introduction to meteorological radar. energy returned to radar size of particle at a given...
Post on 15-Jan-2016
227 views
TRANSCRIPT
![Page 1: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/1.jpg)
Introduction to Meteorological Radar
![Page 2: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/2.jpg)
En
erg
y R
etu
rned
to R
adar
Size of Particle
At a Given Wavelength
En
erg
y R
etu
rned
to R
adar
Radar Wavelength
Target Diversity At Different Wavelengths
Spheres
MoistureFluctuations
NEXRAD10-cm
CloudRadar(3-8 mm) Wind
Profilers
![Page 3: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/3.jpg)
NEXRAD or WSR-88D
[Next Generation Radar][Weather Surveillance Radar, 1988, Doppler]
![Page 4: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/4.jpg)
Pulse Lengths for WSR-88D Radar[Weather Surveillance Radar, 1988, Doppler]
• Total radiated power in a radar pulse
• Range Resolution:
• Long Pulse:
• Short Pulse:
Total t peakP P
2
c
4.7 ( 1410 )s c m 1.57 ( 471 )s c m
![Page 5: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/5.jpg)
Volume Coverage Patterns (VCP) for the WSR-88D (NEXRAD) Radar
VCP Scan Time (min)
Elevation Angles Usage Attributes
11 5 14 angles: 0.5-19.5° convectionclose to radar
Best Vol. coverage
12 4 14 angles: 0.5-19.5°9 angles < 6°
convection far from radar
21 6 9 angles: 0.5-19.5° shallow precipitation
long dwell time
31 10 5 angles: 0.5-4.5° subtle boundaries/snow
long-pulse
32 10 5 angles: 0.5-4.5° increased sensitivity
long pulse
212 5.5 9 angles: 0.5-19.5°9 angles ≤ 6°
Better velocity data required
variable PRF
![Page 6: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/6.jpg)
Volume Coverage Maps
VCP-21 VCP-31
![Page 7: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/7.jpg)
How to read the intensity scale
Clear-Air ScalePrecipitation Mode Scale
Light Precipitation
Very light precipitation
Fog, Clouds, Smoke
Dust, Insects, Birds
♦The time listed is usually in UTC or Z time. To convert this to eastern daylight time, subtract 4 hours; for standard time subtract 5.
♦Units are decibels of Z (reflectivity).
ExtremeIntenseSevere
Heavy
Moderate
Light
Very light
![Page 8: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/8.jpg)
Yesterday
![Page 9: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/9.jpg)
Clear-Air Mode
Gulf Coast Sea-Breeze (South of Tallahassee)
![Page 10: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/10.jpg)
Hanley, Cunnigham, and Goodrick
INTERACTION BETWEEN A WILDFIRE AND A SEA-BREEZE FRONT
![Page 11: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/11.jpg)
The Radar “Bright” Band
![Page 12: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/12.jpg)
Multiple “Bright” Bands
![Page 13: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/13.jpg)
Ground Clutter○Most prevalent on 0.5°
reflectivity and velocity images○Radar beam is striking
stationary ground targets○Usually appears as an area of
uniform returns surrounding radar site
○Velocities usually near zero on velocity images
○Some is filtered but it is impossible to remove it all
○Especially bad during inversions or after frontal passages
![Page 14: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/14.jpg)
Beam Spreading
•The beam widens as it moves away from the radar. If a small storm is a considerable distance from the radar...it may not be big enough to completely fill the beam.
•Since the radar cannot discern things thinner than the beam, it assumes the storm is filling it entirely. This can make a storm look bigger than reality.
Actual Depicted
![Page 15: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/15.jpg)
Beam Height vs. Distance
○Lowest elevation slice is 0.5° so it is not totally horizontal.
○Earth’s curvature also plays a role.
○Radar beam gets higher off the ground farther from the radar.
○Makes low level precipitation invisible to radar at considerable distances.
![Page 16: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/16.jpg)
Anomalous Propagation
Greater density slows the waves more.
Less dense air does not slow the waves as much.
Since density normally decreases with height, the radar beam is refracted toward the surface of the Earth.
![Page 17: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/17.jpg)
Refraction
![Page 18: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/18.jpg)
Subrefraction
If the decrease in density with height is more than normal, then the beam bends less than normal and this is called subrefraction.
In this case the beam might shoot over the target and miss the precipitation.
![Page 19: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/19.jpg)
Subrefraction (Cont.)
![Page 20: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/20.jpg)
Superrefraction
If the decrease in density with height is less than normal, then the beam bends more than normal and this is called superrefraction.
In this case the beam bends more toward the surface of the Earth, and it may undershoot the target.
![Page 21: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/21.jpg)
Superrefraction (Cont.)
![Page 22: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/22.jpg)
Ducting
If the decrease in density with height is much less than normal, the beam may bend down to the surface of the Earth in a process called ducting.
If the beam is backscattered to the receiver, it may result in Anomalous Propagation (AP) or “false echoes”.
![Page 23: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/23.jpg)
Ducting (Cont.)
![Page 24: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/24.jpg)
The Birds and the Bees
![Page 25: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/25.jpg)
Products Available
▪Reflectivity Images
▪Velocity Images (Doppler)
▪Precipitation Estimates
▪Vertically Integrated Liquid
▪Echo Tops
▪Animated Loops of Most Products
▪Many Other Products
![Page 26: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/26.jpg)
Reflectivity ImagesBase Reflectivity and Composite Reflectivity
Base Reflectivity
Composite Reflectivity
○0.5° elevation slice
○Shows only the precipitation at the lowest tilt level
○May underestimate intensity of elevated convection or storm cores
○Displays the maximum returned signal from all of the elevation scans
○Better summary of precipitation intensity
○Much less deceiving than Base Reflectivity
○Subtle 3-D storm structure hidden
![Page 27: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/27.jpg)
Reflectivity ImagesComposite Reflectivity
○Displays the maximum returned signal from all of the elevation scans to form a single image
○Can often mask some Base Reflectivity signatures such as a hook echo
![Page 28: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/28.jpg)
Which is which?
▪Notice the lighter returns ▪Notice the heavier returns and more coverage
Base vs Composite Reflectivity
Base Reflectivity Image Composite Reflectivity Image
![Page 29: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/29.jpg)
Velocity ImageryWarm colors are winds moving away from radome(reds, +)
Cool colors are winds moving toward radome(greens, -)
Tight area of opposing winds (+ and -) can indicate convergence or rotation. Circled area called a couplet. Indicates a possible tornado.
Wind speed is in knots
![Page 30: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/30.jpg)
Detecting Rotation
A velocity couplet may indicate rotation.
X
+ (radar site)
inbound radial velocities
outound radial velocities
![Page 31: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/31.jpg)
Detection Rotation (Cont.)
Not all velocity couplets indicate rotation.
+ (radar site)
inbound radial velocities
outbound radial velocities
Linear (straight line) flow over the radar site.
![Page 32: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/32.jpg)
Hail Detection
•Returns > 55 dBz usually indicate hail.•However, the probability of hail reaching
the ground depends on the freezing altitude.•Usually, a freezing level above 14,000
feet will not support much hail.•This is because the hail melts before
reaching the ground.•Freezing level can be determined from an
upper air sounding.
![Page 33: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/33.jpg)
Hail?
Max return of 60 dbZ Max return of 65 dbZ
Freezing level was 7,000 feet Freezing level was 17,000 feet
Produced golfball sized hail Produced no hail
Hence, hail production depends directly on freezing level.
![Page 34: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/34.jpg)
Vertically Integrated Liquid (VIL)■Take a vertical column of the atmosphere:
estimate the amount of liquid water in it.■High VIL values are a good indication of hail.
•The white pixel indicates a VIL of 70.
•This storm produced golfball size hail.
•Trouble with VIL is that the operator has to wait for the scan to complete before getting the product.
![Page 35: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/35.jpg)
The Hail SpikeAlso called Three-Body Scattering
▪A dense core of wet hail will reflect part of the beam to the ground, which then scatters back into the cloud, and is bounced back to the antenna.
▪The delayed returns trick the radar into displaying a spike past the core.▪Usually, will only result from hail 1 inch in diameter or larger (quarter size).
![Page 36: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/36.jpg)
Echo TopsFairly accurate at depicting height of storm tops
Inaccurate data close to radar because there is no beam angle high enough to see tops.
Often has stair-stepped appearance due to uneven sampling of data between elevation
scans.
![Page 37: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/37.jpg)
Precipitation EstimatesAn incredibly powerful tool to the meteorologist
Storm Total Precipitation
●Total estimated accumulation for a set amount of time.●Totals are in inches●Time range is
sometimes listed on image.●Resets storm total
whenever there is no rain detected for an hour.
![Page 38: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/38.jpg)
-Updated once per volume scan.
-Shows accumulated rainfall for the last
hour.-Useful for
determining rainfall rate of ongoing
convection.
One Hour Precipitation Total
![Page 39: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/39.jpg)
Precipitation EstimateAdvantages and Limitations
●Great for scattered areas of rain where no rain gauges are located
●Has helped issue flash flood warnings more efficiently
●Helps fill in the holes where ground truth information is not available
●Much better lead time for warnings
●Provides a graphical ‘map’ of rainfall for an entire region
●Data can be overlaid with terrain and watersheds to predict reservoir and waterway crests
●Estimates based on cloud water levels and not ground level rainfall
●‘Hail Contamination’ causes highly inflated values
●High terrain causes underestimates
●Lower resolution than reflectivity images
●Useful as a supplement, not replacement for ground truth information
![Page 40: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/40.jpg)
How Doppler Wind Is Displayed Inbound velocities (towards the radar) are shaded blue, with pale shades for light winds and dark shades for strong winds. Outbound velocities (away from the radar) are shaded orange with pale shades (yellow) for light winds and dark shades (red) for strong winds.
![Page 41: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/41.jpg)
Clear-Air Wind Profilers
![Page 42: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/42.jpg)
Ene
rgy
Abs
orbe
d by
Atm
osph
ere
Radar Wavelength
35 GHz
94 GHz
MaximumPropagation
Distance
20-30 km
10-15 km
8 mm3.2 mm
![Page 43: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/43.jpg)
The DOE Cloud Radars
![Page 44: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/44.jpg)
Small Cloud Particles Typical Cloud Particles Very Light Precipitation
Surface
10-km
20-km
Cloud Radar Data from Southern Great Plains
Black Dots:Laser MeasurementsOf CloudBase Height
7:00 pm 7:00 am 7:00 pmtime
![Page 45: Introduction to Meteorological Radar. Energy Returned to Radar Size of Particle At a Given Wavelength Energy Returned to Radar Radar Wavelength Target](https://reader034.vdocument.in/reader034/viewer/2022052317/56649d805503460f94a646f1/html5/thumbnails/45.jpg)
Small Cloud Particles Typical Cloud Particles Very Light Precipitation
Surface
10-km
20-km
Cloud Radar Data from Southern Great Plains
Black Dots:Laser MeasurementsOf CloudBase Height
ThinClouds
Insects
7:00 pm 7:00 am 7:00 pmtime