Tag: pressure belts

• Both atmospheric pressure and  the density of air decrease with altitude.
  
• This is due to the fact that air molecules are constantly being pulled downwards (towards the center of the Earth) by Gravity.
•  So, air molecules are tightly packed near the surface of the earth, compared to some higher altitude.
  

Isobars are imaginary lines joining the places having equal values of pressure. The horizontal distribution of pressure is shown by isobars. For convenience all the local level pressures are converted to sea level. Closely spaced isobars indicate strong pressure gradient and widely spaced isobars indicate weak pressure gradient.

Anemometer is a device which is used for measuring the speed of wind in the atmosphere. It also measures wind pressure. Anemometers are important tools for meteorologists, who study weather patterns. They are also important to the work of physicists, who study the way air moves. Anemometer has three or four cups attached to horizontal arms. The arms are attached to a vertical rod. As the wind blows, the cups rotate, making the rod spin. The stronger the wind blows, the faster the rod spins. The anemometer counts the number of rotations, or turns, which is used to calculate wind speed.

At a high altitude pressure is low as at higher elevations, there are fewer air molecules above a given surface than a similar surface at lower levels.

Due to the intense heating from sun rays around the equator, the air in this region gets hot and hence ascends upwards, thus creating a low pressure in the region. Hence it is the equatorial low-pressure belt and is also called doldrums as it is the region of extreme calmness, not as much as a breeze.

Although air is well mixed throughout the atmosphere, the atmosphere itself is not physically uniform but has significant variations in temperature and pressure with altitude, which define a number of atmospheric layers i.e. when lower layers have atmospheric pressure and higher ones have low atmospheric pressures due to the altitude.

Air pressure increases when air descends. Lower pressure at higher altitudes cause the temperature to be colder on top of a mountain than at sea level. As air rises, the pressure decreases. It is this lower pressure at higher altitudes that causes the temperature to be colder on top of a mountain than at sea level.

The factors which affects in the distribution oof atmospheric pressure are, altitude, temperature and rotation of the earth. Atmospheric pressure decreases with increaseing altitude. Regional variation of pressure are produced by temperature. Movement of wind are also responsible for pressure channge, prevailing wind systems are caused by rotation of the earth.

The weight of water vapor per unit weight of air is called Specific humidity. It is usually expressed as grams of vapor per kilogram of air. The rate of evaporation of water from any surface is directly proportional to the specific humidity, the difference between the surface and the adjoining air. It is an extremely useful quantity in meteorology. Specific humidity does not change with temperature and pressure.

Wind
Air moves from the high-pressure areas to low-pressure areas, creating the wind.
Now with the difference in speeds of traveling wind, it may be called as the storm, hurricane, etc.