Geography 1900 Midterm 2 10/23

Thunderstorm 3: Supercell Storm

Storms producing a minimum of A) 3/4 inch hail and or/ b) winds gusts of 50 knots and/or c) tornado winds, classify as severe.

Causes of atmosphric turbulence

Thermals - Heat from the sun makes warm air masses rise and cold ones sink. Jet streams - Fast, high-altitude air currents disturb the air nearby. Mountains - Air passes over mountains and causes wave and turbulence on the other side. Wake turbulence - Near the ground a passing plane or helicopter sets up small, chaotic air currents, or Microbursts - dry, wet and hybrid

Saturation

There is an equilibrium between evaporation and condensation during saturation. Upon saturation, evaporation rate equals condensation rate.

Low stratocumulus clouds

generated by convection inside boundary layer. convection is driven by cloud-top longwave cooling and evaporative cooling.

lightning duration

.00003 second

Formation of supercell thunderstorms

1.Horizontal vortex tube Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. 2.updraft and mesocyclone Spinning horizontal vortex tubes created by surface wind shear may be tilted and forced in a vertical path by updrafts. This rising, spinning, and often stretching rotating air may then turn into a mesocyclone. winds aloft push the rain and downdraft away and the updraft is not weakend. 3. Tornado: Most strong and violent tornadoes form within this area of strong rotation.

Deposition

Water vapor (gas) can change directly into ice or snow(solid)

Wet Microburst

A rain foot may be a visible sign of a wet microburst.

Cloud-to-ground lightning

20% of lightning occurs when electrical discharge travels between the base of the cloud and the surface.

Derechos

A derecho (spanish word meaning "straight ahead") is a widespread, long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms (often a squall line). By definition, the wind damage swath extends more than 240 miles and wind speed > 57 mph. Can produce destruction similar to that of tornadoes. The damage typically is directed in one direction along a relatively straight swath. Serial, progressive, hybrid, and low dewpoint derechos. May, June and July. Oklahoma

Mesoscale Convective Complex (MCC)

An organized mass, or collection, of thunderstorms that extends across a large region up to 1000 x larger than individual storms. Last for upwards of 12 hours and may bring hail, tornadoes, and flash floods.

Damages

Annual mean fatalities 69 for u.s 600 world-wide. Hundred of people are permanently injured. Annual mean property loss $38 million for u.s. Lighting is the leading cause of wildfires (25,000 each year). Especially caused by lightning in dry thunderstorms (virga)

Clouds

Are instrumental to the Earth's energy and moisture balances, and constitute a wild card for climate change.

Humidity

Around of water vapor in air

Fog

Can be considered a cloud with base at ground level. Air has either been: cooled to dew point, had moisture added, mixed with warm moist air. 5 different types: radiation, advection, upslope, precipitation, steam.

Properties of Clouds

Cloud top height/pressure. Cloud thickness (optical depth). Cloud coverage.

Why do clouds constitute a wild card for climate change?

Clouds are both good reflections of solar radiation (cooling effect) and good absorbers of earth emitted longwave radiation (warming effect). The net effect (cooling or warming) depends on the types of clouds. IN changing climate, increases in high thin clouds would promote warming, while increases in low thick cloud would cause cooling. Climate models have difficulties in stimulating clouds, especially low thick clouds (stratocumulus).

Bergeron Process: Growth in Cold/Cool Cloud

Clouds are usually composed of liquid water, super-cooled water, and/or ice (supercooled water exists down to t=-40 C) Supercooled can exists at t<0C because of ice formation requires ice nuclei, which, unlike condensation nuclei, are rare unless the temperature is very cold. coexistence of ice and supercooled water is critical to the recation of cool/cold precipitation is the Bergeron Process. Key: saturation vapor pressure of ice< that of super-cooled water at the same temperature.

Thunderstorm 2: Multicell Storms

Cool downdraft leaving a mature and dissipating storm may offer relief from summer heat, but they may also force surrounding, low-level moist air upward. Hence dying storms often trigger new storms and the successive stages may be viewed in the sky.

Component 1: Ocean

Covers 70% of the Earth's surface

Absolute Humidity

Density of water vapor expressed in g/m^3

Downbursts

Downbursts are gusts of wind that can reach speeds in excess of 270km/hr (165mph), and are potentially deadly. Three common types: Derechos (1000 km) ,Haboobs (10-100 km),Microbursts (1 km).

Torando Damage

Enhanced Fujita Scale (EF-0 54-85 mph, EF-5 >200 mph)

Sublimation

Ice or snow(solid) can turn directly into water vapor (gas)

Component 3: Land

Ice sheet, glaciers and snow cover. Greenland ice sheet holds 7m of global sea level equivalent. Mountain glaciers provide the fresh water supply for millions of people. >1000 major rivers flow on the seven continents. Mississippi River(#6), Amazon River (#1), Yangtze River (#4)

Thunder

It takes about 3 seconds for thunder to travel 1kilometer (5 sec per mile).

cloud-to-cloud lightning

Lightning is a discharge of electricity, a giant spark 80% of lightning occurs when clouds discharge electricity. Occurring when voltage gradient overcomes the electrical resistance of the air.

Dew

Liquid condensation on surface. Occurs early morning on windless cloudless days. air immediately above ground cools, reaches dew point. Diabatic process.

Specific Humidity

Mass of water vapor (g) per mass of air (kg) in (g/kg)

Squall Line

May contain several severe thunderstorms, some possibly supereclls, extending for more than 1000 kilometers. Always contain a convective precipitation region and a trailing stratiform precipitation region.

Evaporation

Molecules escape into the overlying volume as water vapor during evaporation. energy must be available at the water surface. water vapor increases in air as surface water evaporates.

Precipitation Fog

Rain occurs and some evaporates as it falls toward earth. Sometimes this will lead to saturation near surface and cause fog. Adiabatic process.

Frozen Dew

Results when saturation occurs slightly above 0 degrees C. Liquid dew formed, when Temp drops liquid dew freezes. From thin sheet of ice, tightly bound to surface. Dangerous- black ice.

Saturation Vapor Pressure

Saturation vapor pressure is temperature dependent. Saturation vapor pressure increases with temperature. Warmer air can hold more water vapor. It's nonlinear increase. at low temperatures the saturation vapor pressure increases slowly but it increases rapidly at high temperatures.

Relative Humidity

The amount of water vapor in the air relative to the possible maximum.

Nitrogen Cycle

The enormous energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides. These dissolve in rain, forming nitrates that are carried to the earth. Contributes some 5-8% of the total nitrogen fixed. was probably the only source of fixed nitrogen for the earliest forms of life.

Thunderstorm 1: Ordinary Storms

Three stages have been identified in ordinary thunderstorms.a)Developing: unstable atmosphere, vertical updrafts keeping precipitation suspended. B) mature: entrainment of dry air that causes cooler air from evaporation triggering downdrafts and falling precipitation and gust fronts. C) Dissipating: weakening updrafts and loss of the fuel source after 15-30 minutes.

Tornado Occurrance

Tornadoes from all 50 states of the U.S. Add up to more than 1000 tornadoes annually, but the highest frequency is observed in the tornado alley of the Central Plains. Great setting for potent mixing of air masses. Tornado season March-July. Oklahoma has the most tornadoes.

Haboobs

Very strong horizontal winds over desert regions create sandstorms called haboobs (from the Arabic word meaning "wind"). Occur regularly in arid regions throughout the world

Dry Microburst

Virga in the sky: defined as wisps or streaks of water or ice particles falling out of a cloud but evaporating before reaching the earth's surface as precipitation.Blowing dust/dust rings at surface

Component 4: Atmosphere

Water vapor flows in the atmosphere. Precipitation drives many atmospheric circulations which in turn transport water around the world. A significant fraction of the human body is water (~75%). Every 16 days nearly 100% of the water in a human body is exchanged. So the water we drink may com from all over the world. Therefore we need to protect the environment because any pollution we put into the environment may someday come back into our bodies.

Condensation

Water vapor molecules randomly collide with the water surface and bond with adjacent molecules during condensation.

Mesoscale convective systems

a cloud system that occurs in connection with an ensemble of thunderstorms and produces a contiguous precipitaiton area on the border of 100 Km or more in at least one direction, and often last for several hours to a couple of days.

Charge Separation

charge layers in the cloud are formed by the transfer of positive ions from warmer graupel to colder ice crystals when they collide with each other.

Return stoke

a region of positive ions move from the ground toward this charge, which then forms a return stoke into the cloud.

Tornadoes

about 100-600m last 1 mintute to 1 hour

thunderstorms

about 10Kim, last 10 minutes to a couple of hours

Diabatic processes

add/remove heat. Conduction (e.g. movement of air mass over a cold surface). Radiation ( e.g. cooling of boundary layer air by long wave radiation)

lightning safety

always take cover in a building. do not stand under a tree or a tall object-> lighting rod. Avoid standing on mountain summits, ridges, rooftops. Avoid caves and open water.

Mixing ratio

around of water vapor (g) relative only to mass of dry air (kg)

precipitation formation

cloud drop growth. not all clouds precipitate due to their small sizes and slow fall rates. balance between gravity and frictional drag-> eventually become equal to achieve terminal velocity. Which is proportional to the square root of cloud drop radius. For a cloud to drop to fall, its terminal velocity must exceed the vertical velocity of the upward moving air parcel. otherwise it will be carrie dup. cloud drop growth is required for precipitation to form.

Hail

concentric layers of ice build around graupel. require very strong updraft. gruapel carried aloft in updrafts-> high altitudes freezing temperatures. water accreting to graupel freezes and forming a layer. hail begins to fall, carried aloft again by updrafts, process repeats. hailstones are very heavy-high density. capable of tremendous amounts of damage.

Upslope Fog

develops due to adiabatic cooling. occurs when air is lifted over topographic barriers, mountains. Air expands and cools as it rises. Common in region between Great Plains and Rocky Mountain foothills.

Global desertification

drying of global soil moisture.

inversion

encounter a layer of stable air. A rising air parcel may reach a stable upper air environment. the cooling rate will exceed that of the ambient air. the parcel will slowly cease ascension and come to rest at some equal temperature level. three types: radiation, frontal, subsidence.

freezing rain

form similarly to sleet, however the drop does not completely solidify before striking the surface.

lake effect

heat and moisture fluxes from warm lake enhance snowfall in downstream regions.

Saturation specific humidity

highest specific humidity for a given temperature and pressure

Graupel

ice crystals that undergoes extensive riming. Lose six sided shape and smooth out either falls to the ground or provides a nucleus for hail.

Microburst

is a very localized column of downdraft (sinking air) in a thunderstorm that is less than 2.5 miles in scale. Produces damaging divergent and straight-line winds at the surface as high as 150mphis similar to, but distinguishable from, tornadoes, which generally have convergent damage.can produce dangerous situations at airports, as they impede air travel. 3 types: dry, wet, hybrid

Snow

is precipitation that forms by the Bergeron process, riming and aggregation and reaches the surface without melting. Crystals form (habit) varies with T and RH. Large, soggy snowflakes associated with moist air near freezing.

Riming (or accretion)

liquid water freezing onto ice crystals

Saturation vapor pressure (SVP)

maximum amount of vapor that can exist at a given temperature, increase w/ Tair.

Saturation mixing ratio

maximum mixing ratio

Steam Fog

mixing of warm, moist air with cold air. Adiabatic process (no net change of energy). e.g. common when cold air moves over warm lake/streams in autumn. Can see plums rising.

Formation of Clouds

most clouds form as air parcels in boundary layer are lifted and cooled to saturation. The air parcels could be lifted by mountains; meeting of different air masses, surface convergence, and local convection.

Adiabatic Processes

no addition/removal of heat. Add water vapor to air. mix warm air with cold air. Cooling of air parcel when it rises (because air parcel expands when ti rises, like a balloon).

Dart leader

not all of the first stroke neutralizes the negatively charged ions and results in another leader in 1/10 or a second.

Tornado outbreak

number > 6

Radiation Fog

occurs when near surface air chills diabatically through loss of long wave radiation-> reaches dew point. Requires cloudless nights and light wind to create mixed layer. "burns" off with sunrise- evaporates from below due to surface heating.

Advection fog

occurs when warm moist air moves across a cooler surface. Air is chilled diabatically to saturation. Common on the U.S west coast -> warm, moist air from Pacific advects over the cold California current. Frequently develop near boundaries of opposing ocean temperatures. E.g. northeast coast of the U.S, Gulf Stream and Labrador current.

Ozone Production

ozone was named after the Greek verb ozein, from the peculiar odor in lighting storms. Nitrogen oxides produced by lightning can react with others in the presence of sunlight to produce ozone. since most lightning occurs inside a storm, the added ozone tends to show up several miles high rather than near the earth's surface, so it doesn't add significantly to ozone pollution at ground level.

Collision Coalescence: Growth in warm clouds

process begins with larger collector drops which have higher terminal velocities. Collector drops collide with smaller drops and merge with them (coalesce). Coalscence efficiency is generally very high, indicating that most collisions result in two drops joining. If collector drop is too big: compressed air beneath falling drop forces small drops inside. if collector drop is too small (same-size as other drops) it will fall at same speed and no collision will occur.

when convection happens

rising up of air parcel (called updraft). Formation of clouds and sometimes precipitation. Heating up the environment because parcel temperature is warmer than the environment.

Component 2: Sea Ice

sea ice

Frost

similar to dew BUT saturation occurs below 0 degrees C. Deposits white ice crystals -> known as hoar frost. E.g. car windshield. Phase change form vapor directly to solid (deposition). Diabatic process

Sleet

sleet begins as ice crystals which melt into rain as they fall through the atmosphere. before reaching the surface they solidify into a frozen state.

Different Precipitaiton

snow, rain, sleet, freezing rain, graupel/hail

Dew Point Temperature

temperature at which saturation occurs in air (generally colder than Tair, equals Tair when saturated)

aggregation

the joining of ice crystals through the bonding of surface water builds ice crystals, producing snowflakes, collisions combined with riming and aggregation allow formation of crystals large enough to precipitate within 1/2 hour of formation.

Vapor Pressure

the partial pressure exerted by water vapor

entrainment

turbulent mixing of ambient air into parcel. leads to evaporation along cloud boundaries. evaporation uses latent heat, cooling the cloud-> reduces buoyancy.

Water

water is unique on earth because it can exist in all 3 states (phases). 3 states (gas, liquid, solid) depending on how the molecules are connected together. Can change form any state to any other state. Latent heat is consumed or released in a phase change. Evaporation -> liberation of water molecules, requires energy.

Stepped leader

when the negative charge near the bottom of the cloud is large enough to overcome air's resistance, a stepped leader forms.