Met 421 Final Exam Flashcards
What does the acronym RADAR stand for?
Radio Detection And Ranging
The 2 types of radar images?
Plane Position Indicator: horizontal cross section
Range Height Indicator: Vertical cross structure
NEXRAD
Next generation radar
WSR-88D
What can WSR-88D measure?
- Storm intensity
- Storm movement
- Detection of hail
- Rainfall estimates
- Detection of tornado
- Wind fields within storms
What 3 pieces of info does a radar use to determine target location?
- Azimuth angle
- Elevation angle
- Distance to target
Azimuth Angle
Angle of beam with respect to north
Elevation Angle
Angle of beam with respect to ground
Cone of Silence
Area directly above the radar that the radar cannot detect because of elevation limitations.
Clear air mode
5 Elevations, 10 Minutes
Used with no precipitation, can be used to detect snow.
Most sensitive mode.
Precipitation mode
- Faster antenna
- 9-14 scans 5-6 minutes
- Good for precipitation
Base Reflectivity
- shows reflectivity over Single elevation scan
- Useful for precip detection
Composite Reflectivity
- Shows reflectivity over all elevation scans
- Good for thunderstorm
2 types of precipitation estimate
- 1-3 hour precipitation
- Storm total precipitation
Doppler Effect
-Frequency changes because objects are moving away or towards radar
Radial Velocity
Hydrometeors moving toward/away from radar
- positive values = away (Red)
- negative values = towards (Green)
Base velocity
-Relative to ground
Storm relative velocity
-Storm motion subtracted. Used to detect motion in storm.
Zero Isodop Prolem
Radar cant detect movement when directly perpendicular to object.
Echo Tops
Top of the precipitation core is located
Vertical Integrated Liquid (VIL)
Used to detect hail
Converts reflectivity into liquid equivalent
Ground Clutter
Trees
Mountains
Buildings
Animals
Sun Strobes
Occur around dawn/dusk
E-M radiation
Anomalous propagation (AP)
Beam refracted into ground
Appears similar to intense precipitation
Phased Array
- 30 sec volume scans
- Very expensive
- Higher resolution
GOES Satelite
U.S.
5 visible/IR channels
3 axis stabalized always facing earth
MTSAT Satellite
Japan
INSAT Satellite
India
METEOSTAT Satellite
European
Wind Profilers
- Doppler radar that measures winds in the troposphere
- Around 30 around in the U.S.
NWP model
Programs that integrate equations forward in time to predict variables for the future.
NWP Sigma coordinates
Sigma coordinates are terrain following
Grid point vs Spectral Models
Grid Point
- Regional
- Deal w lateral boundary issues
Spectral
- Global
- Provides lateral boundary info
Parameterization
Expressing unknown quantities in terms of other variables
Accounts for unresolved processes without introducing new unknowns
Microphysics
-Uses grid spacing and the weather variables within the grid for forecasting.
Grid size
- Currently 12 km in NAM model. This accounts for storms partially resolved. Requires some CP.
- < 4 km = storm fully resolved. No CP required.
How do convective storms affect larger scales?
- Redistribute heat, moisture, and momentum
- Generate precip in unsaturated model grid cells
- Stabilize atmosphere
Grid length and Convective Parameterization CP
-As grid length decreases -> turn off cp and use explicit convection
What is ensemble forecasting?
Several model runs called members are used to provide accuracy through ensemble average
Errors in NWP
- Errors in initial conditions
- Errors in model physics
- Predictability limitations
- Errors are random and/or symmetric
What is ensemble forecasting used for?
- Extended range forecasting
- Short range forecasting
- Climate prediction
- Air quality forecasting
Benefits of Ensemble forecasting
- Improve forecasting through average
- Quantitative measure of the reliability of the forecast
- Provide info for targeted observations
Ensemble strategies
- Initial Conditions
- Model physics
2 main ensemble systems used by NCEP
- Global ensemble (GFS)
- Short range ensemble forecast (SREF)
