Incorporation of steep mountains into numerical forecasting
                        models

Egger, J.

doi:10.3402/tellusa.v24i4.10647

Cited by 9 publications

(4 citation statements)

References 4 publications

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“…The second key innovation introduced with pressure coordinates mentioned above relates to the introduction of wall-mountains. The basic idea goes back to Egger [173], who argued that σ-coordinates would do well with representing large-scale lifting and ascent associated with major mountain ranges such as Greenland and Antarctica, but not with orographic blocking associated with steep mid-latitude mountain ranges such as the Alps. Indeed, a high knife-edge mountain would be smoothed to zero in σ-coordinates, when in fact it would stop all air from flowing normal to it.…”

Section: Wall-mountains and Step Coordinatesmentioning

confidence: 99%

“…Indeed, a high knife-edge mountain would be smoothed to zero in σ-coordinates, when in fact it would stop all air from flowing normal to it. Egger [173] designed a wall-mountain topography, by enforcing the condition v n = 0, where v n is the component of the horizontal wind normal to the mountain ridge. Distinct from σ-coordinates, which approximately conserve the mountain volume (or even increase it if some form of envelope topography is used), wall mountains have zero volume but represent the blocking effect.…”

Section: Wall-mountains and Step Coordinatesmentioning

confidence: 99%

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Crossing Multiple Gray Zones in the Transition from Mesoscale to Microscale Simulation over Complex Terrain

et al. 2019

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This review paper explores the field of mesoscale to microscale modeling over complex terrain as it traverses multiple so-called gray zones. In an attempt to bridge the gap between previous large-scale and small-scale modeling efforts, atmospheric simulations are being run at an unprecedented range of resolutions. The gray zone is the range of grid resolutions where particular features are neither subgrid nor fully resolved, but rather are partially resolved. The definition of a gray zone depends strongly on the feature being represented and its relationship to the model resolution. This paper explores three gray zones relevant to simulations over complex terrain: turbulence, convection, and topography. Taken together, these may be referred to as the gray continuum. The focus is on horizontal grid resolutions from ∼10 km to ∼10 m. In each case, the challenges are presented together with recent progress in the literature. A common theme is to address cross-scale interaction and scale-awareness in parameterization schemes. How numerical models are designed to cross these gray zones is critical to complex terrain applications in numerical weather prediction, wind resource forecasting, and regional climate modeling, among others.

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Section: Wall-mountains and Step Coordinatesmentioning

confidence: 99%

Section: Wall-mountains and Step Coordinatesmentioning

confidence: 99%

Crossing Multiple Gray Zones in the Transition from Mesoscale to Microscale Simulation over Complex Terrain

et al. 2019

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“…The sea level pressure deficit in the lee grows with . The crossing of Greenland by cyclones from the west has been investigated numerically by Egger (1972) who found a splitting of the cyclones at the western wall and some kind of cyclogenesis in the lee when the low's upper part arrives above the lee slopes. Schwierz (2001) calculated the stationary response of Greenland to impinging barotropic westerly flow.…”

Section: Introductionmentioning

confidence: 99%

Winter time flow over and around Greenland: trajectories related to torques

Egger¹

2006

Tellus A: Dynamic Meteorology and Oceanography

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A B S T R A C T Results of first steps towards a dynamically oriented climatology of winter time flow over and around Greenland are presented. The synoptic situations in the Greenland area are classified with respect to Greenland's axial mountain torque. This torque is positive (negative) if the surface pressure at the eastern slope is higher (lower) than at the windward side. Mean trajectories are calculated from correlations of observed flows with the torque. Three classes of trajectories are formed: 'blocked', 'over' and 'around'. It is found for low-level starting points west of Greenland, that blocked trajectories are most common for positive torques while the bulk of the trajectories is deflected around Greenland or crosses the massif for negative torques. These results are shown to be broadly consistent with the standard non-dimensional height criterion. Flow splitting is common to the west of Greenland. Stagnation points are found west of Greenland but also above the eastern slopes. Tip jets occur for negative torque events only.

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“…For the general circulation of the atmosphere, it is an interesting problem to examine the effect of mountains on baroclinic waves. Egger (1972) and Edelmann (1974) investigated numerically the effect of mountains on a particular cyclone or anticyclone and simulated splitting of low pressure area and jumping of the low center. It may be expected that the activity of baro-clinic waves is changed by mountains and hence its contribution to the general circulation may also be varied.…”

Section: Introductionmentioning

confidence: 99%

Dynamical Effects of Mountains on the General Circulation of the Atmosphere: III. Effects on the General Circulation of the Baroclinic Atmosphere

Nakamura

1978

Journal of the Meteorological Society of Japan

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In order to investigate dynamical effects of mountains on the general circulation of the baroclinic atmosphere, the model developed in Part I is integrated for about 150 days. A simplified diabatic heating function and the Newtonian cooling evaluated from observational data are adopted for the thermal process in the model. The 6.5*K/km convective adjustment is used to parametarize the vertical convective mixing of heat. The nonlinear viscosity and the vertical momentum diffusion are also included. Time integrations are performed with and without an idealized steep mountain like the Tibetan Plateau. The model without the mountain simulates' successfully the gross features of the general circulation similar to the real atmosphere. That is, the westerly wind in the middle latitudes, the easterly wind in the tropics and the meridional three cell circulation are well simulated. Baroclinic unstable waves are well developed, though a little less active than the real ones. However, there are some defficiency in the model atmosphere. For example, the subtropical jet is too strong and its position is too south compared with the real atmosphere due to the large latitudinal gradient of the diabatic heating near 20*latitude. The active region of baroclinic waves is limited to relatively higher latitudes. Incorporating the mountain does not change these features largely. The most remarkable change is the northward shift of the subtropical high. It is located at 30* latitude in the model without the mountain while it is at 45* latitude in the model with the mountain. The region of the downward motion in the subtropics also expands northward. This is due to the geostrophic adjustment of the pressure field to the westerly wind weakened by the blocking effect of the mountain. This phenomenon may be one of the causes of the northward shift of the dry area in the Eurasian continent. We may also speculate that this process contributes to the formation of the Siberian high to some extent. The mountain does not excite stationary planetary waves so much as expected from the observation and other studies, because of the weak westerly wind over the mountain. In addition, a zonally symmetric circulation is obtained. Though there is a large difference between it and the real atmosphere, it is considerably similar to the real atmosphere compared with the results of Hunt (1973) who also investigated a zonally symmetric circulation. It is supposed that one of the causes of the difference between the two results is the difference of the scheme used for the nonlinear horizontal viscosity in the two models.

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Incorporation of steep mountains into numerical forecasting models

Cited by 9 publications

References 4 publications

Crossing Multiple Gray Zones in the Transition from Mesoscale to Microscale Simulation over Complex Terrain

Crossing Multiple Gray Zones in the Transition from Mesoscale to Microscale Simulation over Complex Terrain

Winter time flow over and around Greenland: trajectories related to torques

Dynamical Effects of Mountains on the General Circulation of the Atmosphere: III. Effects on the General Circulation of the Baroclinic Atmosphere

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