Evidence audit · NASA SUCCESS observations and Jensen et al. (1998)
How a narrow aircraft trail spread in cold, moist, sheared air
A NASA field-campaign case combined satellite and in-situ observations with a large-eddy simulation. The comparison showed how high ice supersaturation, crystal growth, sedimentation, and wind shear can transform a line into a broader ice cloud over 15–180 minutes.
Case verdict
What the study did
Jensen and colleagues investigated persistent-contrail evolution using a large-eddy simulation with detailed ice microphysics. Rather than evaluate an unverified photograph, the researchers compared their simulation with satellite and in-situ measurements collected during NASA’s SUCCESS field campaign. The simulated window covered 15 to 180 minutes after formation—long enough to examine the transition beyond the initial aircraft wake.
| Evidence | Role | Strength | Limitation |
|---|---|---|---|
| Satellite measurements | Track horizontal cloud structure and spreading over a larger area. | Independent remote view over time. | Finite pixel size and indirect microphysical retrieval. |
| In-situ measurements | Constrain the trail environment and cloud properties along the aircraft sampling path. | Direct local sampling at flight level. | A flight path samples a small portion of a changing three-dimensional cloud. |
| Large-eddy simulation | Test whether known microphysics, shear, radiation, and humidity can explain evolution. | Mechanistic and time-resolved. | Depends on initial conditions, parameterizations, and representativeness. |
| Model–observation comparison | Evaluate whether simulated width/optical behavior agrees with measured behavior. | Stronger than an unvalidated visual analogy. | Agreement does not prove every modeled process was uniquely determined. |
The physical story supported by the case
Ice crystals survived the wake
Ambient air was sufficiently moist with respect to ice that crystals did not simply sublimate when the exhaust plume diluted.
Vapor deposited onto the crystals
Under the highly supersaturated simulated conditions, crystals grew. The paper reports simulated crystal lengths greater than 200 µm within about 45 minutes.
Crystals fell through a sheared environment
As larger ice crystals sedimented, different wind at different heights displaced portions of the cloud, increasing its horizontal extent.
Radiative heating affected motion
The simulation included strong localized radiative heating that generated an updraft and lifted the contrail core by several hundred meters—an example of cloud–radiation feedback within the evolving trail.
The model approximately matched persistence and spread
The authors found that growth and precipitation of contrail ice could approximately explain the observed spread and sustained optical depth when ambient humidity was very high.
The study abstract identifies relative humidity with respect to ice above roughly 125 percent in the relevant simulations. That value describes this modeled/observed case and should not be converted into a universal “contrail starts here” rule. Persistence becomes thermodynamically possible at ice saturation; the rate and appearance of growth depend on how far above saturation the environment is and on many other variables.
Why this evidence chain is stronger than a map overlap
A public map normally starts with a flight track and forecast grid, then infers a possible trail. The SUCCESS case adds two independent observation systems and a physics-based simulation. Each answers a different question:
- Did ice cloud persist?
- Satellite and in-situ observations support yes.
- Was the environment supportive?
- Measured/model-constrained high humidity supports yes.
- Can known physics explain spreading?
- The large-eddy simulation approximately reproduced key behavior using crystal growth, sedimentation, shear, and radiation.
- Was the mechanism uniquely proven?
- No. Model agreement supports the mechanism but retains uncertainty in initial state and process representation.
How Contrail Research should reproduce this kind of audit
- Preserve the source track with timestamps and actual sample gaps rather than only a smoothed line.
- Use a vertical humidity profile and calculate RHi, instead of relying only on a broad pressure-level proxy.
- Advect a trail ensemble across plausible wind and humidity uncertainties rather than drawing one deterministic path.
- Compare against time-resolved satellite labels for width, orientation, and lifetime.
- Score positives and negatives in a held-out validation set and publish false alarms.
The map performs a simpler hypothesis-screening role. It can identify where to look, but it does not resolve ice microphysics or simulate a research-grade three-dimensional cloud.
Alternative interpretations
Natural cirrus caused all observed spreading
Natural cirrus can coexist and merge with a trail. However, the campaign’s coordinated observations and the simulation’s initialization around the contrail make aircraft-origin ice a supported component. The case does not imply that every later ice crystal in the scene can be assigned uniquely to exhaust.
Wind alone spread a passive line
Shear explains displacement, but a passive ice line in dry air would sublimate. The persistence and modeled crystal growth require moisture; dynamics and microphysics work together.
The modeled humidity proves exact atmospheric humidity everywhere
It does not. Model initial conditions and local observations constrain a scenario. Humidity is spatially variable, and agreement is approximate rather than a complete reconstruction of every parcel.
Limitations and transferability
- The case concerns one persistent trail in a particular environment; it is not a fleet-average result.
- Large-eddy simulations resolve more detail than an operational global weather model but still parameterize some processes.
- Reported optical-depth agreement and spreading do not independently identify every microphysical parameter.
- We rely on the peer-reviewed abstract and NASA publication record here; readers should consult the full paper for configuration and sensitivity tests.
- The case supports the importance of RHi and shear, not unsupported claims about visible-trail chemistry or intent.
Sources
- Jensen, E. J., Ackerman, A. S., Stevens, D. E., Toon, O. B., & Minnis, P. (1998). Spreading and growth of contrails in a sheared environment. Journal of Geophysical Research, 103, 31,557–31,568.
- NASA GISS publication record and abstract for Jensen et al. (1998).
- NASA Earthdata: SUCCESS campaign overview.
Numbers in this analysis are tied to the cited case and should not be generalized to other events.