Continuation: Air Movements

• Winds change in strength and direction within the year.
• Winds are affected by mountains, continents, and oceans.
• They grow colder while rising over mountains. They become warmer as they sink. In summer winds are warmed by continents and warmed by oceans. Continents and oceans exposed to sunlight absorb heat in the same way as they do the seashore and the sea.
• Generally, high pressure centers develop over the oceans and low pressure centers over the continents in summer.
• In winter, the high pressure centers are over the continents and the low pressure centers over the oceans.
  
• Isobars - lines of equal pressure that include many island separated by seas.

• Monsoons - winds that blow by season toward either continents or oceans because of differences in air temperature and air pressure.

THE WIND SYSTEMS IN THE PHILIPPINES

• The cold air from the high pressure area in Siberia moves toward the low pressure area over the north Pacific Ocean. But the Coriolis effect gradually turns it to the right in a giant arc that reaches the Philippines from the northeast direction. This large mass of moving air passing over the Philippines, called the northeast monsoon, is drawn to the low pressure center over Australia. This wind system is locally called AMIHAN. The figure below shows the Northeast Monsoon or Amihan (November - February)
  

• The highest temperature in the Philippines occur from march to May, resulting in warm rising air over the country. The northeast trade winds occasionally rise over this warm rising air.
• From June to about September, sometimes until October or even November, the Philippines is in the path of strong winds that start from southern hemisphere. These winds originally blow from southeast direction coming from the area of Australia.
• The area between northwestern India and Pakistan becomes a heat center, thus a low pressure area. The winds from Australia move toward the low pressure area at or near the equator, slowly turning , slowly turning left while in the southern hemisphere. When the winds cross the equator they begin to turn right due to the Coriolis effect. They are drawn instead to the low pressure center over India and pakistan, first passing over the low pressure center over India and Pakistan, first passing over the Philippines from a southwesterly direction. This wind system appears from about June to November and is called the Southwest Monsoon or Habagat. The figure below shows the southwest monsoon or habagat (June - September).
  

• Habagat brings much rain throughout the country, having absorbed moisture from the surrounding seas before reaching the Philippines.
• During the monsoon periods farmers take advantage of the rains to irrigtae the ricefields and start the planting season.
• For fisherman the monsoons mean less catch because they cannot go far out to sea. At these times of the year the seas are very rough and dangerous. The monsoons are thus both beneficial and harmful.