VIDEO LESSON

LESSSON OBJECTIVES

At the end of this lesson, you will be able to:

• Explain the factors responsible for the formation of world climatic regions, and
• Visualize the impact of several factors on the formation of global climate zones
• Explain how the local, continental and global climate varies

Keywords:

• Atmospheric Circulation
• Continentality
• Centrifugal
• Elevation
• Latitude
• Ocean Circulation
• Subtropical High Pressure

BRAINSTORMING QUESTIONS

Why does latitude have anything to do with climate?

How do you explain the combined effects of revolution, rotation, and tilt in the area closer to the equator and areas closer to the pole?

Dear Online Learner! The global climate distribution are influencing by several controlling factors discussed as follows.

1. Latitude (Seasonality)

Dear Online Learner! On any given day, solar energy insolation strikes the earth at a decreasing angle from 90⁰ (direct overhead) to 0⁰ (where the sun is on the horizon). Above the horizon, when the sun’s angle is lower, there is less intense insolation (i.e. closer to 0⁰). Solar rays flow through the atmosphere most efficiently when the sun is directly overhead (i.e., at a 90⁰ sun angle) at equatorial.

Every day, 12 hours of bright sunlight will be experienced in the low latitude zone (equatorial locales).

On the other side, high latitude regions have highly distinct seasons, with cool summers and relatively long days. Winters are bitterly cold, and the nights are long.

The change in solar declination and day duration is explained by the shifting relationships between the earth’s surface and the sun over the year.

2. Combined Effects of Revolution, Rotation and Tilt of the Earth

Dear Online Learner! The difference in day length from December to June is smaller the closer an area is to the equator, whereas the difference in day length from December to June is bigger the closer it is to the pole or high latitude.

In June, for example, the daylight covers more than half of any parallel latitude in the northern hemisphere, whereas darkness covers more than half of any parallel latitude in the southern hemisphere.

 In December, however, more than half of any latitude in the northern hemisphere is in darkness, while more than half in the southern hemisphere is in the sunshine

On June 21, the day length in the northern hemisphere increases from 12 hours at the equator to 24 hours at the Arctic Circle. Nights are longer than days in the southern hemisphere from

March 21 to September 22 (centered on June 21), since the South Pole is tilted away from the Sun during this time.

Figure 2.6 Relationships between Earth’s axis and the circle of
illumination during the course of the year (a,b)

3. Continentality (distance to large water bodies)

Dear Online Learner! Large bodies of water are capable of storing massive amounts of energy during high-energy times (i.e. hotter in the summer) and slowly releasing this energy to the atmosphere during low-energy times (i.e. colder in winter).

Seasonal extremes are greatest over the world’s largest landmass (i.e., Asia, the greatest continentality on earth).

Lakes, swamps, and marshes, for example, can generate significant temperature variations.

Windward (upwind) locations of the lake see more dramatic temperature changes than leeward locations (downwind).

Insolation at the water or land surface also adds to temperature variation.

Evaporation converts radiant energy into latent energy, which cannot be used to heat air at the same time (sensible energy).

4. Atmospheric Circulation

Dear Online Learner! According to the second law of thermodynamics, the job of atmospheric circulation is to balance energy inequities across latitudes. Horizontal inequalities in atmospheric pressure produce the circulations that result in climate differences throughout space.

Figure 2.7: Global atmospheric circulation

“High pressure” refers to pressure above mean sea level, whereas “low pressure” refers to a pressure below mean sea level. In either the vertical or horizontal directions, atmospheric mass or air travels from additional air, i.e. high-pressure regions, to lower pressure locations.

5. Seasonal Movement of Subtropical High Pressure

Dear Online Learner! Because the Subtropical High Pressure (STH) is the source of surface westerlies, the seasonal migration of the STH has climatic implications. The STH about 30⁰ latitude, according to the general circulation model, pulls surface air toward the pole and equator. The inter-tropical convergence zone (ITCZ) is located in low-pressure zones that receive the most heat from the sun. Rising motions of trigger clouds and precipitation-forming processes connected with thunderstorm weather are triggered by the convergence of winds into a low-pressure center or cyclone.

Figure 2.8 Subtropical high belts

6. Coriolis Effect, Centrifugal Acceleration, and Friction

Dear Online Learner! The Coriolis Effect (CE) is when other factors cause air to shift its trajectory and speed.

The apparent outward-directed force on an item traveling along a curved trajectory is known as centrifugal acceleration (CA). It is an example of inertia in action. The other force that influences wind direction and velocity is friction. It is greatest at the surface and diminishes with increasing height until it is negligible in the free atmosphere (friction-free zone).

7. Ocean Circulation

Dear Online Learner! Ocean circulation, like air circulation, is a process for balancing energy on the surface.

8. Topography, altitude or elevation

Dear Online Learner! In the lower atmosphere or troposphere, the normal temperature decrease with height is 6.4⁰C per kilometer. Radiation, convection, and condensation all affect the normal or ambient lapse rate, which is highly changeable.

If the altitude of Ras Dejene Mountain is 4620 m above sea level and assuming that the temperature at sea level is 30⁰ C.

What will be the expected temperature at the top of the mountain?

1000 m=6.4⁰C

4620 m=?

Temperature at sea level-([Elevation x normal laps rate or 6.4⁰C]/1000)) =temperature at the top of the mountain. (4620m x 6.4⁰C)/ (1000 m) =29.57⁰C.

Therefore, the temperature at the top of the mountain= 30⁰C -29.57⁰ C=0.43⁰C.

Figure 2.10: Orographic rainfall type

The orographic rainfall falls on the windward side of the mountains.