JetLag, the Lagrangian jet tracking algorithm

The JetLag data sets and documentation will be released shortly
Sign up for the JetLag mailing list to be notified.

What is JetLag?

JetLag is a jet tracking algorithm developed in collaboration with Dr. Jezabel Curbelo at Universitat Politècnica de Catalunya with the support of Centre de Recerca Matemàtica.
JetLag relies on Lagrangian descriptors of the general circulation, hence the name.

Why JetLag?

Many jet tracking algorithms have been developed in the past, but significant limitations remain:

• Most algorithms define the jets in the Eulerian framework (instantaneous or time-averaged meteorological fields) and therefore overlook the coherence of jets over time;

  JetLag defines jets as Lagrangian coherent structures to account for their spatial and temporal coherence

• Most algorithms rely on a variety of empirical, climatological parameters to define jet features (e.g. latitude and wind magnitude thresholds). Such algorithms are by design tailored to the current state of the climate and may not be suited to other climate states;

  JetLag’s 2 parameters are rooted in wave dynamics, independent of the state of the climate

• Most algorithms are tailored to track either the subtropical jet or the polar front jet, but not both;

  JetLag identifies both jet types with the same method

How does JetLag work?

The algorithm uses a Lagrangian descriptor of the general circulation, the ‘M function’, which is defined at any location (x,y,z,t) as the length of the Lagrangian parcel trajectory initiated at (x,y,z,t) and integrated over a chosen time interval {t-$\tau$ ; t+$\tau$}. The main parameter used in JetLag is the length of that time interval, $\tau$, which can be determined objectively based on the scales of interest, and to which the output exhibits virtually no sensitivity.

The M function highlights Lagrangian coherent structures–organizing features of the circulation that correspond to maxima in atmospheric displacement and that are invariant over the chosen integration interval. JetLag relies on these features to locate jets that are coherent in space and in time, effectively separating jets from underlying waves.

What will JetLag provide?

A data set based on ERA5 is ready for 1941-2020, for the subtropical jets and the polar front jets. We expect its public release in the coming months.

Other products will be released over time, including products for CMIP6 model runs.

Contact us if you are interested in a product that is not available.

Can I get involved?

We’d love to hear your thoughts. You can reach out to us via the mailing list (once you’ve subscribed, email: jetlag-owner [replace with at symbol] lists (dot) fas (dot) harvard (dot) edu) or directly via my professional email (lrivoire [replace with at symbol] mit (dot) edu).