GEO Exam 2
Influence of day length
- Day length varies by latitude
Milankovich theory
- Three separate cyclic movements of the earth combine to produce variations in the amount of solar at the top of the earth's atmosphere: 1. eccentricity 2. precession 3. obliquity - relationships with ice ages and ice advantages - but orbital changes are not totally responsible for changes in ice sheet
Observed changes in temperature
- two warming trends are apparent: 1910-1945 and since 1976. - 1880-2013 warming was ~0.85°C
relative humidity
- ratio of the amount of water vapor actually in the air compared to the maximum amount of water vapor required for saturation at a particular temperature and pressure - expressed as a percentage - dewpoint is when the relative humidity is 100% - RH = water vapor content/ water vapor capacity * 100
other potential effects
- reduction in sea ice - sea-level rise - changes in atmospheric and oceanic circulation such as the strength of the midlatitude cyclones - changes in the frequency and severity of extreme events (heat waves, food, hurricanes, severe storms), but in what ways severe weather will change is still highly uncertain -- remember that it is very difficult to associate a single extreme event with climate change
cirrocumulus
- small, rounded puffs - mackerel sky
cloud classification: form
- stratus - layered - cumulus - puffy - cirrus - wispy
Volcanic activity cont.
- sulfur dioxide forms small droplets of sulfuric acid - sulfuric acid has a longer residence time in the atmosphere than dust - thus, impact of volcano depends on: location and magnitude, dust content, and chemical composition of the magma - effects of one eruption may upset climate for 1-2 years. clustering of several volcanoes believed to be necessary for any long term effects
T/F: As the sun angle increases (the father the sun is located above the horizon), the amount of energy receives per unit area decreases
False. Solar energy that strikes the earth's surface perpendicularly is more intense than solar energy that strike the surface at a more oblique angle.
high clouds
cirrus (Ci), cirrostratus (Cs), cirrocumulus (Cc) - composed mostly of ice crystals - thin, wispy
The sun angle at lansing 43N on september 21st (the fall equinox) is: -a. 0 degrees -b. 23.5 degrees -c. 43 degrees -d. 47 degrees -e. 70.5 degrees
D. For each degree of latitude you move away from the declination point, the sun becomes one degree lower in the sky. On sep 21, the declination in the equator. In other words, the sun is directly overhead the equator on this date. Lansing is 43 degrees from the declination point so the zenith angle would be 43 degrees. 90- 43 = 47 = sun angle
Between July 5, and July 10, the day length at middle latitude locations in the Norther Hemisphere (say, between 35-50 degree latitude): - a. increases - b. decreases - c. does not change - d. is 12 hours long
Decreases
Why do sun angle and day length vary?
Earth-sun relationships
Sun angle
Higher sun angle --> more insolation per unit area. Lower sun angle --> less insolation per unit area Higher sun = more solar radiation
climate sensitivity
the relationship between the measure of forcing and the magnitude of the climate change response
Precession refers to:
the wobble of the earth on its axis
Which of the following statements in incorrect reguarding the conditions during an equinox: - a. the days and nights are of equal length - b. the sun at noon is directly overhead the tropic of cancer - c. the earths axis is neither tilted toward the sun or away from the sun
B. The approximate dates of the equinoxes are march 20 and september 22.
which of the following is not a reason why water warms and cools much more slowly than on land? a. solar energy penetrates deeper into water b. heat energy is mixed to a deeper layer of water c. a portion of the solar energy that strikes water is used to evaporate it d. it takes more heat to raise the temp of a given amount of soil 1°C than it does to raise the temp of the same amount of water 1°C
d. specific heat is the ratio of the heat absorbed by a unit mass of a substance to the corresponding temp rise or fall. specific heat of water is 5x greater than that of soil
the smallest annual temperature range (warmest month average and coldest month average difference) is likely to be found at:
a location on an island near the equator
feedback mechanism
a process that changes the sensitivity of the climate response
T/F windy nights tend to have colder minimum temps compared to calm nights
false. the wind will mix the colder air next the earth's surface with warmer air above. the temp of the air near the ground will not be as cold on a windy night compared to calm nights
mixing ratio
mass of water vapor divided by the mass of dry air. units: grams per kilogram - specific humidity and mixing ratio remain constant as long as water vapor is not added to or removed from the parcel
specific humidity
mass of water vapor divided by the total mass of the air. units: grams per kilogram
The imaginary plane that passes through the center of the earth at every position in the earth's orbit around the sun is referred to as the:
plane of ecliptic
positive feedback
process increases the magnitude of the response
negative feedback
process reduces the magnitude of the response
T/F: The distance between the earth and the sun is greatest on approximately july 5th
true, the earth revolves around the sun in an elliptical rather than circular path. Consequently, the actual distance from the earth to the sun varies during the year. The distance between the earth and the sun is shortest on approximately January 3rd and greatest July 5. ELLIPTICAL ORBIT IS NOT CAUSE OF OUR SEASONS
evaporation feedback
why does the temp of the tropical oceans appear to have changed little between glacial and interglacial periods? - evaporative cooling is one explanation - negative feedback
cloud feedback: low clouds
- composed of water droplets - promote a net cooling effect - reflect much of incoming solar radiation - relatively warm so radiate considerable infrared energy to space - current net effect of clouds on global energy budget is negative - clouds are one of the major uncertainties, thus, both the cloud amount and the distribution of cloud types are extremely important for climate studies
cloud classification: height
- high clouds ~ >6 kilometers - middle clouds ~2-7 kilometers - low clouds ~ <2 kilometers - clouds with vertical development
typical diurnal variation of relative humidity
- high in the nighttime and morning hours - low in the afternoon
relative humidity in the home
- in winter, buildings often have very, very low relative humidity
upslope fog
- moist air moves gradually upslope - air parcels cool by expansion
dewpoint temp
- temperature to which air would have to be cooled (with no change in air pressure or moisture content) for saturation to occur. -- it is determined with respect to a flat surface of pure water -- if determined with respect to flat surface of ice, it is called the frost point
saturation
- the amount of water vapor in the air is the maximum possible at the existing temperature and pressure - visualization: water molecules move more rapidly when temps are warmer, thus, more water molecules escape the water surface - warm air has a greater capacity for water vapor than does cold air
Given the increase in greenhouse gases, why is there uncertainty about climate change?
- the climate system is a complex with many positive and negative feedbacks
Southeastern US - a warming hole
- there are regional trends in warming - the us southeast is one example of a warming hole - possible reasons for the warming hole: -- natural climate variability such as El nino -- irrigation from agriculture --changes in circulation over the gulf of mexico can have caused more clouds and precipitation --aerosols: the southeast is heavily reliant on coal and release of sulfate aerosols could result in regional cooling
what is an air parcel?
- tiny puff of air - composed of dry air components (nitrogen, oxygen, etc.) and water vapor - the puff can expand and contract depending on the air pressure - does not mix with the air around idt - remains as a single unit - parcel's temperature is determined by the average speed of the molecules within the parcel
GCMs are used to:
- understand past climates - project future climates - to investigate the relative role of different forcing mechanisms - projected global surface air temp changes using only natural forcing agents from multiple GCMs - projected global air temp changes using both natural and anthropogenic forcing agents from multiple GCMs
Temperature profiles near the surface
- very different temperature profiles near surface for day versus night - temperature decreases with height near the surface during the day - temperature increases with height near the surface during the night
Suggested mechanisms for climate change: volcanic activity
- volcanoes are a source of carbon dioxide, sulfur compounds, water vapor, and fine dust - dust in the stratosphere most important as dust in the troposphere quickly washes out - fine particles in stratosphere can scatter and reflect sunlight
water vapor radiative feedback
- warm air can hold more water vapor than cooler air - warmer temps may mean more water vapor in the atmosphere - water vapor is an excellent greenhouse gas - positive feedback - water vapor feedback is believed to nearly double the estimated sensitivity of the climate
advection fog
- warm air moves over a cold surface - frequently occurs as warmer air moves over cold air (e.g. a cold ocean current) - can also occur when warmer air moves over cold ground or a snow surface - sometimes fog can be caused by a combination of advection and radiation
Dew
- water that has condensed onto objects near the ground when the object's temperature has fallen below the dewpoint of the air next to the surface - favorable conditions: clear nights, calm winds, surface temperature inversion
Precession
- wobble as earth rotate on its axis - cycle of about 23,000 years - presently, earth is closer to the sun in January and farther away in July. This should reverse in about 11,000 years.
solar energy output is generally _____ when the number of sunspots is large a. larger b. smaller. c. no connection between solar radiation and number of sunspots
a. larger. sunspots are large magnetic storms on the sun and they are accompanied by increased faculae solar radiance
last night was cloudy. tonight weather forecasts clear skies. from this you would conclude (all other conditions such as wind speed and direction remaining similar) that tonight's minimum temp is likely to be: a. higher than last night b. lower than last night c. the same as last night
b. clouds are good absorbers of longwave radiation and trap it, trapping heat as well.
orchard growers often attempt to protect their crops from damaging nighttime cold temps by sprinkling the crops with water. which of the following best describes the physical reason why this would be an appropriate means of protecting against cold damage? a. evaporation of the water droplets warms the atmosphere b. the ice that forms on the fruit limits the amount of convection taking place c. latent heat is released when the water droplets freeze
c. unfortunately the grower has to keep applying water throughout the night
large volcanic eruptions with high sulfur content and an ash veil that enters the lower stratosphere are believed to cause _____ at the earths surface
cooling. the particles ejected into the stratosphere reflect solar energy which causes the surface to cool
On which of the days listed would you expect the sun to be overhead at noon at Burkina Faso (in West Africa, latitude 12N) - a. December 22 - b. February 4 - c. March 10 - d. April 23
d. locations between the topics of cancer 23.5N and tropics of capricorn 23.5S see the sun overhead at noon twice a year. A is the date of the winter solstice where the sun is directly overhead the tropic of capricorn and b and c are wrong because the sun is directly overhead locations in the southern hemisphere during the period from september 22-march 20.
the highest temp of the day is usually observed at:
the middle of the afternoon around 3pm
At the south pole, the sun will disappear below the horizon on approximately: 1. june 21st 2. september 22 3. december 21 4. january 1st 5. March 20
5, march 20. the south pole has six months of darkness from the equinox on march 20 to september 21st and six months of daylight from september 21st to march 20. the sun disappears below the horizon at noon on the march equinox.
The arctic circle is the southernmost location that receives 24 hours of darkness at the time of the winter solstice. What is the latitude of the arctic circle?
66.5 degree
Path of the sun above the horizon
At lansing: - always look to the south to see the sun at noon - on the equinoxes the sun rises in the east and sets in the west - on the winter solstice the sun rises in the southeast and sets in the southwest - on the summer solstice the sun rises in the northeast and sets in the northwest
Declination (subpolar point)
Latitude circle at which the sun is directly overhead at noon
Solar panels on a solar home built in the middle of high latitudes of the Southern Hemisphere should face what direction?
North. Places located poleward of the Tropic of capricorn never see the sun directly overhead and must look to the north to see the sun at noon
Seasons
Summer solstice - june 21st Autumnal equinox - september 22 Winter solstice - december 21 Vernal equinox - march 20 - declination point is the equator (0 degree latitude) - sun one degree lower in sky at noon for each degree of latitude one moves away from the equator - equal day and equal night
What if the axis wasn't tilted?
Sun angle at noon would vary with latitude, but for a particular latitude the sun angle at noon would be the same throughout the year.
circle of illumination
The edge of the sunlit hemisphere that is a great circle separating the Earth into a light half and a dark half
T/F on June 21st, the amount of insolation at the top of the earth's atmosphere is greater at 90N latitudes compared to 23.5N latitude
True. Even though the sun angle at noon is larger on June 21 (summer solstice) at 23.5N compared to 90N, the day length is much longer a 90N resulting in a greater amount of incoming solar radiation at the topic of the atmosphere.
Noon sun angle and zenth angle
Zenith angle = Latitude - declination ex: latitude of lansing ~43N, declination of the sun -17. 43 - (-17) = 60 degrees. Sun angle = 90 - |zenith angle| ex: 90 - |60| = 30
Glacial versus interglacial
- 18000 years ago glaciers covered vast areas of Europe and North American. At present, glaciers cover less than 10% of the earth's land surface - slight warming occurred during the 11th and 14th centuries - a little ice age occurred during the 15th to 19th centuries - It is likely that the rate of warming of the 20th century is larger than any other time during the last 1000 years.
South-facing versus north-facing slope
- At middle latitudes in the Northern hemisphere: objects facing south receive more sunlight than those facing north - south facing leads to more evaporation and drier soils
What affects the amount of incoming solar radiation (insolation) at a location?
- Day length - Sun angle
Winter solstice
- December 21st - Declination point is 23.5 degrees S latitude (the tropic of capricorn) - Longer days/shorter nights in southern hemisphere - shorter days/longer nights in Northern hemisphere - At least 24 hours of darkness poleward of the arctic circle - At least 24 hours of daylight poleward of the antarctic circle
The water molecule
- H2O: two atoms of hydrogen and one atom of oxygen - bipolar molecule -- one end has a negative charge and the other end has a positive charge
frost
- occurs when dewpoint temp is below freezing (now referred to as the frost point)
Daily temperature lag
- on a typical day, the warmest temperatures occur around 3 pm and the coldest temperatures occur at or just after sunrise
how do scientistis study such a complex system?
- paleoclimatic studies are important - global climate models (GCMs) are also a very important analysis tool -- attempt to predict the climate using basic physical principles
vapor pressure
- partial pressure: pressure exerted by a particular gas alone - Pair = Pnitrogen + Poxygen ... + Pwater vapor - actual water vapor pressure versus saturation vapor pressure - change in saturation vapor pressure with temperature - saturation vapor pressure over ice
radiation fog vs advection fog
- radiation fog tends to form on clear, felatively calm nights when cool, moist surface air is overlain by drier air and rapid radiation cooling occurs - advection fog forms when the wind moves moist air over a cold surface and the moist air cools to its dew point
more concepts
- the future climate will depend on how greenhouse gas concentrations change in the future - need to develop "scenarios" or "pathways" of future changes in greenhouse gases - land areas are expected to warm more than oceans, particularly in the norther high latitudes - precipitation is expected to increase in the norther high latitudes and decrease in the subtropics
fog
- cloud resting on the ground - visibility < 1 km (0.62 mile) - formed by cooling as air is cooled below its dew point - water vapor is added to the air by evaporation and the moist air mixes with relatively dry air
Impact of cloudiness on the diurnal temperature range
- clouds suppress the diurnal temperature range. - afternoon temperatures are cooler - nighttime temperatures are warmer
cloud feedback: high clouds
- composed of ice cystals - promote a net warming effect - thin, so allow much of solar radiation to pass through - cool, so absorb more longwave radiation than emit upwards
condensation
- condensation is the phase change from water vapor to liquid water - deposition is the phase change from water vapor to ice - a surface is required for condensation and deposition to take place - condensation nuclei: enter atmosphere from dust, volcanoes, smoke, forest fires, salt from ocean spray, sulfate from ocean phytoplankton, and other sources
clouds
- cooling by lifting - classification done by Luke Howard 1803. -- 10 principal cloud groups based on the height of the cloud base above the ground and on the form (appearance) of the cloud
Ice albedo feedback
- effect of snow and ice cover is to elevate the albedo (reflectivity) - if snow and ice are removed, then albedo would be lower - positive feedback - great warming hypothesized for high latitudes
general concepts
- equations solved for time steps of a few minutes to 30 minutes - usually have horizontal resolution between 100 to 800 km (sometimes smaller) - multiple vertical levels
Seasonal temperature lag
- for land areas, late july or early august tends to be the warmest time of the year, and late january tends to be the coldest time of the year. - for locations near large bodies of waters, late august or early september tends to be the warmest time of the year and february tends to be the coldest time of the year
evaporation (mixing) fog
- forms when unsaturated parcels with contrasting temperatures and moisture mix - often seen when cold, dry air moves over warm water -- water evaporates from the water to the air -- causes dewpoint to increase -- if mixing sufficient, air above water surface becomes saturated -- often called "steam" fog -- ex: seeing your breath - another example of evaporation is when warm rain falling through a layer of cold moist air (frontal fog) - even in summer, warm air rising above thermal pools in Yellowstone National Park condenses into a type of steam fog
cloud feedback
- likely to have more water vapor in the atmosphere - could induce change in cloudiness - clouds increase the albedo BUT reduce longwave emission: alternatively stated, clouds reflect incoming solar radiation but also absorb longwave radiation
types of aerosols
- natural aerosols include volcanic gases, ash and dust, soil dust, sea salt, gases released from oceans. natural aerosols tend to be relatively large - anthropogenic aerosols include industrial dust, soot, and particles from fossil fuel and biomass burning. anthropogenic aerosols tend to be small.
Summer solstice
- June 21 - declination point is 23.5 degrees N (the tropic of cancer) - only equator has equal day and night - longer days/shorter nights in Northern Hemisphere - shorter days/longer nights in southern hemisphere - At least 24 hours of daylight poleward of the arctic circle (66.5N) - at least 24 hours of darkness poleward of the antarctic circle (66.5S)
Water heats and cools more slowly than land
- Land is opaque whereas water is fairly transparent. - land is solid whereas water is fluid - evaporation is greater rom a water surface than from a land surface - water has a higher specific heat compared to land
Controls of temperature
- Latitude - Elevation - Land versus water - Atmospheric circulation - Ocean currents (warm vs cold ocean currents)
Revolution of earth around sun
- Once per 365.24 solar days. - Counterclockwise around sun - Elliptical orbit: - perihelion - january 3, 147 million kilometers - aphelion - july 5 - 152 million kilometers
Reconstructing past climate includes evidence from:
- Pollen records from sediments - Ocean and lake sediments - Ice cores from greenland and antarctica - tree rings - historical records (planting, flooding) - isotope ratios of corals - borehole temperature profiles
Tropic of capricorn and cancer
- See the sun directly overhead at noon only once a year - Locations between the tropic of cancer and capricorn see the directly overhead at noon twice a year - Locations poleward of the tropic of cancer or capricorn never see the sun directly overhead at noon
Tilt of the earth on its axis
- The plane of the ecliptic is the imaginary plane that passes through the Sun and through the Earth at every position in the Earth's orbit around the sun. - Earth rotates on its axis every 24 hours. counterclockwise (eastward) when viewed from above the North Pole - Earth's axis is tilted 66.5 degrees from the plane of the ecliptic. - Earth's axis is tilted 23.5 degrees from a perpendicular to the plane of the ecliptic - Equatorial plane is tilted 23.5 degrees from the plane of the ecliptic
Changes in atmospheric aerosols can also affect climate
- aerosols are microscopic liquid and solid particles in the atmosphere - direct effects include absorption or reflection/scattering of radiation - indirect effects include modification of clouds - the net effect of anthropogenic aerosols is cooling, although soot has a small warming effect - aerosols have a short lifespan in the troposphere.
land use/land cover changes can also affect climate
- anthropogenic land use changes and climate-induced land use changes. - changes in the amount and type of vegetation produces: changes in albedo, changes in soil moisture, changes in the transpiration to the atmosphere
Development of climate models today include
- atmosphere - land surface - ocean and sea ice - sulfate aerosol - non sulfate aerosol - carbon cycle - dynamic vegetation - atmospheric chemistry
Impact of wind on the temperature near the surface
- calm days: larger vertical gradient in temperature near the surface - windy day: smaller vertical gradient in temperature near the surface
Suggested mechanisms for climate change: variations in solar output
- changes are evident from month to month on decadal time scales and even longer - solar disturbances may affect the solar output: sunspots are magnetic storms and are cooler, darker regions on the sun's surace. Faculae are bright areas on the sun's surface - lower sunspot activity (called maunder minimum) overlaps at least partially with the Little Ice Age - the correlation between sunspots and bright faculae is not perfect, so estimates of solar activity based on sunspots records may be off somewhat - finding a mechanism (direct link) between change in solar output and the Earth's climate has been difficult - sunspots are a contributor to climate change
what anthropogenic changes could impact the climate system?
- changes in greenhouse gases - times with high carbon dioxide concentration also has higher temperatures, as inferred from proxy records
Eccentricity
- changes in the shape of the earth's orbit - cycle of approximately 100,000 years - presently, we are in a period of relatively low eccentricity. more circular - less extreme weather
Obliquity
- changes in the tilt of the earth's axis - tilt varies from about 22° to 24.5° - cycle of about 41,000 years
how can relative humidity be changed
- changing the water vapor content of the air - changing the air temperature
radiation fog
- clear skies - light winds (<5 knots) - high humidity near the surface (often with drier air above) - often "burns off" in the morning hours - more common in late fall and winter when nights are long - often forms in low-lying areas - central valley of california in winter
