THE COMPOSITION OF THE ATMOSPHERE
The atmosphere is a huge cloud of gas surrounding Earth. It becomes thinner as you get closer to outer space. The atmosphere is held into position by gravity. The Sun also keeps the atmosphere in place. If there was no Sun, the atmosphere would freeze and collapse to Earth, which would then lead to harmful UV radiation as the Earth moved in a straight line through outer space. Global temperatures would plunge to absolute zero within a couple of weeks, killing all life on Earth, except for some types of bacteria, such as archaea, which live in extreme environments.
The dry parts of the atmosphere include nitrogen, oxygen, argon, carbon dioxide, and other gases. Nitrogen, oxygen, argon, and CO2 are the most abundant gases in the atmosphere, in total making up over 99% of it, with nitrogen being the most common, at 78%.
Nitrogen dilutes oxygen and it prevents the Earth’s surface from burning up.
Oxygen is necessary for respiration and it is also necessary for things to burn or combust.
Argon preserves paper and it is also used in light bulbs.
CO2 is a greenhouse gas, just as NOAA says it is. CO2 does in fact keep some heat from escaping into outer space, in which the heat is absorbed by the CO2 molecules, and then gets reflected back to Earth’s surface and heats it again. However, to the contrary of NOAA’s and NASA’s beliefs, CO2 is a very weak greenhouse gas.
According to a chemistry teacher I know, “the CO2 molecule is very rigid due to its double bond structure and very low polarity due to symmetry. CO2 is a lousy greenhouse gas. Nitrogen and Oxygen are NOT greenhouse gases due to their double and triple bond structures, and even lower polarity. CO2, unlike O2 and N2, does have some greenhouse characteristics, [which makes it a greenhouse gas], but as a greenhouse gas, it is very weak. It just happens to be the second most abundant greenhouse gas in the atmosphere. The only reason CO2 is on the radar is due to its abundance in the atmosphere. If CO2 was a major contributor [to global warming], we would see the results quite vividly. The fact that we don’t proves it is not.”
In addition, carbon dioxide only makes up 0.04% of Earth’s atmosphere. Furthermore, only 4.6% of CO2 in the atmosphere has come from human emissions. A new study has shown that the CO2 levels would be at 392 ppm without man-made emissions. That is only 19 ppm less than the current levels of 411 parts per million. The energy that CO2 absorbs is very little and the heat reflected back to Earth’s surface is even less than what is absorbed. Therefore, any global warming taking place has to be influenced by other factors, such as the Sun or ocean cycles.
Water vapor is a much bigger greenhouse gas than CO2, which means that an increase in H2O concentration in the atmosphere would be somewhat alarming, however, that is something that is probably not going to happen, because the climate system is designed so that there won’t be an increase in water vapor levels in the air.
Water vapor can make up to 4% of the atmosphere at maximum and 0% at minimum, depending on the region of the Earth you are looking at. In deserts, there are dry winds, which keep the H2O concentration at 0%. In tropical climates, the levels are at 3%, pushing closer to 4% closer the equator.
THE LAYERS OF THE ATMOSPHERE
The atmosphere has five different layers, each separated by a ‘pause.’
- The outermost layer of Earth’s atmosphere.
- Extends from the top of the thermopause to 6,000 miles (10,000 km) above the Earth.
- Atoms and molecules escape to outer space in this layer.
- Satellites orbit the Earth here.
- Separated from the thermosphere by the thermopause, which is around 375 miles (600 km) above Earth.
- Extends from the top of the mesopause to 375 miles (600 km) above Earth.
- Extremely thin, but becomes denser as you get closer to Earth’s surface.
- UV radiation from the Sun gets absorbed by the air molecules in the thermosphere, which causes a huge temperature increase from -184°F (-120°C) at the bottom, to 3,600°F (2,000°C) at the top.
- The extremely hot temperature would actually feel really cold to our body, because the thermosphere has extremely thin air. There are less molecules in the air, so the amount of energy absorbed by the molecules is not enough to heat our skin.
- Within the thermosphere, lies the ionosphere, which extends between 37 miles (60 km) and 190 miles (300 km) above Earth’s surface.
- It is divided into three layers; the F-Layer, E-Layer, and D-Layer.
- During the daytime, the F-Layer splits into two layers, then it recombines during nighttime.
- The E-Layer was discovered in 1901, while Marconi was transmitting a signal between Europe and North America. The signal showed that it had to bounce off of an electrically conductive region, approximately 62 miles (100 km) above Earth’s surface. The region was named the E-Layer (Electrical-Layer) in 1927 by Sir Edward Appleton. In addition to the E-Layer, the F-Layer and D-Layer were discovered later on.
- The ionosphere exists because of the UV radiation being absorbed by molecules.
- The density of the ionosphere changes from day to night. All layers of the ionosphere are denser during the day because of the Sun. The opposite happens at night, and the layers become less dense, with the D-Layer simply disappearing altogether.
- The ionosphere is important, because it bounces radio signals transmitted from a radio.
- Extends from the stratopause, about 31 miles (50 km) to 53 miles (85 km) above the Earth’s surface.
- Temperatures increase as you get closer to Earth, because the air gets denser; with the temp rising to about 5°F (-15°C).
- The molecules here are now dense enough to slow down meteors and meteorites.
- Extends from the tropopause, about 4 to 12 miles (6 to 20 km) above the surface to 31 miles (50 km).
- The stratosphere consists of most of the gases in the atmosphere, except for water vapor. (There is only a little bit of water vapor in the stratosphere).
- Unlike the mesosphere, the temperature increases with height here. The temperature goes from -60°F (-51°C) at the bottom to 5°F (-15°C) at the top.
- The increase in temperature means that warm air is atop the cooler air. This prevents convection because there is no vertical movement of the gases in the atmosphere. You can easily see the bottom of the stratosphere by looking at the anvil-shaped top of a cumulonimbus cloud.
- Extends from Earth’s surface to about 4 to 12 miles (6 to 20 km) above the Earth’s surface depending on the terrain and shape of the atmosphere surrounding the Earth. At either pole, the top of the troposphere is about 4 miles (6 km) above the surface. At 50°N and 50°S, it is about 5.5 miles (9 km) above the Earth’s surface, and at the equator, it is about 12 miles (20 km).
- This layer is known as the lower atmosphere.
- All weather occurs here.
- Temperature decreases with height; it goes from about 59°F (15°C) to -60°F (-51°C).
The atoms and molecules in the air that make up the atmosphere constantly move. When they touch a surface, they apply a force on the surface of that object. We call this pressure. Even though each atom and molecule are tiny, a large number of them can exert a noticeable force when striking a surface.
Air pressure can be increased or decreased in two ways. The first way to increase air pressure is by adding molecules to a container. A greater quantity of molecules will increase the number of collisions with the container’s boundaries, which will increase the pressure. This can be observed by pumping air into a tire. When pumping air into a tire, the number of molecules will increase, which will in turn increase the number of collisions with the tire’s boundaries. The increase in collisions makes the tire pressure higher, which causes the tire to inflate, or expand. To decrease the air pressure, you simply do the opposite of what you do to increase the pressure.
The other way to increase or decrease air pressure is by adding or subtracting heat. The addition of heat to an object will cause the object to expand. This is because the heat adds energy to air molecules. The increased energy in air, increases the number of collisions with an object’s boundary, which increases the pressure.
As elevation increases, the number of air molecules decrease, which makes the air less dense. This causes a decrease in atmospheric pressure. One half of the total air molecules in the Earth’s atmosphere are within 18,000 feet (5.6 km) of Earth’s surface.
The decrease in air pressure with height makes it difficult to compare the air pressure at ground level from location to location because of elevation. In order to compare the air pressures at any two or more given locations, there has to be a common denominator to which we convert the air pressure at that location to the common denominator. This is done by converting it to sea-level elevation. The number we would get from doing the conversion would be equal to the air pressure reading if the station were to be at sea-level.
The most common units to measure air pressure in the United States are ‘Inches of Mercury’ and ‘Millibars.’ According to the National Weather Service,
“Inches of mercury refers to the height of a column of mercury measured in hundredths of inches. This is what you will usually hear from the NOAA Weather Radio or from your favorite weather or news source. At sea level, standard air pressure is 29.92 inches of mercury.”
“Millibars comes from the original term for pressure “bar.” Bar is from the Greek “báros” meaning weight. A millibar is 1/1000th of a bar and is approximately equal to 1000 dynes (one dyne is the amount of force it takes to accelerate an object with a mass of one gram at the rate of one centimeter per second squared). Millibar values used in meteorology range from about 100 to 1050. At sea level, standard air pressure in millibars is 1013.2. Weather maps showing the pressure at the surface are drawn using millibars.”
Air pressure is constantly changing. The changes in air pressure are due to changes in air density. Air density is closely related to temperature. Cooler air is denser than warmer air because the molecules in warmer air have a greater velocity. They are also farther apart in warmer air than in cooler air. While the average altitude of the 500 millibar level is approximately 18,000 feet (5,600 m), the elevation will be higher in warm air than in cooler air.
Air pressure changes most noticeably at 4 a.m./4 p.m., which is when pressure is at its lowest, and at 10 a.m./10 p.m. when pressure is at its highest. This is due to the heat of the Sun. The air pressure change is usually greater at the equator than at the poles because the equator receives a lot more solar energy than the poles do. Air pressure also changes due to weather systems moving. These systems are easily identified on a weather map. The blue H represents and area of high pressure and the red L represents an area of low pressure.
So how do changes in weather influence air pressure changes? In 1948, Reverend Dr. Brewer of England wrote this in A Guide to the Scientific Knowledge of Things Familiar.
“The FALL of the barometer (decreasing pressure)
- In very hot weather, the fall of the barometer denotes thunder. Otherwise, the sudden falling of the barometer denotes high wind.
- In frosty air, the fall of the barometer denotes thaw.
- If wet weather happens soon after the fall of the barometer, expect but little of it.
- In wet weather if the barometer falls expect much wet.
- In fair weather, if the barometer falls much and remains low, expect much wet in a few days, and possibly wind.
- The barometer sinks lowest of all for wind and rain together; next to that wind, (except it be an east or north-east wind).
The RISE of the barometer (increasing pressure)
- In winter, the rise of the barometer presages frost.
- In frosty weather, the rise of the barometer presages snow.
- If fair weather happens soon after the ruse of the barometer, expect but little of it.
- In wet weather, if the mercury rises high and remains so, expect continued fine weather in a day or two.
- In wet weather, if the mercury rises suddenly very high, fine weather will not last long.
- The barometer rises highest of all for north and east winds; for all other winds it sinks.
The barometer UNSETTLES (unsteady pressure)
- If the motion of the mercury be unsettled, expect unsettled weather.
- If it stands at “MUCH RAIN” and rises to “CHANGEABLE” expect fair weather of short continuance.
- If it stands at “FAIR” and falls to “CHANGEABLE”, expect foul weather.
- Its motion upwards, indicates the approach of fine weather; its motion downwards, indicates the approach of foul weather.”
Rev. Dr. Brewer’s observations are true for multiple other locations, but not all of them. In the United Kingdom, storms bring huge pressure changes because the UK is near the end of the Gulf Stream. The only places in the U.S. that have large pressure changes are in the northern tier of the Lower 48 and in Alaska. None of Brewer’s observations hold true for the tropics, because there is little daily change in air pressure, unless there is a tropical cyclone inbound.
THE SUN’S MOVEMENT OF ENERGY & HEAT
The main driver of the climate system is the Sun. The Sun gives out energy to the planets in the solar system. This energy comes from TSI (Total Solar Irradiance) and sunspot count. The energy is given out by the Sun is energy in motion, otherwise known as kinetic energy. Temperature is a measurement of the amount of kinetic energy possessed by the particles of an object. The more energy that is given out by the Sun means that Earth will be warmer. The less energy given out by the Sun means that Earth will cool. There are three ways for which this energy is transferred through Earth’s atmosphere. They are radiation, conduction, and convection.
When the Sun’s rays enter the atmosphere, this is known as radiation. Some of this energy given out by the Sun is absorbed by the atmosphere, some gets reflected back into outer space by clouds, while some of it reaches the Earth’s surface. The rest of the energy gets absorbed by plants for the process of photosynthesis. The energy that is absorbed by the atmosphere will heat up the atmosphere. The energy that reaches Earth’s surface is an example of radiation. The energy heats the surface, then gets reflected back into outer space. The heat reflected helps heats the air, which is an example of conduction.
Most of the energy that is reflected off of the Earth’s surface is sent back into outer space. Some of the energy, however, gets trapped in the atmosphere as extra heat energy. Greenhouse gases like water vapor, ozone, methane, and carbon dioxide absorb this heat. Those greenhouse gases reflect the energy back to Earth’s surface and heat it again, while a portion of it is once again used for photosynthesis. This extra energy getting reflected back to Earth may result in more plant growth. As we have previously stated above, CO2 has very little effect on the global climate system.
Sooner or later, all of the energy given out by the Sun to Earth will escape back into outer space.
The solar energy the Earth receives is not evenly distributed around the globe. This is because of the Earth’s shape and the tilt of the Earth’s axis. The amount of energy received by Earth changes at different latitudes. This changes from season to season. The poles receive the least amount of solar energy while the Equator gets the majority of it, which is why the equator is hot and the poles are cold.
The climate system likes to try and balance the unevenly distributed energy by moving it around the globe, particularly from the equator to either pole. The oceans and air currents help move this energy around daily.
Near the equator, there is more energy in the atmosphere. This allows thunderstorms to develop. The cumulonimbus clouds force warm air to rise. The warm air will move toward the north or south pole depending upon atmospheric conditions.
The rising warm air cools with altitude. As the air cools, low pressure forms. This lower atmospheric pressure makes temperatures cooler and the weather stormier. When the air circulates downward, the air compresses, which increases the number of air molecule collisions with the ‘boundary’ which increases the air pressure. High pressure usually makes the weather dry and hot, but fair. In between each of the circulations lies areas of high and low pressure. High pressure areas are located at 30° N and at 30° S latitude and at each pole. These areas tend to house deserts (Fun Fact! Antarctica is a desert too). Low pressure bands are located at 50° to 60° N and 50° to 60° S latitude and also at the equator. These areas, especially on the west coasts of continents tend to have lots of precipitation because of the way storms move around those areas. This pattern of circulating air forms ‘cells.’
There are three circulations flowing toward each pole due to the Earth’s rotation.
- Hadley Cell | Lower latitude air moving toward the equator. With heating, it rises vertically, then moves poleward in the upper atmosphere.
- Ferrel Cell | Mid-latitude air circulation where air flows toward the poles and eastward close to the surface, and flows toward the equator and westward in upper air.
- Polar Cell | Air rises, then diverges and travels poleward. The air cools as it moves northward or southward. As it cools, the air sinks over the poles, compressing the air, which is what forms the polar highs. Once the air reaches the surface, the air diverges outward from the polar highs. Surface winds also known as polar easterlies, flow eastward.
This circulating air in the atmosphere is what causes wind. The air in the atmosphere acts like a fluid in the process of convection. The Sun’s radiation reaches the Earth’s surface, which warms the ground. As the Earth’s surface warms due to conduction, the heat from the ground will get reflected back into the air. This forms a bubble of warm air, which is surrounded by cooler air. As the air rises, the ‘bubble’ itself cools with the heat still inside. Eventually, the warm air will get replaced by the cool air surrounding it. The cooler air is denser, which sinks to the bottom, as we just stated. The warm air getting replaced with cool air is felt by us as wind. This circulating pattern of warm air forms cells all over the globe. These cells keep the heat moving around the atmosphere. The movements of these air masses can be localized, such as in cumulus clouds, or they can cover a large area, in the cells. These circular movements are a big part of the weather patterns in Earth’s atmosphere.
THE JET STREAM
There is actually more than one jet stream! The jet stream most of us think of is the Polar Jet Stream, which recently brought us the historic and prolonged Arctic outbreak during the Christmas Holidays in 2017 into January 2018.
Jet streams are narrow bands of strong wind in the upper atmosphere. The winds blow from the west to the east because of the Earth’s rotation, while the flow shifts from north to south depending on the phase of the NAO (North Atlantic Oscillation) and other atmospheric conditions. The jet streams follow the divide of cool and warm air. These boundaries are most noticeable during the winter months of both the Northern and Southern Hemispheres.
Areas around 30 N and S and 50 N and 50 S have the largest temperature swings and the strongest winds. Due to the increase in temperature differences, the wind speed must also increase. The 50° N and S areas house the Polar Jet Streams while the 30° N and S areas house the Subtropical Jet Streams. Wind speeds within each jet can reach an upward of 275 miles per hour (239 kts or 442 km/h).
These jet streams may shift and appear differently due to multiple factors such as where areas of high and low pressure reside as well as warm and cool air masses and the seasons. These jet streams may dip or rise (in altitude or latitude), they may split, or they may disappear completely and reform elsewhere.
During seasonal changes, the jet streams shifts toward the poles in the summer. In the winter, the jet streams shift toward the equator.
THE HYDROLOGIC CYCLE
The Hydrologic Cycle otherwise known as the Water Cycle is the continuous circulation of water in from the ground to the atmosphere and back again. There are many steps in this cycle, however, the most important and well-known are evaporation, transportation, condensation, precipitation, and runoff.
Over land, the Water Cycle is very complicated. There are a lot of steps.
Evaporation is the change of state in something from a liquid to a gas. In atmospheric science, the main substance that evaporates is water.
Water evaporates with energy. The more energy applied to something makes the object hotter, in this case, it is liquid water. The energy being applied to the liquid water is making the molecules in the water move faster, which causes the temperature to rise, which causes water to evaporate. This energy can come from the Sun, atmosphere, the Earth’s surface.
Transpiration is a form of evaporation. It is the evaporation of water from plants through the stomata (stomata are the pores in leaves connected to the plant’s vascular tissues). Transpiration is controlled by the humidity of the air and moisture content of the soil. Only 1% of water passing through the plant is used in the growth of the plant, while the other 99% is emitted into the atmosphere.
Condensation is when water vapor in the air is changed from a gas into a liquid. In meteorology, condensation appears as clouds or dew. In everyday life, you may see it on the edge of a cold drink, or on the inside or outside of a water bottle.
It does not matter what the temperatures is for condensation to occur. It is the difference between two temperatures, which are the air temperature, and the dewpoint. The dewpoint is the temperature where dew can form. If it is cool enough, the air becomes saturated with water. If it becomes cooler, the water vapor in the air will condense into a cloud. In order for fog to occur, the temperature and the dewpoint have to be equal.
Precipitation is what happens after the condensation of water molecules become too heavy for the rising air masses to support. Therefore, the water molecules fall to Earth in the form of rain, hail, sleet, freezing rain, or snow.
Runoff is what occurs in result of excessive precipitation. Due to the excessive precipitation, the ground becomes overly saturated, which means that the ground can not absorb any more water. Rivers and lakes have been formed due to excessive runoff, which is a process that takes thousands of years. Very little evaporation occurs in a river or lake, so in order for the water to escape, it will eventually flow into the ocean, in which the water will get evaporated for the cycle to start again. In a lake, evaporation is the only way that water molecules can be returned to the atmosphere. On occasion, the water molecules may contain grains of salt. Since salt does not evaporate at the temperatures water can, the salt grains are left in a lake, which in turn may make the lake salty.
The ocean also plays a big, but simple role in the Hydrologic Cycle.
Nearly all of the water used in the Hydrologic Cycle is contained in the oceans. In fact, over 96.5% of Earth’s water is contained in the ocean. On average, about 45 inches (114 cm) of water evaporates from the ocean annually. It can take up to a thousand years for one molecule of water to move from the oceans to the atmosphere. The highest rate of evaporation occurs in winter in the Northern and Southern Hemispheres. The east coasts of North America, South America, Asia, Africa, and Australia tend to have more evaporation than the western sides. This is because winter storms (in North America, Australia, and Asia) move off of the east coasts which have stronger winds than the west coasts. These winds carry the water vapor away from its starting point. This allows more evaporation to occur.
Warm ocean currents, such as the Gulf Stream play a big role in the evaporation. Warm water is carried northward by the ocean currents. Cold air masses drift over the warm water. This makes the atmosphere unstable, which causes a huge difference in ocean temperatures and air temperatures. The unstable atmosphere makes water evaporate more. The increased evaporation combined with an unstable atmosphere fuels winter storms. More powerful winter storms increase the amount of snow that the storm will produce. The excessive snowfall will eventually melt, which will increase the runoff, which causes massive flooding. However, over 90% of the evaporated water from the ocean falls back into the ocean. The other 10% falls over land.
WINTER & SUMMER SOLSTICE, AUTUMN & SPRING EQUINOX
As we have previously discussed, the equatorial region of Earth receives the majority of the Sun’s energy, but not always directly. The Earth’s axis is currently tilted at 23½°. The amount of radiation that a given place receives varies throughout the year. In the Northern Hemisphere’s winter, the Southern Hemisphere is in its summer. Therefore the Northern Hemisphere receives the lesser amount of solar energy, while the Southern Hemisphere receives the majority of the solar energy. The lowest amount of energy that the Northern Hemisphere receives in December 21st or 22nd depending upon the year. The opposite occurs during the Northern Hemisphere summer. The Northern Hemisphere receives the majority of the Sun’s heat while the Southern Hemisphere receives the least amount of energy. On June 22, the Northern Hemisphere receives the greatest amount of daylight and energy. On March 21 and September 23, both hemispheres get the same amount of daylight hours and energy.
There are many things needed for precipitation to occur and form. The first and probably most important thing you need is moisture, otherwise the air is going to be dry and you will simply get nothing out of it. Most of the moisture comes from evaporated water from the Gulf of Mexico and the Atlantic and Pacific Oceans. The winds flowing around high or low pressure systems will drive the moisture inland. Clouds will then form by the lifting of the air. The air is usually lifted by being forced upward close to the fronts of low pressure areas. The air may also be forced up and over mountains.
The evaporated water in the clouds form water droplets or ice crystals (if cold enough).
Water droplets are too small and lightweight to fall to the ground as precipitation. In order for rain to occur, we go through a process called the collision and coalescence process (a.k.a. warm rain process). Collisions will occur between all of the water droplets. None of the water droplets are the same size, so their speed is different. When colliding, they fall and stick together forming larger rain drops, which is known as coalescing.
In order for rain, snow, sleet, or hail to occur, all you need are heavy ice crystals and water droplets in a cold cloud. This is known as the ice crystal process. Water vapor will drop onto the ice crystals, which causes the crystals to grow in size. Sooner or later, the ice crystals will become too heavy to be sustained in the cloud, so they will fall to the ground as snow or sleet if the Earth’s surface is cold. If the surface is well above freezing (45°F or more), the ice crystals will melt as cold rain.
- Rain | Rain is the most common type of precipitation. The droplets are 0.02 inch to 0.5 mm or more.
- Drizzle | Drizzle is kind of like rain, but the droplets are very small and they are very close together. They appear to ‘float’ when following the wind or air currents. Drizzle often occurs with fog.
- Hail | Small or large ice balls that usually come from thunderstorms. Hail size tends to be about 1/4 of an inch (5 mm) to 1 inch (2.5 cm). Hail larger than 1 inch (2.5 cm) usually comes from severe thunderstorms.
- Graupel | White ice grains that look like little balls of snow. The diameter is about 1/4 inch (5 mm).
- Sleet | A form of precipitation that is nearly transparent in color and small odd shaped ice pellets.
- Freezing Rain | Cold rain that freezes when it hits the ground.
- Snow | Frozen form of rain. Snow is white and generally branches off into six-pointed stars.
- Ice Crystals | Ice crystals usually fall in cold regions such as Canada. These ice crystals are frozen particles of water, but they appear kind of like fog.
- Mist | Mist is visible water particles in the atmosphere that reduce visibility to less than 7 miles (11 km) and more than or equal to 5/8 mile (1 km). Mist and haze appear the same, but the difference lies with the difference between the air temperature and the dewpoint. If the difference between the air temperature and the dewpoint is 3°F (1.7°C) or less, then we define the obscuration as mist.
- Fog | Fog is a type of cloud that made up of visible water droplets near the Earth’s surface that reduce visibility to less than 5/8 mile (1 km). Fog is like drizzle, but instead of falling to the ground, it just floats in the air.
- Smoke | Smoke is made up of small particles that are suspended in the air. Smoke is created from combustion. If the particles travel between 25 and 100 miles (40 to 160 km) or more, the smoke may become haze.
- Haze | Haze is the suspension of very small dry particles that are invisible to the human eye. Due to the numerous amount of these particles, the cluster becomes visible to the naked eye. Haze and mist look alike. If the air temperature and the dewpoint are greater than 3°F (1.7°C), then the obscuration is called haze, NOT mist.
- Volcanic Ash | Volcanic ash comes from erupting volcanoes. It contains rock powder that may get trapped in the atmosphere for a long time before falling back to Earth.
- Dust | Dust is made up of small particles of dirt, sand, rock, or other Earth matter that when carried by strong winds, may reduce visibility. This occurrence is known as a dust storm.
- Sand | Sand, when carried by wind, may reduce visibility. This occurrence is called a sandstorm.
OTHER WEATHER TYPES
- Sand/Dust Swirls | A swirling, vertical column of sand or dust that kind of resembles a tornado.
- Squall | A squall is strong wind that suddenly occurs. Wind speed must increase at least 18 miles per hour (16 knots or 30 km/h) and blow for 25 miles per hour (22 knots or 41 km/h) or more for at least a minute. These sudden winds usually occur along thunderstorms (term ‘squall line’). These squalls may also occur with passing snow showers, which is called a snow squall.
- Tornado | A tornado is a rotating column of air often containing debris. A funnel cloud is basically the same thing, but the column does not touch the ground.
- Waterspout | A waterspout is a tornado over water. It is a rotating column of air over the water.
Clouds are visible minute water or ice particles in the atmosphere. They can weigh up to tens of millions of tons and be carried by winds of 150 miles per hour (240 km/h) or stay still as the wind passes through the cloud. Clouds usually cool the air, but they may also keep warm air near the surface.
So how do clouds form? Clouds need two things to form; water vapor and nuclei.
Water molecules in the atmosphere are too little to bond together, so they need flatter surface objects with a radius of at least one micrometer to form a bond. These ‘objects’ are called nuclei. These nuclei are solid and liquid particles suspended in the atmosphere. Some of these particles are from fires, volcanoes, ocean spray or wind-blown soil.
However, these particles and water droplets can’t bond together without a saturation point. The temperature must be equal to the dew point (saturation point) for evaporation to equal condensation. Clouds will form when a block of air called a parcel has water vapor; this block of air has to cool below the dew point. The easiest way for this to occur is for the air to lift from the surface into the atmosphere. As the air increases in altitude, the air moves into an area of low pressure. This allows the block of air to grow in size. As it expands in size, the heat energy gets removed from the parcel, which results in the cooling of the parcel, which forms a cloud. This is known as the adiabatic process. These parcels cool at different rates as they rise. The rate at which the parcel cools as it rises is referred to as the lapse rate. For example, if the air has a relative humidity <100%, the parcel will cool 5.5°F every 1,000 feet (9.8°C per km). If the relative humidity reaches 100%, then excess water vapor will condense onto the cloud resulting in the formation of a cloud droplet. Once the block of air (parcel) reaches the saturation point, which is when relative humidity is at 100%, vaporized water will condense onto the cloud’s nuclei in the form of a cloud droplet. Because the atmosphere is always changing, the rising air combines with dry air. This allows condensation and evaporation to continuously occur. With all of this occurring, clouds are continuously able to change shape and appear or disappear.
There are many different sizes and shapes of clouds, but there are four basic forms of clouds; cirro-form, cumulo-from, strato-form, and nimbo-form.
- Cirro-form | Cirro-form clouds are white and they look like strands of hair; as the Latin word for curl of hair is ‘cirro.’ Cirro-form clouds are made up of ice crystals, and they are high in the sky. They first appear before a low pressure area such as a thunderstorm, supercell, or tropical storm system.
- Cumulo-form | Cumulo-form clouds look like white cotton balls. They are tall vertically, in which they show thermal uplift of air in the atmosphere.
- Strato-form | Strato-form clouds are like a big gray blanket over the sky. These clouds are very wide and they form from non-conductive rising air. Strato-form clouds usually form to the north of warm-fronts.
- Nimbo-form | Nimbo-form clouds are rain clouds. Since almost all precipitation occurs from these clouds, nimbo-form clouds have the largest vertical height.
THE HEIGHT OF CLOUDS
The divide between the polar and temperate regions is the Arctic Circle at 66.5°N in the Northern Hemisphere and at the Antarctic Circle at 66.5°S in the Southern Hemisphere. The divide between the temperature and tropical regions are the Tropics of Cancer 23.5°N and the Tropics of Capricorn at 23.5°S. However, the division between these regions very from day to day, day to night, from season to season, and from year to year. The jet streams divide these layers with the Polar Jet Streams dividing the polar and temperate regions and the Subtropical Jet Streams dividing the temperate and tropical regions.
Because the jet streams are strong winds, the flow makes the maximum altitude of the tropopause decrease in each region when you move from the equator to either pole. As the tropopause decreases in height, so do the elevations at which clouds form. However, low clouds are the only exception, because they generally form between the Earth’s surface and 6,500 feet above.
The base of cumulus and cumulonimbus clouds can sometimes be higher than 6,500 feet (2,000 meters). During summertime, the base of these convective clouds will be well in to the mid-level cloud range in the non-mountainous areas of the southwest United States.
Cumulus cloud bases have been observed up to 9,000 feet (2,750 meters) over North Central Texas and thunderstorms, with cloud bases from 11,000 to 12,000 feet (3,350 to 3,650 meters), have occurred near San Angelo, Texas.
This happens when, despite the dry lower level of the atmosphere, the atmosphere in the mid-levels is fairly moist and unstable. The dryness of the lower level is such that parcels of air need to rise up to two miles (3 km), and sometimes more, before the they cool to the point of condensation.
Some places around the world are characterized as being ‘hot.’ However, heat isn’t just always the threat when it comes to high temperatures. Humidity is usually associated with hot weather, especially in tropical regions. In deserts, humidity is low because the air is dry, therefore, the heat is the threat.
Heatwaves are tend to kill the most people in the United States than all tornadoes, floods, and hurricanes combined. An estimated 124 people die each year due to heatwaves in the U.S.
Heatwaves happen every summer in both hemispheres and they occur due to the buildup of heat near the surface. Heatwaves are caused by high atmospheric pressure 10,000 to 25,000 feet (3,000 to 7,600 m) above the Earth’s surface. This ridge of high pressure resides in the middle layers of the troposphere on the equator side of the jet stream. The high pressure will strengthen over several days or weeks, over a large area. It strengthens because summertime weather patterns do not change as quickly as they do in the wintertime. Because the weather patterns change slowly in the summer means that the high pressure area will also move slowly. During a heatwave, the high pressure area will sink toward the Earth’s surface, which makes the sinking air act like a dome, which traps heat inside. This is where we get the term ‘heat dome’ from. The trapped heat will not lift. Without the air lifting, there will be very little convection taking place, which will not allow water to evaporate to form cumulus or cumulonimbus clouds. Without these clouds, rain chances are slim to none.
Humidity (relative humidity) is the measure of the amount of water vapor in the air, divided by the maximum amount the air can hold. This is expressed as a percent. Therefore, a relative humidity of 80% means that the air contains 4/5 of the water vapor the air can hold. However, the total amount of water vapor the air can hold depends upon the temperature. The higher the temperature, the more water vapor the atmosphere can hold. The cooler the temperature, the less water vapor the atmosphere can hold. When the humidity is high, the temperature will feel around 15°F (23°C) warmer and this can be a big health risk if you are outside.
- At 32°F (0°C), the air can hold 0.16 ounce of water.
- At 80°F (27°C), the air can hold 1 ounce of water.
Like there are hot places, there are also cold places, such as the Arctic and Antarctic. In these regions the humidity is no problem, but the wind chill is. In these cold regions, or in any given area where the temperatures may get cold for a certain amount of time, the wind chill is a big health risk, just as much as the humidity can be. Wind chill is what we feel as the temperature based on the rate of heat loss from exposed skin from the flow of the wind and the extremely cold temperatures.
When the wind speed goes up, the body loses heat, which makes the skin temperature fall. For example, if the temperature is 10°F (-12°C), with a wind speed of 25 miles per hour (13 kts or 24 k/ph), the wind chill would be -11°F (-24°C). Besides the health risks due to the wind chill making the temperature feel colder than it actually is against your skin, the wind chill also increases risk for frostbite or hypothermia.
In meteorology, we use ‘real feel’ temperatures, no matter the temperature; whether freezing, cold, chilly, cool, mild, warm, hot, or extremely hot.
When there is really hot temperatures, we use what is called the heat index chart.
When the temperatures are really cold, we use the wind chill chart. Wind chill has almost no effect on most objects. The only effect it really has is to shorted the amount of time for the object to cool, such as radiators or water pipes. These objects will not cool below the air temperature.
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