Statistics of potential radiative forcing of persistent contrails

Contrails affect climate if they are persistent, that is, if they are located in an ice-supersaturated region (ISSR). They do this by reflecting sunlight back to space (cooling) and by blocking thermal radiation from the Earth surface and lower atmosphere (warming). During night, there is always net warming since sunlight and thus it’s possible reflection is absent. In most (daytime) cases there is substantial cancellation of the warming and cooling effects, but occasionally (in particular during night) the long-wave warming effect dominates such that the respective contrail has a particularly strong contribution to climate warming. This is a Big Hit, and such contrails should be avoided already in the flight planning phase. Such an avoidance strategy needs of course a reliable prediction of the conditions under which contrails actually are that strong climate warmers. The topic of this presentation is how situations with strong warming contrails can be characterised and whether and how reliably it is possible to predict them

Theory of Contrail Formation for Fuel Cells

The theory of contrail formation for fuel cells is derived. It is a variant of the well-known Schmidt-Appleman theory. The contrail factor or G-factor for fuel cells is much larger than for jet engines, such that condensation of the exhaust water vapour can happen even at the Earth’s surface in sufficiently cold (a few degrees above zero) weather. Contrail formation from fuel cells will occur frequently in the lower troposphere and is unavoidable below moderate temperature limits, in the upper troposphere and in the stratosphere. Despite the high frequency of contrail formation from fuel cells, their climate impact is lower than that of contrails from jet engines. Most fuel cell contrails will be short and those persistent ones will be optically thinner and have on average a shorter lifetime than traditional persistent contrails. From a climate point of view, the introduction of fuel cells into aviation can be recommended

Contrails, contrail prediction, contrail avoidance

Einführung in 1) Was sind Kondensstreifen, wie entstehen sie, wie entwicken sie sich 2) Strahungs- und Klimawirkung von Kondensstreifen 3) Vermeidung von Kondensstreifen und die dazu notwendige Verbesserung der 4) Vorhersage eisübersättigter Regionen (und damit der Möglichkeit persistenter Kondensstreifen

Technical note: On the intercalibration of HIRS channel 12 brightness temperatures following the transition from HIRS 2 to HIRS 3/4 for ice saturation studies

For studies of trends in ice supersaturation in the upper troposphere we need very long time series of upper tropospheric humidity. The set of HIRS channel 12 satellite data can be used for this purpose, since Shi and Bates (2011) had provided an intercalibrated time series of channel 12 brightness temperatures. In the current paper we improve the intercalibration at the low tail of brightness temperatures, which leads to a more homogeneous time series of upper-tropospheric humidities

Forecasting conditions for contrail development

Der Vortrag beschreibt 1) die aktuellen Probleme bei der Vorhersage persistenter Kondensstreifen zum Zwecke der umweltgerechten Flugplanung 2) Wo diese Probleme herrühren 3) Wie diese Probleme zu lösen sin

Contrail formation and persistence conditions for alternative fuels

In order to counteract global warming, the European Green Deal was made to improve the journey to a sustainable future. This also has an impact on aviation, because in the future the growth in air traffic must no longer lead to rising emissions, but even all aviation CO2 emissions have to be reduced to zero to achieve the goal of climate-neutral aviation by 2050. There are several approaches for new propulsion solutions and sustainable vehicle configurations and operations. A promising approach is the use of modern fuels. These include drop-in fuels (kerosene-like fuels) but also revolutionary concepts such as the use of liquid hydrogen or liquid natural gas, electric flying, and mixed forms of these. These approaches have certain advantages regarding the climate impact, but not all processes and effects are fully understood, especially their effects on contrails and their properties, frequency, and lifetime. In this study, we analyse 10 years of airborne and reanalysis data of temperature and humidity to see, how much more persistent contrails would be formed if kerosene were replaced by alternative fuels of different energy-specific water vapour emission indices, which are generally higher for alternative fuels. It turns out, that the amount of additional persistent contrails is quite minor for drop-in fuels, which are already used nowadays, but it is larger for other kinds of fuels, such as methane and liquid hydrogen

Forecasting ice supersaturation and persistent contrails

In diesem Vortrag werden Ergebnisse aus den Projekten ACACIA und BeCoM gezeigt. Die Arbeiten hatten und haben zum Ziel, die Vorhersage persistenter Kondensstreifen verläßlicher zu machen

Towards an aviation weather forecast for green operations

Aviation contributes about 3.5% of the total anthropogenic global warming through both CO2 and non-CO2 effects. This problem is aggravated by the large growth rate of the aviation sector (>4% per year), which was only temporarily interrupted by the Covid-19 pandemic. It is evident that measures need to be taken to lessen the climate impact by aviation. CO2 has a very long residence time, such that its climate impact does not depend on when and where it is emitted. In contrast, non-CO2 emissions act on shorter time scales and their effect thus depends on the weather and synoptic situation at the time and location of the emission. This is particularly evident for contrails whose individual impacts range from strong cooling to strong warming, depending on the actual situation. It is thus possible to lessen the climate impact of aviation by planning flights such that climate-sensitive regions (i.e. regions where emissions would have a particularly strong warming impact) are avoided. To make such ideas real, new developments in aviation weather forecast are needed. One example is the implementation of so-called algorithmic climate change functions which provide measures of potential climate impact of emissions depending on actual weather variables (e.g. temperature and geopotential). The result can be provided in different ways, e.g. as costs, such that they can be used directly as additional cost-functions in flight routing. Another example is the prediction of persistent contrails in order to avoid them either tactically (by directives of air traffic control to pilots en-route) or strategically (as above, during flight routing). As one requirement for contrail persistence is ice supersaturation, this atmospheric state must be represented by the numerical weather prediction models, which is currently challenging. Another possibility is a probabilistic prediction of contrails using the standard weather variables. In this talk we will present how ideas from several projects for a better mitigation of contrails and other aviation non-CO2 effects on climate can be incorporated into aviation weather forecast models

Can we successfully avoid persistent contrails by small altitude adjustments of flights in the real world?

This paper describes the first-ever operational contrail avoidance trial in the real world, which took place in the region of Maastricht Upper Area Control (including the northwest of Germany, the Benelux countries and part of the North Sea) in the year 2021. Contrail avoidance could be an efficient method for mitigating the climate impact of aviation. Applying a deliberate experiment design, air traffic was deviated every other day by changing the flight altitude by up to 2000 ft up or down if potential persistent contrails were predicted. Whether deviations were successful on average was checked using satellite images of high clouds and by application of a contrail detection algorithm, which makes use of the properties of contrails. Despite the fact that forecasting persistent contrails remains a challenge, the trial was successful at a significance level of 97.5 %, i.e., on average persistent contrails can be avoided for regular flights in the real world with a small intervention in the vertical flight path. The experiment is an important step towards a regular operational reduction of the aviation climate impact by means of air traffic management. Nevertheless, many open questions need to be solved prior to an operational implementation of contrail avoidance or climate optimised flight trajectories in legal ATM procedures

Can we successfully avoid persistent contrails by small altitude adjustments of flights in the real world?

This paper describes the first-ever operational contrail avoidance trial in the real world, which took place in the region of Maastricht Upper Area Control (including the northwest of Germany, the Benelux countries and part of the North Sea) in the year 2021. Contrail avoidance could be an efficient method for mitigating the climate impact of aviation. Applying a deliberate experiment design, air traffic was deviated every other day by changing the flight altitude by up to 2000 ft up or down if potential persistent contrails were predicted. Whether deviations were successful on average was checked using satellite images of high clouds and by application of a contrail detection algorithm, which makes use of the properties of contrails. Despite the fact that forecasting persistent contrails remains a challenge, the trial was successful at a significance level of 97.5 %, i.e., on average persistent contrails can be avoided for regular flights in the real world with a small intervention in the vertical flight path. The experiment is an important step towards a regular operational reduction of the aviation climate impact by means of air traffic management. Nevertheless, many open questions need to be solved prior to an operational implementation of contrail avoidance or climate optimised flight trajectories in legal ATM procedures