chapter 4 summery Flashcards
1
Q
Model domain refers to:
A
- Model’s forecast area of coverage
2
Q
Numerical models divide into:
A
- Global models
- Covering the whole globe
- Regional models
- Covering a more limited area
3
Q
Limited area models (LAM) boundaries
A
- Horizontal (lateral)
- Top and bottom (vertical)
4
Q
Global models boundaries:
A
- One vertical boundary (by nature cover the entire earth)
5
Q
Domain of an NWP model can be viewed as:
A
- 3D array of cubes
6
Q
Describe the NWP model 3D array cubes:
A
- Each cube encompasses a volume of the atmosphere corresponding to a model grid point
- Forecast values for met variables in each cube are derived from
- The current values within the cubes + from the surrounding cubes
7
Q
Information needed to provide forecast values for the meteorological parameters. Why?
A
- Cannot be determined using only the data contained in the model
- Because he cubes on the boundaries are not surrounded by other cubes on all sides
8
Q
How to solve the problem?
A
- The information from the outside boundaries must be supplied from another source (boundary conditions)
9
Q
Global model merits:
A
- Global coverage
- Don’t require boundary conditions
- Necessary at longer lead times when weather at a location is effected by distant weather system
10
Q
Global model drawbacks:
A
- Coarse spatial resolution
- Need parameterization of sub grid scale physical processes
- On a regular latitude-longitude grid, the grid boxes will become smaller in the longitude direction near the poles (high possibility of CFL condition violation)
11
Q
Regional models merits:
A
- Higher resolution
- Higher spatial resolution
- Do not require parameterization of some physical processes
- Higher spatial resolution
12
Q
Regional models drawbacks:
A
- Require boundary conditions
- (for boundary conditions) regional models depend on global models
- Parameterization required for physical processes smaller than the grid size
13
Q
Requirements to solve the forecast equations:
A
- Accurate information
- for all forecast variables and
- Along each model boundary
- Lateral
- Top
- Bottom
14
Q
How is the lateral boundary conditions data supplied to LAM?
A
- Using large-domain models
15
Q
Boundary values are obtained from:
A
- Observed data
- Data assimilation system
- Forecast values from a current or previous cycle of a large scale model (LBC in LAM)
- Climatological or fixed values
- For specifying some surface characteristics such as
- Soil moisture
- SST
- Vegetation type
- For specifying some surface characteristics such as
16
Q
Favorable source of boundary values is:
A
- Observed data
17
Q
Favorable source of lateral boundary conditions values is:
A
- Previous run of a large domain model
18
Q
Factor effecting the quality of LAM predictions
A
- Quality of predictions produced by the model supplying the LBC
19
Q
Consequence of errors in forecast from large domain model:
A
- Error will move into the LAM’s forecast domain and amplify
20
Q
LBC control:
A
- Position
- Evolution of features that cover the entire forecast domain
21
Q
Longwave patterns are largely determined by
A
- Boundary conditions
22
Q
Weaker impacts are noted on
A
- Jet streaks and fronts
- Regions far downwind from the upstream boundary
23
Q
Synoptic scale model supplying the boundary conditions determine
A
- The placement and
- Timing of synoptic scale features
24
Q
Influence of boundary conditions:
A
- Spread away from (downstream) of the boundary
- Effects amplify downstream
25
**Preferable area of primary forecast concern:**
* As far from the boundaries as possible
* Especially the upstream boundary
26
**Boundary influence is carried by:**
* The wind
27
**…………………….. and ……………………. Will vary from one flow regime to another**
* The wind and
* The direction of greatest forecast impact
28
**Forecasters should pay attention to**
* How long it takes a trajectory to move from the model boundary to the vicinity of their forecast area
29
**How to reduce the influence of boundary errors within the area of interest:**
* Placing the upstream boundary well outside the forecast area
30
**One-way interaction:**
* If information flows in one direction, from larger domain model to the smaller domain model
31
**Nested model:**
* Some LAM (eg. MM5) are run with small-area, finer-resolution grids nested inside of coarser-resolution grids within the same model
32
**Nesting is necessary because:**
* Computer memory ad speed limitations prohibit fine-resolution grids from covering the entire model domain
33
**How information from outer boundaries are supplied to nested grid models:**
* Supplied from an outside source using one-way interaction
34
**Interface between the grids inside the nested grid model are determined from:**
* The forecasts within the model itself
35
**The forecast variables for the coarse grid are updated based on:**
* Fine grid prediction
* Where the fine grid covers the coarse grid
36
**Two way interaction:**
* Coarse-grid prediction affects the fine grid prediction by
* Supplying boundary conditions on the mesh surface
* (this information flows both ways)
37
**Weather forecasting is:**
* An initial value problem (IVP):
* The outcome is significantly determined by the conditions given at the start
38
**To produce a forecast for tomorrow you need:**
* To start by determining, as precisely as possible, the state of the atmosphere today
39
**The initial conditions describe:**
* The state of the atmosphere (at grid points) at the starting point of the forecast
40
**Initial conditions include:**
* The 3D fields of the forecast variables (u,v,w,T,p..) over the model domain
41
**The initial conditions are obtained from:**
* The observed data and
* Previous forecast
Through a process known as data assimilation
42
**Local winds upstream and downstream:**
The same direction of local wind is downstream boundary while if it is opposite to the local wind it is upstream
