Air Masses And Fronts | badz.info
Types of fronts A front always causes a change in weather because the air masses that meet do not mix and their different densities and air pressure produce. When a moving cold air mass meets a warm air mass, that is lighter, it tends to Since the surface of contact between the two masses is quite steep and ascent the cold dry polar air meet, and generally a depression vortex is formed in which . Two of these air masses are the cP and cA systems that originate in Alaska and central As the warm air mass meets the cold air mass, it is cooled and some of the When that happens, the cold air mass behind the cold front eventually.
For example, air over the tropical ocean becomes exceptionally hot and humid. Air over a high latitude continent may become cold and dry.
You have probably noticed the temperature rapidly dropping on a nice warm day as a cold air mass pushed a warm one out the way. Fronts The location where two air masses meet is called a front. They can be indirectly observed using current weather maps, which can be used to track them as the move across the Earth. Cold fronts, generally shown in blue, occur where a cold air mass is replacing a warm air mass. Warm fronts, shown in red, occur where warm air replaces cold air.
Jet Streams The local weather conditions that we experience at the Earth's surface are related to these air masses and fronts.
However the environment far above us impacts their movement. High in the atmosphere, narrow bands of strong wind, such as the jet streams, steer weather systems and transfer heat and moisture around the globe.
As they travel across the Earth, air masses and global winds do not move in straight lines. Similar to a person trying to walk straight across a spinning Merry-Go-Round, winds get deflected from a straight-line path as they blow across the rotating Earth. In the Northern Hemisphere air veers to the right and in the Southern Hemisphere to the left. This motion can result in large circulating weather systems, as air blows away from or into a high or low pressure area.
Hurricanes and nor'easters are examples of these cyclonic systems. Air Masses North American airmassesAn air mass is a large body of air with generally uniform temperature and humidity. The area from which an air mass originates is called a "source region.
The United States is not a favorable source region because of the relatively frequent passage of weather disturbances that disrupt any opportunity for an air mass to stagnate and take on the properties of the underlying region. The longer the air mass stays over its source region, the more likely it will acquire the properties of the surface below. The four principal air mass classifications that influence the continental United States according to their source region are: As these air masses move around the Earth they can begin to acquire additional attributes.
For example, in winter an arctic air mass very cold and dry air can move over the ocean, picking up some warmth and moisture from the warmer ocean and becoming a maritime polar air mass mP - one that is still fairly cold but contains moisture.
If that same polar air mass moves south from Canada into the southern U. This is called a continental polar air mass cP. The Gulf Coast states and the eastern third of the country commonly experience the tropical air mass in the summer.
Continental tropical cT air is dry air pumped north, off of the Mexican Plateau. If it becomes stagnant over the Midwest, a drought may result. Maritime tropical mT air is air from the tropics which has moved north over cooler water.
Air masses can control the weather for a relatively long time period: Most weather occurs along the periphery of these air masses at boundaries called fronts. Fronts Fronts are classified as to which type of air mass cold or warm is replacing the other. For example, a cold front demarcates the leading edge of a cold air mass displacing a warmer air mass.
A warm front is the leading edge of a warmer air mass replacing a colder air mass. If the front is essentially not moving i. Fronts don't just exist at the surface of the Earth, they have a vertical structure or slope as well. Warm fronts typically have a gentle slope so the air rising along the frontal surface is gradual. This usually favors the development of widespread layered or stratiform cloudiness and precipitation along and to the north of the front.
The slope of cold fronts are more steep and air is forced upward more abruptly. This usually leads to a narrow band of showers and thunderstorms along or just ahead of the front, especially if the rising air is unstable. Cold fronts typically move faster than warm fronts, so in time they "catch up" to warm fronts. As the two fronts merge, an occluded front forms. In the occluded front, the cold air undercuts the cooler air mass associated with the warm front, further lifting the already rising warm air.
Fronts are usually detectable at the surface in a number of ways. Winds usually "converge" or come together at the fronts. Also, temperature differences can be quite noticeable from one side of the front to another. Finally, the pressure on either side of a front can vary significantly.
Here is an example of a location that experiences typical warm frontal passage followed by a cold frontal passage: Clouds lower and thicken as the warm front approaches with several hours of light to moderate rain. Temperatures are in the 50s with winds from the east. As the warm front passes, the rain ends, skies become partly cloudy and temperatures warm into the mid 70s.
Winds become gusty from the south. A few hours later, a line of thunderstorms sweeps across the area just ahead of the cold front.
After the rain ends and the front passes, winds shift to the northwest and temperatures fall into the 40s and skies clear.
When air masses meet - Eniscuola
Heat In bad heat waves many of those who are killed are elderly. A summer heat wave sets in many areas of Japan after the June rainy season is over. In many places it is very hot with little relief many days in a row.
Areas near mountains sometimes experience high temperatures associated with the foehn wind effect. Heat generated in Tokyo is blown against the mountains in Saitama.
Unusually high summer temperatures have been attributed to global warming, rising air currents and very strong high pressure over the Pacific Ocean. In high temperatures were blamed on rising air currents created by the La Nina phenomena in the Pacific and rising air currents in India, creating a funneling effect that strengthened the rising air currents over Japan.
When extremely hot days and tropical nights continue for extended periods the asphalt of the roads and walls of buildings do not cool down sufficiently at night, resulting in high room temperatures in office buildings from early in the morning, This boosts demand for air conditioning and electricity. During heat waves in Japan the sale of air conditioners, beer soft drinks and watermelons increases.
Japanese, Chinese and Koreans crave watermelons when the weather is hot and give them as summer present at Bon events. Demand was so strong for watermelons in the heat wave of that shortages were reported and prices were significantly higher than what they were in and In some cities, temperatures in some cities have increased 5.
In other cities, the seasons have occurred as many as 20 days earlier than they have in the suburbs. In the summer the increases have been greatest between midnight and 5: In the winter, it means no snow in places that once had snow.
In the autumn, leaves that used to change color in November now change in December. In the spring, flowers bloom when there uses to be snow. Heat is emitted from air conditioners and vehicles. The highest temperature readings in cities usually occur along streets and are lowest in parks, gardens and rivers. Large cities act like radiators. During the day asphalt roads, car exhaust, roofs, car bodies and concrete building absorb heat.
At night they release it, making the nights much warmer than they otherwise would be. Cities near large bodies of water draw in warm moist air in the afternoon as the heat trapped by the city starts to be released and warm air rises.
The moist air and the warm city air collide and push other air higher. As it rises it cools and creates clouds and rain. Prevailing winds blow the clouds so that down wind areas of large cities get more rain than areas upwind. The Japanese are attempted to battle heat island effect by replacing dirt fields in school yards with grass ones and using water-retentive blocks made from crushed, recycled asphalt and concrete as paving material.
The water-retentive blocks are just as strong as ordinary paving blocks but reduce heat and produce a cooling effect when water is evaporated from them. Because the blocks are made from recycled material they are also environmentally friendly. Tokyoites battle the heat island effect by splashing water all over the place on pavement and concrete.
Around Tokyo station trees were planted on rooftops, water-retentive pavement has been installed and a building was knocked down to create a wind channel to dissipate some of the heat that builds up there.
Air masses and fronts
New technology, water systems and grass allow gardens to built without damaging existing roofs. City planners have discussed building pipelines under the cities to bring in cool water from local bays. Air conditioner sales have boomed in recent years. Precipitation In order for precipitation to form, particularly over a large area, several ingredients are necessary.
First there must be a source of moisture. The primary moisture sources in the U. Winds around high and low pressure systems a subject of another lesson transport this moisture inland. Once the moisture is in place, clouds still need to form. The most effective way to do this is by lifting the air. This can be accomplished by forcing the air up and over mountains or, more commonly, by forcing air to rise near fronts and low pressure areas.
So there must be a process es for the cloud water, or ice, to grow large enough to fall as precipitation. One process is called the collision and coalescence or warm rain process. In this process, collisions occur between cloud droplets of varying size, with their different fall speeds, sticking together or coalescing, forming larger drops.
Finally the drops become too large to be suspended in the air and they fall to the ground as rain. The other process is the ice crystal process. This occurs in colder clouds when both ice crystals and water droplets are present.
In this situation it is "easier" for water vapor to deposit directly onto the ice crystals so the ice crystals grow at the expense of the water droplets. The crystals eventually become heavy enough to fall. If it is cold near the surface it may snow, otherwise the snowflakes may melt to rain. The vertical distribution of temperature will often determine the type of precipitation rain vs.
More often than not, the temperature does not decrease with height but increases, many times by several degrees, before decreasing. This increase, then decrease is called an inversion.
In winter, an inversion can be critical in determining the type or types of weather. As snow falls into the layer of air where the temperature is above freezing, the snow flakes partially melt. As the precipitation reenters the air that is below freezing, the precipitation will re-freeze into ice pellets that bounce off the ground, commonly called sleet.
The most likely place for freezing rain and sleet is to the north of warm fronts. The cause of the wintertime mess is a layer of air above freezing aloft.
Freezing rain will occur if the warm layer in the atmosphere is deep with only a shallow layer of below freezing air at the surface. The rain falls back into the air that is below freezing but since the depth is shallow, the rain does not have time to freeze into sleet.
Upon hitting the ground or objects such as bridges and vehicles, the rain freezes on contact. Some of the most disastrous winter weather storms are due primarily to freezing rain. Hail Hail is a form of precipitation that occurs when updrafts in thunderstorms carry raindrops upward into extremely cold areas of the atmosphere where they freeze into ice.
How fast does hail fall? We really only have estimates about the speed hail falls. However, the hailstone is not likely to reach terminal velocity due to friction, collisions with other hailstones or raindrops, wind, the viscosity of the wind, and melting. Also, the formula to calculate terminal velocity is based on the assumption that you are dealing with a perfect sphere. Hail is generally not a perfect sphere! How does hail form? There are two ideas about hail formation.
In the past, the prevailing thought was that hailstones grow by colliding with supercooled water drops. Supercooled water will freeze on contact with ice crystals, frozen rain drops, dust or some other nuclei. Thunderstorms that have a strong updraft keep lifting the hailstones up to the top of the cloud where they encounter more supercooled water and continue to grow. The hail falls when the thunderstorm's updraft can no longer support the weight of the ice or the updraft weakens.
The stronger the updraft the larger the hailstone can grow. Recent studies suggest that supercooled water may accumulate on frozen particles near the back-side of the storm as they are pushed forward across and above the updraft by the prevailing winds near the top of the storm.
Eventually, the hailstones encounter downdraft air and fall to the ground. Hailstones grow two ways: In wet growth, a tiny piece of ice is in an area where the air temperature is below freezing, but not super cold.
When the tiny piece of ice collides with a supercooled drop, the water does not freeze on the ice immediately. Instead, liquid water spreads across tumbling hailstones and slowly freezes. Since the process is slow, air bubbles can escape resulting in a layer of clear ice. Dry growth hailstones grow when the air temperature is well below freezing and the water droplet freezes immediately as it collides with the ice particle.
The air bubbles are "frozen" in place, leaving cloudy ice. Hailstones can have layers like an onion if they travel up and down in an updraft, or they can have few or no layers if they are "balanced" in an updraft. One can tell how many times a hailstone traveled to the top of the storm by counting the layers. Hailstones can begin to melt and then re-freeze together - forming large and very irregularly shaped hail. The different ways precipitation is formed determines what type of precipitation it becomes.
Hail is larger than sleet, and forms only in thunderstorms. Hail formation requires air moving up thunderstorm updraft that keep the pieces of ice from falling. Drops of supercooled water hit the ice and freeze on it, causing it to grow. When the hailstone becomes too heavy for the updraft to keep it aloft, ot it encounters downdraft air, it falls. Sleet forms from raindrops that freeze on their way down through a cloud. Snow forms mainly when water vapor turns to ice without going through the liquid stage.
There is no thunderstorm updraft involved in either of these processes. Hail falls when it becomes heavy enough to overcome the strength of the updraft and is pulled by gravity towards the Earth. How it falls is dependent on what is going on inside the thunderstorm. Hailstones bump into other raindrops and other hailstones inside the thunderstorm, and this bumping slows down their fall.
Drag and friction also slow their fall, so it is a complicated question! If the winds are strong enough, they can even blow hail so that it falls at an angle. This would explain why the screens on one side of a house can be shredded by hail and the rest are unharmed!
Winter Weather Three basic ingredients are necessary to make a winter storm. An example of lift is warm air colliding with cold air and being forced to rise over the cold dome. The boundary between the warm and cold air masses is called a front. Another example of lift is air flowing up a mountainside. Air blowing across a body of water, such as a large lake or the ocean, is an excellent source of moisture. SnowMost precipitation that forms in wintertime clouds starts out as snow because the top layer of the storm is usually cold enough to create snowflakes.
Snowflakes are just collections of ice crystals that cling to each other as they fall toward the ground. Precipitation continues to fall as snow when the temperature remains at or below 0 degrees Celsius from the cloud base to the ground. Types of snow eather. No accumulation or light dusting is all that is expected. Some accumulation is possible.
Accumulation may be significant. Snow squalls are best known in the Great Lakes Region. Sleet occurs when snowflakes only partially melt when they fall through a shallow layer of warm air. These slushy drops refreeze as they next fall through a deep layer of freezing air above the surface, and eventually reach the ground as frozen rain drops that bounce on impact.
Freezing Rain occurs when snowflakes descend into a warmer layer of air and melt completely. When these liquid water drops fall through another thin layer of freezing air just above the surface, they don't have enough time to refreeze before reaching the ground. Because they are "supercooled," they instantly refreeze upon contact with anything that that is at or below O degrees C, creating a glaze of ice on the ground, trees, power lines, or other objects.
A significant accumulation of freezing rain lasting several hours or more is called an ice storm. Snow Snow forms when water vapor condenses into a crystal.
In humid conditions, the corners of a snowflake grow more quickly and have larger more elaborate branches. Before a snowflake lands on earth it is blown by winds tossed around by clouds and struck by other snowflakes, all of which affect a snowflakes structure and appearance.
The bumps grow into branches and they in turn develop their own formations. Because all six sides are exposed to the same changes, they grow the same way. A typical snowflake has a billion, billion water molecules. Its shape is unique because each snowflake has followed it own unique route between the cloud, where it forms and its finale destination. On the matter of snowflake uniqueness, Dr. A British zoologist once suggested that some bacteria actually trigger clouds to form as a means of distributing themselves.
Scientists have known for a long time that the sun has an year cycle during which radiation measured by sunspots on the surface reaches a peak then falls. But pinning down a clear link to weather has proved harder. David Fogarty, Reuters, October 9, ] "Our research confirms the observed link between solar variability and regional winter climate," lead author Sarah Ineson of the UK Met Office told Reuters in an email.
Air masses are typically at least 1, miles 1, km wide and several miles thick. Four naturally occurring mechanisms on Earth cause air to rise: This phenomenon occurs when an airflow encounters elevated terrains, such as mountain ranges. Like a speeding car heading toward a hill, the wind simply powers up the slope. As it rises with the topography, water vapor in the airflow condenses and forms clouds. This side of the mountain is called the windward side and typically hosts a great deal of cloud cover and precipitation.
The other side of the mountain, the leeward side, is generally less lucky. The airflow loses much of its moisture in climbing the windward side. Many mountain ranges virtually squeeze incoming winds like a sponge and, as a result, their leeward sides are home to dry wastes and deserts.
When a warm air mass and a cold air mass collide, you get a front. Remember how low-pressure warm air rises and cold high-pressure air moves into its place? The same reaction happens here, except the two forces slam into each other.
The cold air forms a wedge underneath the warm air, allowing it to basically ride up into the troposphere on its back and generate rain clouds.