Contrail forecasting case study

Background

Contrails are left behind by aircraft flying at high altitudes and are an everyday observable phenomenon. These “man-made” cirrus clouds can persist from seconds to hours, depending on the characteristics of temperature, humidity, wind, and the stability of the air aloft. Contrails that persist for several hours (and those that have significant horizontal spreading across the sky), are known to influence the radiation balance of the atmosphere, and, therefore, have potential global climate implications. In order to mitigate the overall impact of contrail-related clouds, understanding the aviation industry’s contribution to climate change is of vital importance.

Figure 1 – Contrail observations of LH430 (FRA-ORD) over city of Cambridge at approximately 1230 UTC, on April 10th 2020.
Figure 2 – Forecasted air temperature profile (black) and critical air temperature for contrail formation (red) over Cambridgeshire on 10th April 2020 at 1300 UTC. The probability of persistent contrails is shown by the colours.

Solution

SATAVIA has created a high-resolution (5km spatial resolution) regional climate model product to forecast the likelihood of contrail formation for flight corridors across Europe and Asia. We calculate the likelihood of contrail formation by comparing model-predicted temperature and humidity values to the critical values needed for their formation and maintenance. SATAVIA’s model could be used for short-term forecasts (up to 36 hours) of contrail layers. Contrail forecasts could be incorporated for flight planning purposes to intelligently re-route flights around those regions of the atmosphere that are susceptible to the effects of contrails.

Figure 3 – Terra satellite image over the British Isles (at approximately 11:41 UTC on April 10th 2020) showing a series of contrails over the Irish Sea
Figure 3 – Terra satellite image over the British Isles (at approximately 11:41 UTC on April 10th 2020) showing a series of contrails over the Irish Sea

Case study

On 10 April 2020, high pressure conditions over Western Europe led to calm, blue skies over much of the United Kingdom. At approximately 1230 UTC, a contrail was observed and photographed by three different observers (see Fig. 1), lasting longer than 5 minutes. The aircraft was identified as a Boeing 747-830, at an altitude of 36000 feet at the time of observation.

SATAVIA’s model predicted a layer of persistent contrails with high probability between 34000 and 40000 feet 1300 UTC (see Fig. 2). This is consistent with the visual observations at the time (Fig 1).

The nearest-in-time satellite imagery (Terra/MODIS) was approximately an hour earlier (at 11:41 UTC) than the photos shown in Fig.1 and clearly shows a series of persistent contrails left behind by several transatlantic flights over Wales and the Irish Sea (Fig 3).  SATAVIA’s contrail prediction system predicted an extensive area of potential for long-lasting contrails over most of the British Isles near this time, yet near zero chance over northern France.  This appears to match favourably with the satellite image.

Figure 4 – Terra/MODIS satellite image over the British Isles (left), and forecasted probability of persistent contrails at 36000 feet on 10th April 2020 (right)