Shifting global wind patterns are the driving force behind monsoons. They are traditionally defined as a seasonal reversals in winds that are partnered with corresponding changes in precipitation. Usually, the term monsoon is used to refer to the rainy part of the season which occurs during the warm summer months. Technically, there is also a dry phase, which happens during the winter when low pressures sit over the Indian Ocean and highs are found above the land, including the Tibetan plateau.
What is a Monsoon?
These rainy seasons are primarily a result of global wind direction shifts which bring extreme amounts of rainfall. During most of the year the wind will blow from land to ocean, making the air dry; these land originating winds are called continental. During certain months of the year, the winds begin to blow from the ocean to the land, which adds moisture to the air. These winds are called maritime. This moist ocean air is what causes monsoonal rains over many countries through out the world.
Where Do They Occur?
Every summer, moist air masses move inland from the surrounding ocean and with them they bring torrential rains and floods. These rains affect Asia, North America, South America, and Africa. Due to the large land to water ratio, the most intense monsoon systems of the world are found in the West African and Asia-Australian regions. Less intense seasons occur in North and South America.
How Does the Uneven Heating of Earth Cause a Monsoon Season?
Monsoons are in essence large-scale sea breezes which occur when the temperature on land is dramatically different than the temperature of the ocean. These temperature imbalances are a result of the uneven heating of the Earth's surface. Water and land absorb heat differently. Water takes longer to warm but holds its heat better than land. Therefore, bodies of water stay at a more mild temperature while land temperatures are more variable. When the land heats up it warms the air above. Warm air is less dense so it will expand and rise, forming a low pressure system; consequently, there will be a high pressure above water. Air moves from high to low pressure, this movement creates a breeze from the sea, bringing moist air to land. To complete the convection current, this moist air will rise, cool, and condense, resulting in copious amounts of rain over land. In colder months the cycle is reversed, and a dry season ensues.
What Kind of Damage Can They Cause?
The effects of winter monsoons are very different from the summer ones. These systems cause droughts and destruction of crops during the winter while bringing excess moisture and floods in the warmer months. This extreme moisture variation has an adverse affect on agriculture patters. It also has the potential to cause damage to the infrastructure of the affected area. These events are seasonal and predictable, many people have even learned to live with and adapt to the dry and wet seasons.
What Area is Affected the Most by Monsoons?
The region affect the most by these changing precipitation patterns is India. This is due flat elevated land of the Tibetan Plateau, found to the north of India. This is one of the largest and highest plateaus on Earth. Here, the high elevation allows strong low pressure systems to develop. These pressure differences cause the convection currents responsible for delivering rain and drought.
The rainy monsoon season is a welcome relief to drought conditions in many areas of the world. The droughts that these systems create bring about widespread famine. On the other side, too much rain can kill hundreds of people in floods. While Asian and Indian monsoons are famous, they also do occur in the United States..