An Overview of Atmospheric Modeling
1. What are Barotropic Models?
Models were developed to be used in the first electronic calculators, which were developed in the USA in the 1940s. These are the simplest models and are based on what is known as the “barotropic assumption.” This assumption states that the isobaric surfaces of constant pressure coincide with the surfaces of constant density. Consequently, the gradient is zero, and the isobaric geostrophic wind does not vary with height. With this hypothesis, the EDP system is reduced to a single differential equation for vorticity and solved in a single vertical level.
2. What Makes a Baroclinic Model?
A baroclinic atmosphere is defined as one in which isobaric and isopycnic surfaces do not match. Therefore, the isobaric temperature gradient is nonzero, and the geostrophic wind varies with height, but only in magnitude and not direction. In this way, the baroclinic model may reflect a certain vertical structure of the atmosphere and can provide variables that vary vertically. The first operational baroclinic model was integrated in the USA and was a three-tier model.
3. What Role Did Primitive Equation Models Play in Weather Forecasting?
Primitive equation models accounted for the first type of numerical models, and the results were good enough to be used in daily weather forecasting in meteorological services. Considered as a vertical structure of the whole atmosphere, they started with ten vertical levels, which increased over time.
4. Advantages and Disadvantages of Using Isentropic Coordinates
A high isentropic surface is one in which the potential temperature, θ, is constant. An advantage of this coordinate system is that for dry adiabatic motions, each air parcel conserves its potential temperature; d θ / dt = 0. Another advantage is that the coordinate θ provides better resolution in the vicinity of fronts.
Disadvantage: For the same reasons as height and pressure, the use of potential temperature as a vertical coordinate gives problems near the ground.
5. What are Hybrid Coordinates and Their Advantages?
Hybrid coordinates are a type of sigma coordinate σ = p / ps, where ps is the surface pressure. Models that use this type of coordinates have the advantage of combining sigma surfaces at the bottom, which become isentropic surfaces with height.
6. What are the Two Main Deficiencies Found in Early EDP Models?
From the first models developed, EDP was found to have new deficiencies in results that were not due to poor formulation of the EDP resolved to build the model but to two main causes.
One was the horizontal and vertical resolution of the grid integration. It could not be expected to describe the weather in a place with a grid that had 200 km between two adjacent points or with only ten vertical levels. The second reason was that they could not take into account processes taking place in the atmosphere whose spatial and temporal scale was much lower than the resolutions of the model. For example, convection, with the scale of large convective clouds in the order of several kilometers, it is clear that its effects could not be directly included in models with a horizontal resolution of 200 km.
8. What is the Parameterization of Physical Processes?
There are many physical processes that cannot be solved explicitly using scale models. Parameterization is reformulating large-scale to small-scale effects. Sometimes it is not clear the scale of certain phenomena. To take into account the effects of these phenomena, we should establish some hypotheses on their functioning. The basic hypothesis is to assume that “there is a statistical equilibrium between phenomena whose scale is smaller than the grid and solved by the variables in the grid.”
9. What are the Main Processes Included in Numerical Models?
Radiation
This process takes into account the effects produced in the atmosphere and soil by the absorption of shortwave radiation from the sun and longwave radiation from the Earth. It also considers the interaction that these radiations produce with different atmospheric components (ozone, cloud liquid water, water vapor, etc.). This is the most important process of all that parameterize because solar radiation is the energy that drives the atmospheric engine.
Convection
Convection is a form of vertical motion in the atmosphere consisting of local vertical currents, casual or organized, which have sections on the order of a few meters to several kilometers. Most of these movements, especially in the lower atmosphere, are due to thermal convection created by differential heating. As air laden with steam rises, the vapor condenses and releases large amounts of heat, originating liquid water droplets, which are then converted into precipitation. Schemes try to simulate convection in the models, the dramatic effects on the condensation of atmospheric water vapor, and the exchanges of momentum produced by the strong vertical convective currents. This is one of the most important schemes of the physics of a model.
Soil Surface Atmosphere Exchange
This process takes into account the latent heat exchange (due to the evaporation of water from oceans, rivers, and lakes), sensible heat (due to air contact with the ground), and momentum (due to braking that occurs in the atmospheric flow with friction with the floor).
Turbulence
This is the impact on the atmosphere by the interaction of eddies of different size and scale that occur within this flow because it is laminar. It is also a very significant impact because they produce a vertical exchange of momentum (either to slow or accelerate the flow of other vertical layers) that helps maintain the atmospheric balance.
Condensation on a Large Scale
This process takes into account precipitation production (rain or snow) from atmospheric levels where there is supersaturation as a result of all processes that have been taken into account in the model (advection of moisture, evaporation from the surface, etc.).
Braking Gravitational Waves
. This is the way in which the braking occurs at low flow by contact with the terrain is transmitted to higher levels of the atmosphere. 10. What are global general circulation models and what
serve? are those models that are integrated over the entire globo.Se mainly used for: 1. Control experiments, ie oriented to the description of climate
contemporáneo.2. quantify the response to future climate perturbations induced by human activities. That is, the response to change in any of the parameters and processes that control the system status. Attempt to explain how the climate system respond to such a disturbance trying to restore balance. 11. What are the features advantages and disadvantages of a mesh model? Features 1. The data are represented in a fixed set of grid points. 2. The resolution is a function of the spacing of grid points. 3. All calculations are performed on the mesh points. 4. Approaches used to solve finite difference equations derived from the model. 5. An error is introduced through finite difference approximations of the primitive equations. 6. The degree of error is a function of grid spacing and time interval. Disadvantages 1. Finite difference approximations of the equations of the model introduces a considerable error. 2. Noise accumulates small when the equations are integrated for long periods. 3. The magnitude of computational errors is usually higher than in comparable resolution spectral models. 4. Errors in the boundary conditions can spread to regional models and may affect the ability of the forecast. Advantages 1. Can provide a high horizontal resolution in regional and mesoscale applications. 2. No need to transform the physics calculations and from the space mesh. 3. As physical models become more complex operations, mesh models become more competitive with spectral models from the computational point of view. 4. The non-hydrostatic versions can predict the details of convection explicitly, given a proper resolution and sufficient detail in the initial conditions