1Radar consists of
transmitter which EMITS pulses of electromagnetic radiation and a receiver that MEASURES the characteristics of the radiation scattered back to the radar site
2Transmission of radar waves transmits radiation with
wavelengths of _ cm or __
cm
3 , 10
3 Average transmitted power of about
450,000 watts
4Transmission lasts about
0.0000016 seconds
5Receiver then listens for about
0.00019 seconds
6Pulses are typically transmitted about
1300 times per second
7___ Doppler sites in USA
160
8The intensity of the returned signal is used to determine
type and intensity of precipitation that is backscattering the radiant
energy to the receiver
9use a reflectivityainfall relationship (Z-R equation)
relate the magnitude of the backscattered energy to the rainfall rate
10(Z = aRb) Z:
Magnitude of the backscattered energy
11(Z= aRb) R:
Rainfall rate
12(Z= aRb) a and b
determined coefficients
13Beam Spreading
The energy transmitted by a radar pulse which spreads out in a
CONICAL shape as it moves away from the site
14The width of the beam expands at a rate of roughly
___ m (~1000 ft) for every __ km (10 mi) it travels
300 , 16
15The effect of beam spreading is to ________ the spatial resolution as distance from the radar site _________
REDUCE , INCREASES
16effect of beam spreading is to make it ____ difficult for the radar to detect ______ features as their distance from the radar _________
MORE , SMALL , INCREASES
17(Doppler base) Short Range
124 mn
18(Dopple base) Long Range
248 nm
19WSR-88D can complete an elevation scan in __ to ___ seconds depending on the scanning mode
20 , 120
20Volume Scan
series of elevation scans conducted at different elevations are COMBINED into a SINGLE scanning product
21NWS Radar sites THREE basic scanning modes:
• 1. Clear air mode
• 2. Precipitation detection mode
• 3. Severe weather detection mode
22clear air mode: ____ elevation scans
(elevation of 0.5, 1.5, 2.4, 3.4 and 4.3
degrees) in ___ minutes
5 , 10
23Clear air mode is called
VCP 31
24Clear air mode radar antenns has
SLOWEST rate of rotation
25Precipitation Detection Mode: ____ (elevation scans of 0.5, 1.5,
2.4, 3.4, 4.3, 6.2, 10, 14, and 19.5 degrees) in
___ minute
9 , 6
26Clear Air Mode used when
NO significant precipitation echoes
27Precipitation Detection Mode called
VCP 21
28In Precipitation Mode...
the radar scans several elevation levels using a pulse repetition frequency (PRF) that allows forecasters to quickly receive information about the atmosphere
29Severe Weather Detection Mode: ___ Elevation Scans (at 0.5, 1.5, 2.4, 3.4, 4.3, 5.3, 6.2, 7.5, 8.7, 10, 12, 14, 16.7, and 19.5 degrees) in ___
minute
14 , 5
30Severe Weather Mode called
VCP 11
31Severe Weather mode is the
FASTEST mode and used to moniter severe convective systems
32Base reflectivity
energy backscattered to the radar during a SINGLE elevation scan
33Composite reflectivity
the MAXIMUM energy backscattered to the radar for each location
during a COMPLETE volume scan
34Base velocity displays
radial velocity data (i.e., the rate of motion TOWARD (GREEN) or AWAY (RED) from the radar site)
35Storm relative velocity
subtracts the movement of the storm from the base velocity to determine the MOTION relative to the storm (Wind's motion as if the storm was stationary)
36Mesocyclone detection
algorithm that identifies vertically correlated three-dimensional wind
shear regions within a storm
37Tornado Vortex
Signature (TVS)
algorithm which identifies embedded smaller-scale circulations and is designed to alert the user to areas that indicate a very high threat of tornadic circulations
38Dual Polarization
Pulses are sent HORIZONTALLY and VERTICALLY through the atmosphere (better sense of size and shape of targets)
39Benefits of Dual-Polarization
1. Identify large hail and tornadic debris
2. Identify thunderstorm updraft locations and
intensities
3. Identify winter precipitation types
4. Separate non-weather scatterers (bugs and
birds) from the data
40Differential Reflectivity (ZDR)
logarithm ratio of the horizontally polarized reflectivity to the vertically polarized reflectivity
41Differential Reflectivity (ZDR) can identify
hail shafts, detect updrafts, determine rain drop size, and identify aggregation of dry snow
42(ZDR Table) Rain:
(normally) >1 - 5 (large drops)
43(ZDR Table) Snow:
less than 0.5
44(ZDR Table) Hail:
between -1 & 1
45Correlation coefficient (CC) provides
a measure of the CONSISTENCY of the shapes and sizes of targets within the radar beam
46Low (cc) < 0.8
birds, insects, etc
47Moderate (cc) 0.8-0.97
hail, melting snow, etc
48High (cc) > 0.97
rain, snow, etc
49Specific Differential Phase (KDP)0
product that identifies regions of heavy rain
50Positive KDP
GREATER phase shift in HORIZONTAL than vertical
54Increasing KDP =
An increase in the size and concentration of rain drops (an
increase in rain rate)