Jet Streaks Meteorology 311 Fall 2010Jet Stream/Jet Streak • Jet stream: an intense, narrow, quasi-horizontal current of wind that is associated with strong vertical shear. – Found at or near the tropopause. • Intense: at least 30 m/s for upper troposphere. • Narrow: ~1/2 to 1 order of magnitude less in width than its length. • Strong vertical wind shear: At least 5-10 m/s per km; At least ½ to 1 order of magnitude greater than synoptic scale shear. • Jet streak: an isotach maximum embedded within a jet stream.Methods of explanation • Curvature • PVA/NVA • Ageostrophic wind • Confluence/Difluence (?)Pretty Picture 1Pretty Picture 23D CirculationsDirect/Indirect Circulation • Entrance region: direct thermal circulation • Exit region: indirect thermal circulation – Creates temperature advections at the surface which provide positive feedback to upper level support in that region.Jet Streaks characteristics • Jet streak on left side of trough Deepens and amplifies (digs) the trough. • Jet streak on right side of trough Weakens and de-amplifies (lifts) the trough. • Jet streaks are caused by low level temperature gradients – Not necessarily surface temperature gradients, but low level gradients.Banana/Curved Jets • Most jets in nature are not linear. • Motions are enhanced on the inside curve of the jet. • Motions are suppressed on the outside curve. – At this point, one typically labels these areas undeterminable.Ageostropic Explanation • Va = V – Vg • Equation (in class) • Entrance region: As parcel accelerates, an ageostropic wind blows perpendicular toward lower heights. • Exit region: As parcel decelerates, an ageostropic wind blow perpendicular toward higher
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