Hurricane/Tropical Storm/Depression Ike:
- Damage in the billions, however only 40 lives were lost due to good planning and evacuation procedures. Caused flooding from significant rains in St. Louis, MO.
Calendar/Time line:
- Homework #2 due in one week (Tues 9/27)
- Test 1 next Thursday (Thurs 9/29)
- Next Tuesday reserved for going over material on test 1
Summary of how water behaves:
- If RH = 100% (Td = T), there will be no net evaporation or condensation, since rate of evaporation = rate of condensation
- If RH < 100% (Td < T), any liquid water present will evaporate, since rate of evap. is greater than the rate of cond.
- If RH > 100% (Td > T), water vapor will condense to liquid water until the RH falls back to 100% (Rate of cond. is greater than rate of evap.) When this occurs it is. temporary until sufficient water vapor condenses. - Condensation will take place: 1st onto existing liquid. surface, if available. 2nd onto solid surfaces (dew), and 3rd onto cloud condensation nuclei (clouds)
Boiling Pot of Water Example:
- Air parcel that is very warm and nearly saturated just above the water in the pot
- As air parcels move away from the heat source, they cool (T decreasing)
- As they cool, there is more water vapor than the saturation amount (at lower temperature) so condensation occurs on CCN (steam)
- As steam parcels move away, they mix with drier air and the air surrounding the droplets is no longer saturated so the droplets evaporate
- RH goes from less than 100%, to 100+%, then back to less than 100%
Rising Air Cools, Explained:
- A parcel of air has an internal pressure equal to that of the surrounding air
- As a parcel of air is elevated, it's volume increases and pressure decreases to equal the surrounding air
- Energy is expended by the parcel to increase it's size, so temperature decreases
- Vice versa with a falling parcel, energy is absorbed by the surrounding air, so temperature increases
- Further lifting causing further expansion which causes further cooling
Conditions for Cloud Formation:
- Surface heating and free convection: ground heats lowest layer of air and convection occurs
- Surface convergence: air converging at the surface causes air to rise (Surface low pressure centers)
- Surface divergence: surface high pressure centers
- Upper-Level Divergence: air diverging in the atmosphere causing air to rise from below to fill "the void" of the diverged air (Tropopause doesn't allow air to fall into upper-level diverging air, it must rise from below)
- Topography lifting: Mountains causing air to rise which causes clouds to form, clear skies on the far side of the mountain
- Frontal boundaries: Warm air rises over cold frontal boundaries, causing clouds from up drafts and rain in down drafts
Precipitation:
- Clouds normally cover 60% of the Earth at any one time, not all are causing rain or snow though
- Average sized cloud droplets are 0.02mm in diameter (sub visible), average sized rain drop is 2mm.
Tropical Cyclones and Hurricanes:
Tropical Weather:
- Very little seasonal change and night/day change
- Warm oceans cover the majority of the tropics, resulting in net evaporation and cloud/storm formation
- Tropical "Waves": Convergence on the eastern side of the wave with divergence to the west of the convergence
Trade Winds:
- 30N-0: Northern hemisphere has NE Trade Winds
- 30S-0: Southern hemisphere has SE Trade Winds
- Intratropical Convergence Zone (centered on equator but moves slightly with seasons)
Tropical Cyclones:
- Surface low pressure system over tropical waves
- Tropical Depression: <39 mph surface winds
- Tropical Storm (named): 39-74 mph
- Hurricane: 74+mph
- Typhoon: used in the north Pacific Ocean
- Severe Tropical Cyclone: SW Pacific Ocean
- Severe Cyclonic Storm: Indian Ocean
- Tropical Storms are the only natural disasters that get their own names due to their longevity
- Tropical Cyclones have central low pressure at surface
- In Northern Hemisphere, surface winds rotate counter-clockwise and converge toward the low center
- Wind speed is determined by how rapidly the air pressure changes along the horizontal surface (how low the pressure at the center of the storm is, the lower the center pressure, the stronger the winds)
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