BASICS

Question 1

Q 3.. Type of observations

Answer 1

• GTS data (Conventional observations) : SYNOP, SHIP, BUOY, SYNOR, TEMP, PILOT, AIREP, AMDAR, ACAR, SATEM, SATOB).
• Non Conventional Data (Data not transmitted through GTS, and private in general) : RADAR, TOVS, SSMI, …etc
• Old forecast valid at the time of this initial situation (used to compensate data in regions devoid of observations).

Question 2

Post processing

Answer 2

• post processing calculates a large number of diagnostic fields
• post-processing applications are very heavy but mostly serial
• (the sun grid: most of the servers are dedicated for post processing and graphics creation)
• Post-processing fields is a part of the models operational suites
• Post processing techniques such as model output statistics (MOS) have been developed to improve the handling of errors in numerical predictions

Question 3

Model operational suit in NWP

Answer 3

• WRF/U.A.E operational suit uses mainly GRADS and NCL to produce graphics
• 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.
• Will perform all tasks needed to produce the forecast with no further manual intervention. There are, however, facilities to manually override tasks should any problems occur. The operational suite embraces all the individual tasks that are required to produce a forecast. Most of the software within the operational suite has been written in-house. The suite itself is controlled by what is known as the suite control system (SCS). The SCS can be used to select which tasks are run, how they are run and when they are run.
• It is based on Unix/Linux/Perl Command Languages.
• It requires an HA (High Availability) and HPC (High Performance Computing) computing machine.
• It must be permanently monitored by specialized operators.

Question 4

Models operational suites:

Answer 4

• 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

Question 5

Weather forecast range from

Answer 5

24 hours to 7 days

Question 6

Numerical Weather Prediction (NWP)

Answer 6

ois the part of Meteorology Science which is dealing with modeling of the atmospheric conditions and trying to predict these conditions in the near future.

oIt is among the most expensive technologies in term of CPU consumption.

Question 7

oAt GHQ Meteorological Department, It is based on three specific models:

Answer 7

• WRF (Weather Research & Forecasting) model for weather parameters prediction
• WAM (Wave Model) for sea state forecast
• WRF-CHEM for pollutants and dust transport

Question 8

—NWP consists in :

Answer 8

1. Subdividing a chosen geographic 3D area in thousands (or millions) of little cubes (boxes)
2. Gathering all current (and past) actual information about atmosphere and ocean : all types of observational data.
3. Affecting one value for the main meteorological parameters (Pressure, Temperature, Wind, Humidity) in each cube.
4. Calculating through complex equations (momentum, thermodynamics, physics) the modifications affecting these meteorological parameters in time.
5. Presenting the predicted parameters values in a comprehensible standard format (charts, meteograms, soundings, …etc).

Question 9

Horizontal resolution

Answer 9

• ◦When resolution is fine enough (< 10km), small scale phenomena (thunder storms, convective cells, sea breeze, local sand storms… etc) could be well depicted.
• ◦Otherwise, only large scale phenomena (systems movement, large scale precipitations, Jet Stream evolving, … etc) could be well simulated.

Question 10

—Vertical resolution.

Answer 10

◦Fine near the surface, weak upward.

◦When the number of vertical levels is large enough, convective circulation is better taken into account by the models.

Question 11

Increasing horizontal resolution by a factor of two (2) increases

Answer 11

—the number of “cubes”, and implies computation machines 8 times faster.

Question 12

The horizontal resolution of an NWP model is directly related to

Answer 12

—the size of the weather feature it can simulate.

Question 13

—The horizontal resolution of an NWP model is directly related to the size of the weather feature it can simulate.

The resolution is related to

Answer 13

—either the spacing between grid points for grid-point models or

the number of waves used to represent weather data for spectral models.

Question 14

Models Grids Vertical Resolution

Answer 14

1. Vertical resolution must be quite fine (on the order of a few millibars) near the earth’s surface.
2. An increase in resolution is necessary near and below the tropo-pause to predict the jet stream accurately.
3. Different numerical models use a variety of vertical coordinates types to represent atmospheric layers.

Question 15

Hydrostatic approach

Answer 15

—assume hydrostatic equilibrium, in which the downward weight of the atmosphere balances the upward-directed pressure gradient.

Question 16

Non-hydrostatic

Answer 16

—processes and their effect become important when the length of a feature is approximately equal to its height.

◦Convective storms.

◦Gust fronts.

◦Gravity waves (mountain waves and turbulence)

Question 17

Necessity of physics parameterization

Answer 17

—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

Question 18

Global models

Answer 18

• —resolve atmospheric equations on the whole glob.
• —They can not use very fine resolution because of computers limitations.
• —Because of their weak resolution, they can not detect small scale phenomena.

Question 19

—The most popular global models are :

Answer 19

• ◦ECMWF/IFS (partially public and received on MDD) : http://www.ecmwf.int.
• ◦NCEP/GFS (completely public) : http://www.ncep.noaa.gov.
• ◦Météo-France/ARPEGE (not available on the net).
• ◦German DWD global model.
• ◦METOFFICE/UKMO Unified Model.
• ◦Japan Meteorological Agency JMA Global Model.

Question 20

Global models are used to

Answer 20

—forecast general synoptic circulation and to provide Initial and Lateral Boundary Data for Limited Area models.

Question 21

Limited Area Models (LAM).

Answer 21

• —They resolve the atmospheric equations on regional or local limited area domains.
• —They can use very high resolution (100m to 50km) and more vertical levels. They can catch very small phenomena.

Question 22

Limited Area Models (LAM).

—They resolve the atmospheric equations on regional or local limited area domains.

—They can use very high resolution (100m to 50km) and more vertical levels. They can catch very small phenomena.

Answer 22

—They are adequate to incorporate complex physics parameterizations (especially microphysics, deep/shallow convection and boundary layer turbulence).

They can run on small to medium computers (normal PCs, workstations, Servers, Clusters)

Question 23

Limited Area Models (LAM).

They are obliged to get

Answer 23

LBC and Initial data from global models

Question 24

—The most popular LAMs are:

Answer 24

• ◦WRF / NMM (Weather Research & Forecasting) developed by an international community and maintained at NCAR (USA)
• ◦ALADIN (Private Consortium guided by Meteo-France : 15 European and north African countries)
• ◦COSMO / LM (COnsortium for Small scale MOdeling guided by DWD).
• ◦HIRLAM (Private Consortium : Scandinavian countries and Spain).
• ◦COAMPS, RAMS, RUC, …etc.
• ◦ETA (used in more than 50 Centers and Universities).
• ◦MM5 (AFWA and more than 20 centers over the world).

Question 25

U.A.E. WRF

Answer 25

2km

Question 26

Initial Data.

Answer 26

—The actual situation used by the model to start integrate equations.

Question 27

initial data is created by techniques called

Answer 27

data assimilation

Question 28

—The information used to create initial data are:

Answer 28

◦GTS data (Conventional observations) : SYNOP, SHIP, BUOY, SYNOR, TEMP, PILOT, AIREP, AMDAR, ACAR, SATEM, SATOB). ◦Non Conventional Data (Data not transmitted through GTS, and private in general) : RADAR, TOVS, SSMI, …etc ◦Old forecast valid at the time of this initial situation (used to compensate data in regions devoid of observations).

Question 29

The process of initial data creation (analysis and data assimilation) is

Answer 29

—more complicate than the forecast model itself, and more consumer in term of CPU time.

Question 30

Lateral Boundary Conditions data

Answer 30

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.

Question 31

LBC data come from

Answer 31

—global or regional models including the LAM domain.

Question 32

WRF/U.A.E. can use LBC either from

Answer 32

NCEP/WAFS or from NCEP/GFS.

Question 33

The operational suite of a model is a

Answer 33

—set of programs developed to automate all its execution steps from the gathering of data until the production of outputs.

Question 34

—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. It is based on

Answer 34

—Unix/Linux/Perl Command Languages.

Question 35

—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. —It is based on Unix/Linux/Perl Command Languages. It requires

Answer 35

an HA (High Availability) and HPC (High Performance Computing) computing machine

Question 36

Output products. The raw outputs concern only

Answer 36

—only the prognostic variables (Pressure, Temperature, Wind, Humidity).

Question 37

Post-processing

Answer 37

calculates a large number of diagnostic fields.

Question 38

The direct raw model outputs could be in a format

Answer 38

—not understandable by the forecasters (spectral, gridded binary, …etc).

Question 39

—The direct raw model outputs could be in a format not understandable by the forecasters (spectral, gridded binary, …etc). They must be

Answer 39

—transformed to comprehensible standard charts by a graphics procedure.

Question 40

—WMO recommends the use of GRIB format of output products for the following reasons :

Answer 40

* ◦GRIB files are auto documented. * ◦GRIB files are portable on all kind of platforms. * ◦GRIB data are coded in compressed binary form, their size is optimized. * ◦GRIB data are very easy to transform into graphics charts. They can be ingested by most available graphics software. * ◦GRIB data could be exchanged very easily.

Question 41

NWP charts

Answer 41

—consist in visualizing model prognostic and diagnostic variables in fields form. —One chart can contain more than one field (Height, Temperature, Wind for example).

Question 42

—NWP charts consist in visualizing model prognostic and diagnostic variables in fields form. —One chart can contain more than one field (Height, Temperature, Wind for example). —The charts can be produced for relevant levels:

Answer 42

* ◦Surface (wind, Gust, temperature, pressure, humidity, Dust load) * ◦850mb (wind, temperature, height) * ◦700mb (wind, temperature, height, humidity) * ◦500mb (wind, temperature, height, vorticity) * ◦250mb (wind, height) * ◦Level less variables (Clouds, Visibility, Cape, Cin, Mocon, Severe weather indexes) * ◦Some characteristic fields (jet stream level, tropopause , iso-zero temperature, significant wave height and direction, ..etc)

Question 43

Meteograms

Answer 43

* —They correspond to time series of some relevant surface parameters at a given location. * —They are very useful and give a continuous (in time) overview of the meteorological situation at a given location.

Question 44

Meteograms They show generally

Answer 44

—10m wind speed and direction, 2m temperature and relative humidity, mean sea level pressure, hourly accumulated rainfall, convection indexes, visibility …etc.

Question 45

Predicted (T-Phi gram)

Answer 45

* —They correspond to the forecasted vertical profile of temperature, dew point temperature and wind above one given location. * —Their quality depends on the quality of the generating model. * —They give an idea about situation of the air mass on the vertical. They are useful in depicting the occurrence of some phenomena like convection, fog, ..etc.

Question 46

Objective Verification

Answer 46

* —To monitor forecast quality - how accurate are the forecasts and are they improving over time? * —To improve forecast quality - the first step toward getting better is discovering what you're doing wrong. * —To compare the quality of different forecast systems - to what extent does one forecast system give better forecasts than another, and in what ways is that system better?

Question 47

Driven Models

Answer 47

* —Sea/Ocean/Coastal Wave models (WAM, WaveWatch, Swan, ..etc). * —Dust and Aerosol Transport models (DREAM, CARMA-DUST, CHIMERE-DUST, …etc). * —Oil spill models. * —Transport models (pollution, volcanic ash, nuclear and biological pollutants transport, …etc)

Question 48

WRF model HPC Characteristics two components:

Answer 48

* oData assimilation to prepare an initial state for the forecast * oPrediction model

Question 49

oIt is run four times a day at:

Answer 49

* 00:00 and 12:00 to 168 hours forecasts * 06:00 and 18:00 to provide 48 hours forecasts.

Question 50

The operational configuration is covering

Answer 50

othree nested domains with increasing horizontal resolution

Question 51

oThe grid of the model is constituted of:

Answer 51

o4752000 grid points in domain d01 o8694000 grid points in domain d02 o3937860 grid points in domain d03

Question 52

As a result, a model run for 7 days forecast takes

Answer 52

takes 2 hours (all optimizations are ON, and the most consuming physics chosen)

Question 53

The WRF model is running over

Answer 53

three two-way nested domains d01, d02 and d03 with respectively increasing horizontal resolution.

Question 54

1.The WRF model is running over three two-way nested domains d01, d02 and d03 with respectively increasing horizontal resolution. In d03 the horizontal resolution is about

Answer 54

2 km

Question 55

The U.A.E/WRF is performing its own

Answer 55

data assimilation using variational techniques.

Question 56

High Performance Computing (HPC)

Answer 56

* workstations and servers: low to medium performance (cheap prices) * clusters: medium to high performance (acceptatble prices) * mainframes: high performance (expensive)