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Questions and Answers
What condition is necessary for droplet growth to occur?
What condition is necessary for droplet growth to occur?
Frontal precipitation only occurs when one air mass is lifted over another.
Frontal precipitation only occurs when one air mass is lifted over another.
True
Name the three major types of precipitation.
Name the three major types of precipitation.
Cyclonic, convective, and orographic.
A warm front is when a warm air mass ________ a cold air mass.
A warm front is when a warm air mass ________ a cold air mass.
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Match the fronts with their characteristics:
Match the fronts with their characteristics:
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What is a necessary mechanism for producing a good amount of moisture in the atmosphere?
What is a necessary mechanism for producing a good amount of moisture in the atmosphere?
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Cold fronts move faster than warm fronts.
Cold fronts move faster than warm fronts.
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What type of precipitation results from the horizontal convergence of inflowing air into a low-pressure area?
What type of precipitation results from the horizontal convergence of inflowing air into a low-pressure area?
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What happens when one bucket of the tipping bucket raingage receives 0.25 mm of rainfall?
What happens when one bucket of the tipping bucket raingage receives 0.25 mm of rainfall?
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The siphon type automatic rainfall recorder does not use a float mechanism.
The siphon type automatic rainfall recorder does not use a float mechanism.
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Name one source of error in rainfall measurements.
Name one source of error in rainfall measurements.
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The denser the gage network, the more _____ the representation.
The denser the gage network, the more _____ the representation.
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Which of the following types of raingages is also known as a float type?
Which of the following types of raingages is also known as a float type?
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Match the following raingage types with their characteristics:
Match the following raingage types with their characteristics:
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Human errors are not considered a source of errors in rainfall measurements.
Human errors are not considered a source of errors in rainfall measurements.
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Sampling errors of rainfall tend to increase with increasing ____ rainfall.
Sampling errors of rainfall tend to increase with increasing ____ rainfall.
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What is the assigned percentage of error used in the example calculation of the optimum number of raingages?
What is the assigned percentage of error used in the example calculation of the optimum number of raingages?
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The area under a hyetograph represents the total precipitation received in that period.
The area under a hyetograph represents the total precipitation received in that period.
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What is the standard deviation of rainfall given in the sample problem?
What is the standard deviation of rainfall given in the sample problem?
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A mass curve of rainfall is a plot of the accumulated precipitation against _____ .
A mass curve of rainfall is a plot of the accumulated precipitation against _____ .
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Match the following rainfall measurement terms with their definitions:
Match the following rainfall measurement terms with their definitions:
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Which raingage station recorded the highest annual rainfall in the example?
Which raingage station recorded the highest annual rainfall in the example?
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The optimum number of raingages calculated for a 10% error is 8 stations.
The optimum number of raingages calculated for a 10% error is 8 stations.
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How is a hyetograph typically represented?
How is a hyetograph typically represented?
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Which of the following is NOT a type of precipitation?
Which of the following is NOT a type of precipitation?
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Hail is formed only during extremely cold temperatures.
Hail is formed only during extremely cold temperatures.
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What causes dew to form?
What causes dew to form?
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_____ is precipitation in the form of ice crystals resulting from sublimation.
_____ is precipitation in the form of ice crystals resulting from sublimation.
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What is the size threshold for drizzle?
What is the size threshold for drizzle?
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Match the following types of precipitation with their definitions:
Match the following types of precipitation with their definitions:
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Rain is formed by condensation at temperatures below the freezing point.
Rain is formed by condensation at temperatures below the freezing point.
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What must occur for rainfall to be produced?
What must occur for rainfall to be produced?
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What is the primary purpose of constructing perpendicular bisectors in this context?
What is the primary purpose of constructing perpendicular bisectors in this context?
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The Isohyetal Method requires the line drawing of equal rainfall based solely on estimates.
The Isohyetal Method requires the line drawing of equal rainfall based solely on estimates.
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What is the formula for calculating average rainfall using the Thiessen Polygon Method?
What is the formula for calculating average rainfall using the Thiessen Polygon Method?
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The average precipitation over a watershed is found by dividing the total rainfall volume by the total area of the ______.
The average precipitation over a watershed is found by dividing the total rainfall volume by the total area of the ______.
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What is the first step in the Isohyetal Method?
What is the first step in the Isohyetal Method?
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Match the following statements with their corresponding methods:
Match the following statements with their corresponding methods:
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In Problem No. 4, what is the reported average precipitation?
In Problem No. 4, what is the reported average precipitation?
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Step 8 of the Isohyetal Method consists of counting the number of boxes between isohyetal lines.
Step 8 of the Isohyetal Method consists of counting the number of boxes between isohyetal lines.
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Study Notes
Conditions Necessary for Rainfall Production
- Colloidal stability helps droplets remain small, preventing premature falling.
- Droplet growth mechanisms include speed differences between droplet sizes and coexistence of ice crystals and water droplets.
- Sufficient moisture accumulation in the atmosphere is essential to balance evaporation losses to allow for appreciable rainfall.
- Three major types of precipitation: cyclonic, convective, and orographic, each involving different air mass lifting processes.
Cyclonic Precipitation
- Caused by horizontal convergence of air into low-pressure areas, leading to condensation.
- Non-frontal precipitation: solely involves convergence and lifting.
- Frontal precipitation occurs when one air mass is lifted over another, with distinct temperature and density boundaries.
- Warm front: warm air overrides cold air, resulting in widespread cloudiness and continuous heavy precipitation.
- Cold front: characterized by a strong push of cold air underneath warm air, leading to intense, short-duration precipitation.
- Occluded front: formed when a cold front overtakes a warm front, showing precipitation patterns of both types.
Rainfall Measurement Instruments
- Tipping Bucket Type Rain Gauge: measures 0.25 mm increments; buckets tip to record rainfall.
- Siphon Type Automatic Rainfall Recorder: features a float that rises with water level, marking data on a revolving chart.
Errors in Rainfall Measurements
- Main sources of error: instrumental defects, improper gauge siting, and human errors.
Rain Gauge Network
- Accurate mean areal rainfall is influenced by the density of the gauge network.
- Areas with high variability require more gauges for precision.
- Sampling error increases with rainfall mean and decreases with network density, duration, and area extent.
- Statistical assessment is used to determine optimal raingage numbers based on expected estimation errors.
Mass Curve and Hyetograph
- Mass curve: plots accumulated rainfall over time, useful for analyzing storm duration and intensity.
- Hyetograph: bar chart showing rainfall intensity over time, aiding in flood prediction and storm characterization.
Types of Precipitation
- Meteorological precipitation: encompasses all forms of atmospheric water vapor falling under gravity.
- Forms include: drizzle, rain, glaze, sleet, snow, frost, and hail.
- Dew forms from radiational cooling, while frost forms under freezing conditions.
- Drizzle: drops <0.5 mm, <1 mm/hr intensity.
- Rain: drops 0.5 to 6 mm; larger drops disintegrate.
- Glaze: ice from freezing rain; sleet: frozen raindrops.
- Snow: ice crystals formed by sublimation; hail: ice balls >5 mm due to turbulent air currents.
Mechanisms for Rainfall Production
- Cooling of air through pressure reduction during ascent is vital.
- Condensation occurs on hygroscopic nuclei, essential for droplet formation.
Rainfall Estimation Methods
- Thiessen Polygon Method: uses polygons around gauges for area precipitation estimation.
- Isohyetal Method: involves drawing isohyets and calculating average precipitation by analyzing contiguous areas and their rainfall volume.
Example Calculation Adjustments
- For a watershed with multiple raingage stations, statistical methods provide the average numerical error for mean rainfall estimates, with practical applications demonstrated through sample problems reflecting various rainfall amounts.
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Description
Test your knowledge on the necessary conditions for droplet growth and types of precipitation. This quiz covers frontal precipitation, the interaction of warm and cold air masses, and the characteristics of various weather fronts. Challenge your understanding of the mechanisms that produce moisture in the atmosphere.
