air mass, the resulting warm front may produce long periods of precipitation and warmer temperatures.
á When a cold air mass collides and slides under a warm air mass, the resulting cold front may produce thunderstorms and sometimes tornadoes and cooler temperatures.
á When neither a cold air mass nor a warm air mass moves at a frontal boundary, the resulting stationary front may produce long period of precipitation.
á When a cold air mass pushes into a warm air mass that is behind a cool air mass, the warm air mass is pushed up above the cooler air masses. The resulting occluded front may produce long periods of precipitation.
High/Low Pressure Systems
á Warm air rising or cold air sinking combined with the spinning of Earth causes the air to spin forming high and low pressure regions.
á High pressure systems usually signal more fair weather with winds circulating around the system in a clockwise direction.
á Low pressure systems with counterclockwise circulating winds often result in rainy and/or stormy weather conditions.
á Severe weather conditions called storms occur when pressure differences cause rapid air movement.
á Conditions that bring one kind of storm can also cause other kinds of storms in the same area.
á Thunderstorm is storm with thunder, lightning, heavy rains and strong winds; form within large cumulonimbus clouds; usually form along a cold front but can form within an air mass.
á Tornado is a rapidly whirling, funnel-shaped cloud that extends down from a storm cloud; the very low pressure and strong winds can cause great damage to people and property, can have winds up to 300 mph; usually form within strong thunderstorms are also present.
á Hurricane is a low pressure tropical storm that forms over warm ocean water; winds form a spinning circular pattern around the center, or eye, of the storm; the lower the air pressure at the center, the faster the winds blow toward the center of the storm. Hurricanes begin to lose strength and die when the touch land. The most dangerous storms because they are so HUGE and last for up to two weeks.
Other Weather Conditions
á Since weather is a condition of EarthÕs atmosphere at any time, weather conditions may include fair weather, showers or light rain, humid conditions, clear skies with cold conditions, days of clouds and precipitation, or others that do not necessarily involve storms.
Anemometer- A tool used to measure wind speed in miles per hour.
á A tool used to measure wind direction.
á Sometimes referred to as a wind-weather vane or a wind sock.
á Wind direction is described by the direction from which the wind is blowing.
Thermometer - A tool used to measure air temperature in degrees Fahrenheit or Celsius.
Sling Psychrometer- A two-thermometer instrument also referred to as a wet-dry bulb used to measure relative humidity (the amount of water vapor in the air).
á Temperatures readings are converted using a relative humidity table.
Barometer- A tool used to measure air pressure in inches of mercury or millibars (mb).
Rain gauge- A tool used for measuring the amount of precipitation in inches or centimeters.
Weather forecasts are based on weather data collected from direct observations and measurements, weather maps, satellites, and radar.
Weather conditions and patterns can be predicted based on weather data collected from various sources.
Direct Observations and Measurements
.Meteorologists- people who study and make predictions about the weather.
á Basic weather conditions can be observed and/or measured by meteorologists at national weather data collection sites.
á In order to make weather predictions, the data should be collected on a regular basis over a period of time.
á This allows for the development of patterns in weather conditions from the analysis of the data.
á For example, a hurricaneÕs path can be predicted using data on its position over time (plotted on a hurricane tracking map), thereby allowing meteorologists to make predictions concerning the possible warnings to land areas in the hurricaneÕs path.
á Weather maps can help predict weather patterns by indicating high or low pressure systems (isobars), movement of air masses and fronts, or temperature ranges (isotherms).
á Satellite images are used for seeing cloud patterns and movements.
á For example, hurricane clouds and movement can be observed using satellite images.
á Radar images can be used to detect cloud cover, rainfall or storm location, intensity, and movement, as well as the potential for severe weather (for example, hurricanes or tornadoes).
How solar energy affects EarthÕs atmosphere and surface (land and water).
The driving energy source for heating of Earth and circulation in EarthÕs atmosphere comes from the Sun and is known as solar energy.
Some of the SunÕs energy coming through EarthÕs atmosphere is reflected or absorbed by gases and/or clouds in the atmosphere.
á The land heats up and releases its heat fairly quickly, but water needs to absorb lots of solar energy to warm up. This property of water allows it to warm more slowly but also to release the heat energy more slowly. It is the water on Earth that helps to regulate the temperature range of EarthÕs atmosphere.
á Solar energy that is absorbed by EarthÕs land and water surfaces is changed to heat that moves/radiates back into the atmosphere (troposphere) where the heat cannot be transmitted through the atmosphere so it is trapped.
How convection affects weather patterns and climate.
Because warm air near EarthÕs surface rises and then cools as it goes up, a convection current is set up in the atmosphere.
Convection happens on a global scale in the atmosphere and causes global winds. These winds then move weather systems and surface ocean currents in particular directions.
á Due to the spinning of Earth, rising warm air near the equator, and sinking cold air in the polar regions, the global wind belts are set up.
. Global winds or prevailing winds blow 24/7. They are the Trade winds near the equator, the Westerlies at about 40 degree N and S of the equator, and the Polar Easterlies up near the N and S Poles.
á On a smaller scale, convection currents near bodies of water can cause local winds known as land and sea breezes.
á The surface currents of EarthÕs oceans that circulate warm and cold ocean waters in convection patterns also influence the weather and climates of the landmasses nearby.
á The warm Gulf Stream current water influences the eastern Atlantic shoreline of the United States, while the cold California current influences its western Pacific shoreline.
The unequal heating of the Earth drives the weather.
The influence of global winds and the jet stream on weather and climatic conditions.
Global winds are found in each convection region.
á Because of convection in the atmosphere and the Earth is spinning on its axis, global winds appear to curve. This is known as the Coriolis effect.
á In the global wind belt regions, the prevailing direction of the winds and how air movement in these large regions affects weather conditions.
á The trade winds blow from east to west in the tropical region moving warm tropical air in that climate zone.
á The prevailing westerly winds blow from west to east in the temperate region.
á The temperate zone( where we live) temperatures are affected most by the changing seasons, but since the westerly wind belt is in that region, the weather systems during any season move from west to east. Since the United States is in the westerly wind belt, the weather systems move across the country from west to east.
á Tropical weather systems, for example hurricanes, are moved in the prevailing direction of the trade winds. If they enter the westerly wind belt, they are often turned, and move in the direction of that prevailing system. Hurricanes are pushed along by the Trade Winds. The coriolis effect makes them curve upward until they get caught by the Westerlies.
á The polar winds blow northeast to west in the polar region moving cold polar air in that climate zone from the poles toward the west.
Jet stream- A fast-moving ribbon of air that moves from west to east in the Northern Hemisphere around Earth. It dips and bends and constantly changes positions. The Jet Stream acts like a fence that separates cold polar air from warm southern air. Our super cold winter weather happens when the Jet Stream dips down across Georgia.