29 Polar and Highland Climates

Dr. Jitender Saroha

Contents

Introduction

Learning Objectives

Polar Climates: Bases and Types

Polar Tundra Climate

Distribution

Temperature

Precipitation

Natural Vegetation

Ice-cap Climate

Distribution

Temperature

Precipitation

Natural Vegetation

Highland Climate

Distribution

Characteristics

Summary and conclusions

Multiple Choice Questions

Answers

References

Web Links

Introduction

Polar climates are known for their long lasting cold. Polar climates have cold winters and cool summers. Polar winters are associated with periods of persistent night and temperatures are extreme. During summer, cool conditions prevail, though the days are long, but the oblique sun rays produce little warming. Further, high albedo of ice and snow cover reflects majority ofinsolation and some heat is also used in melting of the snow cover. Due to cool summers and extremely cold winters, the annual range of temperatures are excessive.

The highland climates are different from adjoining lowlands. These climates reflect a great diversity over limited distance. The pattern of climates in highland areas is a very complex mosaic. The variety and changeability best describe the climates of highlands.The main climate controls which determine the climates of highlands are: latitude or location, altitude, shape and positioning of highland, exposure to winds, slope and direction of slope i.e. aspect. In this module, focus is on polar climates and climates of highlands.

Learning Objective:

After studying this module, you will be able to:

understand the meaning of polar climates,
differentiate between two major types of polar climates,
describe the distribution and characteristics of polar climates,
understand the variety and changeability of the climate of highlands, an
explain the role of location, altitude, slope and exposure to winds as determinants of the climates of highlands.

Polar Climates: Bases and Types

Although polar climates are classified as humid, precipitation is generally scanty. As temperature remains low, the evaporation is limited. Normally, precipitation is most copious during the summer season when the humidity is the maximum. According to the Koppen’s climatic classification, polar climates are those in which the average temperature of the warmest month is below 100 C. Therefore, the isotherm of 100C of the warmest month limits the polar climates.There are two well recognized sub-types in polar climates – (i) the polar tundra climate (ET) and (ii) the ice cap climate (EF). These are demarcated on the basis of 00C isotherm of the warmest month (Figure 1).

Figure 1: Polar and Ice Cap Climates

Source: http://astro.wsu.edu/worthey/earth/html/im-atmosphere/climate-zone-de.gif

Polar Tundra climate or Tundra climate

Distribution: The polar tundra climate is largely restricted to the Northern Hemisphere. It is distributed in the latitudinal range of 600 – 75 0 N and S, except for the northern coast of Greenland where tundra climate occurs at latitude greater than 800 N. The poleward boundary of tundra climate is demarcated by 00C and equatorward by 100 C isotherms of the warmest month. This climate occupies the northern fringes of North America, including the Canadian islands and Eurasia and ice free shores of northern Iceland and coastal Greenland. In the Southern Hemisphere, no substantial land areas are present in the latitudes where tundra climate prevails. Further, the temperature ofthese small areas hasbeen moderated by proximity of surrounding oceans. In the Southern Hemisphere, Graham Land peninsula of the Antarctica is the only tundra area.

The latitudinal situation and atmospheric stability of polar high pressure system are the major controls of the tundra climate.

Temperature: In polar tundra climates, winters are long, bitterly cold and very severe. The summers are very short and mild. The average temperature of the warmest month is in the range of 00 to 10 0 C. The average annual temperature is – 120C.The mean monthly temperatures are below freezing for 7 to 9 months of the year (Figure 2). Even the warmest month is damp and chilly. The average temperature of the warmest month at Point Barrow, Alaska is 40C. At Upernivik, Greenland (730N), summer season monthly means are barely over 50C.

Figure 2. Distribution of Temperature at Polar Tundra Climate Stations

Source: Frederick K.L and Edward, J.T. (2010), P-446 and 488.

Due to limited variation in day and night temperatures, the diurnal range of temperature is meager. The annual range of temperature is quiet large but not as large as in the taiga climate region. However, at coastal fringes the annual ranges of temperature are usually small due to the moderating maritime influence. For instance, the average temperature of the coldest month at Vardo is 6.10 C due to the warming effect of the North Atlantic Drift, whereas Point Barrow, Alaska, Hebron, Alaska and Ponds Inlet, Canada have respectively -280 C, -300C and -33.30C temperatures due to continentality.AtUpernivik, Greenland, the long, very cold winters bring monthly means as low as -200C. The average annual temperature at Barrow, Alaska and Valgach, Russia is -12.20C and -6.50 C, respectively (Figure 3).

The ground surface remains snow covered for at least 7 to 8 months in a year. The cold and high velocity winds with powdery snow of this region are known as blizzards. The blizzards make it difficult to measure the actual snow fall received at a place. The continental polar (cP), maritime polar (mP) and continental arctic (cA) air masses play significant role in determining temperature and precipitation condition of tundra climate region.

Figure 3. Temperature and Precipitation at Polar Tundra Climate Stations

Source:https://image.slidesharecdn.com/10-110217020031-phpapp02/95/10-34-728.jpg?cb=1297908156

Precipitation: The tundra climate is associated with low precipitation. The annual average precipitation is less than 40 cm. As temperatures remain low throughout the year, the evaporation is limited and consequently the absolute humidity is very low. It is noteworthy that advection of winds from the extremely cold subarctic region not only intensifies the severity of winter but due to stability dryness also prevails. Moreover, the tundra climate region is dominated by polar anticyclonic conditions and divergent system of air circulation.

Figure 4. Distribution of Precipitation at Polar Tundra Climate Stations

Source: Frederick K.L and Edward, J.T. (2010), P-446 and 488.

The tundra region receives most of the precipitation during summer and autumn and relatively warmer conditions prevail. The precipitation is cyclonic in origin and it takes place due to more northerly route followed by cyclones in summer season. Precipitation generally takes place in the form of snowfall. Coastal areas are also prone to fog. In the Greenland, stations show higher precipitation and distribution is also throughout the year (Figure 4). It is because of considerable marine influence on these stations. The warm North Atlantic Drift keeps winter temperatures relatively warm, and maritime polar (mP) air masses bring precipitation throughout the year.

Natural Vegetation: The natural vegetation of the tundra region includes lichens and mosses. In addition, there are different types of flowering herbaceous plants, small shrubs and grasses that mature during the cool and short summer season. The plants are mainly cryophytes. Due to enduring cold and the absence of minimum required threshold of sunlight only 3 per cent species of total world plant species could grow in tundra climate.

The 100 C isotherm of the warmest month that demarcates the equatorward limit of tundra climate also demarcates the poleward limit of tree growth. Hence, the tundra is treeless and aregion of grasses, sledges, mosses and lichens. During the enduring cold winter season, plants become dormant or inactive, but as the short and cool summer season begins these plants mature and produce seeds with substantial swiftness. The growing season is less than 50 days in a year.

Due to short and cool summers, the frozen soils of this region normally melt up to the depth of less than a meter. Therefore, the subsoil maintains permafrost position. These conditions obstruct the downward movement of water and consequently poorly drained boggy soils develop. The marshes, swamps and bogs make the summer tundra terrain difficult to transverse. In Canada and Alaska, this type of landscape is called muskeg. Vegetation is scarce on exposed dry slopes and summits – these rocky pavements are known as ‘fell-field’, the Danish term which means ‘rock desert’. Tundra is a Finnish term which means barren land.

The Ice-Cap Climate

Koppen identified the ice-cap climate on the basis of criterion of temperature less than 00C for the warmest month. It means the mean temperature of every month is below freezing. Due to subfreezing temperatures the landscape has permanent ice and snow cover. There is limited information about climatic and weather conditions of this climatic regions because, the climate is extreme and weather stations are limited.

Distribution: This climate is distributed mainly in the latitudinal zone of 650 to 900 N and S. This climate extends over a large area of about 15.5 million square km or about 9 per cent of earth’s land area. It includes the ice sheets of Antarctica and Greenland and scattered areas in high mountains.

Temperature: The EF climate has extremely low average annual temperatures.The polar ice-cap climate records the lowest annual average temperatures. For instance, the average annual temperature at Eismitte, Greenland is -30.50C. The average temperature of winter at Eismitte is -400C and the warmest month has -110C (Figure 5).

The causes of extremely low temperatures in EF climate are following – (i) latitudinal position; (ii) the ice cover has high albedo and about 80 per cent of the limited insolation received is reflected back without utilization;(iii) the majority part of energy available in this region is used in melting of ice and not for increasing air temperature; the effectiveness of the warmth is lost by latent heatand

(iv) finally, elevation also plays a significant role. For instance, Antarctica has the highest average height among the continents. Likewise in Greenland majority part is elevated except coastal fringes.

Figure 5. Temperature and Precipitation at Ice-cap Climate Stations

Source:https://image.slidesharecdn.com/10-110217020031-phpapp02/95/10-36-728.jpg?cb=1297908156

The average annual temperature at the Russian Antarctic Meteorological Station, Vostok, Antarctica, is -570C. It is noteworthy that Vostok recorded the world’s lowest temperature ever on August 24, 1960 as -88.30C.

The air adjacent to ice cover gets very cold and inversion of temperature is normalaffair. Temperature of thesurface is as much as 250 to 350 C colder than air just a few hundred meters above surface. The cold and heavy air slides along slopes due to gravity resulting into strong winds and blizzards. These Katabatic winds are a common characteristic feature of the weather of highlands in ice-caps.The ice covered parts of Antarctica and Greenland have presence of thermally induced anticyclones. At still greater height, there are deep cyclonic vortices associated with high velocity westerly winds. These circulations are more persistent over Antarctica in winter.

Precipitation: The average annual precipitation in EF climate is meager and normally less than 10 cm. These areas are also known as polar deserts. Although the precipitation is low but it is more than evaporation. Therefore, this climate is basically humid. The precipitation is received as snow or as small crystals of dry and hard ice. Some precipitation is received in the form of a mist of powdery ice when cyclones strike at the margins of the ice plateaus.

Natural Vegetation and Animal Life: This climate is hostile to any form of vegetation. Due to presence of permanent ice cover it is nearly vegetation less. But various kinds of fish, seal, walrus and polar bears are found in these latitudinal belts. The coastal areas of Antarctica are inhabited by aquatic birds, dominantly penguins.

Highland Climates

Distribution: In North America, highland climates are found in the Rockies, Sierra Nevada, Cascade, Coastal ranges and the mountains and interior plateau of Mexico. In South America, the Andes represent a continuous zone of highland climate that extends over about 8000 km. The greatest extend of highland climates stretches from western China, across southern Eurasia, to northern Spain, and one of its branch join from the Himalayas to the Pyrenees i.e. also known as Mid Continental Belt region. Atlas Mountain in Africa is also part of this belt. In Africa, highland climates are also found in the Ethiopian highland or the Eastern highlands. In Europe, Alps, Carpathian ranges and Scandinavian highlands are the most significant. In Australia the Great Dividing Range and in New Zealand the Southern Alps have highland climates.

Characteristics: The main climate controls which determine the climates of highlands are: latitude or location, altitude, shape and positioning of highland, exposure to winds, slope and direction of slope, i.e. aspect.

At the same latitude or in same latitudinal zone next to the distribution of land and water, altitude is probably the most significant factor to produce climate differences. With increase in height, pressure, temperature and precipitation undergo some well defined changes. The well known climatic effects of highlands are that the pressure and temperature decrease with altitude. But winds, precipitation, fog and clouds show an increasing trend. The highlands are colder and often wetter than lowlands.

The highland climates are characterized by their distinct zonation by altitude. For instance, in tropical highland the Andes Mountains (eastern slope), tropical rainforest climate is found in the foothills up to the height of 1200 m. In the height range of 1200 to 2400 m, subtropical climate prevails; the next zone of 2400 to 3200 m is characterized by mesothermal climate; the 3600 to 4800 m zone is occupied by microthermal climate. Beyond this altitude, there is permanent snow cover resembling the polar climates. The altitudinal zones positions in highlands also depends on latitudes (Figure 6). Location factor such as coastal location or interior location also plays a significant role. Towards poles, the tree line and snow line are found at lesser height in highlands. Climate changes with altitude are fast and complex. It is generalized that 300 m climb is equivalent to 500 to 1000 km towards the poles. The broad generalization is this that as climate changes from equator to pole similarly it changes with altitude.

Figure 6A: Altitudinal Zones in Highland Climates

Source:https://sites.google.com/site/climatetypes/_/rsrc/1317062967962/highland/El evation%20Temperature.png?height=381&width=400

Figure 6B: Altitudinal Zones in Highland Climates

Source:http://apollo.lsc.vsc.edu/classes/met130/notes/chapter17/graphics/climate_hgt.jpg

The relief variations are common in highlands. Therefore, exposure is another important factor in highland climates. Every change in slope with respect of the Sun’s rays results into a different micro climate. In Northern Hemisphere, south facing slopes are warmer as they receive direct insolation. The exposure affects the daily departureof temperature. East facing slopes have relatively warmer mornings and cooler afternoons as compared with the cooler mornings and warmer afternoons of west facing slopes. Slope aspect also plays an important role in determining the distribution of settlements, cultivation of crops and types of plants.

Exposure to winds is another significant determinant of highland climates. The peaks and exposed slopes have stronger winds due to minimum friction as compared to lower slopes. In highlands, mountain and valley breezes are common. During day time valley breezes or anabatic winds operate up-slope from valley to mountain. These up-slopes winds result in to atmospheric instability and cumulus and cumulonimbus clouds bring precipitation normally in the afternoon. The down-slope winds normally induce the inversion of temperature condition by uplifting the warm and moist air of valleys. In winter the lower valley parts may have below freezing point temperatures resulting into fog and frost. Further, this uplifting may result into unstable conditions and clouds and precipitation may be the result. Magdalena valley and the Lianos of Columbia receive majority of their precipitation in this manner.

Highlands obstruct the flow of winds. On the windward slopes winds are forced to ascend. The ascending warm and moist winds cause precipitation, whereas descending winds become warmer and dry due to adiabatic change and evaporation dominates. The chinook (snow eater) winds along the eastern slopes of the Rockies Mountains and foehn winds in Alps are hot and dry and result in to snow melting.

In mountain areas,topography is the dominant factor in determining the distribution of precipitation. As relief variations are intense, the distribution of precipitation is complex. In low latitudes, generally the precipitation increases up to the height of about 1500 m and above this it starts decreasing. But in the middle latitudes the trend upto the peaks is increasing precipitation. In the highlands of arid areas greater amount of precipitation provides water for adjoining arid lowlands for drinking, irrigation and power generation.

Normally, in highland areas more precipitation is received during summer as compared to winters and also more during day time as compared to nights. The windward slopes receive heavy precipitation. The leeward sides are generally rain shadow areas. The uprising air along the crest also produce precipitation on the higher slopes of leeward sides, but it is limited to a short distance (Figure 7).

Figure 7. Distribution of Precipitation on the Windward and Leeward Sides

Source:https://www.slideshare.net/lschmidt1170/10-6955975

It is noteworthy that the seasonal temperature cycles and precipitation distribution of highland stations often resemble the adjoining lowland places. For instance, a peculiar characteristic of highland climate in the tropics is a larger diurnal than annual range of temperature. The temperature at Quito, Ecuador over the months shows almost no change, but its diurnal range of temperature is more than 100C (Figure 8). This characteristic feature is common to tropical equatorial climates where diurnal ranges are more than annual ranges of temperature. Likewise, the similarity in precipitation throughout the year is also clearly evident. Similarly the seasonal distribution of temperature and precipitation at Shimla (Highland) and Delhi(Lowland) is matching;the difference is only of valuesand not of pattern(Figure 9).

Figure 8. Mean Monthly Temperature at Quito and Guayaquil

Source: http://www.goes-r.gov/users/comet/tropical/textbook_2nd_edition/media/graphics/guay_quito_topo.jpg

Figure 9: Temperature and Precipitation at Shimla and Delhi

Source: http://geography.name/wp-content/uploads/2016/08/4577-1.jpg

Summary and Conclusions

Polar climates have cold winters and cool summers. Due to cool summers and extremely cold winters, the annual range of temperatures isvery high.The polar climates are divided into two sub types on the basis of 00 C isotherm of the average temperature of the warmest month – tundra climate (ET) and ice-cap climate (EF). The polar tundra climate is largely restricted to the Northern Hemisphere. The poleward boundary of tundra climate is demarcated by 00C and equatorward by 100C isotherms of the warmest month. This climate occupies the northern fringes of North America, including the Canadian islands and Eurasia and ice free shores of northern Iceland and coastal Greenland. In the Southern Hemisphere, Graham Land peninsula of the Antarctica is the only tundra area.The latitudinal situation and atmospheric stability of polar high pressure system are the major controls of the tundra climate.

The mean temperature of every monthin ice-cap climate isbelow freezingpoint. Due to subfreezing temperatures, the landscape has permanent ice and snow cover. This climate is distributed mainly in the latitudinal zone of 650 to 90 0 N and S. This climate extends over a large area of about 15.5 million square km or about 9 per cent of earth’s land area. It includes the ice sheets of Antarctica and Greenland and scattered areas in high mountains. The EF climate has extremely low average annual temperatures. The polar ice-cap climate records the lowest annual average temperatures.The ice covered parts of Antarctica and Greenland have presence of thermally induced anticyclones. At still greater height, there are deep cyclonic vortices associated with high velocity westerly winds. These circulations are more persistent over Antarctica in winter. The average annual precipitation in EF climate is meager and normally less than 10 cm. These areas are also known as polar deserts.

The highland climates are different from adjoining lowlands. These climates reflect a great diversity over limited distance. The pattern of climates in highland areas is a very complex mosaic. The variety and changeability best describe the climates of highlands.The main climate controls which determine the climates of highlands are: latitude or location, altitude, shape and positioning of highland, exposure to winds, slope and direction of slope, i.e. aspect. In this module,thefocus was on polar climates and climates of highlands.It is noteworthy that the seasonal temperature cycles and precipitation distribution of highland stations often resemble the adjoining lowland places.

you can view video on Polar and Highland Climates

References

Barry, R.G. and Chorley, R.J. (1998) Atmosphere, Weather and Climate, Routledge, London. Frederick, K.L and Edward, J.T. (2010) The Atmosphere – An Introduction to Meteorology, PHI Learning Private Limited, New Delhi.
Husain, M. (2002) Fundamentals of Physical Geography, Rawat Publications, Jaipur.
Lal, D.S. (1993) Climatology, Chaitanya Publishing House, Allahabad.
Lal, D.S. (2009) Physical Geography, Sharda PustakBhawan, Allahabad.
Singh, S. (2015) Physical Geography, Pravalika Publications, Allahabad.
Strahler, A.N. and Strahler, A.N. (2001) Modern Physical Geography, John Wiley and Sons, Singapore.
Trewartha, G.T. and Horne, L.H.(1968) An Introduction to Climate, McGraw-Hill, New York.

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