contrails & climate studies
DESCRIPTION
CONTRAILS & CLIMATE STUDIES. Patrick Minnis NASA Langley Research Center Hampton VA, USA 30 October 2003. MOTIVATION. • Air traffic increasing 2 - 5%/year over the globe • Ice supersaturation exists 10-20% of the time at flight altitude - PowerPoint PPT PresentationTRANSCRIPT
Langley Research Center
CONTRAILS & CLIMATE STUDIES
Patrick MinnisNASA Langley Research Center
Hampton VA, USA
30 October 2003
Langley Research Center
MOTIVATION
• Air traffic increasing 2 - 5%/year over the globe
• Ice supersaturation exists 10-20% of the time at flight altitude
• Aircraft produce persistent contrails => cirrus aviaticus
• Cirrus clouds affect radiation budget, possibly water budget
• Aircraft exhaust might affect microphysics of extant cirrus
• Contrail/cirrus impact least certain effect of aircraft on climate
Can contrails have an effect large enough for concern?
- Mitigation efforts by aircraft industry (new technology)
- Mitigation efforts by air traffic control (new routing)
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Aircraft exhaust short circuits natural cirrus formation
- high humidities normally needed to make cirrus (C)
- cirrus can exist at lower humidities (B) but need formation boost
- no cirrus for RHI < 100% (A)
T < -39°C
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GOES-8 IR LOOP FOR NOVEMBER 18, 2001, 1015 - 2115 UTC
QuickTime™ and aGIF decompressor
are needed to see this picture.
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11-12 µm temperature difference from 1-km satellite data 24 October 2003; Okla, Ark, Kan, Missouri
NOAA-15 1250 UTC
NOAA-17 1738 UTC
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<= Terra MODIS 2025 UTC
NOAA-12 IR 2251 UTC
Contrails have become cirrus clouds
11-12 µm temperature difference from 1-km satellite data 24 October 2003, Okla, Ark, Kan, Missouri
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11-12 µm temperature difference from 1-km satellite data 24 October 2003, Midwest
<= NOAA-15, 1250 UTC
NOAA-12, 2111 UTC =>
More contrail cirrus
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11-12 µm temperature difference from 1-km satellite data 24 October 2003, Other areas
TEXAS
CA coast
Idaho
Pacific NW
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CONTRAILS
• Ubiquitous feature of our skies
- increase cirrus coverage over areas with air traffic
• Can affect climate by altering
- Radiation budget (warming, cooling)
- Changing moisture budget of upper troposphere?
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Fig. 11. LW, SW, and net radiative forcing at TOA and surface (SFC) for cirrus cloud with D = 24
and 60 µm for ice water path of 5.3 gm-2 at 250 mb over land with surface albedo of 20% andmean surface temperature of 283 K with diurnal range of 17 K.
THEORETICAL RADIATIVE EFFECTS OF CONTRAILS
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Fig. 12. Change in daily mean atmospheric heating rates for contrail over clear and cloudyscenes. Contrail has = 0.3 and D = 60 µm. Calculations for midlatitude spring atmosphereduring April at 45°N with surface albedo of 0.2 and cloud optical depth of 20.
MEAN DAILY HEATING RATES DUE TO CONTRAILS
= 0.3
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CONTRAIL UNKNOWNS
• contrail-cirrus coverage
- geographical & temporal
- now & future (requires modeling)
• microphysics: optical depth, particle size
- mean between 0.1 and 0.4, varies between 0.01 & 2
- De changes over life cycle (5 -100 µm)
• radiative forcing
- depends on when and where it occurs
• vertical spreading
- dries the UT?
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APPROACH
Can it be significant?
• Estimate lower & upper bounds of current contrail-cirrus impact
- use empirical-theoretical estimates in RTM
- relate cirrus change to air traffic
Can we accurately predict it?
• Develop climatology of contrail coverage, frequency, microphysics, radiative forcing
- surface & satellite observations
• Relate contrail observations to meteorological conditions
- develop empirical-theoretical models to predict contrail coverage & properties
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• European studies
- regional coverage from linear features in AVHRR imagery
- tuned global coverage from ECHAMP/ECMWF output (Sausen et al. 98)
- recently estimated = 0.11 from AVHRR, similar from GCM
- GCM simulations of CRF (Contrail Radiative Forcing)
• US studies
- LaRC estimated = 0.30 from AVHRR & GOES data over US
- NASA GISS GCM simulation of CRF (Rind et al. 2000)
- LaRC simulation of CRF from European tuned output/ISCCP/ERBE
- lower bound (Minnis et al. 99)
BACKGROUND
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LaRC Contrail Minimum Radiative Forcing Estimates
=> Global contrail forcing:
FSW = -0.003 to -0.012 Wm-2, FLW = 0.011 to 0.033 Wm-2
Fnet = 0.008 - 0.020 Wm-2 ; 0.017 Wm-2 for = 0.3
European estimate 0.003 Wm-2 for = 0.15
Greater over areas with heavy air traffic!
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Current Estimates of contrail radiative forcing
-90
-60
-30
0
30
60
90
0 0.2 0.4
Latitude (°)
F (Wm
-2
)
0 0.2 0.4
F / c (Wm
-2
%
-1
)
a) b)
Minnis et al. 1999, GRL
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LaRC Contrail Maximum Radiative Forcing Estimates
• Estimate change in cirrus cloudiness due to air traffic
- primary : sfc obs 1971-1995
• Repeat CRF calculations with cirrus change estimate
- assume linear scaling with coverage, = 0.15 - 0.25
• Use GCM conversion factors to estimate temperature changes
Rind et al. (2000):
= > 0.025 Wm-2 for = 0.25
New range of global radiative forcing = >0.006 - 0.025 Wm-2
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To estimate upper bound contrail radiative forcing:
• Measure trends in cirrus where contrails form & do not form (air traffic patterns)
• Estimate impact of relative humidity
• Estimate cirrus change for no humidity change
- no trend over USA
Study in "Contrails, Cirrus, and Climate," Minnis et al., 2003, accepted J. Climate
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EVIDENCE FOR CHANGE IN CIRRUS CLOUDINESS DUE TO CONTRAILS IS
PILING UP!
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Trends in cirrus cover ( SFC OBS, 15+ yrs) & RH(300 hPA), 1971-1995
1992 contrail cover RH
Cirrus trend Cirrus trend, conf level 90%
from Minnis et al. 2004
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Cirrus & contrail seasonal trends
Satellite contrail coverage: 1990s (Mannstein et al. 1998, Palikonda et al. 2002)
Surface cirrus: 71-95
USA Europe
Satellite contrail frequencies: 1993-94 & 98-99 (Minnis et al. 2002)
-Contrails consistent with cirrus trend over USA, not Europe
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Table 2. Contrails, mean cirrus cover, and cloudiness trends (%/decade) over air traffic regions from surface (CC) and ISCCP (CCI) data. The numbers in parentheses indicate the interannual variability in CC. The 1971-95 trends in CC are all significant at the 99% confidence level, except over WEUR where no trend is apparent.
Region
1992 ECO
N
(%)
Mean CC
(%)
1971-95
CC Trend
1971-95
Total Cloud Trend
1971-95
CC Trend,
1983-95
CCI Trend,
1983-95
WASIA 0.08 36.2 (1.0) -0.9 -0.7 -2.0 -2.1
EUR 0.60 18.5 (1.3) -1.2 -0.4 -0.4 0.0
WEUR 1.52 19.8 (1.4) 0.0 -0.7 1.8 0.9
USA 1.75 29.2 (1.1) 1.0 0.5 0.3 2.3
LOR 0.09 24.5 (0.5) -1.6 -1.4 -1.5 -0.6
NA 0.32 15.3 (0.7) 0.7 0.0 0.3 0.2
NP 0.16 15.7 (0.8) 0.9 0.8 1.6 -0.4
OOR 0.13 14.4 (0.6) 0.7 1.2 0.8 0.1
Minnis et al. 2004,
J. Climate
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Zerefos et al. 2003, JGR
Cirrus coverage trends more positive over areas of heavy air traffic in a given region
Based on ISCCP data
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Mannstein et al., AAC, 2003
Over Europe, cirrus coverage, especially thin cirrus, coverage highly dependent on air traffic
Based on Meteosat imagery
linear contrail coverage over Europe only 0.3%
cirrus delta = 3%
Contrail spreading a factor of 10!
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INTERIM SUMMARY
• Cirrus coverage is increasing over USA (consistent w/ seasonal contrail frequency
steady over Europe (inconsistent)
decreasing over western Asia, but not in areas of heavy air traffic
decreasing most over other land areas
• Cirrus is increasing over ocean (not many obs in pristine areas)
Is increase due to air traffic or weather changes?
- Zerefos and Mannstein results suggest the former
- Minnis et al. (2004) agree
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ESTIMATION OF TEMPERATURE CHANGE OVER USA DUE TO CONTRAIL CIRRUS BASED ON GCM STUDY & CIRRUS OBS
Minnis et al. 2004, J. Climate
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IMPACT OF CIRRUS TREND
• Contrail cirrus can account for all of observed warming over USA between 1975 & 1994
- Ozone impact not included!
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con < 0.2%
QuickTime™ and aGraphics decompressorare needed to see this picture.
-0.15
-0.05
0.05
0.15
0.25
0.35
-90 -60 -30 0 30 60 90LATITUDE (°)
MSU Observed
min contrail
max contrail
CHANGES IN ATMOSPHERIC TEMPERATURE, 1979-1997 200-850 mb FROM SATELLITE DATA AND ESTIMATED
CONTRAIL RADIATIVE FORCING
data from J. R. Christy
Minnis et al. GRL (1999)
present study
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ESTIMATES OF ALL AVIATION FORCING WITHOUT CONTRAIL SPREADING
- IPCC (1999)
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BETTER UNDERSTANDING & PREDICTION
• IMPROVED OBSERVATIONS OF LINEAR CONTRAILS & SPREADING
- provides data for developing & validating models
• RELATIONSHIP BETWEEN AIR TRAFFIC, CONDITIONS, & CONTRAILS
- gives basis for parameterizing cirrus aviaticus
• PREDICT WHEN & WHERE CONTRAILS WILL FORM
Contrails are a problem, what can we do?
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Linear Contrail Climatology
Automated Contrail Detection
NOAA-12 AVHRR, April 1997
10.8-µm image detected contrailsmethodology from Mannstein et al. 1999
VA
NC
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DECEMBER
LINEAR CONTRAIL COVERAGE DURING 2001 FROM AVHRR
730 AM APRIL 230 PM
DECEMBER
Palikonda et al. 2003)
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CONTRAIL DETECTION FROM SATELLITES
• Very sensitive to particular imaging instrument response
- need careful tuning of technique
• Sometimes mistakes cirrus streaks as contrails
- need error budget
• Sometimes misses larger contrails
- need more error budget
This work is underway!
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Optical depths nearly identical for both NOAA-15 & 16
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Comparison of contrail coverage (%)
USA
Time Sausen et al. 98 Palikonda et al. 98 present (NOAA-16, 15)
1993-94 2001
Dec 1.6 2.1 (Dec) 0.8 (0.9)
Apr 2.0 2.0 0.7 (1.3)
Jul 0.5 1.3 0.3 (1.1)
Oct 1.9 1.9 0.8 (1.0)
-------------------
Sausen et al. 98, Global Annual 0.087
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Comparison of contrail properties
Source Time OD NCLRF (Wm-2)
Minnis et al. 98, USA Apr 0.30
Minnis et al. 99, Global
(theoretical) Annual 0.30 27
Palikonda et al. 98 Apr (0.27) 12.4 (14.2)
N14, 93-94, USA Jul (0.30) 16.0 (22.3)
( N15&16, 01, USA) Oct (0.27) (10.4))
Dec (0.27) 11 (12.0)
Meyer et al. 02, Europe Annual 0.11 14
(NOAA14, 95-97)
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CONTRAIL PREDICTION
• To relate contrails to the conditions, we have acquired a database of flight tracks for commercial air traffic over USA for 3 years
- Garber et al. 2003 (NASA RP in review)
• Use NCEP Rapid Update Cycle (RUC-2) experimental product to predict contrail occurrence
- realtime USA contrail predictor online
new RUC data not very good for contrails
• Compare with satellite data
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Contrail boundaries and relative humidity with respect to ice (RHI)
1600 UTC, November 18, 2001
MODIS T4-T5 ImageRHI from RUC-2 analysis, 225 mb
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QuickTime™ and aGIF decompressor
are needed to see this picture.
CONTRAIL OUTBREAK OVER GREAT LAKES, 9 OCT 2000
"Fly" aircraft through RUC fields, simulate formation & spreading
from Duda et al. 2003, JAS, accepted
Langley Research Center Garber et al. 2003, NASA
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OCTOBERSEPTEMBER
Comparison of contrail amount from satellite data and frequency of potential contrail conditions from RUC-2 data
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• Humidity fields critical for contrail formation, but correlations not always apparent because
- extant cirrus may prevent detection of contrails from satellite
contrail/cirrus conditions often equivalent
- afternoon contrails may be less detectable because of overlap
• 2001 coverage much less than 1993-94
- 1993-94 period one of moistest upper troposphere in 30 years (45.5%)
- 2001 one of driest at high altitudes in 30 years (39.4%)
- NOAA-16 may be less sensitive to contrails than NOAA-11
- NOAA-11 tendency for overestimation (~0.5%)
SUMMARY
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UPPER TROPOSPHERIC HUMIDITY
OLD CONTRAILS
ROADBLOCKS TO ACCURATE CONTRAIL PREDICTION
THE AIR TRAFFIC SHUTDOWN CASE
2001 air traffic shutdown removed some impediments for contrail study
- System cleared of commercial air traffic contrails by 0000 UTC, 12 September 2001
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GOES-8 IR LOOP FOR SEPTEMBER 12, 2001, 1045 - 2345 UTC
QuickTime™ and aGIF decompressor
are needed to see this picture.
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By studying the few contrails that occurred during the shutdown, we can tune a model that simulates contrails
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12 SEPTEMBER CONTRAIL ANALYSES
• Use GOES images to track & compute spreading
• Estimate heights using stereographic analysis
- GOES-8 & AVHRR, MODIS, or GOES-10
- Flight levels between 10.5 and 12.5 km
• Compute optical depth using RUC temperature at 11.5 km (225 hPa) and adjacent clear-sky temperature
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Terra MODIS 1 -km Infrared Image
1545 UTC, 12 September 2001
NOAA-15 AVHRR 1-km Infrared Image
1245 UTC, 12 September 2001
3-hour change in observed contrails
H
E
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DURING THIS EVENT
MEAN CONTRAIL LIFETIME IS 6.5 hr
MEAN AREAL COVERAGE FOR EACH CONTRAIL IS 2270 km2
MEAN OPTICAL DEPTH IS 0.23
In the mean, over a 6.5 hour period, 8 contrails covered 18,000 km2
=> We need to relate the contrails to the humidity fields at altitude!
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Model humidity
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Comparison of RHI profiles from radiosondes & RUC-2 analyses 12 UTC, September 12, 2001
AE,F,G B,C,D,H
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NEED TO ARTIFICIALLY ENHANCE MOISTURE PROFILES
OBSERVED & MODELED HUMIDITIES TOO LOW!
RHI for adiabatic cirrus ~ 150%
RHI for persistent contrails > 100%
Nevertheless, there appears to be a relationship between the vertical structure of RHI and the lifetime, spreading, and optical depths of the observed contrails
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Comparison of persistent contrail occurrence and sonde RH, SLC, Utah
RHI corrections based on frost-point hygrometer data
Miloshevich et al. 2001, JAS
Sassen, 1999, BAMS
RHI correction for sonde profiles used here
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Radiosonde profiles of RHI in contrail areas after correcting for dry bias, 12Z, September 12, 2001
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Contrail simulation for September 12 over northeastern USA• Assume air traffic is equal to September 5
- use database from Garber et al. 2003
• Apply Appleman criteria, use RHI > 70% to define persistence
• Assume RHI for a flight track = that of nearest RUC level
• Compute spreading, assuming fall speed of 3 cm/s
- max width = 12 km, shear determines spread rate (mean = 6 km/h, same as observed for military contrails)
- no new nucleation, optical mass = OD*width
- OD = f(t), peaks at 2 hours
• Advect old & add new contrails
• Delete trails if RHI < 70% or older than 6 hr
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Hourly simulation of contrails over northeastern USA September 12 2001, assuming air traffic for September 5
QuickTime™ and aGIF decompressor
are needed to see this picture.
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QuickTime™ and aGIF decompressor
are needed to see this picture.
ANOTHER VIEW
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Estimate of linear contrail coverage over northeastern US for September 12, 2001 assuming air traffic for Sept. 5
Coverage could have been at least 200,000 km2 if traffic were normal
Daily global mean is 200,000 - 400,000 km2!
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ALTERNATIVES FOR MITIGATION
• Predict locations & altitudes where contrails most likely
- provide alternate routing (height change)
- our proposal
• Fly lower all the time
- German study 2003
• Use liquid hydrogen fuels
- German study 2003
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CONCLUDING REMARKS
• Understanding has increased rapidly but remaining issues
- accuracy of contrail coverage
- where does contrail impact occur
how much is local? spread around?
- contrail optical depths
0.1 - 0.3?
geographic dependence?
- indirect effects on cirrus clouds
does AC exhaust increase opt depth, decrease De?
do AC exhaust aerosols reduce formation threshold
leading to more cirrus?
- is there an effect on the moisture budget?
- how accurately can we model cirrus aviaticus?
need good natural cirrus model (satellite comparisons)
- what are best mitigation options?
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FUTURE RESEARCH AT LANGLEY
• Continue climatology development
- examine relationship of natural cirrus to environment
• Compute radiative forcing for simulations
• Apply more sophisticated contrail model, account for natural Ci
- match flights to vertical details of RHI
- improve precip, spreading, dissipation
• Improve threshold for contrail persistence from models
- find a new data source (RUC changed April 19)
• Determine source of differences in lifetimes and spreading
• Push for improved UT RH
• Provide realistic real time predictions of contrails in clear air
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REFERENCES & MISCELLANEOUS
• All references can be found on our main web page
http://www-pm.larc.nasa.gov/
click on "SASS", then on "Related References"
• Other imagery and examples are available on the same main web page, click on "PATHFINDER", "SUCCESS" or "SASS"
• A near-real-time contrail predictor is available on the main web page, click on "Contrail Forecast" (not so good since RUC change)