Climate and Environment

• Climate is the greatest constraint on organisms.
• Weather is the combination of temperature, humidity, precipitation, wind, cloudiness, and other atmospheric conditions at a specific place and time.

Climate Defined

• Climate is the long-term average pattern of weather that may be local, regional, or global.
• Geographic variations in climate, mainly temperature and precipitation, determine the distribution of plants and terrestrial ecosystems.

Factors determining physical environment

• Seasonality
• Rainfall patterns
• Temperature difference
• Air & water circulation patterns

Solar Radiation

• Solar radiation drives the Earth's energy system and is electromagnetic energy from the sun.
• Solar radiation is conceptualized as a stream of photons/energy packets.
• Energy waves are characterized by wavelength (λ) (distance between crests) and frequency (V) (crests passing per second).
• A hotter object emits more energetic photons and shorter wavelengths.
• The sun (~5800° C) emits shortwave radiation while the Earth's surface (15°C) emits long wave radiation.

Electromagnetic Spectrum

• The sun emits electromagnetic radiation across a range of wavelengths.
• Visible light consists of wavelengths of 400-700 nm.
• Photosynthetically Active Radiation (PAR) includes wavelengths used by plants for photosynthesis.
• Shorter wavelengths than visible light are ultraviolet (UV) light.
• UV-A has wavelengths from 315 to 380 nm.
• UV-B has wavelengths from 280 to 315 nm.
• Longer wavelengths than visible light is infrared radiation.
• Near-infrared radiation spans approximately 740-4000 nm.
• Far-infrared(thermal) radiation spans 4000-100,000 nm.

Solar Radiation Variation

• The amount of solar energy intercepted varies by latitude.
• Incoming radiation hits higher latitudes at steeper angles, spreading sunlight over a larger area.
• Radiation at steep angles must travel through more atmosphere, encountering more reflective particles
• Temperature decreases from equator to the poles due to variance in solar radiation with latitude.
• Earth tilting on its side gives rise to the seasons

Factors causing seasons

• The Earth tilts on its side causing the seasonal variations in temperature and day length.
• Earth rotates about the north and south poles.
• Earth travels around the sun.
• The Earth's axis is tilted at an angle of 23.5 degrees.
• Day and night are exactly 12 hours long at the equator.
• During the vernal (spring) equinox (March 21) and autumnal equinox (September 22), solar radiation falls directly on the equator, providing greatest input of shortwave radiation.
• At summer solstice (June 22), solar rays fall directly on the Tropic of Cancer (23.5 degrees north latitude).
• During the winter solstice (December 22), solar rays directly strike the Tropic of Capricorn (23.5 degrees south latitude).

Air Temperature

• Air temp decreases with altitude due to decreasing air pressure.
• Changes in latitudinal, seasonal, and daily temperatures don't explain why air cools with altitude.
• Mount Kilimanjaro has ice and snow at its peak despite being in tropical East Africa.
• The weight of air molecules surrounding the earth is 5600 trillion tons.

Properties of Air

• The weight of air acts as a force on Earth's surface.
• Atmospheric Pressure / Air Pressure is the amount of force exerted over an area
• Pressure at any point is measured by the total air mass above it.
• Air mass declines with elevation.
• Air pressure and density decrease as altitude increases.
• Air temperature does not decline continuously with increasing height.

Atmospheric Layers

• Atmospheric scientists use specific altitudes to distinguish atmospheric regions like the troposphere, stratosphere, mesosphere and thermosphere.
• Boundary zones are the tropopause, stratopause, and mesopause.
• The most important regions for climate and life are the troposphere and stratosphere.
• A warming air volume at the surface becomes buoyant/rises.
• Air volume rises and decreases under decreasing pressure, causing to expand and cool.
• Adiabatic cooling occurs when air temperature decreases through expansion instead of heat loss.
• Environmental lapse rate refers to how temperature decreases with altitude.

Air Mass Circulation

• The equatorial region gets the most solar radiation annually, which causes warm air rises.
• Air heated in the equatorial area raises and creates a low pressure zone on ground level.
• Rising air pushes other air masses to spread north and south toward the poles, where they cool, become heavier and sink.
• Sinking air raises surface air pressure (high-pressure zone).
• Cooled air flows towards the equator's low pressure zone, which replaces the rising air.
• Without landmasses, earth would have atmosphere circulating from equator to the poles and back.
• Earth spins west to east with complete rotation every 24 hours.
• Speed of rotation varies with latitude and circumference.
• The speed of rotation is 1674 km/hour at the equator (circumference 40,176 km).
• At 60° north/south, Earth's circumference is is 20,130 km and the speed of rotation is 839 km/hour.

Law of Angular Motion

• Momentum of object moving from a greater circumference to a lesser circumference will deflect in the direction of spin.
• Object moving from a lesser circumference to a greater circumference deflects in the direction opposite that of spin.
• The Coriolis Effect deflects air masses and objects in the Northern Hemisphere to the right (clockwise) and in the Southern Hemisphere to the left (counterclockwise).
• The Coriolis effect prevents air from flowing directly from the equator to the poles & generates belts of prevailing winds named for direction they come from.
• Belts break the surface air and flow aloft into six cells, three per hemisphere.
• Areas of low and high pressure are produced as air masses ascend and descend.
• Air heated in the equatorial zone rises , creating the equatorial low pressure zone near the surface, which is balanced by air flow from the north and south.
• Warm air spreads, diverging toward the poles and cooling.
• In the Northern Hemisphere, the Coriolis effect pushes air east, slowing its progress north.
• At 30° north latitude, cool air sinks, closing the Hadley cells.
• The descending air makes a semipermanent high pressure belt on the surface, which is called the subtropical high.
• As cool air descends, splits into two currents flowing over the surface.
• One current moves toward the pole, diverted right by the Coriolis effect to become the prevailing westerlies and the other current moves south toward the equator.
• Deflection to the right by Coriolis effect makes the strong, reliable trade winds.
• In the Northern Hemisphere, these are the northeast trades & in the Southern Hemisphere these are the southeast trades.
• Air from the westerlies encounters cold air moving down from the pole, making a boundary zone called the polar front, a zone of low pressure /subpolar low where surface air converges & rises.
• Rising air moves until it reaches ~30° latitude (subtropical high), and sinks, closing the Ferrel cell.
• As northward-moving air reaches the pole, it sinks and flows back towards the polar front, making the polar cell.
• Coriolis effect deflects air to the right, creating the polar easterlies; similar flows occur in the Southern Hemisphere.

Ocean Currents

• Prevailing winds pattern determine major surface water flow
• Water movement patterns makes currents.
• Oceans are dominated by two circular water motions (gyres).
• Currents in ocean gyres move clockwise in the Northern Hemisphere & counterclockwise in the Southern Hemisphere.

Air Moisture Content

• Latent Heat is the energy released/absorbed (per gram) during a state change.
• Evaporation transforms water from liquid to gas.
• Condensation transforms water vapor to a liquid, releasing energy.
• Vapor pressure is the pressure water vapor exerts independently of dry air pressure.
• Saturation vapor pressure is water vapor content of air at saturation.
• Relative humidity is the % of water vapor in the air compared to the saturation vapor pressure.
• Relative humidity is 100% at saturation vapor pressure.
• Dew point temperature is the temperature that achieves saturation vapor pressure.

Global Precipitation Patterns

• Precipitation is highest at the equator, declining as one moves north and south, while this decline is not continuous.
• Warm trade winds gather moisture across tropical oceans.
• The Intertropical Convergence Zone (ITCZ), where trade winds meet near the equator, leads to high precipitation.
• Air piles up where two air masses meet, warm humid air rises and cools.
• Clouds form and rain falls when the dew point is reached, explaining high precipitation in tropical regions of eastern Asia, Africa, and South/ Central America.
• After losing moisture, cooled, ascending air splits and moves toward the subtropical high at ~30° north/south.
• Descending air warms, draws water, and creates arid conditions, forming the world's major deserts.
• As air moves north/south, it draws moisture again but to a lesser degee, which encounters cold air masses from the poles at ~60° north and south.
• Ascending air mass cools at convergence of surface air masses and precipitation occurs, leading to precipitation peaks between 50° and 60° north and south.
• From this point to the poles, the cold temperatures and low-saturation vapor prevent precipitation.

Topography Effect on Precipitation

• Mountainous topography effects local/regional precipitation as mountains intercept air flow.
• As an air mass rises, it ascends, cools, relative humidity rises, temperature cools to the dew point, causing precipitation on the windward side.
• Descending dry, cool air warms on the leeward side, declining relative humidity.
• The windward side of mountains supports denser vegetation than the leeward side.
• Rain shadows are formed on areas with arid, desert-like conditions.

Microclimates

• Most organisms live in local microclimates that don't match the larger region surrounding them.
• Specific environments differ based on if they're underground, on the surface, under plants, on exposed soil, on mountain slopes, or at the seashore.
• Heat, light, moisture, and air transfer heat energy affect climates locally.
• Microclimates define the conditions organisms live in.

Microclimate Examples

• Flies are attracted in early spring to sap on a maple tree stump.
• Areas shaded by plants are lower in temperature than exposed areas.
• Topography and slope direction affects local conditions; south-facing slopes get more solar energy in the Northern Hemisphere.
• Ground depressions and areas on concave valley surfaces protected from wind experiences microclimatic extremes.