Weather and Climate - GEOL 7

The approximate specific heat, in cal/g/°C, for water is 1, for dry sand 0.2, and for ice 0.5. Calculate the temperature increase in degrees Celsius when (a) 20 cal of heat is added to 5 g of water; (b) 120 cal of heat is added to dry sand having a mass of 60 g; (c) 20 cal of heat is added to 5 g of ice having an initial temperature of -10°C.

(a) 4°C, (b) 10°C, (c) 8°C (The formula for temperature change of a mass given an input of heat energy is ΔT = Q/(m x c), where Q = heat energy (cal), m = mass (g), c = specific heat (cal g-1 °C-1), and ΔT = temperature change (°C).)

Convert the following Celsius temperatures to Fahrenheit temperatures: 0°C, 100°C, -10°C, 10°C, 20°C, 30°C.

0°C = 32°F, 100°C = 212°F, -10°C = 14°F, 10°C = 50°F, 20°C = 68°F, 30°C = 86°F (Use formula depicted in Table 4.1 for conversion)

Describe the relationship between the kinetic energy of the atoms or molecules composing a substance and the temperature of that substance.

Temperature is directly proportional to the average kinetic energy of the atoms or molecules composing a substance. Therefore, as the average kinetic energy of a substance increases, so does its temperature.

What is the Callendar effect? Describe how atmospheric CO2 concentration has increased since the beginning of the Industrial Revolution.

The Callendar effect is the theory that anthropogenic carbon dioxide emissions particularly from fossil fuel burning, enhance Earth's natural greenhouse effect, leading to global climate change. Since the beginning of the Industrial Revolution in the mid-1700s, atmosphere carbon dioxide levels have increased, with acceleration beginning in the late 1900s, indicating human activity is highly likely for the increase.

Explain why the tropopause is lower over the middle latitudes than over the tropics.

The air over the middle latitudes is colder than over the tropics. Colder air is denser than warmer air, causing the height of the tropopause to be lower over the middle latitudes.

Provide a definition of air pressure that applies to Earth's surface and any altitude within the atmosphere.

The air pressure at a given location on Earth's surface is the weight per unit area of the column of air above that location. The pressure at any point within the atmosphere is equal to the weight per unit area of the atmosphere above that point.

If water is used in place of mercury in a glass-tube barometer, what is the required height of the tube? The density of mercury (Hg) is 13.6 g/cm3 and the density of water is 1.0 g/cm3.

The glass tube for a mercury barometer is about 1 m in length. If water is used instead of mercury, the glass tube would have to be about 13.6 m in length because the density of mercury is 13.6 times the density of water. The column of water must be tall enough (close to 34 ft.) to exert the same pressure at its base as does the mercury column.

Suppose thunderstorms are in the flight path of an airline. What guidance would you give the pilot about which level in the atmosphere to reach cruising altitude to have the smoothest flight?

The guidance would be for the pilot to cruise in the lower stratosphere in order to avoid thunderstorms that can extend through much of the troposphere.

Air, especially still air, is a poor conductor of heat. Provide some examples of how this property of air is used to conserve energy for space heating and cooling.

Air is used to insulate heat as in thick fiberglass blankets used as attic insulation in homes. Air is trapped between the fiberglass elements. Also, double paned storm windows make use of air's very low heat conductivity; air is trapped between panes of glass. The air space between panes is so thin that convective circulation of air is inhibited.

How and why would the temperature of an Arctic air mass change as the air mass moves from snow- covered ground to bare ground?

Air mass properties depend on the surface over which they form. An Arctic air mass that forms over snow-covered ground would be relatively cold but would become warmer as it moves over bare ground.

At a location, the air pressure typically drops more slowly with altitude on a cold day in January than on a warm day in July. Explain the difference.

Air pressure drops more rapidly with elevation in cold, dense air than in warmer, less dense air.

What is an adiabatic process? Do adiabatic processes occur in the atmosphere? If so, provide an example.

An adiabatic process is a thermodynamic process in which no heat is exchanged between a mass and the environment. This is approximated in the atmosphere because rapid vertical movements of large bodies of air reduce the flow of energy to or from the ascending or descending body of air. Examples of adiabatic processes occurring in the atmosphere are expansional cooling and compressional warming of air.

What is an air mass? What governs the temperature and humidity of an air mass?

An air mass is a huge volume of air with uniform temperature and humidity properties that are often indicative of where it was formed. For example, an air mass that develops over a warm ocean surface becomes warm and humid.

How would you expect the Bowen ratio of agricultural land to change as drought conditions worsen? Explain your response.

As a drought persists, soils dry out and plants become dormant so that more of the heat available at Earth's surface is used for sensible heating than for latent heating. Consequently, the Bowen ratio increases in value.

Explain how air pressure tendency can be a useful indicator of future weather.

As a general rule, the weather becomes (or remains) fair as the air pressure at Earth's surface rises and the weather turns stormy as the air pressure falls. Pressure tendency is an indication of an approaching low pressure (stormy weather) system or an approaching high pressure (fair weather) system.

On a particularly warm and humid evening, a sportscaster comments that baseballs hit to the outfield "will not carry far in this heavy air." How valid is the sportscaster's observation?

Baseballs hit to the outfield should travel farther through a hot, humid atmosphere. Air becomes less dense with increasing temperature and increasing humidity, thereby offering less resistance to a batted ball.

An unsaturated air parcel has an initial temperature of 20°C. If the parcel is lifted 2000 m and remains unsaturated, what is its new temperature?

Because the air parcel remains unsaturated, use the dry adiabatic lapse rate (9.8°C per 1000 m). The temperature at 2000 m would be 0.4°C.

Identify some natural processes and human activities that alter the concentration of carbon dioxide in the atmosphere. How might variations in the atmospheric concentration of CO2 affect global climate change?

Carbon dioxide is a byproduct of burning coal, oil, natural gas, and other organic matter, as well as the natural decay of organic matter. Hence, human activities increase the atmospheric concentration of carbon dioxide by burning fossil fuels (for space heating and cooling, transportation) and through slash- and-burn deforestation. Furthermore, removal of vegetation reduces photosynthesis, a natural process that takes CO2 from the air. Carbon dioxide slows the flow of Earth's heat to space and thus more CO2 in the atmosphere may cause additional global warming.

How do Charles' law and Boyle's law help form the ideal gas law?

Charles' law defines the relationship between density and temperature in an ideal gas with constant pressure. Boyle's law defines the relationship between pressure and density when temperature is held constant. These two laws combine to make the ideal gas law.

On a visible satellite image, why do cloud tops and snow-covered surfaces appear bright white while forest-covered land and oceans appear relatively dark?

Cloud tops and snow-covered areas appear bright white on a visible satellite image because they are highly reflective surfaces, while forests and ocean areas are less reflective and thus appear dark. Visible satellites produce images of areas that are lit by the Sun.

Describe the type of weather that usually accompanies a high (anticyclone) and a low (cyclone) in middle latitudes.

Fair weather usually but not always accompanies a high (anticyclone) whereas cloudiness and rain or snow usually but not always accompany a low (cyclone).

Distinguish between a fair-weather cumulus cloud and a cumulonimbus cloud.

Fair-weather cumulus form on a sunny day and look like small white puffs of cotton floating in the sky. They typically do not produce precipitation and usually vaporize rapidly near sunset. A cumulonimbus is a thunderstorm cloud accompanied by lightning and thunder. It forms from cumulus clouds that grow and merge.

Describe some ways whereby the atmosphere interacts with Earth's hydrosphere, geosphere, and biosphere.

The atmosphere can be impacted by the geosphere through outgassing that occurs during volcanic eruptions, releasing a new or different mix of gases. The hydrosphere supplies water vapor to the atmosphere, which subsequently condenses into clouds that may rain on the geosphere. Gases released during photosynthesis impact the atmosphere biologically, just as rain from the atmosphere impacts the growth of plants in the biosphere. It is the combination and coevolution of each of these spheres that make up the Earth's atmosphere.

Why do temperature changes accompany the vertical (up and down) motions of air parcels?

The atmosphere compresses descending air, causing the air to warm. At the same time, when air rises, it expands and cools.

Compare the properties of the troposphere with those of the stratosphere.

Most cloud and weather systems are confined to the troposphere and within the troposphere the temperature generally decreases with increasing altitude. Few clouds and little weather occur in the stratosphere. Within the stratosphere the mean temperature is either steady or increases with altitude. Also, the ozone shield occurs within the stratosphere. The tropopause is the transition zone or boundary between the troposphere and the stratosphere.

Why are near-simultaneous weather observations essential for drawing weather maps?

The atmosphere is dynamic, varying from one place to another and across time. The most accurate and complete representation requires weather observations that are taken at the same time at various locations and transmitted immediately to weather forecast offices for analysis.

Describe how the composition and appearance of a cloud change with increasing altitude.

The composition and appearance of clouds are impacted by the surrounding air. The air at different levels of the atmosphere can vary greatly, therefore the properties of a cloud vertically building through the atmosphere will vary as well. At lower altitudes, the cloud is typically composed of water droplets, making the cloud edges sharply defined. At higher altitudes, the cloud is more likely to contain ice crystals and appear more fibrous.

All other factors being the same, how does cloud cover affect the day's minimum air temperature?

The day's minimum temperature is typically higher with cloud cover than when the sky is clear. Water droplets and/or ice crystals composing clouds strongly absorb infrared radiation emitted by Earth's surface. Clouds then radiate some of the absorbed radiation as IR to space and some back to Earth's surface, thus raising the minimum air temperature.

What is the basis for subdividing the electromagnetic spectrum into various forms of electromagnetic radiation?

The electromagnetic spectrum is subdivided because we detect, measure, generate, and use the forms differently. They have varying wavelengths, frequencies, and are used for different purposes, including medical and communication.

Distinguish between weather and climate.

Weather is the state of the atmosphere at a particular place and time. Variables used to describe weather include: temperature, humidity, and cloudiness. Climate describes the weather in an area averaged over a period of time. Weather describes daily atmospheric conditions while climate looks at longer periods of time and utilizes seasonal averages of rainfall, snowfall, and temperature.

How does a change in temperature affect air density? How does a change in humidity affect air density?

When air is heated, air density usually decreases. When the concentration of water vapor (humidity) increases, air density usually decreases as well.

Apply Wien's displacement law in comparing the radiational properties of the Sun versus those of the Earth-atmosphere system.

Wien's displacement law states that with increasing absolute temperature, the wavelength of the maximum radiation emitted or absorbed will decrease. Therefore, hot objects such as the Sun emit radiation that peaks at shorter wavelengths than relatively cool objects such as Earth.

An intense low pressure system tracks northeastward just offshore from Cape Hatteras, NC to just east of Cape Cod, MA. Describe the general direction of surface winds over New England as the center of the storm moves toward Nova Scotia (just northeast of New England).

Winds around a low pressure system blow in a counterclockwise and inward spiral as seen from above. If the center of a low is near Nova Scotia, then the winds associated with that low will be coming from the west or northwest in New England.

In the Northern Hemisphere, Earth is closer to the Sun during the winter than during the summer and yet winter is colder than summer. Please explain.

Winters are colder than summers because maximum solar altitudes are lower (less intense solar radiation striking Earth's surface) and daylight is shorter in winter than in summer.

How does solar altitude affect the length of the path of solar radiation through Earth's atmosphere?

With increasing solar altitude, the solar beam's path length through the atmosphere decreases, reducing the attenuation of incoming solar radiation by reflection, scattering, and absorption.

What instruments are used to measure incoming and outgoing radiation?

The pyranometer measures the intensity of solar radiation striking a horizontal surface on the Earth. The instrument consists of a sensor enclosed in a transparent hemisphere that transmits total (direct plus diffuse) solar short-wave radiation. Sensors onboard weather satellites measure scattered or reflected visible solar radiation (processed into visible satellite images) and emitted infrared radiation (processed into infrared satellite images). The infrared radiometer selectively measures the intensity of infrared radiation emitted by the surface of some object such as land, cloud, or ocean.

Define vapor pressure. How does Dalton's law of partial pressures apply to vapor pressure?

Vapor pressure is the pressure exerted by the water vapor component of air. Dalton's law of partial pressures states that the total pressure of a gas mixture (e.g., air) is equal to the sum of the pressures of each constituent gas. Therefore, each gas constituent, including water vapor, exerts a pressure as though it were the only gas present.

Why does the circulation within a cyclone usually bring cloudy, stormy weather?

Viewed from above, surface winds in a Northern Hemisphere cyclone blow counterclockwise and inward. As surface winds converge toward the center of the cyclone, air ascends. Ascending air undergoes expansional cooling and the relative humidity increases. If saturation is achieved, clouds will form and precipitation may result. Consequently, cloudy, stormy weather is usually associated with a cyclone.

A saturated air parcel ascends in the atmosphere. What is the parcel's initial relative humidity? What happens to the value of the relative humidity of the saturated parcel as it continues to ascend? What does this imply about the vapor pressure of the ascending saturated parcel?

If the parcel is initially saturated, its relative humidity is 100%. As the parcel ascends, its relative humidity will remain constant at 100%. However, some water vapor will condense as the temperature of the rising parcel lowers. With the loss of water vapor, both the actual and saturation vapor pressures will decrease as the temperature decreases.

What is the significance of stratospheric ozone for life on Earth?

In the formation and dissociation of ozone, incoming ultraviolet (UV) radiation is absorbed. This reduces the amount of UV radiation, which lethal to life, from reaching Earth's surface.

Under what circumstances is a natural component of the atmosphere considered an air pollutant?

Natural components of the atmosphere such as sulfur dioxide or carbon monoxide are considered air pollutants when they occur at a concentration that threatens the wellbeing of living organisms or disrupts the orderly functioning of the environment.

Is there an altitude that clearly marks the top of the atmosphere? Explain your response.

No one altitude can be defined as the top of the atmosphere because atmospheric density decreases as height increases until the air density gradually assumes the same density of outer space.

Compute the number of heating degree-days on a day when the minimum air temperature was 10°F and the maximum air temperature was 40°F.

40 heating degree-days (Use heating degree-days = 65°F - [(max. temp. + min. temp.)/2]

Define force and name the forces that govern wind speed and direction.

A force is a push or pull that leads an object at rest to move or alters the movement of an object already in motion (acceleration). A force has both direction and magnitude. The forces that influence wind include the pressure gradient force, centripetal force, Coriolis Effect, friction, and gravity.

A location experiences an approaching warm front and then a cold front. Describe the changing nature (e.g., cumuliform) of the clouds in the sky.

Ahead of the warm front, clouds are typically stratiform. As the cold front approaches, cumuliform clouds develop, occurring just ahead of and along the front. If a storm forms, cumulonimbus clouds may be seen.

Define atmospheric river and describe the importance of atmospheric rivers in the global water cycle.

An atmospheric river is a fairly narrow band of concentrated water vapor transport in the lower atmosphere responsible for most of the horizontal flow of water vapor outside of the tropics. Atmospheric rivers transport a significant amount of water evaporated from the ocean surface to land regions and thus play an important role in this transport of water from sea to land as part of the global water cycle.

Why are clouds and precipitation more likely on the windward slopes of a mountain range than the leeward slopes?

As air is forced to ascend the windward slopes of mountain ranges, it expands and cools, resulting in an increase in relative humidity. The air continues to cool as it rises, eventually reaching saturation and producing clouds. When air descends the leeward slopes of a mountain range, it is compressed and warms, thus losing moisture and saturation. This causes cloud particles to evaporate. When the clouds have evaporated away, the relative humidity decreases as the subsiding air continues warming by compression.

How and why does the moisture content of the top soil affect the maximum air temperature in the lower troposphere?

As the moisture content of top soil increases, evaporation increases. Evaporation is a cooling process, therefore top soil with a high moisture content will keep temperatures cooler than dry soils would.

How does distillation convert ocean water to freshwater?

As water evaporates from the ocean surface, materials dissolved in ocean water, such as salt, are left behind. The atmospheric water vapor subsequently condenses and eventually falls as fresh water.

Explain how the Sun drives the global water cycle.

Solar radiation from the Sun strikes Earth's surface and is absorbed (converted to heat). Some of this heat evaporates water or sublimates snow and ice. The water vapor in the air condenses or deposits to cause cloud particles to form, which can lead to precipitation. Solar radiation, therefore, powers the water cycle, which is a continuous flow between water and energy among ocean, land and the atmosphere.

On a clear calm day, why does the relative humidity usually decrease from a maximum shortly after sunrise to a minimum in the early or mid afternoon?

At constant vapor pressure, relative humidity varies inversely with the air temperature because the saturation vapor pressure increases with rising air temperature. As the air temperature rises from its daily minimum on a clear calm day near sunrise to a maximum in the early to mid-afternoon, the saturation vapor pressure also increases. Because the air is calm and there is no gain or loss of water vapor, the actual vapor pressure remains essentially constant. Consequently, the relative humidity is highest when the air temperature and saturation vapor pressure are lowest (near sunrise) and it is lowest when the air temperature and saturation vapor pressure are highest (mid-afternoon).

For which atmospheric scales does the Coriolis Effect generally need to be accounted for and why?

At the microscale and mesoscale, the Coriolis Effect is negligible because weather phenomena on these scales are small and short lived. By contrast, the Coriolis Effect is important in synoptic- and planetary-scale circulation systems due to their large size and long duration.

How does stability affect the vertical development of cumuliform clouds?

Stable air suppresses vertical motion, while unstable air enhances vertical motion, convection, and expansional cooling. Hence, unstable air will favor the continuing development of cumuliform clouds whereas stable air will suppress their development. The most unstable air favors very large convective clouds and likely formation of rain and thunderstorms.

Provide examples of how Earth's surface properties influence air temperature in the lower troposphere.

Surface properties that influence air temperature are snow cover and moisture content. Snow has a relatively high albedo and reduces the amount of solar radiation that is absorbed. Dry soil has less moisture for vaporization so more of the available heat is channeled into raising the air temperature through convection and conduction. For example, air temperature is generally higher in July than in January (in the Northern Hemisphere), during the day than at night, under clear rather than overcast daytime skies, when the ground is bare instead of snow-covered, and when the ground is dry rather than wet

On televised weathercasts, air pressure is often reported in units of length (inches) rather than units of pressure (millibars). Explain why.

Surface weather observations have long been reported in British units in the U.S., and the general public has been resistant to change to metric units. Also, weathercasters typically use inches of mercury rather than millibars because "at home" barometers typically display in inches.

Identify several of the technological advances of the 20th century that significantly improved weather observation and forecasting.

Technological advances of the 20th century included development of new instruments (e.g., radiosonde, radar, satellite sensors) which provide a more complete and accurate representation of the state of the atmosphere (weather). These advances in turn make it possible to more accurately initialize numerical models of the Earth-atmosphere system, key to predicting accurate forecasts. Innovations in communications technologies (e.g., radio, television, Internet) allow rapid transmission of weather information to forecasters and the general public.

What are the components of ASOS and where is the observational data initially sent?

The Automated Surface Observing System (ASOS) consists of electronic sensors for measurements, computers, and automated communications ports. ASOS directly feeds data to NWS communications networks 24 hours a day to Forecast Offices and airport control towers.

Describe how the Coriolis Effect varies with wind speed and latitude.

The Coriolis Effect causes the horizontal wind to be deflected to the right of its initial direction in the Northern Hemisphere and to the left of its initial direction in the Southern Hemisphere. The magnitude of the Coriolis Effect varies with wind speed; the faster the wind the greater the Coriolis Effect. The amount of deflection also varies with latitude, with the maximum deflection at the poles and no deflection at the equator.

Why does the Coriolis Effect reverse direction between the Northern and Southern Hemispheres?

The reversal in direction of the Coriolis Effect between the Northern and Southern Hemispheres stems from the contrast in the frame of reference of Earth's rotational direction in the two hemispheres. To an observer high above the North Pole, Earth appears to rotate in a counterclockwise direction whereas to an observer high above the South Pole, Earth appears to rotate in a clockwise direction.

Why does the amount of precipitable water vary with the mean temperature of the troposphere?

The saturation vapor pressure increases as temperature increases. The greater the temperature of the troposphere, the greater the concentration of water vapor in the air needed for saturation to occur. Assuming the availability of water at Earth's surface, the mean air temperature of the troposphere decreases as you move poleward, causing evaporation to decrease with an increase in latitude. This results in less precipitable water in polar regions. In general, warmer air has more precipitable water than colder air due to evaporation rates.

Define the solar wind and describe how Earth's magnetosphere is produced.

The solar wind is a stream of high-speed, electrically-charged, subatomic particles that continually flows from coronal holes on the Sun and travels through space. Earth's magnetic field deflects the solar wind and deforms it into the teardrop-shaped magnetosphere that surrounds the Earth.

In late autumn or early winter, cold air flows on northwest winds from snow-covered ground across the ice-free waters of Lake Superior. Describe the changes in temperature, vapor pressure, and stability of the cold air as it flows over the warmer surface waters of the lake.

The temperature of the water surface is higher than that of the snow-covered land surface. Hence, air that moves from snow-covered land to ice-free lake waters is heated from below causing the air temperature to warm and the stability to decrease. The water content of the air will increase due to increased evaporation as it moves over the lake, causing the vapor pressure to increase.

Identify the mechanisms involved in poleward heat transport within the Earth-atmosphere system.

The three mechanisms involved in poleward heat transport are air mass exchange, storm systems, and ocean currents.

Describe the principal mechanism whereby clouds form in the atmosphere.

Water evaporates, and the air molecules containing the water vapor ascends in the troposphere. As the air rises, pressure decreases, and the air expands and cools causing the relative humidity to increase. Once the relative humidity of the air reaches saturation (100%), condensation occurs on cloud nuclei and a cloud forms.

Provide a convincing argument that water vapor is the principal greenhouse gas.

Water vapor is the principal greenhouse gas because it causes the greatest amount of warming at Earth's surface. For example, in areas with very little water vapor in the air, infrared radiation readily escapes to space, causing lowered temperatures than would otherwise occur at Earth's surface. In areas with a great amount of cloud cover or high tropospheric water vapor content, water vapor strongly absorbs infrared radiation emitted by Earth and emits some IR back to Earth's surface, having the effect of warming Earth's surface.

Describe the types of instruments that monitor wind speed and direction near Earth's surface. Which type is used in the NWS Automated Surface Observing System?

Wind vanes, wind socks, cup anemometers, hot wire anemometers, aerovanes, and sonic anemometers measure wind near Earth's surface, primarily over land. ASOS uses sonic anemometers, which measure the effect of wind on the propagation of sound waves and replaced cup anemometers. Over the ocean, scatterometers flown on satellites (or aircraft) provide accurate and continual monitoring of near-surface ocean wind speeds and directions.

Determine the relative humidity if the... (a) vapor pressure is 5 mb and the saturation vapor pressure is 25 mb, (b)vapor pressure is 10 mb and the saturation vapor pressure is 10 mb, (c) mixing ratio is 15 g/kg and the temperature is 25°C

(a) RH = [(vapor pressure)/(saturation vapor pressure)] x 100% = [(5 mb)/(25 mb)] x 100% = 20%, (b) RH = [(vapor pressure)/(saturation vapor pressure)] x 100% = [(10 mb)/(10 mb)] x 100% = 100%, (c) Use Table 6.3 to find the saturation mixing ratio, RH = [(mixing ratio)/(saturation mixing ratio)] x 100% = [(15 mb)/(20.44 mb)] x 100% = 73.4%

Are convective clouds (e.g., cumulus, cumulonimbus, and clouds that grow by convection) more likely to form over snow-covered ground or bare ground? Explain your reasoning.

Convective clouds are more likely to form over bare ground than snow-covered ground. Bare ground, with its lower albedo, absorbs more incident sunlight, warms up, and warms the air above. The heating promotes convection. Air temperatures over snow-covered ground remain low and convection is inhibited.

How does Dalton's law apply to the atmosphere?

Dalton's law of partial pressures states that the total pressure exerted by a mixture of gases equals the sum of the pressures produced by each constituent gas. Each gas species in the mixture exerts a pressure as though it was the only gas present. For example, the pressure exerted by water vapor (vapor pressure) can be considered as though it was the only gas present.

Compare Earth's diameter to the depth of the atmosphere.

Earth's diameter is considerably larger than the depth of the atmosphere. Compared to the planet's diameter (12,740 km or 7918 mi.), the atmosphere is like the thin skin of an apple. About 99% of the mass of the atmosphere is located below an altitude of 32 km (20 mi.).

Speculate on some ways Earth's planetary albedo might increase. What would be the climate implications?

Earth's planetary albedo would increase in correspondence with significant increases in types of surfaces with high reflectivity values. Examples include a large-scale increase in sea ice, glacial ice, and snow cover, and a significant increase in high cloud cover. An increase in albedo would, on average, decrease Earth's surface temperatures.

How does the roughness of Earth's surface affect horizontal wind speed and direction within the atmospheric boundary layer?

Earth's surface roughness (frictional resistance) slows the wind and causes the wind to blow more directly across isobars and toward low pressure. The rougher the surface the greater the eddy viscosity of the wind.

Provide an example of how gravity influences air motion.

Gravity causes air parcels to be pulled toward Earth. It influences air that is ascending or descending, such as updrafts or downdrafts in a thunderstorm or the downhill drainage of cold air in the mountains.

A traffic sign along an Ohio highway warns motorists that a bridge freezes before the road surface. Why does the bridge surface freeze first?

Heat always flows in response to temperature gradients from locations of higher temperature to locations of lower temperature. In this example, heat is conducted and convected to cooler air from both the top surface and underside of the bridge. The roadway leading to and away from the bridge loses heat to cooler air only from its upper surface. The underside of the roadway receives heat conducted from the ground that partially counters heat loss from the surface to the air. Hence, the bridge surface cools at a faster rate than the road surface so that, all other factors being equal, the bridge surface temperature drops below freezing sooner.

Explain how heat transfer follows the second law of thermodynamics.

Heat transfer follows the second law of thermodynamics by flowing from where the temperature is higher to where it is lower.

What causes horizontal air pressure gradients? How do air parcels respond to a horizontal air pressure gradient?

Horizontal air pressure gradients are caused by air pressure changes along a surface of constant altitude, such as at sea level. Consequently, horizontal air pressure gradient forces act directly toward lowest pressure and perpendicular to isobars, causing air parcels to move toward lowest pressure.

What is the relationship between the horizontal wind speed and the spacing of isobars on a surface weather map?

Horizontal wind speed is strong and fast where the air pressure gradient is steep and tight, indicated by closely spaced isobars. Horizontal wind speed is light or calm where the horizontal air pressure gradient is weak, indicated by widely spaced isobars.

Describe the water vapor measurement capabilities of the Joint Polar Satellite System. How is this type of satellite imagery aiding the understanding of atmospheric rivers?

JPSS satellites carry five instruments onboard to measure atmospheric water vapor. Three of the instrument packages are the Advanced Technology Microwave Sounder (ATMS), the Visible Infrared Imaging Radiometer (VIIRS), and the Cross-Track Infrared sounder (CrIS). The ATMS instrument provides information on vertically integrated water vapor in an air column, expressed as precipitable water. Microwave imagery can then be used to understand the development, physical characteristics, and impacts of atmospheric rivers, with a focus on the eastern Pacific Ocean and western North America.

During which phase changes is latent heat absorbed from the environment? During which phase changes of water is latent heat released to the environment?

Latent heat is absorbed from the environment when ice melts (melting), liquid water evaporates (evaporation), or snow sublimates (sublimation). Heat is released to the environment when water freezes (freezing), water vapor condenses (condensation), or water vapor deposits as ice (deposition).

On a global annual average basis, what is the most important process in cooling Earth's surface?

Latent heat transfer associated with evaporation is the most important cooling process at Earth's surface on a global annual average. It is more important than radiational cooling and sensible heat transfer.

Distinguish between sensible heating and latent heating of the atmosphere.

Latent heating refers to the transport of heat energy through phase changes of water. Sensible heating includes both conduction and convection.

Differentiate between evaporation and condensation.

On an interface between water and air, evaporation refers to the water changing phase from liquid to vapor and condensation refers to the water changing phase from vapor to liquid. When evaporation prevails at the water/air interface, there is a net loss of liquid water mass. When condensation prevails, there is a net gain of liquid water mass.

Describe how weather radar detects the location and movement of areas of precipitation.

Operating in the reflectivity mode, weather radar locates and tracks the movement of areas of precipitation. Based on the intensity of the reflected signal (echo), weather radar distinguishes the intensity of precipitation. Operating in the velocity (Doppler) mode, weather radar can determine the circulation within thunderstorms and provide early warning of the development of severe weather (e.g., tornadoes).

Why is the moist adiabatic lapse rate less than the dry adiabatic lapse rate?

Rising dry air is cooled by expansion while rising saturated air is simultaneously cooled by expansion and acts to warm by the release of latent heat (due to the phase change of water vapor to liquid or ice). Therefore, the moist adiabatic lapse rate is less than the dry adiabatic lapse rate.

What mechanism is thought to have contributed to the initial buildup of atmospheric oxygen more than 2 billion years ago?

Photosynthesis by cyanobacteria in the ocean are thought to be principally responsible for the build- up of oxygen in the ocean and atmosphere more than 2 billion years ago.

Why are air pressure readings adjusted to what they would be if the weather station were located at sea level?

Pressure readings are adjusted to sea level in order to observe changes in air pressure on a horizontal plane. It helps scientists identify air masses and weather changes and helps aid in weather forecasting.

Although the Keeling curve and the trend in global mean annual temperature show increasing trends, the two curves are not parallel. Explain why.

The Keeling curve is a depiction of carbon dioxide levels at one location in Hawaii. The global annual mean temperature includes land and ocean as well as higher latitudes that may be experiencing polar amplification of global climate change

The Kelvin scale has no negative values. Explain why.

The Kelvin scale is the best representation of average kinetic molecular energy. When a substance has a temperature of 0 K it is at "absolute zero" and essentially has no kinetic energy because all molecular motion has ceased. A substance cannot have negative kinetic energy.

What is the principal mission of the National Weather Service Cooperative Observer Network?

The NWS Cooperative Observer Network is made up of approximately 8700 volunteers (additional weather stations) that monitor NWS provided instruments and take daily observations. Their mission is to record data for climatic, hydrologic, and agricultural purposes.

What is the significance of the Stefan-Boltzmann law when applied to the Sun versus the Earth- atmosphere system?

The Stefan-Boltzmann law shows that small changes in the temperature of a blackbody result in a much greater change in radiational energy. The Sun's temperature is much higher than that of Earth and therefore its energy output emits exponentially more, almost 190,000 times that of Earth's.

Under what atmospheric condition is the actual air temperature, dewpoint, and wet-bulb temperature the same?

The air temperature, dewpoint, and wet-bulb temperature are equal when air is saturated.

Rising unsaturated air cools at a rate of 9.8°C per 1000 m ascent. Rising saturated air cools at a lower rate which varies with temperature, but an average cooling rate of 6°C per 1000 m can be assumed. If the actual decrease in temperature with height in the atmosphere on a particular day is 8°C per 1000 m, and a rising parcel would remain unsaturated, determine whether that atmosphere is stable or unstable. If the parcel were saturated, is the atmosphere stable or unstable? Explain how you made both determinations.

The atmosphere is stable. Utilizing a thermodynamic diagram and following a dry adiabatic upwards, a parcel of unsaturated air rising 1000 m would experience a temperature drop of about 9.8°C. Meanwhile, the temperature of the air surrounding the parcel at the end of its trip would only be 4°C colder than the air surrounding the parcel at the beginning of its trip. Consequently, the rising parcel would end up being cooler than the air surrounding it. Being cooler, it is also denser, so it would sink toward its initial elevation. Air displaced vertically that tends to return to its initial elevation is stable air. For saturated air, the parcel would be 2°C warmer than the surrounding air after 1000 m ascent, and therefore less dense and unstable.

What was the chief source of Earth's early atmosphere? Does this mechanism still operate today?

The chief source of the early atmosphere was outgassing, which refers to the release of gases (e.g., water vapor, nitrogen) to the atmosphere that accompanies a volcanic eruption or meteor impact on Earth's surface. While outgassing occurred at a rapid pace within a million years of the planet's formation, a small amount of outgassing still takes place today.

Compare the climates of San Francisco, CA and St. Louis, MO.

The cities are at about the same latitude and receive similar solar energy input, but San Francisco is downwind of the Pacific Ocean and has a maritime climate whereas St. Louis has a continental climate. Both cities experience a seasonal temperature cycle, but San Francisco experiences much less of a seasonal contrast than does St. Louis.

Explain the origin of reporting air pressure by the length of the mercury column.

The mercury barometer is the standard instrument used for measuring air pressure and monitoring air pressure changes. In a mercury barometer, mercury rises up from a reservoir at the bottom of the barometer into a tube to the point where the pressure of the mercury column in the tube balances the pressure of the atmosphere acting on the surface of mercury in the reservoir. The column rises with increasing atmospheric pressure and falls with decreasing atmospheric pressure. The vertical extent of mercury in the tube is typically given in inches of mercury.

What parameters are most commonly used to describe the climate of some locality?

The most commonly used climate parameters are thirty-year average monthly and annual temperatures and precipitation totals. Other climatic parameters are average seasonal snowfall, length of growing season, percent of possible sunshine, and number of days with dense fog.

Explain how the Antarctic ozone hole is caused mainly by catalytic destruction of ozone by chlorine.

The peak concentration of ozone, a molecule made up of three atoms of oxygen, occurs in the middle stratosphere. Within the stratosphere, solar ultraviolet radiation powers two sets of chemical reactions that continually create and destroy ozone. The presence of certain chlorofluorocarbons (CFCs) in the stratosphere disrupts this balance. For example, intense UV radiation breaks down CFCs, releasing chlorine that reacts with and destroys ozone. The products of this reaction are chlorine monoxide and molecular oxygen. Chlorine readily gives up the oxygen it bonded with to break apart another ozone molecule. In fact, a single chlorine atom can destroy tens of thousands of ozone molecules, leading to the formation of an ozone hole.

The significance of an atmospheric gas or aerosol is not necessarily related to its amount or concentration. Explain this statement and provide a few examples.

The principal gases in the homosphere are nitrogen and oxygen and are significant and essential, however other gases and aerosols in small quantities are significant constituents. Water vapor, carbon dioxide, and ozone are minor components of the atmosphere. Water vapor is an essential component of the water cycle and the major greenhouse gas in the atmosphere. Carbon dioxide is necessary for photosynthesis. Ozone formation and dissociation in the stratosphere shields living organisms on Earth's surface from exposure to lethal levels of solar ultraviolet radiation.

Air is a compressible mixture of gases. How does this property of air affect the rate at which air pressure decreases with increasing altitude?

The weight of the overlying air determines the air pressure. The lower the location in the atmosphere, the greater the air pressure, the greater the air is compressed, and the greater the air density. Conversely, as altitude increases, the amount of the air above decreases, compressional forces decrease, and air thins as the air pressure declines.

Provide some examples of how the physical characteristics of Earth's surface affect the ratio of how much rainwater (or snow melt) runs off versus how much infiltrates to the ground.

Topography greatly influences the amount of water that runs off. Mountainous terrain usually causes fast run off, and the steeper the slope, the faster the water will flow. Water falling on flat land will more likely infiltrate the ground. The physical properties of the land surface also affect how much water runs off or soaks into the ground. Rainwater (or snow melt) that falls onto sandy or unfrozen surfaces will infiltrate to the ground. However, water that falls onto frozen ground or city streets will run off. Vegetation can also intercept precipitation, as vegetated areas may intercept some precipitation before it reaches the ground.

Explain how converging surface winds can cause clouds to form.

When surface winds converge, the air will be forced to rise. As the air rises, it will cool and expand causing the relative humidity to increase. Once the expanding air reaches saturation, clouds will form.

In northern climates in winter, how does the depth of the snow cover influence the depth to which the ground freezes?

A layer of snow includes open spaces that are occupied by air. Air (especially motionless air) is a relatively poor conductor of heat so that a snow cover with trapped air insulates the soil from heat loss to the colder air overlying the snow. As the snow depth increases, the insulation effect increases, reducing the heat loss from the ground and the depth to which freezing occurs.

What is a blackbody? Is the Earth-atmosphere system a blackbody?

A blackbody is a perfect radiator, that is, it absorbs all incident radiation at all wavelengths and emits all radiation at all wavelengths. No radiation is reflected or transmitted. Blackbody does not refer to the color of the radiating object. The Earth-atmosphere system is not a blackbody.

Would you expect a cold, dry air mass or an equally cold but more humid air mass to exert the greatest air pressure? Explain your answer.

A cold dry air mass has a greater density than a more humid air mass. This means that the drier air mass has higher air pressure because the molecular weight of dry air is greater than the molecular weight of water.

The altitude of the tropopause generally decreases with increasing latitude. Explain why.

Air is heated primarily by Earth's surface, which is heated by solar radiation. The lower the latitude, the greater amount of solar energy received and the warmer the surface. The warmer the surface, the greater the heating of the air immediately above. Because air expands as it is heated, the warmer the air at the surface, the higher it will rise, resulting in a warmer troposphere and a higher tropopause. Consequently, the tropopause has the highest altitude in the tropics and is lowest at the poles.

A jet aircraft is cruising at the 300-mb level, that is, at the altitude where the air pressure is 300 mb. What fraction of the atmosphere's mass is below the altitude of the aircraft?

Assume the air pressure at sea level is 1000 mb so 1000 mb - 300 mb = 700 mb and 700/1000 = 0.7. About seven-tenths (or 70%) of the atmosphere's mass is situated below the 300-mb level.

What is the significance of the Tropic of Cancer and the Tropic of Capricorn relative to incident solar radiation?

At 23.5 degrees N and S latitudes respectively, the Tropics of Cancer and Capricorn mark the poleward boundaries of the zone of the Earth where, at certain times during the year, the noon Sun reaches an altitude of 90 degrees (directly overhead).

Distinguish among the various types of scientific models used in meteorology and climatology.

Atmospheric scientists use four different types of models: physical, graphical, conceptual, and numerical. All models are subject to error but are increasing in accuracy. Physical models create small scale replications of weather systems. Graphical models (e.g., weather maps) represent the state of the atmosphere at a specific time and geographical area. Conceptual models portray the interaction of atmospheric variables such as wind, temperature, and pressure. Numerical models use mathematical equations describing the Earth-atmosphere system to forecast the weather and climate.

Explain how auroral activity varies directly with solar activity.

Auroral activity varies directly with solar activity. During an active solar phase, the auroras are visible over a greater distance because the belts of activity (auroral ovals) expand toward lower latitudes. This happens as greater numbers of electrically charged particles from the Sun interact with Earth's magnetic field.

Explain how thunderstorms transfer heat from Earth's surface to the middle and upper troposphere.

During a thunderstorm, sensible heating combines with latent heating to channel heat from Earth's surface into the troposphere. Updrafts in convection currents surge to great altitudes to form cumulonimbus clouds.

Explain why clouds and precipitation are often associated with fronts.

Fronts are transition zones between two air masses. The property differences and air movements between the air masses give rise to cloudiness and precipitation.

Why would a local TV weather broadcast typically rely on GOES satellite data?

GOES data is continuous and provides a complete view of much of North America and adjacent portions of the Pacific and Atlantic Oceans. A GOES satellite revolves around Earth at the same rate and in the same direction as the planet rotates so that the satellite is always positioned over the same spot on Earth's surface and its sensors have a consistent field of view. A few satellite images of interest include visible, infrared and water vapor.

Distinguish between GOES and POES weather satellites.

GOES orbits Earth at a very high altitude but at the same rate as the planet rotates on its axis, so that the satellite is always positioned above the same spot on Earth's surface (the subsatellite point) and its sensors always observe the same portion of the planet. POES is much closer to the surface but orbits Earth in a north-south direction passing near the poles. The satellite's orbit traces out a plane in space while the planet rotates underneath. A sun-synchronous polar-orbiting satellite scans the same area twice a day.

Identify the two main factors in global sea-level rise and compare their relative importance.

Global sea level rise is caused by ocean thermal expansion of seawater, as well as glacial melt. The IPCC states that there is high confidence of these factors accounting for about 75% of the observed sea level rise. From IPCC reporting and the NCA4, ocean thermal expansion has been the dominant factor accounting for 30-55% of 21st century global mean sea-level rise, while glaciers account for 15-35%.

Explain how it is possible for stratiform clouds at different altitudes to move in different directions.

Horizontal winds can blow from different directions at different altitudes. Clouds move with the wind so it is possible (in fact, common) for clouds at different altitudes to be observed moving in different directions.

According to the inverse square law, if the distance between Earth and the Sun were triple its present magnitude, then the solar constant would be reduced to what fraction of its present value?

If the distance between Earth and the Sun tripled, the solar constant would be reduced to 1/9th its present value.

Distinguish between scattering, reflection, and absorption.

In the process of scattering, a particle disperses solar radiation in all directions—up, down, and sideways. Reflection is a special case of scattering, where some of the solar radiation striking an interface between two different media is backscattered. During absorption some of the radiation striking the surface of an object is converted to heat energy.

What advantages does an infrared satellite image offer over a visible satellite image for monitoring the state of the atmosphere?

Infrared satellite sensors detect infrared radiation that is continually emitted to space by the Earth- atmosphere system. Hence, infrared images can be obtained 24 hrs a day. Visible satellite sensors detect sunlight reflected by the Earth-atmosphere system. Hence, visible images are possible only during daylight hours.

How does the local air pressure change as a cyclone approaches your location?

Local air pressure falls as a cyclone approaches a particular location.

The concentration of methane in the atmosphere is so low that it must be measured in parts per billion (ppb). Why then is methane considered an important greenhouse gas?

Methane is a very efficient absorber of infrared radiation (about 21 times more effective in trapping heat than carbon dioxide). Although it has fluctuated over the past 400,000 years, it is now at its greatest concentration. Its concentration is on the rise due to rice cultivation, cattle, landfills, termites, coal mining, wastewater treatment, and petroleum systems.

Speculate on why the highest temperature of the day usually occurs in mid-afternoon rather than noon.

Mid-afternoon is usually the time of day when the air temperature reaches its maximum because it is when the daytime solar heating has passed its maximum and is equivalent to the outgoing radiation from Earth's surface. Before that time, the solar heating is greater than the outgoing radiation and after that time, the outgoing radiation dominates. However, if a front passes through a locality and the new air mass is sufficiently different in temperature, it is possible for the air temperature to reach its highest temperature at some other time during the day.

How are radiosonde and dropsonde data critical to understanding weather phenomena?

Radiosonde and dropsonde data determine the vertical structure of temperature, dewpoint, pressure, and wind speed and direction through soundings. This data is key to understanding current weather and initializing weather models.

Why are many automated surface weather stations placed at airports?

Real-time surface observations are critical to safe flight operations, especially for aircraft takeoff and landing.

How would analyzing recent rainfall patterns help temperature forecasting?

Recent rainfall is important to temperature forecasting because daytime air temperatures tend to be higher when the ground is dry rather than wet. Even though the intensity of solar radiation striking the Earth's surface is the same, air over a dry surface warms more than air over a moist surface. Over a dry surface, absorbed radiation is used mainly for sensible heating of the air. Over a wet surface, much of the absorbed radiation is used to evaporate water (latent heating), leading to less sensible heating and lower air temperatures.

Define remote sensing. What are two types of instrumentation used in remote sensing of the atmosphere?

Remote sensing is the measurement of environmental conditions by processing signals either emitted by an object or reflected back to a signal source. Remote sensing instruments are never in direct contact with whatever is being measured and include both radar and Earth-orbiting satellites.

What is meant by the response time of a thermometer? What type of thermometer has the fastest response time?

Response time refers to the rapidity at which an instrument resolves changes in temperature. Electrical resistance thermometers have a rapid response time while bimetallic thermometers typically have the slowest.

How is global radiative equilibrium an example of the law of energy conservation?

The law of energy conservation means that on a global scale, the input of solar radiation must equal the output of terrestrial infrared radiation to space. An imbalance would cause temperatures on Earth to rise or fall (depending on the direction of the imbalance) until a new equilibrium is established. If Earth has a constant planetary temperature, we can assume that Earth is emitting the same amount of energy as the amount being received from space.

Identify the main hypotheses for the origin of water on Earth. How is an examination of the isotopic structure of water key to determining where it originated?

The main hypotheses concern comets, asteroids, and water being indigenous to Earth. Scientists have hypothesized that Earth's water was delivered by Oort cloud comets located inside of Neptune's orbit, Jupiter-family comets originating in the Kuiper belt outside of Neptune's orbit, or asteroid-like small bodies near Jupiter. Other scientists hypothesize that water originated in or is innate to Earth's system. Scientists examine the ratio of deuterium (an isotope and heavier form of hydrogen) to hydrogen (the D/H ratio) to attempt to determine where it originated. The nucleus of a hydrogen atom has a single proton, but deuterium, which is very rare on Earth, has both a proton and a neutron in its nucleus. Scientists investigate the origin of Earth's water by matching the D/H ratio of Earth's ocean to other objects in space.

Identify the various sources of weather information that are available to the public.

The public may obtain weather reports, maps, and forecasts via NOAA Weather Radio, local television or radio, The Weather Channel or other cable-TV weather reports, newspapers, and the Internet.

Explain why, on the equinox, the length of daylight is not precisely 12 hrs.

The sunrise and sunset times vary due to optical effects of the atmosphere on the solar beam. The incoming solar beam refracts downward so that the sun appears to be higher than it actually is. This lengthens the period of daylight.