Upper air soundings taken every three hours are used
to examine a cold front of average intensity over a period
of 24 hours. Vertical cross sections of potential temperature
and wind and horizontal analyses are compared and adjusted
until they are consistent with one another. These
analyses are then used to study the evolution of the front.
The front is found to consist of a complex system of
fronts occurring at all levels of the troposphere. Low
level fronts are strongest at the surface and rapidly
weaken with height. Fronts in the middle and upper troposphere
are much more intense. The warm air ahead of the
fronts is nearly barotropic while the cold air behind the
fronts is baroclinic through deep layers. A deep mixed
layer is observed to grow in this cold air.
Examination of cross sections of potential temperature
and potential vorticity indicates that the air in at least
the upper portions of the upper level fronts originates in
the stratosphere. No evidence is found, however, of an extrusion
of stratospheric air to very low levels. Diabatic
processes seem to destroy the extrusion as it descends.
The structure of the upper level fronts is complex.
These fronts are observed to split apart, recombine, and
descend to low elevations. This descent is due to the incorporation
into the front of pre-existing stable/baroclinic
layers.
An equation for parcel-following frontogenesis in
isentropic coordinates is developed and applied. No single
process was found to be dominant in changing frontal intensity.
Frontogenesis occurs on the leading edge of the
fronts and frontolysis on the trailing edge. The magnitudes
of the computed frontogenesis decrease downstream
from the axis of the upper level trough.
Isentropic trajectories are constructed in order to
verify the computed values of parcel-following frontogenesis.
Poor correlations are found between the computed and
trajectory-following values of frontogenesis. This is believed
to be due to nonlinearities in the field of frontogenesis
and to errors in the trajectories. Such nonlinearities
cast doubt on the usefulness of conventional
data for the study of frontogenesis.
Vertical velocities are computed using a kinematic
technique. Reasonable fields of vertical velocity are
obtained in the vicinity of the fronts and jet streaks.
Good correlations are found between the vertical displacement
between endpoints of the trajectories and the value of
computed vertical velocity integrated over the path of the
trajectory. The field of vertical velocity is also found
to be highly nonlinear. / Graduation date: 1977
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29008 |
| Date | 05 April 1977 |
| Creators | Frank, Albert E. |
| Contributors | Barber, David A. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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