Siberian high

The combined effect of the Madden-Julian oscillation (MJO) and Arctic oscillation (AO) on the temperature variation over Asia is investigated using the thermodynamic budget equation. Because of the distinct geographical origin of the two atmospheric modes, the influence of AO is more dominant in the higher latitude, whereas the MJO impact is more predominant in the lower latitude. Hence, the physical process responsible for the surface cold anomaly is different for northern and southern Asia. Cold anomaly appears in most of Asia 20-25 days after the MJO phase 6 (corresponding to the phase 2-3). However, more strengthened cold anomaly occurs over northern Asia under the negative AO state and it is caused by advection of temperature anomaly by climatological northerly wind associated with the East Asia winter monsoon flow. On the other hand, much stronger cold anomaly is seen over southern Asia under the positive AO state for the same lag day of the initial MJO phase 6. Aside from the upward overturning circulation forced by the tropical MJO over the subtropics and lower midlatitudes, the weakening of the East Asia subtropical jet by the positive AO induces additional upward motion over southern Asia to adjust the thermal wind balance. The combined effect of the MJO and AO also influences on the occurrence of extreme cold event. Under the negative (positive) AO phase, the extreme cold event occurrence probability over northern (southern) Asia increases by 90% (60%) compared to that for all winter days. The relative increase rate for the MJO phases 2-3 is ~30% over southern Asia. The cold event occurrence probability for the combined modes is about the twice that for only MJO impact, suggesting that an incorporation of both modes enhance the predictability of extreme cold event.

This study highlights an important and previously overlooked summer North Atlantic Oscillation (NAO) influence over the eastern Mediterranean. The featured analysis is based on a synergistic use of reanalysis data, satellite retrievals, and coastal and buoy meteorological observations. The physical mechanisms at play reveal a strong summer NAO involvement on the pressure fields over northern Europe and the Anatolian plateau. Especially during August, the summer NAO modulates the Anatolian low, together with the air temperature, meridional atmospheric circulation, and cloudiness over the eastern Mediterranean. Including the dominant action centers over Greenland and the Arctic, the identified modulations rank among the strongest summer NAO-related signals over the entire Northern Hemisphere.

Instrumental records indicate a close relationship between the El Niño-Southern Oscillation and the East Asian winter monsoon (EAWM) on interannual to decadal time scales. However, few studies have examined possible links between them on centennial/millennial time scales. In Northeast China, modern observations show that the immigration of temperate forest trees such as Pinus (pine) and Quercus (oak) into cold temperate boreal forest is sensitive to changes in winter temperature. Here we present a continuous high-resolution pollen record from Lake Moon in the central part of the Great Khingan Mountain Range, Northeast China. The record reveals increasing contents of Pinus and Quercus pollen after ~6.0 ka cal. BP, which may indicate a gradual weakening of the EAWM. It is broadly coupled with an increasing El Niño frequency since the middle Holocene, and we observe a statistically significant correlation between the percentages of Pinus and Quercus and a time series of El Niño events. On the centennial to millennial time scale, the results of wavelet analysis and band-pass filtering show that the occurrence and development of El Niño have also promoted a weaker EAWM after ~6.0 ka cal. BP, which is inversely correlated with the variation of the ca. 500-year cycle originated from changes in solar output. These results imply that the climate transition in the mid-Holocene is caused by the change of variations in solar activity and amplified by ocean circulation El Niño-Southern Oscillation to influence the East Asian Monsoon system, especially the EAWM, and finally change the vegetation in Great Khingan Mountain Range.

This paper attempts to find the associations between the atmospheric circulation patterns ranging from regional to global scales and winter precipitation patterns over Iran. This study utilizes Principal Component Analysis (PCA), running correlations and composite maps for extremely dry and wet conditions. A PCA of winter precipitation reveals five components that account for 63% of the total variance. Analyses of SLP and GPH fields reveal five anomalous pressure centers over Kazakhstan, Syria, the Indian Peninsula, the North Sea and the northwestern African coast during wet conditions in Iran. These pressure centers make a special wind pattern, causing prevailing westerlies towards the Arabian Peninsula, that curve northward by an anticyclonic wind pattern over the Indian Peninsula. This pattern is destroyed in dry conditions and is replaced by the cold and dry northeasterly winds. The results also show that the zonal (meridional) wind during wet conditions is weaker (stronger) than the dry conditions. The five pressure centers are also found to be associated with some atmospheric indices. The strongest results are found for the North Sea-Caspian Pattern (NCP) and the Western Mediterranean Oscillation (WeMO) indices. These two indices have the most significant correlation with the PCs in Iran. Analyses of the results also reveal that the winter precipitation in Iran is mainly related to the Black Sea and the Mediterranean SLP. The best linkage is found between the Black Sea SLP and the PC4, expressed by correlation coefficients varying from 0.43 to 0.57. Our results also indicate that, the Red Sea trough under wet winter conditions in Iran is accompanied by a deep 850 and 500-hPa trough, located west of the Mediterranean. This trough is strongly weakened during dry conditions. We also found that, the winter precipitation PCs are controlled by some atmospheric indices. The best result is found for the PC1 that is affected by the WeMO and the Scandinavian Pattern.

In recent decades wildfires have occurred frequently over eastern Siberia, which favors increased atmospheric carbon dioxide and air pollution. However, it is not well understood what factors have contributed to the recent increase in these wildfires. Here, we analyzed meteorological and satellite data to show that background Arctic warming related to summer Russian Arctic sea-ice decline can account for about 84% of the increase in eastern Siberian wildfires during 2004-2021 with the remaining 16% related to internal atmospheric variability associated with changes in Siberian blocking events. We further demonstrate that Siberian blocking events occur at higher latitudes, are more persistent and have larger zonal scales over 2004-2021 than during 1979-2003 due to reduced meridional potential vorticity gradients caused by background Arctic warming during the latter period. These changes lead to more persistent, widespread and intense wildfires and their poleward migation, thus contributing to the recent increases in eastern Siberian wildfires.

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During the past decade (2004/05–2013/14), the number of cold days in Hong Kong (NCD), as a proxy of the temperature of southern China, appeared to have increased from the historical minimum, in contrast to a remarkable decline in the entire postwar period. This is related to the recent apparent changes in the large-scale circulation upstream and downstream of the East Asian winter monsoon (EAWM) region: the increase in Ural blocking (UB) that enhances cold advection from the polar region and reinforces the Siberian high and the decrease in a western Pacific (WP)-like index that corresponds to increasing meridional gradient of geopotential height over the EAWM region. Overall, UB and WP account for 26.4% of the interannual (≤8 yr) variance and 83.7% of the decadal (>8 yr) variance of NCD for the period 1948/49–2013/14, indicating that further study could lead to improvement in the prediction of NCD.

Expansion of agricultural practices from the Fertile Crescent to China during the mid and late Holocene are believed to have shaped the early network of Silk Road routes and possibly regulated the dynamics of trade and exchange in the urban oases along the Silk Road throughout its existence. While the impacts of climate change on the Silk Road are more or less documented for the medieval period, they remain poorly understood for early history of the Silk Road, especially in Central Asia. We analyze hydroclimatic proxies derived from fluvial stratigraphy, geochronology, and tree-ring records that acted on various time scales in the Lake Balkhash Basin to learn how changes in water supply could have influenced the early farmers in the Semirechye region of southern Kazakhstan. Our approach aims to identify short-term and long-term variability of regional runoff and to compare the hydrological data with cultural dynamics coupled with the archaeological settlement pattern and agricultural production. The reconstructed runoff variability underscore the contribution of winter precipitation driven by the interaction between the Arctic oscillation and the Siberian High-Pressure System, to Central Asian river discharge. We show that Saka people of the Iron Age employed extensive ravine agriculture on the alluvial fans of the Tian Shan piedmont, where floodwater farming peaked between 400 BC and 200 BC. The early Silk Road farmers on the alluvial fans favored periods of reduced flood flows, river stability and glacier retreat in the Tian

The EMEP precipitation chemistry network was used in combination with the Reanalysis NCEP/NCAR archive to analyze the influence of climatic-scale variations in atmospheric circulation on summertime wet sulfate deposition over central Europe from 1984 to 1999. Correlation of deposition with hemispheric and global circulation patterns indicates a significant role (49% of the variance) for the North Hemispheric Pacific Transition (PT) teleconnection in the wet deposition of sulfate over central Europe in August. The seasonal correlation of air temperature at shallow tropospheric layers reveals significantly cooler air masses over central Europe, Alaska and the southwestern US coast and warmer air over Greenland, the Barents and Kara Sea and the South Atlantic and Indian Ocean. The geopotential height (GPH) anomalies for sulfate-rich deposition years exhibit a pattern consistent with the seasonal correlation. A weakening of both belts of Sub-Polar lows and Antarctic Polar Highs is also observed. In the Northern Hemisphere, a distinct dipole in GPH is observed, with a positive anomaly over Iceland and the Norwegian Sea and a negative anomaly over Russia and Scandinavia. Composite plots of the most loaded/unloaded days of sulfate deposition yielded a prominent signal of the associated mean atmospheric field patterns. The composite sea-level pressure (SLP) for the 20 highest deposition days shows an average intensification of 1 hPa and a northeastward migration of the Azores Subtropical High, leading to a significant anomaly in the negative meridional wind component at the 925-hPa level. This flow presumably enables the transport and oxidation of SO 2 emitted from major upwind pollution sources toward central Europe. The observed downward trend in sulfate deposition suggests that the study period was characterized by predominantly warm zonal circulation. More frequent zonal flows in the future, together with further reductions in sulfur dioxide emissions are likely to lead to lower sulfate deposition.

Increased use of solar photovoltaic electricity requires a better understanding of the impact of large‐scale atmospheric teleconnections on incident short wave (SW) solar radiation. Our focus is on the relationship between winter (December to February) SW radiation in northwest Europe and the dominant Euro‐Atlantic atmospheric teleconnection patterns using multiple multi‐decadal observational and gridded reanalysis datasets, with a focus on the islands of Ireland and Britain. Our study reveals that the previously reported west–east seesaw in the correlation pattern between the winter North Atlantic Oscillation (NAO) index and winter SW radiation across the United Kingdom is complex, involving several zonal changes in the sign of the NAO–SW correlations (multiple seesaws). By comparison with the NAO, the east Atlantic pattern exerts only a weak control on winter SW radiation across the United Kingdom and Ireland, although in the western part of the Iberian Peninsula and adjacent Atla...

Eurasian snow, one of the most important factors that influence the Asian monsoons, has long been viewed as a useful predictor for seasonal monsoon prediction. In this study, observations and model simulations are used to demonstrate a bridging role of the winter snow anomaly over northern China and southern Mongolia (NCSM) in the relationship between the East Asian winter monsoon (EAWM) and the East Asian summer monsoon (EASM). Enhanced snow in NCSM results in local surface and tropospheric cooling, strengthening the EAWM through cold-air intrusion induced by northerly wind anomalies. In turn, the stronger EAWM provides a favorable condition for enhanced snowfall over East Asia to the south, indicating an active snow-EAWM interaction. The continental cooling could be maintained until summer due to the memory effect of snowmelt and moistening as well as the snow-monsoon interaction in the spring, causing changes in the meridional temperature gradient and associated upper-level westerlies in the summer. The interaction between the strengthened westerlies over the northern Tibetan Plateau and the topography of the plateau could lead to anomalous downstream convergence and compensating divergence to the south. Therefore, anomalous cyclonic circulation and increased rainfall occur over northeastern China and the Korean Peninsula, but anticyclonic circulation and decreased rainfall appear over the subtropical East Asia-Pacific region. Moreover, limited analysis shows that, compared to sea surface temperature feedback, the direct impact of snow anomaly on the EAWM-EASM connection seems more important.

Eurasian snow, one of the most important factors that influence the Asian monsoons, has long been viewed as a useful predictor for seasonal monsoon prediction. In this study, observations and model simulations are used to demonstrate a bridging role of the winter snow anomaly over northern China and southern Mongolia (NCSM) in the relationship between the East Asian winter monsoon (EAWM) and the East Asian summer monsoon (EASM). Enhanced snow in NCSM results in local surface and tropospheric cooling, strengthening the EAWM through cold-air intrusion induced by northerly wind anomalies. In turn, the stronger EAWM provides a favorable condition for enhanced snowfall over East Asia to the south, indicating an active snow–EAWM interaction. The continental cooling could be maintained until summer due to the memory effect of snowmelt and moistening as well as the snow–monsoon interaction in the spring, causing changes in the meridional temperature gradient and associated upper-level weste...

The East Asian winter monsoon (EAWM) not only plays an important role within the Asian climate system, but also carries cold air from the high northern latitudes across the Equator to the Southern Hemisphere, acting as a link between the polar and tropical climate systems. However, past changes of the EAWM have not been clearly established so far due to the lack of suitable proxy records. Here, we at first establish an index of the EAWM by comparing the results of a sediment trap experiment and 100year sedimentary record from Huguang Maar Lake (HML) with modern records of the EAWM, Siberian High (SH) and Arctic Oscillation (AO). Secondly, we present a continuous record of the strength of the EAWM for the past 14,500 years based on sedimentary diatom assemblages in HML. The record is derived from fluctuations in the relative abundance of two planktonic diatom species. The link with the EAWM intensity is through high wind speeds inducing turbulent mixing, which stimulates the productivity of the meroplanktonic species Aulacoseira granulata. The diatom record of the past 14,500 years shows that the EAWM shifted from strong to weak from the early to late Holocene. This linked to both changes in winter temperature at high-latitudes and in El Niño conditions in the tropics. Our record shows that the EAWM and East Asian summer monsoon (EASM) as recorded in stalagmites, were in-phase instead of anti-correlated on orbital time scales during the Holocene. On a millennial time scales, the EAWM was anti-phase with the EASM during the Last GlacialeHolocene transition. However, during the early emiddle Holocene the relationship between the EAWM and EASM shows spatial variations. In northern China, the records show significant anti-phase, but in southern China the anti-phase was not observed. During the late Holocene, we did not find any clear relationship between the EAWM and EASM. We also explored the link between the EAWM and the Australian summer monsoon (ASM). Anti-phase of the ASM with summer insolation in the Southern Hemisphere is an enigmatic exception that cannot be explained by the classic theory of insolation. During early Holocene the EAWM was in-phase with the Australian summer monsoon (ASM), which provides the first direct evidence to support the hypothesis that the intensity of the EAWM affected, at least in part, the strength of the ASM.

To clarify the interannual variability of winter surface air temperature (SAT) over Asia and the surrounding oceans, the authors applied principal component analysis to normalized monthly SATs. The first mode represents the Asian north–south dipole pattern with a node over the Tibetan Plateau. This component has close relationships to the Arctic Oscillation and cold surge variability around Southeast Asia, showing decadal oscillation with signal changes in 1988 and 1997. The second mode is the inner-Asian mode with a center to the north of the Tibetan Plateau. This component connects to fluctuations of not only the western Siberian high but also the Icelandic low, which is associated with the pattern of the polar vortex over Eurasia. A recent warming trend and possible relationship to solar activity are also shown. The modes of Asian SAT variability associated with ENSO are extracted as the north–south dipole mode over the tropical western Pacific and Japan (the third mode) and Silk...

Extreme winter daily temperature is an important parameter for determining winter precipitation. This study used a principal component analysis and k-means clustering to characterize the circulation patterns of extreme daily temperatures for 19 winter seasons in Sapporo, Hokkaido, Japan. Climatological anomaly maps were constructed for sea level pressure (SLP) and the 500-hPa geopotential height for the identified minimum (Tmin 10 ; 239 days) and maximum (Tmax 90 ; 236 days) daily temperature extremes. The Tmax 90 SLP anomaly pattern was the opposite (west-east orientation) of the Tmin 10 pattern. The circulation patterns that predominantly contributed to winter rainfall were derived from cyclones over the Sea of Japan via instability created by abundant heat and moisture over the ocean and a strong positive 500-hPa height anomaly over Hokkaido. KEY WORDS Aleutian low; geopotential height; maximum daily temperature extreme; minimum daily temperature extreme; sea level pressure; Siberian high

Istanbul, as one of the four anchor megacities of Europe, has shown a rise of 0.94 ∘ C in average annual temperature over the long period of 1912-2016 under impacts of anthropogenic climate change. A notable increase in temperatures has started after the 1940s, which is in parallel with the beginning of industrialization era in Istanbul. This warming is associated with an extensive population growth and accompanied the decrease in vegetation cover. Increasing in minimum series of temperature is more evident than maximum values and the rising rate of temperature values has been more pronounced during recent decades. The first significant upward trend in precipitation series has periodically started in 1920s, while there has been a stable trend from 2001 till today. The daily average of rainfall amount increased with a mean value of 58 mm during the total study period. Rising rate of daily maximum precipitation has been more evident in the last 3 decades, which is shown by the increased frequency of heavy rainfall. In this regard, both of the temperature and precipitation series had higher mean values (13.9 ∘ C and 878 mm) for the final period (1965-2016) compared to the mean values (13.6 ∘ C and 799 mm) belonging to the first period (1912-1964).

Oxygen (d 18 O) and carbon (d 13 C) isotope records of calcitic carbonate components (Chara sp. algal encrustations and Bithynia tentaculata gastropod opercula) from a lake-sediment succession on the Baltic Sea island of Gotland, southeastern Sweden, have been obtained to investigate regional climate dynamics during the Holocene. The hydrological sensitivity of the small lake, particularly in terms of spring snowmelt contribution to the local water budget, provides a means of tracing past changes in the influence of snow-bearing easterly winds across the Baltic Sea Proper, which signifies the wintertime strength of the Siberian High. Repeated episodic depletions in 18 O at the centennial scale correlate with events of increased potassium concentration in the GISP2 ice-core record from Greenland, which indicates a coupling to large-scale fluctuations in atmospheric circulation patterns. A corresponding correlation with simultaneous depletions in 13 C suggests repeated responses of the local lake hydrology to snow-rich winters through decreasing water residence time, perhaps augmented by methanogenesis due to prolonged ice-cover seasons under the influence of an expanding Siberian High. Frequency analysis of the isotopic records reveals well-defined fluctuations at quasi-500-520-, 670-, 830-and 1430yr periodicities, and a gradually stronger impact of Polar air outbreaks across the southern Baltic Sea region with time after ca 6000 cal. BP.

Istanbul, as one of the four anchor megacities of Europe, has shown a rise of 0.94°C in average annual temperature over the long period of 1912–2016 under impacts of anthropogenic climate change. A notable increase in temperatures has started after the 1940s, which is in parallel with the beginning of industrialization era in Istanbul. This warming is associated with an extensive population growth and accompanied the decrease in vegetation cover. Increasing in minimum series of temperature is more evident than maximum values and the rising rate of temperature values has been more pronounced during recent decades. The first significant upward trend in precipitation series has periodically started in 1920s, while there has been a stable trend from 2001 till today. The daily average of rainfall amount increased with a mean value of 58 mm during the total study period. Rising rate of daily maximum precipitation has been more evident in the last 3 decades, which is shown by the increased...

The dominant mode of sea level pressure (SLP) variability during the winter months in the Northern Hemisphere (NH) is characterized by a dipole with one anomaly center covering the Arctic with the opposite sign anomaly stretched across the mid-latitudes. Associated with the SLP anomaly, is a surface temperature anomaly induced by the anomalous circulation. We will show that this anomaly pattern originates in the early fall, on a much more regional scale, in Siberia. As the season progresses this anomaly pattern propagates and amplifies to dominate much of the extratropical NH, making the Siberian high a dominant force in NH climate variability in winter. Also since the SLP and surface temperature anomalies originate in a region of maximum fall snow cover variability, we argue that snow cover partially forces the phase of winter variability and can potentially be used for the skillful prediction of winter climate. Introduction Over the past decade great strides have been made in unde...

Trends are very important in climate research and are ubiquitous in the climate system. Trends are usually estimated using simple linear regression. Given the complexity of the system, trends are expected to have various features such as global and local characters. It is therefore important to develop methods that permit a systematic decomposition of climate data into different trend patterns and remaining no-trend patterns. Empirical orthogonal functions and closely related methods, widely used in atmospheric science, are unable in general to capture trends because they are not devised for that purpose. The present paper presents a novel method capable of systematically capturing trend patterns from gridded data. The method is based on an eigenanalysis of the covariance/correlation matrix obtained using correlations between time positions of the sorted data, and trends are associated with the leading nondegenerate eigenvalues. Application to simple low-dimensional time series models and reanalyses data are presented and discussed. Copyright  2006 Royal Meteorological Society KEY WORDS empirical orthogonal functions; inverse-rank correlation; trend empirical orthogonal functions; trend patterns; North Atlantic Oscillation; Siberian high

The prediction skill for the East Asian winter monsoon (EAWM) has been analyzed, using the observations and different climate models that participate in the APEC Climate Center (APCC) multi-model ensemble (MME) seasonal forecast. The authors first examined the characteristics of the existing EAWM indices to find a suitable index for the APCC seasonal forecast system. This examination revealed that the selected index shows reasonable prediction skill of EAWM intensity and well-represents the characteristics of wintertime temperature anomalies associated with the EAWM, especially for the extreme cold winters. Although most models capture the main characteristics of the seasonal mean circulation over East Asia reasonably well, they still suffer from difficulty in predicting the interannual variability (IAV) of the EAWM. Fortunately, the POAMA has reasonable skill in capturing the timing and strength of the EAWM IAV and reproduces the EAWM-related circulation anomalies well. The better ...

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In many fields including agroclimatology, pedology, plant introduction, environmental health and agricultural transfer, detection of areas of similar climate is of significant interest. Numerical methods including cluster analysis, similarity measures, and other techniques were used to compare climatic data from Islandian meteorological stations to classify them according to similar homoclimate. Using Euclidean distance and City-block (Manhattan) distance, data from Iceland, Finland, Sweden, Norway, and Alaska state of the USA were analyzed to reveal homoclime. One of the conclusions from the study is that Iceland has a similar climate to Alaska and Norway. Climate change is already affecting agriculture, with effects unevenly distributed across the world. These changes will undoubtedly lead to a reconsideration of the question of allocation of appropriate agricultural crops to given areas and evaluation of bioclimatic resources in territories with similar climate. Results from this...

This study reveals a marked enhancement in the relationship between the variations in location of the winter East Asian Polar Front Jet (EAPJ) and the surface air temperature (SAT) in Eurasia since the mid-1990s. Before the mid-1990s, an evident wave train related to the meridional location of the EAPJ exhibited an anticyclonic anomaly over northern Europe and a cyclonic anomaly in northwestern Asia. With an equatorward shift of the EAPJ after the mid-1990s, the wave train experiences a notable adjustment that is conducive to East Asian cooling, displaying an anticyclonic anomaly around the Kara-Laptev Seas and a cyclonic anomaly near northeastern Asia. Arctic warming anomalies and sea ice loss contributed significantly to these decadal changes. Simulation experiments forced by observed Arctic sea-ice variability further confirm this result. Since the mid-1990s, Arctic sea ice loss (or Arctic warming anomaly) has contributed to a reduction in westerly winds in high latitudes by modu...

Oxygen (d 18 O) and carbon (d 13 C) isotope records of calcitic carbonate components (Chara sp. algal encrustations and Bithynia tentaculata gastropod opercula) from a lake-sediment succession on the Baltic Sea island of Gotland, southeastern Sweden, have been obtained to investigate regional climate dynamics during the Holocene. The hydrological sensitivity of the small lake, particularly in terms of spring snowmelt contribution to the local water budget, provides a means of tracing past changes in the influence of snow-bearing easterly winds across the Baltic Sea Proper, which signifies the wintertime strength of the Siberian High. Repeated episodic depletions in 18 O at the centennial scale correlate with events of increased potassium concentration in the GISP2 ice-core record from Greenland, which indicates a coupling to large-scale fluctuations in atmospheric circulation patterns. A corresponding correlation with simultaneous depletions in 13 C suggests repeated responses of the local lake hydrology to snow-rich winters through decreasing water residence time, perhaps augmented by methanogenesis due to prolonged ice-cover seasons under the influence of an expanding Siberian High. Frequency analysis of the isotopic records reveals well-defined fluctuations at quasi-500-520-, 670-, 830-and 1430yr periodicities, and a gradually stronger impact of Polar air outbreaks across the southern Baltic Sea region with time after ca 6000 cal. BP.

A Singular Value Decomposition (SVD) analysis was performed jointly on extreme temperature events in Argentina and sea surface temperature (SST) in the South Atlantic and South Pacific. Sea level pressure (SLP) patterns associated with the first SVD coupled mode were also analyzed. Winter is the season of the year that is best represented by the first mode, accounting for up to 70% of the winter covariance between temperature events and SST. The warm and cold events in Argentina are essentially a consequence of the creation of meridional atmospheric circulations over the continent. Such atmospheric patterns result from displacements and intensity changes of the subtropical anticyclones over the oceans and of the continental low-pressure center in northwestern Argentina. The temperature events in southern Argentina are also closely related to the warming and cooling of the coastal waters in the South Atlantic and South Pacific. The analysis suggests that in summer and winter, high (low) occurrence of warm events and low (high) occurrence of cold events are related to similar oceanic and atmospheric circulation situations. The temperature events in Argentina show higher correlation with the Atlantic than with the Pacific, which reflects the importance of the ''orographic barrier'' of the Andes Mountains in driving the atmospheric circulation. The only exception to this rule concerns the warm events in spring, for which the warming of the equatorial Pacific (the ENSO pattern) appears as the dominant mode. The temporal patterns of the temperature events in Argentina exhibit significant interannual variability in fall, winter, and spring, with periods of 3 to 5 years. The summer patterns suggest a very low-frequency variation with a period longer than 20 years.

Fifteen temperature indices recommended by the ETCCDI (Expert Team on Climate Change Detection and Indices) were applied to evaluate spatiotemporal variability and trends in annual intensity, frequency, and duration of extreme temperature statistics in Finland during 1961–2011. Statistically significant relationships between these high-resolution (10 km) temperature indices and seven influential Northern Hemisphere teleconnection patterns (NHTPs) for the interannual climate variability were also identified. During the study period (1961–2011), warming trends in extreme temperatures were generally manifested by statistically significant increases in cold temperature extremes rather than in the warm temperature extremes. As expected, warm days and nights became more frequent, while fewer cold days and nights occurred. The frequency of frost and icing days also decreased. Finland experienced more (less) frequent warm (cold) temperature extremes over the past few decades. Significant le...

Fifteen temperature indices recommended by the ETCCDI (Expert Team on Climate Change Detection and Indices) were applied to evaluate spatiotemporal variability and trends in annual intensity, frequency, and duration of extreme temperature statistics in Finland during 1961–2011. Statistically significant relationships between these high-resolution (10 km) temperature indices and seven influential Northern Hemisphere teleconnection patterns (NHTPs) for the interannual climate variability were also identified. During the study period (1961–2011), warming trends in extreme temperatures were generally manifested by statistically significant increases in cold temperature extremes rather than in the warm temperature extremes. As expected, warm days and nights became more frequent, while fewer cold days and nights occurred. The frequency of frost and icing days also decreased. Finland experienced more (less) frequent warm (cold) temperature extremes over the past few decades. Interestingly,...

In Part I of this study, the impact of Ural blocking (UB) on the warm Arctic–cold Eurasian (WACE) pattern associated with the winter (DJF) arctic sea ice loss during 1979–2013 is examined by dividing the arctic sea ice reduction region into two dominant subregions: the Barents and Kara Seas (BKS) and the North American high-latitude (NAH) region (Baffin and Hudson Bay, Davis Strait, and Labrador Sea). It is found that atmospheric response to arctic sea ice loss resembles a negative Arctic response oscillation with a dominant positive height anomaly over the Eurasian subarctic region. Regression analyses of the two subregions further show that the sea ice loss over the BKS corresponds to the UB pattern together with a positive North Atlantic Oscillation (NAO+) and is followed by a WACE anomaly, while the sea ice reduction in the NAH region corresponds to a negative NAO (NAO−) pattern with a cold anomaly over northern Eurasia. Further analyses reveal that the UB pattern is more persis...

Expansion of agricultural practices from the Fertile Crescent to China during the mid and late Holocene are believed to have shaped the early network of Silk Road routes and possibly regulated the dynamics of trade and exchange in the urban oases along the Silk Road throughout its existence. While the impacts of climate change on the Silk Road are more or less documented for the medieval period, they remain poorly understood for early history of the Silk Road, especially in Central Asia. We analyze hydroclimatic proxies derived from fluvial stratigraphy, geochronology, and tree-ring records that acted on various time scales in the Lake Balkhash Basin to learn how changes in water supply could have influenced the early farmers in the Semirechye region of southern Kazakhstan. Our approach aims to identify short-term and long-term variability of regional runoff and to compare the hydrological data with cultural dynamics coupled with the archaeological settlement pattern and agricultural production. The reconstructed runoff variability underscore the contribution of winter precipitation driven by the interaction between the Arctic oscillation and the Siberian High-Pressure System, to Central Asian river discharge. We show that Saka people of the Iron Age employed extensive ravine agriculture on the alluvial fans of the Tian Shan piedmont, where floodwater farming peaked between 400 BC and 200 BC. The early Silk Road farmers on the alluvial fans favored periods of reduced flood flows, river stability and glacier retreat in the Tian

The relationship between the ENSO condition and the winter condition in Hong Kong is investigated in this study. The winter monsoon over southern China tends to be weaker (stronger) during El Niño (La Niña) winters and Hong Kong tends to have higher (lower) mean winter temperatures against the background of the warming trend. On the other hand, there are more (fewer) surge events, which represents the southeastward advance of the Siberian cold air across the East Asian coast, affecting Hong Kong. Analyses showed that Hong Kong tends to be warmer with a shorter duration for the longest cold spell during the winter without blocking event over the Eurasian continent. Furthermore, blocking events are also less common during El Niño winters.

Blocking variability over the Ural Mountain region in the boreal winter and its relationship with the East Asian winter climate is investigated. The climate shift around mid 1970s has been shown to exert a significant influence on the blocking pattern. In contrast with the years before 1976/1977, the Ural blocking signal after 1976/1977 is found to propagate less into the stratosphere and more eastward in the troposphere to East Asia, which therefore exerts more influence on the East Asian winter climate. This enhanced Ural blocking-East Asian climate relationship amplifies the impact of Ural blocking on East Asia and, with the background of decreasing Ural blocking, contributes to the higher frequency of warm winters in this region. Further analyses suggest that the NAM-related stratospheric polar vortex strength and its modulation on the propagation of atmospheric stationary waves can account for this change, with the key area being located in the North Atlantic region.

Trends are very important in climate research and are ubiquitous in the climate system. Trends are usually estimated using simple linear regression. Given the complexity of the system, trends are expected to have various features such as global and local characters. It is therefore important to develop methods that permit a systematic decomposition of climate data into different trend patterns and remaining no-trend patterns. Empirical orthogonal functions and closely related methods, widely used in atmospheric science, are unable in general to capture trends because they are not devised for that purpose. The present paper presents a novel method capable of systematically capturing trend patterns from gridded data. The method is based on an eigenanalysis of the covariance/correlation matrix obtained using correlations between time positions of the sorted data, and trends are associated with the leading nondegenerate eigenvalues. Application to simple low-dimensional time series models and reanalyses data are presented and discussed. Copyright  2006 Royal Meteorological Society KEY WORDS empirical orthogonal functions; inverse-rank correlation; trend empirical orthogonal functions; trend patterns; North Atlantic Oscillation; Siberian high

, the air temperature in the arid region of northwest China had a significant rising trend (P < 0.001), at a rate of 0.343 C/decade, higher than the average of China (0.25 C/decade) and that of the entire globe (0.13 C/decade) for the same period. Based on the analysis of the data from 74 meteorological stations in the region for 1960-2010, we found that among the four seasons the temperature change of winter has been playing the most important role in the yearly change in this region. We also found that the winter temperature in this region has a strong association with the Siberian High (correlation coefficient: R = À0.715) and the greenhouse gas emission (R = 0.51), and between the two the former is stronger. We thus suggest that the weakening of the Siberian High during the 1980s to 1990s on top of the steady increasing of the greenhouse emission is the main reason for the higher rate of the temperature rise in the arid region of the northwest China.

An area-weighted k-means clustering method based on pattern correlations is proposed and used to explore the relationship between the Siberian High (SH) and Arctic Oscillation (AO) during the winter months (December-January-February) of 1948–2014. Five regimes are identified. Four of these five regimes (comprising 171 of 201 months) show a negative correlation between the SH and AO indices, while the last regime (30 months) shows a positive correlation. The location of the SH shifts southward into China under two of the four negative correlation regimes (117 months), with pressure variations over the center of activity for the SH opposite to pressure variations over the climatological center of the SH (which is used to define the SH index). Adjusting the SH index to account for these spatial shifts suggests positive rather than negative correlations between major variations in the SH and AO under these regimes. Under one of the two remaining negative-correlation regimes, pressure anomalies are weak over the Arctic Ocean. In total, only one regime comprising 21 of 201 months strictly obeys the negative correlation between the SH and AO reported by previous studies. The climate regime characterized by an intensified SH is associated with a greater frequency of cold surges over northern and southeastern China, and the weakening of the East Asian winter monsoon during the 1980s was accompanied by a sharp reduction in the occurrence of this regime.

The present study investigates the overall changes in
occurrences of winter cold surges over Southeast China for the
period 1961-2012, using instrumental observations, reanalysis and
model simulation datasets. Based on objectively defined criteria,
cold surges were classified into 3 types according to their dynamical
origin as inferred from daily evolution patterns of surface pressure
systems with a focus on the Siberian High (SH): type A with an
amplification of a quasi-stationary SH associated with high-pressure
anomalies over the Ural mountains, type B with a developing SH
associated with fast traveling upper-level waves, and type C with a
high-pressure originated in the Arctic. Examination of the long-term
change in cold surge occurrences shows different interdecadal
variations among the 3 types. During 1961-2012, type A events
(37.8%) decreased, while type B events, accounting for the majority
(52.5%) of total winter cold surges, increased slightly. The contribution
by type C to the total occurrence of the cold surges was
small (8.8%) compared to that of A and B, but it became more
frequent in the latest decade, related to the tendency of the Arctic
Oscillation (AO) being more in its negative phase. Overall, we found
slightly increased occurrences of cold surges over Southeast China
since the early 1980s, despite the weakened SH intensity and warmer
mean temperature compared to previous decades. The climate model
projections of the phase 5 of the Coupled Model Intercomparison
Project (CMIP5) suggests similar trend in the late 21st century under
warmer climate.