Dust plumes over the Pacific, Indian, and Atlantic oceans: Climatology and radiative impact

Zhu, Aimei; Ramanathan, V.; Li, Fang; Kim, Dohyeong

doi:10.1029/2007jd008427

Cited by 188 publications

(151 citation statements)

References 124 publications

(164 reference statements)

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“…Off western Africa, NAMMA airborne observations pointed out that the SAL generally extends up to 4 to 6.5 km, with a characteristic temperature inversion at its base at about 2 km (Ismail et al, 2010), which agrees with shipborne lidar measurements in the same region (Immler and Schrems, 2003). Also, SAGE II climatological data reveal one dust layer in the eastern north tropical Atlantic located between 2 and 6 km (Zhu et al, 2007). On the The cyan line at 6.5 km of each cross section marks the ocean, while the color line above it, between 7 and 8 km, is the MODIS AOD at 550 nm.…”

Section: Summer (Jja)supporting

confidence: 64%

“…The SAL has been studied at dedicated sites with observations at both sides of the tropical Atlantic (e.g., Chiapello et al, 1995;Prospero and Lamb, 2003), during specific campaigns (e.g., Reid et al, 2002;Ansmann et al, 2009) or using space observations (e.g., Zhu et al, 2007;Doherty et al, 2008). Some campaigns have used lidar observations in order to describe the vertical distribution of SAL, e.g., LITE, SHADE, AMMA, SAMUM, AMAZE-08 and SALTRACE.…”

mentioning

confidence: 99%

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The seasonal vertical distribution of the Saharan Air Layer and its modulation by the wind

Chédin²,

et al. 2013

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Abstract. The Saharan Air Layer (SAL) influences largescale environment from western Africa to eastern tropical Americas, by carrying large amounts of dust aerosols. However, the vertical distribution of the SAL is not well established due to a lack of systematic measurements away from the continents. This can be overcome by using the observations of the spaceborne lidar CALIOP onboard the satellite CALIPSO. By taking advantage of CALIOP's capability to distinguish dust aerosols from other types of aerosols through depolarization, the seasonal vertical distribution of the SAL is analyzed at 1 • horizontal resolution over a period of 5 yr (June 2006-May 2011. This study shows that SAL can be identified all year round displaying a clear seasonal cycle. It occurs higher in altitude and more northern in latitude during summer than during winter, but with similar latitudinal extent near Africa for the four seasons. The south border of the SAL is determined by the Intertropical Convergence Zone (ITCZ), which either prohibits dust layers from penetrating it or reduces significantly the number of dust layers seen within or south of it, as over the eastern tropical Atlantic. Spatially, near Africa, it is found between 5 • S and 15 • N in winter and 5-30 • N in summer. Towards the Americas (50 • W), SAL is observed between 5 • S and 10 • N in winter and 10-25 • N in summer. During spring and fall, SAL is found between the position of winter and summer not only spatially but also vertically. In winter, SAL occurs in the altitude range 0-3 km off western Africa, decreasing to 0-2 km close to South America. During summer, SAL is found to be thicker and higher near Africa at 1-5 km, reducing to 0-2 km in the Gulf of Mexico, farther west than during the other seasons. SAL is confined to one layer, of which the mean altitude decreases with westward transport by 13 m deg −1 during winter and 28 m deg −1 , after 30 • W, during summer. Its mean geometrical thickness decreases by 25 m deg −1 in winter and 9 m deg −1 in summer. Spring and fall present similar characteristics for both mean altitude and geometrical thickness. Wind plays a major role not only for the transport of dust within the SAL but also by sculpting it. During winter, the trade winds transport SAL towards South America, while in spring and summer they bring dust-free maritime air masses mainly from the North Atlantic up to about 50 • W below the SAL. The North Atlantic westerlies, with their southern border occurring between 15 and 30 • N (depending on the season, the longitude and the altitude), prevent the SAL from developing further northward. In addition, their southward shift with altitude gives SAL its characteristic oval shape in the northern part. The effective dry deposition velocity of dust particles is estimated to be 0.07 cm s −1 in winter, 0.14 cm s −1 in spring, 0.2 cm s −1 in summer and 0.11 cm s −1 in fall. Finally, the African Easterly Jet (AEJ) is observed to collocate with the maximum dust load of the SAL, and this might promote the differential...

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Section: Summer (Jja)supporting

confidence: 64%

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confidence: 99%

The seasonal vertical distribution of the Saharan Air Layer and its modulation by the wind

Chédin²,

et al. 2013

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“…As a result, in between rainy days, the aerosol concentration builds up. For example, dust concentrations reach peak values during the monsoon season (Zhu et al, 2007) because dust transport into India reaches a peak during the wet season.…”

Section: The Large Scale Context Of the Observationsmentioning

confidence: 99%

Black carbon emissions from biomass and fossil fuels in rural India

et al. 2011

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Abstract. Black carbon (BC) emission from biofuel cooking in South Asia and its radiative forcing is a significant source of uncertainty for health and climate impact studies. Quantification of BC emissions in the published literature is either based on laboratory or remote field observations far away from the source. For the first time under Project Surya, we use field measurements taken simultaneously inside rural households, ambient air and vehicular emissions from highways in a rural area in the Indo-Gangetic-Plains region of India to establish the role of both solid biomass based cooking in traditional stoves and diesel vehicles in contributing to high BC and organic carbon (OC), and solar absorption. The major finding of this study is that BC concentrations during cooking hours, both indoors and outdoors, have anomalously large twice-daily peak concentrations reaching 60 µg m −3 (median 15-min average value) for indoor and 30 µg m −3 (median 15-min average value) for outdoor during the early morning (05:00 to 08:00) and early evening (17:00 to 19:00) hours coinciding with the morning and evening cooking hours. The BC during the non-cooking hours were also large, in the range of 2 to 30 µg m −3 . The peak indoor BC concentrations reached as high as 1000 µg m −3 . The large diurnal peaks seen in this study lead to the conclusion that satellite based aerosol studies that rely on once-daily daytime measurements may severely underestimate the BC loading of the atmosphere. The concentration of OC was a factor of 5 larger than BC and furthermore optical data show that absorbing brown carbon was a major component of the OC. The imprint of the cooking hour peaks were seen in the outdoor BC both in the village as well as in the highway. The results have significant implications for climate and epidemiological studies.

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“…Between the two spectrum ranges, the SW DREs are larger compared to the LW ones, in absolute terms, thus explaining their predominance when the corresponding calculations are made for the NET (SW + LW) radiation (e.g. Pérez et al, 2006;Zhu et al, 2007;Woodage and Woodward, 2014). The perturbations of the radiation budget at the surface and in the atmosphere determine the DRE at TOA (e.g.…”

Section: Introductionmentioning

confidence: 99%

Direct radiative effects during intense Mediterranean desert dust outbreaks

et al. 2018

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Abstract. The direct radiative effect (DRE) during 20 intense and widespread dust outbreaks, which affected the broader Mediterranean basin over the period March 2000-February 2013, has been calculated with the NMMB-MONARCH model at regional (Sahara and European continent) and shortterm temporal (84 h) scales. According to model simulations, the maximum dust aerosol optical depths (AODs) range from ∼ 2.5 to ∼ 5.5 among the identified cases. At midday, dust outbreaks locally induce a NET (shortwave plus longwave) strong atmospheric warming (DRE ATM values up to 285 W m −2 ; Niger-Chad; dust AODs up to ∼ 5.5) and a strong surface cooling (DRE NETSURF values down to −337 W m −2 ), whereas they strongly reduce the downward radiation at the ground level (DRE SURF values down to −589 W m −2 over the Eastern Mediterranean, for extremely high dust AODs, 4.5-5). During night-time, reverse effects of smaller magnitude are found. At the top of the atmosphere (TOA), positive (planetary warming) DREs up to 85 W m −2 are found over highly reflective surfaces (Niger-Chad; dust AODs up to ∼ 5.5) while negative (planetary cooling) DREs down to −184 W m −2 (Eastern Mediterranean; dust AODs 4.5-5) are computed over dark surfaces at noon. Dust outbreaks significantly affect the mean regional radiation budget, with NET DREs ranging from −8.5 to 0.5 W m −2 , from −31.6 to 2.1 W m −2 , from −22.2 to 2.2 W m −2 and from −1.7 to 20.4 W m −2 for TOA, SURF, NETSURF and ATM, respectively. Although the shortwave DREs are larger than the longwave ones, the latter are comparable or even larger at TOA, particularly over the Sahara at midday. As a response to the strong surface day-time cooling, dust outbreaks cause a reduction in the regional sensible and latent heat fluxes by up to 45 and 4 W m −2 , respectively, averaged over land areas of the simulation domain. Dust outbreaks reduce the temperature at 2 m by up to 4 K during day-time, whereas a reverse tendency of similar magnitude is found during nighttime. Depending on the vertical distribution of dust loads and time, mineral particles heat (cool) the atmosphere by up to 0.9 K (0.8 K) during day-time (night-time) within atmospheric dust layers. Beneath and above the dust clouds, mineral particles cool (warm) the atmosphere by up to 1.3 K (1.2 K) at noon (night-time). On a regional mean basis, negative feedbacks on the total emitted dust (reduced by 19.5 %) and dust AOD (reduced by 6.9 %) are found when dust interacts with the radiation. Through the consideration of dust radiative effects in numerical simulations, the model positive and negative biases for the downward surface SW or LW radiation, respectively, with respect to Baseline Surface Radiation Network (BSRN) measurements, are reduced. In addition, they also reduce the model near-surface (at 2 m) nocturnal cold biases by up to 0.5 K (regional averages), as well as the model warm biases at 950 and 700 hPa, where the dust concentration is maximized, by up to 0.4 K. However, improvements are relatively small and do not happen in all ...

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Dust plumes over the Pacific, Indian, and Atlantic oceans: Climatology and radiative impact

Cited by 188 publications

References 124 publications

The seasonal vertical distribution of the Saharan Air Layer and its modulation by the wind

The seasonal vertical distribution of the Saharan Air Layer and its modulation by the wind

Black carbon emissions from biomass and fossil fuels in rural India

Direct radiative effects during intense Mediterranean desert dust outbreaks

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