Download Air Pressure: Highs and Lows

 Air Pressure: Highs and Lows source: ​http://www.weatherworksinc.com/high-­low-­pressure If you are a regular viewer of weather broadcasts, chances are you’ve heard the following from your local TV meteorologist: “plenty of sunshine is in store today as high pressure is in control over the area.” Or: “expect rain to spread into the area as a low pressure system approaches.” 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. But have you ever wondered why? 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. So what does this have to do with high and low pressure? Well, as you may have guessed, ​high pressure is associated with sinking air​, and ​low pressure is associated with rising air​. But why? The answer has to do with the typical air flow around high and low pressure. Physically, it seems to make sense to have air flow from high pressure to low pressure. Due to the Earth’s rotation and friction is directed slightly inward toward the low pressure center, and slightly outward away from the high pressure center. This is called the Coriolis Effect. The slightly inward moving air in low pressure causes air to converge and since it can’t move downward due to the surface, the air is forced upward, leading to condensation and precipitation as discussed earlier. The opposite occurs with high pressure. Air is moving away from the high pressure center at the surface (or “diverging”) so as a result, air from above must sink to take its place. The surface flow is accompanied by the opposite behavior at upper levels of the atmosphere, as depicted in this schematic diagram: Now there is much more to it than just high pressure = nice weather and low pressure = bad weather (otherwise I would be out of a job!), but hopefully after reading this, you have a better understanding of why meteorologists talk about pressure systems. Circle or Underline the word that makes the statement true. 1. Air ( rises , sinks ) in an area of ​high​ pressure. 2. Air moves ( clockwise , counterclockwise ) around an area of ​high​ pressure. 3. Air ( rises , sinks ) in an area of ​low​ pressure. 4. Air moves ( clockwise , counterclockwise ) around an area of ​low​ pressure. 5. Clear skies​ are associated with ( low , high ) pressure. 6. Cloudy skies​ are associated with ( low, high ) pressure. Where does Wind Come From? by Gary Wickman Source: http://www.healthguidance.org/entry/13959/1/Where-­Does-­Wind-­Come-­From.html The simple answer is that wind is a movement of air molecules. The more detailed and informative answer is a little more complicated. There are various different molecules in the air, the most notable being the gas ​nitrogen​. Also notable air molecules include ​oxygen​ and ​water vapor​. These molecules are all mixed up in the air and moving constantly around us. As these molecules move they will bump into objects they encounter. The force at which they bump into these objects is known as ​air pressure​. As a general rule, the more molecules there are in a given area, the more force an object is likely to be hit with, and therefore the greater the air pressure. Wind comes from a change in the air pressure​. In these situations the molecules from an area of high pressure will quickly move towards an area of low pressure to form ​equilibrium​ between the two;; it is this movement of the molecules that we know as wind. Different types of wind are caused by differences in air pressure;; areas of high pressure and low pressure which are similar to one another will cause a gentle breeze, while areas of much more extreme change can cause gales or the high winds felt during storms. Winds coming from different areas can also bring subtle changes. Winds coming from over the sea, for example, will contain a little more moisture than those coming from over land. Wind coming from the north is more likely to feel colder than wind coming from the south. Question​: Where do winds come from?