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Climate and Weather extended definition

Weather is considered to be the atmospheric conditions that are happening now or within a few days. On the other hand, Climate represents the long term atmospheric patterns within which weather occurs. As the popular saying goes, "Climate is what you expect, and weather is what you get!".

Tilt/Latitude extended definition

Latitude is a measure of the distance you are located from the equator.  It is commonly shown as an imaginary horizontal line that goes across the earth on maps and is used along with longitude as a reference point to determine location. The tilt of the earth affects the seasons we experience throughout the year.

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1.3 Atmospheric Properties

Temperature ex def

Temperature is the measure of thermal or internal energy of the molecules within an object or gas.    We can measure temperature of an object using either direct contact or remote sensing.  Temperature of air is closely related to other atmospheric properties, such as pressure, volume and density.

Density extended definition

Density measures the ‘heaviness’ of an object or how closely ‘packed’ the substance is.  Density is related to both the type of material that an object is made of and how closely packed the material is.

Pressure extended definition

Pressure is the force exerted over a given area or object, either because of gravity pulling on it or other motion the object has.  Molecules in the air produce pressure through both their weight and movement, and this pressure is connected to other properties of the atmosphere.

Humidity extended definition

Humidity is a measure of the amount of moisture in the air.  It tells you how comfortable it is to be outside, and if there is enough moisture to create clouds and rain.

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1.4 Energy Transfer

Conduction extended definition

Conduction is the transfer of heat through a solid, liquid or gas by direct contact.

Convection extended definition

Convection is the transfer of heat through the movement of liquids and gases.

Radiation extended definition

Radiation is the transfer of energy through air and space by light waves (visible, ultraviolet and infrared waves).

Latent/Sensible Heat extended definition

Latent and sensible heat are types of energy released or absorbed in the atmosphere.  Latent heat is related to changes in phase between liquids, gases, and solids.  Sensible heat is related to changes in temperature of a gas or object with no change in phase.

Evapotranspiration and Evaporation extended definition

Evapotranspiration is the process of evaporating water from leaves through plant transpiration during photosynthesis.  It varies because of a multitude of factors like wind, temperature, humidity, and water availability.

Longwave & Shortwave Radiation extended definition

Everything that has a temperature gives off electromagnetic radiation (light).  The sun is extremely hot and has a lot of energy to give, so it gives off shortwave radiation because shortwave radiation contains higher amounts of energy  The earth is much cooler, but still emits radiation.  Earth’s radiation is emitted as longwave because longwave radiation contains a smaller amount of energy.

Albedo extended definition

Albedo (al-bee-doh) is a measure of how much light that hits a surface is reflected without being absorbed.  Something that appears white reflects most of the light that hits it and has a high albedo, while something that looks dark absorbs most of the light that hits it, indicating a low albedo.

Earth's Energy Balance extended definition

Earth's Energy balance describes how the incoming energy from the sun is used and returned to space.  If incoming and outgoing energy are in balance, the earth's temperature remains constant.

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1.5 The Atmosphere

Structure of the Atmosphere extended definition

The atmosphere has 4 layers: the troposphere that we live in near the surface of the earth; the stratosphere that houses the ozone layer; the mesosphere, a colder and lower density layer with about 0.1% of the atmosphere; and the thermosphere, the top layer, where the air is hot but very thin.

Composition of the Atmosphere extended definition

The atmosphere contains many gases, most in small amounts, including some pollutants and greenhouse gases.  The most abundant gas in the atmosphere is nitrogen, with oxygen second.  Argon, an inert gas, is the third most abundant gas in the atmosphere.

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1.6 Understanding Weather Patterns

isobars and Isotherms extended definition

Isobars and isotherms are lines on weather maps which represent patterns of pressure and temperature, respectively. They show how temperature and pressure are changing over space and so help describe the large-scale weather patterns across a region in the map.

Convergence & Divergence extended definition

Convergence and divergence roughly determine where air will be sinking or rising.  Rising air is associated with clouds and precipitation; sinking air is associated with clear, calm conditions and good weather.

Air Masses extended definition

An air mass is a large uniform volume of air that has consistent properties of density, temperature, and humidity, compared to the air surrounding this air mass which may have different properties.

Fronts extended definition

A front describes the boundary between two air masses containing different temperature and/or water vapor content.

Jet Streams extended definition

Jets are fast moving ribbons of air high up in the atmosphere.  They are responsible for transporting highs and lows.  They affect precipitation and temperatures, and they mark boundaries between massive air masses.

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1.7  Weather Forces

Coriolis Effect extended definition

The Coriolis Effect describes the turn of the wind to the right in the Northern Hemisphere caused by earth's rotation.

What Drives Weather extended definition

Weather is ultimately caused by temperature differences due to variations in solar energy input.  These temperature differences cause pressure variations in the atmosphere.  The wind blows to try and correct these imbalances in pressure.  Regions of low and high pressure moving through an area cause changes in weather as different air masses pass by.

Friction & Turbulence extended definition

Friction slows the wind and changes its direction.  This effect can cause turbulence in winds near the surface or boundaries between areas with different surface roughnesses.  Turbulence mixes the lower part of the atmosphere, stabilizing the temperature.  Turbulence causes eddies in the atmosphere, which are swirls of wind responsible for wind gusts and bumpy plane rides.

Wind Shear extended definition

Wind shear is the change of wind speed and/or wind direction over a certain height.

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1.8  The Water Cycle

The Water Cycle extended definition

About 70% of the earth’s surface is covered with water.  This water evaporates and condenses into clouds.  The clouds cause precipitation and this water falls back to the earth’s surface, ready to start the cycle again. 

Stability extended definition

Atmospheric stability tells you how likely it is air will rise and form clouds and precipitation.  Unstable  air is likely to rise and form tall clouds and often precipitation.  Stable air means any air that rises up will sink back to where it came from.

Lifting Mechanisms extended definition

Lifting mechanisms are forms of lift that cause air to rise. In this topic we cover orographic lift, frontal lift, convergence, and convective lift.

How Clouds Form extended definition

Clouds form when moist, warm rising air cools and expands in the atmosphere.  The water vapor in the air condenses to form tiny water droplets which are the basis of clouds.

Precipitation Types extended definition

There are many types of precipitation.  Rain and drizzle are the only liquid types; the freezing types are snow, sleet, freezing rain, and hail.  Hail is unique because it is frozen precipitation that generally only falls from thunderstorms in the summer.

Cloud Seeding extended definition

Cloud seeding is the process where substances like dry ice and silver iodide are put into clouds in an attempt to make precipitation fall.  Cloud seeding has also been used to dissipate fog and weaken some storms.

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1.9  Severe Weather

Severe Weather Hazards extended definition

Severe weather hazards are dangerous weather phenomena that threaten life and property. Within this topic, we discuss tornadoes, lightning, hail, flash flooding, and downbursts.

Life Cycle of a Thunderstorm extended definition

A basic thunderstorm (single cell) goes through three phases during its lifetime: cumulus, mature, and dissipating. This can last between 30 minutes to an hour.

Thunderstorm Classification extended definition

Although thunderstorms can vary in size and shape, we can classify them into four main groups: single cell, multi-cell clusters, multi-cell lines, and supercells.

Watches & Warnings extended definition

The National Weather Service (NWS) issues watches and warnings all across the United States to warn people of impending, dangerous weather.

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1.10  Measuring Weather and Climate

Instruments extended definition

Weather instruments are used to take measurements of various atmospheric parameters at local weather stations.

Averages and Normals ex def

Average weather and climate conditions describe the expected weather a location is likely to get. Normal conditions describe what is normal for an area using the most recent statistically adjusted 30-year interval of the average weather conditions.

Extremes ex def

Extremes of weather describe the range of possible weather and climate conditions that you can expect to encounter at your location. These can be expressed in a variety of ways, from the highest or lowest temperature ever reported at a site to a probability of occurrence for rare events like heavy rainstorms.

Trends exdef

Trends in climate can be caused by natural changes or variability in ocean currents, land use, solar radiation, or other factors. They can also be the result of manmade influences on climate. While some trends in climate variables reflect local changes in climate at a single location, trends across regions and the globe indicate significant movements away from "average" conditions which could cause disruptions in society and global ecosystems.

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2.1  Circulations

General Circulation of the Atmosphere extended definition

Winds circulate around the globe because of the rotation of the earth and the energy from the sun.

Ocean Circulations extended definition

Much like the earth’s atmosphere, which circulates warm and cold air across the earth, the ocean also circulates warm and cold water across the world.

Temperature Gradient Extended definition

A temperature gradient is the change in temperature across a specified boundary or front.

Sea/land breezes extended definition

Sea and Land Breezes describe the wind that blows onshore from sea to land during the day and blows offshore in the evening.

Monsoon Systems extended definition

Monsoons are massive, seasonally changing sea breeze circulations that form due to temperature differences between land and ocean.

Semi-permanent highs and lows extended definition

Semi-permanent highs and lows are persistent pressure systems that appear over an area during the year and affect how storms and weather systems enter the United States.

MLC extended definition

Mid-latitude cyclones are huge weather systems that form from a low pressure system and cover a wide area with precipitation.

Tropical Cyclones extended definition

Tropical Cyclones are powerful storms that develop over the ocean, mostly during the summer months.  The Southeast is affected by tropical storms that form in the Atlantic Ocean and the Gulf of Mexico.

NAO extended definition

The North Atlantic Oscillation is a weather phenomenon that affects the jet stream and can alter weather patterns in some parts of the world.

PNA extended definition

The Pacific/North American Pattern describes a change from normal in surface temperature and precipitation patterns across the United States.

El Nino extended definition

El Niño is a climate pattern representing an unusual warming of the eastern tropical Pacific Ocean which is linked to impacts on weather and climate patterns around the world.

La Nina extended definition

La Niña is a climate pattern representing the cooling of the eastern tropical Pacific Ocean which impacts weather and climate conditions all over the world.

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2.9  Southeast Climate Patterns

Southeast Temperature extended definition

The information below focuses on the changes of temperature the Southeast United States experiences.

Southeast Precipitation extended definition

The Southeast (as defined here) includes NC, SC, AL, GA, FL, and VA.  The Southeast gets an average of around 50 inches of precipitation each year, including some frozen precipitation in all areas except most of Florida and southern Georgia.

Southeast Frosts & Freezes extended definition

Frosts form when temperatures are near or below freezing and relative humidity values approach 100% near the ground.  A freeze occurs when the temperature is at or below 32oF throughout the area.  In a freeze, surface temperatures can drop to below 28 degrees, which is the threshold for killing damage for many plants.

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2.10  Drought and Heat

Drought extended definition

Drought occurs when sufficient water needed to sustain an area is not available, causing economic impacts on agriculture, society, and ecosystems.  It is most often caused by lack of rainfall over a long time period but can also be affected by unusually high temperatures and dry spells, particularly during summer months.

Effects of drought extended definition

Lessened amounts of precipitation over an area for an extended period of time has many effects on farmland and crops. Drought conditions result from a lack of precipitation and this has many effects on the surrounding land and weather conditions. Drought conditions can worsen after prolonged periods of no rainfall, especially in areas where the water supply is short.

Heat Waves extended definition

Heat waves are extended periods of unusually hot weather that affect human and animal health as well as energy use.

Drought and wildfires extended definition

Wildfires can occur during drought conditions when the land and vegetation have dried out.

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Climate Change


Vegetation ex def

Vegetation covers a considerable portion of the earth and has an effect on weather and climate.  Vegetation influences both albedo of the earth and the amount of water vapor and carbon dioxide in the air. 

Greenhouse Effect ex def

The "greenhouse effect" is the effect of atmospheric gases like carbon dioxide absorbing energy from the sun and earth and "trapping" it near the Earth's surface, warming the Earth to a temperature range that is hospitable for life.

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3.3  Greenhouse Gases

Greenhouse Gases ex def

Greenhouse gases are gases that absorb energy emitted from the earth and radiate it back into the atmosphere.  If there are too many greenhouse gases, the earth could become too warm. If greenhouse gases dramatically decrease, the earth may be too cool for human activities, such as farming, planting, and harvesting, to occur.

Ozone ex def

Ozone isn’t a typical greenhouse gas.  It has two distinct functions in the atmosphere.  High in the stratosphere, it absorbs ultraviolet light from the sun and protects the earth.  Near the ground, it serves as a pollutant and contributor to smog and also has greenhouse characteristics.

Nitrous Oxide ex def

Nitrous oxide is the third most influential greenhouse gas.  It stays in the atmosphere for an estimated 115 years, so the 40% contribution from human activities adds up quickly.  The human contribution comes from sources like fertilizer and livestock and human and animal wastes.

Carbon Dioxide ex def

Carbon dioxide is an abundant greenhouse gas that is believed to be the main cause of global warming.  The concentration is increasing fairly rapidly.  Carbon dioxide is a natural biproduct of animal and plant respiration but is also caused by human activities like fossil fuel burning, deforestation, and biomass burning.

Aerosols ex def

Aerosols are small particles in the atmosphere that often cause cooling by reducing incoming sunlight.  Certain types can cause warming, and all of them change the way clouds behave.

Methane ex def

Methane is second only to carbon dioxide in its impact as a greenhouse gas.  It comes from landfills, livestock, natural gas systems, wetlands, and natural gas stores within the earth.

Water Vapor ex def

Water Vapor is always in the atmosphere, and it absorbs heat from the sun.  Some amount of water vapor is necessary in the atmosphere. Without it, it would never rain and we wouldn’t be able to go outside without dehydrating very quickly. The amount of water vapor in the air has impacts on humidity, cloud formation, and precipitation.

Halocarbons ex def

Halocarbons are the substances responsible for the hole in the ozone layer.  Though they have been heavily regulated, they are still responsible for some amount of global warming.

Ozone Layer ex def

The ozone layer is a region in the Stratosphere where ozone is highly concentrated.

Global Warming vs. Climate Change ex def

"Global warming" describes an average temperature increase of the Earth over time.  "Climate change" describes how weather patterns will be affected around the globe.  These changes could be manifested in changes in climate averages as well as changes in extremes of temperatures and precipitation.  It is likely that the changes will vary depending on what region you are in.  "Global change" describes other effects that don’t fall into either category, like socioeconomic and ecological impacts.

Models ex def

Atmospheric models are used for every day weather events and short-term forecasting while climate models are used for longer term forecasts.  Climate forecasts are generally divided into statistical forecasts, which cover seasonal to annual forecasts, and global climate models, which use equations to simulate the climate across the entire globe over a long time period.

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3.6  Climate Change Causes

Causes of Climate Change ex def

The climate of the earth fluctuates, and there are many things that affect it.  Volcanoes, changes in the orbit and the sun, greenhouse gases and the properties of the earth itself have influence over the climate.

Milankovitch Cycles ex def

These cycles are caused by changes in the earth’s orbit around the sun, like its shape or eccentricity, its precession or wobble, and the tilt of its axis or obliquity.  Each of these have a different effect on how much of the sun’s energy reaches the earth and when the strongest sunlight occurs.

Solar Cycles ex def

The sun has a magnetic field that flips approximately every 11 years.  Sunspots and solar flares are caused by the magnetic activity of the sun. The sunspots and solar flares can affect the earth by changing the amount of incoming sunlight and interacting with the earth's magnetic field. The disruption of our electromagnetic field interferes with our all of our electronics, radios and satellites and can cause the aurora borealis in the Northern Hemisphere.

Effects of CC on SE ex def

The Southeast is experiencing climate change.  Generally, temperatures are expected to become warmer with more extreme heat waves.  Changes in rainfall are less certain.  Sea level rise coupled with increased hurricane intensity could be detrimental  to Southeastern coastlines.

Last modified date: Wednesday, July 18, 2012 - 11:59am