A desert is a piece of land that has small amounts of precipitation throughout the year, no matter how hot of cold. It usually has less than 10 inches (25cm) of rainfall per year.
The deserts cluster along 30 degrees latitude North and South (i.e. Tropic of Cancer and Tropic of Capricorn).
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| Distribution of deserts on the globe |
Convectional precipitation is a type of rain that is formed due to the uplifting of a heated air mass in the atmosphere.
It occurs when there is intense and uneven heating of the Earth's surface, which usually takes place in the morning and early afternoon, where heat from the Sun is strong. When air above the ground is heated intensely, it will rise quickly. The colder air will rush in to take its place.
As the warm air rises, it cools adiabatically*. The temperature of the rising air decreases as it rises, until it reaches the saturation point**, at which relative humidity is 100%. At this point, condensation occurs and clouds form. When the water droplets get too big and heavy, precipitation will occur. This process is known as convectional precipitation.
*Adiabatic Principle: Physical principle that a gas cools as it expands, warms as it compresses
Change in temperature caused only by pressure change
Change in temperature caused only by pressure change
**Saturation point: Also known as dew point, in our book
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| Convectional Precipitation (class) From this picture, the urban land gets heated up faster than the vegetation because concrete (metal) absorbs heats faster. As warm air rises from the urban land, it is cooled adiabetically, and clouds are formed. The cooler air from the vegetation flows to the urban land. However, it is incorrect that the clouds move towards the vegetation and precipitation occurs above the vegetation (as shown from the arrows). If this were true, then the urban land will not receive rain! Instead, precipitation will fall on both urban land and the vegetation. |
Why is Convectional Precipitation common in Singapore?
Singapore is a tropical country. The high temperatures experienced in tropical regions increases the capacity of the air to hold large amounts of water vapour. Therefore, convectional rain is common in tropical regions because relative humidity is high in the Tropics. (When humidity is very high, more water vapour will condense into clouds, resulting in a dense mass of clouds)
Ng Jane Wen, Chelsia
JH402/ (8)
In my opinion, Chelsia's blog entry is clear as it is detailed yet simple to understand. However, I would like to add on to it.
ReplyDeleteAs we all know, the amount of precipitation contributes to the formation of deserts. What some of us may not know is that the temperature of ocean surface currents also influences the climate.
Firstly, a surface current can either warm or cool the air above it. On one hand, winds pick up moisture as they blow across warm water currents, bringing mild rainy weather to the coastal regions. On the other hand, since cold air has less of an ability to hold moisture than warm air, cold water currents tend to bring cool, dry weather to adjacent land areas. Hence, fog is often found off the coast.
Mary Cook (n.d) "Do Ocean Surface Currents Influence Climate?". Retrieved March 30 2011, from http://www.adp.noaa.gov/lessons/ADP_LessonPlan_Climographs_Cook.pdf
Nurul Azirah Binte Johari (11)
According to the readings I have read up on, the small amounts of precipitation that you mentioned could be in the form of advection fog. This fog is formed when cooled winds from sea meets warm air on a warm land surface. This is the reason why there are still some vegetation growth in some deserts. The droplets from the fog onto deserts, when in sufficient amounts can support these vegetation. An example would be the Atacama Desert.
ReplyDeleteChua Cho Ling (JH402)
This findings are not correct and inaccurate
ReplyDelete