scholarly journals Characteristics of aerosol and cloud particle size distributions in the tropical tropopause layer measured with optical particle counter and lidar

2007 ◽  
Vol 7 (13) ◽  
pp. 3507-3518 ◽  
Author(s):  
S. Iwasaki ◽  
K. Maruyama ◽  
M. Hayashi ◽  
S.-Y. Ogino ◽  
H. Ishimoto ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Cirrus Clouds ◽  
Cirrus Cloud ◽  
Particle Counter ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Lidar Measurements ◽  
Optical Particle Counter

Abstract. An optical particle counter (OPC) is used in conjunction with lidar measurements to examine the characteristics of the particle size distribution in cirrus cloud in the tropical tropopause layer (TTL) over Thailand where the TTL is defined as the height at which temperature is lower than −75°C in this paper. Of 11 OPC launches, cirrus cloud was detected at 10–15 km high on 7 occasions, cirrus was detected in the TTL in 6 cases, and simultaneous OPC and lidar measurements were made on two occasions. Comparison of lidar and OPC measurements reveal that the cloud heights of cirrus in the TTL varies by several hundred meters over distances of tens kilometers; hence the height is not always horizontally uniform. The mode radii of particles constituting the clouds are estimated by lidar and OPC measurements to be less than approximately 10 μm. The regression lines of the particle size distribution with and without cirrus cloud exhibit similar features at equivalent radii of <0.8 μm. Enhancement in the integrated number concentration at radii greater than 0.8 μm indicates that liquid particles tend to be frozen at a radius of 0.8 μm, with cirrus clouds above 10 km exhibiting similar features. On the other hand, enhancement in the particle size distribution at radii greater than 0.9 μm and a peak at around 0.8 μm in the ratio of the standard deviation of count values to that of the Poisson distribution of the averaged count values are common features of cirrus clouds in the TTL, where the ratio shows the vertical homogeneity of the particle number. These typical features suggest that the transition from liquid, sulfuric acid aerosol, to ice is more observable in the TTL and the timing of freezing may vary with height in the TTL.

scholarly journals Characteristics of particle size distributions in the tropical tropopause based on optical particle counter and lidar measurements

2007 ◽  
Vol 7 (1) ◽  
pp. 1595-1622
Author(s):  
S. Iwasaki ◽  
K. Maruyama ◽  
M. Hayashi ◽  
S. Y. Ogino ◽  
H. Ishimoto ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Cirrus Clouds ◽  
Cirrus Cloud ◽  
Particle Counter ◽  
Tropical Tropopause ◽  
Cloud Models ◽  
Lidar Measurements ◽  
Optical Particle Counter

Abstract. An optical particle counter (OPC) is used in conjunction with lidar measurements to examine the characteristics of the particle size distribution in cirrus cloud at the tropical tropopause (TT) over Thailand. Of 11 OPC launches, cirrus cloud was detected at 10–15 km high on 7 occasions, cirrus was detected at the TT in 6 cases, and simultaneous OPC and lidar measurements were made on two occasions. Comparison of lidar and OPC measurements reveal that the cloud height of cirrus in the TT varies by several hundred meters over distances of tens kilometers; hence the height is not horizontally uniform. The mode radii of particles constituting the clouds are estimated by lidar and OPC measurements to be less than approximately 10 μm. The regression lines of the particle size distribution with and without cirrus cloud exhibit similar features at equivalent radii of <0.7 μm. Enhancement in the integrated number concentration at radii greater than 0.7 μm indicates that liquid particles tend to be frozen at a radius of 0.7 μm, with cirrus clouds above 10 km exhibiting similar features. In addition, common features of cirrus clouds at the TT include a local maximum in the particle size distribution at 2.0 μm and a peak between 0.5 μm and 1.7 μm in the ratio of the standard deviation of count values to that of the Poisson distribution of the averaged count values. Each feature implies that all ice particles in the clouds may be nucleated by the same mechanism and particles in this size range are actively frozen at the TT. These parameters are thus good indicators for checking the results of cirrus cloud models in the TT.

Approach for correcting particle size distribution measured by optical particle counter in high-pressure gas pipes

2018 ◽  
Vol 57 (13) ◽  
pp. 3497 ◽  
Author(s):  
Lifeng Lu ◽  
Xiaolin Wu ◽  
Zhongli Ji ◽  
Zhiyi Xiong ◽  
Mingxing Wang ◽  
...  
Keyword(s):  
Particle Size ◽  
High Pressure ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Particle Counter ◽  
Optical Particle Counter

scholarly journals Statistical estimation of stratospheric particle size distribution by combining optical modelling and lidar scattering measurements

2008 ◽  
Vol 8 (17) ◽  
pp. 5435-5448 ◽  
Author(s):  
J. Jumelet ◽  
S. Bekki ◽  
C. David ◽  
P. Keckhut
Keyword(s):  
Particle Size ◽  
Refractive Index ◽  
Standard Deviation ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Optical Model ◽  
Solid Particles ◽  
Spherical Particles ◽  
Lidar Measurements ◽  
Distribution Parameters

Abstract. A method for estimating the stratospheric particle size distribution from multiwavelength lidar measurements is presented. It is based on matching measured and model-simulated backscatter coefficients. The lidar backscatter coefficients measured at the three commonly used wavelengths 355, 532 and 1064 nm are compared to a precomputed look-up table of model-calculated values. The optical model assumes that particles are spherical and that their size distribution is unimodal. This inverse problem is not trivial because the optical model is highly non-linear with a strong sensitivity to the size distribution parameters in some cases. The errors in the lidar backscatter coefficients are explicitly taken into account in the estimation. The method takes advantage of the statistical properties of the possible solution cluster to identify the most probable size distribution parameters. In order to discard model-simulated outliers resulting from the strong non-linearity of the model, solutions farther than one standard deviation of the median values of the solution cluster are filtered out, because the most probable solution is expected to be in the densest part of the cluster. Within the filtered solution cluster, the estimation algorithm minimizes a cost function of the misfit between measurements and model simulations. Two validation cases are presented on Polar Stratospheric Cloud (PSC) events detected above the ALOMAR observatory (69° N – Norway). A first validation is performed against optical particle counter measurements carried out in January 1996. In non-depolarizing regions of the cloud (i.e. spherical particles), the parameters of an unimodal size distribution and those of the optically dominant mode of a bimodal size distribution are quite successfully retrieved, especially for the median radius and the geometrical standard deviation. As expected, the algorithm performs poorly when solid particles drive the backscatter coefficient. A small bias is identified in modelling the refractive index when compared to previous works that inferred PSC type Ib refractive indices. The accuracy of the size distribution retrieval is improved when the refractive index is set to the value inferred in the reference paper. Our results are then compared to values retrieved with another similar method that does not account for the effect of the measurements errors and the non-linearity of the optical model on the likelihood of the solution. The case considered is a liquid PSC observed over northern Scandinavia on January 2005. An excellent agreement is found between the two methods when our algorithm is applied without any statistical filtering of the solution cluster. However, the solution for the geometrical standard deviation appears to be rather unlikely with a value close to unity (σ≈1.04). When our algorithm is applied with solution filtering, a more realistic value of the standard deviation (σ≈1.27) is found. This highlights the importance of taking into account the non linearity of the model together with the lidar errors, when estimating particle size distribution parameters from lidar measurements.

scholarly journals Issues related to the retrieval of stratospheric-aerosol particle size information based on optical measurements

2020 ◽  
Vol 13 (4) ◽  
pp. 1909-1920 ◽  
Author(s):  
Christian von Savigny ◽  
Christoph G. Hoffmann
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Aerosol Particle ◽  
Measurement Techniques ◽  
Stratospheric Aerosol ◽  
Solar Occultation ◽  
Lidar Measurements ◽  
Aerosol Particle Size ◽  
Size Estimates

Abstract. Stratospheric-sulfate aerosols play an important role in the physics and chemistry of the atmosphere. The radiative and chemical effects of stratospheric-sulfate aerosols depend critically on the aerosol particle size distribution and its variability. Despite extensive research spanning several decades, the scientific understanding of the particle size distribution of stratospheric aerosols is still incomplete. Particle size estimates (often represented by the median radius of an assumed monomodal log-normal distribution with a fixed width or by the effective radius) reported in different studies cover a wide range, even under background stratospheric conditions, and particle size estimates retrieved from satellite solar-occultation measurements in the optical spectral range show a tendency to be systematically larger than retrievals based on other optical methods. In this contribution we suggest a potential reason for these systematic differences. Differences between the actual aerosol particle size distribution and the size distribution function assumed for aerosol size retrievals may lead to systematic differences in retrieved aerosol size estimates. We demonstrate that these systematic differences may differ significantly for different measurement techniques, which is related to the different sensitivities of these measurement techniques to specific parts of the aerosol particle population. In particular, stratospheric-aerosol size retrievals based on solar-occultation observations may yield systematically larger particle size estimates (median or effective radii) compared to, e.g., lidar backscatter measurements. Aerosol concentration, on the other hand, may be systematically smaller in retrievals based on occultation measurements compared to lidar measurements. The results indicate that stratospheric-aerosol size retrievals based on occultation or lidar measurements have to be interpreted with caution, as long as the actual aerosol particle size distribution is not well known.

scholarly journals A Method for Retrieving Stratospheric Aerosol Extinction and Particle Size from Ground-Based Rayleigh-Mie-Raman Lidar Observations

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 773
Author(s):  
Jacob Zalach ◽  
Christian von Savigny ◽  
Arvid Langenbach ◽  
Gerd Baumgarten ◽  
Franz-Josef Lübken ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Stratospheric Aerosol ◽  
Aerosol Extinction ◽  
Raman Lidar ◽  
Size Information ◽  
Lidar Measurements ◽  
Aerosol Particle Size ◽  
Log Normal

We report on the retrieval of stratospheric aerosol particle size and extinction coefficient profiles from multi-color backscatter measurements with the Rayleigh–Mie–Raman lidar operated at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in northern Norway. The retrievals are based on a two-step approach. In a first step, the median radius of an assumed monomodal log-normal particle size distribution with fixed width is retrieved based on a color index formed from the measured backscatter ratios at the wavelengths of 1064 nm and 532 nm. An intrinsic ambiguity of the retrieved aerosol size information is discussed. In a second step, this particle size information is used to convert the measured lidar backscatter ratio to aerosol extinction coefficients. The retrieval is currently based on monthly-averaged lidar measurements and the results for March 2013 are discussed. A sensitivity study is presented that allows for establishing an error budget for the aerosol retrievals. Assuming a monomodal log-normal aerosol particle size distribution with a geometric width of S = 1.5, median radii on the order of below 100 nm are retrieved. The median radii are found to generally decrease with increasing altitude. The retrieved aerosol extinction profiles are compared to observations with the OSIRIS (Optical Spectrograph and InfraRed Imager System) and the OMPS-LP (Ozone Mapping Profiling Suite Limb Profiler) satellite instruments in the 60∘ N to 80∘ N latitude band. The extinction profiles that were retrieved from the lidar measurements show good agreement with the observations of the two satellite instruments when taking the different wavelengths of the instruments into account.

scholarly journals Statistical estimation of stratospheric particle size distribution by combining optical modelling and lidar scattering measurements

2008 ◽  
Vol 8 (3) ◽  
pp. 8913-8949 ◽  
Author(s):  
J. Jumelet ◽  
S. Bekki ◽  
C. David ◽  
P. Keckhut
Keyword(s):  
Particle Size ◽  
Refractive Index ◽  
Standard Deviation ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Optical Model ◽  
Solid Particles ◽  
Spherical Particles ◽  
Lidar Measurements ◽  
Distribution Parameters

Abstract. A method for estimating the stratospheric particle size distribution from multiwavelength lidar measurements is presented. It is based on matching measured and model-simulated backscatter coefficients. The lidar backscatter coefficients measured at the three commonly used wavelengths 355, 532 and 1064 nm are compared to a precomputed look-up table of model-calculated values. The optical model assumes that particles are spherical and that their size distribution is unimodal. This inverse problem is not trivial because the optical model is highly non-linear with a strong sensitivity to the size distribution parameters in some cases. The errors in the lidar backscatter coefficients are explicitly taken into account in the estimation. The method takes advantage of the statistical properties of the possible solution cluster to identify the most probable size distribution parameters. In order to discard model-simulated outliers resulting from the strong non-linearity of the model, a 1σ-filter is applied to the solution cluster. Within the filtered solution cluster, the estimation algorithm minimizes a cost function of the misfit between measurements and model simulations. Two validation cases are presented on Polar Stratospheric Cloud (PSC) events detected above the ALOMAR observatory (69° N – Norway). A first validation is performed against optical particle counter measurements carried out in January 1996. In non-depolarizing regions of the cloud (i.e. spherical particles), the parameters of an unimodal size distribution and those of the optically dominant mode of a bimodal size distribution are quite successfully retrieved, especially for the mode radius and the geometrical standard deviation. As expected, the algorithm performs poorly when solid particles drive the backscatter coefficient. A small bias is identified in modelling the refractive index when compared to previous works that inferred PSC type Ib refractive indices. The accuracy of the size distribution retrieval is improved when the refractive index is set to the value inferred in the reference paper. Our results are then compared to values retrieved with another similar method that does not account for the effect of the measurements errors and the non-linearity of the optical model on the likelihood of the solution. The case considered is a liquid PSC observed over northern Scandinavia on January, 2005. An excellent agreement is found between the two methods when our algorithm is applied without any statistical filtering of the solution cluster. However, the solution for the geometrical standard deviation appears to be rather unlikely with a value close to unity (σ≈1.04). When our algorithm is applied with solution filtering, a more realistic value of the standard deviation (σ≈1.27) is found. This highlights the importance of taking into account the non linearity of the model together with the lidar errors, when estimating particle size distribution parameters from lidar measurements.

scholarly journals Issues related to the retrieval of stratospheric aerosol particle size information based on optical measurements

2019 ◽  
Author(s):  
Christian von Savigny ◽  
Christoph Hoffmann
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Aerosol Particle ◽  
Measurement Techniques ◽  
Stratospheric Aerosol ◽  
Particle Sizes ◽  
Solar Occultation ◽  
Lidar Measurements ◽  
Aerosol Particle Size

Abstract. Stratospheric sulfate aerosols play an important role for the physics and chemistry of the atmosphere. Key fundamental properties of the aerosols are their size and particle size distribution. Despite extensive research spanning several decades, the scientific understanding of these properties of stratospheric aerosols is incomplete. The particle sizes reported in different studies cover a wide range – even under background stratospheric conditions – and particle sizes retrieved from satellite solar occultation measurements in the optical spectral range show a tendency to be systematically larger than retrievals based on other optical methods. In this contribution we suggest a potential reason for these systematic differences. Differences between the actual aerosol particle size distribution and the size distribution assumed for aerosol size retrievals may lead to systematic differences in retrieved aerosol size. We demonstrate that these systematic differences may differ significantly for different measurement techniques, which is related to the different sensitivities of these measurement techniques to specific parts of the aerosol particle population. In particular, stratospheric aerosol size retrievals based on solar occultation observations may yield systematically larger particle size estimates compared to, e.g., lidar backscatter measurements. Aerosol concentration – on the other hand – may be systematically smaller in retrievals based on occultation measurements compared to lidar measurements. The results question the overall significance of stratospheric aerosol size retrievals based on optical satellite or lidar measurements, as long as the actual aerosol particle size distribution is not well known.

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