The document summarizes the causes and patterns of wind globally and locally. Temperature differences between air masses cause pressure differences as warm air rises and cold air sinks, driving wind flows. On a local scale, this causes sea breezes as land heats up more than water during the day and land breezes as land cools faster at night. It also explains valley and mountain breezes caused by differences in heating and cooling of air in valleys versus mountainsides. Globally, prevailing winds are driven by similar temperature and pressure patterns.
This document discusses climate classification systems and the factors that cause climate change. It begins with an overview of weather versus climate and the Koppen climate classification system. The major climate types are then described in detail, including tropical, dry, mild, continental, and polar climates. Various natural and human factors that can disrupt climate patterns are outlined, such as solar activity, volcanic eruptions, greenhouse gases, and deforestation. Evidence of past climate changes is examined through paleoclimate research techniques. Feedback mechanisms are described that can amplify the impacts of initial changes.
Atmospheric pressure and Atmospheric TemperatureAndino Maseleno
Atmospheric pressure decreases with increasing altitude and is caused by the decreasing mass of air above. It is measured in units like atmospheres and pascals. The scale height is the height where pressure decreases by a factor of e and depends on temperature, molecular mass, and gravity. Atmospheric temperature also varies with altitude, from very cold in the mesopause to very warm in the thermosphere due to radiation. Mean sea level pressure is the pressure at sea level used in weather reports.
Global winds are large air currents that circle the Earth and move air masses across long distances. They include the jet stream over North America, which flows from west to east between warm and cold air masses, and eight major wind types defined by their direction and location. Pictures show the global circulation patterns including the Hadley cells where air rises at the equator and sinks at 30 degrees latitude while rotating east or west.
AS GEOGRAPHY - ATMOSPHERE AND WEATHER - ATMOSPHERIC CIRCULATION MODELGeorge Dumitrache
The document discusses the global atmospheric circulation system. It describes the Hadley cell, Ferrel cell, and polar cell circulation patterns. The Hadley cell features rising air near the equator, poleward flow at high altitudes, and descending air in the subtropics. Together, these three circulation cells transport heat energy from the equator towards the poles and help drive surface wind patterns like the trade winds.
This document discusses global wind patterns. It begins by explaining that wind is the movement of air from high to low pressure areas. It then describes how wind is formed through convection currents caused by uneven heating of the Earth's surface from the sun. The Coriolis effect causes winds to curve due to the Earth's rotation. There are local winds formed by local geographic features and global winds formed by larger air masses. Global wind types include polar easterlies, prevailing westerlies, trade winds, and doldrums. Prevailing winds typically blow from west to east in the mid-latitudes. Nepal experiences a temperate climate due to its location in the Himalayas between the Tropic of Cancer and Arctic
The document discusses different types of fronts including warm fronts, cold fronts, occluded fronts, and stationary fronts. It provides details on their formation, identification, and typical associated weather patterns. Warm fronts have a gradual slope and rising warm air overrides cooler air. Cold fronts have a steeper slope and faster movement as colder air advances. An occluded front is formed when a cold front catches up to a warm front. Stationary fronts have little or no movement with gentle precipitation possible.
The document summarizes the causes and patterns of wind globally and locally. Temperature differences between air masses cause pressure differences as warm air rises and cold air sinks, driving wind flows. On a local scale, this causes sea breezes as land heats up more than water during the day and land breezes as land cools faster at night. It also explains valley and mountain breezes caused by differences in heating and cooling of air in valleys versus mountainsides. Globally, prevailing winds are driven by similar temperature and pressure patterns.
This document discusses climate classification systems and the factors that cause climate change. It begins with an overview of weather versus climate and the Koppen climate classification system. The major climate types are then described in detail, including tropical, dry, mild, continental, and polar climates. Various natural and human factors that can disrupt climate patterns are outlined, such as solar activity, volcanic eruptions, greenhouse gases, and deforestation. Evidence of past climate changes is examined through paleoclimate research techniques. Feedback mechanisms are described that can amplify the impacts of initial changes.
Atmospheric pressure and Atmospheric TemperatureAndino Maseleno
Atmospheric pressure decreases with increasing altitude and is caused by the decreasing mass of air above. It is measured in units like atmospheres and pascals. The scale height is the height where pressure decreases by a factor of e and depends on temperature, molecular mass, and gravity. Atmospheric temperature also varies with altitude, from very cold in the mesopause to very warm in the thermosphere due to radiation. Mean sea level pressure is the pressure at sea level used in weather reports.
Global winds are large air currents that circle the Earth and move air masses across long distances. They include the jet stream over North America, which flows from west to east between warm and cold air masses, and eight major wind types defined by their direction and location. Pictures show the global circulation patterns including the Hadley cells where air rises at the equator and sinks at 30 degrees latitude while rotating east or west.
AS GEOGRAPHY - ATMOSPHERE AND WEATHER - ATMOSPHERIC CIRCULATION MODELGeorge Dumitrache
The document discusses the global atmospheric circulation system. It describes the Hadley cell, Ferrel cell, and polar cell circulation patterns. The Hadley cell features rising air near the equator, poleward flow at high altitudes, and descending air in the subtropics. Together, these three circulation cells transport heat energy from the equator towards the poles and help drive surface wind patterns like the trade winds.
This document discusses global wind patterns. It begins by explaining that wind is the movement of air from high to low pressure areas. It then describes how wind is formed through convection currents caused by uneven heating of the Earth's surface from the sun. The Coriolis effect causes winds to curve due to the Earth's rotation. There are local winds formed by local geographic features and global winds formed by larger air masses. Global wind types include polar easterlies, prevailing westerlies, trade winds, and doldrums. Prevailing winds typically blow from west to east in the mid-latitudes. Nepal experiences a temperate climate due to its location in the Himalayas between the Tropic of Cancer and Arctic
The document discusses different types of fronts including warm fronts, cold fronts, occluded fronts, and stationary fronts. It provides details on their formation, identification, and typical associated weather patterns. Warm fronts have a gradual slope and rising warm air overrides cooler air. Cold fronts have a steeper slope and faster movement as colder air advances. An occluded front is formed when a cold front catches up to a warm front. Stationary fronts have little or no movement with gentle precipitation possible.
Air pressure is the force exerted by air molecules pushing down on a surface. It depends on factors like elevation, temperature, and humidity. Air pressure decreases with increasing altitude and temperature, and increasing humidity. It can be measured using a barometer. Changes in air pressure affect the weather, with low pressure typically bringing stormy conditions and high pressure typically resulting in fair skies.
The document describes several common weather instruments: thermometers measure air temperature, sling psychrometers measure humidity, anemometers measure wind speed, barometers measure air pressure, and weather charts synthesize multiple data points. Thermometers contain a liquid that expands with heat, allowing users to read the temperature. Psychrometers measure humidity by comparing the temperature of a wet bulb to a dry bulb. Anemometers have spinning cups or vanes moved by wind. Barometers measure air pressure in millibars using a column of liquid. Weather charts depict fronts, pressure systems, and symbols to convey current and predicted conditions.
Weather refers to atmospheric conditions over a short period of time, while climate describes average weather patterns over many years. In the Philippines, PAG-ASA monitors and forecasts weather by observing elements like temperature, precipitation, winds, and clouds. Latitude, altitude, topography, and proximity to bodies of water all impact climate by influencing how much solar radiation and moisture an area receives. Different wind systems like the trade winds and polar winds also affect Philippine weather and seasonal climate patterns.
Midlatitude cyclones are large low pressure storm systems that form in the midlatitudes. They develop as warm and cold air masses converge, forming fronts where the air masses meet. As the cyclone moves eastward, the cold front typically advances faster than the storm itself and eventually catches up to the warm front. Meteograms are charts that plot changes in weather conditions over time and can clearly show the passing of fronts and associated changes in temperature, wind, precipitation and other conditions.
The document provides information about mid-latitude cyclones, including:
1) The stages of development of a mid-latitude cyclone are the initial, development, mature, and occlusion stages.
2) Conditions necessary for their formation include contact between warm/moist and cold/dry air masses at the polar front with convergence and disturbances forming a low pressure system.
3) Characteristics include originating in mid-latitudes, moving eastward, rotating counterclockwise, having a diameter of up to 1,000 miles, bringing changing weather over 1-3 days, and being caused by clashes between different air masses.
This document provides information on coastal landforms found in LEDC and MEDC countries. It describes both depositional landforms like beaches, spits, and tombolos, which are built up by material deposited by waves, and erosional landforms like cliffs and caves, which are shaped by erosion. It discusses processes like longshore drift that form features like spits, and provides examples of different coastal landforms like Chesil Beach in the UK and Spurn Head in England.
Thermometers, barometers, rain gauges, hygrometers, weather vanes, and anemometers are the most important meteorological instruments. Thermometers measure temperature and maximum/minimum temperatures, barometers measure atmospheric pressure, rain gauges measure rainfall, hygrometers measure humidity, weather vanes show wind direction, and anemometers measure wind speed. These instruments are used to collect data to predict weather conditions.
The document defines key terms related to weather and climate such as weather, climate, season, temperature, humidity, air pressure, and winds. It describes how weather is the short term atmospheric conditions of a place while climate refers to average conditions over a longer period. Seasons result from the Earth's revolution and axis tilt. Temperature, precipitation, air pressure, winds, and visibility are the main elements that determine weather and climate in a given place. Factors like heat, air pressure, winds, and moisture interact to cause weather. Major wind systems like the doldrums, trade winds, horse latitudes, and prevailing westerlies result from differences in heating and the Coriolis effect.
The document discusses the concepts of latitude, longitude, time zones, and how locations on Earth are specified using these coordinate systems. It explains that latitude lines run parallel east-west and longitude lines run perpendicular north-south, with the Prime Meridian at Greenwich, England defining 0 degrees. It describes how the Earth is divided into 24 time zones that are approximately 15 degrees wide to standardized time globally.
The document discusses temperature, defining weather as short term atmospheric conditions while climate refers to long term patterns, and explores factors that cause variations in temperature between locations including latitude, altitude, distance from bodies of water, and cloud cover. Places at the same latitude can have different temperatures due to other influences on local climate such as elevation, proximity to oceans, and cloud levels that impact how much solar energy reaches and leaves the surface.
The atmosphere consists of 78% nitrogen, 21% oxygen and trace amounts of other gases that make life possible on Earth. It protects the planet from harmful rays and meteorites. Weather occurs in the lower layer of the atmosphere, the troposphere, which extends up to 12 miles high and where temperatures decrease with altitude. Higher layers include the stratosphere, mesosphere, thermosphere and outermost exosphere. Climate is associated with a place and includes daily, seasonal and yearly variations in elements like temperature, precipitation, humidity, pressure and wind. Factors influencing climate include latitude, altitude, land and ocean distribution, barriers and currents.
This document summarizes atmospheric circulation and pressure distributions. It describes the single-cell and three-cell models of atmospheric circulation, including the Hadley cell, Ferrel cell, and polar cell. It discusses global wind patterns, pressure systems like the subtropical high and Intertropical Convergence Zone, and factors that influence winds like solar heating and the Coriolis effect. It also mentions regional circulation features and pressure systems, ocean currents, and mesoscale and microscale atmospheric phenomena.
Waves erode, transport, and deposit material along coastlines. Erosion occurs through hydraulic action, corrosion, corrasion, abrasion, and attrition as waves impact cliff bases. Transportation involves the movement of eroded materials in the sea and along the coast by waves, such as through longshore drift. Deposition happens when waves with less energy drop the eroded materials, creating landforms like beaches and spits.
The atmosphere is composed primarily of nitrogen and oxygen that surrounds the Earth and is held in place by gravity. It protects life by absorbing UV rays, provides warmth through the greenhouse effect, and moderates temperature extremes. The ozone layer located 15-35km above the surface protects the Earth from UV rays by absorbing most of them. Weather occurs over short periods of time, while climate describes patterns over 30+ years and determines temperature and precipitation averages. Climate is influenced by several factors like latitude, altitude, distance from oceans, wind and pressure systems, and ocean currents.
The document describes rudimentary tillage agriculture, which is one of the 13 types of agricultural regions classified by Whittlesey in 1936. Rudimentary tillage agriculture is characterized by permanent settlers farming the same land each year, with fallowing of land to maintain soil fertility. Farmers practice non-rotation of fields. Common crops include maize, millets, rice, vegetables, tobacco, and pulses. The farming is done using simple tools and low mechanization.
Fronts are boundaries between two air masses of differing characteristics. There are four main types of fronts: cold fronts, warm fronts, occluded fronts, and stationary fronts. Cold fronts are steep boundaries where cold air overrides warm air, bringing precipitation. Warm fronts are more gradual, with light, continuous precipitation as warm air rises over cold air. Occluded fronts occur when a cold front catches up to a warm front. Stationary fronts have little or no movement as the air masses are parallel.
This document summarizes key concepts about atmospheric pressure and global wind patterns from a geography textbook chapter. It defines important terms like isobars, high and low pressure systems, and describes the major wind systems - including the trade winds, westerlies, and polar easterlies - that make up the general circulation of the atmosphere. Specific wind patterns like the Hadley cell and subtropical high are explained in terms of atmospheric pressure gradients and the Coriolis effect.
The document discusses solar radiation and the processes that control Earth's heat balance and temperature distribution. It explains that Earth receives energy from the sun which is absorbed and radiated back to space. Some key points are:
- Solar radiation heats the atmosphere through various processes like convection, conduction, and radiation.
- Factors like the Earth's rotation, revolution, latitude, proximity to oceans influence the amount of incoming solar radiation (insolation) at different locations.
- Earth's temperature is determined by the balance between the solar energy received and radiated back to space. Temperature varies based on latitude, altitude, land/sea distribution and ocean/wind currents.
Air pressure is the force exerted by air molecules pushing down on a surface. It depends on factors like elevation, temperature, and humidity. Air pressure decreases with increasing altitude and temperature, and increasing humidity. It can be measured using a barometer. Changes in air pressure affect the weather, with low pressure typically bringing stormy conditions and high pressure typically resulting in fair skies.
The document describes several common weather instruments: thermometers measure air temperature, sling psychrometers measure humidity, anemometers measure wind speed, barometers measure air pressure, and weather charts synthesize multiple data points. Thermometers contain a liquid that expands with heat, allowing users to read the temperature. Psychrometers measure humidity by comparing the temperature of a wet bulb to a dry bulb. Anemometers have spinning cups or vanes moved by wind. Barometers measure air pressure in millibars using a column of liquid. Weather charts depict fronts, pressure systems, and symbols to convey current and predicted conditions.
Weather refers to atmospheric conditions over a short period of time, while climate describes average weather patterns over many years. In the Philippines, PAG-ASA monitors and forecasts weather by observing elements like temperature, precipitation, winds, and clouds. Latitude, altitude, topography, and proximity to bodies of water all impact climate by influencing how much solar radiation and moisture an area receives. Different wind systems like the trade winds and polar winds also affect Philippine weather and seasonal climate patterns.
Midlatitude cyclones are large low pressure storm systems that form in the midlatitudes. They develop as warm and cold air masses converge, forming fronts where the air masses meet. As the cyclone moves eastward, the cold front typically advances faster than the storm itself and eventually catches up to the warm front. Meteograms are charts that plot changes in weather conditions over time and can clearly show the passing of fronts and associated changes in temperature, wind, precipitation and other conditions.
The document provides information about mid-latitude cyclones, including:
1) The stages of development of a mid-latitude cyclone are the initial, development, mature, and occlusion stages.
2) Conditions necessary for their formation include contact between warm/moist and cold/dry air masses at the polar front with convergence and disturbances forming a low pressure system.
3) Characteristics include originating in mid-latitudes, moving eastward, rotating counterclockwise, having a diameter of up to 1,000 miles, bringing changing weather over 1-3 days, and being caused by clashes between different air masses.
This document provides information on coastal landforms found in LEDC and MEDC countries. It describes both depositional landforms like beaches, spits, and tombolos, which are built up by material deposited by waves, and erosional landforms like cliffs and caves, which are shaped by erosion. It discusses processes like longshore drift that form features like spits, and provides examples of different coastal landforms like Chesil Beach in the UK and Spurn Head in England.
Thermometers, barometers, rain gauges, hygrometers, weather vanes, and anemometers are the most important meteorological instruments. Thermometers measure temperature and maximum/minimum temperatures, barometers measure atmospheric pressure, rain gauges measure rainfall, hygrometers measure humidity, weather vanes show wind direction, and anemometers measure wind speed. These instruments are used to collect data to predict weather conditions.
The document defines key terms related to weather and climate such as weather, climate, season, temperature, humidity, air pressure, and winds. It describes how weather is the short term atmospheric conditions of a place while climate refers to average conditions over a longer period. Seasons result from the Earth's revolution and axis tilt. Temperature, precipitation, air pressure, winds, and visibility are the main elements that determine weather and climate in a given place. Factors like heat, air pressure, winds, and moisture interact to cause weather. Major wind systems like the doldrums, trade winds, horse latitudes, and prevailing westerlies result from differences in heating and the Coriolis effect.
The document discusses the concepts of latitude, longitude, time zones, and how locations on Earth are specified using these coordinate systems. It explains that latitude lines run parallel east-west and longitude lines run perpendicular north-south, with the Prime Meridian at Greenwich, England defining 0 degrees. It describes how the Earth is divided into 24 time zones that are approximately 15 degrees wide to standardized time globally.
The document discusses temperature, defining weather as short term atmospheric conditions while climate refers to long term patterns, and explores factors that cause variations in temperature between locations including latitude, altitude, distance from bodies of water, and cloud cover. Places at the same latitude can have different temperatures due to other influences on local climate such as elevation, proximity to oceans, and cloud levels that impact how much solar energy reaches and leaves the surface.
The atmosphere consists of 78% nitrogen, 21% oxygen and trace amounts of other gases that make life possible on Earth. It protects the planet from harmful rays and meteorites. Weather occurs in the lower layer of the atmosphere, the troposphere, which extends up to 12 miles high and where temperatures decrease with altitude. Higher layers include the stratosphere, mesosphere, thermosphere and outermost exosphere. Climate is associated with a place and includes daily, seasonal and yearly variations in elements like temperature, precipitation, humidity, pressure and wind. Factors influencing climate include latitude, altitude, land and ocean distribution, barriers and currents.
This document summarizes atmospheric circulation and pressure distributions. It describes the single-cell and three-cell models of atmospheric circulation, including the Hadley cell, Ferrel cell, and polar cell. It discusses global wind patterns, pressure systems like the subtropical high and Intertropical Convergence Zone, and factors that influence winds like solar heating and the Coriolis effect. It also mentions regional circulation features and pressure systems, ocean currents, and mesoscale and microscale atmospheric phenomena.
Waves erode, transport, and deposit material along coastlines. Erosion occurs through hydraulic action, corrosion, corrasion, abrasion, and attrition as waves impact cliff bases. Transportation involves the movement of eroded materials in the sea and along the coast by waves, such as through longshore drift. Deposition happens when waves with less energy drop the eroded materials, creating landforms like beaches and spits.
The atmosphere is composed primarily of nitrogen and oxygen that surrounds the Earth and is held in place by gravity. It protects life by absorbing UV rays, provides warmth through the greenhouse effect, and moderates temperature extremes. The ozone layer located 15-35km above the surface protects the Earth from UV rays by absorbing most of them. Weather occurs over short periods of time, while climate describes patterns over 30+ years and determines temperature and precipitation averages. Climate is influenced by several factors like latitude, altitude, distance from oceans, wind and pressure systems, and ocean currents.
The document describes rudimentary tillage agriculture, which is one of the 13 types of agricultural regions classified by Whittlesey in 1936. Rudimentary tillage agriculture is characterized by permanent settlers farming the same land each year, with fallowing of land to maintain soil fertility. Farmers practice non-rotation of fields. Common crops include maize, millets, rice, vegetables, tobacco, and pulses. The farming is done using simple tools and low mechanization.
Fronts are boundaries between two air masses of differing characteristics. There are four main types of fronts: cold fronts, warm fronts, occluded fronts, and stationary fronts. Cold fronts are steep boundaries where cold air overrides warm air, bringing precipitation. Warm fronts are more gradual, with light, continuous precipitation as warm air rises over cold air. Occluded fronts occur when a cold front catches up to a warm front. Stationary fronts have little or no movement as the air masses are parallel.
This document summarizes key concepts about atmospheric pressure and global wind patterns from a geography textbook chapter. It defines important terms like isobars, high and low pressure systems, and describes the major wind systems - including the trade winds, westerlies, and polar easterlies - that make up the general circulation of the atmosphere. Specific wind patterns like the Hadley cell and subtropical high are explained in terms of atmospheric pressure gradients and the Coriolis effect.
The document discusses solar radiation and the processes that control Earth's heat balance and temperature distribution. It explains that Earth receives energy from the sun which is absorbed and radiated back to space. Some key points are:
- Solar radiation heats the atmosphere through various processes like convection, conduction, and radiation.
- Factors like the Earth's rotation, revolution, latitude, proximity to oceans influence the amount of incoming solar radiation (insolation) at different locations.
- Earth's temperature is determined by the balance between the solar energy received and radiated back to space. Temperature varies based on latitude, altitude, land/sea distribution and ocean/wind currents.
2. Vejret i Danmark
– påvirket på 3 niveauer
1. Globalt (dvs. det globale vindsystem)
2. Regionalt (dvs. polarfronten/den polare jetstrøms
placering)
3. Lokalt (dvs. placeringen af de enkelte dynamiske
højtryk, lavtryk og fronter).
3. Det globale niveau
Påvirkningen fra det globale vindsystem:
Danmark (56°N) er i det tempererede vestenvindsbælte (30-
60°N)
Vi har mest vestlige vinde, og vejret kommer primært til os fra vest.
Danmark er tæt på polarfronten (og dermed de
subpolare, dynamiske lavtryk med tilhørende fronter) året
rundt
Vi har altid ret ustadigt vejr, og ingen særlige regntider eller tørtider.
Polarfronten bevæger sig sammen med resten af vindsystemet
med årstiderne.
Vores mest ustadige årstider er når polarfronten er meget tæt på
Danmark – dvs. forår og efterår. Vi har mere stabilt vejr, når
polarfronten er længere væk om sommeren og vinteren.
Men dette forklarer ikke vejret mere detaljeret – f.eks. vindretning og temperatur
Her skal vi ned på de regionale og lokale niveauer.
4. Det regionale niveau
Påvirkningen fra polarfrontens placering:
Polarfronten er nord for Danmark
Chancen for højtryk er større, da dynamiske højtryk
normalt er syd for polarfronten. Dermed typisk
strålingsvejr.
Polarfronten er syd for Danmark
Chancen for lavtryk (og fronter) er større, da
subpolare, dynamiske lavtryk normalt er nord for
polarfronten. Dermed typisk strømningsvejr.
Men dette forklarer stadig ikke vejret mere detaljeret – f.eks. vindretningen.
Her skal vi ned på de regionale og lokale niveauer.
5. Det lokale niveau
Påvirkningen fra de enkelte lavtryk, højtryk og
fronter:
Et højtryk er lige over Danmark
Der vil være strålingsvejr.
Et lavtryk med fronter er tæt ved Danmark
Vejret domineres af frontpassager: varm-, kold- og/eller okkluderede
fronter vil passere Danmark.
Dynamiske høj- og lavtryk er tæt ved Danmark, men trykkene
og fronterne er ikke lige over Danmark
Fire forskellige vejrtyper – kaldet luftmassevejr.
6. Hvordan opstår polarfronten og den
polare jetstrøm? Polarfronten er skillevæggen
mellem den lune tropikluft
(middelhavsluft, der dominerer
mellem 30 og 60°N) og polarluften
(nordpolsluft, der dominerer nord
for 60°N).
Jetstrømmene opstår, fordi der
er et trykfald mellem de tre celler,
der udgør det globale vindsystem.
Hadley-cellen ved Ækvator er
varmest = størst tryk. Vindene
søger derfor videre over i
Ferrelcellen og Polarcellen, afbøjes
af Corioliseffekten og danner
kraftige vestenvinde i højden over
hver cellegrænse = subtropiske og
polare* jetstrømme.
7. Strålingsvejr og strømningsvejr
Strålingsvejr
Når et højtryk er over Danmark eller meget
tæt på.
Stabilt, tørt og klart vejr.
Svag eller ingen vind.
Sommer: Meget varmt, evt. tåge om natten.
Vinter: Meget koldt, evt. tåge om natten.
Strømningsvejr
Når de subpolare, dynamiske lavtryk
bevæger sig tæt forbi Danmark = mange
frontpassager.
Ustadigt vejr, nedbør under frontpassager.
Ofte blæsende.
Sommer: Køligt.
Vinter: Mildt.
8. Hvordan opstår varm- og koldfronter?
Et lavtryk dannes (pga. den polare jetstrøm) nord for polarfronten.
Vindene begynder at blæse mod uret rundt om lavtrykket.
Varm luft begynder at stige op over den kolde luft og presse til den kolde
luft. Kold luft presser samtidig til den varme luft på den anden side af
lavtrykket.
Frontsystemet er helt udviklet – her er varmfront, hvor varm luft
langsomt stiger op over kold luft, og en koldfront, hvor kold luft hurtigt
presser varm luft op foran sig.
Nu begynder fronterne at okkludere (klappe sammen), da koldfronten er
hurtigere end varmfronten – koldfronten skal kun skubbe til den varme
luft, mens den varme luft ved varmfronten både skal stige op og skubbe til
den kolde luft. Okklusionen starter tættest ved lavtrykket, hvor afstanden
mellem fronterne er kortest.
Nu er fronten helt okkluderet, men giver stadig noget nedbør, da den
varme luft endnu hænger over den kolde luft. Den varme luft er dog
isoleret fra jordoverfladen og køles af. Når den varme luft er lige så kold
som den omgivende kolde luft, opløses fronten. Lavtrykket forsvinder
også, da trykforskellen udlignes langsomt.
L
L
L
L
9. Hvad sker der, når fronterne passerer?
Koldfronten
I varmsektoren (der er tør og ret skyfri)
tårner høje bygeskyer sig op i horisonten.
Koldfrontens passage kendetegnes af
kraftige byger, om sommeren
tordenbyger (pga. den hurtigt opstigende
varme luft)
Efter frontpassagen bliver det koldere (vi er
tilbage i koldsektoren, nord for
polarfronten). Vinden skifter også, og det
bliver gradvist mindre skyet. Der kan dog
godt være byger efter koldfrontens passage.
Varmfronten
Gradvist mere skyet, i starten høje skyer, til
sidst helt overskyet.
Langsom, vedvarende nedbør under
fronten (heldagsregn – pga. den
langsomt opstigende varme luft).
Efter fronten har passeret, bliver det
varmere (vi er nu i varmsektoren, dvs. syd
for polarfronten).
Vindretningen skifter normalt også ved
frontpassagen.
10. Luftmassevejr i
Danmark
Maritim polarluft (kold+fugtig)
Sommer: Køligt, blæsende, mange byger.
Vinter: Køligt, snebyger, evt. snestorm.
Nordlige Danmark i læ af norske fjelde
(’fønvind’ = tørrere og klarere luft her).
Maritim tropikluft (varm+fugtig)
Sommer:
Varmt, lummert, byger, varmetordenvejr
(konvektionsnedbør).
Vinter: Mildt, overskyet, blæsende. Ofte
nedbør som regn eller slud.
Kontinental polarluft (kold+tør)
Sommer: Tørt, køligt og klart, evt. tåge
om natten.
Vinter: Tørt, meget koldt, klart.
Kontinental tropikluft (varm+tør)
Sommer: Meget varmt, tørt – evt.
hedebølge.
Vinter: Meget koldt, tørt og klart. Bliver
højtrykket hængende, kan der komme
isvinter.