Download L - Marrella

AOS 100/101
Spring 2016
SOLUTIONS
HOMEWORK #7
1)
(a-c) The diagram below has the trough axes marked with solid lines, the ridge
axes marked with dashed lines and the locations of largest positive vorticity marked with
X’s.
500 mb
504 mb
L
N
W
E
S
X
L
H
L
L
X
(d) In class we found that regions of Positive Vorticity Advection (PVA) aloft
were associated with upper-level divergence and hence upward vertical motion in the
underlying atmospheric column. This upward motion and upper-level divergence are
precisely the elements required to reduce the sea-level pressure at the bottom of the
column. Thus, the area that experiences the greatest PVA aloft will be the geographic
location of the surface cyclone. PVA occurs to the east of upper-level troughs in the
Northern Hemisphere.
2)
(a) See accompanying Figure. Point B has a colder temperature than Point A.
L
B
A
N
W
E
S
(b-c) The cold air is headed southward (equatorward in the Northern
Hemisphere) and the warm air is headed northward (poleward in the Northern
Hemisphere).
(d) Transport of warm air to the cooler high latitudes (accomplished by the
southerly flow in the warm sector, Pt. A) acts to warm the high latitudes which annually
lose more radiative energy than they gain. This helps to alleviate the imbalance that
would otherwise exist. Transport of cold air toward the low-latitude, tropical areas
(accomplished by the northerly flow of air west of the cold front, Pt. B) acts to cool the
tropical latitudes which annually receive more radiant energy than they emit. This also
helps to alleviate the imbalance that would otherwise exist. Clearly, the transport of
warm air northward and cold air southward by the mid-latitude cyclone is one mechanism
by which the radiative imbalance is alleviated.
EXTRA CREDIT
(a) The winds will be from the south to the east (west) of the surface low (high)
pressure systems as indicated in the diagram below. This distribution of winds
will push the thickness line northward (southward) to the east (west) of the
surface low and southward (northward) to the east (west) of the surface high as
indicated.
(b) The thermal wind “blows” parallel to the thickness lines in the same way as
the geostrophic wind blows parallel to the isobars. Thus, a thickness line indicates the
direction of the thermal wind. Given that cyclones and anticyclones move in the
direction of the thermal wind, it is clear from the diagram above that the thermal wind is
directed northeastward through the surface lows and southeastward through the surface
highs. Consequently, surface cyclones move toward the pole while surface anticyclones
move toward the equator. This is a well established observational fact and we have just
uncovered the underlying dynamics.