Contrails, contrail cirrus and hole-punch clouds

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1 Contrails, contrail cirrus and hole-punch clouds Philip R.A. Brown, Andy Heymsfield, Jean-Francois Gayet Cloud Microphysics Instrumentation Workshop, Seaside, OR, June 2010

2 Issues Aviation impacts on climate: radiative forcing due to CO 2 emissions ~ 0.03 Wm -2 Contrail-induced cirrus ~ 0.03 Wm -2 Indirect radiative impacts of aviation contrail formation, persistence and growth IPCC(2007) modification of natural cirrus properties via impacts of emitted aerosols

03 Wm -2 Indirect radiative impacts of aviation contrail formation,

3 Heymsfield et al (2010), BAMS: Contrail Microphysics Well-established theory of contrail formation Range of existing microphysical obs. but with suboptimal instrumentation (prone to shattering artefacts) Lack of recent studies of aerosol emission characteristics for current- and future-generation engines Difficulty of measurement in key regions to fullycharacterize the evolution of a contrail (plume-mixing region, vortex region) Need for lab and field obs. of soot IN activity fresh and aged Need for large-scale closure experiments to link contrails sources, vapour availability, microphysical characteristics and radiative impact

future-generation engines Difficulty of measurement in key regions to fullycharacterize the evolution of a contrail (plume-mixing region, vortex region) Need

4 Basic contrail formation physics well understood from the work of Schmidt (1941), Appleman (1953), Schumann (1996) mixing of unsaturated air in engine exhaust and environment generates saturation w.r.t. liquid water contrail formation in the mixing exhaust plume entrainment of contrail into aircraft wake vortices potential for some evaporation of crystals due to descent within the vortices. where environment is super-saturated w.r.t. ice, contrails can grow and spread impacts of turbulence, wind shear, microphysical characteristics in vortex phase (N, IWC).

5 Yang et al. (2010) BAMS: Contrails and Induced Cirrus: Optics and Radiation Ice habit of cirrus and contrails: when are they similar or different? Single-scattering properties of contrail ice. Possible need for separate parametrization in GCMs if optical properties are significantly different Ambiguity of identifying contrail cirrus when evolved beyond the linear stage Need for satellite climatologies of contrail cirrus Need for supporting field campaigns

similar or different? Single-scattering properties of contrail ice.

6 Observations from SUCCESS: Geophys.Res.Lett. special issue In-situ samples at t ~1min Goodman et al. Similarity of optical properties with wave-cirrus Baumgardner and Gandrud In-situ sampling to t ~ 1hr Heymsfield et al. followed by further observation to 6-12hr, - Minnis et al. Well-developed contrail systems can develop most of the characteristics of natural cirrus systems, eg. precipitation trails, convective circulations driven by LW radiative cooling.

et al. followed by further observation to 6-12hr, - Minnis et al.

7 Haywood et al. (2009): A case study of the radiative forcing of persistent contrails evolving into contrail-induced cirrus, J.Geophys.Res. AWACS aircraft flying large circles off the east coast of England Contrail drift simulated using the Met Office NAME atmospheric dispersion model: Lagrangian particles transported by dynamical fields from operational Unified Model forecast. IR satellite images from sequence of polar-orbiters (NOAA 15/17/18, Metop-A, TERRA)

8 20/03/2009 Contrail evolution observed over UK 12UTC surface pressure analysis

9 1006UTC ~ T+1hr 10:06

10 1040UTC ~ T+1.5hr 10:40

11 1130UTC ~ T+2.5hr 11:30

12 1202UTC ~ T+3hr 12:02 Just touching coast near the Humber

13 1342UTC ~ T+4.5hr 13:42

14 1526UTC ~ T+6.5hr 15:26

15 1708UTC ~ T+8hr 17:08 How much of this cloud cover would have been present if the airmass hadn t been seeded by contrails? Contribution from other contrails

16 Haywood et al. (2009): Issues Radiative impact of contrail cirrus is a combination of: Optical depth IWC / R eff Crystal conc. and how this is governed by nucleation and growth processes in the plume / vortex stages spatial extent horizontal and vertical TOA rad.forcing: LW ~ 50Wm-2, SW ~ -60Wm-2 This may be maximised in conditions when the cloud no longer contains clear linear features in static satellite imagery distinction between natural and contrail-derived clouds Timescales initial contrail spreading beyond the vortex stage tens of minutes evolution into cirrus overcast - hours

forcing: LW ~ 50Wm-2, SW ~ -60Wm-2 This may be maximised in conditions when the cloud no longer contains clear linear features in static satellite

17 DLR CONCERT Project A380 contrail case study (19 Nov. 2008) Picture from Tina Jurkat (DLR)

18 Secondary wake Left primary wake Right primary wake DLR Falcon boom Secondary wake Primary wake (vortex phase) Sussmann & Gierens (2001) From Tina Jurkat

19 0.80 < g < < g < < g Secondary wake Altitude (m) Primary wake Relative humidity / ice (%) Asymmetry parameter Vertical profiles of RHi and Asymmetry parameter

20 0.80 < g < < g < < g Altitude (m) Secondary wake Primary wake Conc FSSP D> 1 µm (cm-3) Conc FSSP D> 3 µm (cm-3) Vertical profiles of particle concentration with D > 1 µm and D> 3 µm

21 0.80 < g < < g < < g Altitude (m) Extinction (km-1) IWC (g/m3) Effective diameter (µm) Vertical profiles of Extinction, IWC and Effective diameter

22 1- Primary wake ~ 80 sec. aged (12:17:41 12:17:51 UT) Concentration (l-1 µm-1) Direct SD (FSSP) Inverse SD (PN) FSSP + Mie PN Angular scattering coefficent (µm-1 sr-1) Diameter (µm) Scattering angle ( ) Alt : m Conc1 : 117 cm-3 Deff : 7.8 µm Temp. : C Conc3 : 8 cm-3 g : RHi : 76 % Ext. : 2.15 km-1 NOy : 48 nmol/mol IWC : 5.5 mg/m3

23 4- Secondary wake ~ 200 sec. aged (12:17:41 12:17:51 UT) Concentration (l-1 µm-1) Direct SD (FSSP) Inverse SD (PN) FSSP + Mie PN Angular scattering coefficent (µm-1 sr-1) Diameter (µm) Scattering angle ( ) Alt : m Conc1 : 44 cm-3 Deff : 8.5 µm Temp. : C Conc3 : 9 cm-3 g : RHi : 94 % Ext. : 1.0 km-1 NOy : 11 nmol/mol IWC : 2.5 mg/m3

24 Conclusions from A380 measurements First detailed microphysical & optical observations have been experienced in well defined primary and secondary wakes ( sec. aged) of large-body aircraft. Very small and spherical (ice) particles (Deff = 7.8 µm) are observed in the primary wake with concentration and extinction peaks up to 400 cm -3 and 8 km -1 respectively. Slighly larger and aspherical ice particles (Deff = 8.1 µm) characterize the secondary wake with much higher concentration of particles D> 3 µm (60 cm -3 / 15 cm -3 ) and lower extinction peaks (4 km -1 / 8 km -1 ). The primary wake particles could sublimate (RHi < 85%) whereas the secondary wake particles at higher levels may growth (RHi ~ 100%) by water uptake and turbulent dilution. Within the primary / secondary wake transition the asymmetry factor decreases smoothly indicating a progressive change from spherical to non-spherical ice particles (for plume age ranging between 80 sec. and 150 sec.).

25 Microphysical measurement issues for contrails and contrail cirrus Possible unreliability of previous measurements: ice shattering on probe tips and inlets (2DC / FSSP) inadequacy of probes for counting / sizing small ice (2DC / FSSP) Anti-shattering tips for existing probes Korolev (2010, submitted to BAMS) New instruments, not prone to shattering and adapted to small ice measurements; Small Ice Detector (SID-2) - 2DS High-frequency microwave observations (>200GHz) for IWP retrievals Measurements of crystal residues to identify potential IN Couterflow Virtual Impactor (CVI) Substantial recent progress in instrumentation capability for microphysical measurement in cirrus

26 Microphysical and measurement issues specific to contrails / contrail cirrus Basic microphysical measurement requirements are v.similar to those for natural cirrus Aerosols in jet engine exhaust: physical / chemical characteristics, CCN / IN activity AMS, PSAP, SP2, filter sample, continuous-flow and static diffusion chambers IN activity changes with ageing and transport when emitted in non-contrail forming conditions Onset of freezing in the exhaust / vortex region heterogeneous vs. homogeneous processes Dynamical and thermodynamical evolution in the vortex region crystal evaporation during descent difficulties of sampling careful coordination with a target aircraft Contamination of measurements by contrails from the measurement aircraft - unavoidable limitation on repeated penetrations of a region to observe evolution over time Mixed regions of contrail and natural cirrus how to distinguish? chemical constituents of CVI residues Aerosol Mass Spec. etc.?

27 Recommendations for future measurements and field campaigns 1) Characterisation of aviation-produced aerosols in non-contrail forming situations to develop understanding of the climatology in regions of different air traffic activity. 2) Lab measurements of CCN/IN activity of aviation aerosols AIDA and similar facilities 3) A closure experiment: Contrail formation within a region may have a strong diurnal cycle related to air traffic patterns (eg. timing of transatlantic flights leaving or arriving in W.Europe) seen to some extent in the UK case shown earlier Observe the magnitude and spatial extent of supersaturation within an air mass prior to its being seeded with contrails reliance on relatively poor forecasting of upper tropospheric humidity in-situ observations may initiate the seeding process Followed by characterisation of the micro- and macro-physical properties of the resulting cirrus cloud sheet, radiative impacts etc. 4) Continued development of climatology of upper-tropospheric supersaturation eg. MOZAIC, AMDAR with well-characterized humidity measurements

A Contrail Cirrus Prediction Tool

A Contrail Cirrus Prediction Tool U. Schumann Deutsches Zentrum für Luft- und Raumfahrt (DLR) Institut für Physik der Atmosphäre Oberpfaffenhofen, Germany Keywords: contrails, contrail cirrus, simulation