Geography short answer: Instruction links: (Sever and hazardous weather - CDC: N

Question

Geography short answer: Instruction links: (Sever and hazardous weather - CDC: Natural Disasters and Severe Weather)

1.   Midlatitude cyclones and anticyclones are an important part of weather in the midlatitudes in both hemispheres of the Earth. Describe each of these atmospheric disturbances by focusing on the following items:

a.Weather
•   Does it have fronts?
•   What are the temperature properties?
•   What type of precipitation, if any, is experienced?
b. Pressure
•   Does it have a high or low-pressure center?
c.Wind patterns
•   Does the wind converge or diverge at the surface?
•   Does the wind converge or diverge in the upper atmosphere?
•   Do the winds rotate in a clockwise or counterclockwise direction in the Northern Hemisphere?
•   Do the winds rotate in a clockwise or counterclockwise direction in the Southern Hemisphere?
•   Does the wind rise or descend in the center of the pressure center?

After describing these atmospheric disturbances, use the links in the instructions links above to describe the severe weather elements of Thunderstorms and Heat Waves and to link them with the appropriate atmospheric disturbance.

Explanation / Answer

When two air masses meet, the air within them does not easily mix. That is to say that the air in one air mass will not easily mix with the air from another air mass. Instead, the air stays within its own air mass. Because of this phenomena, a border forms between two clashing air masses as they rub together. This border is called a front.
The term ‘front’ was first used by Norwegian scientists who compared two air masses colliding to two armies as they clash on the battle front. Just like one army taking over another in a battle, one air mass ultimately takes over, pushing the other one away. Fronts should not be thought of as a vertical wall. This is because they are actually sloped, like a hill. Often the slope of a front can be extremely gradual, taking hundreds of miles across the surface of the Earth to reach an altitude of just one mile. While the air in one air mass will not mix easily with the air from another air mass, along a front there is some mixing. The front where air mixes is usually just a few miles or tens of miles across.

A storm is a temporary disturbance in the atmosphere. Storms are transient, meaning that they generally do not stay in one location for very long. Because storms are temporary, they do not last very long, generally dying out after just a few days or weeks. During their short lives, these storms can have a dramatic effect on the atmosphere, creating tremendous excitement. A storm can bring powerful winds, precipitation, and thunder and lightning. As the seasons change,the cooler weather probably brings changing leaf colors and hibernating animals. Later as the warm weather once again returns, so does life. New leaves, flowers, and baby animals welcome spring.
Other areas experience dry and wet seasons. The wet seasons bring life to the vast grasslands. Pools fill with water, frogs and fish come to life. Animals from hundreds of miles around migrate following the rain. Later as the rain slows down and the pools dry up, animals and plant life disappear. Temperature has a dramatic and complex affect on the environments around us. Temperature is the amount of heat contained in an object, in this case, the air. The amount of heat in the air determines the speed of the molecules in the air. The more heat, the faster the molecules move, raising the temperature. The heat in the atmosphere comes from the sun and varies at different levels in the atmosphere. The layers of the atmosphere are determined generally by their temperature. Near the surface of the Earth, the temperature is a factor of how much sunlight an area receives, how much is changed into heat at the Earth's surface and how much of that heat is held near the surface by greenhouse gases or cloud cover. The higher the elevation above the ground, the cooler the air is. Temperature is measured using a thermometer in degrees Fahrenheit or Celsius.

The definition of precipitation is any form of water - liquid or solid - falling from the sky. It includes rain, sleet, snow, hail and drizzle plus a few less common occurrences such as ice pellets, diamond dust and freezing rain. These particles include drizzle, rain, snow, snow pellets, ice crystals, and hail. The essential difference between a precipitation particle and a cloud particle is one of size. An average raindrop has a mass equivalent to about one million cloud droplets. Because of their large size, precipitation particles have significant falling speeds and are able to survive the fall from the cloud to the ground.The transition from a cloud containing only cloud droplets to one containing a mixture of cloud droplets and precipitation particles involves two basically different steps: the formation of incipient precipitation elements directly from the vapour state and the subsequent growth of those elements through aggregation and collision with cloud droplets. The initial precipitation elements may be either ice crystals or chemical-solution droplets.

We know that high pressure is associated with sinking air, and low pressure is associated with rising air. It is well established that high pressure is generally associated with nice weather, while low pressure is generally associated with cloudy, rainy, or snowy weather. In order to understand the types of weather conditions generally associated with high and low pressure systems, we must think “vertically.” The motion of air in the atmosphere above our heads plays a large part in the weather we experience here at earth’s surface. Basically, air cools as it rises, which can cause water vapor in the air to condense into liquid water droplets, sometimes forming clouds and precipitation. On the other hand, sinking air is associated with warming and drying conditions. So the first important point to keep in mind is rising air = moistening, sinking air = drying. Physically, it seems to make sense to have air flow from high pressure to low pressure.

The wind direction will have an important influence on the expected weather. You can often be given a wind direction and you will have a pretty good idea of how the weather will change and what weather can be expected with that wind direction.
The typical wind direction that a location has for a certain time of the year is called the prevailing wind. When the wind is from the prevailing direction then the weather is generally typical. When the wind shifts away from the prevailing direction then it often indicates atypical or changing weather.
Wind direction changes often accompany changes in the weather. The air flows cyclonically around low pressure systems. If the wind changes direction in a cyclonic fashion it often means a low pressure or front is influencing the forecast area. A wind shifting from the south often means warmer air is approaching and a wind from the north often means cooler air is approaching. When the wind changes abruptly it could be a frontal passage or wind direction change caused by thunderstorm outflow.
When the wind speeds are light then a change in wind direction is not as significant. You may have heard the phrase "winds will be light and variable". When the winds are light it indicates there is not much of a steering current to move the wind. When winds are light, mesoscale influences will tend to start influencing wind direction. The winds can continue shifting from a variety of directions when winds are light.

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