Unit 10
the two most basic factors that determine the general circulation of the atmosphere are:
Coriolis effect and uneven heating of the earth with latitude
A front is a narrow zone of transition between air masses that contrast in...
density, humidity, temperature
the eastern blank of a subtropical anticyclone is characters by,
dry climates
the winter monsoon in eastern and southern Asia is characterized by:
dry weather and surface winds blowing from land to sea
a synoptic-scale cyclone is most likely to develop on the ____ side of an upper-air trough.Â
east
horizontal divergence occurs to the ____ of an upper-air trough
east
In the northern hemisphere autumn, the ITCZ shifts
equatorward
The trade winds blow out of the _____ flank of the subtropical anticyclones
equatorward
subtropical anticyclones are ____-core systems
warm
hadley cells are located in _____ latitudes of both hemispheres
tropical
an upper-level pool of cold air that has broken away from the main zonal flow is called:
a cut off low
on a typical day, _____ Rossby long-waves encircle the globe
2 to 5
The subtropical anticyclones on average are centered near ____ degrees latitude
30
the sub polar cyclones on average are centered near ___ degrees latitude.
60
In the middle latitudes why does the wind become more westerly and stronger aloft (above the friction layer)?
Because of the thermal wind relationship - if you’re at the surface there is very little horizontal pressure gradient and if you go up through atmosphere, between tropical and polar are sufficiently different you start increasing gradient throughout the atmosphere and therefore you have this
How do the major wind systems of the planetary-scale atmospheric circulation change with the season?
Follows the sun - north or south - in Jan the ITCZ has moved far south as it gets and then in July its as far north as it gets - the subtropical highs follow along - going from jan to July - will start moving towards the north - the polar front moves northward too - concurrently the southern hemisphere is going from summer to winter and then they are moving to the south
Which two systems are responsible for producing the major precipitation pattern of the earth?
ITCZ most of the precipitation and the midlatitude westerlies where storm systems come through
how is the major poleward transport of heat in the atmosphere accomplished between the equator and about 30 degrees N or 30 degrees S?
ITCZ, subtropical anticyclones and trade winds
the southwest monsoon winds occur in India primarily in
June July and August
We have just come out of _______ and may go into a ________.
La Nina....El Nino
Monsoon: Wet season in South Asia ???? Dry season in South Asia ?????
May-Sept Oct-April
Why is the jet stream strongest above japan? In which season is this so?
Reason is because over interior Asia (siberia, etc) the whole central Asia especialy during winter time gets so cold and the pacific area is still warm and because of the thermal wind relationship - you have a much stronger jet that builds as it goes up through the atmosphere
What are the two basic factors that determine the general planetary scale circulation in the atmosphere?
Spherical earth the poles are cold and tropics are hot - when you have hot topics cold poles, you have a temp gradient which results in pressure and density gradient so therefore the winds start to initially move at surface to upwards - develop hadley cell; Rotating earth causes the Coriolis effect so it changes the planetary circulation so you have the planetary westerlies - and since it is rotating so rapidly you have the waves in the polar front jet stream
How is the transport accomplished poleward of 30 degrees N or 30 degrees S?
Westerlies, subpolar and polar front
Eastern Flank of Subtropical anticyclones
There are extensive areas of subsiding stable air which undergoes compressional warming, which produces low relative humidities and sunny skies; Worlds’ major deserts are located under the eastern flanks of subtropical anticyclones
What role do Rossby waves play in energy transport?
Transport heat and moisture
Blocking system
a cutoff low or a cutoff high that prevents the usual west-to-east progression of weather systems; cutoff masses of air whirl in either a cyclonic or anticyclonic direction; persists for extended periods of time - extreme weather such as drought or anomalous heat or cold often resultÂ
polar front jet stream
a jet stream situated in the upper troposphere between the midlatitude tropopause and the polar tropopause and directly over the polar front
La Nina
a period of unusually strong trade winds and vigorous upwelling over the eastern tropical pacificÂ
a broad region of very light winds or calm conditions prevail
along the horse latitudes
El Nino
an anomalous warming of surface ocean waters in the eastern tropical pacific; accompanied by suppression of upwelling (warm surface waters are replaced by cold, nutrient-rich waters) off the coasts of Ecuador and Peru; interaction between sear and air
jet streak
an area of accelerated air flow within a jet stream
the trade winds of the two hemisphere
are very persistent in direction
in the midwest, drought is most likely associated with a ____ circulation pattern in the westerlies.
blocking
Meridional component
brings about a north-south exchange of air masses and poleward transport of heat. in the northern hemisphere, winds from the south carry warm air masses northward and winds from the north transport cold air masses southward - cold air is thus exchanges for warm air and heat is transport poleward
upwelling
brings cold bottom water to the ocean surface, is the normal situation off the northwest coast of South America, is suppressed during El Nino, supports important fisheries
monsoon circulation
characterizes regions where seasonal reversals in prevailing winds cause wet summers and relatively dry winters
Viewed from above, near-surface winds about a subtropical high in the Northern hemisphere blow
clockwise and outward
surface winds blow _____ about the Icelandic low.
counterclockwise and inward
In the southern hemisphere viewed from above, the direction that the near-surface winds circulate about a subtropical high-pressure cell is...
counterclockwise and outward
Midlatitude Westerlies
govern weather in US and Canada, westerlies flow about the hemisphere in wavelike patterns of ridges and troughs, winds exhibit clockwise (anticyclonic) curvature in the ridges and counterclockwise (cyclonic) curvature in the troughs. Between 2-5 waves typically encircle the hemisphere at one time (Rossby Waves)
subtropical anticyclones
imposing features of the planetary-scale circulation that are centered over subtropical latitudes (on average, near 30 degrees N and S); Highs extend vertically from the ocean surface to the tropopause and exert a strong influence on weather and climate Definition: semipermanent warm-core, high-pressure systems centered over subtropical latitudes of the Atlantic, Pacific and Indian oceans
the polar jet stream over the US is farthest north
in June, July and August
at what height is the wind speed in the jet stream normally the strongest?
in middle latitudes, the most prominent jet stream is situated directly over the polar front in the upper troposphere between the midlatitude tropopause and the polar tropopause.Â
How are Hadley cells related to the ITCZ and subtropical highs?
in the middle and upper troposphere, air flows poleward, away from the doldrums and into the subtropical highs. the coriolis effect shifts these upper-level winds toward the right (N. hemisphere). In the tropics, therefore, the winds aloft actually blow in a direction opposite that of the surface trade winds.Â
The subtropical high-pressure systems usually...
intensify and move poleward in the summer hemisphere
meridional flow patterns aloft are those associated witH
large amplitude wave patterns
in a jet streak, the strongest horizontal divergence takes place in the ____ quadrant
left front
what causes monsoons?
linked to seasonal shifts in the planetary-scale circulation, specifically north-south shifts of the inter tropical convergence zone. monsoons also depend on seasonal contrasts in heating of land and sea.Â
Rossby Waves
long waves, characterize the tropospheric westerlies above the 500-mb level (above the altitude where the pressure drops to 500-mb) - below this waves are distorted by friction and topographic irregularities. Definition: series of long-wavelength troughs and ridges that characterize the planetary-scale weasterlies
how does the barometric pressure within the inter tropical convergence zone compare with that outside the zone?
lower
an extreme El Nino...
may be accompanied by weather extremes in various parts of the world
a blocking pressure system is associated with a _____ flow pattern in the westerlies.
meridional
which one of the following westerly wave patterns fairs the max north-south exchange of air masses? zonal flow, meridional flow, split flow
meridional flow
Intertropical Convergence Zone
most active weather, discontinuous belt of thunderstorms paralleling the equator, located at the latitude of the Earth’s highest mean surface temp - heat equator definition: discontinuous belt of thunderstorms paralleling the equator and marking the convergence of the northern and souther hemisphere surface trade winds
Where are the major wind-driven ocean currents?
most of the time, the southern hemisphere's southeast trade winds drive warm surface waters westward
in the hawaiian islands (at 20 degrees north latitude) the prevailing trade winds are ____ winds
northeast
Southern Oscillation
opposing swings of surface air pressure between the eastern and western tropical pacific ocean - the horizontal pressure gradient thus changes as air pressure to the west rises and air pressure to the east falls
the middle latitude jet stream in the general circulation is
over regions where tropospheric temps change rapidly in horizontal
semipermanent pressure systems
persistent cyclones and anticyclone that are components of the planetary-scale circulation. These pressure cells exhibit some seasonal changes in location and in surface pressures
The global westerlies blow out of the ____ flank of the subtropical anticyclones
poleward
Differences in the annual precipitation regimes for southern california and the southeastern states result primarily because of differences in:
position with respect to the subtropical high-pressure centers
zonal flow patterns aloft are those associated with
predominantly westerly winds
Autumn: horizontal air pressure gradient that effects monsoons
radiational cooling chills the land more than the adjacent sea, setting up a horizontal air pressure gradient directed from land to sea. air subsides over the land, and dry surface winds sweep seaward air rises over the relatively warm sea surface; it drifts landward completing the winter monsoon circulation
Spring: horizontal air pressure gradient that effects monsoons
relatively cool air over the ocean and relatively warm air over the land give rise to a horizontal air pressure gradient directed from sea to land that produces a flow of humid air inland. over the land, intense solar heating triggers convection. hot humid air rises and consequent expansional cooling leads to condensation, clouds and rain. release of latent heat intensifies the buoyant uplift, triggering even more rainfaill
the western flank of a subtropical anticyclone is characterized byÂ
relatively unstable air
Hadley cells are
similar to huge convection cells
the average winter location of the polar front jet stream is
southern US
the average summer location of the polar front jet stream is
southern canada
Monsoon rains typically are
sporadic
across the US, temp contrasts are generally greatest during a ____ circulation pattern in the westerlies.
strong meridional
Western Subtropical anticyclones
subsidence is less and air is not as stable, cloudy, stormy weather are more frequent in these regions
monsoon rainfall across south Asia is governed by north-south shifts of...
subtropical anticyclones and ITCZ
subpolar lows
surface westerlies flow into regions of low pressure - Aleutian low over the north pacific and Icelandic low over the North Atlantic; Mark the convergence of the midlatitude southwesterlies with the polar northeaster lies definition: high-latitude, semipermanent cyclones marking the convergence of planetary-scale surface southerwesterlies of midlatitudes with surface norteasterlies of polar latitudes; icelandic low or aleutian low are examples
Polar Front
surface westerlies meet and override the polar easterlies along the polar front. Dense cold air masses flow toward the equator meet milder, lighter midlatitude air masses moving poleward, not continuous around the globe, where temp gradient is steep, front is well defined definition: transition zone between cold polar easterlies and mild midlatitude westerlies
Trade winds
surface winds blowing out of the southern flanks of the anticyclones, most persistent winds on the planet Definition: prevailing planetary-scale surface winds in tropical latitudes; these blow from the northeast in the northern hemisphere and from the southeast in the southern hemisphere
midlatitude westerlies
surface winds north of the horse latitudes, highly variable, blow from southwest
the most reliable singularity is
the January thaw in New England
as air pressure rises over northern Australia, air pressure falls over the tropical central Pacific Ocean. This phenomenon is known as...
the southern oscillation
Doldrums
the trade winds of the two hemispheres converge into a broad east-west belt of light and variable winds, ascending air induces cloudiness and rainfall definition: an east-west belt of light and variable surface winds where the trade winds of the two hemispheres converge
Hadley Cell
thermally driven air circulation in tropical and subtropical latitudes of both hemispheres resembling a huge convective cell with rising air near the equator and sinking air in the subtropical anticyclones; situated on either side of the ITCZ and extend poleward to the subtropical highs
what are the three characteristics of rossby waves?
wavelength (distance between successive troughs or ridges) amplitude (north-south extent) number of waves encircling the hemisphere
Long-waves in the westerlies undergo changes in
wavelength, number of waves, wave amplitude
the horse latitudes are regions of relatively ____ surface winds near _____ degreesÂ
weak....30
over a broad region about the center of a subtropical high, the horizontal air-pressure gradient is ______ and winds are _____.
weak....calm
meridional flow
westerlies exhibit considerable amplitude and flow in a pattern of deep troughs and sharp ridges, masses of cold air surge southward, and warm air streams northward, where contrasting air masses collide, warm air overrides cold air and the stage is set for the development of cyclones that are then swept along by the westerlies
zonal flow pattern
westerlies flow almost directly from west to east - nearly parallel to latitude circles, with a weak meridional component. north-south exchange or air mass is minimal, cold air masses stay to the north and warm air masses remain in south, United States gets weather from the pacific ocean so west mountain - moist and then dry and mild weather east of Rocky
how is the transport accomplished poleward of 30 degrees N and 30 degrees S?
westerlies, subpolar, polar front, polar easterlies
Monsoon climates feature ______ summers and ____ winters.
wet....dry
Over land, the summer monsoon is ______ and the winter monsoon is _____.
wet...dry
what are the two basic factors that determine the general planetary-scale circulation in the atmosphere?
winds and pressure systemsÂ
When are the westerlies more vigorous?
winter (they strengthen and exhibit fewer waves of longer length and greater amplitude) than in summer (north-south temperature differences are less, pressure gradients are weaker, and as a consequence, so are the westerlies)
the midlatitude westerlies are more energetic in ____ than in ____
winter...summer