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... more
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.
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... more
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... more
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...
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... more
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...
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... more
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... more
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...
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... more
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 ...
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... more
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...
Strong cold surge events (CSEs) are some of the most distinct winter weather events in East Asia, impacting natural ecosystems and over 100 million individuals. The impact of such extreme CSEs as driven by synoptic systems is direct and... more
Strong cold surge events (CSEs) are some of the most distinct winter weather events in East Asia, impacting natural ecosystems and over 100 million individuals. The impact of such extreme CSEs as driven by synoptic systems is direct and immediate. Changes in large-scale synoptic patterns as potentially affected by changes in the Arctic are further expected to influence CSE occurrences in East Asia. Defying a straightforward analysis, semi-permanent atmospheric systems such as the Siberian High (SH), influencing large-scale synoptic patterns, make the atmospheric circulation highly variable and assessment of CSE onset difficult. Rather varied region-specific metrics are currently adopted for predicting CSE occurrence locally but the fundamental understanding of the onset of CSEs continues to be a major challenge. Based on an analysis of monthly synoptic patterns for three unusual CSEs in East Asia and further extended for eight strong to extreme CSEs, we propose a new coupling framew...
As global warming gets worse, the extreme heat exposure time is expected to increase. Considering that the heatwave damages increased by the accumulation of heat stress, it is important to understand the heatwave onset and number of... more
As global warming gets worse, the extreme heat exposure time is expected to increase. Considering that the heatwave damages increased by the accumulation of heat stress, it is important to understand the heatwave onset and number of heatwave days (HWDs). Here, we show that the end of East Asian summer monsoon activity (i.e., Changma retreat date, CRD) could be an indicator in determining the onset of the heatwave, and the barotropic structure induced by the circumglobal and Pacific–Japan teleconnections is a key factor in lengthening the number of HWDs in Korea. The onset of the heatwave is delayed when CRD belated than the climatology late over Korea due to sufficient moisture transportation between the edge of western North Pacific subtropical high and cold polar air mass in July. The number of HWDs from July through August over Korea shows a positive linear relationship with the synoptic stagnation index because the upper-layer anticyclone associated with stagnation is formed aro...
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... more
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... more
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... more
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...
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... more
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... more
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.
