2 Weather vs Climate Weather: Climate: The state of the atmosphere at this moment. Scales of seconds to days.Can only be predicted (forecast) no more than a few days into the future.The average weather that occurs over a region over a long period, Usually decades to millennia.Can make general observations regarding temperature & precipitation. Processes that effect these are: uneven heating of Earth, convection currents, Earth’s rotation, tilt, & ocean currents.
4 Atmospheric Layers Troposphere: Densest layer due to gravity. Air molecules packed closer to Earth.Nitrogen, oxygen & water vapor - gasesWeather is confined to this layer.Air flow is vertically –Air rises & falls due to temperature/humidity differences (in other words density).Rising & falling air is called CONVECTION
5 Warm moist air rises – less dense Humid air is less dense than dry airWarm air is less dense than dry airCooler dry air sinks – more denseDry air is more dense than moist airCool air is more dense than warm air
6 Atmospheric Layers Stratosphere: Temperature inversion – air warms as it increases in altitude.Ozone layer interacting with UV radiation heats this layer.Ozone (O3) – absorbs most UV-B & all of UV-C radiation.Air flow is horizontal –Jet stream – narrow band of high wind that moves W to E (~ 200 mph)Influences weather; approx. three in each hemisphere
8 Temperature Inversions Temperature inversions are when air warms as you increase in altitude.Stratosphere and Thermosphere have temperature inversions.Thermosphere is heated directly by sun’s radiationTemperature inversion in the troposphere can occur:Traps pollution near surface; affects weather; prevents mixing of air
9 Uneven Heating of the Earth Three Causes of Uneven Heating:Variation of Angle –Sun’s rays strike mid-latitudes & polar regions at a more oblique angleSun’s rays strike the equator (tropics) at perpendicular (90 degree) angle.Causes radiation to travel through more atmosphere at the poles = loss of solar energymore energy reaches the tropics than at the mid-latitude & polar regions
11 Uneven Heating Cont. Surface Area Heated by Sun – Perpendicular angle causes energy to be distributed over a smaller surface equator.Thus tropical areas receive more solar energy per square meter than higher latitudes
12 Uneven HeatingAlbedo – the percentage of incoming sunlight is reflected from a surface.The higher the albedo for a surface , more solar energy it reflects, and less it absorbs.
13 Properties of AirAir has four properties that determine how air circulates in the troposphere:DensityWater vapor capacityAdiabatic heating or coolingLatent heat release
14 Density & Water Vapor Capacity Density determines the movement:Less dense = rises; areas of rising air have low air pressureMore dense = sinks; areas of sinking air have high air pressureWater Vapor Capacity is related to temperature:Warm air can hold more water vapor than cool airMaximum amount of water vapor that can be in the air at a given temperature is called Saturation Point.That given temperature is called Dew point. The temperature at which water vapor condenses. Humidity is = 100%
15 Relative humidity is the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.
16 Adiabatic Cooling & Heating As air rises air pressure decreases, so it expands and cools.As air sinks air pressure increases, so it contracts and heats.These processes are called Adiabatic cooling & heating respectively.The adiabatic lapse rate is a decrease of 3.5°F/1,000 ft (6.4°C/km) of altitude under normal conditions. Varies.
18 Latent Heat ReleaseCondensation, changing from vapor to liquid, releases heat (energy).This is known as Latent Heat Release:Energy released in condensation can warm the air such as in storms.
19 Atmospheric Convection Currents Global patterns of air movement that are initiated by the uneven heating of the Earth.As air rises at the equator:Density decreases, moisture increases, and air pressure decreases.Air reaches saturation point (humidity = 100%)Condensation occurs and clouds/precipitation formCondensation releases latent heat which causes air to expand and rise more rapidlyThese processes cause air to continuously rise near equator forming a river of air upward.This is considered an area of LOW PRESSURE!!
21 Atmospheric Convection Currents Global patterns of air movement that are initiated by the uneven heating of the Earth.As air is chilled at the top of the troposphere by adiabatic cooling (Air sinking):Air at this point had little water vapor.It is displaced N or S by the less dense rising moist airDisplaced air sinks to about 30° N or S latitudeAir contracts and heats up as it sinks due to adiabatic heatingThis warm, dry is considered an area of HIGH PRESSURE!!
24 High & Low Pressure Systems Air always moves horizontally across the surface from high pressure to low pressure = WIND!!!!High pressure systems are described as sinking dry air. These are associated with fair weather because no condensation is occurringLow pressure systems are described as rising, moist air. These are associated with stormy weather because condensation occurs.