Atmospheric Stability: 1. How would one normally obtain the environmental lapse rate? To normally obtain the environmental lapse rate, one must determine the rate at which the air temperature alters with elevation. Also, the stability or instability of the air is associated with the environmental lapse rate. 2. Why are the moist and dry adiabatic rates of cooling different? The moist adiabatic rate of cooling is not constant, unlike the dry adiabatic rate of cooling. Instead, it varies greatly with temperature and moisture content. Also, additional condensation in both warm and saturated air liberates more latent heat and as a result, the moist adiabatic rate of cooling is less than the dry adiabatic rate of cooling when the air is warm. However, when the rising air is cool both the moist adiabatic and the dry adiabatic rates of cooling are similar. 3. How can the atmosphere be made more stable? More unstable? The atmosphere can be made more stable by cooling the surface air, warming the air aloft, or by causing sinking air over a large area. The atmosphere can be made more unstable by warming the surface air, cooling the air aloft, or by lifting a layer of air. 4. If the atmosphere is conditionally unstable, what does this mean? What condition is necessary to bring on instability? If the atmosphere is conditionally unstable, the unsaturated air can be lifted to a point where condensation happens and the rising air becomes warmer than that around it. This occurs when the environmental lapse rate lies between the moist adiabatic rate and the dry adiabatic rate. 5. Explain why an inversion represents an extremely stable atmosphere. An inversion represents an extremely stable atmosphere because they act as a lid on vertical air motion. As is noted in the text book, when an inversion exists near the ground, stratus, fog, haze, and pollutants are all kept close to the surface. 6. What type of clouds would you most likely expect to see in a stable atmosphere? In an unstable atmosphere? One should expect to see cirrostratus, altostratus, nimbostratus, or stratus clouds in a stable atmosphere. One should expect to see cumuliform clouds in an unstable atmosphere. 7. There are usually large spaces of blue sky between cumulus clouds. Explain why this is so. There are usually large spaces of blue sky between cumulous clouds because subsiding air prevents the growth of thermals beneath it. As a result, cumulus clouds or visible thermals have large spaces of blue sky between them. 8. Why do most thunderstorms have flat tops? Most thunderstorms have flat tops because as thunderstorm clouds reach the stable part of the atmosphere, the stable atmosphere resists verticle motion. Resultantly, the thunderstorm clouds spread laterally (beneath the stable layer) and flat tops form. General Circulation: 1. Using a diagram, explain how a thermal circulation develops. Two poles: North (cold/H) and south (warm/L); air moves from H to L, up to H across to L and back down to H (at cold north). 2. Why does a sea breeze blow from sea to land and a land breeze from land to sea? sea breeze: land heats more quickly than the adjacent water during the day, and the intensive heating of the air above produces a shallow thermal low. The air over the water remains cooler than the air over the land, hence a shallow thermal high exists above the water -->blows from sea toward the land; Land breeze: higher surface pressure over the land at night, the wind reverses itself and flows from the land toward the water. 3. Most of the United States is located in what wind belt? Westerlies 4. Explain how and why the average surface pressure features shift from summer to winter. As summer approaches, the land warms and the cold, shallow highs disappear; areas of surface low pressure replace areas of high pressure (thermal lows); warm thermal lows are found over the desert southwest of the US, over the plateau of Iran and north of India; winter: strong subpolar lows, subtropical highs dominant; shift toward the north in July and toward the south in January. 5. How does the polar front influence the development of the polar-front jet stream? The north-south temperature contrast along the polar front is strongest in winter and weakest in summer, the polar jet stream shows seasonal variations. 6. Why is the polar jet stream more strongly developed in winter? Speed of jet stream is a function of temperature. Greater temperature gradient in winter, therefore, faster jet stream in winter. 7. Explain the relationship between the general circulation of air and the circulation of ocean currents. As the wind blows over the oceans, it causes the surface water to drift along with it. The moving water piles up, creating pressure differences within the water itself --> further motion several hundreds of meters down into the water; general wind flow around the globe starts the major surface ocean currents moving. El Nino/ El Nina: 1. Describe how the winds along the west coast of North America produce upwelling. wind flows parallel to the coastline --> coriolis force pulls it to the right (away from shore) -->water beneath the surface also moves --> shallow layer of surface water moves at right angles to the surface winds and heads seaward --> cold, nutrient-rich water from below rises (upwells) and replace it 2. (a) What is a major El Niņo event? (b) What happens to the surface pressure at opposite ends of the Pacific Ocean during the Southern Oscillation? (c) Describe how an ENSO event may influence the weather in different parts of the world. (a) El Niņo: warm current of nutrient-poor tropical water often moves southward, replacing the cold, nutrient-rich surface water; large numbers of fish and marine plants die; (b) Air pressure rises over the region of the western Pacific and falls over the eastern Pacific; change in pressure weakens the trades, and during strong pressure reversals, east winds are replaced by west winds; (c) Eastern equatorial Pacific Ocean becomes as much as 6 degrees C warmer; warm tropical water fuels the atmosphere with additional warmth and moisture, which the atmosphere turns into additional storminess and rainfall. 3. What are the conditions over the tropical eastern and central Pacific Ocean during the phenomenon known as La Niņa? Cold surface water moves over the central and easter Pacific, and the warm water and rainy weather is confined mainly to the western tropical Pacific; opposite of El Nino 4. Describe the ocean surface temperatures associated with the Pacific Decadal Oscillation. Long-term Pacific Ocean temperature fluctuation; the ocean surface temperature reverses every 20 to 30 years; a warm phase and a cool phase; warm phase: warm surface water exists along the west coast of North America, cooler surface water over central North Pacific; cool phase: cooler-than-average surface water along the west coast of North America, warmer-than-normal surface water extending from Japan into the central North Pacific Hurricanes: 1. What is a tropical (easterly) wave? How do these waves generally move in the Northern Hemisphere? Are showers found on the eastern or western side of the wave? Also known as African Easterly Waves which are elongated areas of relatively low air pressure. They move from the east to west in the northern hemisphere. Showers are found on the western side of the wave. A tropical wave is normally preceded by an area of sinking, intensely dry air, oriented as a northeast wind. With the passage of the trough line, the wind veers to the southeast, the humidity abruptly rises, and the atmosphere destabilizes, producing widespread showers and thunderstorms, occasionally severe. As the wave moves off westward, the showers gradually diminish. 2. Why are streamlines, rather than isobars, used on surface weather maps in the tropics? Isobars are usually drawn on weather maps to illustrate ridges and troughs. However, there is very little change in atmospheric pressure in the tropics where hurricanes form. Therefore, streamlines or lines indicating wind direction are used. 3. What is the name given to a hurricane-like storm that forms over the western North Pacific Ocean? Typhoons 4. Why are skies often clear or partly cloudy in a hurricane's eye? The eye of a hurricane is a low-pressure area. Air from outside the hurricane tries to move into the eye to equalize the pressure. The air does not go in a straight line towards the eye. It flows in a curve because of the Coriolis force. This curve becomes even greater near the eye, and eventually the air ends up blowing in a circle around the eye. Most of the air never reaches the eye itself, but instead blows in this ring around the eye called the "eyewall". A lot of the air then flows upward in the eyewall, and exits the storm at the top Since the winds end up spinning in a ring around the eye, there isn't enough left to blow in the eye itself, and the eye is relatively calm. 5. What conditions at the surface and aloft are necessary for hurricane development? Hurricanes are born as a result of very special atmospheric conditions. Necessary elements include water temperatures of at least 80 F, high humidity over a vast area, cold air aloft and light winds. A warm layer of ocean water to depths of 200 meters (600 feet) must also exist. 6. (a) Describe the formation of a hurricane using the organized convection theory. (b) In this theory, where do hurricanes derive their energy? In the organized convection theory the energy source that drives the hurricane is the release of latent heat. As a tropical wave moves of the coast of Africa, thunderstorms that accompany it may begin to cluster. The thunderstorms, if the conditions aloft are right, will begin to cluster and rotate counterclockwise. As they cluster they begin to warm each other form the release of latent heat, and thus the air below them, which causes more evaporation. The warm evaporated water that condenses in the thunderstorm releases latent heat, and the process becomes a positive feed back. Once these spinning thunderstoms and clouds reach a sustained surface wind speed of 74 mph the system becomes a hurricane. As vast quantities of latent heat are released in thunderstorms near the eye, surface pressures lower, inducing stronger winds, more air rising, and the development of even stronger thunderstorms (positive feedback). 7. (a) Hurricanes are sometimes described as a heat engine. According to this model, what is the 'fuel' that drives the hurricane? (b) In this model, what determines the maximum strength (the highest winds) that the storm can achieve? The warm ocean water is the fuel that drives the hurricane 'heat engine'. The feature that determines the maximum strength of a 'heat engine' hurricane is the difference between the temperature of the surface of the ocean and the top of the clouds at the tropopause. This difference in temperature causes a very steep horizontal pressure gradient which causes the high winds to form and spiral outward. The greater the temperature gradient between the top of the clouds and the ocean surface the steeper the pressure gradient, thus the stronger the hurricane (highest winds). 8. If a hurricane is moving westward at 10 knots, will the strongest winds be on its northern or southern side? Explain. If the same hurricane turns northward, will the strongest winds be on its eastern or western side? The strongest winds would be on the north side. It would be on its north side because you would add the vector quantity of 10 knots to the winds of the hurricane; if the hurricane is indeed moving westward. The south side of a westward bound hurricane would have the 10 knot vector quantity subtracted from the wind. If the hurricane turned northward and continued to move at 10 knots the area of highest wind would be on the east side for the same reason that a westward moving hurricane had the highest wind on the north side. 9. What factors tend to weaken hurricanes? Hurricanes tend to weaken when they; move over land, move over colder water, or when the surface inflow of air exceeds the upper-level outflow of air. 10. Distinguish among a tropical disturbance, a tropical depression, a tropical storm, and a hurricane. A tropical disturbance is an organized mass of thunderstoms that has a slight cyclonic wind circulation of less than 20 knots. A tropical depression is an organized system of thunderstorms and clouds that have a defined surface circulation and maximum sustained winds of less then 33 knots. A tropical storm is an oraganized system of strong thunderstorms with a defined surface rotation and maximum sustained winds between 34 - 63 knots (or 39-73 mph). Additionally, at this stage the distinctive cyclonic shape begins to form, but there is no eye yet. A hurricane or typhoon is of sustained winds of at least 64 knots or 74 mph. A hurricane of this intensity and greater is likely to develop an eye. 11. In what ways is a hurricane different from a mid-latitude cyclone? In what ways are these two systems similar? Hurricanes and mid-latitude cyclones both can have severe thunderstorms, and tornados. They also both rotate in a counterclockwise manner (in the northern hemisphere). They also begin to die when the inflow of surface air exceeds the upper-level outflow of air. A hurricane and mid-latitude cyclone differ in that a hurricane typically never has lightning (except for Katrina) where a mid-level cyclone can have thunderstorms with lightning. Hurricanes have the potential to produce higher sustained winds then mid-latitude cyclones. Mid-latitude cyclones can survive over land far longer then a hurricane, because the main source of energy of a hurricane is warm water and once it comes on land it instantly begins to die due to the lack of warm water. A mid-latitude cyclone in contrast draws most of its energy from pre-existing horizontal temperature gradients in the atmosphere. 12. Why do most hurricanes move westward over tropical waters? Hurricanes generally move westward over tropical waters because the tropics are located in the easterlies, where the wind blows from the east to the west, pushing the hurricane westward. 13. If the high winds of a hurricane are not responsible for inflicting the most damage, what is? The biggest killer of hurricanes is the storm surge, or the pushing of the ocean water onto the land from the approaching hurricane. Storm surges can range from a couple feet to a devastating 25-30 feet, which was the case for Hurricane Katrina. The two most deadliest natural disasters in the US have been resulted form the storm surges of hurricanes. The deadliest took place in Galveston, Texas in 1900 where the storm surge killed 6,000-12,000 people. The second deadliest natural disaster took place in 1928 at Lake Okeechobee, FL, when a hurricane swept across Florida and created a storm surge on the interior lake causing a massive storm surge killing 2,500. Weather Maps: 1. What are isobars? Isobars are solid lines on isobaric maps that link areas of common air pressure readings, in millibars, together so scientists can gain a better understanding of where high or low pressure systems may be located. 2. On an upper-level map, is cold air aloft generally associated with low or high pressure? What about warm air aloft? On an upper-level map, cold air aloft is generally associated with a low pressure system while warm air aloft is generally associated with a high pressure system.
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