Atmospheric Waves: Geog 2130

Waves

Terminology used to describe upper-level patterns

Gravity Waves

Result from the vertical displacement of a parcel of air in a stable atmosphere. (Gravity is the restoring force of the wave)

Rossby waves

Result from the change in the Coriolis force with latitude. They exists in a horizontal orientation

Long waves

waves in the mid-to upper troposphere of the Westerlies

Size: between 3000 and 5000 km

Short waves

waves in the mid Troposphere of the Westerlies

Size: hundreds to a thousand km

Resultant Waves

Can be thought as the sum of short and long waves

Eastward movement of waves is:

Positive

Westward movement of waves is:

Negative

What is retrograding?

Westward moving waves

Speed of long waves:

-5 to 15 knots

Speed of short waves:

15 to 40 knots

What is a kicker

Progressive short wave, that approaches a long wave trough effectively decreases the wavelength and allows the long wave to become progressive, “kicking” it along.

What is digging

Movement of a trough equatorward

Often occurs when the strongest winds of the jet stream are upstream from the trough

What is lifting out

Movement of a trough poleward

Often occurs when the strongest winds of the jet stream are downstream of the trough

Zonal flow

Primarily east-west flow (low amplitude waves)

Meridional flow

Wave pattern with large areas of north-south flow, following the meridians (high amplitude waves)

Cutoff lows and highs

center of low (high) geopotential heights formed by the “pinching off” of a trough (ridge) to the south (north) of the polar jet. “Cut-off low, weatherman’s woe”

What is blocking

pattern tends to inhibit changes in the wave pattern upstream.

Usually, must persist for 10 days to be considered a blocking pattern

What is a roll-over cycle?

upstream ridge amplifies and “rolls over” a trough to form a cutoff low

What is a build-back cycle?

trough “digs” and the downstream ridge “builds back” over it

What is High-over-low block

Split flow, with a cutoff high north of a cutoff low. Splits the jet stream

Most frequent over North America and Europe

What is an omega block

high sandwiched between two cut-off lows

Meridional flow mostly which makes flying west to east hard

What is a rex block?

resembles a "half figure 8" or "backwards S”.

Vertical not horizontal, cut-off high on top (north) cut off low below (south)

Common in pacific northwest