,ODULE 3 Flashcards
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.
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 ‘tornados’.
CONVECTIONAL PRECIPITATION
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 ‘front’ or ‘frontal surface’.
FRONTAL PRECIPITATION
If a cold air mass drives out a warm air mass, it is called a ‘cold front’.
COLD FRONT
If a warm air mass replaces the retreating cold air mass, it is called a ‘warm front’.
WARM FRONT
If two air masses are drawn simultaneously towards a low- pressure area, the front developed
is stationary and is called a
‘stationary front’.
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 occlusion, and the resulting frontal surface is called an ‘occluded front.
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.
Here the winds blow spirally inward counterclockwise in the northern hemisphere and clockwise in the southern hemisphere.
CYCLONIC PRECIPITATION
(also called hurricane or typhoon) of comparatively small diameter of 300-1500 km causing high wind velocity and heavy precipitation,
tropical cyclone
large diameter up to 3000 km causing widespread frontal type precipitation.
extra tropical cyclone
a light steady rain in fine drops (0.5 mm) and intensity less than 1 mm/h.
Drizzle:
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
freezing of drizzle or rain when they come in contact with cold objects.
Glaze
frozen rain drops while falling through air at subfreezing temperature.
Sleet
ice crystals resulting from sublimation.
Snow
ice crystals fused together.
Snowflakes:
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
moisture condensed from the atmosphere in small drops upon cool surfaces.
Dew
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
a thin cloud of varying size at the surface of the earth by condensation of atmospheric vapor.
Fog
a very thin fog
Mist
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
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.
some regions may experience localized convective precipitation, which is characterized by intense, short-duration storms that are highly variable in space and time.
SPATIAL DISTRIBUTION
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 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 GAUGES
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.
From this 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 GAUGES
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.
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.
TIPPING BUCKET RAIN GAUGE
In this type of rain-gauge, 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.
The rotation of the drum sets the time scale while the vertical motion of the pen records the cumulative precipitation.
WEIGHING TYPE RAIN GAUGE
as the rain is collected
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.
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
Point rainfall is the rainfall at a single station. For small areas less than 50 square kilometers, point rainfall 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,
MEAN AREAL DEPTH
It is obtained by simply averaging arithmetically the amounts of rainfall at the individual rain-gauge station in the area
Pave = P1 + P2 + P3 + ⋯ + Pn/ n = σi=1Pi/n
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.
ARITHMETIC AVERAGE METHOD
This method attempts to allow for non uniform distribution of gauges by providing a weighting factor for each gauge.
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.
THIESSEN POLYGON METHOD
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.
ISOHYETAL METHOD
used to summarize precipitation data, such as the mean, median, and standard deviation of precipitation amounts.
Descriptive Statistics
involves analyzing the changes in precipitation amounts over time, such as seasonal or annual trends.
Time-Series Analysis
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
