Contrail Modeling and Simulation

We develop an idealized, physically based model describing combined effects of ice nucleation and sublimation on ice crystal number during persistent contrail formation. Our study represents the first effort to predict ice numbers at the point where contrails transition into contrail cirrus—several minutes past formation—by connecting them to aircraft soot particle emissions and atmospheric supersaturation with respect to ice. Results averaged over an observed exponential distribution of ice supersaturation (mean value 15%) indicate that large reductions in soot particle numbers are needed to lower contrail ice crystal numbers significantly for soot emission indices around 1015 (kg fuel)−1, because reductions in nucleated ice number are partially compensated by sublimation losses. Variations in soot particle (−50%) and water vapor (+10%) emission indices at threefold lower soot emissions resulting from biofuel blending cause ice crystal numbers to change by −35% and <5%, respectively. The efficiency of reduction depends on ice supersaturation and the size distribution of nucleated ice crystals in jet exhaust plumes and on atmospheric ice supersaturation, making the latter another key factor in contrail mitigation. We expect our study to have important repercussions for planning airborne measurements targeting contrail formation, designing parameterization schemes for use in large‐scale models, reducing uncertainties in predicting contrail cirrus, and mitigating the climate impact of aviation.

ξ = \frac{n (t_{v} + Δ t_{v})}{n (t_{v})} = \underset{primary wake (pw)}{\underset{(1 - η) f_{pw}}{false}} + \underset{secondary wake (sw)}{\underset{η {scriptD}_{sw}}{false}} .

While n ( t v ) decreases by isobaric mixing by a factor

{scriptD}_{sw}

in the fraction of detrained exhaust, it is affected by sublimation losses in the exhaust trapped in the sinking (heating) vortices in which mixing is strongly suppressed.…”

Section: Wake Processing Of Ice Crystals In Persistent Contrailsmentioning

confidence: 99%

Section: Conceptual Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Susceptibility of contrail ice crystal numbers to aircraft soot particle emissions

Kärcher

Voigt

2017

“…Fluid-dynamical models (Huebsch & Lewellen, 2006;Unterstrasser, 2016) and measurements Schumann et al, 2013) have shown that aircraft wake dynamics can have marked effects on contrail properties. This includes the possibility of ice particle losses during the descent of wake vortices Geophysical Research Letters 10.1029/2018GL079390 forcing ice particle sublimation due to adiabatic heating even if the ambient air surrounding the contrail is ice-supersaturated (Kärcher, 2018;Paoli & Shariff, 2016). Assessing contrail properties toward the end of the vortex phase is of particular interest, as they affect properties of evolving contrail cirrus over hours (Unterstrasser & Gierens, 2010).…”

Section: Introductionmentioning

confidence: 99%

In Situ Observations of Ice Particle Losses in a Young Persistent Contrail

Kleine

Voigt

Sauer

et al. 2018

We describe results of in situ observations of a 1‐ to 2‐min‐old contrail in the vortex phase generated from soot‐rich exhaust (>1015 emitted soot particles per kilogram of fuel burned). Simultaneous measurements of soot (EIsoot) and apparent ice (AEIice) particle number emission indices show a pronounced anticorrelation in the vertical contrail profile. AEIice decrease by about 75% with increasing distance below the contrail‐producing aircraft, while EIsoot increase by an equivalent relative fraction, therefore strongly suggesting ice particle formation to be soot‐controlled and losses to be caused by sublimation. Quantifying these losses in measurements helps to validate and improve contrail parameterizations used to estimate the climate impact of contrails and contrail cirrus. Our study further demonstrates the challenges in the performance and interpretation of particle measurements in young contrails and lends itself to suggestions for improving contrail data evaluation.

“…Modeling tools with various degrees of complexity have been developed to study formation stage processes, ranging from microphysical parcel models to fluid‐dynamical large‐eddy simulations (LES; see Paoli & Shariff, , and references therein). Detailed model validation is hampered primarily by a lack of contrail measurements in ice‐supersaturated conditions.…”

Section: Introductionmentioning

confidence: 99%

Contrail Formation: Analysis of Sublimation Mechanisms

Kärcher

Kleine

Sauer

et al. 2018

We study losses of ice crystals in a persistent, soot‐rich contrail in the wake behind a medium‐sized aircraft at cruise. Constraining a model covering ice nucleation, growth, and sublimation phases with an aircraft data set, we track the sublimation history over 2 min of contrail age and relate ice crystal numbers to the number of soot particles emitted by the aircraft engines. We analyze the observed vertical distribution of ice numbers, estimating an exponential scale height in the range 50–100 m and wake‐averaged ice numbers (1.3–1.7) × 1015 (kg‐fuel)−1 after sublimation, removing 60% of the ice crystals that originally nucleated on emitted soot particles. We define soot emission‐ and ice supersaturation‐dependent contrail depths, affecting estimates of horizontal spreading rates of contrails. Our findings have ramifications for the representation of long‐lived contrails in global models.