A copy of Guangbo jiemu bao [Broadcast Program Report] was being passed from hand to hand among a group of young people eager to be the first to read the article introducing the program "What Is Revolutionary Love?" It said: "… Young friends, you are certainly very concerned about this problem'. So, we would like you to meet the young women workers Meng Xiaoyu and Meng Yamei and the older cadre Miss Feng. They are the three leading characters in the short story ‘The Place of Love.’ Through the description of the love lives of these three, the story induces us to think deeply about two questions that merit further examination.

This is How the Discussion Started

A Short Course in Cloud Physics

https://archive-ouverte.unige.ch/unige:30039/ATTACHMENT01

21st century climate change in the European Alps--a review.

. libRadtran is a widely used software package for radiative transfer calculations. It allows one to compute (polarized) radiances, irradiance, and actinic fluxes in the solar and thermal spectral regions. libRadtran has been used for various applications, including remote sensing of clouds, aerosols and trace gases in the Earth's atmosphere, climate studies, e.g., for the calculation of radiative forcing due to different atmospheric components, for UV forecasting, the calculation of photolysis frequencies, and for remote sensing of other planets in our solar system. The package has been described in Mayer and Kylling (2005). Since then several new features have been included, for example polarization, Raman scattering, a new molecular gas absorption parameterization, and several new parameterizations of cloud and aerosol optical properties. Furthermore, a graphical user interface is now available, which greatly simplifies the usage of the model, especially for new users. This paper gives an overview of libRadtran version 2.0.1 with a focus on new features. Applications including these new features are provided as examples of use. A complete description of libRadtran and all its input options is given in the user manual included in the libRadtran software package, which is freely available at http://www.libradtran.org .

/pdf/the-libradtran-software-package-for-radiative-transfer-5fzcfcovgc.pdf

The libRadtran software package for radiative transfer calculations (version 2.0.1)

https://escholarship.org/content/qt7gh3p3z1/qt7gh3p3z1.pdf?t=qgqugr

The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018

The aerodynamic formation flight, which is also known as aircraft wake-surfing for efficiency (AWSE), enables aircraft to harvest the energy inherent in another aircraft’s wake vortex. As the thrust of the trailing aircraft can be reduced during cruise flight, the resulting benefit can be traded for longer flight time, larger range, less fuel consumption, or cost savings accordingly. Furthermore, as the amount and location of the emissions caused by the formation are subject to change and saturation effects in the cumulated wake of the formation can occur, AWSE can favorably affect the climate impact of the corresponding flights. In order to quantify these effects, we present an interdisciplinary approach combining the fields of aerodynamics, aircraft operations and atmospheric physics. The approach comprises an integrated model chain to assess the climate impact for a given air traffic scenario based on flight plan data, aerodynamic interactions between the formation members, detailed trajectory calculations as well as on an adapted climate model accounting for the saturation effects resulting from the proximity of the emissions of the formation members. Based on this approach, we derived representative AWSE scenarios for the world’s major airports by analyzing and assessing flight plans. The resulting formations were recalculated by a trajectory calculation tool and emission inventories for the scenarios were created. Based on these inventories, we quantitatively estimated the climate impact using the average temperature response (ATR) as climate metric, calculated as an average global near surface temperature change over a time horizon of 50 years. It is shown, that AWSE as a new operational procedure has a significant mitigation potential on climate impact. For a global formation flight scenario, we estimated the average relative change of climate response to range between 22% and 24% while the relative fuel saving effects sum up to 5–6%.

/pdf/climate-impact-mitigation-potential-of-formation-flight-152o3s9ums.pdf

Climate impact mitigation potential of formation flight

An operational measure that is inspired by migrant birds aiming toward the mitigation of aviation climate impact is to fly in aerodynamic formation. When this operational measure is adapted to commercial aircraft it saves fuel and is, therefore, expected to reduce the climate impact of aviation. Besides the total emission amount, this mitigation option also changes the location of emissions, impacting the non-CO2 climate effects arising from NOx and H2O emissions and contrails. Here, we assess these non-CO2 climate impacts with a climate response model to assure a benefit for climate not only due to CO2 emission reductions, but also due to reduced non-CO2 effects. Therefore, the climate response model AirClim is used, which includes CO2 effects and also the impact of water vapor and contrail induced cloudiness as well as the impact of nitrogen dioxide emissions on the ozone and methane concentration. For this purpose, AirClim has been adopted to account for saturation effects occurring for formation flight. The results of the case studies show that the implementation of formation flights in the 50 most popular airports for the year 2017 display an average decrease of fuel consumption by 5%. The climate impact, in terms of average near surface temperature change, is estimated to be reduced in average by 24%, with values of individual formations between 13% and 33%.

https://www.mdpi.com/2226-4310/7/12/172/pdf

Assessing the climate impact of formation flights

. A high-resolution
regional-scale numerical model was extended by a parameterization that allows
for both the generation and the life cycle of contrails and contrail cirrus
to be calculated. The life cycle of contrails and contrail cirrus is
described by a two-moment cloud microphysical scheme that was extended by a
separate contrail ice class for a better representation of the high
concentration of small ice crystals that occur in contrails. The basic input
data set contains the spatially and temporally highly resolved flight
trajectories over Central Europe derived from real-time data. The
parameterization provides aircraft-dependent source terms for contrail ice
mass and number. A case study was performed to investigate the influence of
contrails and contrail cirrus on the shortwave radiative fluxes at the
earth's surface. Accounting for contrails produced by aircraft enabled the
model to simulate high clouds that were otherwise missing on this day. The
effect of these extra clouds was to reduce the incoming shortwave radiation
at the surface as well as the production of photovoltaic power by up to
10  % .

/pdf/contrails-and-their-impact-on-shortwave-radiation-and-4numt8l11x.pdf

Contrails and their impact on shortwave radiation and photovoltaic power production - a regional model study

. We investigate the microphysics of contrail formation behind commercial aircraft by means of the particle-based LCM (Lagrangian Cloud Module) box model. We extend the original LCM to cover the basic pathway of contrail formation of soot particles being activated into liquid droplets that soon after freeze into ice crystals. In our particle-based microphysical approach, simulation particles are used to represent different particle types (soot, droplets, ice crystals) and properties (mass/radius, number). The box model is applied in two frameworks. In the classical framework, we prescribe the dilution along one average trajectory in a single box model run. In the second framework, we perform a large ensemble of box model runs using 25000 different trajectories inside an expanding exhaust jet as simulated by the LES (large-eddy simulation) model FLUDILES. In the ensemble runs, we see a strong radial dependence of the temperature and relative humidity evolution. Droplet formation on soot particles happens first near the plume edge and a few tenths of seconds later in the plume centre. Averaging over the ensemble runs, the number of formed droplets/ice crystals increases more smoothly over time than for the single box model run with the average dilution. Consistent with previous studies, contrail ice crystal number varies strongly with atmospheric parameters like temperature and relative humidity near the contrail formation threshold. Close to this threshold, the freezing fraction of soot particles depends strongly on the geometric-mean dry core radius and the hygroscopicity parameter of soot particles. This sensitivity is quite low at ambient conditions far away from the formation threshold. Absolute ice crystal numbers, on the other hand, are controlled by the soot number emission index for all atmospheric conditions. The comparison with a recent contrail formation study by Lewellen (2020) (using similar microphysics) shows a later onset of our contrail formation due to a weaker prescribed plume dilution. If we use the same dilution data, our and Lewellen's evolution in contrail ice nucleation show an excellent agreement cross-validating both microphysics implementations. This means that differences in contrail properties mainly result from different representations of the plume mixing and not from the microphysical modelling. The presented aerosol and microphysics scheme describing contrail formation is of intermediate complexity and thus suited to be incorporated in an LES model for 3D contrail formation studies explicitly simulating the jet expansion. The presented box model results will help interpreting the upcoming, more complex 3D results.

/pdf/box-model-trajectory-studies-of-contrail-formation-using-a-ol9sflqo0e.pdf

Box model trajectory studies of contrail formation using a particle-based cloud microphysics scheme

This work discusses the numerical aspects of representing the diffusional (condensational) growth in particulate systems such as atmospheric clouds. It focuses on the Eulerian modeling approach, in which the evolution of the particle size spectrum is carried out using a fixed-bin discretization associated with inherent numerical diffusion. Focus is on the applications of MPDATA numerical schemes (variants explored include: infinite-gauge, non-oscillatory, third-order-terms and recursive antidiffusive correction). Methodology for handling coordinate transformations associated with both particle size distribution variable choice and numerical grid layout are expounded. Analysis of the performance of the scheme is performed using: (i) an analytically solvable box-model test case, and (ii) the single-column "KiD" test case in which the size-spectral advection due to condensation is solved simultaneously with the spatial advection in the vertical physical coordinate, and in which the supersaturation evolution is coupled with the droplet growth through water mass budget. The single-column problem involves numerical solution of a two-dimensional advection problem (spectral and spatial dimensions). The box-model simulations demonstrate that, for the problem considered, even a tenfold decrease of the spurious numerical spectral broadening can be obtained by a proper choice of the MPDATA variant (maintaining the same spatial and temporal resolution), yet at an increased computational cost. Analyses using the single-column test case reveal that the width of the droplet size spectrum is affected by numerical diffusion pertinent to both spatial and spectral advection. Application of even a single corrective iteration of MPDATA robustly decreases the relative dispersion of the droplet spectrum, roughly by a factor of two at the levels of maximal liquid water content.

Simon Unterstrasser

Papers

Climate impact mitigation potential of formation flight

Assessing the climate impact of formation flights

Contrails and their impact on shortwave radiation and photovoltaic power production - a regional model study

Box model trajectory studies of contrail formation using a particle-based cloud microphysics scheme

On numerical broadening of particle size spectra: a condensational growth study using PyMPDATA