Dominant Modes of Subseasonal Variability of East Asian Summertime Surface Air Temperature and Their Predictions

Subseasonal variability of surface air temperature (SAT) over East Asia is analyzed using the NCEP–NCAR reanalysis of 34 Northern Hemisphere extended summers. An empirical orthogonal function (EOF) analysis is performed with pentad SAT data to identify the leading modes of subseasonal SAT variability. The first (EOF1) and second (EOF2) modes, which together account for about 35% of the total variance, correspond to a monopole structure of SAT anomaly in the whole East Asian region and a dipole structure with opposite signs of variability over the north and south East Asian continent, respectively. Lead–lag regressions are calculated in order to analyze how the large-scale atmospheric circulation evolves in association with the development of the leading SAT modes. An eastward propagation of the Rossby wave from the midlatitude Atlantic Ocean is observed about three pentads before EOF1. EOF2 is influenced by both the tropical Madden–Julian oscillation (MJO) and a midlatitude wave train. These results indicate that there is potential for prediction of the dominant SAT modes on the subseasonal time scale. The subseasonal prediction of the two dominant modes is further evaluated in the operational monthly forecasting system of Environment and Climate Change Canada (ECCC). The model shows a better forecast skill than the persistence forecast. The strength of the subseasonal signal in initial conditions impacts the forecast skill. The forecasts starting with strong EOF in the initial condition are more skillful than those initialized with weak EOF. The findings in the study contribute to improving the understanding of the subseasonal variability and SAT subseasonal forecasting in East Asia.

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Contributors to linkage between Arctic warming and East Asian winter climate

Climate Dynamics ◽

10.1007/s00382-021-05820-x ◽

2021 ◽

Author(s):

Xinping Xu ◽

Shengping He ◽

Yongqi Gao ◽

Botao Zhou ◽

Huijun Wang

Keyword(s):

Sea Ice ◽

General Circulation ◽

Initial Conditions ◽

Wave Train ◽

East Asian ◽

Surface Air Temperature ◽

General Circulation Models ◽

The Arctic ◽

Winter Climate ◽

Arctic Warming

AbstractPrevious modelling and observational studies have shown discrepancies in the interannual relationship of winter surface air temperature (SAT) between Arctic and East Asia, stimulating the debate about whether Arctic change can influence midlatitude climate. This study uses two sets of coordinated experiments (EXP1 and EXP2) from six different atmospheric general circulation models. Both EXP1 and EXP2 consist of 130 ensemble members, each of which in EXP1 (EXP2) was forced by the same observed daily varying sea ice and daily varying (daily climatological) sea surface temperature (SST) for 1982–2014 but with different atmospheric initial conditions. Large spread exists among ensemble members in simulating the Arctic–East Asian SAT relationship. Only a fraction of ensemble members can reproduce the observed deep Arctic warming–cold continent pattern which extends from surface to upper troposphere, implying the important role of atmospheric internal variability. The mechanisms of deep Arctic warming and shallow Arctic warming are further distinguished. Arctic warming aloft is caused primarily by poleward moisture transport, which in conjunction with the surface warming coupled with sea ice melting constitutes the surface-amplified deep Arctic warming throughout the troposphere. These processes associated with the deep Arctic warming may be related to the forcing of remote SST when there is favorable atmospheric circulation such as Rossby wave train propagating from the North Atlantic into the Arctic.

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Influence of ENSO on North American subseasonal surface air temperature variability

Weather and Climate Dynamics ◽

10.5194/wcd-2-395-2021 ◽

2021 ◽

Vol 2 (2) ◽

pp. 395-412

Author(s):

Patrick Martineau ◽

Hisashi Nakamura ◽

Yu Kosaka

Keyword(s):

North America ◽

Air Temperature ◽

North American ◽

Surface Air Temperature ◽

Tropical Pacific ◽

La Niña ◽

Western North America ◽

The North ◽

Subseasonal Variability ◽

La Nina

Abstract. The wintertime influence of tropical Pacific sea surface temperature (SST) variability on subseasonal variability is revisited by identifying the dominant mode of covariability between 10–60 d band-pass-filtered surface air temperature (SAT) variability over the North American continent and winter-mean SST over the tropical Pacific. We find that the El Niño–Southern Oscillation (ENSO) explains a dominant fraction of the year-to-year changes in subseasonal SAT variability that are covarying with SST and thus likely more predictable. In agreement with previous studies, we find a tendency for La Niña conditions to enhance the subseasonal SAT variability over western North America. This modulation of subseasonal variability is achieved through interactions between subseasonal eddies and La Niña-related changes in the winter-mean circulation. Specifically, eastward-propagating quasi-stationary eddies over the North Pacific are more efficient in extracting energy from the mean flow through the baroclinic conversion during La Niña. Structural changes of these eddies are crucial to enhance the efficiency of the energy conversion via amplified downgradient heat fluxes that energize subseasonal eddy thermal anomalies. The enhanced likelihood of cold extremes over western North America is associated with both an increased subseasonal SAT variability and the cold winter-mean response to La Niña.

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North Hemispheric winter air temperature variability and its linkage to North Pacific and North Atlantic SST modes?

10.5194/egusphere-egu2020-16 ◽

2020 ◽

Author(s):

Binhe Luo ◽

Dehai Luo ◽

Aiguo Dai ◽

Lixin Wu

Keyword(s):

North America ◽

Air Temperature ◽

North Atlantic ◽

North Pacific ◽

Wave Train ◽

Surface Air Temperature ◽

Eastern North America ◽

The North ◽

The North Atlantic ◽

The North Pacific

Winter surface air temperature (SAT) over North America exhibits pronounced variability on sub-seasonal-to-interdecadal timescales, but its causes are not fully understood. Here observational and reanalysis data from 1950-2017 are analyzed to investigate these causes. Detrended daily SAT data reveals a known warm-west/cold-east (WWCE) dipole over midlatitude North America and a cold-north/warm-south (CNWS) dipole over eastern North America. It is found that while the North Pacific blocking (PB) is important for the WWCE and CNWS dipoles, they also depend on the phase of the North Atlantic Oscillation (NAO). When a negative-phase NAO (NAO-) concurs with PB, the WWCE dipole is enhanced (compared with the PB alone case) and it also leads to a warm north/cold south dipole anomaly in eastern North America; but when PB occurs with a positive-phase NAO (NAO+), the WWCE dipole weakens and the CNWS dipole is enhanced. In particular, the WWCE dipole is favored by a combination of eastward-displaced PB and NAO- that form a negative Arctic Oscillation. Furthermore, a WWCE dipole can form over midlatitude North America when PB occurs together with southward-displaced NAO+.The PB events concurring with NAO- (NAO+) and SAT WWCE (CNWS) dipole are favored by the El Nio-like (La Nia-like) SST mode, though related to the North Atlantic warm-cold-warm (cold-warm-cold) SST tripole pattern. It is also found that the North Pacific mode tends to enhance the WWCE SAT dipole through increasing PB-NAO- events and producing the WWCE SAT dipole component related to the PB-NAO+ events because the PB and NAO+ form a more zonal wave train in this case.

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Quantifying the contribution of anthropogenic influence to the East Asian winter monsoon in 1960–2012

10.5194/acp-2019-99 ◽

2019 ◽

Author(s):

Xin Hao ◽

Shengping He ◽

Huijun Wang ◽

Tingting Han

Keyword(s):

East Asia ◽

Air Temperature ◽

General Circulation ◽

East Asian Winter Monsoon ◽

East Asian ◽

Surface Air Temperature ◽

Winter Monsoon ◽

Anthropogenic Influence ◽

Anthropogenic Forcing ◽

Asian Winter Monsoon

Abstract. The East Asian winter monsoon (EAWM) can be greatly influenced by many factors that can be classified as anthropogenic forcing and natural forcing. Here we explore the contribution of anthropogenic influence to the change in the EAWM over the past decades. Under all forcings observed during 1960–2013 (All-Hist run), the atmospheric general circulation model is able to reproduce the climatology and variability of the EAWM-related surface air temperature and 500 hPa geopotential height, and shows a statistically significant decreasing EAWM intensity with a trend coefficient of ∼−0.04 yr−1 which is close to the observed trend. By contrast, the simulation, which is driven by the same forcing as All-Hist run but with the anthropogenic contribution to them removed, shows no decreasing trend in the EAWM intensity. By comparing the simulations under two different forcing scenarios, we further reveal that the responses of the EAWM to the anthropogenic forcing include a rise of 0.6 ° in surface air temperature over the East Asia as well as weakening of the East Asia trough, which may result from the poleward expansion and intensification of the East Asian jet forced by the change of temperature gradient in the troposphere. Additionally, compared with the simulation without anthropogenic forcing, the frequency of strong (weak) EAWM occurrence is reduced (increased) by 45 % (from 0 to 10/7). These results indicate that the weakening of the EAWM during 1960–2013 may be mainly attributed to the anthropogenic influence.

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The AMV phase-dependence of the connection between February NAO and March surface air temperature over the Tibetan Plateau

10.5194/egusphere-egu21-9879 ◽

2021 ◽

Author(s):

Jingyi Li ◽

Fei Li ◽

Shengping He ◽

Huijun Wang ◽

Yvan J Orsolini

Keyword(s):

Tibetan Plateau ◽

Air Temperature ◽

Rossby Wave ◽

North Atlantic ◽

Wave Train ◽

Surface Air Temperature ◽

The Tibetan Plateau ◽

The North ◽

Rossby Wave Train ◽

The North Atlantic

The Tibetan Plateau (TP), referred to as the &#8220;Asian water tower&#8221;, contains one of the largest land ice masses on Earth. The local glacier shrinkage and frozen-water storage are strongly affected by variations in surface air temperature over the TP (TPSAT), especially in springtime. This study reveals a distinct out-of-phase connection between the February North Atlantic Oscillation (NAO) and March TPSAT, which is non-stationary and regulated by the warm phase of the Atlantic Multidecadal Variability (AMV+). The results show that during the AMV+, the negative phase of the NAO persists from February to March, and is accompanied by a quasi-stationary Rossby wave train trapped along a northward-shifted subtropical westerly jet stream across Eurasia, inducing an anomalous adiabatic descent that warms the TP. However, during the cold phase of the AMV, the negative NAO does not persist into March. The Rossby wave train propagates along the well-separated polar and subtropical westerly jets, and the NAO&#8722;TPSAT connection is broken. Further investigation suggests that the enhanced synoptic eddy and low-frequency flow (SELF) interaction over the North Atlantic in February and March during the AMV+, caused by the enhanced and southward-shifted storm track, help maintain the NAO anomaly pattern via positive eddy feedback. This study provides a new detailed perspective on the decadal variability of the North Atlantic&#8722;TP connections in late winter&#8722;early spring.

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Asian Jet Waveguide and a Downstream Extension of the North Atlantic Oscillation

Journal of Climate ◽

10.1175/jcli-3228.1 ◽

2004 ◽

Vol 17 (24) ◽

pp. 4674-4691 ◽

Cited By ~ 172

Author(s):

Masahiro Watanabe

Keyword(s):

East Asia ◽

North Atlantic Oscillation ◽

North Atlantic ◽

Wave Train ◽

East Asian ◽

The North ◽

The North Atlantic ◽

The Mediterranean ◽

The North Atlantic Oscillation ◽

Asian Jet Waveguide

Abstract Anomalous atmospheric fields associated with the North Atlantic Oscillation (NAO) are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the NAO is a regional phenomenon. Analyses on the interannual time scale reveal that the NAO signal is relatively confined to the Euro–Atlantic sector in December while it extends toward East Asia and the North Pacific in February. The difference is most clearly seen in the meridional wind anomaly, which shows a wave train along the Asian jet, collocated with an anomalous vorticity source near the jet entrance. Diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi-stationary Rossby waves trapped on the Asian jet waveguide, and effectively excited by the anomalous upper-level convergence over the Mediterranean Sea. It is found that, when the NAO accompanies the Mediterranean convergence (MC) anomaly, most frequently seen in February, the NAO indeed has a much wider horizontal structure than the classical picture, rather similar to the Arctic Oscillation. In such cases interannual variability of the NAO is tied to the East Asian climate variability such that the positive NAO tends to bring a surface warming over East Asia. Similar results are obtained from an analysis of individual NAO events based on low-pass-filtered daily fields, which additionally identified that the downstream extension occurs at the decay stage of the NAO event and the MC anomaly appears to be induced by the Ekman pumping associated with the NAO. The signal of the MC anomaly can be detected even at 5 days before the peak of the NAO, suggesting that the NAO influence to East Asia is predictable to some extent; therefore, monitoring the developing NAO event is useful to the medium-range weather forecast in East Asian countries.

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Influence of the NAO on Wintertime Surface Air Temperature over East Asia: Multidecadal Variability and Decadal Prediction

Advances in Atmospheric Sciences ◽

10.1007/s00376-021-1075-1 ◽

2021 ◽

Author(s):

Jianping Li ◽

Tiejun Xie ◽

Xinxin Tang ◽

Hao Wang ◽

Cheng Sun ◽

...

Keyword(s):

East Asia ◽

Air Temperature ◽

East Asian ◽

Surface Air Temperature ◽

Atlantic Multidecadal Oscillation ◽

Warming Trend ◽

Decadal Prediction ◽

Delayed Effect ◽

Multidecadal Variability ◽

Cold Events

AbstractIn this paper, we investigate the influence of the winter NAO on the multidecadal variability of winter East Asian surface air temperature (EASAT) and EASAT decadal prediction. The observational analysis shows that the winter EASAT and East Asian minimum SAT (EAmSAT) display strong in-phase fluctuations and a significant 60–80-year multidecadal variability, apart from a long-term warming trend. The winter EASAT experienced a decreasing trend in the last two decades, which is consistent with the occurrence of extremely cold events in East Asia winters in recent years. The winter NAO leads the detrended winter EASAT by 12–18 years with the greatest significant positive correlation at the lead time of 15 years. Further analysis shows that ENSO may affect winter EASAT interannual variability, but does not affect the robust lead relationship between the winter NAO and EASAT. We present the coupled oceanic-atmospheric bridge (COAB) mechanism of the NAO influences on winter EASAT multidecadal variability through its accumulated delayed effect of ∼15 years on the Atlantic Multidecadal Oscillation (AMO) and Africa-Asia multidecadal teleconnection (AAMT) pattern. An NAO-based linear model for predicting winter decadal EASAT is constructed on the principle of the COAB mechanism, with good hindcast performance. The winter EASAT for 2020–34 is predicted to keep on fluctuating downward until ∼2025, implying a high probability of occurrence of extremely cold events in coming winters in East Asia, followed by a sudden turn towards sharp warming. The predicted 2020/21 winter EASAT is almost the same as the 2019/20 winter.

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Enhanced Relationship between Central Tropical Pacific Sea Surface Temperature and Eurasian Surface Air Temperature during Boreal Summers

Journal of Climate ◽

10.1175/jcli-d-19-0028.1 ◽

2021 ◽

pp. 1-68

Author(s):

Jing Ming ◽

Jianqi Sun

Keyword(s):

Air Temperature ◽

North Pacific ◽

Wave Train ◽

Surface Air Temperature ◽

Tropical Pacific ◽

Sea Surface ◽

The North ◽

The Relationship ◽

The North Pacific ◽

Mean State

AbstractThis study investigates the relationship between the central tropical Pacific (CTP) sea surface temperature (SST) and the surface air temperature (SAT) variability un-related to canonical El Niño-Southern Oscillation (ENSO) over mid-to-high latitude Eurasia during boreal summers over the past half-century. The results show that their relationship experienced a decadal shift around the early 1980s. Before the early 1980s, the Eurasian SAT-CTP SST connection was weak; after that time, the relationship became stronger, and the SAT anomalies exhibited a significant wave-like pattern over Eurasia. Such a decadal change in the Eurasian SAT-CTP SST relationship could be attributed to decadal changes in the mean state and variability of CTP SST. The warmer mean state and enhanced SST variability after the early 1980s reinforced the convective activities over the tropical Pacific, leading to significantly anomalous divergence/convergence and Rossby wave sources over the North Pacific. This outcome further excited the wave train propagating along the Northern Hemisphere zonal jet stream to northern Eurasia and then affected the surface heat fluxes and atmospheric circulations over the region, resulting in wave-like SATs over Eurasia. However, during the period before the early 1980s, the CTP SST had a weak impact on the North Pacific atmospheric circulation and was consequently not able to excite the wave train pattern to impact the Eurasian atmospheric circulation and SATs. The physical processes linking the CTP SST and Eurasian SAT are further confirmed by numerical simulations. The results of this study are valuable to understanding the variability of summer Eurasian SATs.

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Temperature Variation over East Asia during the Lifecycle of Weak Stratospheric Polar Vortex

Journal of Climate ◽

10.1175/jcli-d-14-00790.1 ◽

2015 ◽

Vol 28 (14) ◽

pp. 5857-5872 ◽

Cited By ~ 15

Author(s):

Sung-Ho Woo ◽

Baek-Min Kim ◽

Jong-Seong Kug

Keyword(s):

East Asia ◽

Temperature Variation ◽

Large Scale ◽

East Asian ◽

Polar Vortex ◽

Tropospheric Temperature ◽

Stratospheric Polar Vortex ◽

The North ◽

Stratospheric Circulation ◽

Upper Level

Abstract The authors investigate the circulation change during the life cycle of a weak stratospheric polar vortex (WSV) event and its impact on temperature variation over East Asia. The lower-tropospheric temperature over East Asia strongly fluctuates despite the slow decay of stratospheric circulation and the continuously negative Arctic Oscillation (AO) pattern during the WSV event. The temperature fluctuation is critically influenced by the variation of the East Asian upper-level coastal trough (EAT), which may be coupled to the stratospheric circulation during the WSV events. The EAT is deepened anomalously during the Peak phase (from lag −5 to lag 5 day) of the WSV, and East Asian temperature is lowest during this phase. During the next period (Decay-1 phase: from lag 6 to lag 16 day), in spite of the slowly decaying WSV condition, the cold temperature anomaly over East Asia is suddenly weakened; this change is caused by a westward-propagating signal of an anticyclonic anomaly from the North Pacific to East Asia. After about two weeks (Decay-2 phase: from lag 17 to lag 27 day), the cold conditions over East Asia are restrengthened by an intensification of EAT, which is related to the eastward propagation of a large-scale wave packet originating from a negative North Atlantic Oscillation (NAO)-type structure in the Decay-1 phase and its delayed influence on the East Asia region.

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