Development and mechanisms of the nocturnal jet

Forecasting the occurrence and strength of the nocturnal jet is important t o aviation, especially to balloonists and small aircraft. Jets also have im plications for pollution transportation and the clearance of low cloud and fog. A one-dimensional model showed that the main mechanism for the develop ment of the nocturnal jet was a hybrid between an inertial oscillation in a layer within and above the jet core and a quasi-steady jet within the inve rsion. The model, supported by observations, suggests that a nocturnal inve rsion is required to produce a jet and that the strength of the jet maximum is approximately 1.3 times the geostrophic wind. A wind profile minimum is also predicted to occur when the inertial oscillation reaches a minimum in the stress-free layer and this wa observed using a tethered balloon flown at Cardington.