Physical Geography: Weather and Climate

Transcription

1 Physical Geography: Weather and Climate Chapter 4 Weather vs. Climate Weather short-term, day-to-day expression of atmospheric processes Ex. - Today is clear, cold and sunny Climate long-term, average conditions Usually at least 30 years of daily weather data (temperatures and precipitation) Ex. - NY Humid Continental, warm summer Meteorology the scientific study of the atmosphere Air Temperature Insolation Solar radiation received at the earth s surface Determined by angle of the sun s rays and number of daylight hours Modifying variables Amount of water vapor in the air Cloud cover Nature of the surface of the earth Elevation Degree and direction of air movement Reasons for Seasons Circle of illumination the travelling boundary that divides daylight and darkness ½ the world is in darkness and ½ in sunlight at any moment Earth rotates counterclockwise Earth Inclination Annual March of the Seasons Axis of the earth tilts at 23.5 Summer Solstice (about June 21) Northern hemisphere tilted toward the sun Vertical rays of the sun at 23.5 N Winter Solstice (about December 21) Northern hemisphere tilted away from the sun Vertical rays of the sun at 23.5 S Spring and fall equinoxes (about March 21 and September 21) Vertical rays of the sun at equator 1

2 Annual March of the Seasons Seasons of the Year Earth-Sun Relations Oceanic & Continental Effects Water heats and cools more slowly Marine environment Cooler summers, warmer winters Temperatures are moderated Oceanic & Continental Effects Marine effect exhibit moderate influences of the ocean (ex. Vancouver, BC) Vancouver - 28 F temp. range Land heats and cools more rapidly Continental environment Hotter summers, colder winters Wider temperature variation Oceanic & Continental Effects Continental effects areas less affected by the sea, therefore have greater range between max and min temperatures (Winnipeg, Manitoba - 49 N) Winnipeg - 64 F Temp range The Lapse Rate Temperature generally decreases as altitude increases Lapse rate Average of 3.5 F per 1000 feet (6.4 C per 1000 m) in the troposphere Temperature inversion Decrease in temperature less than expected (or an increase) Main cause - air near the ground rapidly loses its heat on a clear night - the ground becomes cooled quickly while the air above it retains the heat the ground was holding during the day. Contributes to smog problems 2

3 Moisture in the Atmosphere Humidity water vapor in the air A function of temperature Relative humidity - the ratio of water vapor in the air, compared to maximum water vapor possible Tells us how close we are to saturation Moisture in the Atmosphere Relative humidity Highest at dawn when temperature is lowest Lowest in late afternoon temperatures highest Cooler air = lesser maximum water vapor possible Maximum water-vapor possible Dew point temperature at which air becomes saturated Further cooling results in condensation (dew) Water Vapor 5 a.m. 100% Relative Humidity Water Vapor 11 a.m. 50% Relative Humidity Water Vapor 5 p.m. 20% Relative Humidity Warmer air = greater maximum water vapor possible Atmospheric Lifting Orographic Lifting - air is forced over a barrier (like a mountain range) Windward side wet Leeward side dry Types of Precipitation Orographic rainfall it occurs in the Western Ghats and Himalayas in South Asia resulting in Rain-shadow effect: the area of low rainfall found on the leeward (or downwind side) of a mountain range Rain Shadow Rain Shadow Orographic Lifting Types of Precipitation Frontal Lifting (Cold and Warm Fronts) - along the leading edges of contrasting air masses. Front Zone of separation between two air masses Leading edge of cold air mass is a cold front Leading edge of warm air mass is a warm front Front 3

4 Frontal Lifting - Cold Front Cold Fronts Cumulonimbus clouds may produce large raindrops, heavy showers, lightning and thunder, and hail. Frontal Lifting Warm Front Gentle lifting of the warm, moist air produces nimbostratus and stratus clouds and drizzly rain showers, Weather Phenomena Lake Effect Snow Sleet Freezing Rain Thunderstorms Hail Tornados Lake-Effect Snow cp air masses move south and east Cold air passes over warmer Great Lakes Air masses are warmed and water vapor added Lake-Effect Snow Dangerous Weather Sleet frozen raindrops or partially refrozen snowflakes that bounce when they reach the ground 4

5 Dangerous Weather Freezing Rain precipitation that starts as snow at high altitudes, melts and freezes after it hits the ground Thunderstorms - condensation of large amounts of water vapor creates lots of energy, heating the air - Causes updrafts Raindrops create friction - causing downdrafts Giant cumulonimbus clouds cause dramatic weather Heavy rain, lightning, thunder, hail, heavy winds Hailstones Hailstones Hail is a form of precipitation which consists of balls or irregular lumps of ice Form in strong thunderstorm clouds, particularly those with intense updrafts Falls - updrafts Once it s too heavy for updraft, it falls to ground Stronger the updrafts larger the hail stones Figure 8.21 Birth of a Tornado Air at higher altitudes moves faster than surface air Creating rotation in the air parallel to the ground Birth of a Tornado Updrafts create a shift in the axis of rotation Creating rotation in the air perpendicular to the ground 5

6 Birth of a Tornado Mesocyclone forms as a rotating updraft within the thunderstorm. If one forms, a tornado will descend from the lower portion of the mesocyclone. Mesocyclone a large, rotating atmospheric circulation Fujita Scale scale for rating tornado intensity based on damage to human-made structures, vegetation Category Wind Speed Potential Damage F mph 39% Light Damage: Minor roof damage, gutters, siding damaged Branches broken off trees F mph 36% Moderate Damage: severe roof damage, mobile homes overturned, broken glass F2 F3 F4 F mph 19% mph 5% mph 1% >200 mph <0.1% Considerable Damage: roofs torn off, foundations shifted, large trees snapped, cars lifted off ground Severe Damage: severe damages to large buildings (malls), trains overturned, structures with weak foundations blown great distances Devastating Damage: homes completely leveled, cars thrown, small missiles generated Incredible Damage: houses swept away, cars carried 100 meters, structural damage to highrises Top Ten Deadliest Tornadoes Rank States Date F-Scale Dead Injured Towns 1 MO-IL-IN March 18, 1925 F Murphysboro, DeSoto 2 LA-MS May 7, Nachez 3 MO-IL May 27, St. Louis, E. St. Louis 4 MS April 5, 1936 F Tupelo 5 GA April 6, Gainesville 6 TX-OK-KS April 9, 1947 F Glazier, Higgins 7 LA-MS April 24, Amite,. Pine, Purvis 8 WI June 12, 1899 F New Richmond 9 MI June 8, 1953 F Flint 10 TX May 11, 1953 F Waco Tornado Damage Figure

7 Climate Classification Generalized Climate Regions Köppen system the A climates are tropical climates Tropical equatorial and tropical latitudes the B climates are dry Desert Arid tropical/midlatitudes Semi-arid tropical/midlatitudes the C climates are generally moderate and are found in the middle latitudes Temperate mid-latitudes, mild winters the D climates are associated with continental and high-latitude locations. Continental midlatitudes/high latitudes, cold winters The E climates are polar High latitudes/polar regions Highland climates lower temps than similar latitudes (lapse rate) Tropical Climates (A) Dryland Climates (B) Tropical Rain forest high temps, high precipitation all year Dense vegetation Tropical Monsoon high temperatures, season variation in precipitation Hot deserts high temperatures, Limited rainfall Drought resistant plants/sand Steppe transition zones adjacent to deserts Higher rainfall, more seasonal temperature variation grasslands Humid Midlatitude(C,D) Tropical Climates (A) Mediterranean Mild winters, Marine Humid Humid Subtropical warm Continental West Coast summers warm warm mild winters, temps temps in in summer summer Cool summer Most rain in low sun (winter) East West East side side coast of of continents of continents Subarctic Tundra Ice Cap temperature 7-8 months - warmest continuous extreme month cold, snow summers between cover 32 average o & 50 o, below - winter freezing very cold low Coniferous plants No vegetation & many forest wild flowers called in summer taiga <5 precipitation/year 7

8 Highland Climates (H) Polar Climate Highland (H) Climates change rapidly on mountains, becoming colder the higher the altitude gets. Closely related to the climate of the surrounding climate. The highlands have the same seasons and wet and dry periods as the climate zone Highland (H) Climates change rapidly on mountains related to the climate of the surrounding climate. The highlands have the same seasons and wet and dry periods as the climate zone Mountain climates are very important to mid-latitude climates. Mountain climates are very important to mid-latitude climates. Snow is kept back until spring and summer when it is released slowly as water through melting Climatic Change Long-term climatic change Significant variations over geologic time Ice ages Medieval warm period and little ice age May be due to variations in: shape of Earth s orbit, tilt of the axis, gyration of the rotation axis Short-term climatic change Natural processes Volcanic eruptions, oceanic circulation Human processes Enhanced greenhouse effect Climatic Change Greenhouse effect Certain gases in the atmosphere function as an insulating barrier, trapping infrared radiation Global warming Caused by human activities that have increased the amount of greenhouse gases in the atmosphere Carbon dioxide: burning fossil fuels, deforestation Methane: natural gas and coal mining, agriculture and livestock, swamps, landfills Nitrous oxides: motor vehicles, industry, fertilizers Chlorofluorocarbons: industrial chemicals Climatic Change Evidence of global warming 20 th century was the warmest in 600 years Average surface temp rose over 1 F during the century Winter temps in the Arctic have risen about 7 F since the 1950s Loss of Arctic ice cap Glaciers are thinning and retreating Consequences of global warming include: Rising sea levels Changes in temperature and precipitation patterns Impact on soils, vegetation, agriculture 8