Thunderstorms contain air that is rapidly risingStability ALONE determines location and intensity of convective stormsA non-atmospheric example of stability:Air parcelA distinct blob of air that we will imagine we can identify as it moves through the atmosphereDoesn’t exchange energy with its environmentCare about it’s temperature and if it is saturated/unsaturatedAir Parcels and StabilityStable if the parcel is displaced vertically, it will return to its original positionUnstable if the parcel is displaced horizontally it will accelerateNeutral the parcel will stay in its new vertical locationWhat happens to the size of an air parcel as it moves vertically in the atmosphere?An air parcel will expand as it cools and risesVertical motion causes changes of temperature because of expansion and compressionWhat happens to the temperature of an air parcel as it expands (rises) or compresses (sink)The air parcel cools as it expands (rises)Air parcel warms as it compresses (sinks)Adiabatic a process in which an air parcel does not mix with its environment or exchange energy with its environmentLapse rate the rate as which temperature decreases (lapses) with increasing altitudeDry Adiabatic Lapse Rate that rate at which an unsaturated air parcel will cool if it rises (or warm as it sinks)Applies to an air parcel with a relative humidity of less than 100%Dry adiabatic lapse rate = 10 degHow might this process be different for saturated air?Presence of moistureLatent heat: condensation releases heat into the environmentWill moist air cool faster or slower then dry air?Slower, because there are two competing effects cooling form rising and heating from condensationThe Moist Adiabatic Lapse rate the rate as which a saturated air parcel will cool if it risesmoist adiabatic lapse rate = 6 deg C/kmApplies to an air parcel with a relative humidity of 100%Saturated air follows the moist adiabatic lapse rate as it risesThe air parcel will cool as it risesWater vapor will condense as the parcel rises (a cloud forms)As water vapor condenses latent heat is releasedThe latent heat what is released will offset some of the cooling that occurredEnvironmental Lapse Rate is the lapse rate of the environment around a parcelEnvironment – the atmosphere outside of an air parcelEnvironmental lapse rate – the rate as which the environment’s temperature decreases with increasing altitudeUse the environmental lapse rate to determine the temperature of the environment as you move up or down in the atmosphereUse the dry or moist adiabatic lapse rate to determine the temperature of a parcel as it moves up and downInversion layer - a layer of the atmosphere where the environmental temperature increases with increasing altitudeTo determine the stability we need to compare the temperature of its environmentIf an air parcel is warmer then its environment it will riseIf an air parcel is colder then its environment it will sinkFor these examples an air parcel starts at the surface and has the same temperature as the environment at the surfaceThe air parcel is then lifted 1 kmConditional instability is often critical for storm developmentIf a parcel is unsaturated, it will be stableIf a parcel is saturated, it will be unstableThe parcel always rises at either the DALR or the MALRThe environmental lapse rate will vary, sometimes over the course of a day, sometimes within one profileSUMMARYStability changes when we look at different levels of the atmosphereAs a parcel rises does it dew point temp change? No, it is a absolute measureRemember what happens to an unsaturated air parcel as it is lifted(size, temperature, relative humidity)• What happens when the relative humidity of the air parcel increases to 100%?• Lifting condensation level – the level where condensation first occurs as an air parcel is lifted (where the relative humidity of the air parcel becomes 100%)• Level of free convection – the level where an air parcel first becomes buoyant (warmer than its environment)Diurnal variation: Air near surface warms during the day and cools at night – decreasing stability in the afternoon, increasing stability at nightConvection is not the only lifting mechanismFrontal LiftingLifting along a sea breeze frontLifting by mountainsLocal ConvergenceFour Forces Effect Atmospheric MotionPressure Gradients - The rate at which pressure changes with distancePressure Gradient Force – the force applied on an air parcel due to pressure differenceLower molecular density = Lower air pressureHow to calculate a pressure gradient:Calculate pressure differenceMiami Beach – Homestead: 1000 mb – 925 mb = 75 mbCalculate distance between locationsHomestead – Miami Beach: 42 kmDivide!PG = 75 mb / 42 km = 1.8 mb / kmOn a surface weather map the PGF is always perpendicular to the isobars and points from high to low pressure. The PGF is large when isobars are closely spaced and small when the isobars are spaced far apartThe PGF increases as the pressure gradient becomes larger (isobars areclose together).The wind speed will increase as the horizontal pressure gradient, and horizontal PGF, increases.Gravitational Force balances the vertical pressure gradient forceFrictional Force - a drag force acting in a direction opposite the motion of the airCaused by a mixing of air parcels (turbulence) moving at different speedsMechanical Turbulence occurs when air encounters obstructions on the surfaceIt is larger over a rough surfaceThermal Turbulence occurs when heated air rises and mixes with the air above, most common during the dayShear Turbulence occurs when the wind speed changes rapidly ove a short distanceThe frictional force is generally confined to the atmospheric boundary layerTurbulence, and thus the frictional force, tends to be most important near the surface of the earth, and rapidly decrease as you move away from the surface.Friction layer (boundary layer) – the atmospheric layer in which friction is an important forceThe Coriolis Force1. The Coriolis force causes objects to turn to the right oftheir direction of motion in the Northern hemisphere (leftin the Southern hemisphere).2. The Coriolis force can affect the direction of motion ofan object, but cannot change the speed of the object.3. The Coriolis force is strongest for fast movingobjects and zero for objects that are not moving.4. The Coriolis force is zero at the equator and increasesto a maximum at the poles.5. The Coriolis force is most important for