Question

why are the small particles in soil so important relative to the large particles ?

what causes the clouds at the inter tropical convergence zone?

describe the role that polar stratospheric clouds play in the destruction of ozone in the stratosphere?

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Answer 1

1. Soil particles vary greatly in size, and soil scientists classify soil particles into sand, silt, and clay. Starting with the finest, clay particles are smaller than 0.002 mm in diameter. Some clay particles are so small that ordinary microscopes do not show them. Silt particles are from 0.002 to 0.05 mm in diameter. Sand ranges from 0.05 to 2.0 mm. Particles larger than 2.0 mm are called gravel or stones. Most soils contain a mixture of sand, silt and clay in different proportions.The size of soil particles is important. The amount of open space between the particles influences how easily water moves through a soil and how much water the soil will hold. Too much clay, in proportion to silt and sand, causes a soil to take in water very slowly. Such a soil gives up its water to plants slowly. These soils are sticky when wet. Size of soil particles is important for other reasons, too. It affects the ease of working the soil, what crops can be grown, and the efficiency of certain fertilizers.  Sandy soils that have no fine clay or silt particles filling the pore space cannot hold as much moisture since there is no surface area for the water to cling to and the pores are so large that the weight of the water causes much of it to run down and out of the soil. For this reason, medium and coarse sandy soils, low in clay are known as droughty soils. Crops cannot live long in them without very frequent rains. When fine soil particles fill the large pore spaces, the soil can hold more water for plants because there is more surface area for water to cling to. And since the size of the pores is reduced, the weight of the water is less and it does not run out of the soil so readily.  

2. The ITCZ (Intertropical Convergence Zone) play important role in the global circulation system and also known as the Equatorial Convergence Zone or Intertropical Front. It is a basically low pressure belt encircling Earth near the Equator. It is a zone of convergence where the trade winds meet.In the Intertropical Convergence Zone, the northern and southern trade winds come together. Because of the rotation of the Earth, the winds cannot really cross the equator without losing energy. Instead of continuing over the Earth horizontally, the winds thus move vertically toward the upper atmosphere. The heating of the Earth's ocean currents by the sun assists in this process, making the air warmer and letting it rise. The result is that the Intertropical Convergence Zone has low air pressure near the Earth's surface. The lack of horizontal wind movement in the region caused sailors to nickname the Intertropical Convergence Zone, "the doldrums."he frequent rising of air in the Intertropical Convergence Zone means that moisture constantly is being brought high enough in the atmosphere to a point cool enough to allow the moisture to condense into clouds. The Intertropical Convergence Zone therefore can see incredible amounts of precipitation and high humidity. Although some areas of the zone do have a dry season, others do not. Afternoon showers are a feature of the zone.Rainfall in the Intertropical Convergence Zone typically is not gentle rainfall that lasts for long periods. Instead, the high amounts of energy from thermal and solar heating cause moisture to condense quickly into clouds in the hottest part of the day. Circular typhoons thus often form as the air currents move. Some of the strongest winds on the Earth have been recorded in these storms. Thunderstorms with heavy lightening also are common.

3. Polar stratospheric clouds (PSCs) play a central role in the formation of the ozone hole in the Antarctic and Arctic. PSCs provide surfaces upon which heterogeneous chemical reactions take place. These reactions lead to the production of free radicals of chlorine in the stratosphere which directly destroy ozone molecules.

PSCs form poleward of about 60°S latitude in the altitude range 10 km to 25 km during the winter and early spring. The clouds are classified into Types I and II according to their particle size and formation temperature.

Type II clouds, also known as nacreous or mother-of-pearl clouds, are composed of ice crystals and form when temperatures are below the ice frost point (typically below −83°C).

The Type I PSCs are optically much thinner than the Type II clouds, and have a formation threshold temperature 5 to 8°C above the frost point. These clouds consist mainly of hydrated droplets of nitric acid and sulphuric acid.