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In this study, the variations of annual land surface air temperature (SAT) over Eurasia and the northern part of Africa (0 degrees-180 degrees E, 0 degrees-90 degrees N) were investigated using monthly SAT data from the Climatic Research Unit, University of East Anglia for 1901-2014 and the simulations from the Geophysical Fluid Dynamics Laboratory coupled model. The observed results suggested that the SAT variations exhibited robust non-uniform spatial features at multi-time scales. For the variations in inter-annual to decadal time scales (IDV), the intensity generally increased from south to north, with the strongest intensity being around Siberia and four times that of the weakest intensity found around China. The IDV leading pattern showed a north-south dipole across 40 degrees N. The simulated results suggested that the north-south dipole and the northwards increase of the IDV were due to internal interactions within the complex nonlinear climate system, but the natural and greenhouse gas forcings could intensify the IDV. The warming trend of the SAT was generally homogeneous, but it showed distinctive multi-decadal fluctuations in different regions. The linear secular trends and robust multi-decadal variation around Siberia and China corresponded to the considerable acceleration and deceleration in the warming over the two regions, respectively. The warming around Siberia was mainly caused by greenhouse gases but its modulation due to natural forcing was also considerable because of the robust multi-decadal variations. Around China, the multi-decadal variation, contributed by the natural forcing, can explain more than half the variances in the warming. The warming trend around central Asia was intense and parabolic, and the multi-decadal variation over there was weak and showed few modulating effects.

In this study, the year-to-year variability of surface air temperature (SAT) over China in winter was investigated during 1961–2014. The results indicate that the year-to-year SAT variability can explain more than 30% of the SAT variance over most parts of China, with up to 60% variance over southern China, northeastern China and northwestern China. The leading pattern of year-to-year SAT exhibits homogeneous variability over most parts of China, except in small areas over the Tibetan Plateau and southwestern China. The circulation over the northern Pacific is a key factor of this homogeneous variability pattern. An anomalous anticyclonic circulation and weakening midlatitude westerly jet in the middle and high troposphere over the northern Pacific are associated with the homogeneous warmth over China. The second pattern shows a south–north dipole, with variability in northeastern China opposite to that south of 25°N in China and over the Tibetan Plateau. The south–north dipole pattern is part of a global year-to-year SAT anomaly pattern because it exhibits a significant relationship with the year-to-year SAT over large parts north of 50°N over the Eurasian landmass. The north-cold/south-warm pattern is accompanied by a significant weakening of the Arctic Oscillation. In comparison, the atmospheric circulation anomalies associated with the homogeneous variability pattern are much weaker than those with the south–north dipole pattern. The anomalous Indian Ocean dipole in the previous autumn and the snow cover around China in November are the two key causes of the homogeneous variability pattern. Many factors, such as the tropical central Pacific sea surface temperature (SST), stratospheric quasi-biennial oscillation (QBO), Okhotsk sea ice and western Siberia snow cover, can significantly influence the south–north dipole pattern. Compared to the tropical Pacific SST, the impact of the Indian Ocean SST on the winter SAT over China is much more important.

The relationship between cross-equatorial flow (CEF) during winter and spring and the South China Sea summer monsoon (SCSSM) onset is investigated by data diagnoses for the period of 1979–2013 and numerical experiments. The SCSSM onset is found to have a significant negative correlation with the CEF nearby the Philippines in preceding January, February and March prior to SCSSM onset. A strong CEF during January, February and March tends to be succeeded by an early onset of SCSSM, whereas a weak CEF is likely to be followed by a late onset. The CEF in preceding months links with the SCSSM onset through the subtropical high over South China Sea and western North Pacific in April. The subtropical high in April is weak and eastward shifted (strong and westward shifted) when the CEF in preceding months is strong (weak). The weak and eastward shifted (strong and westward shifted) subtropical high favours (does not favour) the convection developing (depressing) over South China Sea, resulting in an early (late) onset of SCSSM. The anomalies of CEF nearby the Philippines in preceding months and its close relationship with subsequent subtropical high are caused by the sea surface temperature anomalies (SSTA) and atmospheric heating source over tropical western Pacific. The difference of SSTA between south and north of equator in tropical western Pacific and the corresponding atmospheric diabatic heating result in the anomalies of CEF in January, February and March, and impact the activity of subtropical high in April. The positive SSTA in tropical western Pacific, combining with the wet and warm climatic background over northern South China Sea and coastal areas of Southern China in April are favourable for a cyclonic circulation anomaly occurring over northern South China Sea. As a result, the subtropical high is weak and eastward shifted, and the SCSSM onset is early.

Using observational data for 1979–2010, the temporal and spatial variations of wintertime (December–February) snow water equivalent (SWE) over China and their relations to the November SWE, wintertime snowfall, snow evaporation, sublimation and melting are investigated. The results revealed that the SWE is principally distributed in four snow regions of northwestern (NW) China, northeastern (NE) China, the Tibetan Plateau (TP) and the Yangtze–Huaihe River valley (YH). It is found that the impact of the November SWE is confined to the north of 42°N, while the impact of snowfall are relevant over all China, and the impacts of snow evaporation and sublimation are limited to NW, NE and the TP. The effect of snow melting is large in the YH but weak in other regions. On the inter-annual timescale, the snow mass balance shows different features in different snow regions. The wintertime SWE is in line with snowfall. The November SWE has a major effect on the wintertime SWE in NW and NE but not in the TP and YH. The effect of meteorological factors on snow evaporation, sublimation and melting differs in different snow regions. Evaporation is mainly affected by vapour pressure deficit in NW and wind speeds in NE and the TP. Sublimation is controlled by air temperature in NW, wind speeds in NE, vapour pressure deficit in YH and air temperature, pressure and vapour pressure deficit in the TP. Melting is closely related with air temperature in the TP and net radiation in the YH.

This study examined the relationship between the western North Pacific monsoon (WNPM) and the tropical cyclone (TC) activity over western North Pacific during the summer (June to August) in a period from 1977 to 2013. According to the western North Pacific monsoon index (WNPMI), 10 years with high indices (referred to as the positive WNPMI phase) and 10 years with low indices (referred to as the negative WNPMI phase) were chosen. TCs frequently formed in the southeast quadrant of the subtropical western North Pacific in the positive WNPMI phase, and in the northwest quadrant in the negative phase. With respect to the TC track, TCs tended to move northward from the distant sea off the east coast of the Philippines towards Korea and Japan past the East China Sea in the positive WNPMI phase, whereas the characteristic pattern of the negative phase was the TC movement from the Philippines to southern China and the Indochinese peninsula over the South China Sea. As for the TC intensity, the TCs were stronger in the positive WNPMI phase than in the negative WNPMI phase. The anomalous cyclonic circulations in the south of the 30°N signified strong convection, causing the high TC genesis frequency in the positive WNPMI phase. In addition, the East China Sea, Korea and Japan were shown to be influenced by the anomalous southeasterly, which contributed as the anomalous steering flows and was favourable for the TCs to move into these regions in the positive WNPMI phase. Meanwhile, the positive anomaly of 600 hPa relative humidity and sea surface temperature as well as the negative anomaly of vertical wind shear presented in most regions of the subtropical western North Pacific, creating an environment that facilitated the generation of TCs in the positive WNPMI phase.

The interannual variation of the wintertime fog–haze days across central and eastern China from 1972 to 2014 and its relationship with East Asian winter monsoon (EAWM) are investigated based on the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and the surface observation data from the weather stations in China. The results show that the wintertime fog–haze days across central and eastern China have close relation with EAWM in the interannual time scale. The stronger (weaker) the EAWM is, the less (more) the wintertime fog–haze days are. In strong (weak) EAWM winters, both near-surface winds and vertical shear of horizontal zonal winds strengthen (weaken). The strengthened (weakened) near-surface winds enhance (reduce) the outward transport of fog and haze and are unfavourable (favourable) for their accumulation over central and eastern China. The enlarged (receded) vertical shear of horizontal zonal winds intensifies (abates) the atmospheric baroclinic instability and vertical diffusion, leading to less (more) fog and haze in near-surface. In addition, a strong (weak) EAWM is also unfavourable (favourable) for the maintenance of the fog and haze in the lower troposphere through the anomalous divergence (convergence) associated with the intense anticyclonic (cyclonic) anomalies in the upper troposphere over southern China.

The characteristics of extreme cold and warm events (ECE; EWE) over the whole China in December, January and February are investigated using the observed daily surface air temperature for 1961–2012. Among the 3 months, both the EWE and ECE in February are most frequent and strongest and least frequent in December and weakest in January. More than 50% of the EWE and ECE in February and less than 40% of the EWE and ECE in January exhibit persistent feature (lasting at least 5 days). Generally, the persistent ECE are more frequent than the persistent EWE. The EWE (ECE) in February exhibit intensive increasing (decreasing) tendency and show more (less) persistent feature in 1961–1986 than that in 1987–2012. The persistent feature of the EWE (ECE) in December and January is more (less) obvious in 1961–1986 than that in 1987–2012 although the EWE (ECE) in 1961–1986 is less (more) frequent than that in 1987–2012. The significant weakening (strengthening) Siberia high and East Asia trough are the two main key factors for the EWE (ECE) in January and February and they can be found up to 5 days before the occurrence of the EWE (ECE). The ECE (EWE) in December are associated with the three-wave structure anomalies in troposphere, but these anomalies cannot be found before the occurrence of the ECE (EWE). The warm North Atlantic and tropical central-eastern Pacific in previous autumn (SON, September–October–November) trigger significant weakening of Siberia high and East Asia trough in February and thereby cause the occurrence of the EWE. On decadal time scale, the increasing EWE in February seem to be the consequence of the warming North Atlantic. The cold SON Indian Ocean corresponds to significant atmospheric circulation anomalies in December similar to those associated with the ECE in December, indicating its importance in the ECE in December.

The relationship between decadal variability in springtime (March–May) snow water equivalent (SWE) over Eurasia and springtime rainfall over China is investigated for 1979–2004 using satellite-observed SWE, rainfall observations from 595 stations, and NCEP/NCAR reanalysis data. Decreasing springtime SWE in Eurasia corresponded to reduced springtime rainfall over southeastern and northeast China, and more rainfall over southwestern and northwestern China. This relationship was supported by the feedback effect of snow in high-latitude areas to changes in background atmospheric circulation. A decadal shift in springtime Eurasian SWE occurred in the late 1980s, marked by a change from persistent positive phases in 1979–1987 to frequent negative phases. The reduction in Eurasian SWE resulted in reduced upward surface heat flux to the atmosphere and, thereby, higher boundary layer height due to increased downward heat flux into subsurface soil. These changes resulted in reduced upward and poleward wave flux activity, which corresponded to anomalous negative heights/pressures in the Arctic and anomalous positive heights/pressures in mid-latitude regions from the upper-level troposphere to the surface. There was an anomalous anti-cyclonic circulation over Siberia and the western Pacific subtropical high was weakened, accompanied by an anomalous northerly in eastern China and westerly in northwestern China. The anomalous northerly resulted in reduced water vapour convergence in southeastern and northeast China, and reduced water vapour export for southwestern and northwestern China. Thus, negative rainfall anomalies developed over southeastern and northeast China, and positive rainfall anomalies appeared over southwestern and northwestern China. Copyright © 2011 Royal Meteorological Society