Chapter 13

Storms

 

-        Convection-clouds- (cumulonimbus cloud) thunderstorm clouds

-        Three Conditions Must Exist-

1-    Abundant moisture in lower levels atmosphere-latent heat (chapter 11)-upward motion of the cloud.

2-    Mechanism must lift air to allow moisture to condense

3-    Unstable atmosphere- air continues to cool for cloud to grow (cloud warmer than surrounding air)

-        Rising air will continue until it meets stable air-limits cumulonimbus clouds to a height of 18,000 m

-        Thunderstorms last only 30 minutes and 24 km

-        Geography and Movement of air play roles in thunderstorms-Southeastern US

-        Types of Thunderstorms: Classified to what causes the air to rise

1-     Air-Mass Thunderstorm(most common)- unequal heating of Earth’s Surface with in one-air-mass. Mid-afternoon-Mountain and Sea-breeze (extreme temperature differences)

2-     Frontal Thunderstorm-advancing cold fronts and rare warm fronts. Thunderstorms along leading edge of cold front-air pushed up (produce line of thunderstorms). Warm front-slides up over cold air mass (mild thunderstorms).

-Stage Development-Figure 13-3-classified according to the direction in which the air is moving.

1-    Cumulus-air rises-vertically upward-updrafts

2-    Mature-equal amounts updrafts and downdrafts-convection cells

3-    Dissipation-warm air runs out updrafts cease

-Severe Storms:

Thunderstorms-temperature difference between the upper and lower level parts of storm. Updraft and downdrafts intensifies. Supercells-self-sustaining-powerful rotating updrafts

Lightening- caused by the rapid rush of air in a cumulonimbus cloud- friction between updrafts and downdrafts-electrical charges step ladder, return stroke and channel 100 million volts.

Fury of the Wind- Downburst-violent downdrafts concentrated in local areas.

                Microburst- 3 km 250 km/h

                Macroburst- 5 km 200 km/h

-Hail-precipitation-balls of ice-spring

-Tornadoes-associated with thunderstorms

        before reaching ground-called a funnel cloud

        associated with “supercells” and “wind shear” (wind speed and direction change suddenly with height)

horizontal rotation near Earth’s Rotation-tilted to vertical position

Extreme pressure gradient between center outer portion-violent winds

Classification-Fujita Scale-Table 13-2

Formation during later afternoon and evening temperature contrasts-Central US-“Tornado

Alley”

-Tropical Storms

        Tropical Cyclones- Low pressure

Energy from warm tropical oceans-latent heat from evaporation

        Intertropical Convergence Zone (ITCZ)

Rising air creates low-pressure center at ocean surface

Coriolis effect causes the moving air to turn counterclockwise in northern hemisphere

        Basic conditions needed:

1-abundant supply of very warm ocean water

2- disturbance to lift warm air and keep it rising

-        Occur most frequently in late summer and early fall-most stored energy

-        Movement-figure 13-10

-        Stages- figure 13-11- pg. 343

-        Tropical Depression: disturbance over ocean acquires-circulation around center of low pressure

-        Tropical Storm: wind speeds exceed 65 km/h

-        Hurricane: air pressure falls-120 km/h

Eye-calm center

Eyewall- band of strongest winds

-Classification-Saffir-Simpson Scale

        wind speed, air pressure and property damage

        Table 13-4

Lasts until there is no longer energy-usually when it is over land

Storm surges-water towards coastal areas-right side of storm.