scholarly journals Post-flight analysis of detailed size distributions of warm cloud droplets, as determined in situ by cloud and aerosol spectrometers

2021 ◽  
Vol 14 (10) ◽  
pp. 6777-6794
Author(s):  
Sorin Nicolae Vâjâiac ◽  
Andreea Calcan ◽  
Robert Oscar David ◽  
Denisa-Elena Moacă ◽  
Gabriela Iorga ◽  
...  
Keyword(s):  
Cross Section ◽  
Forward Scattering ◽  
Scattering Cross Section ◽  
Size Distributions ◽  
Cloud Droplets ◽  
Cloud Particle ◽  
Fine Grid ◽  
Scattering Cross ◽  
Cloud Parameters

Abstract. Warm clouds, consisting of liquid cloud droplets, play an important role in modulating the amount of incoming solar radiation to Earth's surface and thus the climate. The size and number concentration of these cloud droplets control the reflectance of the cloud, the formation of precipitation and ultimately the lifetime of the cloud. Therefore, in situ observations of the number and diameter of cloud droplets are frequently performed with cloud and aerosol spectrometers, which determine the optical diameters of cloud particles (in the range of up to a few tens of micrometers) by measuring their forward-scattering cross sections in visible light and comparing these values with Mie theoretical computations. The use of such instruments must rely on a fast working scheme consisting of a limited pre-defined uneven grid of cross section values that corresponds to a theoretically derived uneven set of size intervals (bins). However, as more detailed structural analyses of warm clouds are needed to improve future climate projects, we present a new numerical post-flight methodology using recorded particle-by-particle sample files. The Mie formalism produces a complicated relationship between a particle's diameter and its forward-scattering cross section. This relationship cannot be expressed in an analytically closed form, and it should be numerically computed point by point, over a certain grid of diameter values. The optimal resolution required for constructing the diagram of this relationship is therefore analyzed. Cloud particle statistics are further assessed using a fine grid of particle diameters in order to capture the finest details of the cloud particle size distributions. The possibility and the usefulness of using coarser size grids, with either uneven or equal intervals, is also discussed. For coarse equidistant size grids, the general expressions of cloud microphysical parameters are calculated and the ensuing relative errors are discussed in detail. The proposed methodology is further applied to a subset of measured data, and it is shown that the overall uncertainties in computing various cloud parameters are mainly driven by the measurement errors of the forward-scattering cross section for each particle. Finally, the influence of the relatively large imprecision in the real and imaginary parts of the refractive index of cloud droplets on the size distributions and on the ensuing cloud parameters is analyzed. It is concluded that, in the presence of high atmospheric loads of hydrophilic and light-absorbing aerosols, such imprecisions may drastically affect the reliability of the cloud data obtained with cloud and aerosol spectrometers. Some complementary measurements for improving the quality of the cloud droplet size distributions obtained in post-flight analyses are suggested.

scholarly journals Post-flight analysis of detailed size distributions of warm cloud droplets, as determined in situ by cloud and aerosol spectrometers

2021 ◽  
Author(s):  
Sorin Nicolae Vâjâiac ◽  
Andreea Calcan ◽  
Robert Oscar David ◽  
Denisa-Elena Moacă ◽  
Gabriela Iorga ◽  
...  
Keyword(s):  
Cross Section ◽  
Forward Scattering ◽  
Scattering Cross Section ◽  
Size Distributions ◽  
Cloud Droplets ◽  
Cloud Particle ◽  
Fine Grid ◽  
Scattering Cross ◽  
Cloud Parameters

Abstract. Warm clouds, consisting of liquid cloud droplets, play an important role in modulating the amount of incoming solar radiation to Earth’s surface and thus, the climate. The size and number concentration of these cloud droplets control the reflectance of the cloud, the formation of precipitation and ultimately, the lifetime of the cloud. Therefore, in situ observations of the number and diameter of cloud droplets are frequently performed with cloud and aerosol spectrometers, which determine the optical diameters of cloud particles (in the range of up to a few tens of microns) by measuring their forward scattering cross sections in visible light and comparing these values with Mie-theoretical computations. The use of such instruments must rely on a fast working scheme consisting of a limited pre-defined uneven grid of cross section values that corresponds to a theoretically derived uneven set of size intervals (bins). However, as more detailed structural analyses of warm clouds are needed to improve future climate projects, we present a new numerical post-flight methodology using recorded particle-by-particle sample files. The Mie formalism produces a complicated relationship between a particle’s diameter and its forward scattering cross section. This relationship cannot be expressed in an analytically closed form and it should be numerically computed point by point, over a certain grid of diameter values. The optimal resolution required for constructing the diagram of this relationship is therefore analysed. Cloud particle statistics are further assessed using a fine grid of particle diameters in order to capture the finest details of the cloud particle size distributions. The possibility and the usefulness of using coarser size grids, with either uneven or equal intervals is also discussed. For coarse equidistant size grids, the general expressions of cloud microphysical parameters are calculated and the ensuing relative errors are discussed in detail. The proposed methodology is further applied to a subset of measured data and it is shown that the overall uncertainties in computing various cloud parameters are mainly driven by the measurement errors of the forward scattering cross section for each particle. Finally, the influence of the relatively large imprecision in the real and imaginary parts of the refractive index of cloud droplets on the size distributions and on the ensuing cloud parameters is analysed. It is concluded that, in the presence of high atmospheric loads of hydrophilic and light absorbing aerosols, such imprecisions may drastically affect the reliability of the cloud data obtained with cloud and aerosol spectrometers. Some complementary measurements for improving the quality of the cloud droplet size distributions obtained in post-flight analyses are suggested.

Post-flight analysis of the aerosol impact on size distributions of warm clouds’ droplets, as determined in situ by cloud and aerosol spectrometers

2020 ◽  
Author(s):  
Denisa Elena Moacă ◽  
Sorin Nicolae Vâjâiac ◽  
Andreea Calcan ◽  
Valeriu Filip
Keyword(s):  
Size Distribution ◽  
Pure Water ◽  
Weather Forecast ◽  
Cloud Microphysics ◽  
Atmospheric Environment ◽  
Size Distributions ◽  
Cloud Droplets ◽  
Cloud Particle ◽  
Microphysical Properties

<p>The influence of aerosol on the various aspects of the atmospheric properties as well as on the energetic balance is widely recognised in the scientific community and this issue is currently subject to worldwide intense investigations. Among the multiple ways aerosol particles are impacting the atmospheric environment, their interference with the phase transformations of the atmospheric water is of particular importance. Cloud microphysics, on the other hand, is one of the key components in weather forecast and, therefore, in pursuing daily domestic activities ranging from agriculture to energy harvesting and aviation. The micro-physical processes taking place in clouds are strongly influenced by the spatiotemporal variation of the size distribution of the cloud droplets. In this context, as in situ investigations of clouds seem appropriate, one of the most useful types of instruments is casted into the generic name of Cloud and Aerosol Spectrometer (CAS) that can be mounted on specialized research aircraft. The CAS working principle relies basically on measuring the forward scattering cross section (FWSCS) of light with a certain wavelength on a cloud particle and comparing it to the FWSCS computed for pure water spheres. The eventual matching of these values leads to assigning a certain value for the measured particle’s diameter. The light wavelength is usually chosen in a range where pure water has virtually no absorption. However, atmospheric aerosol frequently mixes up with cloud droplets (starting even from the nucleation processes) and alters their optical properties. By increasing absorption and/or refractivity with respect to those of pure water, one can easily show that the FWSCS-diameter diagram changes drastically by becoming smoother and with an overall significant decrease in absolute values. This means that a CAS will systematically count “contaminated” cloud droplets in a lower range of diameters, thus distorting their real size distribution. This effect is inherently degrading the objectivity of CAS measurements and should be more pronounced when levels of sub-micrometer sized aerosol increase at the cloud altitude. The present study aims at pointing out such correlation in order to estimate the reliability of size distributions (and of the ensuing cloud microphysical properties) obtained by CAS.</p>

Scattering from Many Centers in One Dimension

1975 ◽  
Vol 53 (9) ◽  
pp. 874-881 ◽  
Author(s):  
K. K. Bajaj ◽  
Y. Nogami
Keyword(s):  
Cross Section ◽  
Forward Scattering ◽  
Scattering Cross Section ◽  
One Dimension ◽  
Laboratory System ◽  
Dimensional Model ◽  
One Dimensional ◽  
Scattering Cross ◽  
Low Energies ◽  
Nucleus Scattering

The accuracies of the fixed scatterer approximation (FSA) and the Glauber approximation (GA) are examined for an exactly soluble, one dimensional model which simulates nucleon–nucleus scattering. These approximations are found to work well at unexpectedly low energies. For example, the errors in the FSA and GA for the 'nucleon–deuteron' forward scattering cross section at 10 MeV (laboratory system) are only 5 and 7% respectively. The reason for this success is examined.

Measurements of the π−p → π0n forward scattering cross section in the energy region 400–600 MeV

1978 ◽  
Vol 140 (2) ◽  
pp. 279-284 ◽  
Author(s):  
A.V. Kravtsov ◽  
L.A. Kuzmin ◽  
O.N. Nemozhenko ◽  
D.L. Nikolaev ◽  
T.S. Serebrova ◽  
...  
Keyword(s):  
Cross Section ◽  
Energy Region ◽  
Forward Scattering ◽  
Scattering Cross Section ◽  
Scattering Cross

Mass Determination by Direct Measurement of Electron Scattering

1975 ◽  
Vol 33 ◽  
pp. 240-241
Author(s):  
M. K. Lamvik ◽  
A. V. Crewe
Keyword(s):  
Cross Section ◽  
Electron Scattering ◽  
Mass Density ◽  
Variable Mass ◽  
Scattering Cross Section ◽  
Mass Determination ◽  
Number Density ◽  
Cross Sectional ◽  
Thin Slice ◽  
Scattering Cross

If a molecule or atom of material has molecular weight A, the number density of such units is given by n=Nρ/A, where N is Avogadro's number and ρ is the mass density of the material. The amount of scattering from each unit can be written by assigning an imaginary cross-sectional area σ to each unit. If the current I0 is incident on a thin slice of material of thickness z and the current I remains unscattered, then the scattering cross-section σ is defined by I=IOnσz. For a specimen that is not thin, the definition must be applied to each imaginary thin slice and the result I/I0 =exp(-nσz) is obtained by integrating over the whole thickness. It is useful to separate the variable mass-thickness w=ρz from the other factors to yield I/I0 =exp(-sw), where s=Nσ/A is the scattering cross-section per unit mass.

Sign in / Sign up

Export Citation Format

Share Document