Winds Three causes of motion Convection Pressure Differences Coriolis Effect 1. Convection Currents Warm air rises and cool air sinks because of density This is called a convection current Winds are caused by the uneven heating of Earth’s surface. Land heats up and cools off quicker than water So the large amount of water on Earth moderates our temperatures 2. Pressure Differences pressure differences in the atmosphere that are a result of temperature differences WIND ALWAYS FLOWS FROM HIGH TO LOW PRESSURE 3. Coriolis Effect Wind is deflected to the right (Northern hemisphere) due to earth’s rotation effect greatest at poles, decrease to zero at equator Highs and Lows? Winds circle Clockwise around a high Highs generally mean cold dry air that is sinking High pressure usually = fair weather Low Pressure Systems Winds circle counterclockwise around a low Warmer air rises and cools and forms clouds and precipitation Low pressure usually = rainy weather Global Circulation Patterns Global winds are the result of several cell-like circulation patterns brought about by uneven heating of Earth’s surface and compounded by effects of the Earth’s rotation. Doldrums or ITCZ At the equator hot air rises and forms an area known as the doldrums At the boundary between the troposphere and stratosphere it spreads out to the N or S Horse latitudes As it reaches about 30 N and S of the equator it cools and descends Sinking air causes an area of dry weather The sinking air also causes an area with weak winds This caused problems for ships and they sometimes threw their horses overboard Trade Winds Winds flowing south from the horse latitudes is deflected to the west in the northern hemisphere These aided trading by ship Local Wind Patterns Monsoons Land breeze/Sea breeze Chinook Monsoon Dry season In winter, air flow is from cooler (H pressure) to warmer (L pressure) ocean Air from the land is dry Wet season In summer, air flow is reversed Air flows from the cooler ocean to the hotter (L pressure) land Sea Breeze Land breeze reversed Chinook A wind on the eastern side of the Rockies formed when air descends and is compressed and warms Effects: Rapid. Large Temperature Changes Can Occur Beaufort scale Used to estimate wind speeds Originally used by sailors Beaufort Scale on Water And on Land Wind and Pressure Relationship Lab Remember Topographic Maps? Contours are imaginary lines that join points of equal elevation on the surface of the land Now we will use these with equal temperature and pressure Same Concept—Different Use Isotherm=equal temperature Isobar=equal barometric pressure contour interval (CI) The contour intervals vary Isobars often have an interval of 4 Read the directions or look at examples to see the contour level Tips for understanding contour lines. There are a few rules that topographic contours must obey, however, and once you understand these rules the map becomes an extremely useful and easy to use tool. 2) Contour lines can never cross one another. Each line represents a separate temperature or pressure and you can’t have two different temps or pressures at the same point. 3) Points shown are reporting stations There may be areas that do not report or have no station 4) The closer contour lines are to one another, the higher the wind speed. Where is the wind speed high? Where is it low? 5) Inside a series of closed contours (the contours make a circle) is a High or Low pressure