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Chapter 5 Atmospheric Water and Weather Supplemental notes are drawn from Lutgens and Tarbuck, The Atmosphere Significance of Water (1) Vital to all organisms of the Earth (2) Necessary for many Earth system processes (3) Impacts the structure of the Earth’s surface – chemically and physically (4) Has definite functions in human activities (5) Can exist in solid, liquid and gaseous states under normal Earth atmospheric conditions (6) It is slow to heat / slow to cool Water and Atmospheric Moisture - Water on Earth: Location and Properties Humidity Atmospheric Stability Clouds and Fog Air Masses Atmospheric Lifting Mechanisms Midlatitude Cyclonic Systems - Violent Weather Ocean and Freshwater Distribution Figure 5.3 Hydrologic Cycle - Closed system movement of moisture in the Hydrosphere - Absorption and release of energy (latent heat…in calories) “powers” the system - As a proportion, the energy is small, the actual amount is significant - Gain-or-loss of energy results in three major processes and two minor processes Hydrologic Cycle (1) Evaporation / transpiration (2) Condensation (3) Precipitation (4) Sublimation (5) Deposition In general terms, precipitation=evaporation worldwide --- in reality, “too much, too little, too bad” issues of frequency and dependability Continents: precipitation>evaporation Oceans: precipitation<evaporation Water’s Heat Energy Characteristics Figure 5.6 - Moisture in the hydrologic cycle is most frequently locked in H2O vapor - It is a small but, highly variable percentage of the atmosphere by volume - This H2O vapor is concentrated in the lower 18,000’ of the atmosphere There are limits to the volume of H2O that the atmosphere can hold in suspension … temperature is the primary factor As a general rule, the warmer the air, the greater the volume of water vapor that air can hold Saturation and Dew Point saturation or point of saturation - Achieved by: (1) dropping temperature (2) increasing moisture Temperature of saturation is called dew point After saturation, additional cooling or addition of moisture results in condensation Humidity - General term for the measure of the volume of H2O present in the air at a given temperature --- reported as: absolute; relative; specific - We are interested in relative humidity Ratio of H2O in the atmosphere at a given temperature, to the volume of H2O the air can hold at that temperature (H2Oobserved / H2Opossible) x 100 Relative Humidity Figure 5.7 Humidity Patterns Figure 5.10 Atmospheric Stability - Adiabatic Processes --- Dry adiabatic rate (DAR) 10oC/1000m --- Moist adiabatic rate (MAR) 6oC/1000m --- Stable and unstable atmospheric conditions Condensation Process by-which gaseous H2O is changed to a liquid (600 cal release) clouds; fog; dew; frost [though frost is technically different] Requires: (1) air cooled beyond saturation (2) a surface on-which to condensation (condensation nuclei) Fog Simplest: a cloud with base at ground level (1) cooling radiation advection upslope fog ice fog (2) evaporation fog steam fog frontal fog Clouds Buoyant masses of visible H2O or ice crystals Visible sign of atmospheric stability or instability Product of any process encouraging air movement vertical convection convergence subsidence horizontal advection frontal lifting Cloud Forms Classed by altitude and appearance - Altitude “families” High – cirro Middle – alto Low – strato Clouds of vertical formation Cloud Forms, cont - Appearance stratus - sheet, layer (stability) cumulus – globular, pillowy (instability) cirrus – high, white, thin (stable, ice) We also make use of the prefix / suffix nimbo or nimbus to designate precipitationbearing clouds Cloud Types and Identification Figure 5.18 Cumulonimbus Development Figure 5.19 Airmasses - Large masses of air characterized by: - (1) common properties of humidity and temperature at a given altitude - (2) characteristics of their source region Source Region Region whose terrestrial and atmospheric conditions create airmasses (1) extensive and uniform in area (2) area of atmospheric stagnation Airmasses are classified by: (1) Latitude of source region (gives temperature) A; P; T; E; AA (2) Surface area below the airmass (gives humidity) continental – “c” low moisture marine – “m” high moisture * “k” and “w” are added for stability indices Airmass Classification, cont cA – continental Arctic cP – continental Polar (*) cT – continental Tropical (*) mT – marine Tropical (*) mP – marine Polar (*) mE – marine Equatorial cAA – continental Antarctic * consistently influence North America Air Masses Figure 5.24 Front Surface or zone of contact / conflict / discontinuity between airmasses Coined by Norwegian meteorologists in WWI – Polar Front Theory … Norwegian Cyclone Model links cloud patterns, precipitation, wind, barometer, flow aloft, etc Frontal lifting occurs when one airmass is forced to rise/ride above the other Passing through a front frequently brings weather change: temperature; dew point spread; wind speed / direction; atmospheric pressure Atmospheric Lifting Mechanisms Convectional Lifting Orographic Lifting Frontal Lifting ---Cold fronts ---Warm fronts --- Occluded fronts --- Stationary fronts Atmospheric Lifting Mechanisms Figure 5.27 Cold Front Figure 5.31a Warm Front Figure 5.32 Midlatitude Cyclone Figure 5.33 Average and Actual Storm Tracks Figure 5.34 Thunderstorms Best known disturbance weather pattern… not strictly cyclonic flow Worldwide approx 16 million annually Product of warm, moist air lifted to condensation… most are tropical almost unknown at the Poles - may be: convectional; orographic; frontal Thunderstorms Figure 5.36 Thunderstorms, cont Characterized by thunder/lightning; torrential rainfall/hail; strong up-and-downdraft winds; release of latent heat Stages: (1) cumulus (2) mature (3) dissipation Tornadoes From the Spanish tornar – “to turn” Intense center(s) of low pressure … pressure gradient winds may exceed 300 mph … a “whirl-pool” like column of air vortex downward from a cumulonimbus cloud A funnel of condensed H2O, funnel colored by what the tornado contacts Tornado Development and Occurrence - Often produced in association with midlatitude cyclones - < 1% of thunderstorms produce tornadoes - Typically North American (3/4) and spawned in cP-mT air collisions --- 700+ annually; North America dominates Twister! Figure 5.38 Tornadoes Figure 5.39 Life Stages Though a tornado may have a “life” of only minutes, each will go through some combination of the following stages: (1) Funnel cloud (2) Tornado (3) Mature Tornado (4) Shrinking Tornado (5) Decaying Tornado Tornado Destruction Millions of stories about what tornadoes can do Destruction from: (1) high winds - strong updrafts (2) high speed projectiles (3) subsidiary vortices / “down blasts” Tornado Destruction, cont No one has accurately measured the windspeed of a tornado We rate tornadoes by extent of damage; the Fujita Scale (F-Scale) Tornado Watch and Tornado Warning Hurricanes Tropical cyclone with windspeed in excess of 200 mph Lowest pressure recorded in the Western Hemisphere Name from Huracan – Carib Indian god of evil Hurricane Development and Occurrence Giant heat engines taking energy from oceanic latent heat Form over tropical waters 5o to 20o … but not all the tropical waters inside of 5o [no Coriolis] So. Atlantic [cold water currents] The notable exception to a lack of So. Atlantic hurricanes is Hurricane Catarina (2004) Hurricane Development and Occurrence, cont Three stages of development (each can be an end in itself) (1) tropical depression (2) tropical storm (3) hurricane --- wind swirl/rain bands --- eyewall [winds to 200 mph] --- eye [winds approx 25 mph] Profile of a Hurricane Figure 5.42 Destruction Damage from tropical hurricanes range from complete devastation, caused by the passage of the eyewall of a very intense hurricane along the coast, to a minor nuisance, produced by a weak hurricane whose effects resemble those of a strong thunderstorm Annually nearly every portion of the US is effected directly or indirectly by hurricane activity Destruction Forms: (1) wind* (2) storm surge (3) inland flooding* [eye wall may produce 10+” rainfall] (4) ancillary vortices (tornadoes) * function of ground speed Saffir-Simpson Hurricane Intensity Scale Hurricane Watch/Hurricane Warning Some Interesting Ones No Name; Galveston Bay,TX No Name; Okeechobee, FL Camille Agnes Hugo Gilbert Dennis, Floyd, Irene Andrew Katrina Catarina 1900 1928 1969 1972 1989 1994 1999 1992 2005 2004