3.1 - Seasons And Weather

Physical GeographyPhysical Geography

Seasons and WeatherSeasons

• These are determined by the Earth’s tilt. As the Earth revolves around the sun, the hemisphere tilted towards the sun experiences summer (since it’s getting more direct solar exposure) while the other hemisphere has winter.

• The solstice is the day of the year in which the sun is directly overhead either the Tropic of Cancer (23.5o N) or the Tropic of Capricorn (23.5o S)

• When over Cancer, it’s the summer solstice (June 21st) and is the longest day of the year with the shortest night in the northern hemisphere. The winter solstice is Dec. 21st.

• On the vernal (spring) and autumnal equinoxes, solar exposure is even and so are the days/nights

Summer Solstice

Winter Solstice

Equinox

Reflected light during the winter and summer solstices.

Weather

• What’s it’s like at a time in a particular place

• Causes

1. Water vapor

2. Cloud cover

3. Landforms and bodies of water

4. Elevation

5. Air movement

Precipitation

• Snow or rain

• Moisture cools and condenses. Think of sweat on a drink bottle.

• 3 types

1. Convectional

• Sun heats the moist air and rain clouds form. Usually tropical.

2. Orographic

• Mountains force moist air upwards and rain or snow forms when moisture cools.

• Precipitation typically falls on windward side of mountain (the side on which wind is blowing) since it’s blocked by the mountain from falling on the other side. Rain shadow.

3. Frontal

• Two air masses of different temperatures run into each other.

• Warm moist air gets pushed upward where it cools, condenses and turns into precipitation.

Weather extremes

Hurricanes

• Air over at least 80 degree ocean water picks up heat and moisture. Can turn into hurricane.

Categories:• Category 1. Minimal, 74-95 mph (119-153 km/hr): Some damage is

expected, with most of it limited to shrubbery, unanchored houses and items. Some minor flooding will cause pier damage.

• Category 2. Moderate, 96-110 mph (154-177 km/hr): Considerable damage can be expected to shrubbery and some trees may be blown down; there will be damage to mobile homes, signs, roofs, windows and doors. Small craft may be torn from moorings and marinas will probably flood. Some low-lying areas and shoreline residences should be evacuated.

• Category 3. Extensive, 111-130 mph (178-209 km/hr): Large trees and most signs may be blown down; there may be structural damage to small buildings; mobile homes will be destroyed. Serious flooding will occur at the coast, with severe damage to shoreline structures and flooding up to eight miles (13 km) inland at elevations of five feet (1.5 m) or less.

• Category 4. Extreme, 131-155 mph (210-250 km/hr): Expect trees, signs and traffic lights to be blown down, and extensive damage done to roofs, windows and doors. Mobile homes will be completely destroyed. Beaches will be eroded and there will be flooding as far as 6 miles (9.5 km) inland for anything under 10 feet (3 m) above sea level. Anyone staying within 500 yards (457 m) of shore will be evacuated, as will all single-story residences within 2 miles (4 km) of shore.

• Category 5. Catastrophic, 156+ mph (251+ km/hr): Trees, signs, traffic lights will be blown down. There will be extensive damage to buildings and major damage to lower floors of structures less than 15 feet (4.5 m) above sea level within 500 yards (457 m) of shore. Massive evacuation of residential areas 5-10 miles (8-16 km) from shore will be required.

• Hurricane winds also cause storm surges (water flooding in from the ocean) 15 feet or more.

• This is what did the most damage to Galveston in the 1900 hurricane. The highest point on the island was only 8.5 feet. The storm surge was over 15 feet.

• 6,000 to 12,000 people died and the clean up was horiffic.

• To prevent such damage again, a 17 foot wall was built and the entire city was raised 17 feet

Damage to Galveston after the 1900 hurricane

Galveston Seawall

Raising Galveston

• They moved about 440 million cubic feet of sand into the city.

• Everything was raised between a few inches to 17 feet, including the 6 million pound St. Patrick’s Church.

Galveston was known as the New York of the South. It was the largest, most developed, and most modern city in Texas. Houston was a backwater that people sniffed at. After the 1900 hurricane, though, development shifted to Houston and Galveston was forever left behind.

Hurricane Rita

Katrina

Tornadoes

• Powerful spiraling air

• Can range from 300 feet to 2 miles in diameter

• Can have winds of 65 mph to over 300 mph

• Can travel very short to very long distances

• The Tri-State tornado of 1925 may have traveled 219 miles over Missouri, Illinois, and Indiana before dissipating.

• Measured on the Fujita scale

This is the F5 tornado that hit my hometown of Topeka in 1966. It went 22 miles straight through downtown.

• That tornado killed 17 people and did over $617 million in today’s money.

Blizzards

• Massive snowstorm with high winds

Blizzards

• Massive snowstorm with high winds

Drought

• Long period with little or no rain

• Damages crops, plants, and wildlife

• Can also cause massive wind erosion, as in the Dust Bowl of the early 1930’s.

In South Dakota

Floods

• Lots of rain or runoff causes rivers and streams to overflow their banks