Drylines and Low Level Jets

This is a set of flashcards about drylines and low level jets.

Dryline

A boundary separating a moist air mass from a dry air mass.

General dryline movement

Eastward during the daytime and westward at night.

Dryline Movement factor

Differential heating due to differences in soil moisture and cloudiness.

Continued Heating

Eastward propagation of the dryline.

Discontinuous dryline movement

The dryline movement “jumps” across flat areas of similar terrain to an area where the terrain height abruptly decreases and the depth of the moist layer increases.

When does the dryline advance rapidly ('synoptically')?

When moist sector advection becomes eastward.

Wind shift at dryline

Large during the day, minimal at night.

Dewpoint temperature at dryline

Always higher in the moist sector.

Equivalent potential temperature at dryline

Almost always higher in the moist sector.

Complicated dryline structures

Sometimes drylines are associated with a stepwise decrease in dewpoint temperatures instead of the more common monotonic decrease.

Multiple Drylines

Multiple drylines are analyzed on a surface map with spacing of ~ 10-50 km.

Cap at the Dryline

Result of a warm and dry boundary layer being advected over a moist boundary layer to the east.

Surface convergence near dryline

Between winds with easterly component east of the dry line and westerly component west of the dry line leads to vertical motion.

Dryline bulges

Provide an even greater focus for surface moisture convergence.

Reason for many tornado chase busts

The advection of warm, dry air over the moist layer strengthens the cap or lid faster than the surface heating can overcome its stability

Importance of LLJ

Mesoscale forecasting concern

Horizontal momentum equations in which Coriolis force is considered.

The inertial oscillation can be described mathematically

Ageostrophic wind rotates clockwise

The inertial oscillation va(t) = |va0|sin(ψ0 − ft)