Air Pressure (Unit 5.5) PDF

" Air Pressu L Unit 5.5 Weather and Climate Air pressure is the weight of air that creates a pressing down force onto 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 Unit 5.5...

" Air Pressu L Unit 5.5 Weather and Climate Air pressure is the weight of air that creates a pressing down force onto 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 Unit 5.5 Weather and Climate atmosphere 1 t / low high V'r Ny Warm and m‘A v - 4= Horizontal Movement of air ( wind) Cold and dry L. . sinking air Unit 5.5 Weather and Climate " .! 1 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 -When there are pressure differences on the ground surface, the pressure gradient force is formed. -The pressure gradient force causes the air to flow from high-pressure areas to low-pressure areas (Known as wind). L Low Pressure Department of &trmospheric Sciences University of Mineis at Urbana-Charmpaign Unit 5.5 Weather and Climate A map that summarises the atmospheric conditions over a wide area at a given time A Synoptic Map > et reron v v p - South African Weather Service 2 FAPR ASZA 916 WHAT IS THE WEATHER LIKE IN i A LOW PRESSURE AREA? Vnis=5.5 Weather and Climate (P DT Low Pressure Weather MARK: 124 ‘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 -and precipitation ‘Weather: unstable; rainy, windy (as air from nearby high pressure areas rushes in) ___, Water vapour ~ condenses B I I Warm air L rises *— ‘ Cross-section view \ == Moist, cloudy, rainy, and unstable weather condition Low pressing-down l force = low pressure Unit 5.5 Weather and Low Climate Pressure Weather An extreme low pressure system = typhoon Unit 5.5 Weather and Climate How Tropical Storms Form (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 develops at the centre. Winds form around the column As pressure in the central column (the eye) weakens, the speed of the wind around it Increases Unit 5.5 Weather and Climate ?_ '}l 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 i A HIGH PRESSURE AREA? Unit 5.5 Weather and Climate * + « - Found High in places where Pressure 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 * - Little or no - l — — condensation Cold air = sinks = Clear skies, breeze, and stable weather condition [l High pressing-down force I high pressure Dew, Radiation fog, Frost and Smog. Unit 5.5 Weather and Dew Climate Dew . point point refers to the certain degree of the temperature when the air becomes saturated water vapour, and the condensation starts. with To be more specific: When air temperature decreases, hold water vapor decreases; temperature decreases When its capacity to the air to a certain temperature where the air can no longer hold its current content, point. that certain temperature moisture is called the dew L Unit 5.5 Weather and Climate Radiation A type of fog that forms when Fog the ground and the air above it cool rapidly at night (due to radiation cooling) to the dew point. This results in the suspension of water droplets near the ground surface. The air above cools rapidly to the dew point. Radiation cooling at night ——r—— 4 Unit 5.5 Weather and Climate Radiation _— -— _- Fog (Macau) Why does the fog disappear as the sun rises in the morning? During the day, as the ground starts to heat up, condensation stops and the water droplets in fog . Unit 5.5 Weather and Climate Dew Dew is water droplets on an object’s surface. Dew is formed when the surface of an object cools rapidly at night (due to radiation cooling), and the surrounding air reaches its dew contacts with the cool surface. point when it Unit 5.5 Weather and Climate Fl'ost Frost is layers of ice crystal on an object’s surface. Frost is formed when the surface of an object cools rapidly at night (due to radiation cooling) to below freezing temperatures. reaches its dew When point when the surrounding it contacts air with this cold surface, the moisture directly sublimates from a gaseous through state to form ice crystals without the liquid phase. passing Unit 5.5 Weather and Climate Pollutants and suspended Smog particulates + fog = smog Unit 5.5 Weather and Climate Fog is commonly formed pressure conditions. 1. Winter: in winter under = ¢ low temperature -> cooler ground surface temperature. P R cloud) -> heat can escape increase radiation cooling. - -1 ([Tl (1) easily from the ground -> Unit 5.5 Weather and Climate . Dew is commonly formed air pressure conditions. P in summers R cloud) -> heat can escape increase 1. However, under - =T 1 X(TN ' (1) easily from the ground -> radiation cooling. in winter, when temperatures freezing point, frost is formed drop below instead of dew. Unit 5.5 Weather and Climate When there’s high pressure (no clouds) in summer (high temperature), it may lead to... 1. Formation of dew 1. Heatwave 1. Drought condition 1. Hot air may rise rapidly (formation of lowpressure systems) -> thunderstorms -> flooding. Unit 5.5 Weather and Climate When there’s high pressure (no clouds) in winter (low temperature), it may lead to...