Simulated regional transport structures and budgets of dust aerosols during a typical springtime dust storm in the Tarim Basin, Northwest China

Journal Pre-proof Simulated regional transport structures and budgets of dust aerosols during a typical springtime dust storm in the Tarim Basin, Northwest China

Lu Meng, Xinghua Yang, Tianliang Zhao, Qing He, Ali Mamtimin, Minzhong Wang, Wen Huo, Fan Yang, Chenglong Zhou, Honglin Pan PII:

S0169-8095(19)31192-5

DOI:

https://doi.org/10.1016/j.atmosres.2020.104892

Reference:

ATMOS 104892

To appear in:

Atmospheric Research

Received date:

11 September 2019

Revised date:

5 January 2020

Accepted date:

5 February 2020

Please cite this article as: L. Meng, X. Yang, T. Zhao, et al., Simulated regional transport structures and budgets of dust aerosols during a typical springtime dust storm in the Tarim Basin, Northwest China, Atmospheric Research(2019), https://doi.org/10.1016/ j.atmosres.2020.104892

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© 2019 Published by Elsevier.

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Simulated regional transport structures and budgets of dust aerosols during a typical springtime dust storm in the Tarim Basin, Northwest China 1,2

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Lu Meng , Xinghua Yang , Tianliang Zhao , Qing He , Ali Mamtimin , Minzhong Wang

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Wen Huo , Fan Yang , Chenglong Zhou , Honglin Pan

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Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Key

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Institute of Desert Meteorology, China Meteorological Administration, Urumqi 830002, China

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Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing

Corresponding author at:

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University of Information Science &Technology , Nanjing, Jiangsu 210044, China

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Institute of Desert Meteorology, China Meteorological Administration, Urumqi 830002, China

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E-mail addresses: [email protected]

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Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, Nanjing University of Information Science &Technology , Nanjing, Jiangsu 210044, China;

E-mail addresses: [email protected]

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Abstract

Occupying an area of about 1,020,000 km 2 with the sparse vegetation and the Taklimakan Desert（TD）, The Tarim Basin (TB) is isolated by the surrounding mountains and plateaus, especially to the north of the Tibetan Plateau (TP) with a large drop in elevation. An intense dust storm occurring over TB, Northwest China from April 27 to May 1, 2015 was simulated by using

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the Weather Research and Forecasting model with chemistry (WRF-Chem v3.8.1). The sources of dust emissions were centered over the northeastern TB with the high dust emission flux reaching

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24μgm-2 s -1 injected by strong near-surface northeasterly winds from basin mouth invading the TD.

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A large amount of dust aerosols accumulated in the windward northern slope of the TP. Dry

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deposition is the dominant removal process of dust aerosols from the atmosphere over the arid TB. The spatial distribution of dust dry deposition in the TB was similar to the columnar dust loading

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pattern during this dust storm event. With the impacts of the TB deep terrain structures on

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atmospheric circulation, the high column loading of dust aerosols was concentrated over the

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southeastern TB, where dust aerosols mainly accumulated at the lower troposphere below 3000m. Once dust aerosols were lifted at a high elevation (>3500m), they were exported from the TB driven by the westerlies in the free troposphere, and the zonal transport flux of dust aerosols (>3000 μgm-2s -1 ) peaked at an elevation of approximately 4000m along 41° N over the TB. The eastern border of TB was found to be the largest contributors to dust export from the TB. It was estimated for this intense dust storm that among the dust aerosols emitted from the dust emission sources over the TD, about 22.28% of dust aerosols were relatively inefficiently exported for the downwind dust regional transport from the TB compared to about 27.17% dust aerosols deposited 2

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on the basin surface, and a high fraction of about 50.54% dust aerosols suspending in the atmosphere over the TB, implying a significant implication of dust aerosols from the TD for climate and environment over the central Asian region.

Keywords: Tarim Basin; dust aerosols; WRF-Chem simulation; regional transport; aerosol budget

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1. Introduction

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Mineral dust is the most abundant atmospheric aerosol component, contributing more

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than half of the total global aerosol burden (Andreae et al., 1986; Zender et al., 2003). Dust

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particles affect the Earth’s radiative budget both directly through altering the radiative balance

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between the incoming solar and outgoing planetary radiation in the atmosphere (Sokolik and Toon, 1996; Fu et al., 2009; Han et al., 2012; Zhao et al., 2013) and indirectly by modifying

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the microphysical properties of clouds and radiative properties as the cloud condensation

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nuclei (Ilan et al., 2004; Su et al., 2008; Huang et al., 2010, 2014). The long-range transport

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of dust aerosols not only causes significant changes in radiative forcing and atmospheric chemistry over large areas but also links the biogeochemical cycle of land, atmosphere, and ocean through deposition (Duce et al., 1980; Zhang et al., 1993; Chen et al., 2013; Choobari et al., 2014). The suffering of those in the world from dust storm and therefore caused substantial climatic variability have attracted worldwide attention (Choobari et al., 2014; Wang et al., 2010; Zhao et al., 2011).

The Taklimakan Desert (TD) is one of the largest deserts in the world, and is located in the Tarim Basin (TB) isolated by the Tian Shan Mountains to the north, the Kunlun and the 3

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Altun Mountains connecting with the Tibetan Plateau (TP) to the south and southeast, and the Pamir Plateau to the west with the only an open in the northeastern TB edge (Sun et al., 2001). The TD is one of the most important sources of Asian dust emissions (Gong et al., 2003). Under the influence of the meteorology forced by the large topography of the basin, coupled with the strong desert surface heating, the convection and turbulence movements over the

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underlying desert surface result in the special structures of the atmospheric boundary layer in

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the TD (Raman et al., 1990; Zhang et al., 2011). The "ultra-high" boundary layer at a height

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of 3000-5000m and the unique weather phenomenon of persistently suspending dust aerosols

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are formed in summer over the TB (Li et al., 2015). Emission, deposition, transport and

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spatiotemporal variation of dust aerosols are all restricted by the special boundary layer over the basin, leading to the unique spatiotemporal variation aerosols persistently suspending in

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the atmosphere over the TB and regional transport of dust aerosols from the TB, which is a

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series of climate changes to be further studied.

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Emission, deposition, regional transport and spatiotemporal variation of dust aerosols are of great scientific significance to the environment and climate changes. A dust storm involves the processes of dust emission from the source region, dust aerosol transport and suspending at various atmospheric levels, and then deposition on both the source region and downwind regions (Duce et al., 1980; Uno et al., 2001; Zhao et al.,2003; Li et al., 2015). Deposition is a major process by which dust aerosols are removed from the atmosphere. Deposition could remove dust from the atmosphere but is also bring nutrient pollution to the source region (Frie et al., 2019). When dust particles deposit, they can be sources of essential 4

Journal Pre-proof nutrients or deadly toxicants and also change the Earth’s surface albedo. Increasing evidence from epidemiologic studies suggests that fractions of dust differentially contribute to adverse health outcomes across a range of settings (Liu et al., 2019). Over the arid dust source areas, a large amount of dust aerosols are removed by dry deposition (Zhao et al., 2003). Based on the 44-yr averaged dust budgets, an annual total of 120 Mt of dust aerosols were emitted into the

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atmosphere from Asian desert regions. Of this, most of dust aerosols were deposited in the

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desert regions (51%), part were deposited onto non-desert regions of the Asian subcontinent

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(21%), and some of dust aerosols were transported to the Pacific Ocean and beyond

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(26%)( Zhao et al., 2006). As for the TD, the horizontal dust flux was estimated to be around

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40–50 Ggd-1 (Hara et al., 2008) in summer. Of this, around 30.8 Gg of dust was exported to the Pacific Ocean, of which 65% was deposited in the Pacific Ocean and 18% was transported

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much further, even to the North Atlantic (Yumimoto et al., 2009). In addition, there are part

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of dust that persistently floating in the upper boundary layer with important effects on

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regional aerosol loading and radiation forcing (Li et al., 2015).

Dust aerosols from the TB could be transport to downwind eastern China and the Pacific Ocean with on occasion reaching the North Pacific under the influence of the westerly jets (Duce et al., 1980; Uno et al., 2001; Zhao et al., 2003; Yumimoto et al., 2009; Cottle et al., 2013). The regional transport of Asian dust aerosols from the deserts to East Asian offshore regions were entrained at an elevation of 3000m. However, a small part of the dust aerosols were uplifted into the free troposphere for trans-Pacific transport at 3000–10000m along the latitude 40° N (Zhao et al., 2006). Yumimoto K et al. (2009) showed that a dust veil 1000– 5

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4000m thick was transported between 4000–10000m elevation over eastern Asia, the Pacific Ocean, North America, and the Atlantic Ocean. To understand the transport mechanism of TD dust aerosols to the TP, the model Weather Research and Forecasting model with chemistry (WRF-Chem; v3.8.1) was used to simulate the dust aerosols over eastern Asia Dust aerosols from the TD dust emission sources deposited on the northern slope of TP at the rate of 6.6

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Ggd-1 (Chen et al., 2013).

Due to the deep basin of TB with special impacts of topography on atmosphere

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especially the boundary layer, the spatiotemporal variations of dust aerosol emissions,

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loadings, depositions over the TB with the contribution of regional dust aerosol transport have

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been poorly and even understood comparing to the other Asian deserts with the plain terrains. In this study, the model WRF-Chem was employed to simulate a dust storm event in spring,

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2015 over the TB with further investigation on the dust aerosol budget and transport

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structures over the TB during a dust storm from April 27 to May 1, 2015, following the

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simulation validation and analyses on dust aerosol structures in the companion paper (Meng et al., 2018). Section 2 of this paper described the WRF-Chem modeling settings. Section 3 discussed the dust aerosol emission, loading, and deposition (Section 3.1) as well as the structures of dust transport (Section 3.2) and estimation of the dust aerosol budget (Section 3.3) over the TB. A summary and the outlook for future studies were presented in Section 4.

2. Model settings and validation

For this study, we used the version 3.8.1 of WRF-Chem (Grell et al., 2005) to simulate

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dust aerosol transport within the TB during the study period lasting 8 days starting on April 24, 08:00CST (Chinese Standard Time: UTC+8:00, the same as hereinafter), and the first two days ran as the spin-up period. The initial conditions and the lateral boundary conditions for the modeling were drawn from ERA-Interim reanalysis data available at the spatial resolution of 0.25*0.25 degree and temporal resolution of 6 hrs. The model domains and the topography

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of the target regions were shown in Fig. 1. The WRF-Chem simulation was performed using

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two-way nesting with an outer domain (domain 1) at 16000m horizontal resolution covering

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the TB and surrounding areas with 150×150 grid points and an inner domain (domain 2) at

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4000m horizontal resolution with 345×197 grid points. The TB region in domain 2 included 5

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observation sites: 1) Kashi (KSH), 2) Akesu (AKS), 3) Kuerle (KEL), 4) Tazhong (TZH) and 5) Hetian (HT) (Fig. 1). The simulation was configured with 50 vertical layers up to 100hPa.

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The physical parameterizations used in the WRF-Chem setup were shown in Table. 1. The

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asymmetric convective model, version 2 (ACM2) planetary boundary layer (PBL) scheme

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(Pleim 2007a, b), Noah land surface module (Chen et al., 1996; Chen and Dudhia, 2001), RRTM longwave radiation scheme (Mlawer et al., 1997), the Goddard shortwave scheme, and Morrison two-moment microphysics scheme (Morrison et al., 2005）were used in this study. The GOCART dust emission scheme was coupled with fractional erosion data within the WRF-Chem framework. A detailed description of the GOCART dust emission scheme has been given in Meng et al. (2018), including the mathematical formulation of the dust emiss ion flux in the GOCART scheme, along with the amended soil moisture of desert surface.

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Fig. 1. The nesting domains 1 (entire area) and 2 (area in the white rectangular), and the locations of 5 observation

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sites over the TB isolated by the Tianshan M ountains (TM ) to the north, the Pamir Plateau (PP) to the west and the

Tibetan Plateau (TP) to the south and southeast with the only an open mouth in the northeastern TB edge and the

terrain elevations (m in a.s.l.) in color contours（M eng et al., 2018）.

Table 1. Namelist settings of the physical parameters used in the WRF-Chem setup

Physical parameters

Namelist variable

M odel

Land surface

sf_surface_physics

Noah land-surface model

PBL model

bl_pbl_physics

ACM 2 scheme

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sf_sfclay_physics

Pleim-Xiu

M icrophysics

mp_physics

M orrison 2-moment scheme

Shortwave radiation

ra_sw_physics

Goddard shortwave scheme

Long-wave radiation

ra_lw_physics

RRTM scheme

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Surface similarity

The modeling evaluations with ground-based and remote sensing observation data for

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this 2015 springtime dust storm were detailed description in the companion paper (Meng et al.,

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2018).The results showed that the WRF-Chem model could capture the temporal

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characteristics of the meteorological and PM10 data.

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3. Simulation analysis

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In this study，we focused on a typical dust event over the TB that occurred from April 27

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to May 1, 2015. On April 26, a high-pressure system in the Ural Mountains moved towards northwest China. Accompanying the advanced of high pressure system on April 27, cold northwesterly near-surface winds gradually became stronger over northwestern China, and in the meantime, a low-pressure system developed over the TB. The force from a strong pressure gradient blew cold wind into the basin acrossed the Pamirs Plateau. Meanwhile, part of the cold air changed direction and blew into the basin through crossing the Tianshan Mountains. With continuing southeastward movement of the high-pressure center, the strong northeast winds entered the northeast opening to the basin on April 28. In the following days, the dust 9

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storm occurred across the TB dominated by the strong northeast winds (Meng et al., 2018).

In the following subsections, we discussed the dust aerosol emission, loading and deposition over the TB, analysed the structures of dust transport, and then estimated the budget of dust aerosols for the dust storm from April 27 to May 1, 2015 over the TB based on the WRF-Chem simulation.

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3.1 Dust emission, column loading, and deposition

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Strong winds invaded into the TB accompanied by high pressure systems for triggering

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dust aerosol emission from the desert into the atmosphere over the TB, that was very

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significant for the dust storm formation and long-range transport of dust aerosols. Fig. 2a showed the spatial distribution of the dust emission fluxes averaged over the dust storm. The

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dust aerosol emissions were summed from all eight bins of dust particles. Dust emission

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mainly occurred over the TD desert region. The dust emissions were centered in the

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northeastern basin mouth of the TB (Fig. 1) with high dust emission fluxes exceeding 24 µgm-2 s-1 driven the stronger northeast winds

accelerated by the channel effect of basin open

mouth over the TB (Fig. 2a). The columnar dust loadings over the TB averaged during the dust storm period were presented in Fig. 2b. The high columnar dust loadings reached more than 3.6 gm-2 were mainly distributed over the southeastern part of the basin and strong emission sources. The dust storm swept southwestwards acrossed the TB driven by strong northeasterly air flows (Fig. 2a) with the portions confined to the windward northern slopes of plateaus uplifting into the upper boundary layer to form a floating dust layer over the TB

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(Figs. 2a-2b), reflecting an integrated effect of the dust emission sources over the desert region and the large topography of TP on dust aerosols suspending in the atmosphere over the TB. Deposition is the major process by which dust aerosols are removed from the atmosphere. In this dust storm period without precipitation over the arid TB, dry deposition was the dominant removal process of dust aerosols with wet deposition being a function of

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precipitation. The spatial distribution of dust dry deposition in the source region was similar

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to the columnar dust loading pattern (Figs. 2b-2c), and high deposition zone along the

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southern part of the basin in associated with a floating dust layer over the windward TB

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region (Figs. 2c and 2a ).

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Fig. 2. Spatial distribution of (a) emission flux (µg m-2 s -1) and 10 m wind vectors, (b) column loading (g m-2), and (c) dry deposition fluxes (µg m-2 s-1) of dust aerosols over the TB averaged during the dust storm from April 27 to

M ay 1, 2015 with terrain height (m) above sea level（black contour lines）.

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As shown in Fig. 3, the temporal change of dust emissions averaged over the TB were compared with the corresponding dust dry depositions averaged there during the springtime dust storm, The averaged dust emission fluxes and dry depositions refer to the regional averaged value for the desert areas in the simulated area during April 26-May 2, 2015. The averaged dust emission fluxes increased sharply to peak values exceeding 0.055 Mt m-2 h-1 at

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00:00CST on April 28, 2015 and then rapidly decreased to below 0.005 Mt m-2 h-1 around

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06:00CST on April 29 during the dust storm in Fig. 3. There was another peak of dust

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emissions averaged exceeding 0.02 Mt m-2 h-1 at 12:00CST on May 1. Although the similar

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patterns of temporal changes in dust emissions and dry depositions over the TB, there were

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some inconsistencies between dust emissions and dry depositions. The magnitudes of the simulated dust emission fluxes averaged over the TB, were higher than the values of dry

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deposition fluxes during the dust storm period, except for April 29–30 with higher dry

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deposition fluxes compared with dust emissions over the TB. The difference between dust

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emission and dry deposition fluxes over the TB on April 29–30 could be resulted from the dust aerosols suspending in the boundary layer （BL）from the peak emissions of dust storm before April 29 over the TB (Fig. 3).

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Fig. 3. Daily variations of dust emissions（edust, red curve）and dry depositions (drydep, black curve) averaged

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over the TB from the WRF-Chem simulation of dust storm during April 26 - M ay 2, 2015.

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Fig. 4. Daily variations of dust loadings in the total column (green area), below 5000m (red area) and 3000m (blue

area) during April 26 - M ay 2 averaged over the TB, 2015.

The dust storm triggered with sharp increases in dust loading in different columns over the TB during April 27–28 (Fig. 4). The values of columnar dust loadings reached the peaks around 00:00CST on April 29, and then gradually decreased with the minor peaks of

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columnar dust loading occurred around May 2. Based on the changes of the boundary layer structures during the dust storm over the TB (Meng et al., 2018), we could select 3000m and

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5000m (a.s.l.) respectively for the heights of lower and upper BL. Less dust aerosols were

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loaded in the atmosphere above 5000m compared with the dust column loadings within the

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BL below 5000m and most of the dust aerosols were concentrated within the lower BL below 3000m during dust storm. These changes of columnar dust loading over the TB could be

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related with effects of TB topography and desert surface on the BL structures suspending dust

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aerosols over the basin. Most of dust aerosols suspended within the BL over the basin, and

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only a few amount of dust particles broke through the BL reaching into the free atmosphere over the TB for long-distance transport.

3.2 Structures of dust transport over the TB

To investigate the structures of dust transport over the TB in this dust storm event, Fig. 5 presented a vertical, longitudinal cross-section of the modeled dust aerosol transport flux and wind vectors of zonal and vertical components along 41° N. The purple arrow represented the vertical circulation of dust transport. Most trans-Pacific dust transport occurred in the middle

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troposphere, where the zonal dust transport fluxes reached a maximum (Zhao et al., 2003). The cross-section at 41° N was selected to cut across the lowest terrain in all meridional cross-sections that contributed to representation of the transport of dust aerosols over the basin. The dust storm started over the basin, that is, it was mainly induced by the cold air entering from the northeast. Wind fields showed that northeasterly air masses were

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predominant in the basin (Fig .2a). The elevated dust particles were blown to the western part

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of basin and blocked by the western part of the Tianshan Mountains, leading to massive dust

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uplifted owing to orographic lifting. Noticeable high dust aerosol transport flux (>3000

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µgm-2 s-1 ) area occurred near 4000m, while the dust layer was dominated by westerly winds

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above the TB. Most of the uplifted dust particles were transported eastwards. A small part of dust particles broke through the BL and entered into the free atmospheric layer. The western

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regions.

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airflows played a predominant role driving dust aerosols acrossed the TB to downwind

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Fig. 5. Vertical sections of zonal components (µg m-2 s -1) of dust aerosol transport flux (contour lines) and wind vectors of zonal and vertical components（vertical wind components multiplied by 50） along 41° N averaged over

April 27 to M ay 1, 2015. The dashes depicted negative values indicating the easterly winds, and the vertical

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circulation of dust transport was denoted by purple arrow.

Fig. 6. Vertical sections of meridional components (µg m-2 s-1) of dust aerosol transport flux (contour lines), and wind vectors of meridional and vertical components（vertical wind multiplied by 50）along 83.66° E averaged over

April 27 to M ay 1, 2015. The dashes depicted negative values representing northerly winds, and the vertical

circulation of dust transport was denoted by purple arrows.

Vertical sections of the meridional components, dust aerosol transport flux, and wind vectors of meridional and vertical components along 83.66° E averaged over April 27 to May 1, 2015 were presented in Fig. 6. During this dust storm, the northerly cold air directly 17

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crossed over the Tianshan Mountains into the basin. Dust aerosols were transported to the southern part of the basin by the strong northerly winds. The minimum of meridional components dust aerosol transport flux center around 38° N was about −4000 µgm-2 s-1 , indicated that the northerly wind favored meridional dust aerosol transport over the TB. A large amount of dust aerosols were transported southward and confined to the windward

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northern slopes of plateaus, accumulated at the foot of the Kunlun Mountains. Owing to

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orographic block lifting, part of dust particles lifted up to 6000–7000m along the slopes of the

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TP. Meanwhile, southerly winds dominated the northern basin above 2000m. The cold air

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flowed into the basin from the northeast was divided into two pathways, the northern one

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splited again, the other flowed towards the Kunlun Mountains. The splited cold air flowed to

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the center of the basin and also transported dust to the Tianshan Mountains.

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Fig. 7. Vertical sections of zonal components (µg m-2 s -1) of dust aerosol transport flux at (a) the eastern border

along 90.00° E and (b) the western border along 75.35° E of TB averaged over April 27 to M ay 1, 2015. The blue

contours depicted negative values that represented easterly winds.

To study the structures of dust transport over the TB from the different borders, we selected the eastern, western, northern, and southern border of the TB as the objects. The East 19

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Asian westerly jet was a strong and narrow westerly belt over the eastern Asia in the upper troposphere and lower stratosphere, most of dust aerosols transported from TB were expected to be zonal (Zhang et al., 2008; Chen et al., 2013). Therefore, for estimation of the amount and direction of zonal components of dust transport flux, we used the product of the dust concentration and the zonal wind component U. Positive (or negative) dust transport fluxes

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indicated eastward (or westward) transport of dust aerosols. As Fig. 7a shown, the maximum

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dust aerosol transport flux at the eastern border of TB averaged during the dust storm reached

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more than 2000 µg m-2 s-1 at 4000–5000m around 40° N, while the minimum occurred below

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2000m. Easterly winds prevailing below 3500m in the basin mouth of TB’s eastern sector.

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The strong easterly cold air invaded into the basin from the northeastern mouth of the TB and stirred up the dust. Once the dust aerosols were entrained in the atmosphere above 3500m,

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they were transported under the influence of the westerly jets. Most of trans-Pacific dust

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transport occurred in the middle troposphere between 4000m and 5000m, where the zonal

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dust transport fluxes reached the maximum(Sun et al., 2001; Yumimoto et al., 2009). In the western sector, the westerly wind extended from the surface to 10000m, and cold air easily intruded eastward into the basin. The maximum of dust aerosol transport fluxes center at the lowest elevation of the Pamir Plateau.

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Fig. 8. Vertical sections of meridional components (µg m-2 s-1) of dust aerosol transport flux at (a) the northern

border along 42.50° N and (b) the southern border along 35.00° N of TB averaged from April 27 to M ay 1, 2015.

The blue contours depicted negative values that represented northerly winds.

The vertical sections of meridional components of dust aerosol transport flux at (a) the 21

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northern and (b) the southern border of TB averaged during the dust storm enabled us to explore the relationship between wind field, and dust transport at different borders (Fig. 8). In the analysis, positive values indicated southerly winds, and negative values indicated northerly winds (Fig. 8). The meridional transport of dust characterized the major southward motion with negative values at the northern border of the TB averaged during the dust storm

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(Fig. 8a). A northerly wind that benefited the transport of dust over the basin from the

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opening mouth between 1000m and 3000m around 87–90° E. The northerly cold air crossed

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over the Tian Shan Mountains into the basin and then blew the dust up, whereas a small part

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of dust particles exported from the northern border. The TB was surrounded by the Kunlun

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and the Altun Mountains to the south, connecting with the TP. Dust transported southward to the northern slope of TP and lifted up to 6000–7000m during the dust storm with the

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maximum occurred around 84° E.

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3.3 Estimation of the dust aerosol budget over the TB

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Fig. 9. Vertical profiles of dust aerosol transport rates (M t h-1) at north, south, west and east borders of the TB

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averaged over April 27 to M ay 1, 2015. Positive and negative values of dust transport rates represented net dust

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imported into and exported from the basin respectively.

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Fig. 9 compared the vertical profiles of dust aerosol transport rates (Mt h-1 ) averaged at the eastern, western, northern and southern borders of TB from April 27 to May 1, 2015, shown the contrasting behaviors over the difference borders. With comparison of the four borders, the maximum of dust aerosol transport rates over 0.01 Mt h-1 occurred over the eastern and northern borders below 3000m. It was shown that part of dust aerosols could extend more than 3000–4000m and exported from the eastern and northern borders of the basin. There were the larger negative transport rates for the eastern border than for the northern border, indicated that most of dust aerosols exported from this direction and reached 23

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the maximum at 4000m. The constantly positive dust transport rates, reaching a maximum of 0.0025 Mt h-1 at the western border of TB, indicated the net dust transported eastward and imported into the basin. To evaluate the transport of TB over the TP, we also presented vertical profiles of the dust aerosol transport rates averaged at the southern border of the TB, which showed dust exported from the basin towards TP below 6000m. Above this elevation,

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indicated a small amount of net dust imported into the basin.

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the dust transport rates were slightly increasing with height and then remained steady,

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Table 2. Dust aerosol budget over the TB during the dust storm from April 27 to M ay 1, 2015

1.84

Dust dry deposition

0.50

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net amount of dust export

Dust suspending in the atmosphere

Percentages of dust emission over the TB

100.00%

27.17%

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Dust emission

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Dust aerosol mass (M t)

0.41

22.28%

0.93

50.54%

Dust aerosol emission, dry deposition and net amount of dust export from the TB for the dust storm period, from inner-domain simulations with 4000m horizontal resolution, were calculated in Table 2. The net amount of dust transport from the TB was obtained by summing the dust imported into and exported from the four borders of TB. Positive and negative values represented the net amount of dust imported into and exported from the TB 24

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respectively. During this dust storm, an total of 1.84 Mt of dust emitted from the dust source regions. Although about 27.17% of the total dust emission were redeposited in the source regions via dry deposition (0.5 Mt). Climatological estimation indicated that 22.28% of the total dust emission particles were either exported from the basin, deposited in non-desert regions, or lifted up into the free troposphere for long-range eastward transport. The

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remaining 0.93 Mt could be attributed to dust suspended in the atmosphere over the basin

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during this dust episode, accounted for 50.54% of the total dust emission over the TB. This

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suggested that persistently suspending dust was an important component over the TB during

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this dust episode. It might not be observed near the surface but could have important effects

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on regional aerosol loading and properties (Li et al., 2015). 25% of the TD dust aerosols were transported to remote areas over East Asia in spring (Chen et al., 2017). Their conclusions

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were not in consistent with those from this paper. In Chen’s paper, the net amount of dust

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export only considered dust aerosols exported from the eastern side of the basin, while the

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results were calculated by summing the exports for the four borders of TB during a typical springtime dust storm in this paper.

4. Conclusions

The dust aerosol budget, and structures of dust transport over the TD during an actual dust storm (April 27 to May 1, 2015) were investigated using the WRF-Chem model. From these analyses, the following conclusions were drawn.

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Under the special topography and complicated meteorological conditions in the target area, the simulated spatial distribution of dry deposition averaged over the basin was similar to the dust column loading which mainly occurred southeastern part of the basin and strong emission sources; whereas dust emission flux occurred mainly over the northeastern mouth of the basin.

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Most of dust aerosols remained confined by the lower BL below 3000m. Dust aerosol

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transport flux reached more than 3000 µgm-2 s-1 around 4000m along the latitude 41° N over

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the TB. As for the meridional transport, a large amount of dust was transported southward and

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lifted up to 6000–7000m along the slopes of the TP.

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The eastern border was found to be largest contributors to the dust transport. At the

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eastern border of TB, dust imported into the basin below 3500m. Once dust aerosols were

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entrained above that height, they exported from the basin under the influence of the westerly

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jets.

Regarding the dust aerosol budget for the TB, 22.28% of the total dust emission particles were exported for downstream long-range transport of dust transport from the TB, which is quite limited, relatively to about 27.17% dust aerosol for dry deposition onto the TB, and the large amount of 50.54% dust aerosols suspending in the atmosphere over the TB, which could exert a large impact on regional changes of climate and environment over the TB and surrounding regions.

In this paper, the estimation of dust aerosol budget was drawn from a typical springtime 26

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dust storm case simulation over the TB. In order to comprehensively understand dust aerosol change with the implication on weather, climate and environment over the TB, more cases need to be further researched. Furthermore, the modeling problems of meteorology and dust aerosol emissions over the complex terrain and deep basin over the study should be addressed in future studies.

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Acknowledgements Funding: This work was supported by The National Science Foundation for Young Scientists of

No.41875019) ， Central ）

，

Atmospheric

Science

Research

Foundation （ Grant

The National Natural Science Foundation of China (Grant No.

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No.CAAS201913

As ia

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(Grant No.41905014) ， The National Natural Science Foundation of China (Grant

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China

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41775030)，Flexible Talents Introducing Project of Xinjiang (2018, 2017)

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Author contributions:

Lu Meng: Conceptualization, simulation, formal analysis, visualization, original draft; writing.

Xinghua Yang: Methodology, resources, supervision, Writing- Original draft preparation, project administration

Formal analysis, review & editing.

Minzhong Wang: Investigation.

Investigation.

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Fan Yang:

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Wen Huo: Investigation.

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Ali Mamtimin:

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Data curation, software, visualization.

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Qing He:

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Tianliang Zhao: Conceptualization, funding acquisition, resources, supervision, review & editing.

Chenglong Zhou: Resources.

Honglin Pan: Data curation.

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Declaration of interests

The authors declare that they have no known competing financial interests or personal

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relationships that could have appeared to influence the work reported in this paper.

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The Taklimakan Desert (TD) is located in the Tarim Basin (TB) isolated by the surrounding

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mountains and plateaus with the only an open in the northeastern TB edge. The effect of

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topography especially the Tibetan Plateau on dust aerosol distribution over the TB. Once dust aerosols were lifted at a high elevation (>3500m), they were exported from the TB driven by the westerlies in the free troposphere, and the zonal transport flux of dust aerosols (>3000 μgm-2 s-1 ) peaked at an elevation of approximately 4000m along 41° N over the TB. The eastern border of TB was found to be the largest contributor to dust export from the TB. The high fraction of 50.54% dust aerosols suspending in the atmosphere over the TB potentially exerted a large impact on regional changes of climate and environment over the TB for this dust storm event.

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• A strong effect of the Tibetan Plateau on the dust aerosol distribution over the Tarim Basin. • The zonal transport flux of dust aerosols peaked at an elevation of approximately 4000m over the Tarim Basin. • The eastern border of Tarim Basin was found to be largest contributor to the downwind regional transport of dust aerosols.

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• A high fraction of about 50.54% dust aerosols suspending in the

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atmosphere over the Tarim Basin.

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