17.1 Climate and its causes

Learning Targets Describe the effect of latitude on climate Diagram the Hadley, Ferrell, and Polar atmospheric circulation cells and show how they influence the climate of various locations Discuss position in the global wind belts, proximity to a large water body, position relative to a mountain range

Climate Climate is the long-term average of weather Weather is unpredictable Climate is predictable

Climate Factors influencing region’s climate: Latitude Three Global Wind Belts Prevailing Winds Continental Position Ocean Currents Altitude

Factor # 1 - Latitude The main factor influencing region’s climate Low latitude = high solar energy Equator Sun directly overhead; equal night and day High latitude = low solar energy Poles Sun at low angle; long days, long nights High albedo What is latitude? The amount of solar energy a particular location receives is the most important factor in determining that location’s temperature. Tropics are warmer and polar regions are colder. Temperate regions are in between, both in latitude and average air temperature.

Factor # 2 – Global Wind Belts #1 ITCZ – Intertropical Convergence Zone Low Pressure boundary between two Hadley Cells, lots of precipitation. Equator 00 - Doldrums Areas where air mostly rises or sinks creates no wind. ITCZ migrates north in Northern Hemisphere summer, because there are more land areas than in Southern Hemisphere

The ITCZ migrates slightly with the season The ITCZ migrates slightly with the season. Land areas heat more quickly than the oceans. Since there are more land areas in the Northern Hemisphere, the ITCZ is influenced by the heating effect of the land. In Northern Hemisphere summer, it is approximately 5 o north of the equator while in the winter, it shifts back and is approximately at the equator. As the ITCZ shifts, the major wind belts also shift slightly north in summer and south in winter, which causes the wet and dry seasons in this area

Factor # 2 – Global Wind Belt #2 Hadley and Ferrell Cell Boundary High Pressure – sinking cold air causing evaporation Horse latitudes - 300 N/S Areas where air mostly rises or sinks creates no wind. Where did all the moisture go at the Hadley and Ferrell Cell Boundary?

Factor # 2 – Global Wind Belt #3 Ferrell and Polar Cell Boundary Polar jet stream – cold air from poles meet warmer air from tropics, very stormy 500 to 600 N/S latitude Areas where air mostly rises or sinks creates no wind. As Earth orbits the Sun, the shift in angle of incoming sunlight causes polar jet stream to move.

Factor # 3 - Prevailing Winds Global wind belts create H and L zones Bring weather from locations they come from H  Dry Cold air descending causes evaporation L  Wet Warm air rising and losing its water

Where are low pressures located in regards to the three global convection cells? At equator between the 2 Hadley cells & 60 degrees where Ferrel and Polar cells meet. (warm and rainy) Where is the high pressure? 30 degrees where Hadley and Ferrel cells meet, areas where deserts are located such as Sahara and Sonora. (cooler and drier) ITCZ – Intertropical Convergence Zone - air rises up at the equator and then travels away from the equator. As the air rises, it cools and condenses to create clouds and rain. Climate along the ITCZ is therefore warm and wet. In an area where the air is mostly rising, there is not much wind.

Due to Coriolis Effect – winds are deflected to right.

high pressure zone where the Hadley cell and Ferrell cells meet, air is fairly warm since much of it came from the equator. It is also very dry for two reasons: (1) The air lost much of its moisture at the ITCZ, and (2) Sinking air is more likely to cause evaporation than precipitation. low pressure zone is between the Ferrell and Polar Cells at around 50-60o. This is the usual location of the polar jet stream, where cold air from the poles meets warmer air from the tropics and storms are common.

Factor # 4 - Continental Position Water regulates air temperature Higher specific heat than land Maritime climate – influenced by nearby large body of water Less extreme Continental climate – greater temperature differences between day/night & summer/winter More extreme Maritime climate its climate is strongly influenced by the nearby sea: summers are not too hot and winters are not too cold. Temperatures also do not vary much between day and night. Continental climate is more extreme, with greater temperature differences between day and night and between summer and winter.

What this means is that it takes 4 What this means is that it takes 4.184 Joules of heat to raise 1 gram of water 1 degree Celsius.

cities is located at 37°N latitude within the westerly winds (prevailing winds)

Factor # 5 - Ocean Currents Surface and deep water currents affect air temperatures along the coast Cold water moves towards the equator California current cools Southern California Warm water moves towards the poles Gulf stream warms Northern Europe Cold upwelling can cool or heat surrounding land Coastal upwelling also brings cold, deep water up to the ocean surface off of California, which contributes to the cool, coastal temperatures. Further north, in southern Alaska, the upwelling actually raises the temperature of the surrounding land because the ocean water is much warmer than the land.

One portion flows northward between Great Britain and Northern Europe, the other moves south along Europe and northern Africa. These warm waters raise temperatures in the North Sea, which raises air temperatures over land between 3 to 6oC Because air traveling over the warm water in the Gulf Stream picks up a lot of water, London gets a lot of rain.

Other ocean currents

Factor # 6 - Altitude Mountains affect climate by Lowering temperature Temperature decreases with altitude in the troposphere Rainshadow Effect Air is dry after it has been forced over mountains  no precipitation e.g. California compared to Nevada Gravity pulls air molecules closer together at sea level than at higher altitudes. The closer molecules are packed together, the more likely they are to collide. Collisions between molecules give off heat, which warms the air. At higher altitudes, the air is less dense and air molecules are more spread out and less likely to collide.