7Wet Equatorial Climate Moist climate of the equatorial zone10°N to 10°SLarge annual water surplusWarm temps all yearDominated by ITCZmE & mT air massesAnnual rainfall can exceed2500 mmIquitos, Peru, 9°S
8Trade-wind Coastal Climate Moist, low-latitude climateRainfall peak in high-sun seasonShort dry period in low-sun seasonEast side of continents5-25°N & SWarm all yearBelize City, Belize, 17°N
10Wet-Dry Tropical Climate Located 5-30°N & SEach year very wet & very dry seasonHigh-sun season → ITCZ influence → WetLow-sun season → STH influence → DryWet season → mT & mE airDry season → cT airDrought-resistant plantsTimbo, Guinea10°N
11Monsoon Coastal Climate Coastal South AsiaWet high-sun seasonAsiatic lowDry low-sun seasonSiberian highSmall temp range
18Moist Subtropical Climate East side of continents 25-35°N & SMoist mT air from STHWater surplusLarge annual temp rangeSome cP air in winterWinter precip commonfrom midlatitude cyclonesCharleston, SC, 33°N
21Requirements for Tropical Cyclone Development Warm water (>26.5 °C)The right adiabatic lapse rate (6.5 °C/km)Mid-level moistureCoriolis Force (minimum distance of 500 Km from the equator) to initiate rotation
22Requirements for Tropical Cyclone Development A “seed” low level disturbance (tropical wave)Lack of vertical wind shearFavorable steering currents
23The tropics heat up MUCH more than the poles The tropics heat up MUCH more than the poles. Especially the South Atlantic and the GulfHurricanes are parasites on warm water….it is the fuel for their growth.The summer sun drops about 5000 watts of energy on a square meter per day in the tropics.The tropical oceans absorb and STORE solar energy in the form of heated water.
24A gallon of aviation gas has about 1.4 x 108 Joules of energy. A Joule is energy expended (or work done) in applying a force of one newton through a distance of one meterCalorie: the energy needed to increase the temperature of 1 gram of water by 1 °C. This is about 4.2 joulesIn a week the sun puts about that much energy into a square meter of the tropics.The Sun essentially makes the tropics into a high-octane fuel source for Hurricanes.
27Where you don’t get Tropical Cyclone Development Middle latitudes: Water is too cold, westerly winds produce too much shearNear the equator: Not enough Coriolis ForceSouth Atlantic: Cool water, wind shear, and lack of tropical waves from the ITCZMediterranean: Sometimes get tropical-like systems, but generally the sea is too smallGreat Lakes?
28The Physics of Hurricanes What drives hurricanes is latent heat from water evaporation and water condensation.Water releases 2257 kJoules/kilo (2.3 x 106J/kg) on condensationA cyclone will cycle ~1014 kilos of water a day or about 100 billion tons…..A fraction of this heat is converted into mechanical energy that drives wind speedMostly goes into updrafts which increase cloud height and speed up condensation, releasing more energyIn a day a cyclone releases ~200 x 1018 J720 megatons of TNT70 times world energy consumption
29Tropical Cyclone Cross Section Extremely low pressure/Strong pressure gradientIntense convergence & uplift → Heavy rainfallLatent heat release provides energy
30Positive Feedback in a Tropical Cyclone Easterly wave initiates convectionLow pressure forms at surfaceWarm, moist air spirals inward from oceanAir rises, expands, cools, and condensesCondensation release latent heat into stormWarmer air rises fasterFaster rising air drives inward spiral of airAnd so on…
34Tropical Cyclone Hazards Wind Damage – some produce wind gusts >200 mphFresh Water Flooding – can extend far inlandEarthflows – due to heavy rainfall & saturated soilStorm Surge – most serious – can inundate coastdue to low pressure and high winds
37The Physics of Hurricane Damage Work or Energy = ½ mass x velocity2 =1/2 mv2This is the energy in a moving object…..and it scales by the square of velocity!Take wind…..the energy deposited by 1 kilo of airCat 1 (40 m/s) = ½ x 1kg x (40m/s)2 = 800 JCat 3 (55 m/s) = ½ x 1kg x (55m/s)2 = 1512 JCat 3 (80 m/s) = ½ x 1kg x (80m/s)2 = 3200 JA factor of 4 increase in energy from doubling the wind speed.
38Storm SurgeWaves are worse since water is denser so carries more kinetic energy per unit volume.Take a modest wave, say 3 meters, hitting a house….Mass ~ 200,000 kgVelocity = 3 m/sEnergy ~ 900,000 joulesAbout the same as driving a truck into the house at 50 mph.
40Heat driving atmospheric banding and storms is not unique to Earth. The banding on Jupiter (and the other gas-giant planets) is caused by the same process.In this picture the rising atmosphere is light, the sinking is dark. The knothole-looking things are essentially hurricanes.
41The “Red Spot” on Jupiter is a hurricane that has lasted at least 400 years. It was first seen by Galileo using the first astronomical telescope.
42Cyclical Patterns of Atlantic Hurricanes was down time for Atlantic stormsSince 1995:Warmer water off east coast of USOn average, more hurricanes each yearOn average, more major hurricanes each year2005 was record year with 28 stormsLikely due to cycle in thermohaline circulationNext 20 years likely continued high hurricane activity