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

. Recently, several Lagrangian microphysical models have been developed which use a large number of (computational) particles to represent a cloud. In particular, the collision process leading to coalescence of cloud droplets or aggregation of ice crystals is implemented differently in various models. Three existing implementations are reviewed and extended, and their performance is evaluated by a comparison with well-established analytical and bin model solutions. In this first step of rigorous evaluation, box model simulations, with collection/aggregation being the only process considered, have been performed for the three well-known kernels of Golovin, Long and Hall. Besides numerical parameters, like the time step and the number of simulation particles (SIPs) used, the details of how the initial SIP ensemble is created from a prescribed analytically defined size distribution is crucial for the performance of the algorithms. Using a constant weight technique, as done in previous studies, greatly underestimates the quality of the algorithms. Using better initialisation techniques considerably reduces the number of required SIPs to obtain realistic results. From the box model results, recommendations for the collection/aggregation implementation in higher dimensional model setups are derived. Suitable algorithms are equally relevant to treating the warm rain process and aggregation in cirrus.

https://gmd.copernicus.org/articles/10/1521/2017/gmd-10-1521-2017.pdf

Collection/aggregation algorithms in Lagrangian cloud microphysical models: Rigorous evaluation in box model simulations

Large-eddy simulations (LES) with Lagrangian ice microphysics were used to study the early contrail evolution during the vortex phase. Microphysical and geometrical properties of a contrail produced by a large-sized aircraft (type B777/A340) were investigated systematically for a large parameter range. Crystal loss due to adiabatic heating in the downward moving vortices was found to depend strongly on relative humidity and temperature, qualitatively similar to previous 2-D simulation results. Contrail depth is as large as 450 m for the investigated parameter range and was found to be underestimated in a previous 2-D study. Further sensitivity studies show a nonnegligible effect of the initial ice crystal size distribution and the initial ice crystal number on the crystal loss, whereas the contrail structure and ice mass evolution is only barely affected by these variations. Variation of fuel flow has the smallest effect on crystal loss. At high supersaturations, our choice of contrail spatial initialization may underestimate the ice crystal loss. The set of presented sensitivity studies is a first step toward a quantitative description of young contrails in terms of vertical extent and crystal loss. Concluding contrail-to-cirrus simulations demonstrate the relevance of vortex phase processes and its three-dimensional modeling on the later contrail-cirrus properties.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013JD021418

Large‐eddy simulation study of contrail microphysics and geometry during the vortex phase and consequences on contrail‐to‐cirrus transition

We investigate the evolution of contrails during the vortex phase using numerical simulations. Emphasis is placed on microphysical properties and on the vertical distribution of ice mass and number concentration at the end of the vortex phase. Instead of using a 3D model which would be preferable but computationally too costly, we use a 2D model equipped with a special tool for controlling vortex decay. We conduct a great number of sensitivity studies for one aircraft type. It turns out that atmospheric parameters, namely supersaturation, temperature, stability and turbulence level have the biggest impact on the number of ice crystals and on the ice mass that survives until vortex breakup and that therefore makes up the persistent contrail in supersaturated air. The initial ice crystal number density and its distribution in the vortex, are of minor importance.

/pdf/the-evolution-of-contrail-microphysics-in-the-vortex-phase-3bvruj8rb7.pdf

The evolution of contrail microphysics in the vortex phase

. This paper presents various techniques to speed up the Lagrangian ice microphysics code EULAG-LCM. The amount of CPU time (and also memory and storage data) depends heavily on the number of simulation ice particles (SIPs) used to represent the bulk of real ice crystals. It was found that the various microphysical processes require different numbers of SIPs to reach statistical convergence (in a sense that a further increase of the SIP number does not systematically change the physical outcome of a cirrus simulation). Whereas deposition/sublimation and sedimentation require only a moderate number of SIPs, the (nonlinear) ice nucleation process is only well represented, when a large number of SIPs is generated. We introduced a new stochastic nucleation implementation which mimics the stochastic nature of nucleation and greatly reduces numerical sensitivities. Furthermore several strategies (SIP merging and splitting) are presented which flexibly adjust and reduce the number of SIPs. These efficiency measures reduce the computational costs of present cirrus studies and allow extending the temporal and spatial scales of upcoming studies.

/pdf/optimisation-of-the-simulation-particle-number-in-a-5dtmsih08e.pdf

Optimisation of the simulation particle number in a Lagrangian ice microphysical model

Air traffic is important to our society and guarantees mobility especially for long distances. Air traffic is also
contributing to climate warming via emissions of CO2 and various non-CO2 effects, such as contrail-cirrus or
increase in ozone concentrations. Here we investigate the climate impact of a future aircraft design, a multi
fuel blended wing body (MF-BWB), conceptually designed within the EU-project AHEAD. We re-calculate
the parameters for the contrail formation criterion, since this aircraft has very different characteristics
compared to conventional technologies and show that contrail formation potentially already occurs at lower
altitudes than for conventional aircraft. The geometry of the contrails, however, is similar to conventional
aircraft, as detailed Large-Eddy-Simulations show. The global contrail-cirrus coverage and related radiative
forcing is investigated with a climate model including a contrail-cirrus parameterisation and shows an increase
in contrail-cirrus radiative forcing compared to conventional technologies, if the number of emitted particles
is equal to conventional technologies. However, there are strong indications that the AHEAD engines would
have a substantial reduction in the emission of soot particles and there are strong indications that this leads
to a substantial reduction in the contrail-cirrus radiative forcing. An overall climate impact assessment with
a climate-chemistry response model shows that the climate impact is likely to be reduced by 20% to 25%
compared to a future aircraft with conventional technologies. We further tested the sensitivity of this result
with respect to different future scenarios for the use of bio fuels, improvements of the fuel efficiency for
conventional aircraft and the impact of the number of emitted soot particles on the radiative forcing. Only the
latter has the potential to significantly impact our findings and needs further investigation. Our findings show
that the development of new and climate compatible aircraft designs requires the inclusion of climate impact
assessments already at an early stage, i.e. pre-design level.

Simon Unterstrasser

Papers

Collection/aggregation algorithms in Lagrangian cloud microphysical models: Rigorous evaluation in box model simulations

Large‐eddy simulation study of contrail microphysics and geometry during the vortex phase and consequences on contrail‐to‐cirrus transition

The evolution of contrail microphysics in the vortex phase

Optimisation of the simulation particle number in a Lagrangian ice microphysical model

Assessing the climate impact of the AHEAD multi-fuel blended wing body