EART 80C – Quiz 4 August 22, 2008
Name:______
1. What type of air mass is abbreviated mT? Which parts of the United States are often influences by this type of air mass, and where do these air masses come from?
mT is the abbreviated form of “maritime tropical” air. The m is representative of the face that the air mass originated over the ocean and will typically be humid and it will be warm since the air originates in an area south of the US which is warmer than US.
• Warm and moist
• Can be unstable because of high heating from the warm waters – perfect for precipitation!
• In summer, land is even warmer creating even more instability, often triggering thunderstorms.
• In winter, often warmer than underlying land (more stable), bringing widespread fog and low level precipitation.
• Strongly influences southeastern US much of the year (keeping the south relatively warm and\muggy). During summer, influence extends further north, bringing the NE US its muggy and hot weather also.
2. What is a Warm Front? Describe the typical weather pattern for a warm front.
A warm from is a discontinuity at the forward edge of an advancing warm air mass that is displacing cooler air in its path. The first sign of the approaching warm front is cirrus clouds. These high clouds form where the overrunning warm air has ascended high up the wedge of cold air, 1000km or more ahead of the surface front. As the front nears, cirrus clouds grade into cirrostratus that gradually blend into denser sheets of altostratus. At about 300km ahead of the front, thicker stratus and nimbostratus clouds appear and precipitation commences.
• Less intense precipitation
• Transition of clouds
• If you see cirrus clouds – 24 hours or so till you have precipitation starting
• There is warming following the precipitation (1.5-2 days)
3. What is a step-leader? What is its role in the formation of lightning?
A step-leader is the conductive path of ionized air that forms near a cloud base prior to a lightning stroke. The initial conducive path is referred to as a step leader because it extends itself earthward in short, nearly invisible bursts. (basically a bunch of leaders connected together is a step-leader). These tubes provide the pathway for the electrons to flow from the cloud to the ground and in which the air is heated to a very high temperature and flashes.
4. What is a mesocyclone? How does it form? What is its role in tornado formation?
A mesocyclone is a vertical cylinder of cyclonically rotating air (3-10km in diameter) that develops in the updraft of a severe thunderstorm and that often precedes the development of damaging hail or tornadoes. Mesocyclones start out as rotating bodies of air at the ground due to vertical wind sheer. As a thunderstorm passes over this rotating body it can be carried into the cloud and be oriented vertically. The mesocyclone starts out with w wider diameter that begins to elongate, become narrower and because of the conservation of angular momentum, spin faster. As the mesocyclone elongates and spins faster it can protrude out of the bottom of the thunderstorm forming the wall cloud. As the mesocyclone begins to spin faster you can have an even smaller in diameter and faster spinning protrusion descends from the cloud. This will be a funnel cloud, and once it makes contact with the surface it becomes a tornado.