Land cover

The Arctic lands are commonly subdivided into the High and Low Arctic based on broad climatic, geographical and biological grounds (Bliss, 1997) although many ecologists recognize five subzones (Walker et al., 2002). As a general statement, the High Arctic is characterized by more severe environmental conditions than the Low Arctic, reflected in the type and distribution of vegetation. Land in the High Arctic is characterized by tundra, a Finnish term for treeless upland. More generally, tundra...

Cloud cover

A very important factor influencing global radiation is cloud cover. The Arctic is cloudy, especially during summer when low-level stratus is prevalent. Mean fields of cloud cover were presented back in Figure 2.24. By far, the dominant effect of clouds is to reduce the downwelling shortwave flux at the surface, largely due to their high albedo (60-75 for Arctic stratus). Cloud absorption is generally only a small percentage (Herman and Curry, 1984). However, attenuation of the downwelling flux...

Fields of the net cloud radiative forcing at the surface

The ISCCP-D data indicate that the cloud radiative forcing is positive for all of the Arctic from October through March. It turns negative over the low-albedo Atlantic side of the Arctic in April. Except near the Pole, it is negative everywhere from June through August. It is hence negative for a much longer time over the sea ice cover than suggested from Curry and Ebert (1992) and may represent shortcomings in the satellite-derived fields or the Curry and Ebert model. This serves to reinforce...

Ice fog

Detailed studies of ice fog characteristics were carried out at Fairbanks, Alaska, in the 1960s by Benson (1970). The most notable feature of its formation involves the injection of hot, supersaturated exhaust air into a very cold (< 35 C) saturated air mass. This forms 10 m diameter ice crystals in contrast with the roughly 30 m diameter crystals that form as diamond dust in suspension at about 40 C. Low temperatures at Fairbanks conducive to ice fog development are associated with...

Ice concentration

Ice concentration was also introduced in Chapter 2. Recall that concentrations (the part of a given area covered by ice) in the interior pack (the PIZ) typically exceed 97 during winter but decrease during summer to 85-95 , with large variability and lower concentrations in the MIZ. Plate 4 shows a typical pattern of ice concentration for winter based on charts from the National Ice Center (NIC). This represents conditions for the 7-day period January 5-11, 1994. The NIC charts are based on a...

Ice sheet influences on atmospheric circulation

Modeling studies indicate that the Quaternary ice sheets strongly influenced the atmospheric circulation. A number of different global climate models indicate that the winter jet stream over North America was split due to the large extent and height of the Laurentide Ice Sheet. One branch of the jet went around the northern edge of the ice sheet, while the other branch curled south of the ice sheet, so that storm tracks were displaced (Kageyama et al., 1999). The LGM ice sheets also seem to...

Definition

The tropopause is the transition between the troposphere and stratosphere (see Figure 4.1). The tropopause can be defined on both thermal and dynamic criteria. The thermal definition is based on the lapse rate. The standard World Meteorological Organization definition of the tropopause is the lowest level above 500 hPa where the vertical temperature gradient decreases to less than or equal to 2 C km-1 (provided that the average gradient in the upper 2 km layer is less than 2 C km-1). The...

Overview

The Arctic is home to a wide variety of climate conditions. This spectrum reflects, among other things, regional characteristics of the atmospheric circulation, elevation, distance from moisture sources (continentality), and the properties of the underlying surface. The present chapter both summarizes and builds upon what we have already learned through a focus on some of these different climatic regimes. Up to now, relatively little attention has been paid to the Greenland Ice Sheet. This...

Regional aspects of the LGM 1051 Northern Eurasia

The LGM in northern Eurasia occurred around 27 ka to 15 ka. The LGM is relatively well documented, although uncertainties remain in northwestern Russia and in the Barents and Kara seas. Velichko et al. (1984, 1989) and Larsen et al. (1999) provide useful summaries. The glacial history of the Eurasian Arctic has recently become much better understood through the programs for Polar North Atlantic Margins and Quaternary Environments of the Eurasian North. As this book came to press, efforts were...

The Arctic Climate System

The Arctic can be viewed as an integrated system, characterized by intimate couplings between its atmosphere, ocean and land, linked in turn to the larger global system. This comprehensive, up-to-date assessment begins with an outline of early Arctic exploration and the growth of modern research, followed by an overview of the Arctic's basic physical characteristics and climatic features. Using an integrated systems approach, subsequent chapters examine the atmospheric heat budget and...

Selected websites

Arctic Centre, University of Lapland Arctic Research Consortium of the United States (ARCUS) Byrd Polar Research Center Climate Diagnostics Center (CDC) Cold Regions Research and Engineering Laboratory (CRREL) Cooperative Institute for Arctic Research (CIFAR) CRYSYS - CRYosphere SYStem in Canada European Centre for Medium-range Weather Forecasts (ECMWF) Geophysical Institute (GI), University of Alaska Institute of Arctic and Alpine Research (INSTAAR) Intergovernmental Panel on Climate Change...

Anomalies in September ice conditions

There has been a general downward trend in Arctic sea ice extent (the region with at least 15 ice concentrations) during the passive microwave era (1979 onwards) Plate 5 Mean September ice extent (all colored regions) and anomalies in ice concentration (see color bar) for the years 1990, 1993, 1995, 1998, 2002 and 2003 based on SSM I data. The panels for 2002 and 2003 show the median September ice extent. Concentration anomalies and median extent are both referenced to the period 1988-2000...

Arctic Ocean

In general, the Arctic Ocean climate during the LGM featured cold winters, while summers were mostly dry and cooler than present. Mean annual SATs over the Arctic Ocean ranged between -19 C and -26 C as implied from amino acid analysis of molluscs (Barry, 1989). Ice conditions in the Arctic Ocean during the LGM are still poorly known and controversial. One hypothesis is that there were large floating ice shelves, up to 2-3 km thick, over the trans-oceanic ridges. This is evidenced by deep ice...

Internal oscillations

Based on a statistical analysis of 40 years of annual sea ice concentration (SIC) and winter SLP data, Mysak and Venegas 1998 postulate an approximately 10-year SLP over northern North Atlantic and Greenland Sea climate cycle in the Arctic and sub-Arctic that involves the NAO AO. They provide a conceptual feedback loop to explain the relevant processes (Figure 11.20). The diagrammatic approach has already been described in Chapter 5. Starting at the top of the loop, large positive anomalies of...

Mean circulation ice zones and concentration 721 Mean annual circulation

While the characteristics of ice motion will be examined in detail in Section 7.3, it is useful at this point to examine the mean annual drift. Since 1979, the IABP has maintained a network of drifting buoys in the Arctic Ocean. Ice drift records are also available from the NP program. Additional data have been collected by manned US drifting camps, for example T-3. Gridded fields assembled from these Lagrangian drift records provide for assessments of the large-scale ice drift. Figure 7.3...

Definition and bathymetry

The Arctic Ocean covers an area of 14 million km2 according to Welsh et al. (1986). But definitions of the Arctic Ocean and its various seas have tended to be somewhat imprecise and or arbitrary. Definition can be important, in terms of determining the freshwater runoff from the Arctic lands into the ocean and its effects on the salinity. Russian sources commonly divide the ocean into several climatic regions. Figure 2.2 provides a breakdown from Russian sources based more on geographic...

Level Method

Figure 8.4 Map of estimated mean annual sublimation for the Greenland Ice Sheet. Positive values mean transfer from the surface to the atmosphere (from Box and Steffen, 2001, by permission of AGU). Figure 8.4 Map of estimated mean annual sublimation for the Greenland Ice Sheet. Positive values mean transfer from the surface to the atmosphere (from Box and Steffen, 2001, by permission of AGU). In the polar deserts, mean annual temperatures are quite low and only exceed the freezing point in one...

Primary sea ice types

Sea ice is a complex material, comprising a solid component of ice crystals, a liquid component of brine solution in pockets, and a gaseous component of air pockets. While there are many different types of sea ice (World Meteorological Organization, 1989), some of which will be introduced in the next section, there are several basic categories. Firstyear ice (FYI), which comprises up to about 40 of the Arctic sea ice cover (Rothrock and Thomas, 1990 Romanov, 1991) represents the ice growth of a...

Radiation regime

Some aspects of Greenland's radiation were examined in Chapter 5. To summarize and expand, during winter, net allwave radiation is strongly negative. This is a function of the high elevation of the ice sheet and the relative lack of cloud cover compared to other areas of the Arctic, which helps to keep the downwelling longwave flux low. Solar radiation is of course essentially absent in winter. It follows that, compared to other Arctic regions, the summer downwelling solar radiation flux over...

Skin temperature SAT and vertical structure 591 The radiative boundary layer

Surface Sensible Heat Flux Arctic

A number of winter studies (e.g., Overland and Guest, 1991 Overland et al., 1997 Overland et al., 2000) have examined linkages between the skin temperature (the temperature at the very surface), the overlying SAT, the vertical temperature structure Figure 5.11 Daily average surface energy balance components for forest and tundra during (a) summer and (c) spring and the average hourly sensible heat flux for forest and tundra during (b) summer and (d) spring. Standard errors are indicated by the...

Surface air temperature

The high elevation, large extent and high albedo of the ice sheet are significant factors for local and regional surface air temperatures although latitude and distance inland are also involved. Steffen and Box (2001) provide a useful summary. For both the eastern and western slopes of the ice sheet, surface air temperatures decrease by about 0.8 C per degree of latitude. As for general elevation effects, from normalizing all AWS station data to 70 N, annual mean surface air temperatures...

The beginning of systematic observations

The modern basis of Arctic science, and meteorology in particular, was the outcome of Karl Weypricht's suggestion for an International Polar Expedition. Planning began at a conference in Hamburg in 1879, with 11 nations pledging support. Weyprecht died in 1881, but the first International Polar Year (IPY) was mounted in 1882-3. Barr (1985) provides a detailed account of the various national expeditions. Figure 1.2 shows the distribution of the 12 principal stations established in the North...

Cloudradiation feedback

Numerous modeling studies suggest that changes in cloud fraction that would accompany global warming will modify the surface temperature. However, the sign of the feedback between different models ranges from negative (clouds cause cooling) to strongly positive (clouds cause warming). The issue is complicated in that there are feedbacks not only related to cloud fraction, but to cloud height, optical depth, and cloud microphysical properties. In turn, because of its unique thermodynamic and...

An example Resolute Bay NWT

Resolute Bay (Cornwallis Island, Canadian Arctic Archipelago) is typical of a polar desert location. Figure 8.5 summarizes this site's mean annual cycles of surface air temperature, precipitation, cloud cover and downwelling solar radiation. Mean temperature ranges from a low of about -33 C in February to 4 C in July. Precipitation exhibits a pronounced August maximum of about 33 mm, compared to winter-month precipitation totals of < 5 mm. These are raw precipitation totals with no...

Annual and monthly fields of PET

The mean annual field of aerological P ET based on NCEP NCAR over the period 1970-99 is provided in Figure 6.8. Fields for the mid-season months appear in Figure 6.9. The data have been smoothed to try and eliminate most of the problems mentioned earlier. The fields shown here are very similar to those from ERA-15 and ERA-40. Figure 6.8 Aerological estimates of mean annual precipitation minus vapotranspiration (P - ET) based on NCEP NCAR data for the period 1970-99 (mm). Contours are at every...

Description of the annual cycle

Arctic Reanalysis Data

With the basic terms introduced, it is instructive to step through the mean annual cycle of the energy budget. Our ability to assess the budget components has improved since the Nakamura and Oort (1988) study. More accurate TOA radiation fluxes have been obtained by ERBE, although these only cover about a four-year period. Trenberth and Stepaniak (2003) used data from the NCEP NCAR reanalysis to compute grid cell values of vertically integrated energy fluxes, divergences and tendencies for the...

Global climate models

GCMs are in general agreement that the effects of anthropogenic greenhouse warming will be first seen and will be largest in the polar regions, in large part due to feedbacks involving sea ice and snow cover, and the strong stability of the lower troposphere. There is a growing body of evidence pointing to significant change in the Arctic climate system over at least the past several decades. The emerging view is that at least part of the observed changes can be linked to human activities. It...

Hi

Nmniirimtiriasoii iijoznnjfiradiiiaijoiisaa * H fi ana em ta fin SSSSSHi SU S SS 55 i S SI 5 g g S SSSSSHi SU S SS 55 i S SI 5 g g S l l i l l l l i l l l l i i l l l i i f i f i i i * 111111111 1111__ center, and being regenerated. Convection moves the plates in different directions. We now believe that the supercontinent Pangea broke up roughly 200 Ma during the early Jurassic period. Continental drift is of course still occurring, but by about 2 Ma the continents looked largely as they do...

Natural climate variability

Natural climate variations from day-to-day (weather), week-to-week, and within a season, stem largely from the internal dynamics of the atmosphere. This is seen in the passage of baroclinic waves and variations in the planetary waves. Daily to seasonal variations in climate are also influenced by properties of the land and ocean. A number of studies, starting with Lamb (1955), have demonstrated links with snow cover. It has long been known that variations in the onset and strength of the Asian...

Radiation fluxes from surface observations examples from SHEBA

Persson et al. (2002) provide a complete description of the surface energy budget at the SHEBA site in the Beaufort Sea. This is one of many articles outlining SHEBA research results in the 15 October 2002 issue of Journal of Geophysical Research (107, C10). Figure 5.9 shows the mean annual cycles in net radiation, albedo, incoming shortwave radiation and incoming longwave radiation. The SHEBA results are given along with estimates from several other studies. The reader is referred to Persson...

Primary sources

The remainder of this chapter focuses on the Quaternary period. As mentioned, the Quaternary started around 1.8 Ma and comprises the Pleistocene (1.8 Ma to 11.5 ka) and Holocene (11.5 ka to present) epochs (Figure ). The Quaternary is recent enough that many different types of paleoclimate evidence are preserved, especially from the last interglacial onwards. A wealth of information has been obtained by coring the polar ice sheets, such as from GISP2, GRIP and Antarctic ice core projects (e.g.,...

Mean hydrographs

Long-term annual mean runoff ought to balance P ET, but this is not true of means for seasonal and shorter time scales. The most obvious reason is that, for much of the year, the net precipitation is stored in the snowpack. There are also subsurface storages. The typical annual cycle is as follows. In the cold months, runoff is small, and can even cease for small basins. Runoff begins to climb in April or May when the snowpack begins to melt. It then increases sharply, generally with a June...

Radiationclimate feedbacks 5101 The concept of feedbacks

The basic idea behind a feedback is that an initial perturbation to the climate system can be either amplified (a positive feedback) or dampened (negative feedback) through interactions with other climate variables. Kellogg (1973) developed a simple conceptual framework to understand feedbacks, which still finds wide use. Schlesinger (1985) provides a formalized description for use in surface energy balance models. As outlined in the excellent review by Curry et al. (1996), there are a number...

Summary of observed variability and change 1121 Surface air temperature

If we restrict ourselves to zonal means, SAT variability over northern high latitudes can be estimated over the past century. Figure 11.1 shows SAT records for 19002004 for the 55-85 N zonal band expressed as anomalies with respect to 1950-81 means. The plots are based primarily on land stations. Data coverage during the early part of the record is sparse, in particular for high Arctic latitudes. Nevertheless, some useful conclusions can be drawn. Over the twentieth century, zonally averaged...

Typical surface albedos of major surface types

Typical albedos for major surface types in the Arctic are summarized in Table 5.3. There is a wide range of values even within the general categories. In part, the range is explained by small-scale topography as it influences the geometry of insolation and heterogeneities in the physical properties of the surface being considered. For example, the albedo of tundra or boreal forest can differ strongly over small space scales due to variations in species distribution, leaf area, soil...

The THC basic considerations

Ocean transports act along with atmosphere transports to convey heat from low to high latitudes (Chapter 3). Much of the oceanic heat transport is associated with the thermohaline circulation (THC). The THC is the part of the circulation driven by horizontal and vertical gradients in ocean salinity and temperature (hence density gradients). This contrasts with the wind-driven circulation. In the North Atlantic, there is an intense winter heat loss from the ocean to the atmosphere. Cooling of...

Maritime Arctic 831 Characteristics

Boulder Rainfall Annual

The major characteristics of the maritime Arctic are extensive cloudiness, high humidity and a small range in annual temperature. Such climatic conditions are best developed in the Atlantic sector of the Arctic, such as at Jan Mayen (Svalbard) and Iceland. On Jan Mayen the mean temperature is near -7 C in February and 7 C in August. There is fairly ample precipitation in all months with an autumn maximum (Wilson 1969). Nome in western Alaska is another example of a maritime site, but in this...

Wind regime

A prominent feature of the Greenland climate is its katabatic wind regime. In the right conditions such drainage winds can reach gale force. In its most generic sense, a katabatic wind (from the Greek word katabikos - to go down) refers to any downslope wind flowing from high elevation mountains, plateaus or hills down to valleys or plains. But more commonly, the term is reserved for winds that, despite the effects of adiabatic compression during descent, are colder than the air displaced at...

General model types

Single-column models (SCMs) As the name suggests, these have been developed to examine processes in a single column, such as that extending from the surface through some depth in the atmosphere, or from the surface to some depth of the soil. Examples are radiative transfer models and models of active layer thickness in permafrost regions. An attraction of SCMs is that robust physics can be incorporated with relatively modest computer resources. Frequently, SCMs are applied to a two-dimensional...

Characteristics over tundra

The fundamental difference between the Arctic Ocean and tundra in how net radiation is apportioned is in the energy used to melt snow and ice (Ohmura, 1984b). Once the snow is melted from the tundra, energy can be apportioned in sensible heating and to evaporate water. The snowmelt process over tundra tends to be completed over a rather short time interval, typically two weeks or so (Weller and Holmgren, 1974). The consumption of heat through melt on the ice-covered ocean is much larger than on...

The icealbedo feedback

Positive Feedback Mechanism

This is probably the best known of feedbacks. If the climate warms, the extent of snow and ice cover will decrease. The Earth's surface albedo decreases, meaning greater absorption of solar radiation at the surface. The climate hence warms more, melting more snow and ice, and so on. The mechanism can work in reverse, whereby cooling allows more snow and ice to remain on the surface, increasing the Earth's albedo, causing further cooling. The feedback is positive in that, through the chain of...

The Younger Dryas

Gisp2 Ice Core Temperature Data

Figure 10.7 illustrates the YD in terms of high calcium concentrations recorded in the GISP2 ice core. The YD was also associated with high dust concentrations and high magnesium levels. These features imply an intensified circulation over continental regions and increased aridity. In addition, ammonium, nitrate, sulfate, sodium, chloride and potassium concentrations rose (Mayewski et al., 1993). These large increases cannot be explained by increased windiness alone. Destruction of biomass due...

The Arctic Oscillation AO

In 1998, a paper appeared in Geophysical Research Letters by D. Thompson, then a Ph.D. student at the University of Washington, Seattle, and his advisor, J. Wallace (Thompson and Wallace, 1998). Follow-on papers were published shortly thereafter (Thompson and Wallace, 2000 Thompson etal., 2000 Wallace, 2000). Thompson and Wallace (1998) argue that NAO should be considered as a regional manifestation of a more basic mode of SLP variability, which has come to be known as the AO, or NAM. They...

Cyclone activity

It should come as no surprise that the NAO AO is allied with pronounced signals in cyclone frequency. Serreze et al. (1997a) inspected the NAO time series from 1966 through 1993. For each cold-season month (October through March), they extracted the seven years with the most positive and most negative NAO index values. For each month of the seven-year period, they extracted records of cyclone events over the North Atlantic, using an automated detection and tracking algorithm applied to SLP...

Historical perspective

The major centers of action in the Northern Hemisphere circulation - the Azores and Pacific highs, the sub-polar Icelandic and Aleutian lows, and the Siberian High, had been identified in the 1880s by Teisserene de Bort. By 1920, the Bergen School had developed ideas on the characteristics of extratropical cyclones. The nature of the general circulation of the atmosphere was interpreted in terms of a three cell model by Bjerknes, Rossby and others. This model includes thermally direct Hadley...

Mean annual cycles for the major terrestrial drainages 631 PP ET and ET

Some of the results just presented are summarized in Figure 6.10 as mean annual cycles (1960-89) of P, P ET and ET for the four major drainage basins of the Arctic (the Ob, Yenisey, Lena and Mackenzie). The monthly values are simple averages of the data at all grid points located within each basin. Following earlier results, in all four basins, precipitation is at a minimum in February and March and is at a maximum during July. P ET tends to peak during autumn. These autumn maxima arise from...

Sudden stratospheric warmings

An important aspect of variabililty in the stratospheric circulation, and in particular the distortions just mentioned, is sudden stratospheric warmings. Scherhag (1960) first noted these in the 1950s and they were subsequently found to be a characteristic late winter phenomenon (Hare, 1961 Wilson and Godson, 1962, 1963 Labitzke, 1968 1981). Limpasuvan et al. (2004) provide a valuable composite analysis of the lifecycle of sudden stratospheric warming events in the Northern Hemisphere from the...

The Fram Strait outflow

As the primary region for the export of sea ice and low-salinity water out of the Arctic, the Fram Strait outflow merits special attention. A number of efforts have been made to estimate the ice area or volume flux through Fram Strait based on mass balance requirements, measurements of ice drift and thickness through the strait, models or a combination of models and observations. The total ice flux comprises a wind-driven and a current-driven component. Determining the volume flux requires...

References

C. (1989). The role of sea ice and other fresh waters in the Arctic circulation. J. Geophys. Res. 94(C10), 14485-14498. Aagaard, K. and Greisman, P. (1975). Toward new mass and heat budgets for the Arctic Ocean. J. Geophys. Res. 80, 3821-3827. Abdalati, W. and Steffen, K. (1995). Passive microwave-derived snow melt regions on the Greenland ice sheet. Geophys. Res. Lett. 22, 787-790. (1997). Snowmelt on the Greenland ice sheet as derived from passive microwave...

The NAOAO framework merits and shortcomings 1141 SLP and temperature

SLP fields can be used to infer surface winds. An analysis of SLP can hence help us understand how the NAO AO relates to high-latitude SAT variability and recent trends. Figure 11.11 shows SLP patterns, composite anomalies and composite differences for the region north of 50 N based on extremes of Hurrell's NAO index. Data are drawn for the years 1947-96. Immediately evident is that the SLP signature, while strongest in the vicinity of the Icelandic Low (a maximum difference of 22 hPa between...

Development processes

As outlined by Renfrew (2003), Polar Lows develop over open water. When moving over land or the sea ice cover, they tend to rapidly dissipate. They can be thought of as hybrid systems, typically having features both baroclinic and convective in nature. A common feature of Polar Lows seen in satellite imagery is a spiral cloud (comma cloud) signature. Some systems develop a clear eye at the center similar to tropical cyclones (Figure 4.15). Generally, Polar Lows are warm cored, and many have...

Surface and nearsurface circulation 451 Centers of action

Fields of mean sea level pressure (SLP) for the four mid-season months are provided in Figure 4.9. The mean January circulation at sea level, representative of winter, is dominated by the three well-known sub-polar centers of action (1) the Siberian High over east-central Asia (2) the Icelandic Low off the southeast coast of Greenland (3) the Aleutian Low in the North Pacific basin. The central Arctic Ocean appears as a saddle of relatively high pressures between the eastern Eurasian landmass...

Annual runoff for the major drainage basins

Table 6.2 provides basin-averaged values for the four major river systems of precipitation (P), P ET, ET and runoff (R) along with estimates of the runoff ratio (R P) and the fraction of precipitation lost through ET (ET P). These are calculated over the water year, taken as October through September. Precipitation is based on the analysis of Serreze et al. (2003a). Runoff is based on updated records in R-ArcticNET. In contrast to previous results, ET is estimated as the difference between P...

The North Atlantic Oscillation NAO

Nao Slp Eof

The NAO has long been recognized as a major mode of atmospheric variability. In its simplest definition, the NAO describes co-variability in SLP variations between the Icelandic Low (IL) and Azores High (AH), the two centers of action in the atmospheric circulation of the North Atlantic. When both are strong, the NAO is taken to be in its positive mode. When both are weak, the NAO is in its negative phase. This co-variability is associated with prominent high-latitude signals in SAT, cyclone...

Singlecolumn models

Chapter 5 has already provided a few examples of the applications of single-column models. These include assessments of cloud radiative forcing over the sea ice cover (Section 5.6), processes that maintain the low-level Arctic temperature inversion (Section 5.9.2) and the application of a radiative transfer model to a grid array to provide fields of surface radiation fluxes and surface albedo from AVHRR data (the APP-x products, see, for example Figure 5.3). Another good example is provided by...

Causes of the Quaternary glacial cycles

It is widely accepted that the principal controls on the Quaternary glacial cycles involve the modulation of solar radiation received at the surface by variations in the Earth's orbit. These orbital variations involve three factors. The first, eccentricity, varies over an approximate 100 000 year cycle. The Earth's orbit is not circular, but elliptical. As such, Earth-Sun distance varies through the year. Radiation receipts are greatest at the time of minimum Earth-Sun distance (perihelion) and...

Distribution of surface albedo

While albedo is a frequently measured variable, surface observations are insufficient to allow the construction of maps to assess the basic spatio-temporal patterns across the Arctic. However, satellite-derived surface albedo is a standard variable of ISCCP-D and APP-x. Monthly fields from APP-x are displayed for April through September (Figure 5.3). Over land areas, regional albedos for April typically range from 0.40 to 0.80. Those over the Arctic Ocean are from 0.70 to 0.80. The high albedos...

Fields of estimated monthly precipitation

Mean annual precipitation is shown in Figure 2.25. Maps for the four mid-season months based on the same data sources appear in Figure 6.3. A number of different Figure 6.3 Mean precipitation north of 60 N for the four mid-season months, based on data from land stations and the Arctic Ocean with bias adjustments, the NCEP NCAR reanalysis and satellite retrievals (over open ocean). Contours are at every 10 mm up to 80 mm and at every 50 mm (dotted) for amounts of 100 mm and higher (by the...

The stratospheric circulation 421 Mean thermal structure

The Arctic stratosphere extends upward from about 10 km to 40-50 km altitude. It is essentially a very dry, statically stable region where ozone dominates the absorption of solar ultraviolet radiation and emission of infrared radiation. In the troposphere (the region between the stratosphere and the surface, which contains about 80 of the atmospheric mass), the mean thermal structure is maintained by an approximate balance between infrared radiative cooling to space, surface radiative heating...

Surface of mean annual runoff

Mean Annual Runoff Depth China

Recall that runoff is discharge divided by the catchment area. It has units of water depth. Gauge data can be used to construct surfaces of runoff. Plate 3 is the mean annual runoff Plate 3 Mean annual runoff surface for the Arctic drainage over the period January 1960 to December 1989. White areas within the southern Ob Basin represent internal drainage basins. Large areas along the Arctic Ocean coast and the Canadian Arctic Archipelago (shown as white) are ungauged. The lines over the Arctic...

Precipitation

Arctic precipitation is another key climate variable, which, like cloud cover, is still inadequately determined. The density of observing stations is generally quite low, particularly over the Canadian Arctic Archipelago, the Greenland Ice Sheet and the Arctic Ocean, making it difficult to obtain accurate regional precipitation estimates. The station density problem is becoming more severe as fiscal constraints in Canada and Russia have led to the closure of many stations. In recognition of...

Snowline altitude

The average climatic snowline is the elevation above which snow will survive the summer melt season. It is indicative of both snowfall amount and SAT, the latter especially in summer. It is around 1200-1400 m in Iceland and 700-900 m in Jan Mayen, decreasing northeastward. In Svalbard, it is only 200 m in western coastal regions, Figure 2.20 Mean surface air temperature ( C) for January, April, July and October (adapted and updated from Rigor et al., 2000, by permission of AMS). Figure 2.20...

Distribution of net radiation

Kolorowanki Druku Trudne

The net allwave radiation (or more simply net radiation) is the sum of the shortwave and longwave fluxes (Equation 5.1). Fields of net radiation based on ISCCP-D for the four mid-season months are provided in Figure 5.6. Values across the Arctic are negative from October through March. During polar darkness, the fields are of course essentially identical to those for the net longwave flux. For April, the ISCCP-D fields indicate that net radiation is slightly positive over the Arctic Ocean. The...

Abbreviations

AAAS American Association for the Advancement of Science ACIA Arctic Climate Impact Assessment ACSYS Arctic Climate System Study ADEOS Advanced Earth Observing Satellite AGCM Atmospheric Global Climate Model (or General Circulation Model) AMIP Atmospheric Model Intercomparison Project AMS American Meteorological Society AOGCM Atmosphere-Ocean Global Climate Model (or General Circulation Model) AOMIP Arctic Ocean Model Intercomparison Project ARCMIP Arctic Regional Climate Model Intercomparison...

Ecosystem models

As discussed by Kittel etal. (2000), terrestrial ecosystems in the Arctic and boreal forest regions are expected to be highly sensitive to climate change and may play a strong role in biospheric feedbacks to global climate. This sensitivity arises from complex interactions among ecosystem structure and function, soil and permafrost processes, and regional climate. Biophysical and biogeochemical dynamics of these landscapes in turn impact the global climate system through control over...

Lowlevel temperature inversions

Jfmamjjasond Months

A prominent feature of the Arctic environment is the frequent occurrence of low-level temperature inversions (i.e., temperature increases with height). This was first demonstrated by Brooks (1931) from kite ascents over Siberia. More detailed studies from kite and captive balloon ascents made by Sverdrup (1933) during the Maud expedition provided some of the first detailed information on inversion structure. Wexler (1936) was the first to address physical controls behind the formation of Arctic...

North America and Beringia

During the last glacial advance (known as the Wisconsin in North America), the major Laurentide Ice Sheet covered most of Canada. It merged in the west with the Cordilleran Ice Sheet and reached into the northern United States. The glacial history of the early Wisconsin is little known as paleoclimate information over land was largely destroyed by the extensive late Wisconsin ice. More problematic is the ice extent in the Canadian Arctic Archipelago. England (1999) and O'Cofaigh et al.(1999)...

Distribution of downwelling and net longwave fluxes

Again there are insufficient direct measurements of the downwelling longwave flux to compile maps for the Arctic. While a number of empirical formulae have been derived that employ the surface air temperature we rely on the ISCCP-D fields. Figure 5.4 and Figure 5.4 Mean monthly downwelling longwave radiation at the surface (W m-2) for the four mid-season months based on ISCCP-D data (courtesy of J. Key, NOAA, Madison, WI). Figure 5.4 Mean monthly downwelling longwave radiation at the surface (W...

Sea ice deformation

Imagenes Excavacion Terreno

Ice thickness and concentration are strongly determined by differential ice velocity. Consider two neighboring plates (floes) of ice. If the velocity difference between the neighboring plates is such that they tend to move apart (diverge), a lead is created. During winter, new ice may form in the lead. If the motion changes, such as by a change in the winds so that the neighboring plates move toward each other (converge), the lead closes. Any new ice that was formed in the lead must rearrange...

Frozen ground

Perennially frozen ground, known as permafrost, underlies nearly all of the Arctic land area. Permafrost is said to be present whenever ground temperatures are below freezing through two summer seasons. Ground ice need not be present, although in sediments ice may be present either in segregated form throughout, or as lenses and wedges (French, 1996). The upper part of the ground in permafrost regions, termed the active layer, thaws seasonally. The active layer depth (the maximum thaw depth)...

Ozone characteristics

Ozone measurements can provide three types of information. The first is the total ozone in an atmospheric column. This is measured with the Dobson spectrophotometer, which compares the solar radiation at a wavelength where ozone absorption occurs with that in another wavelength where such effects are absent. Second is the spatial pattern of total ozone. This is determined by satellite sounders such as NASA's Total Ozone Mapping Spectrometer (TOMS) aboard Nimbus-7, Meteor-3 and ADEOS (Advanced...

The basic Arctic heat budget 321 Overview

With the basic role of the Arctic in the global climate system established, focus turns to the energetics of the Arctic itself. Following the framework of the classic paper by Nakamura and Oort (1988), we consider the heat budget of a simplified northern polar cap, taken as the region from 70 to 90 N. Additional information can be found in Piexoto and Oort (1992). Following discussion of the budget equation, we examine the mean annual cycle of the budget terms, drawing strongly from NCEP NCAR...

Radiative processes

During polar night, the radiation budget is almost entirely determined by longwave fluxes (starlight and moonlight provide a negligible shortwave flux). Referring back to Equation (5.1), infrared radiation is emitted by the surface as a function of its temperature and emissivity, scaled by the Stefan-Boltzmann constant. Part of the emitted energy from the surface escapes to space through the atmospheric windows, primarily in the 8-12 m region. The remainder is absorbed in the lower atmosphere...

River discharge and runoff 641 River discharge data

The most comprehensive network of discharge gauging stations in the terrestrial Arctic drainage is represented by R-ArcticNET, which was compiled from original national sources by investigators at the University of New Hampshire, Durham. Version 2.0 of R-ArcticNET holds data from 3754 sites. Figure 6.12 gives the location of the subset of gauges for basins of at least 104 km2. Also shown is a digital river network at 30 min x 30 min resolution (longitude x latitude) (known as STN-30p) developed...

Cyclonic and anticyclonic regimes

Proshutinsky and Johnson 1997 document two regimes of wind-forced circulation of the Arctic Ocean. They simulated ocean currents, sea level height and ice drift on the Arctic Ocean from 1946 to 1993 using a two-dimensional, wind-forced model that includes coupling between the ocean and ice. Based on the modeled sea level and ice motion, the wind-driven circulation in the central Arctic alternates between cyclonic and anticyclonic regimes, with each regime persisting from 5 to 7 years....

Precipitation over Greenland

Direct observations of Greenland precipitation are particularly scanty. Stations with long records are limited to the coasts. As mentioned, in recent years, data over the ice sheet have been acquired from automatic weather stations. But quite a few measurements have been made of annual snow accumulation over the ice sheet. Bender ( ) provides a synthesis of observed annual accumulation (snow water equivalent) over the ice sheet, modified along the coast with a simple model of orographic...

Frontal activity

Early studies of frontal activity in the Arctic, such as those of Reed and Kunkel (1960) and Barry (1967), were based on manual analysis. While extremely time consuming, manually depicted fronts always contain an element of subjectivity. With the advent of fast computers, thinking has turned to the application of automated methods. Hewson (1998) provides a comprehensive review. Of the various methods that can be found in the literature, one that seems to work fairly well is a thermal front...

Net precipitation from the aerological method

In hydrologic analysis, net precipitation, or P ET, is itself a valuable term, and can be readily obtained in the absence of direct surface measurements of the two variables. Consider the moisture budget of an atmospheric column, extending from the surface to a height above which moisture content is negligible (about 300 hPa). The budget can be expressed as where the moisture content of the atmosphere, W, is expressed as precipitable water (the equivalent water depth of the vapor in the...

Topography and permanent ice masses

The physiography of the Arctic lands is summarized in Plate 1. Much of the Arctic land area is low lying, especially western and central Siberia, the western part of the Canadian Arctic Archipelago and coastal Alaska. Mountains and high plateaus are prominent in the eastern Canadian Arctic, coastal regions bordering the Greenland Ice Sheet, interior Alaska, northeastern Siberia and Scandinavia. The highest mountain north of the Arctic Circle is Gunnbjorns Fjaeld (86.92 N, 29.87 W), which rises...

Sea ice formation growth and melt 711 The existence of the sea ice cover

To build on concepts introduced in Chapter 2, it is useful to draw from the review of Maykut (1985) and compare the processes of ice formation in a freshwater body with those that occur in the Arctic Ocean. Figure 7.1 gives the temperature versus density relationship for freshwater. For most substances, decreased temperature results in higher density. But freshwater is a very unusual substance. Down to a fixed threshold temperature, cooling results in increased density. Below this temperature...

Sea ice zones

Marginal Zone Ice Winter Satelite

The sea ice cover can be divided into different ice zones. Again following Maykut (1985), the perennial ice zone (PIZ) is where ice is present throughout the year. The PIZ can be broadly considered as the area north of the mean September ice margin shown in Figure 2.4. During winter, the PIZ typically consists of 10-15 FYI formed in leads, and the remainder MYI. In summer, most of the FYI melts. The Arctic's perennial ice zone contains about two-thirds of all the MYI in the world's oceans....

Ice cores

Snow that falls on an ice sheet is compressed by subsequent snowfall, becomes firn, with a density of 550 kg m-3 around 10 m depth, and then ice (density of at least 840 kg m-3). This occurs at depths of about 60 m in Greenland. Seasonality of snow accumulation leads to annual layers of ice that can be identified back to around 40 ka in central Greenland. Researchers drill vertically through the ice to recover cores comprising layer upon layer of fossil snow. Among the most valuable records...

The modern era

World War II demonstrated the strategic importance of the Arctic seas, Greenland and Alaska. Germany established a number of clandestine weather stations in Spitsbergen and East Greenland during 1940-5 (Blyth, 1951 Selinger and Glen, 1983), while the USA established air bases in West Greenland. Strategic concerns were reinforced with the advent of the Cold War. Between 1947 and 1950, the Canadian and US governments established five weather stations in the Canadian Arctic Archipelago and the...

Moisture budget

As part of their summary of high-latitude NAO impacts, Dickson etal.(2000) compared patterns of the vertically integrated moisture flux across 70 N for winters associated with NAO extremes. The data set spanned the years 1974-91. Their analysis (Figure 11.15) shows that the poleward meridional moisture flux for longitudes along the Nordic seas is much higher under the positive NAO phase. The positive NAO is also associated with a stronger equatorward moisture flux between about 70 and 140 W...

The Arctic and the global heat budget 311 The radiation balance

Global Balance Heat

Considered as a whole and for long-term annual means, and assuming a stationary climate, the Earth is in a state of radiative equilibrium. The ultimate energy source to the Earth is solar radiation. About 99.9 of the radiation emitted by the Sun is in wavelengths of 0.15 to 4 m with a peak intensity near 0.5 m. About 50 of the total emitted energy is within the visible spectrum (approximately 0.4-0.7 m). The net incoming (i.e., the available) solar radiation to the Earth system, defined as that...

Basic climatic elements 231 Snow cover

Most of the Arctic land and sea ice surface has a snow cover for at least 6-8 months of the year. For a number of reasons snow cover is a key climatic variable. These include (1) its high albedo (reflectivity in solar wavelengths), typically 0.80 to 0.90 for new snow (2) the insulating effect it has on the underlying tundra or sea ice and (3) its Figure 2.15 Average number of weeks of snow cover over the Northern Hemisphere, based on the NSIDC blended weekly product for 1972-2001 (courtesy of...

The albedo of snow

As outlined by Nolin and Liang (2000), snow can be considered as a layered particulate medium composed of ice spheres in air. Scattering by the spheres is primarily through refraction. Using the refractive indices of ice and an optically equivalent ice sphere radius, Mie theory (appropriate when the effective particle radius is much larger than the wavelength of the interacting radiation) can be used to calculate single-particle scattering and absorption (i.e., the scattering and absorption of...

Climate model projections

The recently completed Arctic Climate Impact Assessment (ACIA), an international activity with about 300 participating scientists, was aimed at evaluating and synthesizing Arctic climate variability and change (ACIA, 2005). One of the components of the ACIA was to provide scenarios of future Arctic climate. The ACIA made use of five different AOGCMs. These are (1) CGCM2 (Canadian Climate Center, Canada) (2) CSM (National Center for Atmospheric Research, USA) (3) ECHAM4 OPYC3 (Max Plank...

The Greenland Ice Sheet 811 General features

Isostatic Rebound

The Greenland Ice Sheet (Figure 8.1) is by far the largest terrestrial ice mass in the Arctic and is the second largest in the world (following the Antarctic Ice Sheet). The ice sheet covers an area of 1.71 x 106 km2. Other glaciers and ice caps on Greenland cover a further 0.049 x 106 km2 (Table 2.2). The ice sheet reaches a maximum elevation of 3208 m at Summit (72.6 N, 37.5 W). A secondary elevation maximum on the southern part of the ice sheet rises to about 2800 m. The surface slope over...

Polar Lows 461 Definition

Polar Lows are intense maritime mesocyclones of typically 100-500 km in diameter. They may intensify rapidly and surface wind speeds can sometimes reach hurricane force (Businger and Reed, 1989). They tend to be short lived, generally lasting only 3-36 hours. Polar Lows are the most intense category of the family of mesoscale cyclonic vortices found poleward of the main polar front, which are known generically as polar mesoscale cyclones. Polar Lows, which can present significant hazards to...

Numerical weather prediction models

Almost any study of observed variability in the Arctic atmospheric circulation makes use of output from the data assimilation cycles of NWP models. From the preceding discussion, NWP output is also commonly used as lateral forcing for regional climate models or to provide wind forcing for sea ice and coupled ice-ocean models. Output from GCMs is also commonly verified against output from NWP models. We hence 91 96 101 106 111 116 121 126 131 136 141 146 151 Figure 9.13 Time series of 24-48 hour...

Partitioning of net radiation 581 Characteristics over sea ice

Figure 5.10, also from Persson et al. (2002), illustrates annual cycles of the turbulent energy fluxes and conduction at the SHEBA site in comparison with other estimates. Recall that our convention is that non-radiative fluxes are positive when directed away from the surface and negative when directed toward the surface. The SHEBA results are representative of reasonably thick ice. They show the sensible heat flux as directed toward the surface in winter and variously toward or away from the...

Clouds

Cloud cover has first order impacts on the Arctic surface radiation balance (see Chapter 5). Cloud microphysical and radiative properties are hence a vibrant area of research. While much is being learned from modeling and special observation programs (e.g., SHEBA and the Department of Energy Atmospheric Radiation Monitoring program), a continuing problem is the general lack of accurate data on even cloud amounts over the Arctic. Curry et al. (1996) provide a comprehensive review of the problem....

Nonradiative terms

The net radiation at the surface must be balanced by non-radiative energy transfers. Namely, where S and L are the sensible and latent heat fluxes respectively, M is melt and C is conduction. The sign convention used here is that non-radiative fluxes are positive when directed away from the surface and negative when directed toward the surface. The net radiation is positive when directed downward and negative when directed upward. With this convention, when both sides of Equation (5.2) are...

The sea ice cover

The surface of the Arctic Ocean is characterized by its floating cover of sea ice. The processes of sea ice growth, melt, circulation and variability are discussed at length in Chapter 7. As will become clear in the next few chapters, sea ice is intimately coupled with the atmospheric energy budget, the atmospheric circulation, the surface energy Figure 2.2 Definition of Arctic seas, based on Russian sources. 1. Greenland Sea, 2. Labrador Sea, 3. Baffin Bay, 4. Canadian Arctic Archipelago, 5....

Precipitation accumulation and sublimation

Some aspects of precipitation and accumulation over the ice sheet were outlined in Chapter 6. Accumulation basically represents the net effects of direct precipitation, its redistribution on the surface via wind scour and drifting, and mass losses due to melt and evapo-sublimation. Accumulation is typically assessed via snow pits or ice cores. Based on coastal station observations of precipitation, adjusted for wind speed, and accumulation data from recent ice cores, the annual precipitation...

Late Holocene cooling and the LIA to present

As just discussed, the HTM in some regions occurred quite early, while for others it ended as late as 3 ka. The HTM was nevertheless followed by a period of cooling. For example, reconstructions by Koc etal. (1993) indicate that by about 5 ka, warm Atlantic waters had retreated to the central GIN seas, attended by strengthening of the cold East Greenland Current. By 3 ka, the sea ice cover had expanded along eastern Greenland. A variety of sources points to a subsequent period of warming...

Precipitation frequency and phase

Rain Frequency

Present weather codes that represent part of the synoptic reports in COADS were used by Serreze et al. (1997b) to examine the characteristics of precipitation frequency and phase (solid, liquid, mixed) over the Arctic Ocean. The techniques follow those Figure 6.6 Modeled annual precipitation averaged for 1985 though 1999 (mm). The contour interval is 200 mm, but 100 mm if smaller than 400 mm, and 300 mm if larger than 1000 mm (from Bromwich et al., 2001b, by permission of AGU). Figure 6.6...

Poleward energy transports

Latitudinal Variation Energy Budget

The implication of Figures 3.1 and 3.2 is that there must be poleward transports of energy by the atmosphere and oceans that warm the polar regions and cool the equatorial regions. The uneven solar heating results in a mean poleward decline in tro-pospheric temperatures and hence the height of pressure surfaces, inducing a pressure gradient. The atmosphere works to reduce these gradients. In lower latitudes, where the Coriolis parameter is fairly small, the poleward atmospheric energy transport...

Features of the Quaternary 1031 General timeline

Mis Stages

How many major ice advances and retreats occurred over the Quaternary is unclear and there are discrepancies to be resolved between continental and deep-sea chronologies. Ice-rafted detritus (IRD) in marine sediments dated to around 2.6 Ma marks the initiation of glaciation at sea level in the circum-North Atlantic region (Ehlers and Gibbard, 2003). This implies that the base of the Pleistocene epoch (and the Quaternary period) might be better placed earlier than the international stratigraphic...