Meteorology: Chpater 7
In many places, sea breezes influence the amount of cloud cover and rainfall. The Florida peninsula experiences increased summer precipitation partyly because of convergence associated with sea breezes from both the Atlantic and Gulf coasts. In midsummer the convective lifting associated with a sea breeze can lead to extensive thunderstorm activity over the Florida peninsula.
A daily wind similar to land and sea breezes occur in mountainous regions. During the day, air along mountain slopes is heated more intensely than air at the same elevation occur the valley floor. The armer air glides up the mountain slope and generates a valley breeze. Valley breezes can often be indentified by the cummulus clouds that develop over adjacent mountain peaks.
What are subtropical jet streams?
A semipermanent jet located about 30 degree latitude in both hemispheres. -At an alitude of about 13 kilometers, the subtropical jet strean is mainly a wintertime phenomenon. Somewhat slower than the polar jet, this west-to-east current is centered on the poleward side of the Hadley cells. -They are often charcterized by a band of middle to high clouds that don't usually result in stormy weather. -The jet can contribute to major winter snowstorms over the midlatitudes in the Northern Hemisphere, when it interacts with the polar jets.
What is the Siberian high?
A very strong gigh pressure center positioned over the frozen landscape of northern Asia. It is the most prominent feature on the January pressure map. -A weaker polar high is located over the chilled North American continent. -These cold anticyclones consist of very dense ait that accounts for the significant weight of these air columns. -The subsidence within these air columns results in clear skies and divergent surface flow.
During the transition from autumn to winter, the Arctic highs strengthen over the continents, while the subtropical highs situated over the oceans become weaker. The Bermuda/Azores high, which is found near the island of Bermuda in July migrates eastward toward Azores which is west of Portugal, in the winter.
Aleutian low and the Icelandic low are two strong semipermanent low-pressure centers which are situated over the North Pacific and North Atlantic, repectively. These are hybrid pressure cells (composits of numerous cyclonic storms that traverse these regions). So many midlatitude cyclones occur during the winter that these regions almost always experience low pressure. As a result, the areas surrounding the Aleutian and Icelandic lows are frequently cloudy and receive abundant precipitation.
This region of ascending moist air is marked by abundant precipiation. Because the trade winds converge, it is also called the intertropical convergence zone (ITCZ). It is visible as aband of clouds near the equator. On either side of the equator at about 20 and 35 degree latitude, where the westerlies and trade winds originate and go their seperate ways, are the high pressure zones known as the subtropical highs. In these zones, a subsiding air column produces weather that is normally warm and dry.
Another low pressure belt is situated at about 50 and 60 degrees latitude, in a position corresponding to the polar front. The polar easterlies and the westerlies clash in the low-presure convergence zone know as the subpolar low. This zone is responsible for much of the stormy weather in the middle latitudes. Near the Earh's poles are the polar highs, from which the polar easterlies originate. The polar highs result from surface cooling. Because air near the oles is cold and dense, it exerts higher than average surface pressure.
What are the katabatic winds?
Areas adjacent to highlands experience these fall winds which originate when cold, dense air situated over a highland area begin to to move. -Gravity causes the cold air to cascade over the rim of a highland like a waterfall. -Although the air is heated adiabatically, the initial temperatures are so low that the wind arrives in the lowlands still colder and denser than the air it displaces. -As this frigid air descends, it occasionally is channeled into narrow valleys, where it acquires velocities capable of significant destruction.
When the subtropical jet sweeps northward in the winter, it may bring warm, humid conditions to the Gulf states, particularly southern Florida. There is no strong temperature contrast in the subtropics. Instead, the subtropical jet is mainly a consequence of Earth's rotation, primarily because of the fact that Earth rotates faster at the equator than places at higher latitudes.
As the air moves poleward as part of the upper Hadley circulation, it conserves its rotaional velocity, called angular momentum, such that it moves faster than Earth's surface. As a result, the subtropical jet is created as air aloft moves toward the poles, and the Coriolis force turns these accelerating winds to the right until finally, at about 30 degree latitude, they are moving eastward. The resulting fast-moving stream of air, traveling from west to east, is known as the subpolar jet stream.
Upwelling, the rising of cold water from deeper layers to replace warmer surface water, is a common wind-induced vertical movement. It is most characteristic along the eastern shores of the global oceans, most notably along the coasts of California, Peru, and West Africa. As the currents in these locations move equatorward, the Coriolis force causes the surface water to turn away from the shore.
As the surface layer moves away from the coast, it is replaced by nutrient-filled water that "up-wells" from below the surface. Thsi water is coolor than what replaced it before which is favorable for plant growth and marine life.
Because the position of the polar front migrates freely between 30 and 70 degrees latitude, most midlatitude areas receive ample precipiation throughout the year. The polar regions are dominated by high pressure and cold air that holds little moisture. Annually, these regions experience only meager precipitation.
Because Earth's susrafce is not uniform, the only true zonal distribution of pressure exists along subpolar low in the Southern Hemisshere, where the ocean is continuous. The equatorial low is also continuous. At other latitudes, particularly in the Northern Hemisphere, the zonal pattern is replaced by semipermanent cells of high and low pressure. They are reffered to as semipermanent because they move and vary in intensity with the seasons.
This seesaw pattern of atmospheric pressure between the eastern and western pacific is called the Southern Oseillation. Together, El Nino and the Southern Oscillation are called ENSO. The link between the weather occuring in widely seperated regions of the globe are called a teleconnection. There appears to be a teleconnection between as trong El Nino and a weak Asian monsoon
Because seas-surface temperatures are often predicable months in advance, understanding teleconnection patterns aloows meteorologists to make climatic predications for distant locations. National Weather Service predictions for periods from 1 month to 13 months into the future are called climate outlooks.
Near the equator, where trade winds converge, lies the equatorial low (ITCZ), which produces abundant precipitation in all seasons. At about 30 degrees latitude in each hemisphere, we find the two subtropical high pressure belts. In these regions, subsidence sontributes to dry conditions throughout the year. Because these pressure systems migrate seasonally with the Sun's vertical rays, the regions between the equalorial low and subtropical highs receive most of their precipiation in the summer, when they are under the influence of the poleward-moving ITCZ.
By contrast, in the winter they experience a dry season caused by the subtropical high moving equatorward. The midlatitudes recieve most of their precipiation from traveling cyclonic storms. This region is the site of the polar front, the convergence zone between cold polar air, and the warm westerlies.
During the summer months, the subtropical high over the North Atlantic migrates westward and becomes stronger than during the winter months. These strong high-pressure centers dominate the summer circulation over the oceans and pump warm moist air toward the continents that lie to the west. This results in an increase over eastern North America America.
Drier regions tend to be located near the semipermanent subtropical highs and the polar highs. Wetter regions are found near the semipermanent tropical low (ITCZ) and the subpolar lows. Because cold air has a lower capacity for moisture than warm air, we would expenct a latitudinal variation in precipiation with low latitudes (warm regions) recieving the greatest amounts of precipitation and high latitudes (cold regions) receiveing the least.
What is a chinook?
Dry wind that flows down the leewrd side of mountain slopes in the U.S. and Canada. -As the air descends the leeward slopes of the mountains, it is heated adiabatically (by compression). -Because condensation may have occured as the air ascended the windward side of the mountain, releasing latent heat, the air descending the leeward side is iften much warmer and drier than at similar elevations on the windward side. -Similar winds in the Alps are called foehns.
A La Nina event is associated with colder than normal seas surface tmeperatures in the central and eastern equatorial Pacific. The atmospheric circulation is dominated by stronger than average trade winds. These wind systems generate a strong equatorial current tah flows westward away from South America toward Indonesia and Australia. This circulation pattern associated with low pressure can result in flooding in northeastern Australia and Indonesia, whereas drier than normal conditions occur along the coastal areas of western South America.
During La Nina, the cold ocean current that flows equatorward along the coast of Chile and Peru intensifies. This surface current, called the Peru Current, encourages upwelling. Thus La Nina has become known as "gift giver" because th nutrients carried upward are a boon to marine life, making fishing particularly good duing these periods of strong upwelling.
Fisherman from Ecuador and Peru were the first to recognize a graduale warming of waters in the eastern Pacific in December or January. Bceuase the warming usually occured near the Christmas season, the event was named El Nino (Christ child). These periods of abnormal sea-surface warming occur at irregular inervals of 2 or 7 years and usually persist for spans of 9 months to 2 years. El Nini is noted for its potentially catastrophic impact on the weather and economics of Peru, Chile, Indonesia, and Australia.
During normal conditions, there is ahigh pressure off the coast of equatorial South America west of Ecuador. This high is associated with sinking air and dry consitions, as well as upwilling of nutrient-rich water. Strong trade winds blow westward from this equatorial high pressure zone toward an area of low pressure located in the western Pacific.
Hurricanes often move from east to west or northwest. Once hurricanes move into the belt of the westerlies, they tend to change course and move in a northeasterly direction. When we examine a hurricane more closely by flying an airplane through it, some of the small-scale aspects of the storm become noticable. As the plane approaches the outer edge of the system, it is evident that the large rotating cloud consists of many individual cumulonimbus towers (thunderstorms).
Each of these cumulonimbus clouds lasts for afew hours, and they must be continually replaced by new ones for the hurricane to persist. During the flight, we also realize that the individual thunderstorms are made up of sammler scale turbelences.
In 2010 to 2011, La Nina contributed to a deluge in Australia, resulting in extensive flooding. La Nina impact is more frequent hurricane activity in the Atlantic. A recent study concluded that the cost of hurricane damages in the U.S. is 20 times greater in La Nina years than in El Nino years.
El Nino and La Nina events are strongly related to changes in the glibal pressure patterns. Each time an El Nino occurs, the atmosphere pressure drops over large portions of the eastern Pacific and rises in the tropical portions of the western Pacific.
What is the single-cell model?
George Hadley in 1735 proposed that the large temperature contrast between poles and the equator create a large convection cell in both the Norther and Southern Hemispheres. -In Hadley's model, warm equatorial air rises until it reaches the tropopause, where it spreads towards the poles. Eventually, this upper-level flow reaches the poles, where cooling causes it to sink and spread out at the surface as equatorward moving winds. -As this cold polar air approaches the equator, it is reheated and rises again. Thus the circulation has upper-level air flowing poleward and surace air moving equatorward. Hadley's model does not take into account Earth's rotation. -Our knowledge of global winds comes from patterns of pressure and winds observed worldwide and theoretical studies of fluid motion.
What are jet streams?
High speed inds within the westerly flow aloft that typically meander for a few thousand kilometers. -Occur near the top of the troposphere and have widths that vary from less than 100 kilometers to over 500 kilometers. -Their existence was first dramatically illustrated during WWII, when American bombers heading westward toward Japanese occupied islands sometimes encountered unusually strong headwinds. -Modern commercial aircraft pilots use the strong flow within jet streams to increase their speed when making eastward flights around the globe. They avoid these currents on westward flights.
These large temperature contrasts occur along narrow, sowhat linear zones called fronts. The most prevalent jet stream occurs along amajor frontal zone called the polar front and is appropriately named the polar jet streams or polar jet. In the winter, this is usually found in the middle latitudes. On average, the polar jet travels at 125 kilometers per hour int he winter and roughly half that speed in the summer.
In sync with the zone of maximum solar heating, the jet moves northward during the summer and southward in winter. During the coldest winter months, the polar jet stream may extend as far south as Florida. With the coming of spring, the zone of maximum solar heating and therefore the jet, begins a gradual northward migration. By midsummer, its average postion is near the Canadian border.
What is the three-cell circulation model?
In the 1920s, a new model had finally incorporated Earh's rotation was proposed. Although this model has been modified to fit upper-air observations, it remains a useful tool for examining global circulation. -Hadley Cell-In the zones between the equator and roughly 30 degree latitude north and south, the circulation closely resembles the convection model proposed by Hadly. -Ferrel Cell-The circulation between 30 degrees and 60 degress latitude was proposed by William Ferrel to account for the westerly surface winds in the middle latitudes. Prevailing westerly winds are more sporadic and less reliable than the trade winds for sail power. It is the migration of cyclones and anticylcones across midlatitudes that disrupt the general westerly flow at the surface. -Polar Cell-The circulation is driven by subsidence near the poles that produces a surface flow that moves equatorward, called the polar easterlies in both hemispheres. As these cold polar winds move equatorward, they eventually encounter the warmer westerly flow of the midlatitudes. The region where the flow of the cold air clashes with warm air has been called the polar front.
With such variations in wind direction of westerlies, why are the given that term?
It is an attempt to simplify descriptions of the atmosphere circulation by sorting out events according to size and the time frame in which the wind systems occur. -Motion in the atmosphere vary in size from the tiniest wind gusts to wind systems that encircle the globe.
Most local winds are linked to temperature and pressure differences that result from variations in topography or in local surface conditions. Local winds are named for the direction from which they blow t the surface (a sea breeze blows from the seas toward the land).
Land and sea breezes occur in coastal locations in the tropics throughout the year as well as in the midlatitudes during the summer months. These local winds arise from differential heating between a large body of water and adjacent land.
What are monsoons?
Large seasonal changes in Earh's global circulation. -It does not necessarily mean a "rainy season", rather it refers to a particular wind system that reverses its direction twice each year. -Winter is associated with winds that blow predominantly off the continents called the winter monsoon. -In summer, warm moisture-laden air blows from the sea toward the land. Thus the summer monssons is usually associated with abundant precipiation over affected land areas.
These breezes may account for late-afternoon thundershowers that occur on warm summer days. After sunset, the pattern is reversed, rapid heat is loss along the mountain slopescools the air, which drains in ot the valley and causes a mountain breeze. Similar cool air drainage can occur in hilly regions with modest slopes. The result is that the coldest pockets of air are usually found in the lowest spots.
Like many other winds, mountain and valley breezes vary by season. Valley breezes are most common during warm seasons, when solar heating is most intense, whereas mountain breezes tend to occur more frequently during cold seasons.
What are mesoscale winds?
Middle sized winds that last for a few minutes to several hours. -They are often less than 100 kilometers across, but can be up to 1000 kilomaters wide. -They include strong updrafts and downdrafts and are referred to as local winds. -Some mesoscale winds have a strong vertical component, which means that the strong downdrafts within thunderstorms have speeds exceeding 100 kilometers per hours and may be accompanied by heavy rain and hail. -Tornadoes are the most destructive mesoscale winds, and tropical storms as well as small hurricanes are also considered mesoscale wind systems.
This subsiding air is relatively dry because it has released its moisture near the equator. Adiabatic heating during descent further reduces the air's relative humidity. This subtropical zone of subsidence is the site of many of the world's great desserts. Surface winds tend to be weak so this belt was named the horse latitudes.
Near the center of the horse latitudes, as the sinking air approaches the surface, it splits into two branches, one flowing poleward and one flowing toward the equator. The equatorward flow is deflected by the Coriolis force to form the reliable trade winds, which enabled early sailing ships to move goods between Europe and North America.
A few better known katabatic winds have local names. Most famous is the mistral, which blows from the French Alps toward the Mediterrainean Sea. Another is the bora, which originates in the mountains of the Balkan Peninsula and blows to the Adriatic Sea.
One mesoscale wind, country breeze, is associated with large urban areas. The circulation pattern is characterized by a light wind blowing into the city from the surrounding countryside. It is most likley to develop on a relatively clear, calm night. Unforturnatly, pollutants emitted near urbam perimeter tend to drift in and concentrate near the city's center.
Summertime temperatures in the interior of Southern Asia often exceed 104 degrees fahrenheit. This intense solar heating generates a thermal low over th continent similar to that associated with a sea breeze, but at a much larger scale. The low pressure over southeastern Asia causes moisture-laden air from the Indian and Pacific Oceans to flow over the land, generating cloudy conditions and heavy precipiation typical of summer monsoons.
One of the world's rainiest regions is found on the slopes of the Himalayas, where orographic lifting of incoming moist air from the Indian Ocean produces copious precipiation. Asian monssons are strongly influenced by the seasonal change in solar heating of the vast Asian continent. In addition, this monsoon circulation is associated with a large seasonal migration of the ITCZ. The timely arrival of monsoon rains often means the difference between adequete nutrition and widespread malnutrition.
The North American monsoon has a circulation pattern that produces a dry spring followed by a relatively rainy summer. This experienced in the Southwest, particularly Arizon which has a rainier August and a dry May. The supply of atmospheric moisture from nearby marine spurces (Gulf of Mexico) coupled with with the convergence and upward airflowof the thermal low (extreme surface heating), generates the precipiation this region experiences during the hottest months.
Rossby waves consist of four to six meandering westerlies which flow in a wavy path. Westerlies do not flow along a straight path. Rossby waves can have a tremendous impact on our daily weather, especially when they meander from north to south.
What are microscale winds?
Small, chaotic winds that normally last for only a few seconds or minutes. -Ex-Dust devils and small tornadoes. -Dust devils resemble tornadoes , but are only a few meters in diamter and reach heights not greater than about 100 meters. -Unlike tornadoes which are associated with storm clouds, dust devils form on days when clear skies dominate and develop from the gorund upward. -Because surface heating is critical for their formation, they typically occur in the afternoon, when surface temperatures are the highest. -When air near the ground is warmer than air a few dozen meters overhead, the layer of air near Earth's surace becomes unstable causing warm air to rise and forming a whirlwind.
A sea breeze has a significant moderating influence in coastal areas. Shortly after a sea breeze begins, air temperatures over land begin to drop. The cooling effect of these breezes his genrally noticable for only 100 kilometers inland in the tropics, often less tha half that distance in the middle latitudes. Relatively cool sea breezes generally begin before noon and reach their greatest intensity, about 10 to 20 kilometers per hours, by midafternoon.
Smaller scale sea breezes can also develop along the shores of large lakes. Cities near the great lakes, such as Chicago, benefit from the "lake breeze" during the summer, when residents typically enjoy cooler temperatures near the lake compared to warmer inland areas.
Near the equator, warm rising air that releases latent heat during the formation of cumulus towers is believed to provide the energy that drives the Hadley cells. As the the flow aloft moves poleward, the air begins to subside in a zone between 20 and 35 degrees latitude. As upper-level flow moves away from the stormy equatorial region, radiation cooling becomes the dominant process. As a result, the air cools, becomes denser, and sinks.
The Coriolis force becomes stronger with increasing distance from the equator, causing the poleward-moving upper air to be defelcted into a nearly west-toeast flow by the time it reaches 30 degree latitude. This restricts the poleward flow of air. The coriolis force causes a general pileup of air (convergence) aloft.
Energy is passed from moving air to the surface of the ocean through friction. Positioned north and south of the equator are two westward-moving currents. These currents derive energy principally from the trade winds that blow from the northeast and southeast, respectiviely, toward the equator.
The Coriolis force deflects surface currents poleward to form clockwise spirals in the Nothern Hemisphere and counterclockwise spirals in the Southern Hemisphere. These nearly circular ocean currents, called gyres, are centered under the five major subtropical high pressure systems, located in both the southern and northern Atlantic and Pacific Oceans and in the Indian Ocean.
Meteorologists now recognize that La Nina and El Nino are part of the global atmospheric circulation pattern that affects the weather at great distances from the equatorial regions of the pacific. Although the effect of these circulation patterns are not always predictable, some locales appear to be affected more consistenly than others. Significanlty wetter winters are experienced in the southwestern U.S. and lower-than-average number of Atlantic hurricanes.
The El Nino of 2015 to 2106 was particularly strong. Impacts included mudslides in California, heavy snows in Arizona, and flooding in Missouri. California's drought was quickly replaced by widespread flooding and coastal erosion. The Midwest, enjoyed a warmer than normal winter.
In the North Atlantic, the equatorial current is deflected northward through the Caribbean, where it becoms the Gulf stream. As the stream moves along the eastern coast of the U.S., it is strengthened by the prevailing westerly winds. As it continues northeastward beyond the Grand Banks, it gradually widens and slows until it becomes a vast moving current known as the North Atlantic Drift.
The North Atlantic Drift splits as it approaches Western Europe. Part moves northward past Great Bitain toward Norway, wile the other portionis deflected southward as the cool Canary Current. As the Canary Current moves south, it eventually merges with the North Equatorial Current. The North Atlantic Drift keeps Western Europe warmer than would be expected for their latitudes.
In the Northern Hemisphere, the trades blow from the northeast, while in the Southern Hemisphere, the trades are from the Southeast. The trade winds from both hemispsheres meet near the equator, in a region that has a weak pressure gardient. This zone is called the doldrums.
The idealized three-cell model provides a foundatio for Earth's global wind patters, but it is still a simplified model. If Earh's surface was uniform, each himsphere would have mainly east-west oriental belts of high and low pressure. Near the equator, the warm rising branch of the Hadley cells is associated with the low-pressure zone known as the equatorial low.
What is the origin of the distinctive energetic winds that exist within the somewhat slower general westerly flow?
The key is that large temperature differences at the surface produces steep pressure gradients aloft and hence fater upper-air winds. -In winter and early spring, southern Florida will have warm balmy days and and Georgia will have near-freezing temperatures. -Such large wintertime temperature contrasts lead us to expect faster westerly flow at that time of the year.
What are macroscale winds?
The largest wind patterns are divided into two categories: planetary-scale and synoptic-scale. -Planetary-scale are explified by the westerlies and trade winds that carried sailing vessels back and forth across the Atlantic during the opening of the New World. These large scale flow patterns extend around the entire globe and can remain essentially unchanged for weeks at a time. -Synoptic scale winds (weather map scale) are about 1000 kilometers in diamter and are easily identifiedon weather maps. Two well known synoptic scale systems are the graveling midlatitude cyclones and anticyclcones that appear on weather maps as areas of low and high pressure .
What are the Santa Ana winds?
The local name for chinook-like winds that characteristically sweep through southern California and northwestern Mexico in the fall and winter. These hot, dry winds are infamous for fanning regional wildfires. -They are driven by strong high pressure systems with subsiding ait that tend to develop in the fall over the Great Basin. -The 2003 southern California wildfires became the worst fire disaster in the state's history costing the Fderal Emergency Managment Agency over 2.5 billion dollars, with 300 homes destroyed and 26 people killed.
The polar jetstream plays a very important role in the weather of the midlatitudes. In addition to supplying energy to help drive storms, it also directs the paths of these storms. Determining changes in the location and flow pattern of the polar jet is important for weather forecasting.
The location of the polar jet stream also affect other surface conditions, particularly temperature and humidity. When it is situated substantially equatorward, the weather will be colder and drier than normal. When the polar jet moves poleward, warmer and more humid conditions will prevail.
With the approach of El Nino, the high pressure off the coast of South America weakens, which reduces the strenght of trade winds and creates a strong equatorial countercurrent, which amasses large quantities of warmer-than-normal water along the west coast of South America. This is associated with low pressure in the equatorial Pacific causes normally arid areas such as Ecuador, Peru, and Chile to receive above average rainfall.
The result can be major flooding and the blocking of nutients by upwelling for small feeder fish. However, Indonesia and other areas in the western Pacific tend to be drier than usual. The circulation associated with El Nino eventually returns to ormal or is replaced by La Nina, which is the strengthening of normal conditions.
The pressure pattern over the Northern Hemisphere changes dramatically in summer. High surface temperatures over the continents generate lows that replace wintertime highs. These thermal lows consist of warm ascending air that triggers inward directed surface flow and cloudy conditions.
The strongest of these low-pressure centers devlop over Sourthern Asia, while a weaker thermal low is found in the southwestern United States. The winds resulting from these seasonal pressure patterns over the continents generate monsoon winds and precipitation.
Large land masses in the middle latitudes commonly experience decreased precipiation toward their interiors. Mountain barriers alter precipiation as well. Windward mountain slopes receive abundant precipitation, whereas leeward slopes and adjacent areas are usually deficient in moisture. As a result, these regions such as the American Southwest are found on the leeward (rain shadow) side of a mountain barrier or in the interior of a continent.
The subtropics don't have the desserts or abundant rainfalls. This pattern occurs because the subtropical high pressure centers that dominate the circulation in these latitudes have different characteristicson their eastern and western sides. Because these anticylcones tend to crowd the eastern side of an ocean, particularly in the winter, the eastern portions of the continents adjacent to subtropical highs are arid. The surface air that flows out of western highs often traverses larges expanses of warm water. As a result, this air acquires moisture through evaporation that acts to enhance instability. They then tend to receive ample precipiation throughout the year (southeastern United States).
This pressure difference causes the air aloft to blow away from the land (area of high pressure) toward the water (area of low pressure). The flow aloft is called the return, even though it generally develops before the sea breeze. The mass transfer of air aloft from land toward the ocean creates a surface high pressure area over the ocean, where the air collects, and low pressure over land.
The surface circulation that develops from this redistribution of mass if from the sea toward land, hence the name sea breeze.. At night, the land cools more rapidly than the sea, and and a land breeze may devlop.
These fires are nature's way of burning out chaparral thickets and sage scrub to prepare the land for new growth. When people began building homes and crowding into the fire prone area between Santa Barbara and San Diego, fire prevention efforts increased and with fewer fires, plant material accumulates to larger than normal quantities. So when fires occur, they are larger and more destructive.
These conditions occur in any part of the U.S. The National Weather Service issues a Red Flag Warning when strong winds, low relative humidity, and dry vegetation combine combine to create conditions in which fires will ignite quickly and grow rapidly. Under the Red Flag Warning you should: -Report a small fire. -Not light fires, including campfires and barbeque grill. -Not park cars on or drive over dry grass.
Chinooks are common east of the Colorado Rockies in the winter and spring, when the affected area may be experiencing subfreezing temperatures. Within minutes of a chinook's arrival, the temperatures often climb 20 degrees celsius, or much more. These winds can rapidly melt snow cover, which is why they are called snow-eaters.
They have been known to melt more than a foot of snow in a single day. Chinooks are sometimes viewed as beneficial to ranchers east of the Rockies because they keep the grasslands clear of snow during much of the winter. The benefit is offset by the loss of moisture that the snow would add to the soild if it remained until the spring melt.
A sea breeze usually develops on calm, sunny days when the land is significantly warmer than the adjacent water body, and it alternates with the usually weaker, nighttime land breeze. A sea breeze begins to form after sunrise as the temperature of the air above the land surface increaseswhile the temperature over the ocean remain largely unchanged.
This differential heating between land and water produces warmer air column over land adjacent to a cooler air column over water. The pressure aloft in the warm air column over land is higher than the pressure aloft over the water body at the same altitude.
The best known and best developed monsoon circulation occurs in southeastern Asia, affecting India, parts of China, Korea, and Japan. Asian monsoons are driven by pressure differences generated by unequal heating of Earth's surface. As winter approaches, long nights and low Sun angles result in the accumulation of frigid air over the vast landscape of northern Russia, which generates the cold Siberian high.
This dominates Asia's winter circulation. The subsiding dry air of the Siberian high produces surface flow that moves across southern Asia, producing predomiantly offshore winds. By the time this flow reaches India, it has warmed considerably but the air remains extremely dry.
How does the Earth transfer heat from the equator towards the poles?
This is accomplished by the wavy flow (Rossby waves) of the westerlies centered on the polar jet stream. -There may be periods when the flow in the polar jet is essentially west to east. When this condition prevails, relatively mild temperatures occur south of the jet stream, and cooler temperatures prevail to the north. -Then, the flow aloft may begin to meander and produce large-amplitude waves that exhibit a more pronounced north to south flow. -Such a change causes cold air to advance equatorward and warm air to flow poleward. A cold air mass may become detached and produce very cold conditions and strong storms along its margins.
