Topic Number: 2 (version of 5 July 2013)Contrails and contrail impact on cirrus formation

Ulrich Schumann, Andy Heymsfield, Patrick Minnis

Klaus Gierens, Kaspar Graf, Stephan Kox, Bernhard Mayer, Andreas Minikin, Martin Schnaiter, Simon Unterstraßer, Christiane Voigt et al.

dedicated to Hermann Mannstein (9 November 1952 - 25 January 2013)

Presentation Layout (as suggested by Darrel Baumgardner)

1. General Description of Topic Theme and Objectives of the Topic Working Group

2. Brief Status of this Topic after the July, 2010 workshop

3. What progress has been made in the last three years?

4. What are the remaining unknowns and uncertainties and how do they impact our fundamental understanding of the atmosphere, climate change, weather and society in general?

2

Contrail formation types

3

• Exhaust contrails• Aerodynamic contrails• Distrails• short living contrails• persistent contrails• contrail cirrus • soot cirrus

exhaust contrail

aerodynamiccontrail

cloud holes & distrails

short living and persistent contrails

Persistent contrails / contrail cirrus

soot cirrus ????3

Theme and Objectives of the Topic Working Groupwhat do we currently understand about ice particle properties in contrails?• Contrail formation, in particular of exhaust contrails• Approximate cover, ice particle concentration, habits, optical properties and

radiative forcing estimateswhere are the gaps in our knowledge base?• Nucleating and sublimation process from engine to end of wake vortex phase• Crystal concentrations, sizes, shapes, composition• "preactivation" and chemical aging of ice nuclei• Sublimation of contrails• Competition for humidity between contrails and cirrus• Aggregation, sedimentation, fall streak formation• Cover for given -threshold (with contrail-contrail and contrail-cirrus overlap)• Aerodynamic contrails, distrails and their effects on ice clouds• Life cycle and life time • Aerosol (soot etc.) impact • Accurate radiative forcing why do these gaps exist and how do we move forward to fill these gaps?• multi-scale issue! - requires• multi-sensor observations in airborne campaigns • laboratory simulations, e.g. of preactivation and aging• Lagrangian model and observation studies from first nucleation to globe

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Brief Status of this Topic after the July 2010 workshop (see BAMS article)

Reference: Baumgardner et al., IN SITU, AIRBORNE INSTRUMENTATION - Addressing and Solving Measurement Problems in Ice Clouds, Bull. AMS, 93 (2), ES29-ES34, 2012

Contrails and contrail-induced cirrus were addressed (by Philip R.A. Brown, Andy Heymsfield, and Jean-Francois Gayet). www.uni-leipzig.de/~meteo/en/forschung/airborne_workshop.php(see also Heymsfield et al., BAMS, 2010)

Findings as of 2010:Key unresolved questions with respect to contrail cirrus: • relative roles of homogeneous and heterogeneous nucleation, • relationship between ice nuclei (IN) and ice crystal concentration,, optical

properties of ice crystals as a function of habit.• Instruments limitations (ice crystal shattering and sample volume) for

small cloud particles (< 50 um) (basically similar to those for natural cirrus)

New since then: from contrail formation to contrail life cycle5

6

specific from 2010:

Still true. In addition, stronger use of MODIS and MSG

At least 78 new publications since 2010 workshop:

[Atlas and Wang, 2010; Bedka et al., 2013; Burkhardt and Kärcher, 2011; Burkhardt et al., 2010; Carleton et al., 2013; Carleton and Travis, 2013; Chen et al., 2012; De Leon et al., 2012; Demirdjian et al., 2012; Duda et al., 2013; Ewald et al., 2013; Field et al., 2012; Forster et al., 2012; Frömming et al., 2011; Frömming et al., 2012; Gayet et al., 2012; Gettelman and Chen, 2013; Gierens, 2010; Gierens, 2012; Gierens and Dilger, 2013; Gierens et al., 2011a; Gierens et al., 2011b; Graf, 2013; Graf et al., 2012; Guignery et al., 2012; Heymsfield et al., 2010; Heymsfield et al., 2011; Irvine et al., 2012; Irvine et al., 2013; Iwabuchi et al., 2012; Jacobson et al., 2011; Jeßberger et al., 2013; Jones et al., 2012; Kärcher and Burkhardt, 2012; Kärcher et al., 2010; Kox, 2012; Kübbeler et al., 2011; Laken et al., 2012; Lee et al., 2010; Lewellen, 2012; Liou et al., 2013; Mannstein et al., 2010; Mannstein et al., 2012; Markowicz and Witek, 2011a; Markowicz and Witek, 2011b; Minnis et al., 2013; Misaka et al., 2012; Naiman et al., 2011; Naiman et al., 2010; Newinger and Burkhardt, 2012; Paoli et al., 2013; Paugam et al., 2010; Ponater, 2010; Ponater et al., 2012; Rädel and Shine, 2010; Rap et al., 2010a; Rap et al., 2010b; Ryan et al., 2011; Schumann, 2012; Schumann and Graf, 2013; Schumann et al., 2011a; Schumann et al., 2012a; Schumann et al., 2013; Schumann et al., 2011b; Schumann et al., 2012b; Spangenberg et al., 2013; Unterstrasser and Gierens, 2010a; b; Unterstrasser and Sölch, 2010; Unterstrasser et al., 2012; Vázquez-Navarro et al., 2010; Vázquez-Navarro et al., 2012; Voigt et al., 2011; Voigt et al., 2010; Wong and Miake-Lye, 2010; Xie et al., 2012; Yang et al., 2010; Yi et al., 2012]

7for details, see separate list

What progress has been made in the last three years?

ModelingLES (3d turbulence resolving + 2-moments, Lagrangian, binned microphysics)

Global contrail cirrus simulations

Field experimentsICE-L (above -32°C, with aerodynamic contrails), 2007, US

CONCERT 2008 and 2011: analysis of particle shape, aircraft effects, soot emissions, DE

COntrails Spreading Into Cirrus (COSIC 2011) , UK

TC2 SAFIRE (contrails and climate, ongoing), F

preparation of ML-CIRRUS with HALO, DE

Satellite observationsLinear contrail cover, microphysics, RF, life time, cirrus, OLR, RSR, tau, ztop

More insight in detection efficiency

contrail cirrus transition (cover, tau, OLR, RSR)

Aviation induced cloud changes deduced from 8 years of MSG data in NAR

ground based contrail and cirrus observations, with hints for soot cirrus

GeneralAircraft-Induced holes

Aerodynamic contrails

Aviation induced cloud changes analyzed from observation and model results

New BC and traffic data

8

Remaining unknowns and uncertainties and impact

General issue:What are the effects of contrail cirrus and from aviation induced cloud changes on the atmosphere and on climate?

Key science issues (containing several sub-issues; maybe, a somewhat subjective selection)

• What is the life time of contrails?

• What controls radiative forcing?

• Does aviation soot impact cloudiness?

Many others, e.g• Given the vast amount of traffic around major airports, what are the local

effects of aircraft on precipitation via aerodynamic contrails?• Interaction of contrails and aggregation effects in contrails

9

10

the following 30 selected slides will be explained only briefly.

They serve to illustrate the progress in understanding and the open issues

Aerodynamic contrails

Form by by adiabatic cooling above curved aircraft structures in atmospheres with about -43°C < T < -25°C(Gierens and Dilger, 2013)

Uncertain but likely <1.E13/kg ice particles per fuel mass.

Likely short lived and of small climate impact

11

250 hPa

300 hPa

450 hPa(Gierens et al., 2011)

Mid-latitudePersistence probability < 0.2

(Gierens et al., 2009; Kärcher et al., 2009)

Distrail example, possibly in liquid water clouds

photo by Bernhard Mayer (2013)

ADSB data analysis (U. Schumann):Time 14:52 UTC 7 March 2013DLH61Afrom Barcelona to MunichA321548 km/h48.085°N , 11.476°Esinkingat about 2 km altitude asl

ambient temperature around freezing level:-5°C < T < 2°Caccording to radiosoundingMunich-Schleissheimof 12 and 24 UTC 7 March 2013

12

Heymsfield et al. (2011)13

forms by freezing of supercooled liquid clouds

similar to some distrails

Holes may result from ice generated by aerodynamic contrails at air temperatures above -40°C.

Heymsfield et al. (2011)

14

Exhaust contrail formationmostly well known

• Form from engine exhaust H2O mixing with cool (and humid) air after liquid saturation (Schmidt-Applemancriterion); slightly engine dependent (Schumann, 1996)

• Soot and volatile aerosols influence ice formation during jet phase (Kärcher et al. ,1996; Schumann et al., 2013)

• Contrails interact with jet dynamics, primary and secondary wakes vortices, shear. Some particle get lost by mixing and adiabatic warming in sinking wake (Greene, 1986; Unterstrasseret al., 2012).

• Contrails persist in ice supersaturated or lifting air masses

• Contrail ice particles grow by mixing with ambient air and uptake of ambient humidity

G= ee/Te

ice saturation

liquid saturation

1: short-lived, 2: persistent, 3: threshold, 4: no contrail.

)1()/(2

2

fuelairOH

OHp

QMMpEIc

G

15

Wake evolution in four wake regimes (Gerz et al., 1998). Slide from Roberto Paoli, CERFACS

t = 0 s.

a few hours

t ~ 1000 s.

t ~ 100 s.

t ~ 10 s.

Vortex regime

Dissipation regime

Diffusion regime

Jet regime

~ 1 km

~50 m

Contrail and plume dynamics in aircraft wakes

Vortex roll-up;jet/vortex interaction

Vortex descent;Crow(elliptic) instability

Stratification; vortex break-up

Atmospheric variability ... to global scales

Zw = ua/c tua/c = 250 m/s (cruise)

ZwOCrow instability

16

Vortex bursting and tracer transport of a counter-rotatingvortex pair

Misaka, Holzäpfel et al., Phys. Fluids (2012)

17

Unterstrasser, Sölch and Gierens (Atmospheric Physics, 2012)

Relative particle concentrations in contrails

RHI 120% 1 min 3 min 5 min 5min, RHI 110%

Formation of vortices on the wing tipsIn-mixing of the emissionsDownward transport and dilutionice crystal sublimation

Ice number densities in the vortex phase

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Fraction of ice particles surviving the wake vortex phase important for contrail climate impact

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full curve: Bulk microphysics module (BM) with log-normal size distribution

dashed: Lagrangian particle tracking microphysics module (LCM)

Unterstraßer and Sölch (ACP, 2010)

Importance based on global contrail simulation with CoCiP (Schumann et al., GRL, 2013):

Increase of ice particle number at end of wake vortex phase by factor of 2 implies

increases of: by a factor net RF: 1.64tau: 1.27 cover: 1.29age: 1.16width: 1.22

open: Ice particle formation from engine exhaust until jet mixing with primary and secondary wakes

(Unterstrasser, TAC, 2012)

How do multiple contrails and contrails and cirrus interact and compete for ambient humidity?

4 h of animation, color: extinction - time/min:

20

High (ice concentration × size) in contrails consumes ambient supersaturation and hence reduces further cirrus formation

Air outside of contrails ice super or sub- saturated RHI in contrails relaxes near 100%RHI sensitive to temperature accuracy

Kaufmann, Voigt, Schäuble, (TAC, 2013)

Here N*r 1000 m cm-3, -> approach of saturation within < 10 s

How does supersaturation in contrails change in diluted contrail and for quick vertical lifting?

Korolev and Mazin (2003) 21

Schröder et al., JAS, 2000

Contrail ice particle size distribution and microphysicalprocesses

SublimationDilution

Growth

Sedimentation

Deposition/Aggregation

0.1 1 10

0.1

1

10

100

1000

dn/d

logD

(cm

-3)

d (µm)

Contrail

Cirrus

(Voigt et al., GRL (2011)

How sensitive are these results to the old FSSP-300 used?22

0 2 4 6 8 0 2 4 6 8FSSP-300 Extinction (km-1) FSSP-300 Extinction (km-1)

8

6

4

2

0Pol

ar N

ephe

lom

eter

Ext

inct

ion

(km

-1)

a b

Shattering effects likely small for small contrail ice particles

Extinction coefficients from FSSP-300 and Polar Nephelometer (PN) measurements. FSSP-300 with different size calibrations:

(a) for spherical particles (red data) (b) for spherical (red)/aspherical (blue data) FSSP size calibrationdepending on PN-derived asymmetry parameter g. Red: g > 0.85; blue: g < 0.85. - Gayet et al. (2012)

23

young plume with PN and FSSPmounted onopposite wings:

separately in and out of contrail

(Schumann et al., JAS 2010)

Exhaust dilution and contrail ice particles in aircraft wakes: higher ice number concentration than expected

25

Schumann, Jeßberger, Voigt (GRL, 2013)

If ice nucleated on soot, than at least 1015/kg of soot particles per burnt fuel mass. Ice particle sublimate in sinking and adiabatically heating wake vortex.Note: 3 × more aviation BC than expected so far (Stettler et al., 2013, subm.)

Impact of aircraft type on total contrail extinction EA

Jeßberger, Voigt, Schumann et al., ACPD, 2013

Total extinction EA = dA B × (Unterstrasser and Gierens, part I, 2010) with A contrail cross section, B width, extinction, optical depthEA depends linearly on fuel consumption per flight distanceas a consequence, contrail climate impact depends on aircraft properties

A319

A340

A380

0 2 4 6 8 10 12 14 160

20

40

60

80

100

120

140Observations (FSSP-300) and linear fit

Observations (PN)

Febre et al. (2009)

Sussmann and Gierens (1999)

tota

l ext

inct

ion,

EA

(m)

fuel consumption mF (kg/km)

26

27

AWACS example: Contrails initiate cirrus formation in air masses without other clouds - how often is this the case?

(Schumann, 2002)

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Possibly more often: Contrails form inside and co-exist with thin cirrus in ice-supersaturated air masses

28(Immler et al., 2008)

29

In humid air, contrails particle grow by deposition and possibly aggregation, sediment and end in fallstreaks

(Miloshevich and Heymsfield, JAOT, 1997)

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(Freudenthaler, PhD thesis, Munich, 2000)

(Atlas et al., 2006)

(Schumann, Ann. Geophys., 1994, based on observations by M. E. Reinhardt)

distance in km (0-40 km)

altit

ude

in k

m (7

.5 -

11 k

m)

distance in km (9.5-13 km)

altit

ude

in k

m (1

0.8-

11.3

km

)

Lidar: Contrails spread by wind shear and end in fall streaksbackscatter signal from Lidar on Falcon

Contrails occurrence observed with CALIPSO and MODIS and simulated with CoCiP, based on ECMWF and ACCRI traffic

Observed (Iwabuchi et al., 2012) Simulated (Schumann, 2012, )

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Optical depth pdf derived vom CALIPSO and models2006

Solar optical thickness0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Freq

uenc

y

0.00

0.05

0.10

0.15

0.20

TAUW

Iwabuchi et al.(2012)

Kärcher and Burkhardt (2012)

32Immler et al. (2008)

Voigt et al. (2011)

(Duda et al., 2013, ACCRIBAMS paper tbs; NASA Langley, using Mask B, traffic filtered, fractional cover in %, 2006).

Issues:large cover over North Atlantic,low cover over Europe/USA,CDA mask sensitivity,traffic filtering

CDA detection efficiency depends on - land/ocean contrast, - contrail-cirrus overlap, - satellite overpass times relative to traffic diurnal cycle

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Contrail cover from MODIS

Computed contrail cover (with CoCiP, based on ACCRI traffic and ECMWF meteorology)

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There are far more (overlapping) contrails than detected from satellites

(Schumann and Graf, 2013)

By far not all linear contrails are detectable by contrail detection algorithms

Of the contrails observed with the all-sky camera of 1–5 km width 60–65% are visually detectable in AVHRR data while only 17% are identified by an automated contrail detection algorithm (CDA).

(Mannstein et al., 2011)35

From MODISdata:

Microphysics of contrail cirrus compared to linear contrails

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Minnis et al. (GRL 2013)

The mean optical depths and effective particle sizes of the contrail cirrus were 2–3 times and 20% greater, respectively, than the corresponding values retrieved for the adjacent linear contrails. When contrails form below, in, or above existing cirrus clouds, the column cloud optical depth is increased and particle size is decreased.

(a) Contrail average particle size vs. contrail temperature for day (solid line) and night (dashed line). (b) Average contrail optical depth vs. contrail temperature. (c) Number of contrail pixels in each temperature bin.

Bars show one standard deviation about the mean.

(Bedka et al., 2013; NASA Langley).

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Contrail properties from 2006 Aqua MODIS retrievals.

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Net contrail radiativeforcing from MODIS and a model

during JAJO 2006 from Aqua MODIS data (Spangeberg et al., 2013; NASA Langley).

---->

far smaller than computed with CoCiP, see below

38

CoCiP, Schumann and Graf (2012)

Remaining unknowns and uncertainties and impact

obviously much progress but many details remain unknown or uncertain

General issue:What are the atmospheric and climate effects of contrail cirrus and from aviation induced cloud changes?

Key science issues (containing several sub-issues)

• What is the contrail cover for the fleet, life time of single contrails?

• What controls radiative forcing?

• Does aviation soot impact contrails, cloudiness, hydrological cycle?

39

How can we understand

- relative humidity inside and outside of contrails

- particle losses in young and aged contrails

- spreading of individual contrails

- Interaction of neighbouring contrails (competition for humidity)

- formation of contrail outbreaks

- ice particle aggregation, sedimentation and fall streaks

- dryout by subsidence and mixing with dry air

- contrail - cirrus - interactions

- impact of mean and fluctuation vertical motions

- others?

Science questions, part 1:Life time of contrails cirrus

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What determines the life time (or cover) of contrails

RHi=1

RHi>1 depth

VT=f(r)Contrail life timedepends on • initial number of ice particles• ambient RHi, T, p• mixing with ambient air • sedimentation• ambient vertical motion incl. waves• interaction with ambient cirrus and other

contrails• radiative heating

Number of ice particles in young contrail determined mainly by• emissions and wake dynamics• number of soot particles• ambient RHi, p, Temperature• and particle losses in sinking

wake vortex

Importance: Cover and RF scale approximately with the square of age, because area per flight length = age width(t) dt

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Contrail cirrus may persist for, e.g., 18 hours

(Haywood et al., JGR, 2009)

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Animation shows: Contrails can be tracked in MeteosatScenes

An automatic contrail tracking algorithm, M. Vazquez-Navarro, B. Mayer, H. Mannstein,

Atmos. Meas. Tech. (2010)

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Life time of ISSR and contrails: mean < 1 h

derived from MSG-observed (i.e., thick) contrails

(Vazquez-Navarro; Mannstein et al., 2012)

Model results, depend strongly on particle loss processes in the model:

aggregation, sedimentation, turbulent sublimation

(Schumann, 2012) 44

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The diurnal traffic cycle in the North Atlantic: a fingerprint for aviation induced cirrus

Annual mean Air traffic density (ATD) in km/(km2 h)

Vertically integrated traffic data above 6 km from EUROCONTROL at 15 min time resolution

NAR EUR-M

MSG-Visibility

(Graf et al., GRL, 2012)

46

• uses 7 IR channels of SEVIRI• cirrus detection at day and night. • combines morphological and multi-spectral threshold tests• detects optically thin (> 0.2) ice clouds.• Data include 8 years of 15 min cirrus cover, Feb 2004–Jan 2012

(Krebs, Mannstein, Bugliaro, Mayer, 2007; Ewald et al., 2012; Vazquez-Navarro et al., 2012, Graf et al., 2012, Graf , PhD 2013; Kox, PhD, 2012)

Retrieval of integrated longwaveand shortwavetop-of-atmosphere irradiances from MSG/SEVIRI(RRUMS) (Vazquez-Navarro et al., AMT, 2012)

See also COCS(Kox, 2012)

Cirrus cover and top of the atmosphere radiances determined from Meteosat SEVIRI (day and night time)

Graf et al. (GRL; 2012); Schumann and Graf

(JGR, 2013)

Life time of contrail cirrus reflected in cirrus response to air traffic double wave over North Atlantic; see animation:

• can this analysis be supported by in-situ data?• what explains the remaining differences?• weather dynamics? contrail-humidity interaction? soot effects?

model physics?47

Besides cirrus cover, also the optical depth diurnal cycle can be derived from Meteosat SEVIRI using neural network trained with CALIPSO observations(Kox, Ph.D thesis 2012)

Further results show diurnal cycle in cover and optical depth in correlation with air traffic.

See also Graf et al. (2012)48

- how much of the soot contributes to ice nucleation in contrails (up to 100%?) and cirrus (0.1-10%?)

- do soot particles or soot aggregates from sublimating contrails or cirrus particles contain ice remainders (Edwards et al., 1970)

- does this processed (wet) soot cause renucleation of ice particles > laboratory investigation required!

- how gets soot processed chemically in contrails and cirrus?

- what is the soot life time globally? (models compute weeks to months)

- what are the differences in cirrus/soot properties before and after passage of major air traffic density?

- can aviation-soot -cirrus be observed?

Science questions, part 2: Soot cirrus

Soot concentration (grey) and number NCVI of ice crystals > 5 m (line)

(Ström and Ohlson, JGR, 1998)49

soot aggregation?

Examples of ice particles measured with HOLIMO II (HOLographicImager for Microscopic Objects II) in mixed phase clouds at Jungfraujoch

Henneberger, Fugal, Stetzer, Lohmann, HOLIMO II (ATMD, 2013)

Are these soot aggregates?Do such soot aggregates occur in cirrus particles?

- is it possible to setup a data set to constrain radiative fluxes?

from

- insitu

- airborne remote sensing

- space (SEVIRI, CALIPSO, MODIS, METOP, etc.)

- ground (e.g. Lidar, Radar, balloons, radiometers, webcam, supersites)

- weather analysis

- models-

Climate impact:

why is the global warming effect from contrail RF less than for CO2? (efficacy of contrail RF 0.3 to 0.6), see Ponater (2010); Rap et al. (2010); Ponater et al. (2005, 2006, 2012), Hansen et al., (2005)

Science questions, part 3: Radiation and climate impact

51

Global contrail radiative forcing in mW m−2. Wide range of net and absolute |SW | /LW ratio values

52

Optical depth s at 550 nm given when fixed

Column ”d.c.”: diurnal traffic cycle included.

LW: longwaveSW: shortwavenet: LW+SW

(Schumann and Graf, 2013)

Spangenberg et al. (2013) obs, yes 17.9, -7.3, 10.6, 0.41

LW warms, SW cools; hence:Net effect (LW+SW) decreases when the |SW | /LW ratio increases

Burkhardt and Kärcher (Nature Clim. Change, 2011)

Total radiative forcing by contrail cirrus is far larger than from linear contrails (from ECHAM GCM)

net RF young

contrails

net RF contrail cirrus

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Radiative forcing from contrail cirrus: SW/LW ratio?

LW SW Ci Net

47 -9 -7 31

mW/m2

LW SW Net

126 -77 49

mW/m2

RF/

(mW

/m2 )

100

0

50

RF ECHAM4 CoCiP-CCMOD

Burkhardt and Kärcher (2011) Schumann and Graf (2013)

54

Longwave (LW)/shortwave (SW)RF depends on:

contrail properties(, reff, habit, T)

and (!!!) on

solar and terrestrial parameters(RSR, SDR, OLR, ambient cirrus)

also on 3d cloud structures and cloud heterogeneity

(Schumann et al., 2012)

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RSR= reflected shortwave radiationSDR= solar direct radiationOLR= outgoing longwave radiation

Models compute number and volume of ice -> rvolOptical depth depends on volume and cross-section -> reff

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Schumann et al. (JAS, 2011)

=?

depends on shape of size distribution and habit

What determines radiative forcing (RF) from contrails?

based on optical microphysicsfrom Key et al. (2002) and Yang

et al. (2005) andlibRadtran (Mayer and Kylling, 2005),

Schumann et al. (JAMS, 2012)

among others: , reff, shape, Temperature, soot content

solar / terrestrial parameters are also very important

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Shape of ice particles in young contrails – A380Fraction of quasi spherical particles decreases with contrail age

A380A380 Gayet, Shcherbakov, Voigt et al. (ACP, 2012)

Large fraction of aspherical particles (low g) already in rather young contrails, aspherical fraction increasing with ageOpen: particle details (shape, roughness, aerosol mixing state, soot absorption, , size distribution, dependence on T and RHi, w, contrail age, ambient cirrus etc.)

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Conclusionswhat do we currently understand about ice particle properties in contrails?• Contrail formation• Approximate cover, ice particle concentration, habits, optical propertied and

radiative forcing estimateswhere are the gaps in our knowledge base?• Nucleating and sublimation process from engine to end of wake vortex phase• Crystal concentrations, sizes, shapes, composition• "preactivation" and chemical aging of ice nuclei• Sublimation of contrails• Competition for humidity between contrails and cirrus• Aggregation, sedimentation, fall streak formation• Cover for given -threshold (with contrail-contrail and contrail-cirrus overlap)• Aerodynamic contrails, distrails and their effects on ice clouds• Life cycle and life time • Aerosol (soot etc.) impact • Accurate radiative forcing why do these gaps exist and how do we move forward to fill these gaps?• multi-scale issue! - requires• multi-sensor observations in airborne campaigns • laboratory simulations, e.g. of preactivation and aging• Lagrangian model and observation studies from first nucleation to globe

59