A nucleus is a central body around which something may grow, collect, or concentrate. A condensation nucleus is formed when water vapour in the air clings to microscopic, atmospheric particles (usually dust), and then condenses to form water droplets.
Linking Wind and Precipitation to Deserts
Overview of global wind patterns/ action
Overview of global wind patterns/ action
Circulation of air over the Earth's surface is due to the differential heating between the equatorial and Polar Regions, and the fact that hot air being lighter rises above the cold air. Hence, air heated at the equator would rise and reach the Polar regions, where the chilled air would descend to the equatorial regions. Rotation of the earth creates a deflecting force on the winds, known as Coriolis Effect. The Coriolis Effect influences the wind by deflecting it to the right in the northern hemisphere, and to the left in the southern hemisphere.
To see a sequence of weather satellite images showing the actual wind direction, go to Exploring Earth.
Deserts
About one- fifth of Earth's land surface is desert. A desert is a geological region that receives little precipitation. Generally, deserts are defined as areas that receive an average annual precipitation of less than 250mm (25.4cm). Deserts usually have extreme temperature range.
- Wind and high temperatures
2. Orographic precipitation and arid lands
Rain shadow deserts are formed because tall mountain ranges prevent moisture- rich clouds from reaching areas on the lee of the range. Air masses lose much of its moisture as they move over a mountain range. A desert is then formed on the lee side of the range.
3. Convectional and frontal precipitation
Convectional and frontal precipitation is more common in humid regions than desert regions because humid air is lighter than dry, desert air. Hence, it rises due to buoyancy, and leads to heavy precipitation during most part of the year.
Nur Shahanaz (10)
Hi Shahanaz, very interesting post you have there! :D I think the idea of Cloud Condensation Nuclei (CCN) that was brought up in class the other day was pretty interesting. So i went and did further research on it. It turns out that these CCN forms the basis for cloud seeding. And CCNs need not always be man-made and can be produced natually. One good example is sulfate aerosol (SO42- and methanesulfonic acid droplets). These sulfate aerosols form partly from products produced by phytoplankton in the open ocean. :D However, the idea of cloud seeding also brings us back to the concept of "systems". So is cloud seeding necessarily a good thing afterall? :O
ReplyDelete-Chiam Paula (JH402)
Hi. In your post you mentioned one of the causes that leads to formation of deserts, which is the rain shadow effect produced by high mountain ranges. I have found another cause of deserts, predominantly to account for the deserts along the western coasts. At these coasts, when wind blows parallel to the coastline, the winds push surface water seaward at right angles to the direction of the wind. TAKE NOTE: This would not have happened if not for the rotation of the earth. Air and water from the south are then pushed to the left of the southern hemisphere. Similarly, water from the north is pushed to the right of the northern hemisphere. These are only made possible by the Coriolis effect. As a result, to replace the air pushed out to sea, cold water from the sea surface to ocean surface. The presence of this cold air causes any air that pass by this region of cold water to be cooled, preventing any moisture to build up. This gives rise to deserts, where moisture is minimal.
ReplyDeleteChua Cho Ling (JH402)
For the above comment, i made reference to Geography: an integrated approach By David Waugh.Thank you.
ReplyDeleteHi, in response to Paula's post: most of the condensation nuclei used in cloud seeding have minimal impact on the environment, like AgCl. While it's not perfect, I don't think it will affect our environmental system presently but in the long term it may be a problem, because if the concentration keeps increasing it might wreck havoc in the atmosphere. But, problems are inevitable because it is after all human intervention - I'm all for it if it's not used intensively and only for the people who really need it.
ReplyDeleteHI SHAHANAZ :)
ReplyDeletewell, my comments is about how the little precipitation that deserts receive not only contributes to the hot and dry weather in the day, it also contributes to the extreme cold at night.
The interesting feature of how deserts are extremely hot in the day and cold at night is due to the same reason of how the air in the deserts is very dry. Dry air holds little moisture and hence it cannot hold much heat, when the sun sets. Dry air results when there is little water vapor in the atmosphere, reducing the amount of heat trapped, allowing radiation to escape to outer space quickly. Furthermore, the cloudless skies which are due to little water vapor also release heat quickly at night, contributing to low temperatures at night.
Hence, interestingly, the dry air results both in hot days and cold nights.
References: http://geography.about.com/library/faq/blqzcolddesert.htm
http://www.weatherquestions.com/Why_are_deserts_so_hot.htm
-Li Lin
In response to Paula and Yi Shien's comments: Cloud Condensation Nuclei(CCNs)can be both good and bad, it depends on the circumstance and concentration.
ReplyDeleteWhy good:
1. CCNs could be considered to have a very significant role in precipitation. If there is insufficient amount of CCNs, even though there is enough water vapour, precipitation cannot be formed as water vapour is not condensed.
2. By seeding the air with condensation nuclei, people can create rainfall artificially to help those regions that are short of water.
Why bad: Large concentration of CCNs is related to bad weathers such as hailstone, freezing rain and heavy rain which may cause flood to occur. Large amount of CCNs can be produced by coal-fired factories, hence in those regions heavy rain usually occurs.
--Jingxuan(16)