Background and Basics
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!".
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.
1.3 Atmospheric Properties
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 measures the â€˜heavinessâ€™ of an object or how closely â€˜packedâ€™ 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 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 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.
1.4 Energy Transfer
Conduction is the transfer of heat through a solid, liquid or gas by direct contact.
Convection is the transfer of heat through the movement of liquids and gases.
Radiation is the transfer of energy through air and space by light waves (visible, ultraviolet and infrared waves).
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 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.
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. Earthâ€™s radiation is emitted as longwave because longwave radiation contains a smaller amount of energy.
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 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.
1.5 The Atmosphere
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.
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.
1.6 Understanding Weather Patterns
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 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.
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.
A front describes the boundary between two air masses containing different temperature and/or water vapor content.
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.
1.7 Weather Forces
The Coriolis Effect describes the turn of the wind to the right in the Northern Hemisphere caused by earth's rotation.
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 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 is the change of wind speed and/or wind direction over a certain height.
1.8 The Water Cycle
About 70% of the earthâ€™s surface is covered with water. This water evaporates and condenses into clouds. The clouds cause precipitation and this water falls back to the earthâ€™s surface, ready to start the cycle again.
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 are forms of lift that cause air to rise. In this topic we cover orographic lift, frontal lift, convergence, and convective lift.
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.
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 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.
1.9 Severe Weather
Severe weather hazards are dangerous weather phenomena that threaten life and property. Within this topic, we discuss tornadoes, lightning, hail, flash flooding, and downbursts.
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.
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.
The National Weather Service (NWS) issues watches and warnings all across the United States to warn people of impending, dangerous weather.
1.10 Measuring Weather and Climate
Weather instruments are used to take measurements of various atmospheric parameters at local weather stations.
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 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 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.
Winds circulate around the globe because of the rotation of the earth and the energy from the sun.
Much like the earthâ€™s atmosphere, which circulates warm and cold air across the earth, the ocean also circulates warm and cold water across the world.
A temperature gradient is the change in temperature across a specified boundary or front.
Sea and Land Breezes describe the wind that blows onshore from sea to land during the day and blows offshore in the evening.
Monsoons are massive, seasonally changing sea breeze circulations that form due to temperature differences between land and ocean.
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.
Mid-latitude cyclones are huge weather systems that form from a low pressure system and cover a wide area with precipitation.
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.
The North Atlantic Oscillation is a weather phenomenon that affects the jet stream and can alter weather patterns in some parts of the world.
The Pacific/North American Pattern describes a change from normal in surface temperature and precipitation patterns across the United States.
El NiÃ±o 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 NiÃ±a is a climate pattern representing the cooling of the eastern tropical Pacific Ocean which impacts weather and climate conditions all over the world.
2.9 Southeast Climate Patterns
The information below focuses on the changes of temperature the Southeast United States experiences.
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.
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.
2.10 Drought and Heat
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.
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 are extended periods of unusually hot weather that affect human and animal health as well as energy use.
Wildfires can occur during drought conditions when the land and vegetation have dried out.
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.
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.
3.3 Greenhouse Gases
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 isnâ€™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 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 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 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 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 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 wouldnâ€™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 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.
The ozone layer is a region in the Stratosphere where ozone is highly concentrated.
"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 donâ€™t fall into either category, like socioeconomic and ecological impacts.
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.
3.6 Climate Change Causes
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.
These cycles are caused by changes in the earthâ€™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 sunâ€™s energy reaches the earth and when the strongest sunlight occurs.
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.
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.