Meteorology1

1. The Atmosphere: composition and structure. Looks good. JL Water vapor composition can vary between 1-4% at the sfc.  TH
 * Nitrogen and Oxygen make up 99% of the volume of clean dry air. ** ** N-78%, O-21% **, ** Argon, CO2, He, Methane, H, Water vapor and other trace elements make up the remaining 1%. **
 * Troposphere: The bottom layer of the atmosphere; temperature decreases with increasing altitude and is the layer where all weather occurs. **
 * The average environmental lapse rate is 6.5°C per kilometer. **
 * Stratosphere: The atmosphere's ozone resides in this layer. **
 * Mesosphere: The coldest temperature anywhere in the atmosphere is in the mesosphere **
 * Thermosphere: uppermost layer of atmosphere. **
 * BW **

Looks good. JL
 * Composition - variable components are water vapor, aerosols and ozone; can significantly affect weather and climate **
 * Pressure and density decrease rapidly with altitude (50% lies below 5.6 km) **
 * Layers determined by changes in temperature with altitude **
 * "Pauses" in temperature change between layers - tropopause, stratopause, mesopause **
 * Stratosphere - temperature increases with altitude because ozone absorbs UV and releases heat **
 * First 3 layers (up to ~80 km) are homosphere (composition remains constant) **
 * Thermosphere - no defined outer limit; very high temperatures, but essentially no heat transfer due to lack of molecules; gases become ionized due to absoption of solar radiation **
 * DS **

2. Earth/Sun relationship: rotation, revolution and seasons. This is good. JL See questions 82 and 83 for seasons. Insolation is increased on the side of the earth receiving the sun, and most when that area is at a sun angle closest to 90 degrees (replaces underlined text), LK
 * Rotation is defined as the spinning of an object on an internal axis. Revolution is the rotation of an object about an external axis. i.e. The earth rotates once every 24 hours and revolves once every year around the sun. Since the earth is tilted on its axis 23.5° and that axis remains fixed in its orbit around the sun the amount of insolation (incoming solar radiation (?)) __changes drastically when the earth is on one side of the sun compared to the other__. At this time in the earth's gyroscopic precessional period it is actually closer to the sun during winter and further from the sun in the summer. In 11,000 years or so it will be the opposite case but the main reason the seasons exist is due to the tilt of the earth on its axis. **
 * BW **

3. Heat transfer methods This is good. JL
 * Conduction, Convection, and Radiation: Conduction is heat transfer by direct contact. Convection is heat transfer by the wholesale movement of the medium. Radiation is electromagnetic waves traveling through space such as visible light, infrared radiation, UV, etc... **
 * BW **
 * I would like to add: **
 * Conduction transfers heat by molecular motion and is meteorologically insignificant. An increase in molecular motion produces friction and causes the medium to heat up. **
 * Convection - mass or material in motion; liquids and gases (fluid motion); vertical and horizontal (advection) **
 * Radiation – no motion **


 * These are the roles that these mechanisms play in meteorology: **
 * Conduction (least significant because air is a poor conductor or an insulator) – heat is transferred from Earth’s surface to the air immediately in contact with the surface. **


 * Convection – heat acquired in the lowest layer of the atmosphere by way of radiation and conduction is transported by convection. As warm, less dense air above a parking lot buoys upward, it is replaced by the cooler air above the woodlands nearby. Here, convective flow is established. On a larger scale, the global convective circulation of the atmosphere, is driven by the unequal heating of the Earth’s surface. These complex movements are responsible for the redistribution of heat between hot equatorial regions and frigid polar latitudes. Circulation in the atmosphere is both vertical (convection) and horizontal (advection) which allows for both vertical and horizontal heat transfer. Advection occurs for the polar air masses and warm, moist air masses, etc. **

This is good. IB
 * Radiation – mechanism of heat transfer that travels through the vacuum of space; ultimate source of energy that drives weather; rapid vibrations of extremely hot molecules on the Sun create electromagnetic waves that travel through space and, upon being absorbed, increase the molecular motion of other groups of molecules – including those that make up the atmosphere, Earth’s land – sea surface, and even our bodies. The absorbed radiation heats the atmosphere. **
 * JI **

4. Heat vs. Temperature, including the types of heat in meteorology
 * Heat is the transfer of energy into or out of an object and its surroundings due to a temperature difference between them. **
 * Temperature is the quantity that describes how warm or cold an object is relative to some standard measure. Temperature is related to the average kinetic energy of the molecules that make up an object. In the thermosphere for instance the temperature is very high because the gas molecules are moving very fast. There would be little heat exchanged between you and the environment up there however because the amount of gas is very small. In other words it would not "feel" hot. **
 * BW **

Looks good. JL
 * I would add the types of heat in meteorology: **
 * Latent heat (mentioned below) which is energy absorbed or released during a phase change without a change in temperature. It can be thought of as stored or potential energy. **
 * Sensible heat is the energy associated with the temperature of an object; the greater the temperature the more sensible heat. It is kinetic energy. **
 * DS **

5. Water: physical states, phase changes and the temperature changes associated with them.
 * Water is the only substance that exists naturally in three states (solid, liquid, gas) on Earth. Phase changes requiring energy include melting (solid to liquid) and vaporization (liquid to gas). Vaporization can occur throughout the liquid at the boiling point or from the surface of the liquid, below the boiling point, through evaporation. Phase changes which release energy include condensation (gas to liquid) and freezing (liquid to solid). The melting/freezing point of water are the same, 0°C and the vaporization/condensation point of water are the same, 100°C. The energy that is gained/lost during melting/freezing is called latent heat of fusion. The energy that is gained/lost during vaporization/condensation is called latent heat of vaporization. The energy that is absorbed/realeased during a phase change is not sensible heat, in other words phase changes occur without a change in temperature. The absorption and release of heat during phase changes provides energy which drives weather. **
 * PM **


 * I would add sublimation (solid to gas) and deposition (gas to solid). Deposition releases latent heat to the environment and sublimation absorbs latent heat from the environment. (Atmosphere. Lutgens/Tarbuck. pp. 100-101) **
 * JL **

6. Measures of atmospheric moisture
 * 1) Absolute Humidity - the mass of water vapor in a given volume of air in grams/cubic meter (AH = Mass of water vapor (g)/volume of air (cubic meters)). This tells us the quantity of water vapor contained in a specific amount of air. Absolute humidity is affected by changes in temperature or pressure because these affect volume. **


 * 2) Mixing ratio – the mass of water vapor in a unit of air compared to the remaining mass of dry air in grams/kilogram (MR = mass of water vapor (g)/ mass of dry air (kilograms). This also tells us the quantity of water vapor contained in a specific amount of air. Since the mixing ratio is measured in units of mass, it is not affected by changes in pressure or temperature. **


 * 3) Vapor pressure – the part of the total atmospheric pressure attributable to its water vapor content. It is measured in millibars. The more water vapor there is in the air, the higher the vapor pressure. **


 * 4) Relative humidity - a ratio of the air’s actual water-vapor content compared with the amount of water vapor required for saturation at that temperature (and pressure). Relative humidity is expressed as a percent using the grams of water vapor present/ grams of water vapor at saturation. It indicates how near the air is to saturation rather than the actual quantity of water vapor in the air. **
 * RH = vapor pressure (mb)/ saturation vapor pressure (mb) x 100 **
 * RH = mixing ratio (g/kg)/ saturation mixing ratio (g/kg) x 100 **


 * 5) Dew Point temperature – the temperature to which air needs to be cooled to reach saturation. It is measured in degrees Fahrenheit or Celsius. Cooling below the dew point produces dew, fog, or clouds. Dew point is a measure of the actual moisture content of a parcel of air. It is related directly to the amount of water vapor in the air. High dew points = moist air and low dew points = dry air. **


 * As T increases, air's ability to hold moisture increases exponentially. As T increases, moisture content remains the same, but Relative Humidity goes down. **


 * Relative humidity is a measure of the amount of water vapor in an air mass compared to the saturated amount at a given temperature. Its strength is that it that it gives us an idea of how close an air mass is to saturation with a percentage. It is limited because you can't compare different air masses at different temperatures. Dew point is the temperature at which air must be cooled to be saturated. Its strength is that you ** ** can compare the water vapor content of two air masses at different temperatures. Also, the proximity of dew point to air temperature can give you a good idea of saturation. Its weakness is that you have to use a sling psychrometer or hygrometer to determining the wet-bulb temperature. You then must use a chart to determine dew point using the air temperature and wet-bulb depression. **
 * JI **

7. Atmospheric stability and adiabatic processes
 * A parcel that remains warmer than the environment as it rises will produce clouds and precipitation. As it rises, expands and cools, its water vapor content condenses. **


 * ELR = 5 – 9 C/km **
 * DALR = 10 C/km (unsaturated parcel) **
 * WALR = 5 – 9C/km (saturated parcel) **


 * Environmental lapse rate (averages 6.5◦C/km) - The temperature decrease in the troposphere. This is not constant, but rather can be highly variable and must be regularly measured using radiosondes. It can vary during the course of a day with fluctuations in weather, as well as seasonally and from place to place. Shallow layers where temperature increases with height are called inversions. **


 * Dry adiabatic lapse rate – The rate of adiabatic cooling or warming in an unsaturated air parcel. This is constant at 10◦C/km. This also applies to heating in the opposite direction (sinking). The rate of temperature change is 1◦C per 100 meters or 10◦C for every 1,000 meters. If the air ascends, it cools; if the air descends, it warms by this rate. **


 * Wet adiabatic lapse rate – The rate of adiabatic temperature change in a saturated air parcel. The rate of temperature change is variable, but it is always less than the dry adiabatic rate (due to the release of latent heat of condensation that partially offsets the cooling due to expansion). The rate varies from 5◦C per 1,000m for air with a high moisture content to 9◦C per 1,000m for air with a low moisture content. Air cools or warms at this rate if the parcel has reached its dew point. **


 * Absolute stability – The environmental lapse rate is less than the wet adiabatic rate. The rising parcel of air is always cooler and heavier than the surrounding air producing stability. **


 * Absolute instability – The environmental lapse rate is greater than the dry adiabatic lapse rate. Solar heating causes to lowermost layer of the atmosphere to be warmed to a higher temperature than the air aloft. The result is a steep environmental lapse rate that renders the atmosphere unstable. **

8. Winds: forces involved, differences between surface and aloft, differences between hemispheres
 * Conditional instability – A moist air parcel has an environmental lapse rate between the dry and wet adiabatic rates (between ~ 5◦ and 10◦C per 1,000m). The atmosphere is conditionally unstable when it is stable with respect to an unsaturated parcel of air, but unstable with respect t a saturated parcel of air. Example: A parcel of air is cooler than its surroundings up to nearly 3,000m, where its tendency is to sink toward the surface (stable). Above this level, the parcel is warmer than its environment and will rise because of its own buoyancy (unstable). The release of latent heat at the LCL (Lifted Condensation Level) causes the parcel to become warmer than its surroundings. Here it rises without an outside force. **
 * JI **
 * Good. Just wanted to add a couple general things from our lecture notes:**
 * Atmospheric stability=air's tendency to rise or sink on a given day, and is determined by temperature differences between levels in the still atmosphere and inside rising thermals (bubbles of air).**
 * Still atmosphere cooled by ELR; rising bubble of air cooled by adiabatic lapse rate (expansion)**
 * Adiabatic=vertical motion=heat/cool**
 * Local indicators of stability:**
 * Stable=steady winds, layered clouds, poor visibility (haze)**
 * Unstable=gusty winds, dust devils (turbulence), vertical clouds, good visibility**
 * KMS**
 * Wind is the result of horizontal differences in air pressure. Air flows from areas of higher pressure to areas of lower pressure. Wind is nature’s attempt to balance inequalities in air pressure. Solar radiation is the ultimate energy source for most wind. If the Earth did not rotate and if there were no friction, air would flow directly from areas of higher pressure to areas of lower pressure. Because both factors exist, however, wind is controlled by a combination of forces, including the pressure gradient force, the Coriolis force, friction. The horizontal pressure gradient is the driving force of wind. It has both magnitude and direction. Its magnitude is determined from the spacing of isobars, and the direction of force is always from areas of higher pressure to areas of lower pressure and at right angles to the isobars. On a rotating Earth the Coriolis force acts to change the direction of a moving body to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This deflecting force is always directed at right angles to the direction of airflow, affects only wind direction not wind speed, is affected by wind speed (the stronger the wind, the greater the deflecting force), and is strongest at the poles and weakens equatorward, becoming nonexistent at the equator. Friction significantly influences airflow near Earth’s surface, but its effect is negligible above a height of a few kilometers. Wind increases in strength with an increase in altitude because it is less affected by friction from objects near Earth’s surface. Winds above a few kilometers can be considered geostrophic – that is they flow in a straight path parallel to the isobars at speeds that can be calculated from the pressure gradient. At the surface, friction acts to slow the movement of air by which it also reduces the Coriolis force which is proportional to wind speed.**
 * Lutgens, Tarbuck, __The Atmosphere__, pgs 168-180 PB**

9. Convergence and divergence: implications on weather both at the surface and aloft
 * When air masses converge aloft, they collide and are driven downward. The subsiding air is compressed and warmed. As the air reaches the surface and spreads out, it causes divergence and high pressure at the surface. Stable conditions and fair weather will exist at the surface. **
 * When air masses diverge aloft, air from the surface rises to fill in the vacated space. The rising air is cooled and decompressed. As it rises, surface air comes in to the region, causing convergence and low pressure at the surface. Unstable conditions and stormy weather will exist at the surface. (Atmosphere. Lutgens/Tarbuck. p. 180) **
 * JL **

10. Local winds (sea breeze vs. land breeze, etc.) Looks good. JL
 * Local winds are mesoscale winds (time frame of minutes to hours and size of 1 – 100km [pg192, The Atmosphere]). **
 * Land and sea breeze – daily temperatures differ over land and sea. Air over land heats up during the day and expands, creating area of low pressure. The cooler high pressure air over the water then flows onto the land. At night, land cools faster creating high pressure over land and the breeze reverses. **
 * Mountain and valley breezes – like land and sea breezes, air along mountain slopes heats more quickly than air over the valley floor. Air flows up the slopes generating a valley breeze. At night it is reversed as the mountain slopes cool quickly and air drains to the valley causing a mountain breeze. **
 * Chinooks (foehns in the Alps) – warm, dry winds that move down the east slopes of the Rockies and Cascades. As air descends the leeward side of the mountains, it is warmed adiabatically. Usually occurs in the winter. **
 * Katabatic (fall) – cold air descending from highlands like the ice sheets of Greenland or Antartica. Air remains colder and denser than the air it displaces, occasionally is channeled in narrow valleys where it can increase in velocity. **
 * Country breeze – light wind blowing into an urban area from the surrounding countryside. Urban areas tend to build up heat during the day. In the evening, this air rises and the air from the country moves into the city. **
 * IB **

11. General circulation of the atmosphere, from pole to pole.
 * A simplified view of global circulation is a three cell circulation model for each hemisphere. Because the circulation patterns between the equator and roughly 30º latitude north and south closely resemble a single cell model developed by George Hadley in 1735, the name Hadley cell is generally applied. According to the three cell model, in each hemisphere, atmospheric circulation cells are located between the equator and 30º latitude, 30º and 60º latitude, and 60º latitude and the pole. The areas of general subsidence in the zone between 20º and 35º are called the horse latitudes. In each hemisphere, the equatorward flow from the horse latitudes forms the reliable trade winds. Convergence of the trade winds from both hemispheres near the equator produces a region of light winds called the doldrums. The circulation between 30º and 60º latitude (north and south) results in the prevailing westerlies. Air that moves equatorward from the poles produces the polar easterlies of both hemispheres. The area where the cold polar easterlies clash with the warm westerly flow of the midlatitudes is referred to as the polar front, an important meteorological region. Lutgens, Tarbuck, __The Atmosphere__, pg 220 PB**


 * I would like to add:**
 * Equatorial low – is co-located where the Doldrums and the ITCZ are between 23.5N and 23.5S.**
 * Subtropical high - Horse Latitudes: Deserts ~30N and South**
 * Trades – blow from NE to SW toward equatorial low (Northern Hemisphere) and SE to NW (Southern Hemisphere). The trades converge into equatorial low.**
 * Westerlies – blow from SW to NE (Northern Hemispehre) and make up the prevailing midlatitude flow toward the toward Subpolar low (30 to 60 degrees).**
 * Subpolar Low: Polar front where cyclogenesis occurs (60 degrees)**
 * polar easterlies – blow NE to SW toward Subpolar low**
 * polar high – 90 degrees**


 * Semi-permanent features:**
 * Winter**
 * –Siberian High over land**
 * –Aleutian, Icelandic Low over water**
 * Summer**
 * –Asian Low over land**
 * –Bermuda, Hawaiian High over water**
 * In January, there is usually a weak subtropical high (Azores High) which tends to be toward the eastern margin of the Atlantic Ocean. The center of the subtropical high in the North Atlantic is positioned close to the NW coast of Africa. There is an intense semi-permanent low-pressure center called the Icelandic low found concentrated above the NW region of Iceland.**
 * In July, the subtropical high (Bermuda High) migrates westward and is more intense than in the winter months. This dominates the summer circulation over the oceans n pump warm moist air onto the continents to the west of the high. Also, the Icelandic Low moves westward and becomes less intense. (p. 201 Lutgens)**
 * JI**

12. Clouds: formation and classification
 * In 1803 Luke Howard presented a classification of clouds into main and secondary types and gave them Latin names. He distinguished three principle cloud forms: **
 * //Stratus// (from Latin stratum = layer) – lying in a sheet level **
 * //Cumulus// (from Latin cumulus = pile) – having flat bases and rounded tops **
 * And being lumpy in appearance **
 * //Cirrus// (from Latin cirrus = hair) – having a fibrous or feathery appearance **


 * A second part of cloud classification is the altitude at which clouds occur. Clouds of similar shapes occur at different levels in the troposphere. Those with the term cirrus or prefix cirro are high clouds. Those with the prefix alto are middle clouds. Names for low clouds lack prefixes. An exception to this is the nimbostratus cloud which is classified as both a middle and low cloud. **


 * The prefix nimbo applies to a cloud which rain is falling. It derives from the Latin for “violent rain” **


 * Cirrus (Ci) - Detached clouds in the form of white, delicate filaments, or white of mostly white patches or narrow bands. These clouds have a fibrous (hairlike) appearance or a silky sheen or both. They are formed entirely of ice particles. **


 * Cirrocumulus (Cc) – Thin, white patch, sheet, or layer of cloud without shading composed of very small elements in the form of grains, ripples, etc, merged or separate, and more or less regularly arranged; most of the elements have an apparent width of less than 1 degree (approximately the width of the little finger a arm’s width). Often called a “Mackerel Sky” these clouds are composed of ice particles. **


 * Cirrostratus (Cs) – Transparent, whitish could veil of fibrous or smooth appearance, totally or partially covering the sky. The ice particles form halos around the sun and moon which usually foretell rain or snow within 24 hours. **


 * Altocumulus (Ac) – White of gray, or both white and gray, patch, sheet, or layer of cloud, generally with shading, composed of laminae, rounded masses, rolls, etc., sometimes partly fibrous or diffuse, and may or may not be merged, most of the regularly arranged small elements usually have an apparent width of between 1 and 5 degrees (approximately 3 finger widths at arm’s length). “Wool pack” clouds that are bumpy looking. **


 * Altostratus (As) – Grayish of bluish cloud sheet or layer of striated, fibrous, or uniform appearance, totally or partly covering the sky, and having parts thin enough to reveal the sun at least vaguely, as through ground glass. Altostratus does no show halo phenomena. Often followed by rain or snow; windy. **


 * Nimbostratus (Ns) – Gray cloud layer, often dark, the appearance of which is rendered diffuse by more or less continually falling rain or snow, which in most cases reaches the ground. These clouds are thick enough throughout to blot out the sun. **


 * Stratocumulus (Sc) – Stratocumulus clouds are rough and bumpy. They are gray or whitish, or both gray and whitish, patch, sheet, or layer of cloud that almost always has dark parts, composed of tessellations, rounded masses, rolls, etc., that are nonfibrous (except virga) and may or may not be merged; most of the regularly arranged small elements have an apparent width of more than 5 degrees. **


 * Stratus (St) – Generally gray cloud layer with a fairly uniform base, which may give drizzle, ice prisms, or snow grains. When the sun is visible through the cloud, its outline is clearly discernible. Stratus does not produce halo phenomena. Sometimes stratus appears in the form of ragged patches. **


 * Cumulus (Cu) – “Fair weather clouds” that are detached clouds, generally dense and with sharp outlines, developing vertically in the form of rising mounds, domes, or towers, of which the bulging upper part often resembles cauliflower. The sunlit parts of these clouds are most brilliantly white; their bases are relatively dark and nearly horizontal. Sometimes cumulus is ragged. **


 * Cumulonimbus (Cb) – Heavy and dense cloud, with a considerable vertical extent, in the form of a mountain or huge towers. At least part of its upper portion is usually smooth, fibrous, or striated and nearly always flattened; this part often spreads out in the shape of an anvil or a vast plume. Under the base of this cloud, which is often very dark, there are frequently low ragged clouds either merged with it or not, and precipitation (rain, hail, and squall winds). Violent vertical currents occur in these clouds. **

**page 65-66 (Climatology third edition 2010) GD**

**Good. Just want to add that stratiform clouds are formed by horizontal lift, and cumuliform clouds are formed by vertical lift. Cirrus are thin/white and made of ice crystals due to low temperatures at high altitudes and small quantities of water vapor.** **Not sure if we need these clouds as well, but mammatus are pouch-like clouds, often associated with stormy weather and cumulonimbus clouds and indicate downdraft action; cap and lenticular (lens-shaped) clouds typically form in mountainous areas by orographic lifting. KMS**

13. Air masses
 * An air mass “is a large body of air usually 1600 km or more across that is characterized by homogeneous physical properties at any given altitude.” When it moves out of its source region, it will carry temperatures and moisture elsewhere, eventually affecting a large portion of a continent.**
 * Air-mass weather is where a region is under the influence of an air mass and will probably experience constant weather conditions for possibly several days as the air mass moves through the area.**
 * Areas where air masses originate are called source regions and the nature of the source region usually determines the characteristics of the air mass. Two criteria for an ideal source region are an extensive and physically uniform area, and the area should be characterized by a general stagnation of atmospheric circulation to allow the air to be in equilibrium with the surface.**


 * Air masses are identified by two letters with reference to latitude/temperature and the nature of the surface in the source region: polar ( P), arctic (A), or tropical (T); m (maritime), c (continental).**
 * The following are possible combinations and where they originate in North America:**
 * cA: continental arctic – Arctic Basin/Greenland**
 * cP: continental polar – Interior Canada and Alaska**
 * cT: continental tropical – southwest US, northern interior Mexico**
 * mT: maritime tropical – Gulf of Mexico, western Atlantic, subtropical Pacific, Caribbean Sea**
 * mP: maritime polar – North Pacific, Northwest Atlantic**
 * pgs. 226-228 (Atmosphere, Tarbuck and Lutgens)**
 * KMS**

14. Types of fronts: precipitation characteristics, appearance on weather maps
 * When a warm or cold front stops moving, it becomes a stationary front. Once this boundary resumes its forward motion, it once again becomes a warm front or cold front. A stationary front is represented by alternating blue and red lines with blue triangles pointing towards the warmer air and red semicircles pointing towards the colder air. A noticeable temperature change and/or shift in wind direction is commonly observed when crossing from one side of a stationary front to the other. Gentle to moderate precipitation is likely and if the front remains over an area for several days, flooding is possible. **

=
**A cold front is defined as the transition zone where a cold air mass is replacing a warmer air mass. Cold fronts generally move from northwest to southeast. The air behind a cold front is noticeably colder and drier than the air ahead of it. Symbolically, a cold front is represented by a solid blue line with triangles along the front pointing towards the warmer air and in the direction of movement. Where cold air meets warm air a steep slope forms as warm air is forced aloft. This usually generates thunderstorms along a narrow band just ahead of the front.** ======

=
**A warm front is defined as the transition zone where a warm air mass is replacing a cold air mass. Warm fronts generally move from southwest to northeast and the air behind a warm front is warmer and more moist than the air ahead of it. When a warm front passes through, the air becomes noticeably warmer and more humid than it was before. Symbolically, a warm front is represented by a solid red line with semicircles pointing towards the colder air and in the direction of movement. As warm air ascends over cold air a shallow slope develops as the warm air cools and condenses. Typically, warm fronts produce light to moderate precipitation over a wide area. During warmer seasons however, unstable air can be forced aloft forming thunderstorms.** ======

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**An occluded front forms when a rapidly moving cold front overtakes a warm front. As the cold air wedges the warm front upward, a new front forms between the advancing cold air and the air over which the warm front is gliding. The weather is typically complex. Precipitation is associated with warm air being forced aloft. When conditions are right, the new front can produce its own precipitation. The most common type of occluded front is a cold-type, where the air behind the cold front is colder than the cooler air it is overtaking. If the air behind the cold front is warmer than the air it is overtaking, a warm-type occluded front can form. The symbol for an occluded front is a purple line with triangles and semi-circles on the same side, pointing in the direction of movement.** ======

=
**A dry line is a boundary that separates a moist air mass from a dry air mass. Sharp changes in dew point temperatures can be observed across a dry line. Dry lines are most commonly found just east of the Rocky Mountains, separating a warm moist air mass to the east from a hot dry air mass to the west. The dry line is an important factor in severe weather frequency in the Great Plains.** ======
 * KMS **

15. The Mid-Latitude cyclone: life cycle, characteristic weather
 * Mid-latitude cyclones are low pressure systems with diameters often exceeding 1000km (600 miles) that travel from west to east across the planet. Lasting from a few days to more than a week, these weather systems have a counterclockwise pattern with a flow inward toward their centers. Most mid latitude cyclones have a cold front and a warm front extending from the central area of low pressure. Surface convergence and upward flow initiate cloud development that frequently produces precipitation. The first encompassing model to consider the development and intensification of a mid latitude cyclone was constructed by a group of Norwegian scientists during WWI. This turning point in atmospheric science became known as the polar front theory also known as the Norwegian cyclone model. In this model mid latitude cyclones develop in conjunction with the polar front, which separates the cold polar air from the warm subtropical air. It is along frontal zones where cold, equatorward moving air collides with warm poleward moving air that most middle latitude cyclones form. Lutgens, Tarbuck, __The Atmosphere__, pg 243-244 PB**


 * Would add:**
 * Six stages: **
 * 1) **__ Stationary front __**** develops; cold polar easterlies running along warm westerly air **
 * 2) **__ Wave __**** develops; frontal surface may take on wave shape **
 * 3) **__ Cyclonic circulation __**** established; warm air moves poleward, cold air equatorward **
 * 4) **__ Occlusion __**** begins- once cyclonic circulation develops, general convergence produces lifting and warm air overtakes cold air (occlusion) **
 * 5) **__ Occluded front __**** develops- cold front advances faster than warm front and will completely overtake it,; storm intensifies (winds increase, heavy precipitation) **
 * 6) **__ Cyclone dissipates __**** - once horizontal temp differences have been eliminated, energy source is exhausted; organized counterclockwise flow ceases **
 * (p.262 The Atmosphere)MarkW**

16. Temperature controls (land vs. water, etc.) Looks good. JL
 * 1) **Differential heating of land and water – land heats up and cools more rapidly than water due to differences in specific heat.**
 * 2) **Ocean currents – the transfer of heat by winds and ocean currents equalizes the latitudinal energy imbalances that happen in the northern and equatorial regions on earth.**
 * 3) **Altitude – higher in elevation means a drop in average temperature, there is an approximate drop of 6.5°C/km in the troposphere.**
 * 4) **Geographic position – an example is a leeward vs a windward coastal city. The windward town experiences the moderating effect of the ocean, while the leeward side would experience temperature differences more similar to those in a continental region.**
 * 5) **Cloud cover & albedo – during the day the clouds reflect some incoming radiation keeping our temperatures cooler, at night the clouds absorb outgoing energy from the surface of the earth and emit some of it back to the surface. The amount of radiation reflected during the day deals with how thick the clouds, the thicker the cloud the higher the albedo**
 * (The Atmosphere pp. 69-76) EM **
 * I would like to add the most important temperature control - latitude. It determines the amount of solar radiation a place receives over the course of the year. **
 * DS **

17. Radiation Laws and the role of temperature
 * 1) ** All objects continually emit radiant energy over a range of wavelengths. //Even though the sun is the ultimate source of radiant energy, all objects continually radiate energy over a range of wavelengths. The Sun and other hot objects emit mostly shortwave radiation. The Earth and other objects at everyday temperatures emit mostly longwave radiation.// **
 * 2) ** Hotter objects radiate more total energy per unit area than do colder objects. //This is known as Stefan-Boltzman law.// **
 * 3) ** The hotter the radiating body, the shorter is the wavelength of maximum radiation. //This is known as Wien’s displacement law// **
 * 4) ** Objects that are good absorbers of radiation are also good emitters. Perfect absorbers and emitters are called blackbodies. Earth’s surface and the sun approach being black bodies because they absorb and radiate with nearly 100 percent efficiency. Our atmosphere is a selective absorber and emitter of radiation. **

18. Things that happen to radiation in the atmosphere (scattering, etc.), albedo
 * GD (page 47 The Atmosphere 10th Edition) **
 * Looks good - EM **
 * The average distribution of incoming solar radiation is as follows: **


 * 5% is backscattered to space by the atmosphere. **
 * 20% is reflected by clouds **
 * 5% is reflected from land and sea surface **


 * This means that a total of 30% of insolation is lost to space by reflection and scattering. **


 * 20% or radiation is absorbed by the atmosphere and clouds. **


 * 50% of direct and diffused radiation is absorbed by the land and sea **


 * The fraction of radiation that is reflected by a surface is called its albedo. Fresh snow and thick clouds have a high albedo (good reflectors), whereas asphalt has a low albedo. **


 * Reflection is the process where light bounces back from an object at the same angle and same intensity as when it encounters the surface. **


 * Scattering produces a larger number of weaker rays traveling in different directions. **

19. Calculation of noon solar angle for a given location and time.
 * GD (page 49 The Atmosphere 10th edition) **
 * To find the noon sun angle you need to know: **
 * The latitude of your location **
 * The declination of the sun on the date of observation **


 * Declination – The latitude at which the sun is directly overhead at solar noon **


 * Example: **
 * Calculate noon sun angle at 40N on June 22 **


 * We know that June 22 is the summer solstice and the declination is 23.5 degrees N. **


 * Find the difference between the latitude of interested location and declination **
 * Latitude of location – Declination = Zenith angle **


 * Zenith angle – The angle between a point directly overhead and the sun at solar noon **


 * 40 – 23.5 = 16.5 **


 * Zenith = 16.5 **


 * 90 – 16.5 = 73.5 degrees **


 * 73.5 degrees is the noon solar angle for 40 N **


 * Example: **
 * Calculate noon solar angle at 43S on March 22 **


 * March 22 is the Vernal Equinox the sun is directly overhead at the equator **


 * 43 – 0 = 43 **


 * 90 – 43 = 47 degrees **


 * Example: **
 * Calculate noon solar angle at 64N on December 22 **


 * December 22 is the winter solstice the sun is directly overhead at 23.5 S **


 * Since this is below the equator we will treat this as -23.5 **


 * 64 – (-23.5) = 87.5 **


 * 90 – 87.5 = 2.5 degrees **


 * If you need to find the noon solar angle for any day other than a solstice or equinox you will need to use an analemma (Page 43 Atmosphere 10th Edition), looks sort of like a bottom heavy figure 8, to determine the declination **

GD (page 13 Weather and Climate lab book sixth edition) Looks good. JL Good MarkW