scholarly journals A drop in Sahara dust fluxes records the northern limits of the African Humid Period

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Daniel Palchan ◽  
Adi Torfstein
Keyword(s):  
Humid Period ◽  
Sahara Dust

Rock varnish record of the African Humid Period in the Lake Turkana basin of East Africa

The Holocene ◽  
2021 ◽  
pp. 095968362110116
Author(s):  
Tanzhuo Liu ◽  
Christopher J Lepre ◽  
Sidney R Hemming ◽  
Wallace S Broecker
Keyword(s):  
East Africa ◽  
Lake Level ◽  
Drainage System ◽  
Early Holocene ◽  
Lake Turkana ◽  
Moisture Condition ◽  
Turkana Basin ◽  
Rock Varnish ◽  
Geomorphic Features ◽  
Humid Period

Rock varnish is a manganiferous dark coating accreted on subaerially exposed rocks in drylands. It often contains a layered microstratigraphy that records past wetness variations. Varnish samples from latest Pleistocene and Holocene geomorphic features in the Lake Turkana basin, East Africa display a regionally replicable microstratigraphy record of Holocene millennial-scale wetness variability and a broad interval of wetter conditions during the African Humid Period (AHP). Three major wet pulses in the varnish record occurred during the generally wet interval of the early Holocene (11.5–8.5 ka) when the lake attained its maximum high stand (MHS) at 455–460 m. A >23 m drop from the MHS occurred between 8.5 and 8 ka. Subsequently two additional wet pulses occurred during the early to middle Holocene (8–5 ka) when the lake occupied its secondary high stand at 445 m. Collectively, these five wet phases represent an extended wet interval coincident with the AHP in the region. One moderate wet phase occurred during the subsequent climatic transition from the humid to arid regime (5–4.3 ka) after the lake level dropped rapidly from 445 m to <405 m. Five minor wet phases took place during the overall arid period of the late Holocene (4.3–0 ka) when the lake level oscillated below 405 m. These findings indicate that the AHP terminated rapidly around 5 ka in the Turkana basin in terms of lake level drop, but the regional shift in relative humidity from the AHP mode to its present-day condition lagged for about 700 years until 4.3 ka, hinting at a gradual phasing out in terms of moisture condition. These findings further suggest that Lake Turkana overflowed intermittently into the Nile drainage system through its topographic sill at 455–460 m during the early Holocene and has become a closed-basin lake thereafter for the past 8 ky.

Arctic climate response to the termination of the African Humid Period

2015 ◽  
Vol 125 ◽  
pp. 91-97 ◽  
Author(s):  
Francesco Muschitiello ◽  
Qiong Zhang ◽  
Hanna S. Sundqvist ◽  
Frazer J. Davies ◽  
Hans Renssen
Keyword(s):  
Arctic Climate ◽  
Climate Response ◽  
Humid Period

scholarly journals Observations of Saharan dust microphysical and optical properties from the Eastern Atlantic during NAMMA airborne field campaign

2011 ◽  
Vol 11 (2) ◽  
pp. 723-740 ◽  
Author(s):  
G. Chen ◽  
L. D. Ziemba ◽  
D. A. Chu ◽  
K. L. Thornhill ◽  
G. L. Schuster ◽  
...  
Keyword(s):  
Particle Size ◽  
Optical Properties ◽  
Dust Particle ◽  
Saharan Dust ◽  
Dust Particles ◽  
Small Range ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Field Campaign ◽  
Sahara Dust

Abstract. As part of the international project entitled "African Monsoon Multidisciplinary Analysis (AMMA)", NAMMA (NASA AMMA) aimed to gain a better understanding of the relationship between the African Easterly Waves (AEWs), the Sahara Air Layer (SAL), and tropical cyclogenesis. The NAMMA airborne field campaign was based out of the Cape Verde Islands during the peak of the hurricane season, i.e., August and September 2006. Multiple Sahara dust layers were sampled during 62 encounters in the eastern portion of the hurricane main development region, covering both the eastern North Atlantic Ocean and the western Saharan desert (i.e., 5–22° N and 10–35° W). The centers of these layers were located at altitudes between 1.5 and 3.3 km and the layer thickness ranged from 0.5 to 3 km. Detailed dust microphysical and optical properties were characterized using a suite of in-situ instruments aboard the NASA DC-8 that included a particle counter, an Ultra-High Sensitivity Aerosol Spectrometer, an Aerodynamic Particle Sizer, a nephelometer, and a Particle Soot Absorption Photometer. The NAAMA sampling inlet has a size cut (i.e., 50% transmission efficiency size) of approximately 4 μm in diameter for dust particles, which limits the representativeness of the NAMMA observational findings. The NAMMA dust observations showed relatively low particle number densities, ranging from 268 to 461 cm−3, but highly elevated volume density with an average at 45 μm3 cm−3. NAMMA dust particle size distributions can be well represented by tri-modal lognormal regressions. The estimated volume median diameter (VMD) is averaged at 2.1 μm with a small range of variation regardless of the vertical and geographical sampling locations. The Ångström Exponent assessments exhibited strong wavelength dependence for absorption but a weak one for scattering. The single scattering albedo was estimated at 0.97 ± 0.02. The imaginary part of the refractive index for Sahara dust was estimated at 0.0022, with a range from 0.0015 to 0.0044. Closure analysis showed that observed scattering coefficients are highly correlated with those calculated from spherical Mie-Theory and observed dust particle size distributions. These values are generally consistent with literature values reported from studies with similar particle sampling size range.

scholarly journals Stepwise drying of Lake Turkana at the end of the African Humid Period: an example of forced regression modulated by solar activity?

2016 ◽  
Author(s):  
Alexis Nutz ◽  
Mathieu Schuster
Keyword(s):  
Solar Activity ◽  
Lake Level ◽  
Controlling Factors ◽  
Lake Turkana ◽  
Turkana Basin ◽  
Orbital Precession ◽  
Forced Regression ◽  
Humid Period

Abstract. Although timing of the termination of the African Humid Period (AHP) is relatively well-established now, modes and controlling factors are still being determined. Here, through a geomorphological approach, we characterize the evolution of the final regression of Lake Turkana at the end of the African Humid Period. We show that lake level fall during this period was not constant, yet rather stepwise consisted of five periods marked by rapid rates of lake level fall separated by periods of lower rates of lake level fall. Even the overall regressive trend is associated with regional decreased precipitations due to reduced insolation controlled by orbital precession, we discuss the origin of the five periods of accelerated rates of lake level fall. Finally, we propose that accelerations are associated with periods marked by solar activity minima that locally resulted in the repeated westward displacement of the Congo Air Boundary (CAB), thereby reducing rainfall across the Lake Turkana basin.

Pollen record of early- to mid-Holocene vegetation and climate dynamics on the eastern coast of the Yellow Sea, South Korea

The Holocene ◽  
2018 ◽  
Vol 28 (6) ◽  
pp. 1011-1022 ◽  
Author(s):  
Bing Song ◽  
Sangheon Yi ◽  
Wook-Hyun Nahm ◽  
Jin-Young Lee ◽  
Limi Mao ◽  
...  
Keyword(s):  
South Korea ◽  
Yellow Sea ◽  
Asian Summer Monsoon ◽  
Climate Dynamics ◽  
Cold Climate ◽  
The Yellow Sea ◽  
Eastern Coast ◽  
Pollen Record ◽  
Vegetation And Climate ◽  
Humid Period

To understand the early- to mid-Holocene vegetation and climate dynamics on the eastern coast of the Yellow Sea, we obtained a sedimentary core with high-resolution accelerator mass spectrometry (AMS) carbon 14 (14C) data from the Gunsan coast in South Korea. The palynological analysis demonstrated that the riverine wetland meadow from 12.1 to 9.8 cal. kyr BP changed to temperate deciduous broad-leaved forest in 9.8–2.8 cal. kyr BP. In addition, the cold climate from 12.1 to 9.8 cal. kyr BP became warmer from 8.5 to 7.3 cal. kyr BP. This was followed by another relatively cold period from 7.3 to 2.8 cal. kyr BP. The temperature change was mainly in response to solar factors. However, there are two relatively humid periods from 12.1 to 9.8 and 8.5 to 7.3 cal. kyr BP, which arose for different reasons. The earlier humid period resulted from strong westerlies and a rapidly rising sea level. The later humid period was produced mainly by the strong East Asian summer monsoon (EASM) and may also be linked to La Niña–like activity. The cold ‘Younger Dryas’ event from 12.0 to 11.4 cal. kyr BP recorded in this study may have been produced by a North Atlantic meltwater pulse. This would have reduced temperatures that were already low because of weak insolation, and the strong winter monsoons would have increased the precipitation.

scholarly journals Sahara Dust Events over South-western Bulgaria During the Late Spring of 2013

2015 ◽  
Author(s):  
Assen Tchorbadjieff ◽  
Christo Angelov ◽  
Todor Arsov ◽  
Nina Nikolova ◽  
Ivo Kalapov ◽  
...  
Keyword(s):  
Late Spring ◽  
Dust Events ◽  
Sahara Dust

scholarly journals Aerosol direct radiative forcing during Sahara dust intrusions in the Central Mediterranean

2010 ◽  
Vol 10 (8) ◽  
pp. 20673-20727
Author(s):  
M. R. Perrone ◽  
A. Bergamo ◽  
V. Bellantone
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Spectral Range ◽  
Mediterranean Basin ◽  
Transfer Model ◽  
Clear Sky ◽  
Fine Mode ◽  
The Mediterranean ◽  
The Mediterranean Basin ◽  
Sahara Dust

Abstract. The clear-sky, instantaneous Direct Radiative Effect (DRE) by all and anthropogenic particles is calculated during Sahara dust intrusions in the Mediterranean basin, to evaluate the role of anthropogenic particle's radiative effects and to obtain a better estimate of the DRE by desert dust. The clear-sky aerosol DRE is calculated by a two stream radiative transfer model in the solar (0.3–4 μm) and infrared (4–200 μm) spectral range, at the top of the atmosphere (ToA) and at the Earth's surface (sfc). Aerosol optical properties by AERONET sun-sky photometer measurements and aerosol vertical profiles by EARLINET lidar measurements, both performed at Lecce (40.33° N, 18.10° E) during Sahara dust intrusions occurred from 2003 to 2006 year, are used to perform radiative transfer simulations. Instantaneous values at 0.44 μm of the real (n) and imaginary (k) refractive index and of the of aerosol optical depth (AOD) vary within the 1.33–1.55, 0.0037–0.014, and 0.2–0.7 range, respectively during the analyzed dust outbreaks. Fine mode particles contribute from 34% to 85% to the AOD by all particles. The complex atmospheric chemistry of the Mediterranean basin that is also influenced by regional and long-range transported emissions from continental Europe and the dependence of dust optical properties on soil properties of source regions and transport pathways, are responsible for the high variability of n, k, and AOD values and of the fine mode particle contribution. Instantaneous all-wave (solar+infrared) DREs that are negative as a consequence of the cooling effect by aerosol particles, span the – (32–10) Wm−2 and the – (44–20) Wm−2 range at the ToA and surface, respectively. The instantaneous all-wave DRE by anthropogenic particles that is negative, varies within – (13–7) Wm−2 and – (18–11) Wm−2 at the ToA and surface, respectively. It represents from 41% up to 89% and from 32% up to 67% of the all-wave DRE by all particles at the ToA and surface, respectively during the analysed dust outbreaks. A linear relationship to calculate the DRE by natural particles in the solar and infrared spectral range is provided.

scholarly journals Variability of aerosol properties over Eastern Europe observed from ground and satellites in the period from 2003 to 2011

2013 ◽  
Vol 13 (1) ◽  
pp. 2641-2670
Author(s):  
A. Bovchaliuk ◽  
G. Milinevsky ◽  
V. Danylevsky ◽  
P. Goloub ◽  
O. Dubovik ◽  
...  
Keyword(s):  
Eastern Europe ◽  
Correlation Coefficients ◽  
Single Scattering ◽  
Distinct Pattern ◽  
Spatial Inhomogeneity ◽  
Atmospheric Conditions ◽  
Anthropogenic Aerosols ◽  
Aerosol Loading ◽  
Sahara Dust ◽  
Aerosol Properties

Abstract. The paper presents the study of aerosol variability in the period from 2003 to 2011 over Eastern Europe region with latitude ranging from 40° N to 60° N and longitude from 20° E to 50° E. The analysis was based on the POLDER/PARASOL and POLDER-2/ADEOS satellites and AERONET ground-based sunphotometer observations. The aerosol optical thickness (AOT) of the studied area is characterized by the values (referenced to 870 nm wavelength) ranging from 0.05 to 0.2 except the period of July–August 2010 with strong forest and peat wildfires when the AOT typical values range from 0.3 to 0.5. The analysis of seasonal dynamics of aerosol loading has revealed two AOT high value peaks. The first peak observed in April–May is the result of solitary transportation of Sahara dust in the atmosphere over Eastern Europe, infrequent agricultural fires, transportation of sea salt aerosols by southern winds to Ukraine and Moldova from the Black and Azov Seas. The second peak in August–September is associated with forest and peat wildfires, considerable transportation of Sahara dust and presence of soil dust aerosols due to harvesting activity. The maximum values of AOT are observed in May 2006 (0.1–0.15), April 2009 (0.07–0.15) and August 2010 (0.2–0.5). Furthermore, the study has identified a distinct pattern of anthropogenic aerosols over the industrial areas, especially in the central Ukraine, eastern Belarus, as well as Moscow, Nizhny Novgorod and Stavropol regions in Russia. The comparison of the fine mode AOT (particle radius < 0.3 μm) derived by standard algorithm POLDER/PARASOL from reflected polarized radiances with those recomputed from AERONET inversions was performed over a number of AERONET sites: over Kyiv and Sevastopol sites for the period of 2008–2009 and over Moscow, Minsk, Belsk, and Moldova sites for the period of 2005–2009. The correlation coefficients are 0.78 for Moscow, 0.76 – Minsk, 0.86 – Belsk, 0.93 – Kyiv, 0.81 – Moldova and 0.63 for Sevastopol sites. The deviations are explained by the spatial inhomogeneity of the surface polarization that has stronger effect on aerosol retrieval for clear atmospheric conditions with low aerosol loading when surface impact on satellite observations is more pronounced. In addition, the preliminary analysis of the detailed aerosol properties derived by new generation PARASOL algorithm was accomplished. The AOT and single scattering albedo retrieved by the algorithm over Kyiv were compared with the closest AERONET retrievals within two hour of satellite overpass time and the stable atmospheric conditions.

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