Air masses that form over the ocean, called maritime air masses, are more humid than those that form over land, called continental air masses. The second part of the name describes the temperature of the air mass, which depends on the latitude where it formed. Air masses that form near the equator or in the tropics equatorial or tropical air masses are warmer than air masses that form in polar areas or uin the Arctic polar or arctic air masses.
The word that describes humidity maritime or continental is paired with the word that describes temperature equatorial, tropical, polar or arctic.
For example, if an air mass forms over a tropical ocean, it is called maritime tropical. This mass is drier so precipitation stops. The weather may be cold and clear or only partly cloudy. Winds may continue to blow into the low pressure zone at the front. The weather at a cold front varies with the season.
Along a warm front , a warm air mass slides over a cold air mass. When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable.
Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching. The transition from cold air to warm air takes place over a long distance so the first signs of changing weather appear long before the front is actually over you.
Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. High cirrus clouds mark the transition from one air mass to the other. Over time, cirrus clouds become thicker and cirrostratus clouds form. As the front approaches, altocumulus and altostratus clouds appear and the sky turns gray.
Since it is winter, snowflakes fall. The clouds thicken and nimbostratus clouds form. Snowfall increases. Winds grow stronger as the low pressure approaches.
As the front gets closer, the cold air mass is just above you but the warm air mass is not too far above that. Winds may continue to blow into the low pressure zone at the front. At a warm front , a warm air mass slides over a cold air mass Figure below. When warm, less dense air moves over the colder, denser air, the atmosphere is relatively stable. Imagine that you are on the ground in the wintertime under a cold winter air mass with a warm front approaching.
The transition from cold air to warm air takes place over a long distance so the first signs of changing weather appear long before the front is actually over you. Initially, the air is cold: the cold air mass is above you and the warm air mass is above it. High cirrus clouds mark the transition from one air mass to the other.
Over time, cirrus clouds become thicker and cirrostratus clouds form. As the front approaches, altocumulus and altostratus clouds appear and the sky turns gray. Since it is winter, snowflakes fall. The clouds thicken and nimbostratus clouds form. Snowfall increases. Winds grow stronger as the low pressure approaches. As the front gets closer, the cold air mass is just above you but the warm air mass is not too far above that.
The weather worsens. As the warm air mass approaches, temperatures rise and snow turns to sleet and freezing rain. Warm and cold air mix at the front, leading to the formation of stratus clouds and fog Figure below. An occluded front usually forms around a low pressure system Figure below.
The occlusion starts when a cold front catches up to a warm front. The air masses, in order from front to back, are cold, warm, and then cold again.
Coriolis Effect curves the boundary where the two fronts meet towards the pole. If the air mass that arrives third is colder than either of the first two air masses, that air mass slip beneath them both. This is called a cold occlusion. The turbulence can cause clouds and storms. Instead of causing clouds and storms, some fronts just cause a change in temperature. However, some storm fronts start Earth's largest storms. Tropical waves are fronts that develop in the tropical Atlantic Ocean off the coast of Africa.
These fronts can develop into tropical storms or hurricanes if conditions allow. Fronts move across the Earth's surface over multiple days. The direction of movement is often guided by high winds, such as Jet Streams. Landforms like mountains can also change the path of a front. There are four different types of weather fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts. A side view of a cold front A, top and how it is represented on a weather map B, bottom.
A cold front forms when a cold air mass pushes into a warmer air mass. Cold fronts can produce dramatic changes in the weather. They move fast, up to twice as fast as a warm front. As a cold front moves into an area, the heavier more dense cool air pushes under the lighter less dense warm air, causing it to rise up into the troposphere. Lifted warm air ahead of the front produces cumulus or cumulonimbus clouds and thunderstorms, like in the image on the left A.
As the cold front passes, winds become gusty. There is a sudden drop in temperature, and also heavy rain, sometimes with hail, thunder, and lightning.
0コメント