ISSN 1028-334X, Doklady Earth Sciences, 2019, Vol. 487, Part 2, pp. 995–1001. © Pleiades Publishing, Ltd., 2019. Russian Text © The Author(s), 2019, published in Doklady Akademii Nauk, 2019, Vol. 487, No. 6.

GEOGRAPHY

Climatology and Interannual Movements of Upper-Level Frontal Zones in the Middle Troposphere of the Northern Hemisphere O. A. Razorenovaa,* and P. A. Shabanova,** Presented by Academician R.I. Nigmatulin December 22, 2017

Received February 5, 2018

Abstract—Based on the use of an objective methodology that takes into account the local values of the geo- potential gradients, the long-term average position of the upper-level frontal zones (UFZs) in the middle tro- posphere for the Northern Hemisphere over the period of 1948–2014 is calculated for the first time. The pro- cedure for determining UFZs has consisted in estimation of the monthly-average fields of the module of a horizontal geopotential gradient by the approximation of derivatives using the central difference method. Based on the obtained fields of geopotential gradients, the local highs were identified and the positions of the upper-level frontal zones in different seasons were found. The updated climatology of UFZs significantly refines the earlier information, specifying the position of UFZs and identifying, e.g., UFZs that exist only in particular seasons. The estimates of the interannual movements of HAVZs are also obtained for the first time, which makes it possible to analyze the mechanisms of the observed climate variability in different regions of the Earth.

DOI: 10.1134/S1028334X19080294

Upper-level frontal zones (UFZs) representing which makes it impossible to analyze their long-period transitional high-gradient regions between high cold dynamics and regional features. In this work, we stud- and high warm are important ied in detail the position of UFZs in the middle tropo- indicators of climate dynamics of the atmosphere, the sphere for the different seasons and revealed the inter- position and intensity of which determine the regimes annual movements and intensity of UFZs for the first of atmospheric circulation and their interannual time. movements to a significant effect. Along with the dia- batic inflows of heat and orography, UFZs are an The conventional approach to the identification of important factor that determines the dynamics of the the planetary upper-level frontal zone (PUFZ) by the activity at middle latitudes [13, 15] and the characteristic isohypse is often used during analysis of movement of cyclonic trajectories in the Northern simulated data [3] and to make annual reference Hemisphere, which is one of the most discussed cli- reviews of the general atmosphere circulation at the mate signals today [12]. UFZs are related to the exis- Russian Research Institute of Hydrometeorological tence and development of tropospheric fronts that are Information-World Data Center [5]. The analysis of important to study in terms of short- and long-term the monthly-average maps of the relative topography prediction. In this respect, studying long standing of RT 500 in [6] made it possible to identify the two dynamics of the UFZ position can significantly refine 1000 the predictability characteristics of many atmospheric largest branches of PUFZ: in the American–Atlantic processes. In this case, systematic studies of the UFZ and Asian–Pacific sectors, where the baric and ther- position are rather limited; they are related mainly to mal gradients reach 1.4 dam/100 km and 0.5°С/100 km determination of the characteristic isohypse [1, 2, 10], in summer and 3.0 dam/100 km and 1.2°С/100 km in winter, respectively. The procedure we proposed for esti- mating the UFZ position [8], in contrast to [1, 2, 10], is a Shirshov Institute of Oceanology, Russian Academy based on numerical analysis of the geopotential gradi- of Sciences, Moscow, 117218 Russia ents and identification of the zones of maximum gra- *e-mail: [email protected] dients, which makes it possible to distinguish several **e-mail: [email protected] upper-level frontal zones and thus to identify regional

995 996 RAZORENOVA, SHABANOV

N Winter 90° 6 0.80.8 0 ° 1.01. 6 . 80 0 1.01 1.01 7 . 2.8 ° 0 4 1.21.2 0.80.8 70 1.21. .8 3 2 1.41.4 2.4 60° 0.80 1.81.8 5 2 0.60.6 2.0 50° 1.61.6 1.61.6 .4 2.0 2.42.6 1.01.0 1 1.41 1.81.8 1.6 1 2.2 40° 2.8 1.21.2 1.2 2 1.21.2 1.01.1 2.22. 2.02.0.8 2.02.0 8 .0 2.8 30° 1.81 2.4 2.62.0 0.8

1.41.4 km Dam/100 20° 0.40.4 1.01.0 0.60.6 0.80.8 0.4 0.20.2 10° 0.20.2 0 0° N Spring 90° ° 0.0.8 6 0.80.8 80 6 7 4 2.8 70° 2.4 8 1.01.0 5 60° 0.80. 1.41. 1.21 4 2.0 1.41.4 .2 2 1.41 1.61.6 1.01.0 50° 1.81.8 1.61.6 .4 1.6 1 3 0.80.8 1.61.6 1.81.8 1.81 2 1 2.2 40° 2.02.0 .8 1.21. 1.2 1.61.6 1.21.2 8 2.02.0 30° 1.01.0 0.0.8 8 0.8 0.40.4 0.60.6 0.80.8 0.4 km Dam/100 20° 0.20.2 10° 0 0° N Summer 90° ° 7 0.80.8 80 6 6 0.60.6 0.60.6 4 1.0.0 2.8 70° 1.0.0

6 2.4

. 5

0 0.6 ° 0.6 1.01.0 60 1.21.2 0.60.6 2.0 0.80.8 3 1.41 0.80.8 1 1.21 .4 ° 4 . 50 1.41. 2 1.81.8 1.21.2 .4 1.6 1.61.6 1.61.6 2 1 1.41 40° 0.80. 1.2 0.60.6 0.80.8 8 1.01.0 30° 0.20.2 8 0.20.2 0.40.4 0.8 0.20.2 0.4 km Dam/100 20° 0.40.4 10° 0.20.2 0 0° N Fall 90° 6 80° 0.80.8 6 7 2.8 ° 4 70 1.21.2 2.4 .8 1.01.0 60° 0.80 1.61.6 5 1.61.6 0.80.8 .6 3 2.0 1 1.61 1.81.8 ° .0 8 50 2.02 . .2 2.22.2 1.6 1.81 2.22 2 8 2.22.2 2.02.0 1.81. .4 40° 1.01.0 8 2.42 2.02.0 1.2 1.41.4 1.21.2 1.41.4 1 1.61.6 30° 0.60.6 0.80.8 0.8 20° 0.20.2 0.40.4 0.4 km Dam/100 10° 0 0° 180° 150° 120° 90° 60° 30° WE0° 30° 60° 90° 120° 150° 180°

Fig. 1. Long-term average seasonal distribution of upper-level frontal zones of the Northern Hemisphere at the altitude of the 500 hPa isobaric surface.

UFZs for the areas characterized by the nonunique- ral heterogeneities related to the change in the quantity ness of their position. of assimilated data than the other parameters [13]. The positions of eight UFZs were determined. Their posi- In this work, we used the data on the altitude of the tions and structures have pronounced seasonal vari- Н500 isobaric surface from the NCEP-NCAR reanal- ability characterized by weakening and northward ysis [13] on the 2.5° × 2.5° grid over the period from movement of UFZs in summer and intensification 1948 to 2014. We note that the altitudes of the isobaric and southward movement in winter. Figure 1 presents surfaces in the troposphere and the surface pressure in seasonal maps of the geopotential gradients at an alti- the NCEP-NCAR reanalysis are less prone to tempo- tude of the 500 GPa isobaric surface and seasonal

DOKLADY EARTH SCIENCES Vol. 487 Part 2 2019 CLIMATOLOGY AND INTERANNUAL MOVEMENTS 997

Table 1. Characteristics of upper-level frontal zones Maximum geopotential Maximum geopotential No. Name of UFZ Latitudinal zone gradients in the winter gradients in the summer season, dam/100 km season, dam/100 km 1 Asian–Pacific 30–45° N3.4–3.61.6–1.8 2North Atlantic 35–65° N. 2.6–2.8 1.6–1.8 3 North American 40–75° N2.0–2.21.2–1.4 4 Scandinavian 65–75° N 1.2–1.4 0.8–1.0 5 European–Siberian 55–65° N 1.6–1.8 0.8–1.0 6 East Arctic 70–80° N 0.8–1.2 0.8–1.0 7 Greenland UFZ 70–80° N 1.2–1.4 0.8–1.0 8 Afro-South-Asian 28–40° N 1.4–1.7 0.8–1.0 positions of the main branches of UFZ, the character- Atlantic UFZ extends to the south. Its eastern part is istics being given in Table 1. connected to the Scandinavian and European–Sibe- It is seen from Fig. 1 that UFZs can exist as individ- rian UFZ, the European part of which moves to the ual branches and form rather extended zones of baric north at ~10°. In the springtime, the Canadian part of contrasts when connected to each other. The seasonal the North American UFZ is recorded in the northern variations in the thermal regime and baric topography part of Canada, joining with the East Arctic UFZ. The lead to seasonal movement of UFZs and the corre- Afro-South-Asian UFZ is disintegrated into two sponding tropospheric fronts, as well as to their trans- branches, the weakened South–Asian and the African formation. In winter time, the formation of continen- branch moving to the north at ~2°–5°. tal anticyclones (Siberian, Northern Atlantic, and Canadian) connected to subtropical high pressure In summer, UFZs are located at the greatest lati- regions and deepening of the Icelandic and Aleutian tudes, the Asian–Pacific, North American, and Lows lead to intensification of middle-troposphere North Atlantic UFZs forming a single zone at about UFZ with maximum gradients of 2.8– 45°Ν with the maximum gradients of 1.6– 3.0 dam/100 km. The North American UFZ is con- 1.8 dam/100 km. In northern Eurasia, the Scandina- nected to the North Atlantic one, forming a U-shaped vian UFZ is united with the European part of the UFZ in the latitudinal zone from 40° N to 70° N. The European–Siberian UFZ; the East European UFZ interaction of the , Siberian, and Hawai- extends along the coast of the Arctic Ocean. The geo- ian anticyclones determines the development of the potential gradients reach 1.0–1.2 dam/100 km. The Asian–Pacific UFZ with horizontal geopotential gra- decrease in the temperature differences between the dients of 1.2–2.8 dam/100 km. The European–Sibe- tropical and moderate air masses leads to weakening of rian UFZ over Eurasia in the latitude belt of 55°– the African UFZ (the geopotential gradients do not 60° N divides the cold continental and warm Atlantic exceed 0.8–1.0 dam/100 km), which moves north- air over the European part of Russia (EPR), incoming ward to the Mediterranean region. The Greenland along the southern periphery of the UFZ is observed in the area of 80° N above the north trough and over the Siberian territory, it divides the of Greenland (the geopotential gradients are 1.0– Arctic air mass and the continental moderate air 1.2 dam/100 km), its stability is determined by the formed in the Siberian . The high-latitude year-round existence of the Greenland anticyclone. East Arctic and Greenland UFZs separate large-scale troughs and ridges in the middle troposphere related In the fall, the geopotential gradients increase and correspondingly to the development of the Aleutian reach values of 2.2–2.4 dam/100 km in the Asian– Low, the anticyclone over the eastern sector of the Pacific and North Atlantic UFZs. The position of the Arctic, the Icelandic Low, and the Greenland anticy- North Atlantic and North American UFZs becomes clone. The subtropical latitudes clearly exhibit the more meridional, and the European–Siberian UFZ Afro-South-Asian UFZ dividing the circulation of intensifies, its eastern part moves at 10° to the south moderate latitudes and the subtropical high-pressure with an increase in gradients to 1.4–1.7 dam/100 km. belt. The southward movement of the Greenland and Afri- In spring, the intensity of most UFZs weakens. The can UFZs at 5°–10° is also recorded. The decrease in maximum values of the gradients in the Asian–Pacific the temperature contrasts between the Arctic air and and North Atlantic UFZ reach only 1.8– the continental moderate air formed over the cooling 2.2 dam/100km. The Asian–Pacific UFZ moves at surface of the continent leads to weakening of the East 2°–3° northward, and the western branch of the North Arctic UFZ (to 0.8 dam/100 km).

DOKLADY EARTH SCIENCES Vol. 487 Part 2 2019 998 RAZORENOVA, SHABANOV

N 80° 70° 60° 50° 40° 30° 20° 10° 0° W −160°−−140°−120°−100° 80°−60°−40°−20° 0° 20° 40° 60° 80° 100° 120° 140° 160° E

Fig. 2. Distribution of upper-level frontal zones of the Northern Hemisphere in the winter period at the altitude of the 500 hPa isobaric surface when the zonal (solid line) and meridional (dashed line) processes were dominant.

Thus, the seasonal positions of UFZs obtained on areas of Europe and is also connected to the Euro- the basis of the new procedure allowed us to refine sig- pean–Siberian UFZ. Significant differences in the nificantly their climate position and seasonal dynam- position of upper-level frontal zones are observed over ics, which shows that, in addition to the two main . In the zonal processes, the North zones of increased geopotential gradients [6], stable American UFZ is represented by a separate branch; in regional UFZs related to the regional features of the meridional processes, its southern part is con- atmospheric processes are observed in the Northern nected to the Atlantic UFZ in the east and to the Hemisphere. The more accurate methodology for Asian–Pacific in the west; as a result the single UFZ identifying UFZs also provides the possibility for strongly bends to the north over North America; the studying their interannual movements and under- California branch, which is well-manifested in the standing the causes. In addition, the obtained clima- zonal processes, is rather weakened. The domination tology of the UFZ can be used successfully for study- of meridional processes is characterized by the inten- ing the creation of different forms of atmosphere cir- sification and significant spread of the Greenland culation over the sectors of the Northern Hemisphere. UFZ in both the westerly direction into the area of the The upper-level frontal zones undergo significant Canadian archipelago and in the easterly direction, meridional movements, determining the positions of where it is connected to the Scandinavian branch. The tropospheric fronts and the ways of displacement of Kamchatka branch intensifies, which determines baric formations and thus forming different circula- activization of in Kamchatka, the tion regimes. Figure 2 presents the long-term average Magadan region, and the Chukchi Peninsula. The distribution of the upper-level frontal zones with the extension of the Asian branch to Central Asia also dominant zonal and meridional processes over most of leads to intensification of cyclonic activity in this the Northern Hemisphere in the winter season. The region. There is an increase in the intensity of the winter season was selected for analysis due to the exis- Mediterranean UFZ, which results in active winter tence of maximum contrasts between the links of the cyclogenesis in the Mediterranean countries. During Earth’s climate system. Pogosyan-Pavlovskaya’s index the zonal processes, the African branch is found in its calculated for the different sectors and for the entire extreme southern position and is spread farther west Northern Hemisphere served as the criterion for the into the southern latitudes of the North Atlantic. selection of years with dominant meridional or zonal Figure 3 presents the positions of UFZs and the processes [7]. It is seen in Fig. 2 that even with long- anomalies of the geopotential gradient (Figs. 3а–3d) term averaging of atmospheric processes, including a in particular years with different forms of atmospheric large variety of meridional and zonal forms, the distri- circulation that were also selected based on Pogosyan- bution of UFZs differs when zonal or meridional cir- Pavlovskaya’s index: the winter seasons with domina- culation is dominant. During the zonal processes, the tion of meridional circulation over the entire hemi- Atlantic UFZ over the passes north- sphere (1968–1969) and zonal circulation over the ward of its long-term average position, spreads into the entire hemisphere (1992–1993), as well as the winter Europe north, and is connected to the European– seasons with different types of circulation over the Siberian UFZ; the meridional processes are charac- Northern Hemisphere sectors (1984–1985; 2011– terized by its significant displacement to the south to 2012). The analysis of separate winter seasons demon- the subtropical latitudes in the western part of the strates significant interannual movement and the ocean; in the eastern sector it passes over the central intensity of upper-level frontal zones that depend on

DOKLADY EARTH SCIENCES Vol. 487 Part 2 2019 CLIMATOLOGY AND INTERANNUAL MOVEMENTS 999

N 1968−1969 −0.2−0.2 80° 0.20.2 −0.2−0. 1.2 0.40.4 0.20.2 2 2 .0 . −0.2−0.2 70° 0 0.20 −0.0− −0.6− 0.8 −0.4−0.4 0 60° −1.0− −0.6−0 .4 .6 1.0 −0.8−0.8 .6 −0.4−0 0.4 −1.2−1.2 0.80.8 50° −1.0−1.0 0.40.4 0.60.6 0 .0 −0.2−0 6 0 −0.0−0 .2 0.60. . 0.4 0.80.8 1.01 40° −1−−0.6−−0.41−0.8−00.6.8 0.20.2 −0.4 .0.0 −0.0−0.0 2 .2 0.40.4 0.40.4 . −00.8. 1.01.0 − ° 0 0.0 0 −0.6− 8 0.8 30 −0.2− −0.0− −0.4−00.6 km Dam/100 −0.2− .4 0.40.4 −0.0−0.0 − 20° 0.20.2 −0.0−0.0 1.2 0.20.2 0.0 10° −0.0−0.0 −0.0− N 1984−1985 −0.2−0.2 0.40.4 2 80° 0.20. −0.6− −0.4−0.4 0.6 1.2 70° −0.4−0.4 −0.0− 0.8 4 0.0 60° 0.40.4 −0.4−0. −0.6−0.6 −0.0−0.0 0.4 −0−0.2.2 4 −0.−0.2 50° . −0.2− −0.0−0 −0.0− 0 0 0.2 .0 0. −0.4− −0.0−0 40° 0 0.40.4 .0 −0−0..22 −0.4 .4 0.20.2 ° −0.4−0 0.2.2 −0.8

30 km Dam/100 ° −1.2 20 −0.0−0.0 −0.0−0.0 −0.0−0.0 10° 0.0 −−0.00.0 −0.0− − N 1992 1993 −0− −0.6−0.6 .0 −0.2−0.2 80° 0..22 −0.0−0 0.20.2 0.40.4 .0 0.40.4 −0.0−0 0.60.6 1.2 70° −0.4−0.4 0.60.6 1.01.0 0..66 0.8 0.40.4 0.40.4 0.80.8 1.21.2 −0.0−0.0 0.20 60° .2 −0.2−0 −0.6−0 −0.2− .2 0.4 .6 0.2 0 0 ° 0.60.6 −0.2− .2 . 50 −0.8−0.8 .4 0 0 −−0.40 0.40.4 −0.0− ° 2 −0.6− 0.20 −0.4 40 2 −0.2−0. 0.6 . . 2

0 .4 −0.4−0 0.40 − ° −0.− . 0.8 30 4 −0.2−0.2 km Dam/100 2 0.20. −0.0− 0.20.2 −−0.00.0 −1.2 20° 0.0 −0.0−0.0 0.00.0 .0 10° −0.0−0 −0.0−0.0 2011−2012 N 2 ° 0.20. −0−0..00 0.40.4 0.60.6 80 −0.4−0.4 −0.2− 0 −0.2−0.2 −0.4−0 1.2 . .4 70° −0.2−0.2 2 −0.0−0.0 −0.4−0.4 −−0.20 0.8 ° −0.4−0.4 .2 −0.0−0.0 −0.4−0.4 60 6 6 0.4 0.60. 1.21.2 . 8 0 1.01.0 0.60.6 0 −1.0−1 . ..4 . 0.80 ° 4 0.80.8 −0.6− 0 − 0 50 0.40. −0.0−0.0 0.0.2 −0.20.2 4 .2 ° 0.20 −0.4− 0.6 0.20. −0.4 40 0 −0.6− 0.40.4 2 2 . ° −0.2−0. 4 −0.2−0.2 −0.8 30 .4 0 .2 km Dam/100 −0.4−0 . −0.2−0 0.20.2 0 −1.2 20° −0.0− −0.0−0.0 0.0 10° −0.0−0.0 −0.0−0.0 −0.0− 180° EEE150° W 120° 90° 60° 30° 0° 30° 60° 90° 120° 150° 180°

Fig. 3. Distribution of upper-level frontal zones of the Northern Hemisphere at the altitude of the 500 hPa isobaric surface and anomalies of the geopotential gradient in the winter period in particular years. the development of a definite circulation process. the northeast and was found over the Norwegian Sea, When the meridional processes dominated in the win- which led to the spread of a large trough through all of ter season of 1968–1969, the intense Siberian anticy- North America. clone spread almost throughout the entire Asian con- The circulation conditions considered caused sig- tinent and Eastern Europe, which led to severe winter nificant movement of the North Atlantic branch of the conditions over the entire territory of Russia, the UFZ to the south, the movement of the Greenland Trans-Caucasian Region, and Central Asia. The branch to the north at 5° of its long-term average posi- anomalously deep Aleutian Low moved in the westerly tion, and its connection to the Scandinavian branch. direction to the coast of Kamchatka. Therefore, the The North American UFZ existed as two segments: in Asian–Pacific UFZ was characterized by significant the extreme northwest of the continent and in the intensity (to 3.8 dam/100 km); the Kamchatka UFZ south of the United States, where it was connected to was formed. The Scandinavian branch moved to the the North Atlantic branch. The considered situation is north and connected to the European part of the clearly illustrated in the field of geopotential gradient European–Siberian UFZ, the Siberian part of which anomalies (Fig. 3а); a large region of the negative was weakly manifested. In the same period, the Azores anomaly is found in the zone of the long-term average High was rather weakened as was the North American position of the North American and North Atlantic High, and the center of the Icelandic Low displaced to UFZs. The weakening of the Siberian UFZ is

DOKLADY EARTH SCIENCES Vol. 487 Part 2 2019 1000 RAZORENOVA, SHABANOV reflected in the corresponding center of the negative processes in the European sector due to the formation anomaly in the geopotential gradient. The region of of a stable anticyclone formed from the wedge of the positive anomalies corresponds to the intense Asian– Siberian Anticyclone and a large cyclone with the cen- Pacific UFZ; the Kamchatka branch is clearly seen. ter over the Norwegian Sea, as well as due to the move- In the winter season of 1984–1985, the position of ment of the center to the northeast. the upper-level frontal zones close to the long-term Under such conditions, the cold Siberian air spread average position was recorded in the Pacific sector, along the periphery of the anticyclone to Europe, and the domination of meridional forms of circulation which led to an extraordinary severe winter in this was observed above the American, Atlantic, аnd Euro- region, especially in Southern Europe. The warm pean sectors. The maximum meridional index was Atlantic air was carried along the periphery of the noted in the European region. Most of it was affected high-level trough to the high latitudes of the western by the ridges of the Azores High and the Siberian Anti- Arctic sector, which caused the anomalously warm cyclone; an independent high-pressure area was weather in this region over the entire observation formed over Scandinavia; cyclonic circulation was period. An atypical baric field was observed over the observed primarily over southern Europe. Such pic- North Atlantic: the entire northeastern part of the ture determined the alteration of the troughs with continent to the Great Lakes was under the influence ridges and the formation of atypical branches of the of the trough moving from the eastern center of the upper-level frontal zones in the middle troposphere Icelandic Low; the North American winter High sig- over Europe: the independent branch of UFZ nificantly weakened and spread into the subtropical extended almost meridionally over inland Europe into latitudes, and its center was located in the western part the Black Sea region; the Mediterranean UFZ split of the United States, at about 40° N. Under such cir- into two parts: western and eastern. The Scandinavian culation conditions, the North American UFZ repre- UFZ moved to 80° Ν; the field of anomalies (Fig. 3b) sented two parallel branches in the middle latitudes of illustrates this situation well. Such distribution of the continent. The picture considered led to warm UFZs explains the weather conditions of this season: winter in Canada and the United States, where many the severe winter in the EPR, Karelia, the Baltics, states had abundant snowfall. The intensification of Belarus, and Ukraine; abundant snowfall in France the Californian UFZ caused an increase in precipita- and in northern Africa. On the contrary, intensifica- tion for California and anomalous rains for Texas. The tion and northward movement of the Kamchatka Far East and Pacific sectors dominated by the zonal UFZ determined the mild winter in Chukotka and the circulation type; the upper-level frontal zones had a Magadan region, where the temperatures in January position similar to the long-term average position. were higher than in the Crimea. The development of The winter period of 1992–1993 was characterized the markedly pronounced tripol over the North Atlan- by a high zonal index of circulation in the moderate tic (the Greenland anticyclone → the Icelandic Low → and high latitudes of the Northern Hemisphere, which the Azores High) during all the winter months ensured resulted in the formation of a single high gradient UFZ the intensification of the North Atlantic UFZ and the consisting of the North American, North Atlantic, movement of the Greenland UFZ to the north. The Scandinavian, and European–Siberian branches. The intensification of the North American High led to the region of the positive anomaly of the geopotential gra- westward movement of the middle-tropospheric ridge dient, corresponding to this single UFZ, is clearly seen along 140°W, which caused the eastern part of the in the moderate and high latitudes of the Northern Asian-Pacific UFZ to move significantly northward Hemisphere in Fig. 3e. Under such conditions, the (from 7° to 10°), this is also confirmed by the field of polarly front cyclones moved eastward freely and geopotential gradient anomalies (Fig. 3b). determined a mild winter in the European part of Rus- In the winter season of 2011–2012, the North sia, Karelia, and Finland. That year was also charac- Atlantic branch of the UFZ was recorded to deviate terized by the development of a upper-level frontal from the long-term average position in the eastern zone over Central Asia and Southern Siberia between Atlantic and to extend to the northern part of Western the large-scale trough spreading along 60° E to Cen- Europe (a positive center of geopotential gradient tral Asia, where intense winter cyclonic circulation anomaly in the eastern part of the North Atlantic, was developed, and the large-scale ridge along 85° E spreading to the British Isles and most of Western and (the positive anomaly center of the geopotential gradi- Southern Europe down to the Black Sea, Fig. 3c), the ents from the Caspian Sea to 90° E in the latitudinal Scandinavian UFZ (a negative center of the geopoten- zone of 35°–55° N in Fig. 3d). The development of tial gradient anomaly over Scandinavia) almost disap- this branch of the UFZ ensured a mild winter in Altai. peared, the central part of the European–Siberian This figure shows that the upper-level frontal zones UFZ moved to 70° N (a dipole: the positive anomaly can be successively used to identify the modern cli- in the zone of 70°–80° N and the negative one in the matic variations over the different regions of the Earth. zone of 40°–60° N over the Siberian sector), and the The domination of the zonal circulation forms over Black Sea branch of the UFZ was formed. Such pic- the entire Northern Hemisphere determines the ture is related to the development of the meridional development of the single upper-level frontal zone, as

DOKLADY EARTH SCIENCES Vol. 487 Part 2 2019 CLIMATOLOGY AND INTERANNUAL MOVEMENTS 1001 a rule; while the meridional processes cause the for- REFERENCES mation of separate markedly pronounced branches of 1. M. Kh. Baidal and D. G. Khanzhina, Long-Term Vari- UFZs that undergo significant variations that depend ability and Macrocirculation Factors of the Climate on the development of a particular meridional process. (Gidrometeoizdat, Moscow, 1986) [in Russian]. Since the position of UFZs is determined by the inter- 2. M. A. Duitseva and D. A. Ped’, Tr. Gidromettsentra action of the large-scale troughs and ridges, their dis- SSSR, No. 62, 64–72 (1970). placement allows us to detect the movement of air 3. L. K. Kleshchenko and L. N. Aristova, in Sci. Works masses in the troposphere, to reveal the anomalies of All-Russ. Res. Inst. Hydrometeorol. Inform.–Int. Data the circulation processes, and to study the blocking Center (Obninsk, 2007), Issue 173, pp. 128–136 [in situations. The position of the upper-level frontal Russian]. zones is an objective diagnostic tool for detection of 4. General Circulation of the Atmosphere: Monitoring. the periods with the dominant zonal and meridional Northern Hemisphere. Handbook, Ed. by R. M. Vil’fand forms of circulation. and A. I. Neushkina (All-Russ. Res. Inst. Hydromete- orol. Inform.-Int. Data Centre, Obninsk, 2012) [in Based on the use of an objective numerical Russian]. method, we developed a new seasonal climatology for 5. I. I. Mokhov, Izv., Atmos. Ocean. Phys. 47 (6), 653– the position of the main UFZs and studied their inter- 661 (2011). annual dynamics. The estimated set of upper-level 6. Kh. P. Pogosyan, Planetary Upper-Level Frontal Zones frontal zones made it possible to refine significantly in the Northern and Southern Hemispheres (Gidromete- the regional distribution and movement of UFZs, oizdat, Leningrad, 1955) [in Russian]. while the analysis of the typical isohypse provided a 7. Kh. P. Pogosyan and A. A. Pavlovskaya, Anomalies of more generalized picture without regional features. the Atmospheric Circulations of Surface Pressure and The results obtained can be used during analysis of the Temperature with Respect to Quasi-Two-Year Cycle dynamics of cyclonic activity, in particular the move- (Gidrometeoizdat, Leningrad, 1977) [in Russian]. ments of cyclone trajectories [14] and the frequency of 8. O. A. Razorenova, Russ. Meteorol. Hydrol. 41 (1), 1– blocking anticyclones in the atmosphere [4, 11], as 9 (2016). well as in the studies of an atmospheric circulation 9. O. A. Razorenova and P. A. Shabanov, Oceanology response to the World Ocean signals [9]. (Engl. Transl.) 55 (6), 801–805 (2015). 10. Yu. B. Khrabrov, Tr. Tsentr. Inst. Prognozov, No. 63, 46–61 (1957). FUNDING 11. N. P. Shakina and A. R. Ivanova, Russ. Meteorol. Hydrol. 35 (11), 721–730 (2010). This study was carried out under a state task, project no. 12. T. P. Eichler and J. Gottschalck, Adv. Meteorol. 2013, 0149-2018-0001. 545463 (2013). https://doi.org/10.1155/2013/545463 The calculation of the refined climatology of the upper- 13. S. K. Gulev, T. Jung, and E. Ruprecht, J. Clim. 15, level zones was supported by the Government of the Rus- 809–828 (2002). sian Federation under state assistance to leading scientists 14. E. Kalnay, et al., Bull. Am. Meteorol. Soc. 77 (3), 437– (Contract no. 14.V25.31.0026). The analysis of the interan- 471 (1996). nual movements and positions of UFZs in the years when 15. U. Ulbrich and M. Christoph, Clim. Dyn. 15 (7), 551– the different circulation forms dominated was supported by 559 (1999). a grant of the Russian Science Foundation, project no. 14– 50–00095. Translated by L. Mukhortova

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