When a jet streak is on the right side of a trough, the momentum of the jet streak has the opposite effect as it had on the left side of a trough. The diagram below shows a time series of a jet streak on the right side of a trough and trough lifting. Lifting of a trough means the amplitude of the trough becomes less and the axis of rotation moves to the north or northeast.  A perspective in understanding how a jet streak on the right side of a trough lifts a trough is by studying the left rear convergence quadrant of a jet streak. Mass is added to the left rear quadrant of a jet streak. As the left rear quadrant moves north, the trough will lift because convergence in the base of a trough causes height rises (due to addition of mass) and a subsequent weakening of the trough. The diagram below shows the left rear quadrant of a jet streak that is exiting the base of a trough.  As a jet streak leaves the base of a trough, the left rear quadrant overlaps the base of the trough. Because convergence is occurring within the axis of rotation the trough weakens. Strong upper level convergence raises heights and surface pressure. The diagram below shows the position of the left rear quadrant with respect to the position of the axis of rotation.  Adding to the convergence created by the left rear quadrant is NVA. The PVA and divergence from the left front quadrant will be to the northeast (approximate direction) of the axis of rotation. This will promote a northeast lifting of the trough. The diagram below shows the two mechanisms of convergence (left rear quad and NVA) within the base of the trough and the two mechanisms of divergence (left front quad and PVA) to the northeast of the axis of rotation.  Haby sez: The momentum of a jet streak and convergence created from the left rear quadrant and NVA allow a jet streak on the right side of the trough, which is exiting the base of the trough, to weaken and lift the trough to the northeast. |