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Climate and Weather
David M. Hassenzahl
ENV 206: Introduction to Climate Change
Overview
• Weather and Climate defined
• Determinants of weather and climate
• Please read NASA’s Meteorology - Weather And Climate: A Condensed Primer
Relevant Course Objective
• Define climate and climate change, and explain how climate changes over time
Weather
• The phenomena (temperature, precipitation, humidity, wind) occurring in the atmosphere at a given time
• The atmosphere consists of gases held close to Earth by gravity
Climate
Climate is the typical pattern of weather in a given place over an extended period of time (30 or so years)
• Temperature
• Precipitation
• Humidity
• Wind
Precipitation
• Type– Rain, snow, fog, other
• Amount
• Distribution / Seasonality
Temperature
• Average temperature
• Daily highs and lows
• Seasonal highs and lows
Humidity and Wind
• Humidity– Percent of saturation
• Wind speed matters
Winds
• Uneven heating and cooling lead to winds– Water – Land– Land – Land– North – South– Altitude
• Earth’s rotation drives winds– Coriolis effect (See video library)
Climate and ecology
• Climate, along with geology, determines what sorts of plants, animals, and other life can live in a given place
• Humans have developed methods for controlling local climate – Heating and cooling– Building shelter
Köppen Classification of Climates
• Tropical
• Dry
• Mild mid-latitude
• Cold mid-latitude
• Polar
Examples of Climates: Desert
• Low rainfall (<250 mm / 10 in) per year
• Low humidity
• Often hot
• Mojave (Las Vegas)
• Sahara, Gobi
Source: United States Geological Survey
Examples of Climates:Tropical Rainforest
• 1750 – 2000 mm rain (68 – 78 inches)
• Year-round or monsoon rain
• High temperatures and humidity
Tropical Rain Forest
Source: NASA
Examples of Climates
• Mediterranean
• Tundra
• Taiga
• Steppe
Determinants of Climate
• Insolation
• Geography
• Ocean
• Atmosphere
Insolation
• Aka sunlight• Intensity (solar flux)
– Watts per square meter
• Variability– Solar cycles– Solar flares and sunspots
• Angle of incidence– Earth’s tilt– Varies over time
Source: NASA
Earth Energy Balance
Source: NASA
Geography
• Land masses– Continents– Mountains
• Water bodies– Oceans– Seas and large lakes
• Altitude and latitude
• Albedo (reflectivity)
North Pole Ice
Source: NASA
Ocean
• Ocean currents move hot and cold water around the globe
• Evaporation precipitation
• Cold air warms up over hot water
• Hot, humid air condenses, rains when cooled
Why Europe is Warm
wind direction
Warm water flow
Source: NASA
The AtmosphereSource: NASA
Atmospheric Gases
• Nitrogen – N2 (~78%)
• Oxygen – O2 (~21%)
• Argon – Ar (~1%)
• Water vapor (variable, averages 1%)
• “Trace gases” (parts per million / ppm)
Parts per million
• Parts per million, or ppm
• As a fraction of volume– (Can also measure by mass)
• 1 ppm means one atom out of every 1,000,000 atoms in the atmosphere
Trace Gases Include
• Carbon Dioxide – CO2
– 0.0390 % = 390 ppm
• Methane – CH4
– 1.79 ppm
• Nitrous oxide (N2O)– 320 ppb
• Chlorofluorocarbons– ~1 ppb
• Neon• Helium• Krypton• Hydrogen• Xenon• Ozone• Others
Summary
• Weather is atmospheric conditions
• Climate is typical pattern of weather
• Climate is determined by– Insolation– Geography– Ocean– Atmosphere
• Next: How Climate Changes