MODULE 3: PRECIPITATION Flashcards
It is the general term for all forms of
moisture emanating from the clouds and falling to the
ground.
Precipitation
TYPES OF PRECIPITATION
CONVECTIONAL PRECIPITATION
FRONTAL PRECIPITATION
OROGRAPHIC PRECIPITATION
CYCLONIC PRECIPITATION
This type of precipitation is in the form of local whirling thunderstorms and is typical of the tropics.
CONVECTIONAL PRECIPITATION
It is when the air close to the warm earth gets heated and rises due to its low density, cools adiabatically to form a cauliflower shaped cloud, which finally bursts into a
thunderstorm.
When accompanied by destructive winds, they are called ______.
CONVECTIONAL PRECIPITATION;
TORNADOS
When two air masses due to contrasting temperatures and densities clash with each other, condensation and precipitation occur at the surface of contact.
This surface of contact is called a ____ or ________.
FRONTAL PRECIPITATION;
FRONT or FRONTAL SURFACE
TYPES OF FRONTAL PRECIPITATION
COLD FRONT
WARM FRONT
STATIONARY FRONT
OCCLUDED FRONT
If a cold air mass drives out a
warm air mass, it is called a ____?
COLD FRONT
If a warm air mass replaces the
retreating cold air mass, it is
called a ____?
WARM FRONT
If two air masses are drawn simultaneously towards a low-pressure area, the front developed is _______ and is called a
________.
STATIONARY;
STATIONARY FRONT
Cold fronts move faster than warm fronts and usually overtake them, the frontal surfaces of cold and warm air sliding against each other. This phenomenon is called ________, and the resulting frontal surface is called an ______.
OCCLUSION;
OCCLUDED FRONT
This type of precipitation is caused by the uplift of moist air as it flows over a mountain or other elevated terrain.
As the air rises, it cool and condenses, forming clouds and precipitation.
OROGRAPHIC PRECIPITATION
This type of precipitation is due to lifting of moist air converging into a low-pressure belt, due to pressure differences created by the unequal heating of the earth’s surface.
CYCLONIC PRECIPITATION
Here the winds blow spirally inward counterclockwise in the northern hemisphere and clockwise in the
southern hemisphere.
CYCLONIC PRECIPITATION
2 TYPES OF CYCLONE
TROPICAL CYCLONE
EXTRA TROPICAL CYCLONE
It is also called hurricane or typhoon of
comparatively small diameter of 300-1500 km causing high wind velocity and heavy precipitation,
TROPICAL CYCLONE
This type of cyclone is of large diameter up to 3000 km causing widespread frontal type precipitation.
EXTRA TROPICAL CYCLONE
FORMS OF PRECIPITATION
DRIZZLE
RAIN
GLAZE
SLEET
SNOW
SNOWFLAKES
HAIL
DEW
FROST
FOG
MIST
It is a light steady rain in fine drops (0.5 mm) and intensity less than 1 mm/h.
Drizzle
It is the condensed water vapor of the atmosphere falling in drops from the clouds of sizes larger than 0.5 mm. The maximum size is about 6 mm.
Rain
It is a freezing of drizzle or rain when they come in contact with cold objects.
Glaze
It is a frozen rain drops while falling through air at subfreezing temperature.
Sleet
It is ice crystals resulting from sublimation.
Snow
It is ice crystals fused together.
Snowflakes
It is moisture condensed from the atmosphere in small drops upon cool surfaces.
Dew
It is a small lumps of ice larger than 5 mm in diameter formed by alternate freezing and melting, when they are carried up and down in highly turbulent air currents.
Hail
It is a a feathery deposit of ice formed on the ground or on the surface of exposed objects by dew or water vapor that has frozen.
Frost
It is a thin cloud of varying size at the surface of the earth by condensation of atmospheric vapor.
Fog
It is a very thin fog.
Mist
Characteristics of Precipitation
INTENSITY
FREQUENCY
DURATION
It refers to the amount of precipitation that falls during a specific time period, typically measured in millimeters or inches per hour. Higher intensity precipitation events are often associated with more extreme
weather conditions, such as thunderstorms, hurricanes, or heavy snowfall.
INTENSITY
It refers to how often precipitation
events of a certain intensity occur
over a specific time period, typically
measured in terms of the number of
events per year. Frequency analysis
can be used to identify the
probability of extreme precipitation
events occurring in a given region,
which can help inform planning and
management decisions.
FREQUENCY
It refers to how long a precipitation
event lasts, typically measured in
hours. Longer-duration precipitation
events can lead to more widespread
and sustained impacts, such as
flooding or erosion.
DURATION
Patterns of Precipitation
SPATIAL DISTRIBUTION
TEMPORAL DISTRIBUTION
It refers to the pattern of where precipitation falls over a specific area. This can be influenced by a variety of factors, such as topography, distance from water
sources, and prevailing wind patterns.
SPATIAL DISTRIBUTION
It is expressed in terms of the depth to
which rainfall water would stand on an area if all the rain were collected on it.
PRECIPITATION
It refers to the pattern of
when precipitation occurs over a
specific time period, such as a day,
a month, or a year. This can be
influenced by seasonal and climatic
factors, as well as weather patterns
such as fronts and atmospheric
disturbances.
TEMPORAL DISTRIBUTION
It may be measured by a network of rain gauges which may either be of non-recording or recording type.
RAINFALL
TYPE OF RAIN GAUGES
NON-RECORDING RAIN GAUGE
RECORDING RAIN GAUGE
It is a rain gauge which does not provide the distribution of amount of precipitation in a day. It simply gives the amount of precipitation after 24 hours (daily precipitation).
NON-RECORDING RAIN GAUGE
This is also called self-recording, automatic or integrating rain gauge. This type of rain gauge has an automatic mechanical arrangement consisting of a clockwork, a drum with a graph paper fixed around it
and a pencil point, which draws the mass curve of rainfall.
RECORDING RAIN GAUGE
This consists of a cylindrical receiver 30 cm diameter with a funnel inside. Just below the funnel a pair of tipping buckets is pivoted such that when one of the
bucket receives a rainfall of 0.25 mm it tips and empties into a tank below, while the other bucket takes its position, and the process is repeated.
TIPPING BUCKET RAIN GAUGE
It is where the mass curve, the depth of rainfall in a given time, the rate or intensity of rainfall at any instant during a storm, time of onset and cessation of rainfall,
can be determined.
RECORDING RAIN GAUGE
Types of recording rain gauges
TIPPING BUCKET RAIN GAUGE
WEIGHING TYPE RAIN GAUGE
FLOAT TYPE RAIN GAUGE
The tipping of the bucket
actuates on electric circuit which
causes a pen to move on a chart
wrapped round a drum which
revolves by a clock mechanism.
This type cannot record ____.
SNOW
It is when a certain weight of rainfall is collected in a tank, which rests on a spring-
lever balance, it makes a pen to move on a chart wrapped round a clock-driven drum.
WEIGHING TYPE RAIN GAUGE
It is where the rotation of the drum
sets the time scale while the
vertical motion of the pen
records the cumulative
precipitation.
WEIGHING TYPE RAIN GAUGE
It is where the rain is collected in a float chamber, the float moves up which makes a pen to move on a chart wrapped round a clock driven drum. When the float chamber fills up, the water siphons out automatically through a siphon tube kept in an
interconnected siphon chamber.
FLOAT TYPE RAIN GAUGE
It is where the clockwork revolves the drum once in 24 hours. The clock mechanism needs rewinding once in a week when the chart wrapped round the drum is also replaced.
FLOAT TYPE RAIN GAUGE
____ is the rainfall at a single station. For
small areas less than 50 square kilometers, It may be taken as the average depth over the area. In large areas, there will be a network of rain gauge stations. As the rainfall over a large area is no uniform, the average depth of rainfall over an area is
determined by the following three methods
Point Rainfall
MEASUREMENT METHODS
ARITHMETIC AVERAGE METHOD
THIESSEN POLYGON METHOD
ISOHYETAL METHOD
This method is fast and simple and yields good estimates in flat country if the gauges are uniformly distributed and the rainfall at different stations do not vary very widely from the mean. The limitation can be
partially overcome if the topographic influences and aerial representativity are considered in the selection of gauge sites.
ARITHMETIC AVERAGE METHOD
It is obtained by simply averaging arithmetically the amounts of rainfall at the individual rain-gauge station in the area
ARITHMETIC AVERAGE METHOD
This method attempts to allow for non-uniform distribution of gauges by providing a weighting factor for each gauge. The station are plotted on a base map and are connected by straight lines. Perpendicular
bisectors are drawn to the straight lines, joining adjacent stations to form polygons, known as ______.
THIESSEN POLYGON METHOD;
THIESSEN POLYGON
In this method, the point rainfalls are plotted on a suitable base map and the lines of equal rainfall (isohyets) are drawn giving consideration to orographic effects and storm morphology. The average rainfall between successive isohyets taken as the average of the two isohyetal values are weighted with the area between the isohyets, added up and divided by the total area which gives the average depth of rainfall over the entire basin.
ISOHYETAL METHOD
The results obtained are usually more accurate than those obtained by simple arithmetic averaging. The gauges should be properly located over the catchment to get regular shaped polygons. However, one of the serious limitations of the Thiessen method is its non-flexibility since a new Thiessen diagram has to be constructed every time there is a change in the rain gauge network.
THIESSEN POLYGON METHOD
TYPES OF ANALYSIS OF RAINFALL DATA
DESCRIPTIVE STATISTICS
TIME-SERIES ANALYSIS
SPATIAL ANALYSIS
CORRELATION ANALYSIS
It can be used to summarize precipitation data, such as the mean, median, and standard deviation of precipitation amounts.
DESCRIPTIVE STATISTICS
It involves analyzing the changes in precipitation amounts over time, such as seasonal or annual trends.
TIME-SERIES ANALYSIS
It involves analyzing the distribution of precipitation across a region or area, such as the variation in precipitation amounts between different cities or regions.
SPATIAL ANALYSIS
It involves examining the relationship between precipitation and other variables,
such as temperature, humidity, or atmospheric pressure, to understand the factors that influence precipitation patterns.
CORRELATION ANALYSIS
