Why Northeast China Has a Cooling Trend in 21st century?

2020 ◽  
Author(s):  
Xiang Li ◽  
Hui Gao
Keyword(s):  
Northeast China ◽  
Eastern China ◽  
Negative Temperature ◽  
Significant Negative Correlation ◽  
Empirical Orthogonal Functions ◽  
The Arctic ◽  
Boreal Winter ◽  
Orthogonal Functions ◽  
Leading Mode ◽  
The Arctic Oscillation

<p>    Under the global warming scenarios, the air temperatures (T<sub>2m</sub>) in China in boreal winter shows a remarkable increasing trend since the 1980s, which is quite similar with the change of the globe. But in Northeast China (NEC), the temperature displays an opposite characteristics with an obvious decreasing trend in recent two decades. Results of the empirical orthogonal functions (EOF) of T<sub>2m</sub> in China indicate that the first leading mode is a consistent positive or negative temperature departures in the whole country, but the variance of this mode show a weakening tendency. The second leading mode of T<sub>2m</sub> in China shows a seesaw temperature anomaly pattern in NEC and in other regions of eastern China. Different from the 1<sup>st</sup> EOF mode, variances of this mode show an intensifying tendency. Both statistical analysis and case studies of 20 winters during 2000 to 2019 indicate that this opposite change in NEC may be related to the decadal relationship between the Siberian high and the Arctic oscillation. Previous studies explored that there was a significant negative correlation between the two factors, but this relationship was significantly weakened in the past two decades, which led to the independent influences from the two circulation members on the temperature in NEC, and consequently resulted in an inconsistent variation in the region.</p>

scholarly journals Boreal Winter Links between the Madden–Julian Oscillation and the Arctic Oscillation

2008 ◽  
Vol 21 (12) ◽  
pp. 3040-3050 ◽  
Author(s):  
Michelle L. L’Heureux ◽  
R. Wayne Higgins
Keyword(s):  
Arctic Oscillation ◽  
Active Phase ◽  
Temperature Fields ◽  
The Arctic ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Global Circulation ◽  
Leading Mode ◽  
The Arctic Oscillation ◽  
The Tropics

Abstract There is increasing evidence that the Madden–Julian oscillation (MJO) modifies the mid- to high-latitude circulation and, in particular, appears to have a relationship to the leading mode of extratropical variability, the Arctic Oscillation (AO). In this study, new insights into the observed similarities between the MJO and the AO are explored. It is shown that the eastward progression of the convectively active phase of the MJO is associated with a corresponding shift in the tendency and sign of the AO index. Moreover, the AO and the MJO share several analogous features not only in the global circulation, but also in surface temperature fields. Also, the AO is linked to a pattern of eastward-propagating MJO-like variability in the tropics that is partially reproduced in free runs of the NCEP Climate Forecast System (CFS) model. Finally, it is shown that the structure of the AO, as defined by the leading mode in the 1000-hPa geopotential height field, is significantly altered based on the phase of the MJO.

scholarly journals On the Nonlinearity of Winter Northern Hemisphere Atmospheric Variability

2019 ◽  
Vol 76 (1) ◽  
pp. 333-356 ◽  
Author(s):  
A. Hannachi ◽  
W. Iqbal
Keyword(s):  
North Atlantic ◽  
Polar Vortex ◽  
Principal Component ◽  
Empirical Orthogonal Functions ◽  
The Arctic ◽  
Climate Change Signal ◽  
Two Dimensional ◽  
Orthogonal Functions ◽  
Local Flow ◽  
The North

Abstract Nonlinearity in the Northern Hemisphere’s wintertime atmospheric flow is investigated from both an intermediate-complexity model of the extratropics and reanalyses. A long simulation is obtained using a three-level quasigeostrophic model on the sphere. Kernel empirical orthogonal functions (EOFs), which help delineate complex structures, are used along with the local flow tendencies. Two fixed points are obtained, which are associated with strong bimodality in two-dimensional kernel principal component (PC) space, consistent with conceptual low-order dynamics. The regimes reflect zonal and blocked flows. The analysis is then extended to ERA-40 and JRA-55 using daily sea level pressure (SLP) and geopotential heights in the stratosphere (20 hPa) and troposphere (500 hPa). In the stratosphere, trimodality is obtained, representing disturbed, displaced, and undisturbed states of the winter polar vortex. In the troposphere, the probability density functions (PDFs), for both fields, within the two-dimensional (2D) kernel EOF space are strongly bimodal. The modes correspond broadly to opposite phases of the Arctic Oscillation with a signature of the negative North Atlantic Oscillation (NAO). Over the North Atlantic–European sector, a trimodal PDF is also obtained with two strong and one weak modes. The strong modes are associated, respectively, with the north (or +NAO) and south (or −NAO) positions of the eddy-driven jet stream. The third weak mode is interpreted as a transition path between the two positions. A climate change signal is also observed in the troposphere of the winter hemisphere, resulting in an increase (a decrease) in the frequency of the polar high (low), consistent with an increase of zonal flow frequency.

scholarly journals Interaction between the MJO and Polar Circulations

2013 ◽  
Vol 26 (11) ◽  
pp. 3562-3574 ◽  
Author(s):  
Maria Flatau ◽  
Young-Joon Kim
Keyword(s):  
Indian Ocean ◽  
Southern Hemisphere ◽  
Warm Season ◽  
Cold Season ◽  
The Arctic ◽  
Boreal Winter ◽  
Annular Modes ◽  
The Indian Ocean ◽  
The Arctic Oscillation ◽  
The Tropics

Abstract A tropical–polar connection and its seasonal dependence are examined using the real-time multivariate Madden–Julian oscillation (MJO) (RMM) index and daily indices for the annular modes, the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO). On the intraseasonal time scale, the MJO appears to force the annular modes in both hemispheres. On this scale, during the cold season, the convection in the Indian Ocean precedes the increase of the AO/AAO. Interestingly, during the boreal winter (Southern Hemisphere warm season), strong MJOs in the Indian Ocean are related to a decrease of the AAO index, and AO/AAO tendencies are out of phase. On the longer time scales, a persistent AO/AAO anomaly appears to influence the convection in the tropical belt and impact the distribution of MJO-preferred phases. It is shown that this may be a result of the sea surface temperature (SST) changes related to a persistent AO, with cooling over the Indian Ocean and warming over Indonesia. In the Southern Hemisphere, the SST anomalies are to some extent also related to a persistent AAO pattern, but this relationship is much weaker and appears only during the Southern Hemisphere cold season. On the basis of these results, a mechanism involving the air–sea interaction in the tropics is suggested as a possible link between persistent AO and convective activity in the Indian Ocean and western Pacific.

scholarly journals Investigating the Impact of CO2 on Low-Frequency Variability of the AMOC in HadCM3

2017 ◽  
Vol 30 (19) ◽  
pp. 7863-7883 ◽  
Author(s):  
Edward Armstrong ◽  
Paul Valdes ◽  
Jo House ◽  
Joy Singarayer
Keyword(s):  
Climate Model ◽  
Singular Spectrum Analysis ◽  
Empirical Orthogonal Functions ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Positive Density ◽  
Quasi Equilibrium ◽  
Ekman Pumping ◽  
Orthogonal Functions ◽  
The Impact

Abstract This study investigates the impact of CO2 on the amplitude, frequency, and mechanisms of Atlantic meridional overturning circulation (AMOC) variability in millennial simulations of the HadCM3 coupled climate model. Multichannel singular spectrum analysis (MSSA) and empirical orthogonal functions (EOFs) are applied to the AMOC at four quasi-equilibrium CO2 forcings. The amount of variance explained by the first and second eigenmodes appears to be small (i.e., 11.19%); however, the results indicate that both AMOC strength and variability weaken at higher CO2 concentrations. This accompanies an apparent shift from a predominant 100–125-yr cycle at 350 ppm to 160 yr at 1400 ppm. Changes in amplitude are shown to feed back onto the atmosphere. Variability may be linked to salinity-driven density changes in the Greenland–Iceland–Norwegian Seas, fueled by advection of anomalies predominantly from the Arctic and Caribbean regions. A positive density anomaly accompanies a decrease in stratification and an increase in convection and Ekman pumping, generating a strong phase of the AMOC (and vice versa). Arctic anomalies may be generated via an internal ocean mode that may be key in driving variability and are shown to weaken at higher CO2, possibly driving the overall reduction in amplitude. Tropical anomalies may play a secondary role in modulating variability and are thought to be more influential at higher CO2, possibly due to an increased residence time in the subtropical gyre and/or increased surface runoff driven by simulated dieback of the Amazon rain forest. These results indicate that CO2 may not only weaken AMOC strength but also alter the mechanisms that drive variability, both of which have implications for climate change on multicentury time scales.

Association of Indian Ocean ITCZ Variations with the Arctic Oscillation during Boreal Winter

2013 ◽  
Vol 6 (5) ◽  
pp. 300-305
Author(s):  
Gong Dao-Yi ◽  
Gao Yong-Qi ◽  
Hu Miao ◽  
Guo Dong
Keyword(s):  
Indian Ocean ◽  
Arctic Oscillation ◽  
The Arctic ◽  
Boreal Winter ◽  
The Arctic Oscillation

scholarly journals Where can the Arctic oscillation be reconstructed? Towards a reconstruction of climate modes based on stable teleconnections

2005 ◽  
Vol 1 (1) ◽  
pp. 17-56 ◽  
Author(s):  
G. Lohmann ◽  
N. Rimbu ◽  
M. Dima
Keyword(s):  
Arctic Oscillation ◽  
Ice Core ◽  
The Arctic ◽  
Boreal Winter ◽  
Arctic Oscillation Index ◽  
Climate Modes ◽  
Teleconnection Patterns ◽  
Temperature And Precipitation ◽  
The Arctic Oscillation ◽  
Coral Tree

Abstract. Proxy data can bring observed climate variability of the last 100 years into a long-term context. We identify regions of the Northern Hemisphere where the teleconnection patterns of the Arctic Oscillation are stationary. Our method provides a systematic way to examine optimal sites for the reconstruction of climate modes based on paleoclimatic archives that sensitively record temperature and precipitation variations. We identify the regions for boreal winter and spring that can be used to reconstruct the Arctic Oscillation index in the pre-instrumental period. Finally, this technique is applied to high resolution coral, tree ring, ice core and mollusk shell data to understand proxy-climate teleconnections and their use for climate reconstructions.

scholarly journals Spatial–Temporal Variability of the Calculated Characteristics of the Ocean in the Arctic Zone of Russia by Using the NEMO Model with Altimetry Data Assimilation

2020 ◽  
Vol 8 (10) ◽  
pp. 753
Author(s):  
Konstantin Belyaev ◽  
Andrey Kuleshov ◽  
Ilya Smirnov
Keyword(s):  
Data Assimilation ◽  
Temporal Variability ◽  
Satellite Observation ◽  
Sea Surface Height ◽  
Empirical Orthogonal Functions ◽  
Sea Surface ◽  
The Arctic ◽  
Observation Data ◽  
Arctic Zone ◽  
Orthogonal Functions

The spatial–temporal variability of the calculated characteristics of the ocean in the Arctic zone of Russia is studied. In this study, the known hydrodynamic model of the ocean Nucleus for European Modelling of the Ocean (NEMO) is used with assimilation of observation data on the sea surface height taken from the Archiving, Validating and Interpolation Satellite Observation (AVISO) archive. We use the Generalized Kalman filter (GKF) method, developed earlier by the authors of this study, in conjunction with the method of decomposition of symmetric matrices into empirical orthogonal functions (EOF, Karhunen–Loeve decomposition). The investigations are focused mostly on the northern seas of Russia. The main characteristics of the ocean, such as the current velocity, sea surface height, and sea surface temperature are calculated with data assimilation (DA) and without DA (the control calculation). The calculation results are analyzed and their spatial–temporal variability over a time period of 14 days is studied. It is shown that the main spatial variability of characteristics after DA is in good agreement with the localization of currents in the North Atlantic and in the Arctic zone of Russia. The contribution of each of the eigenvectors and eigenvalues of the covariation matrix to the spatial–temporal variability of the calculated characteristics is shown by using the EOF analysis.

scholarly journals Interannual Variability of the North American Cold Air Stream and Associated Synoptic Circulations

2017 ◽  
Vol 30 (23) ◽  
pp. 9575-9590 ◽  
Author(s):  
Yuki Kanno ◽  
John E. Walsh ◽  
Toshiki Iwasaki
Keyword(s):  
United States ◽  
Interannual Variability ◽  
Rocky Mountains ◽  
Arctic Oscillation ◽  
Potential Temperature ◽  
The Arctic ◽  
Boreal Winter ◽  
Stratospheric Polar Vortex ◽  
Cold Air ◽  
The Arctic Oscillation

In boreal winter, the cold air mass (CAM) flux of air with a potential temperature below 280 K forms climatological mean CAM streams in East Asia and North America (NA). This study diagnoses the interannual variability of the NA stream by an analysis of the CAM flux across 60°N between Greenland and the Rocky Mountains. The first empirical orthogonal function (EOF) represents the variations in intensity of the NA stream. When the first principal component (PC1) is highly positive, the central part of the NA stream is intensified, with cold anomalies east of the Rocky Mountains. At the same time, a stratospheric polar vortex tends to split or displace toward NA. PC1 is highly correlated with the tropical Northern Hemisphere pattern, implying that this pattern is associated with the intensity of the NA stream. The second EOF shows a longitudinal shift of the NA stream toward Greenland or the Rocky Mountains. A highly negative PC2 results in a cold anomaly from western Canada to the Midwestern United States and anomalous heavy snowfall in the northeastern United States. PC2 is positively correlated with the Arctic Oscillation, which suggests that the longitudinal position of the NA stream varies with the Arctic Oscillation. These results illustrate how the intensity and location of cold air outbreaks vary with large-scale modes of atmospheric variability, with corresponding implications for the predictability of winter severity in NA.

scholarly journals Classification of Polar-Night Jet Oscillations and Their Relationship to Fast and Slow Variations in a Global Mechanistic Circulation Model of the Stratosphere and Troposphere

2010 ◽  
Vol 23 (23) ◽  
pp. 6438-6444 ◽  
Author(s):  
Masashi Kohma ◽  
Seiya Nishizawa ◽  
Shigeo Yoden
Keyword(s):  
Low Frequency ◽  
Polar Vortex ◽  
Circulation Model ◽  
Negative Temperature ◽  
The Arctic ◽  
Eof Analysis ◽  
Polar Night ◽  
Low Pass ◽  
Cold Events ◽  
The Arctic Oscillation

Abstract Polar-night jet oscillation (PJO), which is a low-frequency intraseasonal oscillatory variation in the winter stratosphere, is analyzed statistically with a 14 000-yr-long dataset obtained with an idealized global mechanistic circulation model of the stratosphere and troposphere. After performing an empirical orthogonal function (EOF) analysis on the low-pass-filtered time series of the northern polar temperature, 10 647 PJO events are identified and classified into four groups. About 80% of them are two groups of warm events while the rest are two groups of cold events, which are newly identified variations with opposite sign from the warm events by the same EOF analysis. All of them show slow downward propagations of a positive or negative temperature anomaly, with a relatively short or long lifetime. Composite analysis with such a large number of samples shows that each group has its own typical relationship to unfiltered relatively fast variations in the polar stratosphere known as stratospheric sudden warming and polar vortex intensification and to the slow variation in the troposphere known as the Arctic Oscillation. Statistically significant evidence of the downward dynamical influence of PJO on the surface is obtained for a group of warm events with a longer lifetime.

scholarly journals Combined Effects of the MJO and the Arctic Oscillation on the Intraseasonal Eastern China Winter Temperature Variations

2019 ◽  
Vol 32 (8) ◽  
pp. 2295-2311 ◽  
Author(s):  
Lei Song ◽  
Renguang Wu
Keyword(s):  
East Asia ◽  
High Latitude ◽  
Western Europe ◽  
Arctic Oscillation ◽  
Wave Train ◽  
Eastern China ◽  
The Arctic ◽  
Wave Source ◽  
Temperature Anomalies ◽  
The Arctic Oscillation

AbstractThe present study reveals that the Madden–Julian oscillation (MJO)-related temperature anomalies over East Asia have notable differences among positive, neutral, and negative Arctic Oscillation (AO) phases. In MJO phases 2–3, cold anomalies over eastern China occur mainly during positive AO. In MJO phase 7, warm anomalies over eastern China are observed mostly during neutral AO, and in MJO phase 8 warm anomalies appear in positive and neutral AO. Regional mean temperature anomalies over northeastern East Asia tend to be negative during negative AO but positive during positive AO in six of eight MJO phases. In MJO phases 2–3, the AO-related mid- to high-latitude wave train over Eurasia and the MJO convection-triggered poleward wave train work together in contributing to negative height anomalies over eastern China and leading to cold anomalies there. The mid- to high-latitude wave train is stronger when the AO is negative than positive, which is associated with stronger zonal winds. In MJO phases 7–8, the positive AO-related mid- to high-latitude wave train over Eurasia and the MJO-induced poleward wave train cooperate in inducing positive height anomalies and leading to warm anomalies over eastern China. The mid- to high-latitude wave train is the main contributor to negative height anomalies over eastern China when the AO is negative during MJO phases 7–8. Meanwhile, the intensity of the South Asian wave source associated with the MJO convection is subjected to the modulation of southeastward dispersion of wave energy from western Europe during negative AO.

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