Air Pressure and Weather Patterns PDF

| Unit 5.5 Weather and Climate l Air pressure is the weight of air that creates a pressing down force on the Earth’s surface. It is commonly barometer. measured with a Do you remember common unit of measurement the for air pressure? | mb - millibars hPa- hectopascal We will learn: « What...

| Unit 5.5 Weather and Climate l Air pressure is the weight of air that creates a pressing down force on the Earth’s surface. It is commonly barometer. measured with a Do you remember common unit of measurement the for air pressure? | mb - millibars hPa- hectopascal We will learn: « What Air Pressure is + Differences between Low « + . * + Pressure and High Pressure Weather Association of Low air pressure to unstable weather condition Association of High air pressure to stable weather codition High air pressure in summer and winter The formation of dew, fog and frost Formation of smog ' Unit 5.5 Weather and Climate I l atmosphere Warm, moist rising air \/ \ Cold, dry descending/ sinking air Horizontal Movement of air / wind Unit 5.5 Weather and Climate l Why is it important to understand pressure in the atmosphere? air Understanding air pressure in the atmosphere tells us what weather conditions to expect. Knowing what weather to expect will help us to be prepared every day. Unit 5.5 Weather and Climate l ———— —— —— R <~ The influence of the Pressure Gradient Force High Pressure - Low Pressure ~ d Department of &trospheric Sciences University of Minois at Urbana-Champaign Unit 5.5 Weather and Climate l . a map that summarises the atmospheric conditions over a wide area at a given time A Synoptic Map Unit 5.5 Weather and Climate — _ ... I Air always moves from an area of high pressure to an area of low pressure. 2> L This creates moving air called wind. small reat ; : b aza strong gale The greater the difference in air pressure, the faster the air moves, stronger the wind. the African Weather v Service SouthAR o i~ mma‘ 1:20M = . ) - ] oWy T /FAPR ASZA 916 . ? %4%é i/ H— / 7 | R neo ‘ » nnnnn " = : ° WHAT IS THE WEATHER LIKE IN A LOW PRESSURE AREA? Unit5.5 Weather and Climate_| 1) oy Pressure Weather Found in places where temperatures are generally higher (i.e. Equator) than nearby areas Warm, moist air rises Rising warm air = less pressing-down force - low air pressure Warm, moist air rising - increased condensation (Why?) and precipitation Weather: unstable; rainy, windy (as air from nearby high pressure areas rushes in) Moist, cloudy, rainy, Water VT iy 7[‘: colillie G = ] Warm L *~— | rises ‘ Cross-section view ] air and unstable weather condition Low pressing-down force = low pressure Unit 5.5 Weather and Climate Low l Pressure Weather An extreme low pressure ? system = typhoon | Unit 5.5 Weather and Climate I |How Tropical Storms Form I l (additional info) not to be discussed in detail [ How tropical storms are formed High humidity and ocean temperatures of over 26°C are major contributing factors Water evaporates from the |ocean surface and comes into contact with a mass of cold alr, forming clouds A column of low pressure As pressure in the central column develops at the centre. Winds (the eye) weakens, the speed form around the column of the wind around it Increases Unit 5.5 Weather and Climate | Why does the wind speed increase as the pressure decreases? This is why an extreme low pressure system like a typhoon can have very strong winds. WHAT IS THE WEATHER LIKE IN A HIGH PRESSURE AREA? Unit 5.5 Weather and Climate * » « - Found I High in places where Pl'essu re weather temperatures are generally lower (i.e. 30°N/S)than nearby areas Cold air is dry and sinks Sinking air = more pressing-down force > high pressure Since air is sinking, there is little or condensation no precipitation Weather: stable; clear skies; cooled by breezes or light winds - S * IS, — e - Little or no Clear skies, breeze, and | condensation stable weather condition l Cold air il sinks , - High pressing-down force > high pressure Unit 5.5 Weather and Climate ' High Pressure Weather This type of weather is good for .... ? | Unit 5.5 Weather and Climate I High Pressure In Daytime — |+ sunlight is strong in the daytime W © * sky is clear; no clouds block the sun land absorbs heat and gets very hot summer - Unit 5.5 Weather and Climate I High Pressure In Summer Night time * Since there are no clouds in the day, heat from the land is lost quickly so the land becomes cold. + Condensation occurs at ground level and forms dew - s Unit 5.5 Weather and Climate |80 i in | High Pressure In summer areas * « Ground is overheated in the daytime Warm, moist air rises quickly + Heavy thunderstorms. * Flooding may occur. clouds form rainfall occurs. There may be ' Unit 5.5 Weather and Climate | High Pressure In Summer If high pressure remains over an area for a long ' period of time (at least a week), a drought may occur. | Food supplies will be affected increase (food insecurity). and food prices may | Unit 5.5 Weather and Climate I High Pressure In Summer If high pressure remains over an area for a long period of time (at least a week), a heatwave may occur. i_‘g._..__m . A heatwave is a prolonged period of excessive _ heat, often combined with excessive humidity. The map above was generated on the 11" day of a heatwave that affected the central US in July 2020. - A heatwave can have serious impacts on humans and jcause . - and even ' . Compare these two satellite images Which one shows extreme pressure? How do you know? P&‘ 4 Which one shows extreme low pressure? How do you know? Unit 5.5 Weather and Climate High Pressure In Winter Daytime - cold, clear and bright during daytime with relatively | high humidity - water vapour condenses on dust and other particles in air creating | . Unit 5.5 Weather and Climate Fog Formation Ground + air 1. On clear nights, land surfaces release heat out to space. directly above it cools 3. Condensation happens as warm, moist air comes in contact with cool ground = Unit 5.5 Weather and Climate E _— Fog _fll Radiation Fog L Formation | E | Why does the fog disappear as the sun rises in the morning? ~—e During the day, as the ground starts to heat up, condensation stops and the water droplets in fog . — !r: BN l !!E op] Unit 5.5 Weather and Climate | High Pressure In Winter At Night time + Ground heat at night |+ There are no clouds to trap heat at night so the ground cools fast .+« Condensation occurs at ground level - Frost forms in the evening Unit 5.5 Weather and Climate When temperature drops below freezing point (0°C), is formed. S — - I 3 If there is no wind, droplets form at ground level, usually on grass. We " | can see dew in the early morning. Unit 5.5 Weather and Climate | High Pressure In Winter Moistureon ;. - | freezes and forms . Impact: traffic accidents Moistureon - and . freezes Impact: food shortage for animals Frozen @ may burst. Impact: - = in homes ' Unit 5.5 Weather and Climate ‘ Smog Formation SMOG= = (pollutants and suspended particulates) + = smog » occurs often in winter time, when fog is formed with no strong wind to carry suspended particulates 1 (e.g. dust, ash) away. » suspended particulates attach to the excess water droplets in the air Impact: Causes respiratory-related diseases High Pressure And Stable Weather ® Where the temperature is low (l.e. at 30" latitude), the air cools down and becomes heavier. As it becomes heavier, it sinks back onto the ground °s‘mking cold and dry air e ,_#4.';»_*.'\\. surface. ’ exerts a higher pressing down force on the ground, leading to \ 4 A 1 DThe sinking cold and dry air gradually * warms up again as it gets close o the ground, picking up water vapour, so there is decreased no / decreased condensation cloud cover. 01'hervk:re. high air pressure brings less / no precipitation, which is a stable weather. — and .