CDC Vol 1, 009 Effects of Weather on Radar

Question 1

• What effect does heavy cloud coverage and heavy rain have on radar?

Answer 1

The range of the radar is decreased due to attenuation.

Question 2

• How is radar energy lost in attenuation?

Answer 2

Through scattering and absorption

Question 3

• What is the troposphere?

Answer 3

The lowest layer of Earth’s atmosphere. It is the portion of the atmosphere within which our weather occurs.

Question 4

• What causes the bending or refraction of radar energy?

Answer 4

The structure of the troposphere

Question 5

• What are the four basic types of refraction?

Answer 5

• Normal
• Subrefraction
• Superefraction
• Trapping (Also Called Ducting)

Question 6

• Which type of refraction causes radar energy to be curved upward?

Answer 6

Subrefraction

Question 7

• Which type of refraction occurs during cloudy, rainy weather with strong winds?

Answer 7

Normal

Question 8

• 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?

Answer 8

Superrefraction

Question 9

• Which type of refraction causes radar energy to be curved downward equal to or greater than the curvature of the earth?

Answer 9

Trapping (Also called Ducting)

Question 10

• What is one problem caused by strong weather returns?

Answer 10

Masking effect or shadow area; nothing can be seen beyond it.

Question 11

What happens the wavelength of a radiowave is close to the same diameter of the raindrops?

Answer 11

Attenuation, part of the energy is lost by scattering and absorption.

Question 12

Is attenuation greater with larger or smaller raindrops?

Answer 12

Larger raindrops cause greater attenuation.

Question 13

Compared to rain, what is the fraction of attenuation caused by hail and how much attenuation is caused by snow?

Answer 13

• 1/100

- Very little attenuation is caused by snow

Question 14

What are the major atmospheric gases we consider as absorbers of RF energy?

Answer 14

• Water vapor

- Oxygen

Question 15

Gas absorption of RF energy has a negligible effect on electromagnetic sensors because gas absorption occurs about what GHz frequency?

Answer 15

18.5 GHz

Question 16

What are the variables that affect absorption?

Answer 16

• Pressure
• Temperature
• Humidity
• Radar Frequency

Question 17

What part of the atmosphere brings about the factors that affect energy transmission through the atmosphere?

Answer 17

Troposphere

Question 18

How wide is the troposhpere at the equator and the poles?

Answer 18

• 10 miles at the equator

- 5 miles at the poles

Question 19

What is the lowest layer of the Earth’s atmoshere?

Answer 19

Troposhpere

Question 20

What separates the troposphere from the stratosphere?

Answer 20

Tropopause

Question 21

What part of the atmosphere does weather occur?

Answer 21

Troposhpere

Question 22

What causes the bending and refraction of radar energy?

Answer 22

The structure of the troposphere

Question 23

Are energy waves transmitted at low elevation or higher elevation angles more or less susceptible to refraction?

Answer 23

• Higher elevation is less susceptible

- Lower elevation is more susceptible

Question 24

Is radar range significantly increased or decreased by subrefraction?

Answer 24

Reduced

Question 25

Where are subrefraction layers most likely to form?

Answer 25

• 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

Question 26

What type of refraction generally does not disturb the performance of the radar?

Answer 26

Normal Refraction

Question 27

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?

Answer 27

Superrefraction

Question 28

Is radar range increased by superrefraction?

Answer 28

Yes, significantly extended.

Question 29

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?

Answer 29

Normal Refraction

Question 30

Is radar range extended or decreased with trapping/ducting?

Answer 30

Greatly extended but there may be blind spots or radar holes.

Question 31

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?

Answer 31

• Blaning-out effects

- Peculiar radar propagatrion conditions