Contrails, contrail cirrus and hole

Contrails, contrail cirrus and
hole-punch clouds
Philip R.A. Brown,
Andy Heymsfield,
Jean-Francois Gayet
Cloud Microphysics Instrumentation Workshop, Seaside, OR, 25-27
June 2010
Issues
• Aviation impacts on climate: radiative
forcing due to
• CO2 emissions ~ 0.03 Wm-2
• Contrail-induced cirrus ~ 0.03 Wm-2
IPCC(2007)
• Indirect radiative impacts of aviation
• contrail formation, persistence and growth
• modification of natural cirrus properties via impacts
of emitted aerosols
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
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).
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
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.
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)
20/03/2009 Contrail evolution observed over UK
12UTC surface pressure analysis
1006UTC ~ T+1hr
10:06
1040UTC ~ T+1.5hr
10:40
1130UTC ~ T+2.5hr
11:30
1202UTC ~ T+3hr
12:02
Just touching coast
near the Humber
1342UTC ~ T+4.5hr
13:42
1526UTC ~ T+6.5hr
15:26
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
Haywood et al. (2009): Issues
• Radiative impact of contrail cirrus is a combination of:
• Optical depth – IWC / Reff
• 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
DLR CONCERT Project
A380 contrail case study (19 Nov. 2008)
Picture from Tina Jurkat (DLR)
Secondary
wake
Left primary
wake
DLR Falcon
boom
Right primary
wake
Secondary wake
Primary wake (vortex phase)
Sussmann & Gierens (2001)
From Tina Jurkat
0.80 < g < 0.85
0.85 < g < 0.87
0.87 < g
Altitude (m)
Secondary
wake
Primary
wake
Relative humidity / ice (%)
Asymmetry parameter
Vertical profiles of RHi and Asymmetry parameter
0.80 < g < 0.85
0.85 < g < 0.87
0.87 < 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
0.80 < g < 0.85
0.85 < g < 0.87
Altitude (m)
0.87 < g
Extinction (km-1)
IWC (g/m3)
Effective diameter (µm)
Vertical profiles of Extinction, IWC and Effective diameter
Angular scattering coefficent (µm-1 sr-1)
1- Primary wake ~ 80 sec. aged (12:17:41 – 12:17:51 UT)
Direct SD (FSSP)
Concentration (l-1 µm-1)
FSSP + Mie
PN
Inverse SD (PN)
Diameter (µm)
Scattering angle (°)
Conc1 : 117 cm-3
Deff :
7.8 µm
Temp. : -54.1 °C
Conc3 :
g:
0.882
RHi :
76 %
Ext. :
2.15 km-1
NOy :
48 nmol/mol
IWC :
5.5 mg/m3
Alt :
10438 m
8 cm-3
Angular scattering coefficent (µm-1 sr-1)
4- Secondary wake ~ 200 sec. aged (12:17:41 – 12:17:51 UT)
Concentration (l-1 µm-1)
Direct SD (FSSP)
FSSP + Mie
Inverse SD (PN)
PN
Diameter (µm)
Alt :
10650 m
Scattering angle (°)
Conc1 :
44 cm-3
Temp. : -56.7 °C
Conc3 :
9 cm-3
RHi :
94 %
Ext. :
1.0 km-1
NOy :
11 nmol/mol
IWC :
2.5 mg/m3
Deff :
8.5 µm
g:
0.801
Conclusions from A380 measurements
First detailed microphysical & optical observations have been experienced in well
defined primary and secondary wakes (80 – 250 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.).
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
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.
• ?
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)
•
•
Observe the magnitude and spatial extent of supersaturation within an air mass prior
to its being “seeded” with contrails
•
•
•
seen to some extent in the UK case shown earlier
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