Lecture 13: WindsRossby wavesRossby waves are: great waving undulations within: the westerly windsThey occur at the: polar frontThe Rossby waves bring tongues of cold air southward, with warmer tropical air moving northward.There are three stages to Rossby wave formation.1. Upper-air circulation begins to gently undulate2. Rossby waves begin to form, with cyclonic and anticyclonic curvature.3. Strong development produces cells of cold and warm air – high pressure ridges and low-pressuretroughs – so the waves are very pronounced.Jet streams Jet streams are irregular, concentrated bands of windThey are normally 100-300 miles wide and 3000-7000 feet thick. They have core speeds that can exceed 190 mph.They tend to weaken during a hemisphere’s summer and strengthen during the winterThis is because the differences in temperature – and therefore air pressure – are much less throughout a hemisphere in summer than in winter.There are two jet streams: the polar jet stream and the subtropical jet stream. The polar jet stream meanders between 30 and 70 degrees latitude.It can migrate as far south as Texas, steering colder air masses into North America, and influencing the path of storms.It demarcates the Polar Front. It also constitutes the Rossby Waves.The subtropical jet stream occurs near the boundary between tropical and midlatitude air. It meanders from 20 to 50 degrees latitude.T/F: Rossby waves are energy cycles associated with the Hadley cellsT/F Sometimes Rossby waves are gently curving (undulating), sometimes they are very pronounced.What are true about Jet Streams?A. They weaken in winter and strengthen in summerB. They are irregular, concentrated bands of wind.C. There are three main jet streams: polar, sub-tropical and mid-latitudeD. The farthest south the polar jet stream migrates is WisconsinE. They are always very close to 60⁰ N or S to the equator F. The Polar jet varies from roughly 30 ⁰ to 70 ⁰ N latitude; it can go as far south as TexasLocal Winds There are 5 types of local winds:1. Land and sea breezes2. Mountain and valley breezes3. Chinook4. Santa Ana5. Katabatic1. Land and Sea Breezes: occur on coastlines.They are caused by the differential heating_ of land and water.During the day:Land accumulates heat energy faster and is warmer than the water during the day.Low pressure, warm air rises from the land.The cooler, higher pressure air from the water flows toward the low-pressure air over the land.So during the day there is an on-shore_ breeze.During the night:The land cools more quickly than the water, and the air becomes denser, as it is no longer warm and rising so much. The water now becomes warmer than the land, and so the air above the water is of a _lower pressure than the air above the land.The _higher pressure air of the land flows toward the lower pressure air of the water.So at night there is an off-shore breeze.2. Mountain and Valley Breezes: occur when mountain air cools rapidly at night and valley air gains heat during the day. Warm air, being of low pressure, heats up in the valleys and rises upslope during the day, especially in the afternoon. At night, air cools on the mountain tops, and the cool air subsides downslope_ into the valleys. 3. Chinook, or foehn winds: warm, down slope air flows that occur on the leeward side of mountains. As the air flows down the mountain, it compresses and warms up . They can bring a 36⁰F increase in temperature, and very dry conditions. 4. Santa Ana winds are generated when high pressure (from the subtropical high-pressure cells) builds over the Great Basin of the western United States. A strong, dry wind flows out across the desert to southern California coastal areas. Compression heats the air as it flows from higher to lower elevation. Also, the canyons and valleys in California constrict the wind, making it blow faster. This brings dust, dryness, heat, and dangerous fires to places like Malibu, Santa Barbara, LA and elsewhere. People in Malibu call the Santa Ana winds The Devil Winds5. Katabatic winds are: Cold gravity drainage winds that come down from high mountains, and are oflarger regional scale and stronger than mountain-valley breezes.The katabatic winds in France are called the _Mistral. Some winter days can be surprisingly cold in southern France because of this wind. The katabatic winds are called the Bora in the Adriatic Sea and inthe Rockies.Matching: 1. Cold gravity drainage winds that come down from high mountains B2. These winds are generated when high pressure builds over the Great Basin of the western United States. A strong, dry wind flows out across the desert to southern California coastal areas. Compression heats the air as it flows from higher to lower elevation D3. These winds are formed when warm, downslope air flows down the leeward side of mountains. As the air flows down the mountain, it compresses and warms up. A ( true for Santa Ana too)4. Warm air (being of low pressure) heats up in the valleys and rises upslope during the day, especially in the afternoon. E5. At night, air cools on the mountain tops quickly, and the cool air subsides downslope into the valleys E6. They are caused by the differential heating of land and water.CA. Chinook, or Foen windsB. Katabatic windsC. Land-Sea breezesD. Santa Ana windsE. Mountain-Valley Breezes On-shore breezes occur when:A. the land is warm and the ocean is coolerB. The ocean is warm and the land is coolT/F Breezes move up the mountain at night, and down the mountain during the dayT/F Katabatic winds are those with high kinetic energy.Which two winds are warm due to compressing air?A. Katabatic B. Santa AnaC. ChinookD. On-shoreT/F Chinooks are cold drainage winds.Monsoonal Winds Monsoon is defined as: an annual cycle of dryness and wetness, with seasonally shifting winds produced by changing atmospheric pressure systemsWhile it occurs in milder form in a number of places, it is especially prominent around the Asian landmass, which we will focus upon. The word “monsoon” comes from the Arabic word mausim meaning season.Monsoons result from the huge pressure differences that arise over land and sea around the Asian landmass during the course of the year. They act under the same principles – but on a much larger scale – as the land-sea breezes.In the winter, it gets very cold in the interior of the continent, and a huge, intense high pressure cell builds up.