Meteorology 2

five slide review first Quiz Wednesday, 18th

Atmosphere Composition and Properties Atmosphere has weight –14.7 sea level or mb –Half of it is below 18,000 feet –No well defined upper surface but satellite drag data indicates some air at 1,000 miles –Gases each contribute to atmospheric pressure –Water vapour usually less than 1% but can be 3.5%

TROPOSPHERE TROPOPAUSE STRATOSPHERE STRATOPAUSE MESOSPHERE MESOPAUSE THERMOSPHERE 3000 ° IONOSPHERE Vertical Structure SEA LEVEL

Vertical Structure ,000 feet 36,089 feet KM 165,000 feet

HIGH LOW 2 nd low TROUGH COL RIDGE /- WIND

Pressure Areas Lows move at about 500 miles a day in the summer and faster, about 700 miles a day, in the winter. Flying from a HI to a LO “LOOK OUT BELOW” H L

– LAPSE RATES – RADIATION – TEMPERATURE – TURBULENCE – AIR MASSES – FRONTS – WATER DROPLETS

LAPSE RATES

STANDARD LAPSE RATE1.98 O C DRY ADIABATIC LAPSE RATE3 O C SATURATED ADIABATIC LAPSE RATE1.5 O C SATURATED RANGE ACTUALLY 1.1 O C TO 2.8 O C STEEP LAPSE RATE SHALLOW LAPSE CONDITIONALLY UNSTABLE – AIR DRY – STABLE CONDITIONALLY UNSTABLE – AIR WET - UNSTABLE POTENTIAL INSTABILITY – AIR MASS ASCENT

RADIATED AS LONG WAVE SHORT Pg 2-5

Radiation Absorption & Windows Pg 2-4

Radio transmissions less than about 10 metres wavelength (VHF, UHF, RADAR) are refracted downward by the atmosphere, roughly a third beyond the distance to the visual horizon. Radio transmissions less than about 10 metres wavelength (VHF, UHF, RADAR) are refracted downward by the atmosphere, roughly a third beyond the distance to the visual horizon. A strong inversion and a significant humidity decrease with height can cause greater refraction. Such a layer is called a radio duct. It is typically 50 to 1,000 feet deep. The bend in the path is just enough for the wave to curve back to the surface, bounce off the earth, and continue on several further bounces. This is known as anomalous propagation. It is not related to the Ionosphere and its influence on radio waves. Radio Horizon Page 4-10 Air Command Weather Manual

STRATOSPHERE DEEP OVER POLES MAY BE THIN OVER EQUATOR STRATOPAUSE MESOSPHERE MESOPAUSE THERMOSPHERE IONOSPHERE O 2 H 2 N 2 fluoresce SUN’S PARTICLES and UV RADIATION SEA LEVEL OZONOSPHERE ABSORBS UV HENCE TEMP INCREASE HERE O 3 CORROSIVE & HARMFUL feet

SEASONAL HEATING

HEAT & IT’S MOVEMENT The atmosphere is heated from below. Temperature increase decreases density. Advection: horizontal movement of air. Cold air becomes warmed by the ground as it moves over it Convection: sun heats ground, ground heats the air Turbulence: vertical mixing of air due to winds and convection Compression: air sinks, compresses and heats (Chinooks, highs)

AIR IS A HUGE TRANSPORTER OF HEAT BY VIRTUE OF THE MOISTURE EVAPORATED IN IT AS WATER VAPOUR.

HEATING the TROPOSPHERE

Advection: horizontal movement of air. Cold air becomes warmed (infrared) by the ground as it moves over it

CHANGES OF STATE

Convection: sun (short wave) heats ground, ground (longer wave) heats the air

Turbulence: vertical mixing of air due to winds and convection

MECHANICAL TURBULENCE

TURBULENCE Mechanical: Friction between the air and ground causes eddies. Instability in the air aids in turbulence. Thermal: Convection currents such as those found in storm clouds can be great enough to cause structural failure to some aircraft. Frontal: Two opposing air masses produce turbulence in the frontal zone. Wind shear: Any marked changes in wind with height produces local areas of turbulence. CAT: Clear air turbulence (Jet streams)

CLOUD CLASSIFICATION Turbulence related – stable or unstable Rain - showers vs. steady Four families of cloud as below

LOW CLOUD 3,000 ASL

MIDDLE CLOUD 7,000 ASL

MIDDLE CLOUD 11,000 ASL

HIGH CLOUD 30,000 ASL

Turbulence Levels Light: slight changes in attitude, slight strain on seat belts. Moderate: more intense, definite strain Severe: large abrupt changes in altitude, attitude and airspeed. Occupants forced violently against seatbelts.

Mountain Waves Cap clouds, Rotor clouds and Lenticular Clouds Rapid pressure drop associated over crest of hill L L R C

Air Masses An air mass is a large section of the troposphere with uniform temperature and moisture in the horizontal. Weather in an air mass is determined by: –moisture content –cooling process –stability Formed over water: Maritime Formed over land: Continental

Air Mass Stability Weather in an air mass is determined by: –moisture content – saturated or unsaturated adiabatic lapse rate if cooled? –cooling process – various lift types –stability Cold air mass – usually unstable Warm air mass – usually stable

Air Masses of North America Continental Arctic: Ca –not in summer; low water content; warmed from below, strong winds produce turbulence; heap clouds and snow showers; rarely in B.C. except as a cold-air invasion (Continental Polar: Cp) Maritime Arctic: Ma –starts as Ca that spends some time over the northern Pacific ocean; moist and unstable at high altitudes; stratocumulus and cumulus; pe/sn/-shra; Summer: northern lakes affect air mass Maritime Polar: Mp –more time spent over Pacific ocean; warmer in lower levels; more stable than Ma; orographic lifting makes rain west of mountains and dry east of mountains; Summer: Tsra/Cb Maritime Tropical: Mt –very warm and moist; Gulf of Mexico, Caribbean & south of 30°N; Winter: rarely at surface N of Great lakes, but present at high altitudes; unstable when Frontal lift; sn/ra/zr/icing and turbulence; FOG (east coast); Summer: shra/tsra

POLAR FRONT

Fronts The transition zone between two air masses is called a front. Named by the movement of the cold air: –Cold Front: that portion of the front where the cold air is advancing –Warm Front: that portion of the front where the cold air is retreating –Stationary Front: the cold air is neither advancing nor retreating. –Occluded Fronts and Trowals: trough of warm air aloft.

The Cold Front Factors: Moisture of the warm air mass stability of the warm air mass speed and steepness of the frontal surface Wind: Veer, some gusts Temperature: drops Visibility: improves after passage Pressure: approaching front, pressure will drop, then rise after passage Turbulence: usually associated with Cb’s Precipitation: showery in character, usually a narrow band 50 n.m. ColdWarm

Cold Front

The Warm Front Factors: MoistureDegree of overrunning Stability Wind: Veer Frontal Slope: 1 in 150 to 1 in 200 Temperature: gradual rise Visibility: low ceiling and low visibility; fog Pressure: drop, then rise Turbulence: usually little Precipitation: steady precipitation CI, CS, AS, NS Cold Warm

The Warm Front The Warm Front

WIND WARM FRONT

FRONTAL WAVE

FRONTS

FRONTS

Colder Cold Warm OCCLUSION or Occluded Front

Precipitation Precipitation occurs when water droplets grow sufficiently in size and weight and then fall due to gravity. –Showery precipitation: Cumulus –Steady precipitation: Stratus Condensation Nuclei –Smoke, sea salt, etc.

Precipitation.

Precipitation

MOISTURE O C one cubic metre of air can hold 50 grams of water vapour. One M 3 of air weighs about 1.35 kg. This represents about 3.5% by weight. +