On the Spatial Nonuniformity of Some Parameters of ... - Springer Link

ISSN 1028-334X, Doklady Earth Sciences, 2009, Vol. 426, No. 4, pp. 705–709. © Pleiades Publishing, Ltd., 2009. Original Russian Text © V.I. Byshev, V.G. Neiman, Yu.A. Romanov, I.V. Serykh, 2009, published in Doklady Akademii Nauk, 2009, Vol. 426, No. 4, pp. 543–548.

GEOGRAPHY

On the Spatial Nonuniformity of Some Parameters of Global Variations in the Recent Climate V. I. Byshev, Corresponding Member of the RAS V. G. Neiman, Yu. A. Romanov, and I. V. Serykh Received October 30, 2008

DOI: 10.1134/S1028334X09040436

The near-surface temperature began rising in the mid-1970s, and the planetary field of atmospheric pressure considerably rearranged. The average pressure fields and temperatures for two successive 25-year periods prior to and after the rearrangement are compared in this work. Temperature fluctuations between the periods are shown to be in good agreement with variations in the atmospheric circulation due to rearrangement of the barometric field. A decrease in the near-surface temperature average for the periods was observed in regions with an air mass influx from higher latitudes with an increase in wind speeds over the ocean. A rise in the temperature took place in reversed situations. Early in the 21st century, a gradual relapse of the system to the situation antedating the last quarter of the 20th century was noticed. According to [1], long-term atmospheric processes are inevitably global—only the planet as a whole can serve as a “natural synoptic region” for them. The processes correspond to the scale of the general circulation of the atmosphere. The global nature of climatic processes is evidenced by the observed quasi-synchronous changes in thermodynamic characteristics of the ocean–atmosphere subsystem in the Pacific and Atlantic [2, 3] and Pacific and Indian [4, 5] oceans; in the high, middle, and low latitudes [6]; and in the Western and Eastern [7] hemispheres. Our investigations along with the study of individual properties and peculiarities of the climatic system are aimed at acquiring the whole pattern of its interdecadal variability and establishing general causes that form the basis of the observed climatic fluctuations, as well as physical mechanisms which maintain the variability. We consider in this work the peculiar features of the recent global climate dynamics in the period referred to as the global warming. Variations that took place in that period in the fields of the atmospheric pressure and near-surface temperature have been analyzed and natu-

Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovskii pr. 36, Moscow, 117997 Russia

ral processes that could cause those variations have been considered. Used as basic data in diagnostic calculations of oceanic and atmospheric climatically significant characteristics were global monthly fields of atmospheric pressure at sea level [http://www.cdc.noaa.gov/Pressure/Gridded/] and anomalies of the near-surface temperature [http://www. cru.uea/ak/cru/data/temperature/] for the period of 1950–2007. Due to scanty data on observations north of 80° N and south of 70° S, the results of the analysis of the corresponding hydrometeorological fields in these zones should be taken with caution. The lack of data and, hence, inadequate reliability of the investigation results hold true for other regions as well, for instance, in central Africa. Global warming attracted particular attention in the 1970s, when a substantial rearrangement of the planetary field of atmospheric pressure took place [8–10]. This situation formed the basis for the methods used in this work. To get nonrandom, statistically secured quantitative estimates of the above-mentioned rearrangement, we determined differences of global climatic fields of atmospheric pressure at sea level and the near-surface temperature averaged for two 25-year time intervals: 1975–1999 and 1950–1974. The field differences ∆X(ϕ, λ, z0) were determined according to the formula t4

1 ∆X ( ϕ, λ, z 0 ) = ------------- X ( ϕ, λ, z 0, t ) dt t4 – t3

∫ t3

t2

1 – ------------- X ( ϕ, λ, z 0, t ) dt, t2 – t1

∫

(1)

t1

where t is time, and t1 = 01.1950, t2 = 12.1974, t3 = 01.1975, t4 = 12.1999 are time moments. The remaining are common symbols: ϕ designates latitude, λ denotes longitude, and z is vertical coordinate. Moreover, by the same method there were obtained differences of the mentioned characteristics for each month which allow tracing the climatic seasonal transformation of the corresponding fields.

705

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GPa 1.6 1.2 0.8 0.4 0 –0.4 –0.8 –1.2 –1.6 –2.0 –2.4 –2.8 –3.2 –3.6

60° 30° 0° –30° –60° –90° –60°

0°

60°

90°

120° (b)

180°

240°

300° °C

60° 30° 0° –30° –60° –90° –60°

0°

60°

120°

180°

240°

300°

1.0 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0

Fig. 1. Maps of differences of (a) atmospheric pressure at sea level and (b) near-surface temperature between the periods of 1975– 1999 and 1950–1974. Arrows show geostrophic wind speeds.

The atmospheric pressure field rearrangement led to corresponding changes in the general circulation of the atmosphere, the quantitative assessment of which was gained from the known quasi-geostrophic ratios [11]: Ug = –1/fρ(∂P'/∂y), Vg = 1/fρ(∂P'/∂x). They adequately describe the global field of wind speed in the lower troposphere everywhere except for the equatorial zone determined by the Rossbi deformation radius ae: ae = (c/(2β))1/2, c = (gH)1/2, β is the Coriolis parameter f of variations with latitude, g is acceleration of gravity, H is the equivalent height of the baroclinic troposphere, c is the Kelvin equatorial wave velocity, and x and y are Cartesian (orthogonal) coordinates, the positive direction of which is towards the east and north respectively; P' = ∆P(ϕ, λ, z0) is the atmospheric pressure distortion assessed according to (1). To assess the development of climatic events over recent years, differences of the atmospheric pressure and near-surface temperature between the periods of

2000–2007 and 1975–1999 were calculated and analyzed. Figure 1a demonstrates that the global rearrangement of the pressure field in the mid-1970s was accompanied by the appearance of large-scale anomalies of both signs. The average atmospheric pressure at sea level over polar regions (Arctic and Antarctic) and most of the Pacific Ocean considerably decreased from the first to the second 25-year period. At the same time, it increased over the Central Atlantic and the African continent, over the Indian Ocean, Australia, and the region referred to as a “sea continent” [12]. In the Northern Hemisphere, three quasi-stationary regional minimums appeared in the zone of abnormally decreased pressure: (1) in northeastern Canada, the Baffin Sea area included, and in Greenland; (2) in the lower courses of the Ob and Yenisei rivers and in the southern part of the Kara Sea; (3) in the northern part of the Pacific Ocean and in the Bering Sea. On the territory occupied by increased pressure anomalies, belts with higher values DOKLADY EARTH SCIENCES Vol. 426 No. 4 2009

ON THE SPATIAL NONUNIFORMITY OF SOME PARAMETERS

of it and individual local maximums showed up in middle latitudes of both hemispheres: (1) over the Atlantic Ocean and Mediterranean Sea; (2) over central China; (3) south of Africa, over the Antarctic Circumpolar Current; (4) over Australia; (5) over the Drake Strait and the southern edge of South America.

T, °C 3.0

The observed changed characteristics in the structure of the atmospheric pressure field were accompanied by corresponding variations in the general circulation of the atmosphere. An abrupt aggravation of the airflow zoning in middle latitudes of both hemispheres was the most significant consequence of the pressure field rearrangement. In most of these regions, the anomalous western component of the wind was superimposed on the climatic western wind with the resulting real wind intensification. As this took place, evaporation and a vertical exchange appropriately increased, owing to which the near-surface temperature was to decrease. As is evident from Fig. 1b, such a decrease in the temperature was truly observed in the northern parts of the Atlantic and Pacific oceans, as well as in middle latitudes of the Southern Hemisphere. In oceanic regions with an anomalous wind component opposed to its climatic norm, the real wind will become weaker, and, hence, the near-surface temperature will rise slightly. Such a situation developed, for instance, in the ocean south and east of South Africa, as well as in the eastern part of the Pacific near-equatorial zone.

1.5

Intensification of the zonal transfer from the ocean to the land should cause positive temperature anomalies on land in winter and an increase in air humidity, as well as a certain decrease in the temperature in summer. Actually, positive temperature anomalies are observed in middle latitudes in Eurasia and North America (Fig. 1b). By this is meant that the contribution of winter processes to the formation of average characteristics predominated there (this will be discussed below). Moreover, meridional transfers in the atmosphere, which are formed under the effect of the above-mentioned regional pressure minimums and maximums, will greatly affect these characteristics as well. These phenomena are most conspicuous in middle latitudes of the Pacific northern and southern parts. When carrying cold air in the southern direction, northern winds at the western periphery of the Aleutian low intensify the heat exchange between the ocean and atmosphere and thus aggravate the negative climatic temperature anomaly in the North Pacific and form an area of negative anomalies southwest of it, the Sea of Japan included. Southern winds at the eastern periphery of the above-mentioned low-pressure area cause the formation of positive temperature anomalies in Alaska Bay and in the northwestern part of North America. Areas of negative temperature anomalies are formed in the same manner in the western part of the South Pacific under the effect of air flows with the southern component. In the southeastern part of the ocean, in the case of winds with opposite directions, areas of positive temperature anomalies are DOKLADY EARTH SCIENCES Vol. 426 No. 4 2009

2.5 2.0

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5

4

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3

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1

–1.0

2

–1.5 1

2

3

4

5

6

7

8

9

10 11 12 Month

Fig. 2. Monthly differences of the average near-surface temperature between the periods of 1975–1999 and 1950–1974 in individual regions of the Northern Hemisphere. (1) Atlantic Ocean (50°–60° N, 50°–10° W); (2) Pacific Ocean (30°–45° N, 160° E–160° W); (3) Mediterranean Sea (30°–45° N, 20°– 40° E); (4) Eurasia (45°–60° N, 70°–100° E); (5) North America (55°–65° N, 160°–120° W).

formed, which involve the southern part of South America and the Antarctic Peninsula. Southern winds at the eastern periphery of the cyclonic structure with the center located south of the Yamal Peninsula, as well as intensification of the meridional warm air mass transfer from central regions of the Asian continent, in which the masses arrive from the Indian Ocean, assist in the formation of a substantial positive temperature anomaly in Central Siberia, which is quite noticeable in Fig. 1b. Of interest is the fact that despite northern winds the temperature anomaly appears to be positive west of the Yamal low, although it is not so intense as east of it. The reason is probably that part of the warm air mass brought northward to the eastern periphery of the cyclone is incorporated into the Yamal cyclonic circulation. The negative anomaly of the near-surface temperature observed in eastern Mediterranean regions and the Black Sea is confined to the eastern periphery of the increased pressure anomaly where cold air masses are carried away in the southerly direction. Monthly maps of pressure variations from 1950– 1974 to 1975–1999 (maps are not given) showed that in the cold half of the year (November–March for the Northern Hemisphere and April–October for the Southern Hemisphere), the mentioned negative atmospheric pressure anomalies became more profound and caused intensification of the latitudinal heat exchange at their

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GPa

60° 30° 0° –30° –60° –90° –60°

0°

60°

90°

120° (b)

180°

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300°

T, °C

60° 30° 0° –30° –60° –90° –60°

3.0 2.5 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 –3.5 –4.0

0°

60°

120°

180°

240°

300°

1.0 0.8 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0

Fig. 3. Maps of differences of (a) atmospheric pressure at sea level and (b) near–surface temperature between periods of 2000–2007 and 1975–1999. Arrows show geostrophic wind speeds.

eastern and western peripheries. The fact of a strong warming (by 2–2.5°C) in Central Asia and northwestern North America in precisely the winter months is quite consistent with the latitudinal heat exchange (Fig. 2). In the summer period, when the meridional heat exchange slackens, the relative warming made up a mere 0.1– 0.3°C there. Unlike the land, the Pacific and Atlantic areas chosen for the analysis (Fig. 2, curves 1 and 2) lost heat more or less evenly during the year. In the Atlantic Ocean, temperature anomalies varied from –0.21 to –0.43°C during the year. In the Pacific Ocean, the variations were a bit greater: from –0.39°C in November to –1.33°C in May. It turns out that intensification of cold air flows towards the ocean along the western periphery of the atmospheric pressure negative anomalies which become more profound in winter did not result in depression of surface temperature anomalies there at that time. This is because of the density vertical convection developed in

the ocean and extended to large depths due to intensification of the heat exchange with the atmosphere. It should be noted that the results of observations in a series of oceanic experiments carried out during these years are in good agreement with the tendencies presented in Fig. 1b on the near-surface temperature variations during the period 1975–1999. The MEGAPOLYGON experiment [13] was carried out in 1987 from July to November, in the Pacific Ocean east of the Japan Islands, in the area of negative climatic anomalies of the near-surface temperature (Fig. 1b). Calculations made in the course of the experiment showed that the heat balance on the ocean surface was negative. Heat inputs spent on evaporation, the turbulent flow of explicit heat from the ocean to the atmosphere and ocean surface long-wave radiation exceeded the heat influx at the expense of solar radiation consumed by the ocean. The well-known ATLANTEX-90 experiment was carried out from April to June 1990, in the NewfoundDOKLADY EARTH SCIENCES Vol. 426 No. 4 2009

ON THE SPATIAL NONUNIFORMITY OF SOME PARAMETERS

land energy-active zone located in the area of the nearsurface temperature (Fig. 1b). Materials gained during the experiment showed [14] that a large-scale negative anomaly was observed there as well at that time, which made up –2 and –3°C on the surface. Convection spanned at the least the upper 1000-m layer there. According to data from [15], the generation of negative temperature anomalies on the surface during the years 1975–1999 was characteristic of the eastern part of the Mediterranean Sea as well. Hence, our inferences about negative anomalies of the near-surface temperature formed in the last quarter of the 20th century in the Atlantic and Pacific oceans, as well as in the Mediterranean Sea (Fig. 1b), in which Arctic air masses arrived under the effect of surface pressure (Fig. 1a), are corroborated by independent actual materials reflecting the relevant climatic signals. To gain an idea on variations of global fields of the atmospheric pressure and temperature for the most recent period, the differences of the average values of these parameters were calculated for the periods of 2000–2007 and 1975–1999 (Fig. 3). A growth of pressure is seen to exist at the beginning of the twenty-first century (Fig. 3a) everywhere in areas where negative atmospheric pressure anomalies were observed in the last quarter of the former century (Fig. 1a). In areas previously characterized by increased atmospheric pressure, the trend appeared toward its decrease. The opposite trend of climatic processes is revealed in the nearsurface temperature as well (Figs. 1b, 3b). In particular, the temperature rise was registered in the northern part of the Pacific and Atlantic oceans where the cooling occurred prior to it. The most important thing is that we have revealed the corresponding rearrangement in the structure of the atmospheric general circulation, which will unfailingly cause a certain reconstruction of the temperature field. Taken together, these facts suggest that at present there occurs a changing of the phase of quasi-cyclic interdecadal variability of the global climatic system that is likely to be determined by its inner dynamics. CONCLUSIONS The analysis of the temporal variability in the spatial structure of atmospheric pressure and temperature fields in the period 1950–2007 revealed oppositely directed processes of heat redistribution in the near-surface air layer over oceans and continents. While the average surface temperature rose on most continents in the last quarter of the 20th century, compared to the period of 1950–1974, the upper active layer in vast areas of oceans and some seas began cooling. Considering that necessarily related to negative anomalies of the ocean surface temperature are processes of vertical convection involving into the heat exchange between the ocean and atmosphere the whole active layer (~100 m) at the least and sometimes a more extensive water DOKLADY EARTH SCIENCES Vol. 426 No. 4 2009

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sequence (up to 1000–1200 m [14]), then the ocean heat emission equivalent to the observed warming on continents seems to be quite real [1]. There are strong grounds to believe that the “global warming” can be related in large measure to natural heat redistribution between oceans and continents at the expense of the intrinsic dynamics of the climatic system. Moreover, the trend revealed in this work toward the climatic system return to the preceding state characteristic of the last quarter of the 20th century suggests a termination of the observed warming in continents in the near future owing to probable transition of the climatic system to the phase of heat accumulation by oceans. In this case, we get one more argument in the favor of the hypothesis [7] about regular changing of the climatic scenario, which has already begun. ACKNOWLEDGMENTS This work was supported by the Federal Target Program “World Ocean” (State Contract no. 01.420.1.2.0001) and the Russian Foundation for Basic Research, project nos. 06-05-63646 and 07-05-00024. REFERENCES 1. A. S. Monin, Weather Forecast as the Physics Problem (Nauka, Moscow, 1968) [in Russian]. 2. V. I. Byshev, V. G. Neiman, T. G. Pozdnyakova, and Yu. A. Romanov, Dokl. Earth Sci. 381A (9), 1077 (2001) [Dokl. Akad. Nauk 381 (4), 539 (2001)]. 3. M. Yu. Bardin and E. N. Voskresenskaya, Mor. Geofiz. Zh., No. 4, 13 (2007). 4. D. Anderson, Nature 301, 337 (1999). 5. N. A. Vyazilova, Meteorol. Gidrol., No. 8, 19 (2006). 6. I. E. Frolov, Z. M. Gudkovich, V. P. Karklin, et al., Probl. Arktiki Antarktiki, No. 75, 149 (2007). 7. V. I. Byshev, V. G. Neiman, and Yu. A. Romanov, Oceanology 46 (2), 147 (2006) [Okeanologiya 46 (2), 165 (2006)]. 8. V. I. Byshev, V. G. Neiman, and Yu. A. Romanov, Izv. Akad. Nauk, Ser. Geograf., No. 1, 7 (2009). 9. C. Stephens, S. Levitus, J. Antonov, and T. P. Boyer, Geophys. Res. Lett. 28, 3721 (2001). 10. K. E. Tenberth, Bull. Amer. Meteorol. Soc. 71, 988 (1990). 11. A. Gill, Atmosphere–Ocean Dynamics (Academic Press, 1983; Mir, Moscow, 1986). 12. R. Neatle and J. Slingo, J. Climate 16, 834 (2003). 13. Experiment “MEGAPOLYGON” (Nauka, Moscow, 1992) [in Russian]. 14. V. I. Byshev, L. I. Koprova, S. E. Navrotskaya, et al., Dokl. Akad. Nauk 331 (6), 735 (1993). 15. I. I. Zveryaev and A. V. Arkhipkin, Meteorol. Gidrol., No. 6, 55 (2008).