Chapter 3 Flashcards
These long waves also called the
Rossby waves generally found in mid‐ latitude (23.5°N/S‐66.5°N/S) westerlies
Rossby waves form primarily due to
the earth’s geography
Rossby waves form primarily due to the earth’s geography, which results in:
a) Differential heating due to uneven earth’s surface and
b) Vertical motion forced by orography
The length of long waves
vary from around 6,000 to 8,000 km or more
There are usually between ………………… longwaves that encircle the NHS at any given time.
2 and 7
long waves generally move
very slowly from west to east. But occasionally they will become stationary or retrograde (move east to west)
The height of a pressure surface at any level (e.g., the 500 mb surface) is related to
the (density averaged) temperature of the atmosphere below that level
The height of a pressure surface at any level (e.g., the 500 mb surface) is related to the (density averaged) temperature of the atmosphere below that level:
the higher the temerature, the higher the height of the pressure level
Where the height lines bow northward (………………..)
(a ridge) warm air has moved north
where the height lines bow southward (……………)
(a trough), cold air has moved south
warmer than average temperatures can be expected underneath
ridges
colder than average temperatures can be expected underneath
troughs
digging
Cold air moving south results in strengthening or ‘digging’ southward of an upper level trough
building
Warm air moving north results in strengthening or ‘building’ northward of an
upper level trough
compare zonal and meridional patterns
A ‘zonal’ (more flat) 500 mb pattern exhibits little wave structure, while a ‘meridional’ (or amplified) 500 mb pattern contains large northward and southward excursions.
Surface level storm systems, and associated cold fronts, move
very fast from west to east in zonal flows as they have very little north to south (or south to north) movement.
The 500mb pattern can also be used to
locate where surface storms and precipitation are most likely to be occurring
The 500mb pattern can also be used to locate where surface storms and precipitation are most likely to be occurring Surface storms and precipitation are most often found over
areas downstream of 500 mb trough.
The 500mb pattern can also be used to locate where surface storms and precipitation are most likely to be occurring Surface storms and precipitation are most often found over areas downstream of 500 mb trough. this is because
the convergence downstream of the trough forces the surface air to move upward towards the tropopause (dynamical lifting of air).
Conversely, sinking air motion is forced over areas
downstream of ridges, where clouds do not develop. Underneath these areas fair weather is most likely
Thus, by looking at a 500 mb map, one should be able to distinguish where
precipitation is most likely and where fair weather is most likely
The shape and strength of a 500 mb trough often indicates its
dynamical strength, i.e., its potential to force strong rising motion in the atmosphere and hence strong areas of precipitation.
The factors (related to 500 mb pattern), that act to increase divergence and hence rising motion and precipitation are:
- Stronger winds increase divergence. Therefore, the more closely spaced the height lines, the stronger the divergence downwind of troughs.
- The more amplified the pattern (amplitude of the ridge/trough pattern), the stronger the divergence downwind of troughs
- The sharper the curvature of a trough, the stronger the divergence downwind of the trough
- The orientation of the trough axis with respect to a north‐south line.
(GRAPH) Stronger winds increase divergence. Therefore, the more closely spaced the
height lines, the stronger the divergence downwind of troughs.
(GRAPH) The more amplified the pattern (amplitude of the ridge/trough pattern), the
stronger the divergence downwind of troughs.
(GRAPH) The sharper the curvature of a trough, the stronger the divergence downwind of the trough.
(GRAPH) Troughs that are oriented along a northwest to southeast line are said to a have a “negative tilt”, while troughs oriented along a northeast to southwest axis are said to have a “positive tilt.”
shortwave graph
