NWP basics Flashcards
weather prediction forecast range from
24 hours to 7 days
Numerical Weather Prediction (NWP) definition
o) is the part of Meteorology Science which is dealing with modeling of the atmospheric conditions and trying to predict these conditions in the near future.
models of NWP
- WRF (Weather Research & Forecasting) model for weather parameters prediction
- WAM (Wave Model) for sea state forecast
- WRF-CHEM for pollutants and dust transport
NWP consists in:
- Subdividing a chosen geographic 3D area in thousands (or millions) of little cubes (boxes)
- Gathering all current (and past) actual information about atmosphere and ocean : all types of observational data.
- Affecting one value for the main meteorological parameters (Pressure, Temperature, Wind, Humidity) in each cube.
- Calculating through complex equations (momentum, thermodynamics, physics) the modifications affecting these meteorological parameters in time.
- Presenting the predicted parameters values in a comprehensible standard format (charts, meteograms, soundings, …etc).
which type of resolution can show you the small scale phenomenas
When resolution is fine enough (< 10km), small scale phenomena (thunder storms, convective cells, sea breeze, local sand storms… etc) could be well depicted.
Increasing………………………. by a factor of two (2) increases the number of “cubes”, and implies computation machines ………..times faster.
horizontal resolution
8
The horizontal resolution of an NWP model is directly related to
to the size of the weather feature it can simulate.
The resolution is related to
either the spacing between grid points for grid-point models
or the number of waves used to represent weather data for spectral models.
conditions for vertical resolution grids
- Vertical resolution must be quite fine (on the order of a few millibars) near the earth’s surface.
- An increase in resolution is necessary near and below the tropo-pause to predict the jet stream accurately.
- Different numerical models use a variety of vertical coordinates types to represent atmospheric layers.
Atmospheric state at t
t = to + Δt
Atmospheric state
to + N*Δt
Hydrostatic approach
assume hydrostatic equilibrium, in which the downward weight of the atmosphere balances the upward-directed pressure gradient.
Non-hydrostatic
processes and their effect become important when the length of a feature is approximately equal to its height.
Some atmospheric phenomena need to be parameterized in order to take into account their impact, because:
- Computers are not yet powerful enough to directly treat them.
- They are often not understood well enough to be represented by an equation.
- Their effects profoundly impact model fields and are crucial to creating realistic forecasts
Global models
resolve atmospheric equations on the whole globe
global models can not use …………… because of…………………
very fine resolution
computer limitations
global models cannot detect
small scale phenomena
Global models are used to
forecast general synoptic circulation and to provide Initial and Lateral Boundary Data for Limited Area models.
The most popular global models are :
ECMWF/IFS
NCEP/GFS
German DWD global model.
A represents
Schematics for Global Atmospheric Model
B represents
Horizontal grid (latitude-Longitude)
C represents
Vertical Grid (Height or Pressure)
LAM stands for
Limited Area Models
Define LAM
They resolve the atmospheric equations on regional or local limited area domains.
LAM:
They can use…………………………….. and ……………………………… They can …………………………………….
very high resolution (100m to 50km)
more vertical levels
catch very small phenomena
LAM:
They are adequate to incorporate
complex physics parameterizations (especially microphysics, deep/shallow convection and boundary layer turbulence).
LAM:
can run on
small to medium computers (normal PCs, workstations, Servers, Clusters)
LAM:
They are obliged to
get LBC and Initial data from global models (NCEP/WAFS, NCEP/GFS, ECMWF, UKMO, JMA …etc).
LAM:
widely used by
Weather Centers over the world.
The most popular LAMs are:
- ALADIN
- COSMO / LM
- MM5
- ETA
- WRF / NMM (Weather Research & Forecasting)
Initial Data
The actual situation used by the model to start integrate equations.
Initial data is created by techniques called
data assimilation
The information used to create initial data are:
- GTS data (Conventional observations) : SYNOP, SHIP, BUOY, SYNOR, TEMP,
- NonConventional Data (Data not transmitted through GTS, and private in PILOT, AIREP, AMDAR, ACAR, SATEM, SATOB). general) : RADAR, TOVS, SSMI, …etc
- Old forecast valid at the time of this initial situation (used to compensate data in regions devoid of observations).
The process of initial data creation (…………………………………….) is more ……………………………………………………………………………
analysis and data assimilation
complicate than the forecast model itself, and more consumer in term of CPU time.
Lateral Boundary Data are used in
the LAM models
Lateral Boundary Data are used in the LAM models for the following reasons:
- To be able to compute derivatives at the model borders.
- To know what is likely to penetrate the domain of interest from outside.
- To avoid noisy fields at the borders.
LBC stands for
Lateral Boundary Conditions
LBC data come
from global or regional models including the LAM domain.
LBC data are downloaded from the Internet; they are generally………………………………….
very heavy (large size)
LBC data are downloaded from the Internet; they are generally very heavy (large size)
- GFS ~ 3.5 GB per day (0.5 degree horizontal resolution, 25 vertical levels)
- WAFS ~ 120 MB per day (1.25 degrees resolution, 11 vertical levels).
The operational suite of a model is
a set of programs developed to automate all its execution steps from the gathering of data until the production of outputs.
Models Operational Suites:
It is based on
Unix/Linux/Perl Command Languages
Models Operational Suites:
it requires
an HA (High Availability) and HPC (High Performance Computing) computing machine.
Models Operational Suites:
it must be
permanently monitored by specialized operators.
Models Operational Suites
- Gathering and processing observations.
- Getting LBC data
- Getting / Creating INIT data.
- Integrating the forecast model in time.
- Post-processing fields.
- Creating graphics and portable files.
- Dispatching data to different users
- Checking the quality of the forecasts.
