Manabe, S., and T. B. Terpstra, 1974: The effects of mountains on the general circulation of the atmosphere as
identified by numerical experiments. Journal of the Atmospheric Sciences, 31 (1), 3-42.
Abstract: In order to identify the effects of mountains upon the general circulation
of the atmosphere, a set of numerical experiments is performed by use of
a general circulation model developed at the Geophysical Fluid Dynamics
Laboratory of NOAA. The numerical time integrations of the model are performed
with and without the effects of mountains. By comparing the structure of
the model atmospheres that emerged from these two numerical experiments,
it is possible to discuss the role of mountains in maintaining the stationary
and transient disturbances in the atmosphere.
The model adopted for this study has a global computational domain and covers
both the troposphere and stratosphere. For the computation of radiative
transfer, the distribution of incoming solar radiation in January is assumed.
Over the ocean, the observed distribution of the sea surface temperature
of February is assumed as a lower boundary condition of the model. Over
the continental surface, temperature is determined such that the condition
of heat balance at the ground surface is satisfied. The mountain topography
is taken into consideration using the so-called s-coordinate system in which pressure normalized by surface pressure is used
as a vertical coordinate. The grid size for the computation of horizontal
finite differences is chosen to be about 250 km. Nine finite-difference
levels are chosen in unequal pressure intervals so that these levels can
represent not only the structure of the mid-troposphere but also that of
the stratosphere and the planetary boundary layer.
The results of the numerical experiments indicate that it is necessary to
consider the effects of mountains for the successful simulation of the stationary
flow field in the atmosphere, particularly in the upper troposphere and
stratosphere. As predicted by Bolin, the flow field in the upper troposphere
of the mountain model has a stationary trough in the lees of major mountain
ranges such as the Rocky Mountains and the Tibetan Plateau. To the east
of the trough, an intense westerly flow predominates. In the stratosphere,
an anticyclone develops over the Aleutian Arhcipelago. These features of
the mountain model, which are missing in the model without mountains, are
in good qualitative agreement with the features of the actual atmosphere
in winter.
In the model troposphere, mountains increase markedly the kinetic energy
of stationary disturbances by increasing the stationary component of the
eddy conversion of potential energy, whereas mountains decrease the kinetic
energy of transient disturbances. The sum of the stationary and transient
eddy kinetic energy is affected little by mountains. In the model stratosphere,
mountains increase the amplitude of stationary disturbances partly because
they enhance the energy supply from the model troposphere to the stratosphere.
According to wavenumber analysis, the longitudinal scale of eddy conversion
in the model atmosphere increases significantly due to the effects of mountains.
This increase results mainly from the large increase of stationary eddy
conversion which takes place at very low wavenumbers.
The results of the analysis reveal other important effects of mountains.
For example, the probability of cyclogenesis in the model atmosphere increases
significantly on the lee side of major mountain ranges where the core of
the westerly jet is located. Also, mountains affect the hydrologic processes
in the model atmosphere by modifying the field of three-dimensional advection
of moisture, and alter the global distribution of precipitation very significantly.
In general, the distribution of the model with mountains is less zonal and
more realisitic than that of the model without mountains.