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Flashcards in Hydrometeorology Deck (105)
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Describe Evaporation / Transpiration:

Evaporation is the movement of water from a liquid to a vapor state, and is the opposite of condensation. Transpiration is the process whereby soil moisture is taken up by a plant’s root system to drive photosynthesis. The combined effect of evaporation and transpiration is often called evapotranspiration, or ET, and is generally constitutes the largest removal of water from the soil water system.


Describe Condensation:

Condensation is the movement of water from a vapor to a liquid state, and is the opposite of evaporation.


Describe Precipitation:

Precipitation is generally described as water falling to the surface of the Earth, either in the form of liquid or frozen water; therefore, it is also known as hydrometeors (hence, meteorology!).


Describe Runoff/Infiltration:

Runoff is the portion of rainfall that does not infiltrate into the soil. As water infiltrates, some water will flow just below the surface. This is called interflow or through-flow.Infiltration is defined as the downward movement of water through the soil surface into the soil profile.


Describe Storage

Storage is the general amount of water in a particular location and it can be calculated using an accounting budget approach. (Infow) – (Outflow) = (Change in Storage)


Describe Groundwater Discharge

Groundwater discharge occurs when water seeps from aquifers into rivers, streams, and lakes.


Where and in what percentages is out ground water stored?

• The oceans store over 97% of the Earth’s water supply in the form of
• Polar icecaps and glaciers account for slightly more than 2% of the Earth’s
water, and comprise the largest percentage of freshwater on the planet.
• Surface water storage in freshwater lakes, ponds, rivers, and streams
account for less than 0.01% of the total water on Earth.
• Groundwater is normally stored within aquifers, which are subsurface
regions comprised of unconsolidated rock and soil particles. Less than
1% of the Earth’s total water is stored as groundwater or soil moisture.


How does water enter and leave out atmosphere?

Water reaches the atmosphere through transpiration, evaporation, and sublimation, meaning that water vapor is the primary form by which water enters the atmospheric system. Water leaves the atmosphere almost solely through precipitation, either solid (snow, hail, etc.) or liquid (rain, dew).


How does surface water become ground water and how does surface water enter the atmosphere?

Infiltration to become groundwater. Evaporation to enter the atmosophere.


What process inhibits water from draining from soil even when there may still be water present?

Capillary tension.


Define wilting point.

There is a point where the tension of the water to the soil particle becomes so tight that the water cannot be used by plant roots. This is called the wilting point.


Name the soil textures. (Hint 3)

Clay, sand and loam.


What is a confined aquifer?

. In confined aquifers the groundwater is restricted by a nonporous or very low porous layer termed an aquiclude and is not in contact with the atmosphere.


What is an unconfined aquifer?

In unconfined aquifers, the groundwater is in contact with the atmosphere through the pores of the overlaying soil. The top of the groundwater is termed the water table.


Define recharge.

Recharge is the introduction of surface water to the groundwater system.


Define withdrawl.

. Withdrawal is the artificial extraction of groundwater through a well or network of wells. When groundwater withdrawal rates are greater than the recharge of water into the ground, a lowering of the local water table occurs.


Name the two ways that a cloud droplet can form.

homogenous nucleation and heterogeneous nucleation.


Define homogenous nucleation.

Homogeneous nucleation occurs when water droplets form by the chance collision and bonding of water vapor molecules under supersaturated conditions. In other words, water vapor molecules bond to other water vapor molecules with no condensation nuclei involved. This is possible under the absence of atmospheric aerosols and the droplets are inherently small with a high degree of curvature.


Define heterogeneous nucleation.

Heterogeneous nucleation occurs when water droplets form on external hygroscopic (a.k.a., water attracting known as condensation nuclei) particles. Heterogeneous nucleation can occur under saturated or minimally supersaturated conditions. Haze forms under unsaturated conditions.


Explain Condensation Nuclei.

The hygroscopic particles over which droplets are formed are called condensation nuclei. When condensation occurs, the condensation nuclei dissolve to form a solution. The resulting solution further reduces the saturation necessary for condensation to occur. This is because the surface area of the droplet becomes populated by solute, not water.


What is required to get supper cooled water to freeze at temps near 0?

Saturation can occur at below-freezing temperatures, but this does not necessarily lead to the formation of ice crystals. In order for water to freeze at temperatures just below 0°C, an ice nucleus is required. The ice nucleus performs a similar role to condensation nuclei. Ice nuclei are far rarer than condensation nuclei. They must have a six-sided structure, just like ice. Ice crystals themselves act as efficient ice nuclei.


How do cloud droplets form, grow in above freezing conditions?

In above-freezing conditions, cloud droplet growth through condensation is the dominant formation processes. Condensation occurs when air is lifted adiabatically past the lifted condensation level (LCL). Above the LCL, most of the water is drawn to condensation nuclei. In general, there is relatively little water but a lot of nuclei. This creates a large number of smaller particles competing for a limited amount of water. Growth through condensation by itself cannot lead to large water droplets; therefore, other processes must come into play.


In warm clouds, what process leads to precipitation?



Explain the collision-coalescence process.

The collision-coalescence process depends on the differing fall speeds of different sized droplets. The process begins with droplets falling through a cloud where large droplets fall faster than smaller droplets, and eventually overtake smaller droplets. As the droplets collide they form bigger droplets, which fall even faster.

As a collector drop falls, it only collides with some of the drops in its path. The Likelihood of a collision depends on the size of the collector drop and the size of the drops in its path. The larger the collector drop, the lower the collision efficiency, and vice versa. Efficiencies are low for droplets near the same size. When the droplets have the same terminal velocity, it is difficult for the particles to catch up to each other and collide. Surface tension causes droplets to “bounce” off of one another.

Turbulence can cause collision efficiencies over 100%. This is because falling drops entrains particles from outside of the fall path. The centrifugal force of a spinning cloud tends to sort droplets by size with smaller droplets toward the center and larger droplets on the outside. The larger droplets get slung away from the center which allows it to encounter smaller droplets along as it moves.

When a collector and a smaller drop collide, one of two things can happen: The two drops can bounce apart due to surface tension or the two drops can stick together, forming a single larger
droplet (a.k.a., coalescence). Coalescence is the process of two or more drops combining upon collision. Coalescence efficiency is the percentage of drops that coalesce upon collision. Most collisions result in coalescence and coalescence efficiencies are assumed to be near 100%.


Name the temperature layers and corresponding forms of water present in cool/cold clouds.

-4 C: Water droplets make up the lower portion.


Define a cool cloud and a cold cloud.

Cool clouds are characterized as having temperatures both above and below freezing in the region of precipitation generation.

Cold clouds are characterized as having subfreezing temperatures throughout their entire structure. A cold cloud can be composed of both super-cooled water droplets and ice crystals.


How do ice crystals from in cool/cold clouds? (Hint 2 ways)

homogeneous or heterogeneous ice nucleation


Name the ways that ice crystals grow in cool/cold clouds. (Hint 3)

• Diffusion-deposition (Bergeron process).
• Riming (accretion).
• Aggregation.


Define Diffusion-Deposition (Bergeron) Process.

In the diffusion-deposition process, the coexistence of ice and supercooled water is essential to precipitation development. Saturation vapor pressure over ice is less than that over supercooled water at the same temperature. The water vapor necessary to keep a supercooled water droplet from evaporating is more than enough to maintain an ice crystal. Water vapor is preferentially deposited onto ice nuclei, causing the super-cooled water to evaporate due to lower humidity levels


Define Riming.

When ice crystals fall through clouds, supercooled water droplets freeze onto them. This process is called riming, or accretion. The process leads to rapid crystal growth, increased mass, and increased terminal velocity.