SC260 Introduction to Ecology
1. Describe global patterns of atmospheric heating and circulation.? The patterns of atmospheric heating and circulation occur through air movement, and typically happen through convection where there is energy transfer from the earth’s surface (Satoh, 2013). This process takes place because of unequal heating on the earth’s surface, which then influences precipitation patterns. Atmospheric circulation is the large-scale movement of air by which heat is distributed on the surface of the Earth.
The wind belts and the jet streams girdling the planet are steered by three convection cells: the Hadley cell, the Ferrel cell, and the Polar cell. While the Hadley, Ferrel, and Polar cells are major players in global heat transport, they do not act alone.
Disparities in temperature also drive a set of longitudinal circulation cells, and the overall atmospheric motion is known as the zonal overturning circulation.
The global circulation of the atmosphere shifts cold air from high latitudes in the direction of low latitudes, and warm air from low latitudes in the direction of high latitudes. As air rises above the surface it moves away near the top of troposphere and moves to the pole region. Advancing toward the pole the air begins to come together at about 30 degrees north and south latitude.

Mechanisms that produce high precipitations in the tropics, mechanisms that produce high precipitation at temperate latitudes and mechanisms produce low precipitation in the tropics.
Mechanisms that produce high precipitations in the tropics are any product of the condensation of atmospheric water vapor that is pulled down by gravity and deposited on the Earth’s surface. The mechanisms of precipitation include; rain, snow and sleet, it occurs when the atmosphere becomes full with water vapor and then condenses, and precipitates.
Trade winds north of the equator blow from the northeast. South of the equator, they blow from the southeast. The trade winds of the two hemispheres meet near the equator, causing the air to rise. As the rising air cools, clouds and rain develop. This cycling rise and fall is called a Hadley cell. The resulting bands of cloudy and rainy weather near the equator create tropical conditions - temperate latitudes.
The mechanisms that produce low precipitation in the tropics, the sun heats air at the same equator, causing it to expand and rise. This warm, moist air-cools as it rises. Since cool air holds less water vapor than warm air, the water vapor carried by this rising air mass condenses and forms clouds, which produce the heavy rainfall in tropical.
Highly seasonal rainfall in the tropical dry forest and tropical savanna biomes The part of the earth that gets the most direct sunlight at any given time is called the Inter-Tropical Convergence Zone (ITCZ). The ITCZ gets direct sunlight which causes air to become unstable and rise. When the air is unstable the pressure drops. The ITCZ is an area of low pressure due to all the heating and instability in the air. The low pressure causes air to rise and as it rises it cools and condenses into clouds and if it condenses rapidly enough it forms precipitation. The ITCZ is responsible for the wet season in the tropics
The ITCZ is always in an area where the sun is directly overhead or almost directly overhead, which would be in the summertime in the tropics.

In areas of the tropics where the sun is not directly overhead are areas of high pressure which are not conducive to cloud production or precipitation these areas are both to the north and south of the ITCZ are called the doldrums and move seasonally parallel alongside the ITCZ. The Doldrums are responsible for the dry season in the tropics.

Many tropical rain forests lie along the equator and these are in the range of the ITCZ for all or most of the year, so it is rainy for most of the year there.

The tropical wet and dry forests are on either side of the rain forests along the equator and savannahs in the Northern hemisphere are to the north of the wet and dry forests, and in the southern hemisphere to the south of the wet and dry forests. This is because the wet and dry forests spend more time in the ITCZ than savannahs. The global atmospheric circulation model shows how air near the equator tends to rise, due to the temperatures being higher than the surrounding tropics. This leads to high instability and low pressure, acting like a conveyor belt for water and creating high levels of precipitation.
Because of the Earth's axial tilt, the area over which this low pressure zone sits changes from season to season. At its most extreme, the solar equator (the area where the sun is directly overhead) reaches as far as the Tropics of Cancer and Capricorn, and the band of rain oscillates with it.
This results in the perception of seasonal rain. In fact, this rain exists all year round, but the band moves north and south with the seasons, bringing heavy rain in the summer and leaving drought in the winter, creating a monsoon affect in many African countries.
This isn't entirely cut and dry, there are a few other factors in play as well, because some savannahs are along the equator, and some rain forests and wet and dry forests are further away from the equator than most others. A lot of this has to do with rain shadows and ocean currents.

References
Clift, P.D & Plumb, R.A. (2008) The Asian Monsoon: Causes, History and Effects, Cambridge University Press.
Junling Huang and Michael B. McElroy (2014). Contributions of the Hadley and Ferrel Circulations to the Energetics of the Atmosphere over the Past 32 Years.
Yochanan Kushnir (2000). The Climate System: General Circulation and Climate Zones.