In-class Quiz #2 will be administered at the beginning of class on Monday, Oct. 22. It will be closed book, closed note, and closed computer (and other electronic devices).
You will have around 20 minutes to complete the quiz. Like the other in-class quizzes, it will be worth 3.33% of your course grade (after the worst of your four in-class quizzes is automatically dropped.)
The question(s) will be short answer, short essay, and/or simple meteogram analysis and interpretation. The question(s) might test nothing more than basic factual knowledge, but they might also test conceptual understanding, reasoning
ability, and perhaps your ability to communicate your understanding and reasoning.
We will begin covering new material as soon as the quiz is over.
Topics eligible for coverage on the quiz consist primarily of topics addressed in lecture, in lab sessions, and in reading assignments.
(Suggested tactics for preparing and submitting forecasts for the ongoing forecasting assignment will not be addressed by this quiz.)
Some topics addressed in lecture and/or lab include:
- Meteorologically and Astronomically Significant Latitude and Longitude Zones
- Daily temperature cycle
- a conceptual model of how temperature typically varies over the course of 24 hours, based on lots of observations
- Other pattens of temperature in space and in time
(class notes: outline)
- Global variations in temperature with latitude
- Variations in temperature over periods of several days at midlatitudes along the polar front (global temperature patterns) (class notes)
- Example: Temperature pattern at around 10,000 ft. above sea level (representative of the lower troposphere) over North America on Monday, Feb. 27, 2012
- definition (narrow zone across which temperature varies rapidly from one side to the other, separating regions of relatively warmer and colder air within which temperatures are relatively more uniform)
- particular types
- polar front (separates alternating "tongues" of relatively colder and warmer air "protruding" into the midlatitudes from higher and lower latitudes, respectively)
- cold fronts, warm fronts, occluded fronts, and stationary fronts (all of which are enhanced or modified parts of the polar front)
- standard symbols used on weather maps to represent each type of front
- a line is drawn along the warm side of a front
- triangles or half-circles or both are drawn along one or both sides of the line, depending on the type of front
- different types of fronts are distinguished from each other mostly on the basis of the patterns of winds on each side of the front, which determine which way the front moves (or doesn't move)
- cold fronts move in the direction from colder toward warmer air (so the colder air advances and replaces warmer air)
- warm fronts move in the direction from warmer toward colder air (so the warmer air advances and replaces colder air)
- stationary fronts don't move at all
- an occluded front forms when a cold front, which moves faster than a warm front, catches up with part of a warm front ahead of it and replaces it
- Patterns of solar radiation and explanations for them
- Effects of sun angle on insolation at the earth's surface
- Figure 2-1: Solar radiation intensity and sun angle: the "spreading out" effect [PDF file]
- Figure 2-2: Solar radiation intensity and sun angle: the "distance traveled through the atmosphere" effect [PDF file]
- things that can happen to solar radiation when it enters the atmosphere:
- reflection or scattering back to space;
- absorption (converting its energy into heat in the atmosphere); or
- transmission (passing through unaffected and reaching the earth's surface, where it could be reflected back to space or absorbed and converted into heat)
- Solar radiation strikes the earth everywhere in parallel "rays", whereas the earth's surface is curved, so the angle between the sun and the earth's surface varies with location on the earth.
- On the average, sun angle (and hence insolation at the earth's surface) decreases with increasing latitude.
- This might help explain why temperature decreases with increasing latitude (and so is warmest at low latitudes and coldest at high latitudes)
- Because the earth rotates, sun angle (and hence insolation at the earth's surface) varies with time of day
- This might help explain why temperatures vary with time of day
- It can't be a complete explanation, though, because the warmest time of day is usually not when the sun is the highest in the sky and hence when insolation is the greatest (at solar noon)—rather, temperatures are usually the warmest in mid-afternoon, roughly.
- Because the earth's orientation relative to the sun varies depending where the earth is in its orbit around the sun, sun angle and length of daylight (and hence daily total solar radiation reaching the earth's surface) varies with time of year everywhere on the earth
- This might help explain why temperatures vary with time of year, especially at middle and high latitudes (where length of daylight and insolation varies more than in the tropics)
- It can't be a complete explanation, though, because the warmest time of year (middle or late summer) is not when the most solar radiation is received (the first day of summer), and the coldest time of year (mid winter) is not when the least solar radiation is received (the first day of winter)
- Concept map summary of factors affecting insolation at the earth's surface
- Thought Questions on the Seasons (with extensive responses added to the questions)
- Figure 2-5: Solar radiation striking the earth at the solstices and equinoxes [PDF file]
- Some Facts about Relations between the Earth and the Sun [PDF file]
- The earth's axis of rotation is tilted by an angle of 23.5° relative to the plane of the earth's orbit around the sun, and as the earth orbits around the sun, the orientation of the axis of rotation relative to distant stars doesn't change. As a result, at one point in the earth's orbit around the sun, the Northern Hemisphere is oriented (tilted) most directly toward the sun and so the Southern Hemisphere is oriented (tilted) most directly away from the sun. This occurs on June 21 or 22 and is defined as a solstice (the June solstice). On the other side of the orbit (6 months later), the Northern Hemisphere is oriented (tilted) most directly away from the sun and so the Southern Hemisphere is oriented (tilted) most directly toward the sun. This occurs on December 21 or 22 and is also defined as a solstice (the December solstice). Half way between the two solstices (three months from each, on March 21 or 22 and September 21 or 22), the axis of rotation is oriented (tilted) neither toward or away from the sun, but instead to one side. These two times are defined as equinoxes.
- At any particular latitude on the earth, as a result of the varying orientation of the earth relative to the sun as the earth orbits the sun, the sun angle (that is, the angle between the sun and the horizon) at solar noon varies with time of year, and hence so does the intensity of solar radiation on a horizontal surface at the earth's surface. Moreover, the fraction of the latitude circle that is exposed to the sun also varies as the orientation of the earth relative to the sun varies (except at the equator), and hence the number of hours of daylight at that latitude varies (except at the equator). The combination of varying sun angle (and hence insolation) and varying number of hours of daylight with time of year causes the total amount of solar radiation striking the earth's surface each day to vary with time of year. This variation is the basis for defining the seasons. The seasons are opposite in the Northern and Southern Hemisphere's because the orientation of the earth relative to the sun affects each in an opposite sense.
- The earth is closest to the sun in early January and farthest from the sun in early July. (The distance between earth and sun varies by about 3 million miles, which is about 3% of the distance between the earth and the sun, which averages 93 million miles.) This modest variation in distance has a relatively small effect on the total amount of solar radiation striking the earth's surface—much smaller than variations in sun angle and day length have.
- When the earth is at the point in its orbit when the Northern Hemisphere is oriented most directly toward the sun (on June 21 or 22, one of the solstices and the first day of summer in the N. Hemisphere), the Southern Hemisphere is oriented most directly away from the sun (the first day of winter there). The opposite is true at the time of the other solstice. Hence, the seasons in the Northern and Southern Hemispheres are always opposite each other.
- The tropics are the latitudes between 23.5° (The Tropic of Cancer) and 23.5°S (The Tropic of Capricorn). These latitudes of 23.5°N and 23.5°S are significant because they are the farthest north and south (respectively) where the sun is ever directly overhead at solar noon. (This happens on June 21 or 22 at the Tropic of Cancer and on December 21 or 22 at the Tropic of Capricorn.) The sun is directly overhead at solar noon at the equator (0° latitude) at the time of each of the two equinoxes, half way between the two solstices.
- Note that the two solstices and two equinoxes are defined based on the orientation of the earth's axis of rotation relative to the sun, and each of the four seasons (at least, outside the tropics) are defined as 3-month periods between a solstice and an equinox. (For example, winter is the 3-month period between the winter solstice and the spring (vernal) equinox, while spring is the 3-month period between the spring equinox and the summer solstice.)
At any particular location outside of the tropics, the angle of the sun above the horizon (sun angle) at solar noon is either at its highest or lowest for the year at the times of the solstices. (Within the tropics, the times of year when sun angles are highest and lowest are not the same as they are outside the tropics; for that reason, the concepts of "winter", "spring", "summer", etc. don't apply there.) Also, on the days of the solstices the number of hours of daylight are the greatest or least for the year.
- Because of the way that the seasons are defined outside the tropics (that is, in terms of the times when the solstices and equinoxes occur), fall and winter each have the same average number of hours of daylight and solar noon sun angle, and spring and summer each have the same average number of hours of daylight and solar noon sun angle. (This is perhaps counter to our intuition, but it's true!)
- Temperatures and other aspects of weather don't precisely follow the seasons. For example, on the average, winter is colder than fall (though winter and fall have the same average sun angle and number of hours of daylight), and summer is warmer than spring (even though spring and summer have the same average sun angle and number of hours of daylight).
- Principle of Conservation of Energy
- Temperature,Heat, Radiation, and the Principle of Conservation of Energy [PDF file]
- energy can't be created or destroyed, but it can be transformed from one form of energy to another
- heat (energy of random motions of molecules and atoms) and electromagnetic radiation are two of a number of forms of energy
- Animation of a gas (shows effects of adding and removing heat on energy of molecular motions and on temperature) (Java applet)
- temperature is a measure of the average energy of random motions of molecules in matter (so temperature is related to heat but isn't the same thing as heat)
- when matter absorbs radiative energy striking it, the energy in the radiation is transformed into heat in the matter (so the matter gains heat this way)
- when matter emits radiative energy (which most matter does continuously), heat in the matter is transformed into radiative energy, which propagates away (so the matter loses heat this way)
- Basic Laws of Radiation
- Emission spectra (graph) for objects at different temperatures (illustrating several of the laws of radiation; with notes)
- heating coils on an electric stove at different temperature settings (coils are black when at "off" and "medium" heat settings, but glows red when on "high" heat setting)
- solar radiation vs. terrestrial (longwave infrared) radiation (the sun is much hotter than the earth, hot enough to emit most of its radiation at visible wavelengths, short wavelengths of infrared radiation, and ultraviolet radiation, whereas the earth emits most of its radiation at longwave infrared wavelengths)
- Applications of the Principle of Conservation of Energy (expresses as a heat budget) and basic laws of radiation
- the daily temperature cycle at the earth's surface (see Lab #2, Parts III, IV, and V)
- the earth as a whole (that is, the atmosphere and surface combined) in the long-term, global average (see below)
- Weather satellite images and Some Mostly Common-Sense Properties of Features that You Can See on GOES Satellite Images
- interpreting weather satellite images requires understanding of basic laws of radiation and how electromagnetic radiation interacts with material objects (that is, stuff made out of atoms and molecules)
- concept of albedo (fraction or percentage of radiation striking an object that the object reflects)
- Types of Models that we use to understand and try to predict the behavior of the physical world [PDF file]
Relevant Reading Assignments
Relevant Clicker Questions
Assignments, Labs, Quizzes, Handouts, etc. |*|