Meaning of depression in geography: geographyalltheway.com – Key Stage 3 (11 – 14 yrs) – Conoce las especies de Puerto Rico

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Meaning of depression in geography: geographyalltheway.com – Key Stage 3 (11 – 14 yrs)

Royal Meteorological Society Weather Systems –

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Anticyclones, Depressions and Fronts

By the end of the lesson, you will be able to:

Understand the characteristics of depressions and fronts and the sequence of associated weather
Understand the characteristics of anticyclones and the contrast between those in summer and in winter.

Part A – Anticyclones and Depressions

Part B – Fronts

Part C – Life cycle of a Depression

Part D – Depression cross-section and weather sequence

Teachers’ notes

Part A

Anticyclones, Depressions and Fronts

Part A – Anticyclones and Depressions

High pressure systems

A high pressure system, also known as an anticyclone occurs when the weather is dominated by stable conditions. Under an anticyclone air is descending, forming an area of higher pressure at the surface. Because of these stable conditions, cloud formation is inhibited, so the weather is usually settled with only small amounts of cloud cover. In the Northern Hemisphere winds blow in a clockwise direction around an anticyclone. As isobars are normally widely spaced around an anticyclone, winds are often quite light.

Anticyclones can be identified on weather charts as an often large area of widely spaced isobars, where pressure is higher than surrounding areas.

Winter anticyclones

In winter the clear, settled conditions and light winds associated with anticyclones can lead to frost and fog. The clear skies allow heat to be lost from the surface of the earth by radiation, allowing temperatures to fall steadily overnight, leading to air or ground frosts. Light winds along with falling temperatures can encourage fog to form; this can linger well into the following morning and be slow to clear. If high pressure becomes established over Northern Europe during winter this can bring a spell of cold easterly winds to the UK.

Summer anticyclones

In summer the clear settled conditions associated with anticyclones can bring long sunny days and warm temperatures. The weather is normally dry, although occasionally, very hot temperatures can trigger thunderstorms. An anticyclone situated over the UK or near continent usually brings warm, fine weather.

Low pressure systems

A low pressure system, also known as a depression occurs when the weather is dominated by unstable conditions. Under a depression air is rising, forming an area of low pressure at the surface. This rising air cools and condenses and helps encourage cloud formation, so the weather is often cloudy and wet. In the Northern Hemisphere winds blow in anticlockwise direction around a depression. Isobars are normally closely spaced around a depressions leading to strong winds.

Depressions can be identified on weather charts as an area of closely spaced isobars, often in a roughly circular shape, where pressure is lower than surrounding areas. They are often accompanied by fronts.

What to do next

Using this information on pressure systems you should now be able to complete worksheet 1.

Then you can complete Extension 1 or worksheet 2.

Part B

Anticyclones, Depressions and Fronts

Part B – Fronts

A front is a boundary between two different types of air masses, these are normally warm moist air masses from the tropics and cooler drier air masses from polar regions. Fronts move with the wind so over the UK they normally move from west to east. The notes below provide information about the most common types of fronts. The descriptions given apply to active well developed fronts, weaker fronts may not display all the characteristics or they may be less well defined.

Warm fronts

A warm front indicates that warm air is advancing and rising up over the colder air. This is because the warm air is ‘lighter’ or less dense, than the cold air. Therefore warm fronts occur where warmer air is replacing cooler air at the surface. As the warm front approaches there is a gradual deterioration in the weather. Clouds gradually lower from higher cirrus, through altostratus, to stratus and nimbostratus at the front. There is often a prolonged spell of rainfall which is often heavy. Behind the warm front the rain becomes lighter, turns to drizzle or ceases, but it remains cloudy. Temperatures rise behind the warm front and winds turn clockwise, also known as a wind ‘veer’. Pressure falls steadily ahead of and during the passage of the warm front, but then rises slowly after its passage.

The diagram below shows the formation of a warm front in diagrammatic form.

The diagram below shows a cross section through a warm front, with associated cloud, temperature and weather changes.

Cold fronts

A cold front indicates that cold air is advancing and pushing underneath warmer air at the surface. This occurs because the cold air is ‘heavier’ or denser than the warm air. Therefore cold fronts occur where cooler air is replacing warmer air at the surface. The passage of weather associated with a cold front is much shorter lived than that with a warm front. As there is often a lot of cloud in the warmer air ahead of the cold front, there is often little indication of the approaching cold front. As the front passes temperatures fall and there is often a short spell of very heavy rain, sometimes with inbedded thunderstorms and cumulonimbus clouds. Behind the front the weather is much brighter with broken clouds but occasional showers. Winds veer with the passage of the cold front and are often strong and gusty, especially near showers. Pressure rises throughout the approach and passage of the cold front.

The diagram below shows the formation of a cold front in diagrammatic form.

The diagram below shows a cross section through a cold front, with associated cloud, temperature and weather changes.

Occlusions

In a mature depression the warm front normally precedes the cold front. Cold fronts generally travel much quicker than warm fronts, and eventually it will catch up with the warm front. Where the two fronts meet, warm air is lifted from the surface and an occlusion is formed. An occlusion can be thought of as having similar characteristics to both warm and cold fronts. The weather ahead of an occlusion is similar to that ahead of a warm front, whilst the weather behind is similar to that behind a cold front.

The diagrams below depict the formation of an occlusion.

The diagram below shows the occlusion in cross section.

What to do next

Now you can go on to Part C – Life cycle of a Depression.

Anticyclones, Depressions and Fronts

Part C – Life cycle of a Depression

A Norwegian scientist called Vilhelm Bjerknes devised a simple model which described how depressions developed from the meeting of warm and cold air. The model had four stages which are detailed below.

Origin and infancy

Initially a warm air mass such as one from the tropics, meets a cooler air mass, such as one from the polar regions. Depressions which affect the UK normally originate over the Atlantic Ocean.
Maturity
The warm air rises up over the colder air which is sinking. A warm sector develops between the warm and cold fronts. The mature stage of a depression often occurs over the UK.

Occlusion

The cold front travels at around 40 to 50 miles per hour, compared to the warm front which travels at only 20 to 30 miles per hour. Therefore the cold front eventually catches up with the warm front. When this occurs an occlusion is formed.

Death

Eventually the frontal system dies as all the warm air has been pushed up from the surface and all that remains is cold air. The occlusion dies out as temperatures are similar on both sides. This stage normally occurs over Europe or Scandinavia.
What to do next
Now you can go on to Part D – Depression cross-section and weather sequence.

Anticyclones, Depressions and Fronts

Part D – Depression cross-section and weather sequence

Cross-section through a classic Depression

Most depressions have a warm and cold front, more mature depressions may also have an occluded front. The diagram below shows a cross-section through a depression, showing the warm and cold fronts and an indication of the associated weather.

WEATHER ASSOCIATED WITH THE PASSAGE OF A CLASSIC DEPRESSION
	Ahead of the warm front	Passage of the warm front	Warm sector	Passage of the cold front	Cold sector
Pressure	starts to fall steadily	continues to fall	steadies	starts to rise	continues to rise
Temperature	quite cold, starts to rise	continues to rise	quite mild	sudden drop	remains cold
Cloud cover	cloud base drops and thickens (cirrus and altostratus)	cloud base is low and thick (nimbostratus)	cloud may thin and break	clouds thicken (sometimes with large cumulonimbus)	clouds thin with some cumulus
Wind speed and direction	speeds increase and direction backs	veers and becomes blustery with strong gusts	remain steady, backs slightly	speeds increase, sometimes to gale force, sharp veer	winds are squally
Precipitation	none at first, rain closer to front, sometimes snow on leading edge	continues, and sometimes heavy rainfall	rain turns to drizzle or stops	heavy rain, sometimes with hail, thunder or sleet	showers

What to do next

Using this information on the passage of depressions you should now be able to complete worksheet 3, and worksheet 4.

Web page reproduced with the kind permission of the Met Office

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Atlantic Depressions and the British Isles

Frontal depressions have a significant impact on weather across the British Isles. They bring the wet and windy conditions we are used to in the UK.

Depressions are one of the most common features on weather maps across the UK and Ireland. The weather map below shows an example of a depression over the British Isles. If you are not familiar with weather charts the BBC have produced a really handy guide to decoding a weather forecast.

A depression over the UK

A depression is an area of low pressure, where the air is rising. As it rises and cools, water vapour condenses to form clouds and perhaps precipitation. Consequently, the weather in a depression is often cloudy, wet and windy (with winds blowing in an anticlockwise direction around the depression). When the black lines (isobars) on a weather map are close together it means air pressure is changing quickly and therefore windy.

There are usually frontal systems associated with depressions. The red, blue and purple lines represent weather fronts. A red line with semi-circles is a warm front. A warm front has warm air behind it and forms the boundary between a large mass of warm air and cold air. A blue line with triangles shows a cold front. A cold front has cold air behind it and forms the boundary with warmer air. A purple line with semi-circles and triangles is an occluded front. This is an area where the warm front is no longer in contact with the surface of the Earth and sits above cold air.

The video below explores fronts in more detail.

The UK sits between a warm air masses to the south and cold air masses to the north. When a wedge of warm air moves north (or a wedge of cold air moves south) weather fronts form.

Where warm and cold air meets warm humid air is cooled by contact with the cold air. The moisture is condensed and forms cloud and rain. This forms two bands of rain, which can take 1-3 days to pass the UK.

Features of a depression

Depressions typically move over the UK from west to east. The UK is affected by around 100 depressions every year.

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Geological depression – What is a geological depression?

Geological depression – What is a geological depression? – Technical Library Neftegaz.RU

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Geological depressions are formed by various mechanisms

Geological depression – any lowering of the earth’s surface, for example, a depression or basin lying below sea level.
In geomorphology, a depression on the earth’s surface, regardless of its shape or origin.

Depressions are formed by various mechanisms.

Erosion related:

by wind: a depression created by wind erosion, usually in a partially vegetated sand dune ecosystem or on dry soils (eg post-glacial loess environment).
glacier: a depression formed by the erosion of a glacier.
rivers: depression carved by river erosion.
karst subsidence caused by the collapse of an underlying structure, such as sinkholes in a karst area.
endorheic depression, usually containing a permanent or intermittent (seasonal) lake, salt marsh (playa) or dry lake or ephemeral lake.

Sedimentary related: in sedimentology, an area densely filled with sediment in which the weight of the sediment further lowers the bottom of the basin.

Structural or tectonic:

Structural basin: syncline depression; a region of tectonic depression as a result of isostasy or subduction.
Graben or Rift Valley: Linear depressions or basins created by rifting in a region by tectonic extensional forces.
A tectonic basin caused by displacement in a slip or fault transformation (example: Dead Sea area).
Ocean trench: A deep, linear depression on the ocean floor. Ocean trenches are caused by subduction (when one tectonic plate is pushed under another) of oceanic crust under either oceanic crust or continental crust.
Basin formed by an ice sheet: an area indented in the weight of the ice sheet, resulting in a post-glacial rebound after the ice melts (the area adjacent to the ice sheet may be pushed down to create a peripheral depression).

Volcanism – endogenous natural phenomena associated with molten magmatic masses and their gaseous by-products, both in the deep interior and on the surface of the Earth:

Caldera: A volcanic depression resulting from destruction following a volcanic eruption.
Crater: A volcanic depression, smaller than a caldera, formed by the sinking or sinking of the earth’s surface over a void.
Maar: depression resulting from a phreatomagmatic eruption or diatreme explosion.

specialists from the Institute of Geography of the Russian Academy of Sciences solve the mystery of the origin of large depressions in the south of the East European Plain

06/15/2020 12:27

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Manual drilling in the bottom of the Bolshoi Liman, winter field season. Photo: K. Filippova

Large closed relief depressions (depressions), common
on the plains of Ciscaucasia, the Sea of \u200b\u200bAzov and the Northern Black Sea region,
are ancient hollows of blowing – to such
the scientists of the laboratory of paleoarchives of the natural environment came to the conclusion
Institute of Geography of the Russian Academy of Sciences, based on the results of the analysis of digital
terrain models SRTM. The use of GIS technologies has allowed
specialists to quickly receive and analyze a set
quantitative parameters for each fixed depression, and
statistical data processing – substantiate conclusions about
the origin of these landforms.

Depressions of loess plains in southern Russia and southeastern Ukraine
known by various local names – padi, padins, pods,
estuaries. Unlike the so-called “steppe saucers”, large
depressions are an order of magnitude larger: the length is from
the first kilometers to more than two tens of kilometers; depth from
the first meters to twenty meters; area – from one to two hundred
square kilometers.

“The origin of such depressions is a debatable issue,” says
project manager, employee of the laboratory of paleoarchives
Natural Environment Institute of Geography RAS Andrey Zakharov. – Behind
Over the past 80 years, various mechanisms for their formation have been proposed:
subsidence-loess, thermokarst, erosion-suffusion,
firth-lake, tectonic. However, none of these hypotheses
has today as a sufficient factual
substantiation, as well as a reasoned refutation. The current
uncertainty is obviously associated with poor knowledge
geological and geomorphological structure of depressions. And their questions
morphologies are covered in the literature even worse than the features
geological structure,” the scientist emphasizes.

In addition to the origin, the problem of development also remains unresolved.
depressions in the future: do these forms have an upward trend or
are stable? The significance of the forecast for the development of the Western
relief due to the potential threat of a decrease in the quality
agricultural land in the event of an increase in their area. This
due to the fact that within the bottoms of depressions there is an excess
hydration and formation of compacted and poorly drained confluent
soils.

Planned form of the studied depressions is predominantly elongated –
drop-shaped, ovoid, oval, triangular. For depressions
smooth sides without clear edges and rear seams are characteristic.
The planned dimensions of depressions are orders of magnitude greater than their depth, due to
making them difficult to recognize on the ground. According to Andrey
Zakharov, standing in the center of the depression, it is not always possible to immediately understand
that you are inside a closed relief depression. depressions
not evenly distributed over the territory, but grouped into
areas within which there is a specificity of their forms and
sizes. Scientists have identified 7 distribution areas of large
depressions, in which a total of 312 such
forms. “Morphometric data allowed us to establish a high
consistency of the orientation of the long axes of depressions in all
areas, – says Andrey Zakharov. However, it was found
change in the main azimuth of depressions orientation from the area to
range: they seem to unfold in the form of a fan – in the western
areas with their “sharp” end look to the north-north-west, in
central – to the north, in the east – to the north-northeast. At
a number of depressions, the asymmetry of the transverse profile is expressed:
the eastern slope is steep, the western slope is more gentle, complicated
ridge relief. Such features may indicate their
deflationary nature – i.e. formation as a result of wind
blowing loose material from the surface, the scientist emphasizes.
– In addition, we carried out a comparative analysis of depressions with
deflationary basins from different regions of the world: “playas”
Great Plains of the USA, large oval depressions of Manchuria,
deflationary basins of Transbaikalia. Comparison results
showed a high similarity of the shape of our depressions with deflationary
hollows developed on a loess and sandy substrate”, –
clarifies Andrey Zakharov.

Slopes of the Liman Bolshoi depression, Krasnodar Territory. Photo: K. Filippova

Outcrop of the Vorontsovskaya Pad basin from the side of the Taganrog Bay. Photo: A. Zakharov

Within the framework of the RSF project “Geological and geomorphological indicators
changes in atmospheric circulation in the Azov-Caucasian region
over the last 150 thousand years” (http://igras.ru/2117) by a team of scientists in which
also included Evgeny Konstantinov, Evgeniya Selezneva and Ksenia
Filippov, it was revealed that all areas of depressions are located in
conditions of low relief in absolute height with underdeveloped
erosion network. “Weapons intercept most of
surface runoff, practically depriving river systems
opportunities to develop, – Ksenia comments on the situation
Filippova, employee of the laboratory of paleoarchives of the natural environment
Institute of Geography RAS. – Small erosional forms (beams and
hollows) have, as a rule, radial-centripetal
drawing tied to the depressions. The recesses are thus
are unequivocally older than beam-hollow systems, which in
they fall. The age of small erosional forms according to geological
data is estimated at 130-150 thousand years. Therefore, depressions
these are relic forms, formed at the end of the middle
Pleistocene. Threats of land degradation as a result of the growth of depressions
does not exist in the short term,” says the specialist.

Head of the laboratory of paleorchives of the natural environment of the Institute
Geography of the Russian Academy of Sciences Evgeny Konstantinov emphasizes the great importance
wind as a relief-forming agent in semi-arid regions:
“The results obtained are of great value for
paleogeographers. They at least make you think about the power and
the geological role of the wind, capable of transforming the relief on
huge spaces. Territories where similar processes are taking place today
do not flow or are slow, in the past, tens of thousands of years ago,
were the arena for the development of intense eolian processes. This led
on the one hand, to the accumulation of thick layers of loess – in fact,
eolian dust. On the other hand, under conditions where the surface
was dried and devoid of a dense vegetation cover, and the strength
wind exceeded the critical threshold, such
unusual landforms like large depressions. But the final
conclusions about the reasons for the formation of depressions, their localization and age
can be done only after processing all geological
materials collected by our team,” sums up Evgeny
Konstantinov.

Distribution of large depressions: a – position of areas on the overview map, b – area 1, c – area 2, d – area 3, e – area 4, f – area 5, g – area 6, h – area 7. Rose diagrams show the orientation of the long axis of depressions. Topographic base – model SRTM

Asymmetric depressions of the area 3. Longitudinal ridges are visible near the western slope of depressions. Topographic base – model SRTM

[Materials for publication provided by the press service of the Institute
Geography RAS]

Posted by Natalya Bazanova

Institute of Geography RAS
GIS technologies
relief depression
depressions
paleogeographers
origin of depressions
landforms

Information provided by the Information Agency “Scientific Russia”.