CDC Vol 1, 009 Effects of Weather on Radar Flashcards
- What effect does heavy cloud coverage and heavy rain have on radar?
The range of the radar is decreased due to attenuation.
- How is radar energy lost in attenuation?
Through scattering and absorption
- What is the troposphere?
The lowest layer of Earth’s atmosphere. It is the portion of the atmosphere within which our weather occurs.
- What causes the bending or refraction of radar energy?
The structure of the troposphere
- What are the four basic types of refraction?
- Normal
- Subrefraction
- Superefraction
- Trapping (Also Called Ducting)
- Which type of refraction causes radar energy to be curved upward?
Subrefraction
- Which type of refraction occurs during cloudy, rainy weather with strong winds?
Normal
- Which type of refraction causes radar energy to be curved downward more sharply than normal but not as much as the curvature of the earth?
Superrefraction
- Which type of refraction causes radar energy to be curved downward equal to or greater than the curvature of the earth?
Trapping (Also called Ducting)
- What is one problem caused by strong weather returns?
Masking effect or shadow area; nothing can be seen beyond it.
What happens the wavelength of a radiowave is close to the same diameter of the raindrops?
Attenuation, part of the energy is lost by scattering and absorption.
Is attenuation greater with larger or smaller raindrops?
Larger raindrops cause greater attenuation.
Compared to rain, what is the fraction of attenuation caused by hail and how much attenuation is caused by snow?
- 1/100
- Very little attenuation is caused by snow
What are the major atmospheric gases we consider as absorbers of RF energy?
- Water vapor
- Oxygen
Gas absorption of RF energy has a negligible effect on electromagnetic sensors because gas absorption occurs about what GHz frequency?
18.5 GHz
What are the variables that affect absorption?
- Pressure
- Temperature
- Humidity
- Radar Frequency
What part of the atmosphere brings about the factors that affect energy transmission through the atmosphere?
Troposphere
How wide is the troposhpere at the equator and the poles?
- 10 miles at the equator
- 5 miles at the poles
What is the lowest layer of the Earth’s atmoshere?
Troposhpere
What separates the troposphere from the stratosphere?
Tropopause
What part of the atmosphere does weather occur?
Troposhpere
What causes the bending and refraction of radar energy?
The structure of the troposphere
Are energy waves transmitted at low elevation or higher elevation angles more or less susceptible to refraction?
- Higher elevation is less susceptible
- Lower elevation is more susceptible
Is radar range significantly increased or decreased by subrefraction?
Reduced
Where are subrefraction layers most likely to form?
- Dry climates areas during periods of strong incoming radiation (surface heating)
- Elevated plateau locations after several days heating bare ground
- Coastal areas during periods of fog formed by warm moist air (from over ater) moving over ground that has cooled during the night
What type of refraction generally does not disturb the performance of the radar?
Normal Refraction
What type of refraction occurs during in fog formed by cold air moving over warm water or water-soaked ground (as a cold front passing after a heavy rain)—at night with clear skies, calm winds, especially with a source of surface moisture; and on the eastern side of large, high-pressure systems, as after the passing of a cold front?
Superrefraction
Is radar range increased by superrefraction?
Yes, significantly extended.
What type of refraction occurs during rainy weather with strong winds; during midday as heating causes convection mixing evidenced by developing cumulonimbus clouds; and during midday as heating causes increasingly gusty winds?
Normal Refraction
Is radar range extended or decreased with trapping/ducting?
Greatly extended but there may be blind spots or radar holes.
What may occur on your radar scope near the edges of a storm or front due to extreme variations in refractivity caused by abrupt temperature and moisture changes?
- Blaning-out effects
- Peculiar radar propagatrion conditions
