Lesson-4.1-Finals-Meteorology.pptxjjjjjj

Meteo

1. PhSc 116: METEOROLOGY - Ms. Jennifer A. Mata

2. Wind and Air Pressure

3. LEARNING OBJECTIVES: Describe air pressure and explain why it changes with altitude. Identify the three forces that act on the atmosphere to either create or alter winds. Discuss how wind direction is expressed using compass direction.

4. What is Air Pressure? Air pressure refers to the force exerted by the weight of air molecules on a given surface area. Unit of measurement: Millibar (mb) or hectopascal ( hPa ) 1 atm (standard atmospheric pressure at sea level) = 1013.25 mb or hPa Instrument used: Barometer (invented by Evangelista Torricelli in 1643) Mercury barometers and aneroid barometers are the two main types

5. Why Air Pressure Changes with Altitude? As you go higher in the atmosphere: The density of air decreases (fewer air molecules in a given space). There are fewer air molecules pressing down from above. Therefore, air pressure decreases with increasing altitude .

6. Wind is the horizontal movement of air caused by differences in air pressure. Air moves from areas of high pressure to areas of low pressure , trying to equalize the difference.

7. Different Forces Acting on the Atmosphere Pressure Gradient Force (PGF) The primary cause of wind. Air moves from high to low-pressure areas, just like water flowing downhill. The greater the difference in pressure (called the pressure gradient ), the stronger the wind .

8. Different Forces Acting on the Atmosphere 2. Coriolis Effect A deflection of moving air caused by the rotation of the Earth . The Coriolis Effect causes air to curve instead of moving in a straight line .

9. Different Forces Acting on the Atmosphere 3. Frictional Force It is  a force that resists the motion between two surfaces in contact, always acting in the opposite direction to the relative motion or tendency of motion. Occurs near Earth’s surface , where air rubs against landforms, trees, and buildings. Friction slows down wind speed and reduces Coriolis deflection .

10. Interaction of the Three Forces The balance among these three forces determines the direction and strength of wind : PGF initiates movement. Coriolis Effect deflects the air. Friction modifies its speed and angle, especially near the ground.

11. Expressing Wind Direction Wind direction describes the direction from which the wind is blowing . Example: A “north wind” blows from the north toward the south . Measuring Wind Wind vane: shows the direction the wind is coming from . Anemometer: measures wind speed (in km/h or m/s).

12. Expressing Wind Direction Wind Patterns and Weather Wind direction provides clues about upcoming weather: Winds from oceans (sea breeze) → usually moist, cooler air. Winds from land (land breeze) → usually dry, warmer air. Changing wind direction can indicate a shift in weather systems (e.g., incoming storm or cold front)

13. Additional Information: Global and Local Winds

14. Global Wind Systems Due to uneven heating of the Earth, large-scale winds develop: Trade Winds – steady winds blowing from east to west in the tropics. Westerlies – blow from west to east in mid-latitudes. Polar Easterlies – cold winds blowing from the poles toward lower latitudes.

15. B. Local Winds These are short-distance winds caused by local temperature and pressure differences: Sea Breeze and Land Breeze (day-night coastal winds) Mountain Breeze and Valley Breeze (occur in mountainous regions)