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Atmospheric Environment 42 (2008) 2358–2368

www.elsevier.com/locate/atmosenv

Shifts of dust source regions over central Asia andthe Tibetan Plateau: Connections with the Arctic oscillation and

the westerly jet

Yongxiang Hana,b, Xiaomin Fanga,�, Shichang Kanga,c,Huijun Wangd, Fenqing Kangb

aInstitute of Tibetan Plateau Research, Chinese Academy of Sciences, Shuangquing Street 18, Beijing 100085, ChinabLanzhou Arid Meteorological Institute & Key Laboratory of Arid Climatic Change and Reducing Disaster,

China Meteorological Administration, Lanzhou 730020, ChinacState Key Laboratory of Cryospheric Sciences, Chinese Academy of Sciences, Lanzhou 730000, China

dNansen-Zhu International Research Center, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Received 6 June 2007; received in revised form 5 December 2007; accepted 6 December 2007

Abstract

An analysis of dust storms and blowing sand records at 681 stations in China during 1961–2000 and in Mongolia during

1980–2000 reveals that the dust source regions in central Asia and the Tibetan Plateau have monthly and interannual

northward shifts from the Tibetan Plateau to Mongolia. The monthly shift is closely related to the location of the 200 hPa

westerly jet and to the location and intensity of the 500 hPa westerly jet over central Asia and the Tibetan Plateau. The

causes for interannual shifts vary by region. The westerly jet appears to drive the shift on the Tibetan Plateau; the intensity

of the central Asian mid-latitude westerly, the Arctic oscillation (AO) and the East Asian winter monsoon may be the

drivers in the Hexi Corridor region to the north of the Tibetan Plateau; and the AO and the location of the westerly jet in

the Mongolian region. All these causes are closely related to the AO variations, which may provide a connection between

climatic changes in East Asia and the North Atlantic, and the long-distance transport of dust. This connection could

explain the shifts of dust source regions at interannual and millennial timescales and the roughly synchronous climate

changes recorded in the Chinese loess and deep-sea sediments in the North Atlantic Ocean.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Shift of dust source regions; Central Asia and Tibetan Plateau; Arctic oscillation; Westerly jet

1. Introduction

Crustal dust makes up the main aerosol consti-tuent of the atmosphere. Shi (2003) has estimated

e front matter r 2007 Elsevier Ltd. All rights reserved

mosenv.2007.12.025

ing author. Tel.: +86 10 6284 9697;

4 9886.

ess: fangxm@itpcas.ac.cn (X. Fang).

that around 100–200� 106 ton of dust aerosol risesinto the global atmosphere each year, accountingfor nearly one-half of the total aerosol in thetroposphere. Owing to its ‘‘umbrella effect’’, ‘‘icenuclei effect’’, and ‘‘iron fertilizer effect’’, the dustaerosol tends to cool the climate in contrast to thewarming effect of CO2 (Ridgwell, 2002). Bycirculation and geochemical processes, dust aerosols

.

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link together the land, ocean, atmosphere andorganisms, and have been postulated to be one ofthe key linkages of the global mass cycle and climatechange (Martin, 1990; Rea, 1994; Coale et al., 1996;Watson et al., 2000; Bishop et al., 2002; Han et al.,2006). Dust deposition from marine records for thepast 400 ka shows that during each glacial–intergla-cial climate cycle, dust increase predates precipita-tion increases and temperature rises (Rea, 1994).This leading phenomenon has also been recorded inthe Antarctic Vostock ice cores. Of the six high-duststages during the past 420 ka, four record clear dustdecreases occurring prior to the end of the glacia-tions (Petit et al., 1999). In the Dangsgaard–Oesch-ger (D–O) cycle (Dansgaard et al., 1993), high dustconcentrations also occurred before the collapse ofthe ice sheet in the Northern Hemisphere, due to therapid ablation of ice and snow. The increase in dustcontent in ice during the last glaciation has beenregarded as a possible contributing mechanism forthe ice sheet collapse (Overpeck, 1996). All thesefindings have finally led to the proposal of a‘‘dust–CO2–climate’’ feedback mechanism linkedwith the ‘‘iron fertilizer’’ hypothesis (Ridgwell,2002). Dust aerosols thus deserve more study.

Central Asia holds one of the most importantsource regions of dust storms and supplies about95% of the iron to the North Pacific region in theearth’s material cycle (Duce et al., 1980). Therefore,

Fig. 1. Sketch map of dust-storm centers and monthly shift of dust-stor

Plateau; dotted gray areas: centers of dust storms lasting over 20 days a

storm observation data. At Fuyun, Habahe and Hailer the storms invo

central Asia is one of the key regions for under-standing the evolution of ocean–land–atmospherecoupling. Previous studies (Liu, 1985; Zhang, 2001)showed that the source areas of Asian dust areconcentrated in the arid and semiarid regions ofChina, and that dust storms occur mainly fromApril to May. However, we found that the TibetanPlateau lying between 281N and 421N (Fig. 1) is alsoan important dust source region, with dust stormsoccurring mainly in winter (Fang et al., 2004). Thedifferent seasonality of dust storms in differentregions suggests that dust source regions have asignificant monthly shift in central Asia and theTibetan Plateau. Annual dust-storm frequencies onthe Tibetan Plateau, in the Tarim Basin and Hexicorridor region have continuously decreased afterthe 1980s (Shi, 2003; Song et al., 2004), whereas thefrequency trend has clearly increased since 1974 inMongolia (Natsagdorj et al., 2003). Meanwhile,records from loess sediments suggest that dustsource regions have shifted north to south over athousand-year timescale in central Asia (Zhang,2001). Furthermore, the variations of the dustaerosols correlate not only with the full climaticD–O cycle (Dansgaard et al., 1993), but also withthe Bond cycle (Bond et al., 1993) induced byHeinrich (H1–H6) events (Heinrich, 1988). How-ever, the physical mechanism of tele-correlationbetween shifts of the dust source regions in Asia and

m source region in China and Mongolia. Dark gray area: Tibetan

year during 1961–2000; black circles: weather stations with dust-

lve only blowing sand.

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Fig. 2. Sketch map showing the spatial–temporal distributions of

areas with the highest monthly dust storms and the westerly jet in

China. Black solid arrow and number: westerly jet and its

corresponding month(s) (by number); open circle and number in

it: center of dust-storm activity and number of the month with the

highest dust-storm frequency. Shaded area represents the Tibetan

Plateau. Note that there is no obvious dust-storm activity center

for months between August and November.

Y. Han et al. / Atmospheric Environment 42 (2008) 2358–23682360

climate change in the North Atlantic Ocean remainsunclear.

This work investigates monthly and interannualvariations of dust-storm source regions in centralAsia and the Tibetan Plateau by analyzing therecords of dust storms or blowing sand at 681stations in China from 1961 to 2000 and inMongolia from 1980 to 2000 (data available fromthe National Meteorological Center of China). Thisstudy reanalyzed data from the NCAR/NECP at2.5� 2.5 grid sizes and the Arctic oscillation (AO)series (Thompson, 1998) provided by the ClimateDiagnostics Center (USA) to explore the causes ofthe shifts of dust source regions. Possible physicalmechanisms of tele-correlation between shifts of thedust source regions in Asia and climate change inthe North Atlantic Ocean are also examined.

2. Monthly shifts of dust source regions

Analysis of dust-storm days exceeding 20 daysper year at 681 stations in China from 1961 to 2000reveals four centers with high frequency of sourceoccurrences: the southern Tarim Basin, the BadainJaran Desert, the headwater regions of the Yangtseand the Yellow Rivers, and the Qiangtang Plateau(northern central Tibet) near Shenza (30.571N,88.381E). The Tarim Basin shows the highest dust-storm originating frequency (over 20 dust-stormdays per year occurring in 39 of the last 40 years).The Badain Jaran Desert spawns the second highestnumber (420 in 26 of the 40 years), then theQiangtang Plateau (18 of the last 40 years), andfinally the headwater regions of the Yangtse and theYellow Rivers (13 of the last 40 years). Thus, thedust-storm source regions in China occur not onlyin arid and semi-arid regions in the northwest Chinawhere they have been noted by many researchers(Liu, 1985; Zhang, 2001; Fan et al., 2004; Song etal., 2004), but also on the Tibetan Plateau (Fig. 1).

Spatial analysis of station data from the dust-storm source areas indicates a significant monthlyshift of the dust-storm occurrence peak withincreasing latitude (Fig. 1). Dust storms developmainly between December and March with the peakin February on the southern Tibetan Plateau (e.g.,at Shenza and Lazi), a peak in March at theWudaoliang station (35.131N, 93.051E) on thenorthern Tibetan Plateau, peaks in April at theMangai (46.201N, 98.681E) and Minqin stations(38.621N, 103.081E) on the northern edge ofthe Tibetan Plateau and the low-elevation Hexi

Corridor, and finally peaking in July at the north-ernmost area near Tacheng (46.741N, 82.961E) innorthern Xinjiang (Fig. 1).

The spatial–temporal distribution of the highestmonthly frequency of dust storms at 681 stations inChina from 1961 to 2000 shows more clearly thenorthward shift of dust source regions from thesouthern Tibetan Plateau during the December–February period, via the central Tibetan Plateauduring March–April, to the southern Tarim Basin inApril, and the higher-latitude regions even later(Fig. 2). The 40-year mean 200 hPa zonal windvelocity and location along longitude 801E showthat the 200 hPa westerly jet stays mainly between261N and 281N from December to April, with aslightly northward moving trend (Fig. 3a). AfterApril, the jet moves dramatically northwards andreaches 431N in July–August, and then rapidlyretreats southwards and reaches the Tibetan Plateauagain in October. The wind velocity of the westerlyjet is about 40m s�1 from November to March butdecreases dramatically in February and reaches itslowest value of o25m s�1 in May. During May–September the velocity increases slightly but re-mains o35m s�1. Remarkably, the seasonal move-ment of dust source regions closely follows themovement of the 200 hPa westerly jet location overChina, especially on the Tibetan Plateau.

A comparison of Figs. 2 and 3a shows asignificant influence of the 200 hPa westerly jet shift

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Fig. 3. Monthly average meridional section of location and wind speed of the (a) 200 hPa and (b) 500 hPa westerly jets along 801E in Asia

from 1961 to 2000. In (b) shaded areas: zone of the largest wind speed of the 500 hPa westerly winds; solid lines: location of the westerly jet

(lines 1 and 2 indicate the westerly sub-jets flowing around the southern and northern rims of the Tibetan Plateau, respectively; line 3

denotes the westerly jet flowing from the high latitudes).

Y. Han et al. / Atmospheric Environment 42 (2008) 2358–2368 2361

on the monthly moving change of dust storms at4500–5500m on the Tibetan Plateau, but nosignificant effect on the low-elevation arid andsemi-arid regions. The reasons may be related tothe presence of complex topography, especially onthe Tibetan Plateau and in the high mountain areassuch as the Altai and Qilian Mountains. Thecomplex 500 hPa westerly jet (Fig. 3b) reflects suchcomplicated terrains. Three different high-wind-speed areas prevail during different times of theyear: (1) the southern Tibetan Plateau fromNovember to April (the westerly jet passes overthe southern Tibetan Plateau with an average windspeed above 20m s�1 from December to March,averaging 28m s�1 in January–February, but itslacks off considerably from April to October); (2)the northern Tibetan Plateau from March to May(the westerly jet across the northern Tibetan Plateauaverages about 12m s�1, which is the highest wind

speed over central Asia during this period, butdiminishes after May as it joins the other branch ofthe westerly jet from the high latitude); and (3)northwest China from May to October (with windspeeds averaging around 11–15m s�1). After May,the 500 hPa high-latitude westerly jet does notcontinue to move to higher latitudes, as does the200 hPa westerly, but moves southward to 421Nuntil September. Then it returns northward again tothe area near 601N. From November to March the500 hPa westerlies over the central Asian continentmost significantly affect the southern and centralTibetan Plateau, and during the late Fall–Winterperiod this region experiences the highest frequencyof dust storms on the Tibetan Plateau. The highestwind speeds on the Plateau occur from January toFebruary, in agreement with the months of thehighest and second-highest frequencies of duststorms (Fig. 1). During the period of March to

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May, the northern branch of the westerly jetsignificantly impacts the northern Tibetan Plateauand Hexi Corridor regions. Although the windspeeds average only about 12m s�1, the surfacetopographic effects can accelerate the surface windspeed in the Hexi Corridor region. During thistransitional period between winter and spring, thewesterly jet fluctuates markedly and leads to thefrequent intrusion of cold air from the north to thesouth, coupling with abundant dust sources in thedesert and Gobi regions, resulting in the mostfrequent dust storms. During June to October, awesterly jet at 601N moves southward to the areanear 421N and joins the northern branch of thewesterly current flowing around the plateau, therebyleading to a slight increase in the lower surface windspeed. The blowing sand process often replaces thedust-storm process in the higher-latitude regionssuch as Teaching, where the highest frequency ofblowing sand occurs in July or August. This mayrelate to the prolonged presence of the high-levelwesterly jet over the region, and the acceleration ofthe westerly velocity in July–August (Fig. 3).Clearly, the shift of monthly dust-storm sourceregions correlates better with the intensity andlocation of the 500 hPa westerly jet than with thatof the 200 hPa jet, especially for the low-elevationregion.

Num

ber

Fig. 4. Interannual changes of dust-storm s

3. Interannual shifts of dust source regions

Based on the monthly variation of dust stormsdiscussed above, dust-storm source regions can bedivided into three regions from the south to thenorth: the Tibetan Plateau, the Hexi Corridor, andMongolia. We find that these dust-storm sourceregions have also fluctuated significantly overseveral years (Fig. 4).

A period with a high frequency of dust stormslasted from the 1970s to the mid-1980s on theTibetan Plateau (e.g., at the Shennzha and Wudao-liang stations) (Fig. 4). Based on the 1961–2000NECP reanalyzed 500 hPa zonal wind speed dataover the Plateau (20–401N, 60–1101E) from De-cember to March (Fig. 5a), the interannual changeshows a significant positive correlation betweenwind speed of the westerly jet and the dust-stormfrequency. The correlation coefficient is 0.45 at a0.01 confidence level at Wudaoliang and 0.35 at 0.05confidence level at Shenzha. The highest dust-stormfrequency on the plateau correlates closely with thestrongest westerly winds during the 1970s and mid-1980s, whereas the lowest dust-storm frequencycoincides with the period with a weaker westerly jetduring the early to mid-1960s and the 1990s. Dust-storm frequency does not significantly correlatewith the East Asian winter monsoon, since the latter

ource regions in China and Mongolia.

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Fig. 5. (a) Interannual changes of the 500 hPa average zonal wind speed over the Tibetan Plateau (20–401N, 60–1101E) from December to

March, (b) index of East Asia winter monsoon (calculated from mean sea-level pressure according to the definition by Bai and Shi, 2004),

and (c) the averaged Arctic oscillation index from January to December.

Y. Han et al. / Atmospheric Environment 42 (2008) 2358–2368 2363

does not reach the Tibetan Plateau. Hence, duststorms on the Plateau are of the ‘‘westerly jet type’’,and the high-level westerlies drive their creation(Fang et al., 1999a, 2004; Fang, 1999b).

The Hexi Corridor region (Minqin station)experienced two periods with high frequencies ofdust storms, the early 1960s and the 1970s to mid-1980s (Fig. 4). The dust-storm frequency correlatespositively with the wind speed of both the 500 hPawesterly jet and lower levels over the region(40–451N, 80–1101E) (correlation coefficient 0.33at 0.05 confidence level), as well as correlating withthe low-level East Asia winter monsoon (correlationcoefficient 0.35). The dust-storm frequency shows anegative correlation with the AO index (correlationcoefficient �0.36) (Fig. 5c). This suggests that theeffect of high mountains such as on the TibetanPlateau and in the Altai and Qilian Mountains maysignificantly weaken the influence of the upperwesterly on the dust-storm processes in the low-elevation Hexi Corridor region. In the early 1960s,dust storms were affected mainly by the East Asia

winter monsoon controlled by the Siberian High.After the 1970s, they appear affected by the zonalwind speed at 500 hPa and also by the AO and EastAsia winter monsoon.

In the Mongolian region, the frequency of thedust-storm occurrence increases rapidly from lowvalues before 1974 to high values after that(Natsagdorj et al., 2003) (Fig. 4). Dust-stormfrequency over Mongolia (April–August) does notcorrelate with the East Asia winter monsoon andthe zonal wind speed of the 500 hPa jet, but doescorrelate with the average AO index in Decemberand January (correlation coefficient 0.31). Since1970, the AO has increased and was in its positivephase after 1987. During the period following 1970,the average temperatures gradually increased incontinental central Asia and East Asia, resulting inmore arid conditions in these regions. The polarvortices continually moved northward from EastAsia to the polar regions, weakening the SiberianHigh and Aleutian Low and causing a shallowertrough over East Asia (Wu, 2002). These factors led

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to an earlier northward migration and later south-ward retreat of the location of the westerly jet thanin normal years and the stagnation of the westerlyjet over the region. The number of times that coldair invaded central Asia decreased and the path ofthe cold air masses moved through the statisticallywell-known northeast pathway (Gong, 1999). As aconsequence, dust-storm activity on the TibetanPlateau and in the Hexi Corridor region has alsoshown a gradual decrease, while increasing innorthern Mongolia.

4. Discussion

Many researchers consider dust-storm events tobe generated by the winter monsoon and high-levelwesterly jet in central Asia (Duce et al., 1980; Pye,1987; Zhou et al., 2002; Fan and Wang, 2004; Fanget al., 2003; Sun, 2004). Studies of both the paleo-and modern climates indicate that the strengtheningof the westerly jet and the Siberian High issynchronous (Pye, 1987; Gong, 1999; Yu et al.,2001). Therefore, proxies that precisely reflect thechanges in intensity and location of the mid-latitudewesterly jet in central Asia might contribute to anunderstanding of the shift of dust source regionsand related climate changes over Asia and theNorth Atlantic. Westerly circulation ranks high as acause of the paleoclimatic changes over the LoessPlateau, Tibetan Plateau and the high latitudes(Ding et al., 1999; Fang et al., 1999a, b, 2003).Thompson and Wallace (1998) introduced the AOas the main pattern of atmospheric circulation in theNorthern Hemisphere. The AO can better reflect thechange in the intensity of the Northern Hemispherewesterly belt than the zonal indexes introduced by

Fig. 6. Correlation coefficients (black and white shades) between the A

(b) meridional wind speeds, during January–April in central Asia and

Rossby (1939) or the North Atlantic oscillation(NAO) (Dickson et al., 2000; Thompson et al.,2000). Furthermore, the AO has a close relationshipwith the East Asia winter monsoon by affecting theSiberian High and Aleutian Low (Gong et al.,1999). The high correlation between the AO and the500–200 hPa zonal and meridional wind speeds inthe Northern Hemisphere over the same period of1961–2000 indicates a rather constant relationshipbetween them, maintaining a relatively stablecorrelation pattern independent of season, year, orheight (Gong et al., 1999). The correlation betweenthe AO and the 500 hPa zonal wind speed (Fig. 6a)shows a continuous circumpolar zone of positivecorrelation in the high-latitude region north ofroughly 501N. The centers lie in the North AtlanticOcean (correlation coefficient 0.7–0.9) and Siberia(0.3–0.6). However, the correlation becomes sig-nificantly negative in the mid-latitude region, but,unlike in the high latitudes, the regions of negativecorrelation are markedly discontinuous. This regionalso shows two highly correlated of significanceareas: the Atlantic and Europe (correlation coeffi-cient �0.7 to �0.8), and northern China, with itscenter around Shanxi, Gansu, Ningxia and westernInner Mongolia (correlation coefficient �0.6).However, the AO and meridional wind speed ofthe westerly jet over China, Mongolia, and Siberiaexhibit a significant positive correlation, with acoefficient of 0.4–0.6 (Fig. 6b). A stronger meridio-nal wind speed tends to increase the intensity of thesummer monsoon and thereby brings more pre-cipitation to northern China. Since the 1970s, thewinter AO has shown a significant strengthening(Thompson et al., 2000), resulting in the 500 hPawesterly speed weakening in China. Further, it has

rctic oscillation index and (a) the 500 hPa zonal wind speeds, and

the Tibetan Plateau. Inset box indicates the studied region.

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been observed that the annual mean surface windspeed over China has also decreased steadily by28% from 1969 to 2000, due to global warmingfrom human activity (Xu et al., 2006). This impliesthat the human activity may enhance the naturalprocess or both mechanisms work together. Withthe AO strengthening, the temperatures in themiddle and high latitudes of Asia have risen andthe Siberian high and Aleutian low have weakened,so that the Asian winter monsoon and the westerlyin the mid-latitudes of Asia are weakened as well.Thus, cold air invading East Asia decreases ormoves via a more northeasterly pathway (Gong,1999). As a result, dust-storm activities on theTibetan Plateau and in the Hexi Corridor regionhave also gradually decreased, and the dust-stormcenter has moved gradually northwards from theTibetan Plateau (in the 1970s to mid-1980s) tonorthern Mongolia (Fig. 4).

From the analysis of the origin of the Luochuanloess on the Chinese Loess Plateau, Zhang et al.(1997) concluded that the eolian source region inChina has an orbital–timescale shift (Fig. 7). Duringglacial periods, dust aerosols from the westerndeserts in China played an important role, whereasin interglacial periods dust aerosols from thenorthern desert region (mid-western part of the

Fig. 7. Comparison of the contributions of aluminum (Al) to desert

loess–paleosol sequence (Zhang et al., 1977), with North Atlantic Heinr

deserts in China; (b) Northern deserts in China or Mongolia; and (c) H

Mongolia region) played a more dominant role(Zhang et al., 1997). This past dust source regionchange in concert with paleoclimatic fluctuationsmatches the modern interannual change of dust-storm source regions mentioned above, suggestingthat the shift in dust source regions occurs atvarious timescales.

The winter AO not only markedly influences thecirculation of the Arctic, North Atlantic (Dickson etal., 2000), and central Asia, but also affects theextent of sea-ice in the Arctic (Wu, 2002). When thewinter AO is in its positive phase, an increasedseawater temperature at 200m in the North Atlanticleads to an increase in the seawater flux from theNorth Atlantic to the Barents Sea. This gives rise tomore warm seawater moving into the Arctic region,thus decreasing the extent of the sea-ice in theArctic. In contrast, vice versa (Wu, 2002). Duringglaciations, the reduced seawater temperature in theNorth Atlantic may have resulted in a temperaturedecrease of the seawater in the Arctic, leading to anextension of the Arctic sea-ice and a negative-phaseAO. This would enhance the westerlies crossingnorth China and Mongolia, decrease the tempera-ture in central Asia, intensify the Siberian High, andthereby strengthen the East Asia winter monsoonand dust activities. The source regions would also

and Asian dust, based on concentrations from the Luochuan

ich events (Heinrich, 1988) during the last glaciation. (a) Western

einrich events.

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greatly expand and the dust-storm center movessouthwards in central Asia. This sequence of eventswould have resulted in coarser and thicker loessdeposition on the Loess Plateau and TibetanPlateau than during the interglacial period. Theincreased dust aerosol in desert regions of westernChina correlates significantly with the temperaturedrop of the North Atlantic surface water and theatmospheric cooling of Greenland (Zhang, 2001).Such results have also been recorded by the loesssequences (Fang, 1999b; Lu et al., 2004) and icecores on the Tibetan Plateau (Wu et al., 2004),where the coarser size fractions from stronger duststorms correlate well with cold surges of theHeinrich events (Heinrich, 1988) and the Bondcycles (Bond et al., 1993). These correlations lendpaleoclimatic support for the interpretation of theevents above. In addition, the East Asian wintermonsoon controlled by the Siberian High is a fairlythin system, with air mass staying mostly atelevations below 2000m. Consequently, the effectof the East Asian winter monsoon is chieflyrestricted to East Asia, and cannot reach theTibetan Plateau (Tang et al., 1998). Accordingly,the close correlations between climate of the LoessPlateau, climate of the Tibetan Plateau, and marinedeposits at the millennial scale suggest the existenceof a high-grade atmospheric circulation system thathas a substantial impact and can simultaneouslycontrol climates in both the eastern and westernhemispheres. The AO is not only closely related tothe East Asia winter monsoon (Gong, 1999), butcan also reflect both the westerly intensity at mid-latitudes in the Northern Hemisphere and the NAO(Dickson et al., 2000; Thompson et al., 2000). Byway of the AO, the climate changes of East Asiacould be well connected not only to the NorthAtlantic but also to the long-distance dust transportand deposition. Thus, the AO variations might exertthe final driving mechanism for the shift of dustsource regions at various timescales, from inter-annual to millennial, and for the roughly synchro-nous changes of paleo-climates recorded in Chineseloess and deep-sea sediments.

5. Conclusions

In this study, we have used data of the duststorms in China and Mongolia and the data fromthe NECP to explore the relationships among thecentral Asia dust storms, the AO, the East Asian

continent westerly and the East Asian wintermonsoon. The study results are as follows:

(1)

The monthly shift of dust-storm source regionscorrelates closely with the location of the200 hPa westerly jet over central Asia and theTibetan Plateau, as well as with the location andintensity of the 500 hPa westerly jet, despitesome complications due to topographic effects(e.g., the Tibetan Plateau, the Altai and QinglianMts.).

(2)

Various processes drive the interannual shifts ofthe dust-storm source regions: the westerly jetcontrols the shifts on the Tibetan; the intensityof the central Asian mid-latitude westerly, theAO, and the East Asian winter monsoon drivethe shifts in the Hexi Corridor region; and theAO and the location of the westerly jet drive theshifts in the Mongolian region.

(3)

The AO can reflect in a large extent the changein the intensity of the Northern Hemispherewesterly belt and has a close relationship withthe East Asia winter monsoon by affecting theSiberian High and Aleutian Low. In addition,variations of the AO could provide a relation-ship between climate changes of East Asia andthe North Atlantic, with the long-distancetransport of dust. Such a relationship mayexplain the shifts in dust source regions atinterannual and millennial timescales and theroughly synchronous climate changes recordedin the Chinese loess and deep-sea sediments inthe North Atlantic Ocean.

Our results suggest the AO is likely to be thecrucial climate system to reveal the causes of shift ofdust source regions and the relations with climateevents among Central Asia, the Pacific and theNorth Atlantic. This provides a potential approachto understand better some important scientificquestions such as the source of loess, links amongeolian dust–pacific plankton–atmosphere CO2 con-centration–climate changes and land eco-environ-ment evolution in the dust source regions.

Acknowledgments

This study was co-supported by the NationalNatural Science Foundation of China (40675053,40401054, 40571171) and National Basic ResearchProgram of China (2005CB422001). We thank

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Dr. Bill Isherwood for valuable comments andEnglish improvement.

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