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Community Programs. Power of Children Awards. Visiting Artist Application. Corporate Donations. Planned Gifts. Renew your Donor Membership. Current Members. Renew Your Membership. Member FAQ. The Children's Museum Today's Hours: 10 am—5 pm. Buy Tickets. Distance of the Earth from the Sun: These explanations all involve the Earth being closer to the Sun in the summer and farther away from the Sun in the winter. Sun on the other side of the Earth: The idea here is that when the Sun is on your side of the Earth it's summer and when it's on the other side of the Earth it's winter.
Here are the responses of two mixed ability science classes of year-olds one had completed their year's work on the solar system, while the other had not yet started — total of 50 pupils in well established comprehensive schools to the challenge: Use words and diagrams to explain your ideas about why we get the seasons.
A large-scale study focusing on simple astronomical ideas was recently carried out with the general adult public and year-old pupils.
By far the most common response to explaining the seasons is in terms of distance from the Sun. This is based on the common-sense reasoning that if you go closer to a glowing source, then you become warmer.
Voice of the street: The Earth is closer to the Sun in the summer, so it must be warmer. The slightly elliptical orbit of the Earth around the Sun means that we in the Northern Hemisphere are million km from the Sun in summer but million km from the Sun in winter. The Earth is actually nearer to the Sun in winter! This idea is, unfortunately, supported by those textbooks which show the orbit of the Earth around the Sun as a very obvious and flattened ellipse. One thing you should look out for are those children who accept the idea that seasonal changes are due to the tilt of the Earth but then suggest that the tilt makes one hemisphere closer to the Sun, thereby bringing summer.
There is another line of thinking, that experience suggests you are more likely to come across in adults, but it is worth watching out for. Wrong Track: The Sun is lower on the horizon in the winter, so there the rays have to travel through a greater thickness of atmosphere, so they are weaker. Wallace , : Annular modes in the extratropical circulation.
Part I: Month-to-month variability. Ting , M. Visbeck , M. Chassignet , R. Curry , and T. The North Atlantic Oscillation , J. Hurrell et al. Von Storch , H. Zwiers , : Statistical Analysis in Climate Research. Cambridge University Press, pp. Wallace , J. Smith , and C. Bretherton , : Singular value decomposition of wintertime sea surface temperature and mb height anomalies. Wang , B. Chang , J. Liu , J. Li , and T. Zhou , : Another look at interannual-to-interdecadal variations of the East Asian winter monsoon: The northern and southern temperature modes.
Wang , D. Watanabe , M. Liu , : North Atlantic decadal variability: Air—sea coupling, oceanic memory, and potential Northern Hemisphere resonance. Chen , : Regional change in snow water equivalent—surface air temperature relationship over Eurasia during boreal spring. Yang , S. Liu , L. Sun , Y. Lian , and Z. Wang , J.
Li , and F. Mao , and R. Chen , : Circulation anomalies in the mid—high latitudes responsible for the extremely hot summer of over northeast Asia. Oceanic Sci. Wolff , W. Vaneckova , X. Pan , and S. Tong , : Ambient temperature and morbidity: A review of epidemiological evidence. Zhang , R. Sun , R.
Zhang , W. Li , and J. Zuo , : Role of Eurasian snow cover in linking winter-spring Eurasian coldness to the autumn Arctic sea ice retreat. Zhao , W. Yao , D. Nath , and B. Yu , : Interannual variations of the rainy season withdrawal of the monsoon transitional zone in China. Zhou , W. Chan , W. Chen , J. Ling , J. Pinto , and Y. Shao , : Synoptic-scale controls of persistent low temperature and icy weather over southern China in January Zhu , C. Wang , W. Qian , and B. Zhang , : Recent weakening of northern East Asian summer monsoon: A possible response to global warming.
Zuo , J. Sun , L. Xu , and H. Ren , : Impact of the North Atlantic sea surface temperature tripole on the East Asian summer monsoon. Zveryaev , I. Gulev , : Seasonality in secular changes and interannual variability of European air temperature during the twentieth century. Years labeled in c and d correspond to the summertime. Unit of the surface net heat flux has been converted to the unit of SST tendency a constant mixed layer depth of 30 m is assumed. Schematic diagram displaying the physical processes linking interannual variations of the winter and summer SAT anomalies over northeast Eurasia.
This study reveals a pronounced out-of-phase relationship between surface air temperature SAT anomalies over northeast Eurasia in boreal winter and the following summer during — A colder warmer winter over northeast Eurasia tends to be followed by a warmer cooler summer of next year.
The North Atlantic SST anomaly pattern switches to a dipolar pattern in the following summer via air—sea interaction processes and associated surface heat flux changes. The summer North Atlantic dipolar SST anomaly pattern induces a downstream atmospheric wave train, including large-scale positive geopotential height anomalies over northeast Eurasia, which contributes to positive SAT anomalies there via enhancement of downward surface shortwave radiation and anomalous advection.
Barotropic model experiments verify the role of the summer North Atlantic SST anomalies in triggering the atmospheric wave train over Eurasia. Through the above processes, a colder winter is followed by a warmer summer over northeast Eurasia. The above processes apply to the years when warmer winters are followed by cooler summers except for opposite signs of SAT, atmospheric circulation, and SST anomalies.
Surface air temperature SAT anomalies and the accompanying extreme cold spells and heat waves have substantial impacts on human health, agriculture, ecosystem, and socioeconomic development Dong et al. For example, the extreme low temperature and associated severe freezing snow weather over southern China in January of led to substantial damage to the production and transportation of electric power and resulted in many casualties Zhou et al.
The record-breaking high temperature in the summer of over many parts of East Asia caused many forest fires and severely destroyed local agriculture and ecosystem Barriopedro et al. Therefore, it is important to improve the understanding of the Eurasian SAT variations and the associated controlling factors.
Zveryaev and Gulev investigated the dominant modes of SAT variations over Europe in four seasons. AO is the leading mode of atmospheric interannual variability over extratropical Northern Hemisphere Thompson and Wallace , NAO is regarded as a regional manifestation of the AO over the North Atlantic region, characterizing by a meridional dipole anomaly pattern Hurrell and van Loon ; Thompson and Wallace Previous studies generally indicated that negative positive phase of the winter AO can lead to negative positive SAT anomalies over most parts of Eurasia Thompson and Wallace ; Gong et al.
Chen et al. The Scandinavian teleconnection pattern is characterized by a main center of anomalies around Scandinavia and two centers of opposite sign with weaker amplitudes around the west Europe and eastern Russia—western Mongolia Barnston and Livezey Studies indicated that atmospheric circulation anomalies related to Eurasian atmospheric wave trains, such as the circumglobal teleconnection pattern and Silk Road pattern, can exert significant impacts on summer SAT anomalies over Eurasia Ding and Wang ; W.
The abovementioned studies mainly investigated SAT variations over Eurasia during individual seasons. Several recent studies indicated that there exists a close connection of SAT anomalies over Eurasia between boreal winter and spring Chen et al.
Zhang et al. At present, few studies have examined the possible connection between Eurasian SAT anomalies in boreal winter and the following summer. There is evidence for out-of-phase SAT anomalies over Eurasia between winter and the following summer. The above cases have a common feature that the SAT anomalies in winter are followed by opposite SAT anomalies in summer in the next year over a large part of mid—high-latitude Eurasia.
The above evidence suggests that there exists a robust out-of-phase relation between SAT in winter and the following summer over northeast Eurasia.
This study examines the possible factors responsible for this cross-season connection. Citation: Journal of Climate 33, 17; The rest of this study is organized as follows. Section 2 describes the data and methodology employed in this study. Section 3 examines the possible connection of SAT anomalies over Eurasia in boreal winter and the following summer.
Section 4 discusses the plausible mechanism linking Eurasian winter and summer SAT. Section 5 provides a summary and discussion. Geopotential height and winds have a horizontal resolution of 2. The factors and physical processes of SAT variations may not be the same for different time scales e.
This study focuses on investigating the SAT variation on the interannual time scale. In particular, we concentrate on the relationship between interannual variations of winter and the following summer SAT. Interannual component of a specific variable is obtained by subjecting the original anomaly field to a 2—9-yr Lanczos bandpass filter Duchon Use of a 2—7- or 2—yr bandpass filter leads to very similar results not shown.
This study employs the wave activity flux defined by Takaya and Nakamura to describe propagation of stationary Rossby waves. This wave activity flux is expressed as follows:. Subscripts x and y denote the derivatives in the zonal and meridional components, respectively. Climatological mean is calculated based on the period of — Studies have indicated that positive negative SST anomalies in the tropical and subtropical region could lead to anomalous divergence convergence in the upper troposphere that further acts as an effective source of stationary Rossby wave Watanabe ; Hodson et al.
The barotropic model follows a simple barotropic vorticity equation as follows Sardeshmukh and Hoskins ; Watanabe ; Zuo et al. The barotropic model encompasses a linear damping that indicates the Rayleigh friction and a biharmonic diffusion. Solution of the Eq. Previous study indicated that results of the barotropic model simulation do not show obvious differences for basic states chosen from the upper troposphere e. The SVD analysis can capture the coherent spatial patterns between two anomaly fields Bretherton et al.
Results obtained in the following analysis are not sensitive to a slight change in the region of the SVD analysis. The SVD1 explains approximately The correlation coefficient between the expansion coefficient EC time series of winter and summer SAT is 0.
Most of the years of large EC time series in winter correspond to large values of the summer EC time series, including and as mentioned in the introduction. This suggests a strong connection between winter and the following summer SAT anomalies over most parts of northeast Eurasia.
This connection appears stable during the analysis period. This is demonstrated by Fig. The negative correlation remains significant during the analysis period Fig. The results are shown in Figs. This indicates that the SVD1 patterns in Figs. Over the mid—high latitudes of Eurasia, significant cooling is observed over the Russian far east and the region between the Lake Baikal and Caspian Sea in autumn Fig.
Most parts of Eurasia north of Significant negative SAT anomalies are seen around SAT anomalies are weak during the transitional period from winter to the following summer [i. Above analysis indicates that SAT anomalies over northeast Eurasia in winter have a significant negative correlation with the following summer SAT anomalies. A colder warmer winter over northeast Eurasia has a strong tendency to be followed by a warmer cooler summer.
In addition, according to Fig. In this section, we first document the evolution of atmospheric circulation anomalies to explain the formation of the winter and summer SAT anomalies over Eurasia. Then, we analyze the evolution of anomalous lower boundary conditions in relation to the changes in atmospheric circulation anomalies from winter to the following summer. After that, we illustrate the role of summer North Atlantic SST anomalies in Eurasian atmospheric circulation anomaly pattern in simultaneous summer.
Notice that the following descriptions correspond to colder winters followed by warmer summers, but also apply to warmer winters followed by cooler summers except for opposite signs of anomalies. Formations of winter and summer SAT anomalies over Eurasia are closely related to atmospheric circulation changes.
Figure 6 displays regression maps of hPa winds and hPa geopotential height anomalies from winter to the following summer onto the normalized EC time series of summer SAT during — The spatial patterns of atmospheric circulation anomalies at and hPa are similar, indicating a quasi-barotropic vertical structure of atmospheric circulation anomalies in the three seasons.
In winter, the high-latitude region is dominated by large positive geopotential height anomalies and there are negative geopotential height anomalies over the midlatitude North Atlantic—west Europe and the Lake Baikal and positive geopotential height anomalies over eastern Europe Figs.
This geopotential height anomaly pattern resembles that of the negative phase of the AO Thompson and Wallace , In addition, a meridional contrast of geopotential height anomalies is seen over the North Atlantic, similar to the NAO Fig.
Many studies have indicated that negative phase of the AO reduces westerly winds over the mid—high latitudes of Eurasia and leads to negative SAT anomalies over most parts of the mid—high-latitude Eurasia as the weakened circumpolar westerly wind provides a favorable condition for colder air from Arctic to penetrate to the mid—high latitudes of Eurasia Thompson and Wallace , ; Gong et al.
Indeed, anomalous northeasterly lower-level winds control high-latitude eastern Eurasia Fig. This suggests that the winter negative AO-related atmospheric circulation anomalies play a crucial role in forming the continental-scale SAT cooling over Eurasia Figs. In spring, the Arctic region is covered by negative geopotential height anomalies Figs. Large negative geopotential height anomalies are seen over northern Europe and positive geopotential height anomalies are observed around Lake Balkhash Figs.
The notable negative geopotential height anomalies over northern Europe Figs. By contrast, the pronounced positive geopotential height anomalies around Lake Balkhash Figs. In addition, southerly wind anomalies to the west flank of the positive geopotential height anomalies Figs. Thus, the radiative and advective effects contribute to SAT anomalies in different regions. Geopotential height anomalies in spring over northeast Eurasia are weak Figs.
In summer, a wave train—like structure is observed over the mid—high latitudes of Eurasia as indicated by the wave activity flux, with positive geopotential height anomalies over northern Europe and northeast Eurasia and negative geopotential height anomalies to the north of Lake Balkhash Figs. Such a wave train is usually regarded as a stationary Rossby wave Barnston and Livezey ; Scaife et al.
Studies have demonstrated that extreme high temperature events over Eurasia are closely related to local positive geopotential height anomalies Gong et al. Positive geopotential height anomalies over northeast Eurasia are accompanied by decreased total cloud cover Fig. In addition, the southerly wind anomalies over East Asia may also contribute to positive SAT anomalies there via wind-induced horizontal temperature advection Figs.
Above analysis indicates that formations of winter and summer SAT anomalies over Eurasia are related to atmospheric circulation anomalies. In particular, the continental-scale SAT cooling over Eurasia in winter is related to the negative AO-type atmospheric circulation anomalies. In summer, the marked SAT warming over most parts of northeast Eurasia is related to local positive geopotential height anomalies.
What is responsible for the change in atmospheric circulation anomaly pattern from winter to summer that leads to opposite winter and summer SAT anomalies over northeast Eurasia? As the atmospheric anomalies cannot persist through processes in the atmosphere only, the link of atmospheric circulation anomaly pattern between winter and summer is likely related to lower boundary condition changes. Studies indicated that boundary forcings such as the Arctic sea ice, snow cover, and sea surface temperature may play a role in linking atmospheric circulation anomalies during different seasons Ogi et al.
In the following, we examine each of these boundary forcings to investigate which one may be responsible for the change in atmospheric circulation anomaly pattern from winter to summer. It turns out that the Arctic SIC anomalies are generally weak and insignificant from preceding autumn to simultaneous summer not shown.
This implies that Arctic sea ice changes may not be able to explain the out-of-phase relation of the SAT anomalies over northeast Eurasia between winter and the following summer.
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