Weather_and_Climate_chapternotes

updated May 18, 2014


Disclaimer: this is just a guide. I don’t pretend to have all the information on here that may be on a test. Read the book! I update this—so check back. You’ll have to scroll down the chapter of your choice.

 

Test 1: Chapters 1-3

Test 2: Chapters 4-6

Test 3: Chapters 7-9

Test 4:

Chapter 1 Overview of the Earth’s atmosphere

Overview of the physical and chemical structure of the atmosphere and weather

Special focus on water vapor, a source of latent heat energy and the most of the greenhouse gases!

Focus on the increasing concern over carbon dioxide (CO2), and its role in global warming

Air pressure and air density—both decrease with altitude

Temperature does not decrease steadily with altitude in vertical profile; its vertical profile provides a basis for separating the atmosphere into several layers having distinct properties

Ozone layer and ozone hole are introduced here—in particular they will play a role in the amount of UV radiation. UV b radiation is associated with most skin cancers.

What are the elements of weather and the different kinds of storms.

Historical development of meteorology

Ways in which weather and climate can affect our lives, activities, and interests

What are sources of detailed information about weather

How should we think about weather and climate?

Chapter 2 Warming the Earth and the atmosphere

This chapter begins with definitions of temperature and heat, and compares the Kelvin (absolute), Celsius, and Fahrenheit temperature scales.

Heat is the flow of energy between objects with different temperatures and can occur by the processes of conduction, convection, latent heat transport, and radiation. Know these methods of heat transfer!!

Air is a relatively poor conductor of heat but can transport energy efficiently over large distances by the process of convection.

The latent heat energy associated with changes of phase of water is also a very important energy transport mechanism in the atmosphere. A physical explanation of why rising air cools and sinking air warms is given.

The electromagnetic spectrum and the rules which govern the emission of electromagnetic radiation are reviewed next. This provides sufficient background for a detailed study of the atmospheric greenhouse effect and the exchange of energy between the earth's surface, the atmosphere, and space. Because the amounts of energy absorbed and emitted by the earth are in balance, the earth's average radiative equilibrium temperature varies little from year to year.

The energy the earth absorbs from the sun consists primarily of short-wave radiation. Essentially all of the energy emitted by the earth is in the form of infrared radiation. Selective absorbers in the atmosphere, such as water vapor and carbon dioxide, absorb some of the earth's infrared radiation and then radiate a portion of it back to the surface. Because of this effect, the earth's average surface temperature is appreciably higher than would otherwise be the case.

Results from recent research relating to the effect of increasing concentrations of carbon dioxide and other greenhouse gases and the effects of clouds on the earth's energy balance are important to consider in our evaluations of climate change.

Variations in the intensity of sunlight reaching the ground and the length of the day caused by the changing tilt of the earth relative to the plane of its orbit around the sun that are the main causes of seasonal variations on the earth. We follow seasonal changes for a full year in the Northern Hemisphere. By comparison, seasons in the Southern Hemisphere are six months out of phase and moderated somewhat by the larger surface coverage by oceans.

Chapter 3 Air temperature

Daily, seasonal, and geographic variations in temperature have important practical and economic implications.

Note daily heating and cooling cycle in a thin air layer near the ground.

Daily temperature is controlled by incoming energy, primarily from the sun, and outgoing energy from the Earth's surface.

Energy from the sun is generally most intense at noon, but daytime temperatures continue to rise into the afternoon as long as energy input exceeds output.

Because most of the incident sunlight is first absorbed at the ground and then transported into the atmosphere, large temperature gradients can develop between the ground and the air just above, especially under calm wind conditions.

At night, the ground cools more rapidly than the air above and a radiation inversion will often form.

Knowledge of how inversions form is useful for farmers and growers to reduce the severity of a nighttime inversion and to protect cold-sensitive plants and trees.

Temperature varies considerably on a global scale and mean and record temperatures observed throughout the world are summarized.

The main factors that affect the range of temperatures at different locations around the world are latitude, elevation, and proximity to land, water, or ocean currents. Variables, such as mean daily temperature and normal temperatures, mean annual temperature, and annual range of temperature, can be used to characterize the climate of different regions. Additional parameters such as the number of heating or cooling degree-days can be used to estimate a region's heating or cooling needs.

The human body's perception of temperature is influenced by atmospheric conditions. The wind chill index and heat index are examples. A variety of types of thermometers and instruments are used to measure temperature

Know terms!

Chapter 4 Humidity

Discussion of water vapor as souce of energy and weather phenomena. The transformation of water from gaseous to liquid or solid state is an important source of energy in many meteorological processes.

Discussion of ways of measuring and quantifying water vapor concentrations.

Humidity – the amount of moisture in the air

Evaporation – (think about latent heat) heat energy is absorbed during evaporation (the chill you feel when getting out of the pool)

Condensation –(think about latent heat) heat is given off during condensation!

Precipitation

Hydrologic cycle

Transpiration a process by which the water in plants is transferred to the atmosphere

Saturation –--effective upper limit to the amount of water vapor in air—is a function of air temperature.

Vapor pressure--saturation vapor pressure; note in particular the difference in saturation vapor pressure of ice vs. water. That of water is higher! This causes water vapor molecules to diffuse toward ice crystals in clouds (the ice crystals have a lower vapor pressure). Thus, small ice crystals can start the accretion process that creates precipitation.

Relative humidityRh = water vapor content/water vapor capacity

RH = actual/saturtion vapor p X 100 %

Air is supersaturated when it has RH >100%

Dew point  the temperature to which air could be cooled for saturation to occur; a high dew point = high water vapor content—NOTE: this is a better absolute measure of the air’s water vapor content than RH.

Heat index – a practical measure of the effect of a combination of temperature and high humidity have on our perception of temperature.

Condensation: occurs when moist air is cooled below its dew point temperature.  Dew or frost forms at ground level;

When air above the ground becomes saturated, water vapor will condense into small condensation nuclei and form a cloud of small water droplets: fog. Fog can be produced by cooling moist air to saturation or evaporating and mixing water vapor into the air.

 

Cloud forms: 10 basic types, each of which has key characteristics.

 

Chapter 5 –cloud development and precipitation

Chapter examines atmospheric stability and factors that affect development of clouds.

What is precipitation process and what are the different types of precipitation?

 

Stable vs. unstable equilibia:

In atmosphere, stability depends on the change of temperature of a moving parcel of air relative to its surroundings.

A parcel that is given an upward push will become colder and denser than its surroundings and will resist further upward motion.

Clouds that form in a stable atmosphere tend to develop horizontally and have a layered structure.

In an unstable atmosphere, rising air will become warmer and less dense than its surroundings and continue to move upward on its own, commonly producing cumuliform clouds

 

Rising air motions needed to form can be produced by convection, topographic uplifting, convergence, and lifting at frontal boundaries.

Other factors that can affect atmospheric stability include warming or cooling at the ground level and influx of warm or cold air at upper levels.

adiabatic process = air expands and cools or compresses and warms with no interchange of heat from the outside

dry adiabatic rate = unsaturated air cools or warms 10˚ C per 1000 m elev. (5˚ F per 1000 ft)

moist adiabatic rate = less than dry adiabatic rate because latent heat is added during condensation.

environmental lapse rate = the rate of decrease of air temperature with elevation

-air is stable when the environmental lapse rate is small

condensation level

 

Precipitation:

Large droplets form when droplets collide and coalesce. This works best in thick clouds with strong updrafts. Surface tension of drops may inhibit coalescing, so electric charge of droplets and electric field in the cloud may be important.

 

Ice crystal process (Bergeron) is important in middle and high latitudes. Saturation vapor pressure above water droplets is greater than it is above ice crystals. Thus, the water vapor molecules move (diffuse) toward ice (Bergeron process). Thus, ice crystals grow at the expense of water droplets. Accretion or riming of the ice crystals creates snow pellets.

 

The formation of dew, frost, and various types of fog and clouds. 

Dew or frost form when moist air next to the ground is cooled to or below the dew point temperature and water vapor condenses onto objects on or near the ground

            Formation of fog is a progressive process that starts at relative humidities less than 100% when water vapor begins to condense onto hygroscopic condensation nuclei in the air.  Cloud droplets scatter light --- a cloud layer that forms near the ground is officially designated haze or fog depending on the reduction in visibility that it causes.  Fog can be produced under a variety of situations either by cooling moist air to saturation or by evaporating or mixing water vapor into the air.  Note factors that may make a region prone to fog and techniques used to disperse fog.

 

            Note seemingly infinite variety of cloud forms—they can be classified into ten basic types according to their appearance and the altitude at which they form.  How can cloud ceiling can be measured?  Review photographic illustrations of the basic cloud types and several unusual cloud forms. Note discussion of weather satellites and the kinds of information that may be derived from them.  Note the nature of color satellite images.

 

Chapter 6 Air Pressure and Winds

Warm air aloft = H pressure

Cold air aloft = L pressure

A horizontal difference in pressure is a PRESSURE GRADIENT

Thus there is a PRESSURE GRADIENT FORCE (PGF) that results from such differences

Summary: adjacent air masses of warm and cold air also possess pressure differential=> the PGF that thus exists causes air to move toward the L

air pressure = Force/unit area

P is measured by barometers: 2 main kinds

Perfect Gas Law suggests Pressure is proportional to Temp X  Density     P ~ T x ρ

…where ρ is the Greek letter rho which means density

So…P ~ ρ  as long as T does not change

Station Pressure = the pressure measured at a specific location

Sea level pressure = P adjusted to level of mean sea level (used to make synoptic maps so we can predict the weather trends over large areas)

isobars = lines of equal pressure

surface map = shows the H and L pressure cells with Isobars, countour lines of equal pressure.

isobaric map = shows the elevation of the 500 mb pressure level, which allows a 3-D visualization of the H and L pressure cells. Ridges are elongates highs; troughs are elongated lows. This upper air map is important because it shows the upper-level winds and weather cells and allows the determination of whether they are strengthening or weakening.

See more on PGF on p. 151  --causes the winds to blow

Steeper gradient (contour lines closer together) = higher wind velocities

Coriolis force = an apparent force observed on any freemoving object in a rotating system. On Earth this deflection results from Earth’s rotation and causes moving particle including the wind to move to the right in the N hemisphere and to the left in the S hemisphere

This is why we have the geostrophic wind p. 156

gradient wind= wind that blows at constant speed parallel to curved isobars

meridional wind flow = that in which the wind blows in large, looping meanders following a more or less north-south trajectory such as along the west coast of North America.

zonal flow – East-west wind flow

Winds on a surface weather map do not blow parallel to isobars but instead cross them, blowing into areas of L pressure and out of areas of H pressure. This is because of friction of the Earth’s surface. See. fig. 6.19

The friction layer or planetary boundary layer is the lower air layer in contact with the Earth’s surface which is influenced by this friction. It typically extends upward to an altitude of about 1000 meters or 3,000 ft above the surface.

Onshore wind/offshore wind

prevailing wind = the wind pattern most often observed at a location during a given time period

wind rose

wind vane

anemometer

aerovane

wind profiler

 

Chapter 7 Atmospheric Circulations

A wide variety of types of air motion are examined in this chapter, ranging from short-lived microscale phenomena to the semi-permanent circulation patterns found in the earth's global circulation.
 
            The chapter can be divided roughly in half. The first portion begins with a quick classification of the scales of atmospheric motion and looks at the formation of eddies. Wind shear and the turbulent eddies that can form in clear air are of practical importance because they can present a hazard to aviation. The formation of thermal circulations is then covered in some detail. Sea, lake, and land breezes are common examples of thermal circulation and students may have lived in or visited a region where these occur. The role that seasonal changes play in the development of the Asian monsoon, which resembles a large thermal circulation, will also be better appreciated. Several additional local scale winds including mountain and valley breezes, katabatic winds, chinook, and the Santa Ana winds are described.
 
            The Earth's global scale wind and surface pressure patterns are treated in the second half of the chapter. Single-cell and three-cell models have been developed in an effort to understand the underlying cause of the general circulation pattern. Despite some unrealistic assumptions, the three-cell model contains many of the surface features found in the real world. These features and their seasonal movement can have an important effect on regional climate. Approximately 70% of the earth's surface is covered with oceans; weather and climate are strongly affected by interactions between the atmosphere and oceans. The major ocean currents are identified and the chapter ends with discussions of the El Niño/Southern Oscillation phenomenon, as well as other atmosphere-ocean interactions such as the North Atlantic Oscillation and the Pacific Decadal Oscillation.


Be familiar with the different scales of planetary (global) scale wind patterns (Table 7.1)
Eddies and rotors are caused by wind shear.  Shear stress has to do with forces that are parallel but not equal. These are of great interest to aviators owing to the fact that strong wind shear poses a hazard to airplanes.
Billow clouds (fig. 7-2) are evidence of turbulent eddies downwind of a mountain.
Changes in air temperature can cause thermal circulations such as sea breezes and land breezes. 
Monsoons are wind systems that change seasonally, blowing one direction in summer, the other in winter. El Ninos can affect monsoons making summer rains inadequate.
Mountain and valley breezes
Katabatic winds are much stronger than mountain breezes; bora is similar; and Columbia Gorge winds or coho.
Chinook winds are warm because of compressional heating (Chinook wall cloud).
Santa Ana winds  -warm dry winds in southern California caused by high pressure.
Haboob – dust storm in the desert
dust devil -- spinning vortices of wind

Global winds- and general circulation of the atmosphere

Hadley cell –why does this form and why is there convergence near the equator in the  intertropical convertence zone or ITCZ?
Know the basic wind systems and circulation patterns associated with the general circulation pattern of winds on Earth
Polar front Jet stream and subtropical jet stream
How do global winds and the continents affect the major ocean currents?
What causes upwelling?
ENSO: El Nino and the southern oscillation.
What is El Nion and La Nina?  ...and what are the teleconnections of El Ninos?
PDO-Pacific Decadal Oscillation –affects the Pacific Northwest

Chapter 8           Air masses, fronts, and middle-latitude cyclones

air mass = sizeable (1000s of km) body of air whose properties of temp and humidity are fairly similar over extensive horizontal areas having a common altitude (depending on residence time in “source region”

source regions = sizeable areas where air masses acquire their characteristics of moisture and temp.; these areas are typically flattish and have relatively light winds

-types of air masses are related to source regions

-air masses are categorized according to air temp and humidity (Table 8.1 in Ahrens)

            polar air masses (P) come from cold source regions

            tropical air masses (T) come from warm source regions

            maritime air masses (m) come from water areas

            continental air masses (c) –you guessed it! come from continents—can originate over ice and snow in cold regions !

            => continental arctic is a special case of extremely cold air that originates in winter

-thus cP, cT, mP, and mT are the principal types of air masses

-cP is most stable & cold and dry; cT = hot, dry stable air aloft but unstable surface air; mP = cool, moist, unstable; mT = warm, moist, usually unstable

-Temp inversion in winter occurs when cP aloft creates high pressure dome whose subsiding air can undergo compressional warming above colder air: result is stable but includes accumulation of dust, smoke, and pollutants

-topographic barriers – Rocky Mtns, Sierra Nevada, and Cascade Range normally protect west coast from onslaught of cP, however when upper level winds slip over the mtns, cold comes with it. Same thing happens in Appalachians but cold air can sneak over to east seaboard areas

-­economic risk of cold snaps  - 1989 and 1990 frosts brought $480 mill and $500 mill in crop damage to TX and FLA respectively.

-lake-effect snows – cold body of air moves over warm lakes, such as Great Lakes, picks up moisture and dumps huge amounts of snow on east shore areas

-“Siberian express” = nickname for bitterly cold cA air mass coming far to south

-“Pineapple express” = nickname for warm mT hitting west coast of USA to produce heavy rain and extensive flooding. [note: also results in rain-on-snow flooding event (ROS) in Pacific NW, debris flows and landslides everywhere (Pacific coast and also SW such as Grand Canyon). [note linkage of climate and geology!!]

-rain-on-snow flood event = greatly enhanced flood that results when a warm pineapple express dumps lots of rain on snow that has fallen in the “transient snow zone” (lower elevations, e.g. <4,000 ft elevation); typically, ROS can occur right after a big low-elevation snowstorm.

-in Pacific NW in winter: mP comes from Asia and frozen polar regions but is carried E and S over Pacific Ocean while circulating in Aleutian Low, which adds warmth and moisture. By the time it reaches Pacific coast, it is cool, moist and conditionally unstable. How so? ocean keeps air near surface warmer than air aloft!

-in Atlantic along E USA mP air is very cold, but moves west as “nor’easter” less often because prevailing wind is westerly; if farther south they are “Hatteras Lows”

-cT => only source region in North America is in northern Mexico: low humidity: drought can develop when this moves into Midwest and stagnates

-“air-mass weather” = when persistent weather conditions exist

Fronts

front = transition zone between air masses of different densities; note weather before, during and after various fronts have passed in Table 8.4 in Ahrens.

stationary front  = has no movement

cold front = transitional zone where cold, dry polar air is replacing warm, moist

warm front = front that moves such that warm air replaces cold air

occluded front = frontal boundary where cold and warmer air masses have overtaken each other; “cold occlusion” is most prevalent type in Pacific NW

-Fronts typically are associated with “weather” because moist air is forced upward along frontal boundaries. However, fronts are result of movement of middle-latitude cyclones, larger features.

-steepness of frontal zone is due to friction:

fast moving = steep & possible Thunderstorms & squall line

slow moving = less steep & maybe nimbostratus clouds along front

-back door cold front = comes from east or NE

-Table 8.2 summarizes cold front characteristics

-dryline= line separating warm dry air from warm moist air => T-storms form here

-most violent weather = where cold front is just overtaking a warm front!



Chapter 8 vocabulary: front, stationary front, cold front, warm front, occluded front, back-door front, polar front theory, frontal wave, wave cyclone (aka mid-latitude cyclone), open wave, cyclogenesis, lee-side low, northeaster, convergence, divergence, jet streak

 

Middle Latitude Cyclones

-Bjerknes et al: “polar front theory”   = a model of the birth, growth, & decay of mid-latitude cyclones

-Fig. 8.19 simplistic diagrammatic model for life cycle of wave cyclones

REMEMBER:  polar front = semicontinuous global body separating cold polar air from warm tropical air

Fig. 8.19a:  wind shear between 2 highs

8.19 b: wave-like kink forms = frontal wave (in birds-eye view, wave builds and breaks)

8.19c: “open wave” develops after 12-24 hours => central pressure becomes much lower & creates much stronger cyclonic flow; at this stage, precipitation forms in wide band ahead of warm front and along narrow band of cold front

8.19d: faster moving cold front finally overtakes warm front and can become occluded => 8.19e: now occluding=> storm most intense at this point!

8.19f: storm system dissipates –wave cyclones can last for a few days to a week

-fig. 8.20 shows “family” of wave cyclones forming along the polar front

Question: “Where do mid-latitude cyclones form?” => in USA, eastern slope of Rockies is starting point for some (lee side low)

cyclogenesis = development and strengthening of mid-latitude cyclones

-fig. 8.21 shows common paths of cyclone (L) and anticyclones (H)

[remember, in southern hemisphere, they spin in opposite directions!]

REMEMBER:  upper wind flow is key to formation of wave cyclones!  [cyclonic storm systems are also known as wave cyclones]

-developing surface cyclonic storms are deep lows that intensify with height

-so, surface L appears on upper air chart as closed low or “trough”

fig. 8.23 shows relationship between convergence and highs and divergence and lows. Convergence (where isobars get closer together on west side of trough) causes piling up and downward movement of air (strengthens H), whereas divergence (where isobars get farther apart on east side of trough) causes upward movement of air (strengthens L below it)

-The net result of this is that wave cyclones depend on the location of the polar front (i.e. polar jet) for their continued vitality. Since the cyclones move more quickly than the undulations of the Rossby Waves (long waves of the polar front) around the Earth, odds are they will eventually move away from the polar jet after several days and dissipate.

(But don’t fret, new cyclones are always being born!)

Jet Streams

jet streams­ = fast moving currents of air in the upper Troposphere. These usually occur where there is a break in the Tropopause. Polar jet occurs at top of the polar front

see: http://radar.weather.gov/jetstream/global/jet.htm    

jet streak = core of strong winds in the jet stream

NOTE: if surface L exists below divergence in jet above, the warm rising air will be drawn upward into the jet stream=> this can enhance storm (surface low) because the stronger the suction from above the lower the central pressure will be in the Low!

-study figure 8.25 to see the above relationship

-study also “waves in the westerlies” (aka Rossby waves or planetary waves). These move slowly around the Earth. They are thought to be caused by differences in the Coriolis effect with latitude (Dunlop, 2001)

-short waves can deepen trough in long wave.

So, for storm to intensify it must have upper level counterpart! If Polar jet stream swings south of developing storm it can offer “upper air support”, because as storm moves faster and will cross through area of divergence in jet above it, which strengthens storm.

 

 

 Chapter 9 Weather forecasting


Weather forecasts are an important part of many people's daily lives. This chapter looks at how weather observations are collected and analyzed, and at the wide variety of different types of weather forecasts that can be made using this data.

    Forecasts are based on worldwide observations of weather conditions made several times a day. Computer technology and satellite data help meteorologists can provide early warning of developing hazardous weather conditions and are used to develop forecasts. You should know what specific conditions result in issuance of various weather alerts, advisories, and warnings.

    Computers perform the numerical calculations in complex mathematical models of the atmosphere. What are the factors that limit the accuracy of numerical weather predictions. Satellite images from geosynchronous and polar orbiting satellites provide information about cloud height and thickness, and the circulation of water vapor in the atmosphere.

    Different methods of predicting future weather including persistence and steady state forecasts, the analogue method, weather type, and climatological forecasts. Often one method is appropriate in a short-range forecast, while another method would be employed when formulating a longer-range seasonal outlook.  Recent developments including ensemble forecasting are also described.

    The chapter includes a practical guide to weather prediction that is based on observations of local conditions and basic weather principles. The chapter concludes with an example of how a fairly accurate short term forecast could be made using data from a surface chart and a knowledge of the upper level wind pattern.

Chapter 9 vocabulary (see p. 254 in book): weather watch, weather warning, analysis, numerical weather prediction, prognostic chart, AWIPS, metiogram, geostationary satellites (e.g. GOES), polar-orbiting satellites, chaos, ensemble forecasting
Misc forecasting methods: persistence, steady-state (aka trend), analogue method, statistical forecasts (e.g. MOS, model output stats), probability forecasts, weather types, climatological forecast.
types of forecasts (time-based): very short range (nowcast), short-range, medium-range forecast, long-range forecast, teleconnections

 

 

Chapter 15         Light, Color, and Atmospheric Optics

 

This chapter describes and explains a variety of atmospheric optical phenomena. The chapter begins with a brief review of the physical nature of light and explains our physiological perception of light and color. A first group of optical effects discussed in this chapter are all produced by scattering of light. Air molecules selectively scatter the shorter wavelengths of sunlight and give a clean sky its deep blue color. Larger aerosol particles scatter different wavelengths more equally, and can turn the sky milky white. White clouds, the blue color of distant mountains, and crepuscular rays are additional examples of light scattering.

A second category of optical phenomena involves refraction and the dispersion of light. Mirages form when light is bent as it propagates through air layers with different densities. An inferior mirage can cause light from the sky to be bent so that it appears to be coming from the ground, and may make a road surface appear wet on a hot dry afternoon.

Under unusual circumstances, refraction and dispersion can cause a green flash of light to appear as the sun sets below the horizon.

Haloes and sundogs are relatively frequent events and occur when light passes through a high thin cloud layer composed of ice crystals.

In a primary rainbow, light rays are refracted as they enter a raindrop and are then reflected off the back inside surface of the raindrop. To see a rainbow, you must have the sun behind you, and it must be low in the sky.

A brief discussion of corona and cloud iridescence, which are produced by diffraction, is included at the end of the chapter.


 

References

Dunlop, Storm, 2001, Oxford dictionary of weather: Oxford University Press, 260 p. plus appendices.