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Meteorology. Chapter 17-21. Weather vs. Climate. Weather is constantly changing, and it refers to the state of the atmosphere at any given time and place. Climate is based on observations of weather that have been collected over many years. Helps describe a place or region.
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Meteorology Chapter 17-21
Weather vs. Climate • Weather is constantly changing, and it refers to the state of the atmosphere at any given time and place. • Climate is based on observations of weather that have been collected over many years. • Helps describe a place or region.
Major Components • Air is a mixture of different gases & particles • Nitrogen and Oxygen make up 99% of clean, dry air • Each component has its own physical properties
Carbon dioxide (CO2) absorbs energy given off by Earth; therefore, it plays a large role in heating the atmosphere
Variable Components • Include: • Water vapor - the source of all clouds and precipitation. Like carbon dioxide, water vapor absorbs heat given off by Earth. It also absorbs some solar energy • Dust particles – can get too heavy & fall out of suspension • Includes sea salts, pollen, soil, smoke & soot, microbes, and ash • Ozone is a form of oxygen that combines 3oxygen atoms into each molecule (O3). • If ozone did not filter most UV rays, our planet would be uninhabitable for many living organisms.
Human Influence • Emissions from transportation vehicles account for nearly half the primary pollutants by weight
Atmospheric Structure Atmospheric Pressure vs. Altitude • The atmosphere rapidly thins as you travel away from Earth until there are too few gas molecules to detect • Atmospheric pressure decreases with height • Atmospheric pressure is simply the weight of the air above
The atmosphere is divided vertically into 4 layers according to temperature: • Troposphere – gets colder as you go up • All important weather phenomena occurs here • (ground – 12km) 55°C • Stratosphere – temperature remains constant to 20km, then increases until 50km • Ozone is concentrated here. (0°C) • Mesosphere – temperature decreases up to 80km • (-90°C) • Thermosphere – has no well defined upper limit • Temperatures increase (50°C @ 140km)
Earth-Sun Relationship… Motion • Earth has two principal motions—rotation and revolution. • Seasonal changes occur because Earth’s position relative to the sun continually changes as it travels along its orbit.
Earth-Sun Relationship… Solstice & Equinox • The summer solstice is the solstice that occurs on June 21 or 22 in the Northern Hemisphere and is the “official” first day of summer. • The winter solstice is the solstice that occurs on December 21 or 22 in the Northern Hemisphere and is the “official” first day of winter. • The autumnal equinox is the equinox that occurs on September 22 or 23 in the Northern Hemisphere. • The spring equinox is the equinox that occurs on March 21 or 22 in the Northern Hemisphere.
Earth-Sun Relationship… Length of Day • The length of daylight compared to the length of darkness also is determined by Earth’s position in orbit.
Heating the Atmosphere • Heat is transferred from one object to another because of a difference in temperature. • Temperature is a measure of the average kinetic energy of the individual atoms or molecules in a substance. • 3 mechanisms for energy transfer as heat: • Conduction • Convection • Radiation
Conduction – transfer of energy through an object as heat • Examples include: a metal spoon in hot water gets hot or a pot gets hot as it sits on a stove. • Convection – movement of heated substance itself • Warm particles rise b/c less dense; then cool and sink • Can only occur with liquids and gases • Examples include: mantle convection, lava lamp, & fire embers • Radiation– transfer of energy by electromagnetic waves • Doesn’t involve the movement of matter, thus can take place in a vacuum • Examples include: the Sun’s energy traveling thru space and heating up the Earth w/out heating space itself.
Solar Radiation When the sun hits the Earth, usually 3 different results. • Some energy is absorbed, converted to heat • Substances such as water and air are transparent to certain wavelengths of radiation • Doesn’t contribute energy to object • Some radiation bounces off the object without being absorbed
What happens to Solar Radiation • Reflection occurs when light bounces off an object. • Same intensity • 30% reflects back to space • Scattering -rays that travel in different directions. • More light but weaker intensity • Absoption–rays reach surface and is absorbed • 50% gets through to this point • Water vapor and CO2 are the major absorption gases (greenhouse gases)
This diagram shows what happens, on average, to incoming solar radiation by percentage.
Factors that Influence Temperature **In addition to latitude differences as already learned!!** • Land & Water • Graphic Position • Altitude • Cloud Cover & Albedo
Land & Water Mean Monthly Temperatures for Vancouver and Winnipeg • Land heats more rapidly & to a higher temp than water • Land also cools more rapidly & to lower temps than water • Northern Hemisphere: • 61% water • 39% land • Southern Hemisphere: • 81% water • 19% land Winnipeg illustrates the greater extremes associated with an interior location
Geographic Position Mean Monthly Temperatures for Eureka & New York City • Where a city is located on the globe influences temperature • Windward – prevailing winds blow from ocean on the shore • Cool summers & mild winters • Leeward – prevailing winds blow from land to ocean • Mountains can block wind Eureka is strongly influenced by prevailing ocean winds and New York isn’t
Mean Monthly Temperatures for Seattle and Spokane The Cascade Mountains cut off Spokane from the moderating influence of the Pacific Ocean. How does this affect Spokane’s annual temperature range?
Altitude Mean Monthly Temperatures for Guayaquil and Quito • The higher in elevation, the lower the city’s temperature • The lower in elevation, the higher the city’s temperature Quito’s altitude is much higher than Guayaquil’s, causing Quito to experience cooler temperatures than Guayaquil.
Cloud Cover & Albedo • Influences temperatures of the lower atmosphere • Many clouds have a high albedo and therefore reflect back to space a significant portion of the sunlight that strikes them. • During days clouds prevent higher temperatures • At night clouds act as a blanket by absorbing radiation from Earth’s surface causing the temperature not to drop as low.
World Distribution of Temperature • Isotherms are lines on a weather map that connect points where the temperature is the same. • Isotherms generally trend east and west and show a decrease in temperatures from the tropics toward the poles.
Water in the Atmosphere • Precipitation is any form of water that falls from a cloud. • Water vapor is the most important gas in the atmosphere, for understanding atmospheric processes.
Change of States • Water can change states which allows the Earth to be inhabitable and creates the water cycle. • This requires the transfer of energy in the form of heat.
Latent heat is the energy absorbed or released during a change in state • The release of latent heat aids in forming clouds for thunderstorms, tornadoes, & hurricanes.
Humidity • Amount of water vapor in the air • The air becomes saturated when the air has the maximum amount of water vapor it can hold • Warm saturated air contains more water vapor than cold saturated air
Relative Humidity • The ratio of the air’s actual water vapor content compared to the amount of water vapor that can be held at that temperature and pressure. • Indicates how close to saturation rather than the how much water vapor • when the water-vapor content of air remains constant, lowering air temperature causes an increase in relative humidity, and raising air temperature causes a decrease in relative humidity
Dew Point • The temperature that air needs to be cooled to in order to reach saturation • When air is cooled past saturation, the vapor condenses & becomes dew, fog, or clouds • High dew points indicate moist air & low dew points indicate dry air.
Measuring Humidity • We use a hygrometer to measure relative humidity • A psychrometer is a hygrometer with dry- and wet-bulb thermometers. Evaporation of water from the wet bulb makes air temperature appear lower than the dry bulb’s measurement. The 2 temps are compared to determine the relative humidity. • Meteorologists use electric hygrometers in a weather balloon to transmit data back to the ground
Cloud Formation…Air Compression & Expansion • When air is compressed or allowed to expand, the temperature changes. These changes are called adiabatic temperature changes. • Air expands, it cools • Air is compressed, it warms • As you rise through the atmosphere, pressure decreases
Cloud Formation by Adiabatic Cooling As air droplets rise, they cool about 10°C / 1000m until the air reaches the dew point & condensation begins (clouds form). This is the dry adiabatic rate. Air continues to rise, the latent heat is released by condensation reduces the cooling rate to about 5°C / 1000m. This is called the wet adiabatic rate.
Processes that Lift Air • Orographic Lifting – air goes up a mountain slop, adiabatic cooling generates clouds & precipitation. • Occurs on windward mountain slopes • Frontal Wedging – warm air and cold air collide and produce a front • Associated with storms called middle-lattitude cyclones
… Processes that Lift Air • Convergence – when winds from different directions collide and rise. Adiabatic cooling generates cloud formation • Localized Convective Lifting – process which produces thermals (pockets of warm air that rises causing clouds to form & can cause mid-afternoon rain showers.
Stability • Air rises when it is warmer (less dense) than the air around it until it reaches an altitude with the same temperature. This air is said to be unstable. • Stable air tends to resist rising. • Air stability is determined by measuring the temperature of the atmosphere at various heights. • The rate of change of air temperature with height is called the environmental lapse rate. • The most stable conditions occur when temperature increases with height, called temperature inversion
Stability & Weather • When stable air is forced above the Earth’s surface, the clouds that form are widespread and have little vertical thickness compared to their horizontal dimension. • Precipitation, if any, is light to moderate • Clouds associated with the lifting of unstable air are towering & often generate thunderstorms and occasionally tornados
Condensation • For any condensation to occur, the air must be saturated. • Can occur when air cools to the dew point or when water vapor is added to the air
Has to be a surface for water vapor to condense on • Near the ground grass, windows, cars, etc collects the dew • In the atmosphere the only thing for water vapor to condense on is small particulates of matter called condensation nuclei
Clouds & Precipitation • Clouds are classified on form and height
