scholarly journals Profiling Aerosol Optical Properties at the Central Asian Site of Dushanbe, Tajikistan: Pure Dust Cases

2020 ◽  
Vol 237 ◽  
pp. 02027
Author(s):  
Julian Hofer ◽  
Dietrich Althausen ◽  
Sabur F. Abdullaev ◽  
Abduvosit N. Makhmudov ◽  
Bakhron I. Nazarov ◽  
...  
Keyword(s):  
Optical Properties ◽  
Central Asia ◽  
Asian Dust ◽  
Aerosol Optical Properties ◽  
Central Asian ◽  
The Mean ◽  
Ground Based Lidar ◽  
First Time ◽  
532 Nm

Tajikistan is often affected by atmospheric mineral dust originating from various surrounding deserts. The direct and indirect radiative effects of that dust play a sensitive role in the Central Asian climate system and therefore need to be quantified. The Central Asian Dust Experiment (CADEX) provides for the first time an aerosol climatology for Central Asia based long-term aerosol profiling by ground-based lidar (PollyXT type) in Dushanbe, Tajikistan. For pure dust cases, mean depolarization(lidar) ratios of 0.23±0.03(44±3 sr) at 355 nm and 0.32±0.02(38±3 sr) at 532 nm wavelength have been measured. The mean extinction-related Ångström exponent was 0.18±0.15.

scholarly journals Optical properties of Central Asian aerosol relevant for spaceborne lidar applications and aerosol typing at 355 and 532 nm

2020 ◽  
Author(s):  
Julian Hofer ◽  
Albert Ansmann ◽  
Dietrich Althausen ◽  
Ronny Engelmann ◽  
Holger Baars ◽  
...  
Keyword(s):  
Optical Properties ◽  
Full Range ◽  
Anthropogenic Pollution ◽  
Data Set ◽  
Central Asian ◽  
Lidar Ratio ◽  
Ground Based Lidar ◽  
Complex Relationships ◽  
532 Nm ◽  
Depolarization Ratios

Abstract. For the first time, a dense data set of particle extinction-to-backscatter ratios (lidar ratios), linear depolarization ratios, and backscatter- and extinction-related Ångström exponents for a Central Asian site are presented. The observations were performed with a continuously running multiwavelength polarization Raman lidar at Dushanbe, Tajikistan, during an 18-month campaign (March 2015 to August 2016). The presented seasonally resolved observations fill an important gap in the data base of aerosol optical properties used in aerosol typing efforts with spaceborne lidars and ground-based lidar networks. Lidar ratios and depolarization ratios are also basic input parameters in spaceborne lidar data analyses and in efforts to harmonize long-term observations with different space lidar systems operated either at 355 or 532 nm. As a general result, the found optical properties reflect the large range of occurring aerosol mixtures consisting of long-range-transported dust (from the Middle East and the Sahara), regional desert, soil, and salt dust, and anthropogenic pollution. The full range from highly polluted to pure dust situations could be observed. Typical dust depolarization ratios of 0.23–0.29 (355 nm) and 0.30–0.35 (532 nm) were observed. In contrast, comparably low lidar ratios were found. Dust lidar ratios at 532 nm accumulated around 35–40 sr and were even lower for regional background dust conditions (20–30 sr). The reason for these low values may be partly related to the direct emission and emission of re-suspended salt dust (initially originated from numerous desiccating lakes and the Aralkum desert). Detailed correlation studies (e.g., lidar ratio vs. depolarization ratios and Ångström exponent vs. lidar ratio and vs. depolarization ratio) are presented to illuminate the complex relationships between the observed optical properties and to identify the contributions of anthropogenic haze, dust, and background aerosol to the overall aerosol mixtures found within the 18-month campaign.

scholarly journals Vertical variation of optical properties of mixed Asian dust/pollution plumes according to pathway of airmass transport over East Asia

2015 ◽  
Vol 15 (3) ◽  
pp. 3381-3413 ◽  
Author(s):  
S.-K. Shin ◽  
D. Müller ◽  
K. H. Lee ◽  
D. Shin ◽  
Y. J. Kim ◽  
...  
Keyword(s):  
Optical Properties ◽  
Asian Dust ◽  
Optical Characteristics ◽  
Vertical Position ◽  
Depolarization Ratio ◽  
Dust Pollution ◽  
Transport Time ◽  
Lidar Measurements ◽  
The Mean ◽  
532 Nm

Abstract. We use five years (2009–2013) of multiwavelength Raman lidar measurements at Gwangju, Korea (35.10° N, 126.53° E) for the identification of changes of optical properties of East Asian dust in dependence of its transport path over China. Profiles of backscatter and extinction coefficients, lidar ratios, and backscatter-related Ångström exponents (wavelength pair 355/532 nm) were measured at Gwangju. Linear particle depolarization ratios were used to identify East Asian dust layers. We used backward trajectory modelling to identify the pathway and the vertical position of dust-laden air masses over China during long-range transport. Most cases of Asian dust events can be described by the emission of dust in desert areas and subsequent transport over highly polluted regions of China. The Asian dust plumes could be categorized into two classes according to the height above ground in which these plumes were transported: (I) the dust layers passed over China at high altitude levels until arrival over Gwangju, and (II) the Asian dust layers were transported near the surface and the lower troposphere over industrialized areas before they arrived over Gwangju. We find that the optical characteristics of these mixed Asian dust layers over Gwangju differ in dependence of their vertical position above ground over China and the change of height above ground during transport. The mean linear particle depolarization ratio was 0.21 ± 0.06 (at 532 nm), the mean lidar ratios were 52 ± 7 sr at 355 nm and 53 ± 8 sr at 532 nm, and the mean Ångström exponent was 0.74 ± 0.31 in case I. In contrast, plumes transported at lower altitudes (case II) showed low depolarization ratios, and higher lidar ratio and Ångström exponents. The mean linear particle depolarization ratio was 0.13 ± 0.04, the mean lidar ratios were 63 ± 9 sr at 355 nm and 62 ± 8 sr at 532 nm, respectively, and the mean Ångström exponent was 0.98 ± 0.51. These numbers show that the optical characteristics of mixed Asian plumes are more similar to optical characteristics of urban pollution. We find a decrease of the linear depolarization ratio of the mixed dust/pollution plume in dependence of transport time if the pollution layer travelled over China at low heights, i.e., below approximately 3 km above ground. In contrast we do not find such a trend if the dust plumes travelled at heights above 4 km over China. We need a longer time series of lidar measurements in order to determine the change of optical properties of dust with transport time in a quantitative way.

scholarly journals Deriving the effect of wind speed on clean marine aerosol optical properties using the A-Train satellites

2011 ◽  
Vol 11 (22) ◽  
pp. 11401-11413 ◽  
Author(s):  
V. P. Kiliyanpilakkil ◽  
N. Meskhidze
Keyword(s):  
Optical Properties ◽  
Wind Speed ◽  
Optical Depth ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Marine Aerosol ◽  
Marine Aerosols ◽  
Aerosol Optical Properties ◽  
The Mean ◽  
532 Nm

Abstract. The relationship between "clean marine" aerosol optical properties and ocean surface wind speed is explored using remotely sensed data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the CALIPSO satellite and the Advanced Microwave Scanning Radiometer (AMSR-E) on board the AQUA satellite. Detailed data analyses are carried out over 15 regions selected to be representative of different areas of the global ocean for the time period from June 2006 to April 2011. Based on remotely sensed optical properties the CALIPSO algorithm is capable of discriminating "clean marine" aerosols from other types often present over the ocean (such as urban/industrial pollution, desert dust and biomass burning). The global mean optical depth of "clean marine" aerosol at 532 nm (AOD532) is found to be 0.052 ± 0.038 (mean plus or minus standard deviation). The mean layer integrated particulate depolarization ratio of marine aerosols is 0.02 ± 0.016. Integrated attenuated backscatter and color ratio of marine aerosols at 532 nm were found to be 0.003 ± 0.002 sr−1 and 0.530 ± 0.149, respectively. A logistic regression between AOD532 and 10-m surface wind speed (U10) revealed three distinct regimes. For U10 ≤ 4 m s−1 the mean CALIPSO-derived AOD532 is found to be 0.02 ± 0.003 with little dependency on the surface wind speed. For 4 < U10 ≤ 12 m s−1, representing the dominant fraction of all available data, marine aerosol optical depth is linearly correlated with the surface wind speed values, with a slope of 0.006 s m−1. In this intermediate wind speed region, the AOD532 vs. U10 regression slope derived here is comparable to previously reported values. At very high wind speed values (U10 > 18 m s−1), the AOD532-wind speed relationship showed a tendency toward leveling off, asymptotically approaching value of 0.15. The conclusions of this study regarding the aerosol extinction vs. wind speed relationship may have been influenced by the constant lidar ratio used for CALIPSO-derived AOD532. Nevertheless, active satellite sensor used in this study that allows separation of maritime wind induced component of AOD from the total AOD over the ocean could lead to improvements in optical properties of sea spray aerosols and their production mechanisms.

scholarly journals Deriving the effect of wind speed on clean maritime aerosol optical properties using the A-Train satellites

2011 ◽  
Vol 11 (2) ◽  
pp. 4599-4630 ◽  
Author(s):  
V. P. Kiliyanpilakkil ◽  
N. Meskhidze
Keyword(s):  
Optical Properties ◽  
Wind Speed ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Sea Salt ◽  
Marine Aerosol ◽  
Marine Aerosols ◽  
Aerosol Optical Properties ◽  
The Mean ◽  
532 Nm

Abstract. Relationship between "clean marine" aerosol optical properties and ocean surface wind speed is explored using remotely sensed data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the CALIPSO satellite and the Advanced Microwave Scanning Radiometer (AMSR-E) on board the AQUA satellite. Detailed data analyses are carried out over 15 regions selected to be representative of different areas of the global ocean for the time period from June 2006 to June 2010. Based on remotely sensed optical properties the CALIPSO algorithm is capable of discriminating "clean marine" aerosols from other types often present over the ocean (such as urban/industrial pollution, desert dust and biomass burning). The global mean optical depth of "clean marine" aerosol at 532 nm (AOD532) is found to be 0.052 ± 0.038. The mean layer integrated volume depolarization ratio of marine aerosols is 0.016 ± 0.012, the value representative of sea salt crystals. Integrated attenuated backscatter and color ratio of marine aerosols at 532 nm were obtained to be 0.003 ± 0.002 sr−1 and 0.530 ± 0.149, respectively. A logistic regression between AOD532 and 10-meter surface wind speed (U10) revealed three distinct regions. For surface winds lower than 4 m s−1, the mean CALIPSO-derived AOD532 is found to be 0.02 ± 0.003 with little dependency on the surface wind speed. For surface winds from 4 m s−1 to 12 m s−1, representing the dominant fraction of all available data, marine aerosol optical depth is linearly correlated with the U10, with a slope of 0.0062 s m−1. In this intermediate wind speed region, the AOD532 vs. U10 regression derived here is comparable to previously reported relationships. At very high wind speed values (U10 > 18 m s−1), the AOD532-wind speed relationship showed a tendency toward leveling off, suggesting the existence of some maximum value for maritime AOD. Results of our calculations suggest that considerable improvements to both optical properties of marine aerosols and their production mechanisms can be achieved by discriminating "clean marine" aerosols (or sea salt particles) from all other types of aerosols present over the ocean.

scholarly journals Optical properties of Central Asian aerosol relevant for spaceborne lidar applications and aerosol typing at 355 and 532 nm

2020 ◽  
Vol 20 (15) ◽  
pp. 9265-9280 ◽  
Author(s):  
Julian Hofer ◽  
Albert Ansmann ◽  
Dietrich Althausen ◽  
Ronny Engelmann ◽  
Holger Baars ◽  
...  
Keyword(s):  
Optical Properties ◽  
Full Range ◽  
Anthropogenic Pollution ◽  
Data Set ◽  
Central Asian ◽  
Lidar Ratio ◽  
Ground Based Lidar ◽  
Complex Relationships ◽  
532 Nm ◽  
Depolarization Ratios

Abstract. For the first time, a dense data set of particle extinction-to-backscatter ratios (lidar ratios), linear depolarization ratios, and backscatter- and extinction-related Ångström exponents for a Central Asian site are presented. The observations were performed with a continuously running multiwavelength polarization Raman lidar at Dushanbe, Tajikistan, during an 18-month campaign (March 2015 to August 2016). The presented seasonally resolved observations fill an important gap in the database of aerosol optical properties used in aerosol typing efforts with spaceborne lidars and ground-based lidar networks. Lidar ratios and depolarization ratios are also basic input parameters in spaceborne lidar data analyses and in efforts to harmonize long-term observations with different space lidar systems operated at either 355 or 532 nm. As a general result, the found optical properties reflect the large range of occurring aerosol mixtures consisting of long-range-transported dust (from the Middle East and the Sahara), regional desert, soil, and salt dust, and anthropogenic pollution. The full range from highly polluted to pure dust situations could be observed. Typical dust depolarization ratios of 0.23–0.29 (355 nm) and 0.30–0.35 (532 nm) were observed. In contrast, comparably low lidar ratios were found. Dust lidar ratios at 532 nm accumulated around 35–40 sr and were even lower for regional background dust conditions (20–30 sr). Detailed correlation studies (e.g., lidar ratio vs. depolarization ratios, Ångström exponent vs. lidar ratio and vs. depolarization ratio) are presented to illuminate the complex relationships between the observed optical properties and to identify the contributions of anthropogenic haze, dust, and background aerosol to the overall aerosol mixtures found within the 18-month campaign. The observation of 532 nm lidar ratios (<25 sr) and depolarization ratios (around 15 %–20 %) in layers with very low particle extinction coefficient (<30 sr) suggests that direct emission and emission of resuspended salt dust (initially originated from numerous desiccating lakes and the Aralkum desert) have a sensitive impact on the aerosol background optical properties over Dushanbe.

scholarly journals Vertical variation of optical properties of mixed Asian dust/pollution plumes according to pathway of air mass transport over East Asia

2015 ◽  
Vol 15 (12) ◽  
pp. 6707-6720 ◽  
Author(s):  
S.-K. Shin ◽  
D. Müller ◽  
C. Lee ◽  
K. H. Lee ◽  
D. Shin ◽  
...  
Keyword(s):  
Optical Properties ◽  
East Asian ◽  
Asian Dust ◽  
Optical Characteristics ◽  
Vertical Position ◽  
Dust Pollution ◽  
Transport Time ◽  
Lidar Measurements ◽  
The Mean ◽  
532 Nm

Abstract. We use five years (2009–2013) of multiwavelength Raman lidar measurements at Gwangju, South Korea (35.10° N, 126.53° E) for the identification of changes of optical properties of East Asian dust depending on its transport path over China. Profiles of backscatter and extinction coefficients, lidar ratios, and backscatter-related Ångström exponents (wavelength pair 355/532 nm) were measured at Gwangju. Linear particle depolarization ratios were used to identify East Asian dust layers. We used backward trajectory modeling to identify the pathway and the vertical position of dust-laden air masses over China during long-range transport. Most cases of Asian dust events can be described by the emission of dust in desert areas and subsequent transport over highly polluted regions of China. The Asian dust plumes could be categorized into two classes according to the height above ground at which these plumes were transported: (case I) the dust layers passed over China at high altitude levels (> 3 km) until arrival over Gwangju, and (case II) the Asian dust layers were transported near the surface and within the lower troposphere (< 3 km) over industrialized areas before they arrived over Gwangju. We find that the optical characteristics of these mixed Asian dust layers over Gwangju differ depending on their vertical position above ground over China and the change of height above ground during transport. The mean linear particle depolarization ratio was 0.21 ± 0.06 (at 532 nm), the mean lidar ratios were 52 ± 7 sr at 355 nm and 53 ± 8 sr at 532 nm, and the mean Ångström exponent was 0.74 ± 0.31 for case I. In contrast, plumes transported at lower altitudes (case II) showed low depolarization ratios (0.13 ± 0.04 at 532 nm), and higher lidar ratio (63 ± 9 sr at 355 nm and 62 ± 8 sr at 532 nm) and Ångström exponents (0.98 ± 0.51). These numbers show that the optical characteristics of mixed Asian plumes are more similar to optical characteristics of urban pollution. We find a decrease of the linear depolarization ratio of the mixed dust/pollution plume depending on transport time if the pollution layer traveled over China at low heights, i.e., below approximately 3 km above ground. In contrast, we do not find such a trend if the dust plumes traveled at heights above 3 km over China. We need a longer time series of lidar measurements in order to determine in a quantitative way the change of optical properties of dust with transport time.

Sedelnikovaea baicalensis (Lecanoraceae) — new lichen genus and species for Europe

2018 ◽  
Vol 52 (2) ◽  
pp. 407-416
Author(s):  
T. V. Makryi
Keyword(s):  
Central Asia ◽  
Lichen Species ◽  
Significant Part ◽  
The Urals ◽  
Southern Siberia ◽  
Central Asian ◽  
Northeastern Siberia ◽  
Mountain Belts ◽  
First Time ◽  
Vast Range

Sedelnikovaea baicalensis, the Siberian-Central Asian lichen species, is recorded for the first time for Europe. Based on all the known localities, including those first-time reported from Baikal Siberia, the peculiarities of the ecology and distribution of this species are discussed, the map of its distribution is provided. It is concluded that the species was erroneously considered earlier as a Central Asian endemic. The center of the present range of this lichen is the steppes of Southern Siberia and Mongolia. Assumptions are made that S. baicalensis is relatively young (Paleogene-Neogene) species otherwise it would have a vast range extending beyond Asia, and also that the Yakut locations of this species indicate that in the Pleistocene its range was wider and covered a significant part of the Northeastern Siberia but later underwent regression. Based on the fact that in the mountains of Central Asia the species is found only in the upper mountain belts, it is proposed to characterize it as «cryo-arid xerophyte» in contrast to «arid xerophytes». A conclusion is made that the presence of extensive disjunctions of S. baicalensis range between the Southern Pre-Urals and the Altai-Sayan Mountains or the Mountains of Central Asia is unlikely; the lichen is most likely to occur in the Urals and most of Kazakhstan.

scholarly journals A SLR Pre-Processing Algorithm Based on Satellite Signature Effect

2021 ◽  
Vol 11 (19) ◽  
pp. 8880
Author(s):  
Bowen Guan ◽  
Cunbo Fan ◽  
Ning An ◽  
Ricardo Cesar Podesta ◽  
Dra Ana Pacheco ◽  
...  
Keyword(s):  
Mean Value ◽  
Observation Data ◽  
Short Term ◽  
Error Sources ◽  
Effect Model ◽  
The Mean ◽  
The Stability ◽  
First Time ◽  
Satellite Signature Effect

As one of the major error sources, satellite signature effect should be reduced or even erased from the distribution of the post-fit residuals to improve the ranging precision. A simulation of satellite signature effect removal process for normal point algorithm is conducted based on a revised model of satellite response, which fully considers the structural and distribution characteristics of retroreflectors. In order to eliminate both long-term and short-term satellite signature effect, a clipping method for SLR data processing is proposed by defining the clipping location as 5.6 mm away from the mean value of the long-term fit residuals to select effective returns for normal points. The results indicate that, compared to normal points algorithm, the RMS per NP of LAGEOS-1 observation data processed by the clipping method is reduced from 62.90 ± 9.9 mm to 56.07 ± 4.69 mm, and the stability of RMS is improved 53%. This study improves the satellite signature effect model and simulates the fluctuation of normal points caused by satellite signature effect for the first time. The new method based on the simulation of satellite signature effect has stronger robustness and applicability, which can further minimize the influence of satellite signature effect on the SLR production and significantly improve the data property.

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