Air is in constant motion. It changes the temperature and humidity of a region, influencing weather. A large mass of air can affect the weather for a long or a short time. When air masses collide, storms are triggered along their boundary.
Condensation and Precipitation:
Condensation occurs when dew point is reached. The reason is that cold air can hold less water than warm air and thus releases water vapor in the form of rain or snow. If condensation does not occur, then the air mass is called supersaturated or supercooled. Water droplets coalesce around microscopic foreign particles, known as hygroscopic nuclei, in the form of dust, smoke, soot, salt, etc., present in the air. They initiate the formation of droplets, falling as precipitation also cleansing the atmosphere.
Liquid water may be cooled below the freezing point without the formation of ice if the particles that lead to ice nuclei are not present. These include clean dust (dust without biological materials from plants or bacteria) will not act as ice nuclei. Cooling and condensation occur in updrafts, the formed droplets are suspended as clouds. To have precipitation, larger droplets must be formed by coalescence or the Bergeron process.
Coalescence is the formation of drops by collision of droplets, larger droplets growing at the expense of smaller ones. The maximum size of a raindrop is 7 mm. For more information click below.
The Bergeron Process involves clouds that have ice crystals in their upper portions and have become supercooled in their lower portions. Mixing or agitation within allows the ice crystals to come into contact with the supercooled vapor. Acting as nuclei, the ice crystals grow larger from the condensing vapor. The ice crystals melt into large droplets in the warmer lower portion of the cloud and coalesce to fall as precipitation. Thus the three essentials are ice crystals, supercooled vapor, and mixing. For a precise definition of the Bergeron Process and a description of the Process, click below:
Rainmaking: Clouds are seeded with silver iodide crystals, (which have a structure similar to ice) and produced by burning either on the ground or attached to an airplane, or with dry-ice pellets (solid CO2) from an airplane. The temperature of solid dry ice is -79 degrees C (-110 degrees F). So it sublimes (goes directly from a solid to a gas). This rapid cooling triggers the conversion of supercooled cloud droplets into ice crystals. In addition, the released latent heat sets up convection cycles for mixing. Seeding is receiving increasing attention in initiating the precipitation fog to aid airport operations. For more information on rainmaking, click below:
Air Masses: Air mass is a large body of air that takes
on physical characteristics different from surrounding air. The main
distinguishing characteristics are temperature and moisture content.
Source region is the region from which an air mass derives its
characteristics. As an air mass travels, its properties are modified
due to local variations. Air masses are classified according to the
surface and general latitude of their source regions.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
The surface of the source region, abbreviated by a small letter, indicates the moisture content (maritime (m) moister than continental (c)). The latitude, abbreviated by a capital letter, indicates the temperature.
Front is a boundary between two air masses. A warm front is the boundary of an advancing warm air mass over a colder surface, while a cold front is the boundary of a cold air mass over a warmer surface. These boundaries called frontal zones may vary in width from a few to over a hundred miles. Drastic changes in weather, turbulence and storms characterize a front. A cold front moving into a warmer region causes the lighter, warm air to be displaced over the colder air. A cold front moves faster (20 to 25 mph) than a warm front (10 to 15 mph). A faster moving cold front overtaking a warm front causes an occluded front. A cold front occlusion occurs when a cold front advances under a warm front while a warm front occlusion is when a warm front advances up and over a cold front. Fronts traveling in opposite directions cause stationary fronts. Cold fronts are accompanied by more violent or sudden changes in temperature. Warm fronts are characterized by precipitation and storms.
For more details about air masses and fronts, click below:
Storms are atmospheric disturbances that may develop locally within a single air mass or may be due to frontal activity along the boundary of air masses.
Local storms occur over a small area. A heavy downpour with 1 to 3 inches per hour is a rainstorm. A thunderstorm is a rainstorm accompanied by thunder and lightning, and sometimes hail. Lightning is a discharge electrical energy. There is a separation of charge associated with the breaking up of water droplets. Lightning can take place within a cloud, between two clouds, between a cloud and Earth, or between a cloud and the surrounding air. Lightning often strikes tall buildings and trees.
Lightning safety: Electric charge is evidenced by hair standing on end or by skin tingling. Do not take shelter under a tree. Fall to to the ground in as low a point as possible. Elevated positions are greater targets. Stay away from open windows, fireplaces, sinks, and stoves. Avoid use of telephones or other plug-in equipment such as radios, TVs and lamps. Being struck by a lightning causes breathing to fail. Give mouth-to-mouth resuscitation, or some other form of artificial respiration, and keep person warm as a treatment for shock.
For more information on lightning and lightning safety, click below:
A lightning's sudden release of energy explosively heats the air, producing the compressions we hear as thunder. At a distance of less than 330 feet, it is one loud bang or clap. At a distance of 0.62 miles it consists of a rumbling sound punctuated by several large claps. It cannot be heard over 16 miles. Light travels almost instantaneously, while sound travels at 1100 feet per second. So by measuring the time in second from the time the lightning is spotted to the time the thunder is heard, we can determine the distance of the lightning. For example if the time is 5 seconds, the distance is 5500 feet or approximately 1 mile. Every second is 1/5 mile or 1/3 kilometer.
If the temperature of the Earth's surface is below o degrees C, but raindrops do not freeze before striking the ground, the rain will freeze on striking cold ground objects. This ice storm creates a layer of ice which could be over half an inch thick. This ice storm (one occurred in Memphis on February 9, 1993) can damage trees and power lines. Snow is ice crystals that fall from the sky. A snowstorm is an appreciable accumulation of snow. When accompanied by high winds and low temperatures, it is termed a blizzard. The winds whip the snow into blinding swirls, reducing visibility. Obstructions on the flat ground lead to drifts.
For some snow scenes, click here: Snowscapes or here more snowscapes
The Tornado is the most violent of storms with wind speeds of 100 to 300 mph.. Although it has less total energy, it is concentrated in a small region. It is characterized by a whirling, funnel-shaped cloud that hangs from a dark cloud mass. It is also called a twister. Although mainly occurring between the Rockies and the Appalachians, no state is immune. The peak months are April through June, and the peak times are 3:00 to 7:00 P.M. but may occur on any day and at any time. They generally travel from Southwest to Northeast, but may change direction erratically. Usual speed of travel is 30 mph but speeds of 70 mph have been reported. A tornado watch is issued when the atmospheric conditions indicate that tornadoes may form, while a tornado warning is issued when a tornado has been sighted or indicated on radar.
For more information on tornadoes, click here: Tornadoes
Tornado safety:
The basement of a building is the safest place. If without a basement, seek shelter in a closet or under a sturdy piece of furniture in the middle of the lowest floor of the house, and cover your head. Do not stay in a mobile home, and do not try to outrun in your car. Avoid chimneys and windows (broken glass). Try to equalize the pressure inside and outside the house by slightly opening the window
For more on Tornado safety, click here: Tornado safety
Tropical storms are massive disturbances that form over tropical oceanic regions. When wind speeds exceed 74 mph, they are called hurricanes. In Southeast Asia they are called typhoons, in the Indian Ocean as Cyclones, and in Australia as Willy Willies. They are characterized by high-speed rotating winds, whose energy is spread over a large area. A hurricane may be 300 to 600 miles in diameter and have wind speeds from 74 to 200 mph. Hurricanes form over tropical oceanic regions when the Sun heats huge masses of moist air, and an ascending spiral motion results. When the moisture of the rising air condenses, the latent heat provides additional energy and more air rises up the column. This latent heat is the chief source of energy and is readily available from the condensation of the evaporated moisture.
A hurricane gains energy from its source region. With increasing volume of rising air, the hurricane grows, with clouds and more winds that blow in a large spiral around a relatively calm, low-pressure center about 20 to 30 miles in diameter, called the eye. The air pressure is reduced 6 to 8% near the eye. Hurricanes move rather slowly. As it makes landfall, a great dome of water called storm surge about 50 miles wide comes sweeping across the coastline. flooding low lands. Floods are the greatest threats. A hurricane watch is issued for coastal areas when there is a threat of hurricane conditions within 24 to 36 hours, while a hurricane watch indicates that hurricane conditions are expected within 24 hours. For more details of hurricanes and the way they are named, click below:
|
|
|
|
|
|
|
|
|