WEATHER RADAR FUNDAMENTALS Flashcards
METEOROLOGICAL OBSERVATIONS
- Satellite (National to Regional)
- RADAR (Regional to Local)
- In-Situ Stations (Local to Hyperlocal)
First used during WWII for tracking enemy airplanes and ships. After the war, the technology was adapted, used, and improved by scientists for weather analysis.
RADAR
Radars
emit pulsed of electromagnetic energy (microwave) Targets scatter energy in all directions. Some are scattered back toward the radar
“_______” back = “_______” = “Radar returns” = “Radar echoes”
Reflected
Reflectivity
Radar antenna starts at a low angle, sends out a pulse for a fraction of a second, and then “listens” to receive any returning energy.
RADAR SCANNING PATTERN
Types of Radar
- Horizontal reflectivity
- Horizontal Doppler velocity
- 2D reflectivity and velocity
- Identification of precipitation types
- Hail Detection
Types of radar that can provide vertical cross-section view of reflectivity (top) and precipitation type (bottom).
Dual polarization
Don’t have a single rotating antenna and don’t have a single rotating antenna.
PHASED-ARRAY RADARS
What are the two main scanning modes that modern-day radars have?
(i) precipitation scan mode
(ii) clear air scan mode.
What are the main difference of the two modes?
The priority of the scan.
Has steeper elevation scan compared to clear air.
Precipitation scan mode
What is CONE OF SILENCE?
An area in the troposphere that is not scanned by the radar. This is not usually a problem when precipitation is widespread and light-to-moderate, but it can mean that the top portions of thunderstorms within about 20 km (12 miles) will not be observable.
RADAR PRODUCTS
Even though majority of radars are designed to scan up to 200 km, the most accurate datasets are from <= 100 km.
It is a 1MW while returning is 1 nW
Transmitted pulse
REFLECTIVITY SCALES
The radar receiver amplifies the returned scatter and uses its amplitude to calculate the “radar reflectivity factor” (Z).
_______ indicates light precipitation (<= 30 dBZ), while _______ mean heavier precipitation. Above 60 dBZ mean it contains some hail.
low dBZ values
higher values
BASE REFLECTIVITY
The most common type of radar product that indicates precipitation. It is the most common since it is the reflectivity taken from the lowest elevation scan.
COMPOSITE REFLECTIVITY
Shows the maximum dBZ or precipitation at a certain vertical column. Consequently, it gives a plan view of the most intense portions of a precipitating system regardless of its altitude.
Using the concept of Doppler shift, the radar can identify the speed and direction of the wind.
BASE VELOCITY
What red shift (blue shift) indicates ?
the wind is moving away (towards) the radar.
What green (red) scale indicates ?
the winds moving towards (away) the radar.
Radar Limitation
- Radar miscalibration
- Range folding (RF)
- Beam Blockage
- Resolution
- Refraction
- Attenuation
The time between pulses emitted by a radar must be long enough for any scattered energy from the first pulse to return before the radar has transmitted another pulse; otherwise, the radar will interpret the energy scatter from the original pulse as belonging to the second pulse.
Range Folding
BEAM BLOCKING
It is radar viewing angles physical obstructions.
