As currently defined, the convective influence experienced by a parcel is
the time that has elapsed since that parcel has encountered deep convective
clouds, where an encounter with convection is defined as IR brightness
temperatures less than the parcel temperature.
The detailed approach is as follows:
- Calculate 10 day back trajectories from a cluster of points surrounding
selected portions of the flight track.
- Separate out those sections of the flight track that are above 29000
feet. This is done for two reasons. First, deep convection detrains
mostly at high altitudes. Secondly, because parcel temperatures
at low altitudes are warmer, a temperature comparison of parcel and IR
brightness temperatures may define an encounter with thin cirrus as
a convective encounter.
- Create a high resolution cluster of points around each high
altitude segment of the flight track. Each flight as 3-6 high altitude
segments (typically), resulting in 3-6 clusters of points.
- Calculate back trajectories for these clusters at 6 altitudes (29000,
31000, 33000, 35000, 37000, and 39000 feet). Each cluster has its own
initial time (reflecting the time to the nearest hour when the aircraft
sampled in the high altitude segment). Each cluster has 4000-8000 points.
- Run each back trajectory through a set of hourly, global, 11.5 micron
geostationary satellite imagery. A convective encounter is said to occur
when the brightness temperature is less than the temperature along the
trajectory. More restrictive criteria are applied if the parcel is in
the stratosphere and above the temperature minimum.